Stem cells-derived islet transplantation toward clinical translation: Divergent strategies and convergent objectives

Abstract

Diabetes mellitus, a chronic metabolic disease with high global prevalence, is in urgent need of breakthrough therapies due to its high risk of complications and limitations of current treatments. Stem cells-derived differentiated islet transplantation represents a promising therapeutic strategy for diabetes mellitus by enabling the regeneration of functional islet cells and the restoration of endogenous insulin secretion. This review provided a comprehensive overview of stem cells-based islet differentiation and transplantation technologies, including the classification and functional roles of different stem cell types. It systematically compared the current research status and strategic differences among leading centers and platforms. In addition, the major translational challenges were critically analyzed, with particular emphasis on immunological barriers, long term graft function, and clinical scalability, alongside insights drawn from the authors’ clinical experience. Furthermore, this review explored future research directions that are expected to drive clinical translation, including the application of gene editing technologies, the optimization of immunomodulatory strategies, and advances in pancreatic islet cryopreservation. Despite rapid progress in the field, a systematic comparison of stem cells-derived islet strategies, particularly with respect to immune compatibility, manufacturability, and individualized therapeutic potential, remains limited. This review addressed this gap by presenting an integrated analysis of current approaches, contextualized by clinical experience, and by proposing future multidisciplinary strategies that combine gene-editing, localized immunomodulation, and improved cryopreservation techniques to advance stem cell-derived islet transplantation toward broader clinical application.

Key Words: Stem cells-derived islets; Islet transplantation; Diabetes mellitus; Pluripotent stem cells; Regenerative medicine; Immunomodulation

Core Tip: This review systematically compared leading stem cells-derived islet transplantation strategies, including autologous and allogeneic approaches from key research centers. It highlighted the trade-offs among immunogenicity, scalability, and personalization, and proposed future integrative solutions combining gene editing, localized immunomodulation, and cryopreservation advances to overcome current barriers toward a functional cure for diabetes.

INTRODUCTION

According to statistics released by the International Diabetes Federation in 2021, the global population affected by diabetes has exceeded 537 million, and the prevalence continues to increase worldwide[1]. Chronic hyperglycemia in diabetics can lead to a wide range of serious complications, including cardiovascular disease, diabetic nephropathy, retinopathy, and neuropathy. These complications not only significantly diminish patients’ quality of life, but also remarkably increase the risks of disability and mortality[2]. At present, clinical management of diabetes relies predominantly on pharmacological therapies aimed at controlling blood glucose levels. Although such treatments can partially alleviate hyperglycemia, they fail to accurately replicate the physiological functions of the pancreas or its complex feedback regulation mechanisms. Consequently, achieving a definitive cure for diabetes or completely preventing the progression of diabetes-related complications remains difficult[3]. In addition, the requirement for long-term or lifelong medication imposes significant economic and psychological burdens on patients[1]. In this context, islet transplantation has emerged as a promising alternative therapeutic strategy, representing an important advancement in the treatment of diabetes. By transplanting functional islet cells to restore endogenous insulin secretion and physiological glucose homeostasis, islet transplantation has demonstrated favorable long-term safety and efficacy[4,5].

Common transplantation approaches include autologous, allogeneic, and xenogeneic transplantation. The primary advantage of autologous transplantation is that recipients generally do not require immunosuppressive regimens; however, its application is largely limited to patients with chronic pancreatitis or pancreatic trauma. Allogeneic transplantation is appropriate for patients with type 1 diabetes (T1D), as well as certain forms of genetically induced diabetes, while this approach necessitates long-term immunosuppression and is constrained by limited donor availability. Xenotransplantation provides a potential solution to donor shortages; nevertheless, it requires particularly complex immunosuppressive strategies and raises additional ethical and biosafety concerns. In recent years, rapid advances in stem cell technology have provided new directions to overcome these limitations in islet transplantation, promoting the development of effective and scalable therapies for diabetes.

OVERVIEW OF STEM CELLS-INDUCED ISLET DIFFERENTIATION AND TRANSPLANTATION

In 2001, the discovery that human pluripotent stem cells (PSCs) could spontaneously differentiate in vitro into insulin-secreting cells established a critical foundation for stem cell-based replacement therapies for diabetes[6,7]. Since then, rapid advances in stem cell biology and differentiation technologies have positioned stem cell-based approaches as a promising frontier in diabetes treatment, includes fully mature β-like cells, mixed endocrine islet-like clusters, or pancreatic progenitors (PPs) requiring in vivo maturation. At present, two principal categories of stem cells are extensively investigated in terms of islet transplantation: PSCs and mesenchymal stem cells (MSCs), each fulfilling distinct roles in islet regeneration and immune modulation (Figure 1).

Figure 1 Schematic diagram of current stem cell-derived islet transplantation strategies. Xenotransplantation: Animal-derived islets (e.g., porcine) are isolated and directly infused into the patient. This strategy addresses donor organ shortage but faces significant challenges related to xenoimmunity, including hyperacute rejection and zoonotic infection risks, as well as ethical and regulatory hurdles. Allogeneic transplantation: Donor-derived islets from human cadavers are isolated and infused into the patient. While clinically established, this approach is severely limited by donor scarcity and requires lifelong systemic immunosuppression to prevent allograft rejection. Allogeneic stem cell transplantation: Human pluripotent stem cells [PSC; embryonic stem cells or induced PSCs (iPSCs)] are directed to differentiate into insulin-producing islet cells in vitro. Advanced protocols incorporate gene-editing techniques (e.g., CRISPR/Cas9) to reduce immunogenicity by disrupting human leukocyte antigen molecules or overexpressing immune checkpoint proteins (e.g., programmed death-ligand 1, CD47). The resulting “off-the-shelf” cell products enable standardized large-scale manufacturing but still typically require some level of immunosuppression, depending on the engineering strategy. Autologous stem cell transplantation: The patient’s own somatic cells (e.g., fibroblasts, peripheral blood mononuclear cells, or adipose-derived mesenchymal stem cells) are reprogrammed into iPSCs, which are then differentiated into islet cells and reinfused into the same patient. This personalized approach eliminates the need for immunosuppression and avoids allogeneic rejection, but is constrained by lengthy manufacturing timelines, high costs, and limited scalability. Created in BioRender (Supplementary material). SC: Stem cells; MSC: Mesenchymal stem cell; iPSC: Induced pluripotent stem cells; Tx: Transplantation; Allo: Allogeneic; Auto: Autologous; Xeno: Xenogeneic; 3D: Three-dimensional.

PSCs

PSCs are defined by their capacity for unlimited self-renewal and their ability to differentiate into cell types derived from all three germ layers. These properties render PSCs central to studies of pancreatic lineage specification and functional islet cell generation[8]. PSCs primarily include two subtypes: Embryonic stem cells (ESCs) and induced PSCs (iPSCs). ESCs, derived from the inner cell mass of blastocysts, were the earliest PSCs applied to islet differentiation research[6,7,9]. In 2014, Rezania et al[10] reported the successful differentiation of human ESCs (hESCs) into functional pancreatic β-like cells exhibiting glucose-responsive insulin secretion, which resulted in improved glycemic control in animal models. Despite these notable outcomes, the clinical translation of ESC-derived islet cells remains limited by ethical concerns associated with embryo use and by immunological challenges, including the risk of allogeneic immune rejection following transplantation[11].

The iPSCs are generated from somatic cells through cellular reprogramming technologies and exhibit pluripotency properties comparable to those of ESCs[12]. In contrast to ESCs, the use of iPSCs results in ethical concerns associated with embryonic derivation and provides a more accessible and diverse cell source. Furthermore, autologous iPSC-based approaches represent a promising strategy for personalized cell therapy in diabetes, owing to a significantly reduced risk of immune rejection[13]. To date, multiple studies have demonstrated the successful differentiation of iPSCs into functional islet-like cells exhibiting robust glucose-responsive insulin secretion[14]. Notably, a recent clinical case report described the transplantation of iPSC-derived islet cells in a patient with a 25-year history of type 2 diabetes (T2D), resulting in sustained insulin independence for more than three years following treatment[15].

MSCs, as adjunctive therapy vs standard therapeutic agents

MSCs represent a heterogeneous population of adult stem cells with self-renewal capacity, commonly isolated from bone marrow, umbilical cord tissue, and adipose tissue[16]. Although MSCs lack the capacity to directly differentiate into pancreatic β-cells, they play a critical supportive role in islet transplantation and diabetes therapy through paracrine signaling and immunomodulatory functions[17]. MSCs enhance the survival and functional stability of transplanted islets by secreting a broad spectrum of bioactive factors, including vascular endothelial growth factor, transforming growth factor-β, prostaglandin E2, and hepatocyte growth factor (HGF), while concurrently attenuating immune-mediated rejection responses[18-20]. Through these mechanisms, MSCs improve the local transplantation microenvironment, promote neovascularization, and ultimately enhance the overall efficacy of islet transplantation[21]. Consistently, Montanari et al[22] demonstrated that co-transplantation of MSCs with islet cells significantly prolonged graft survival and preserved islet function in murine models.

Islet organoids: Advanced models for developmental and disease models, transplantation candidates

Islet organoids, representing a sophisticated integration of stem cell biology and tissue engineering, have emerged as advanced models that significantly advance the investigation of pancreatic development and the pathophysiology of diabetes. In contrast to conventional two-dimensional culture systems, these three-dimensional (3D), self-organizing structures more accurately reproduce the native islet microarchitecture, intercellular communication networks, and functional maturation. The generation of islet organoids is predominantly dependent on the precise temporal and spatial modulation of key developmental signaling pathways, governing pancreatic organogenesis. Standard differentiation protocols typically commence with the induction of PSCs into definitive endoderm, most commonly mediated through the Activin/Nodal signaling pathway, followed by sequential progression through the primitive gut tube, posterior foregut, and PP stages. Subsequent fine-tuning of developmental cues, including retinoic acid, fibroblast growth factor, bone morphogenetic protein, and Notch signaling, directs endocrine progenitors (EPs) toward the formation of islet-like organoids composed of spatially organized β-, α-, δ-, and pancreatic polypeptide cells[23]. Advanced 3D suspension culture systems, including Matrigel-based matrices and synthetic extracellular matrix analogues, provide essential biochemical and biophysical support, thereby promoting cellular polarization, lineage specification, and higher-order self-organization[24]. Mature islet organoids exhibit several defining characteristics. Firstly, they display a complex multicellular composition with discernible spatial organization, frequently characterized by the preferential localization of β-cells toward the organoid core. Secondly, they demonstrate a high degree of functional maturity, as evidenced by enhanced glucose-stimulated insulin secretion (GSIS) relative to monolayer-derived endocrine cells, and some advanced models exhibited dynamic, biphasic insulin secretion kinetics. Besides, islet organoids possess significant vascularization potential; upon co-culture with endothelial cells or following in vivo implantation, they are capable of inducing host angiogenesis or forming vessel-like networks through self-assembly with donor endothelial cells, a feature being critical for efficient revascularization post-transplantation. Importantly, organoid-derived endocrine cells establish functional syncytia through gap-junctional coupling and exhibit coordinated calcium oscillations, reflecting physiologically relevant electrophysiological integration[25,26].

RESEARCH CENTERS: CURRENT STATUS AND STRATEGIC VARIATIONS

Despite persistent scientific, technical, and translational challenges, remarkable progress has been achieved by several leading research centers in the field of stem cell-derived islet (E-islet) transplantation. Current research efforts are primarily concentrated on a limited number of representative institutions, each distinguished by unique strategies with respect to cell sources, reprogramming and differentiation methodologies, transplantation sites, and immunosuppression requirements. As summarized in Table 1, these parameters provide a structured basis for comparative evaluation of therapeutic efficacy, safety profiles, and remaining translational barriers.

Table 1 Studies on the transplantation of stem cells-induced islets.

Ref.	Stem cell source	Differentiation strategy	Transplantation site	Immune method	Scalability & personalization	Advantages	Challenges
Wang et al[30], 2024	Autologous adipose-derived MSC - CiPSC	Chemical reprogramming + in vitro differentiation	Transplantation into the rectus abdominis muscle	Low/none	Limited scalability and high personalization potential, a patient-specific therapy	Avoid gene-editing risks, with low immunogenicity	Difficulty in large-scale production
Businesswire[33], 2021	Allogeneic iPSC	Standardized in vitro differentiation	Percutaneous transhepatic portal vein infusion	Long-term immunosuppression required	High scalability and low personalization, a one-size-fits-all therapy	Standardized production, with clear therapeutic efficacy	Immunosuppressive side effects, donor dependency
D'Amour[9], 2006	Allogeneic hESC	Gene editing + immunological isolation	Subcutaneous implantable device	Local immune modulation	High scalability and low personalization, a one-size-fits-all therapy	Immunological isolation, capable of avoiding systemic immunosuppression	Fibrotic reactions, with uneven cell differentiation
Wu et al[15], 2024	Autologous PBMC - iPSC	Differentiated in vitro to EnSC - E-islets	Percutaneous transhepatic portal vein infusion	None	Limited scalability and high personalization, a patient-specific therapy	No immune rejection, personalized treatment	Long production cycle, high costs

MSC: Mesenchymal stem cell; CiPSC: Chemically induced pluripotent stem cell; iPSC: Induced pluripotent stem cell; hESC: Human embryonic stem cell; PBMC: Peripheral blood mononuclear cell; EnSC: Endoderm stem cell; E-islet: Stem cell-derived islet; HLA: Human leukocyte antigen.

Chemically reprogrammed autologous iPSC-derived islets and subfascial transplantation into the rectus abdominis muscle

Guan et al[27] and Wang et al[28] established a fully chemical reprogramming platform, enabling the direct conversion of adult somatic cells into PSCs, which are termed as human chemically iPSCs (hCiPSCs). This strategy relies exclusively on defined small-molecule compounds and subsequently directs hCiPSCs toward differentiation into functional pancreatic islet-like cell clusters (hCiPSC-islets).

The chemical reprogramming process is achieved through four precisely regulated, stage-specific phases. During the initial phase, small-molecule combinations, including CHIR99021 and 616452, are applied to disrupt fibroblast lineage identity, promote mesenchymal-to-epithelial transition, and activate the dedifferentiation-associated gene LIN28A. In the second phase, c-Jun N-terminal kinase inhibitors in combination with epigenetic modulators induce a highly plastic intermediate state characterized by open chromatin configuration, enhanced proliferative capacity, and activation of regenerative transcriptional programs. The third phase involves the application of additional epigenetic regulators and signaling pathway inhibitors to activate the core pluripotency gene OCT4, thereby guiding cells through a transient ectoderm-like intermediate state. In the final phase, optimized chemical conditions stabilize and capture hCiPSCs, possessing a complete and functionally integrated pluripotency regulatory network[27,28]. Collectively, this protocol enables fully defined, gene-free, and chemically controlled reprogramming of somatic cell fate. This chemically mediated approach effectively reduces several limitations associated with genetic reprogramming technologies, including insertional mutagenesis, off-target genomic alterations, increased risk of tumorigenicity, and ethical concerns related to genetic manipulation[10,29]. In preclinical studies, hCiPSC-derived islet-like clusters were transplanted under the anterior rectus abdominis sheath in murine models of T1D. Following transplantation, the grafts exhibited robust responsiveness to multiple secretagogues, preserved GSIS, restoration of systemic glycemic homeostasis, and minimal evidence of immune-mediated rejection[27,28].

Guan et al[27] and Wang et al[28] established a chemical reprogramming platform that converted somatic cells into PSCs [chemically iPSCs (CiPSCs)] using defined small-molecule compounds, followed by differentiation into functional islet-like clusters (CiPSC-islets). In contrast to genetic reprogramming, this approach achieved cell fate reversal through transient, stage-specific activation of developmental signaling pathways without introducing exogenous genes, thereby mitigating risks associated with insertional mutagenesis and off-target genomic alterations[27,28]. In a 2024 clinical report, a patient with T1D received autologous CiPSC-islet transplantation. By day 75 post-transplantation, the patient achieved insulin independence, with time-in-range (TIR) increasing from 43.18% to 96.21% and hemoglobin A1c (HbA1c) decreasing to 5.37% at one-year follow-up[30]. While this autologous approach eliminates the need for immunosuppression and demonstrates remarkable clinical efficacy, its scalability remains constrained by personalized manufacturing timelines and costs.

The chemically mediated reprogramming strategy demonstrates broad applicability at both conceptual and technical levels, as it effectively reduces the principal risks associated with gene-based reprogramming approaches while relying on readily accessible autologous somatic cell sources. By avoiding permanent genetic modification, this platform significantly mitigates concerns related to insertional mutagenesis, off-target genomic alterations, and tumorigenic potential. Nevertheless, the principal translational limitation of this approach resides in the intrinsic scalability constraints common to all autologous cell-based therapies. Specifically, the individualized nature of autologous manufacturing poses remarkable challenges for large-scale, cost-effective, and standardized production, thereby markedly restricting its capacity to deliver widespread clinical benefit in a short- to medium-term timeframe.

The transformative potential of this approach has been recognized by the broader scientific community. In 2024, Professor Deng was awarded the Future Science Prize in Life Sciences for his “pioneering research on using small molecules to change cell fate and state”, with the prize committee emphasizing that his “seminal and transformative research has opened a new direction for cellular reprogramming, with broad and long-term impact on stem cell research and regenerative medicine”[31]. An expert commentary published following the 2025 International Society for Stem Cell Research annual meeting characterized the clinical translation of CiPSC-derived islets as a “landmark achievement in regenerative medicine”, demonstrating “remarkable clinical potential”. These external perspectives highlight the significance of this technological pathway while acknowledging, as noted in the commentary, that “scalability remains a significant challenge” as the field transitions from “artisanal lab protocols” to “standardized bioprocessing”[32].

Vertex Pharmaceuticals: Allogeneic iPSC-derived islet differentiation and portal vein transplantation strategy

The VX-880 program developed by Vertex Pharmaceuticals currently represents the most advanced and clinically mature translational effort in the field of E-islet replacement therapy. This strategy employs allogeneic iPSC-derived pancreatic islet cells for the treatment of T1D, delivered via percutaneous infusion into the hepatic portal vein. Owing to the allogeneic nature of the graft, long-term systemic immunosuppressive therapy is required to prevent immune-mediated rejection of the transplanted cells[33].

The phase 1/2 clinical trial of VX-880 (NCT04786262) enrolled 12 patients with T1D who experienced recurrent severe hypoglycemic events and exhibited impaired hypoglycemia awareness[34]. At baseline, fasting serum C-peptide level, reflecting endogenous insulin secretion, was undetectable in all participants, who required a mean daily insulin dose of 39.3 units. Following a single full-dose infusion of VX-880, all 12 patients demonstrated measurable insulin secretion in response to glucose stimulation by day 90. Among the three patients who were followed for at least one year, all achieved the primary efficacy endpoint, which was defined as complete elimination of severe hypoglycemic events, HbA1c levels below 7.0%, and discontinuation of exogenous insulin therapy. VX-880 has thus remarkably exhibited a favorable safety profile, with reported adverse events being limited and generally manageable, including dehydration, diarrhea, and hypomagnesemia[35]. The program has subsequently advanced to phase 3 clinical trials, with expanded patient enrollment planned to further confirm long-term safety, durability of graft function, and therapeutic efficacy.

ViaCyte: Subcutaneous transplantation of allogeneic hESC-derived islets using gene-edited immunoisolation platforms

ViaCyte pioneered a subcutaneous transplantation strategy based on the encapsulation of hESC-derived PP cells in immunoisolation devices designed to shield transplanted cells from host immune attack. The first-generation Encaptra device (VC-01) was engineered as a fully immunoprotective encapsulation system. Subsequently, the second-generation VC-02 device incorporated a microporous architecture in its semipermeable membrane to permit host vascular ingrowth. Structurally, the VC-02 device consists of a multilayered configuration composed of an expanded polytetrafluoroethylene semipermeable membrane with engineered micropores, reinforced by internal polyester mesh grids to provide mechanical stability[36]. This platform was designed to prevent direct immune cell infiltration while allowing passive diffusion of small molecules, including oxygen, nutrients, glucose, and insulin[37].

Despite its conceptual appeal, clinical outcomes associated with this encapsulation strategy have been limited. A major contributing factor is the remarkable foreign-body fibrotic response elicited at the subcutaneous implantation site. Progressive fibrotic overgrowth compromises membrane permeability, thereby impairing oxygen and nutrient diffusion and ultimately reducing graft survival through hypoxia-induced cell loss[38]. In addition, the differentiation state of the transplanted cells represents a critical limitation. The implanted hESC-derived PPs are developmentally immature and rely on in vivo maturation to acquire functional β-cell identity. However, clinical research has demonstrated remarkable inter-individual variability in the efficiency, stability, and completeness of β-cell differentiation following implantation, resulting in inconsistent functional outcomes in human recipients[39].

To address these challenges, ViaCyte initiated a strategic collaboration with CRISPR therapeutics to develop a next-generation product, namely VCTX210. This approach integrates CRISPR/Cas9-mediated genome editing with allogeneic pancreatic endodermal cells (PEC210A) to establish a multi-layered immune-evasive phenotype. The genetic engineering strategy comprises several complementary components: (1) Targeted suppression of human leukocyte antigen (HLA) class I and class II expression to abrogate T-cell mediated recognition via the direct allorecognition pathway; (2) Upregulated expression of non-classical HLA molecules, such as HLA-E, together with the anti-phagocytic signal CD47, to inhibit natural killer (NK) cell- and macrophage-mediated innate immune responses; and (3) Introduction of immunomodulatory ligands, including programmed death-ligand 1 (PD-L1) and Fas ligand, to locally engage inhibitory receptors on T cells and induce apoptosis of activated alloreactive T lymphocytes, thereby promoting localized immune tolerance[40-43].

This integrated hypoimmune engineering platform, representing a central element of CRISPR therapeutics’ broader strategy for developing “off-the-shelf” allogeneic cell therapies, may create a permissive immunological niche that supports long-term graft survival and function without reliance on systemic immunosuppression. Clinical data reported in 2021 indicated that, among 17 patients with T1D who were treated with the VC-02 product, 6 (35.3%) cases exhibited detectable increases in circulating C-peptide level within six months following transplantation[44].

In January 2023, ViaCyte was acquired by Vertex Pharmaceuticals. The VCTX210 program, currently under Vertex ownership, is currently undergoing clinical evaluation to assess the safety, tolerability, and preliminary efficacy of stem cell–derived islet-like cells deployed within an immunoisolation device (ClinicalTrials.gov identifier: NCT05791201). The advancement of VCTX210 into clinical testing represents a critical validation milestone for CRISPR-based hypoimmune engineering in regenerative medicine, extending its application beyond immuno-oncology, involving allogeneic chimeric antigen receptor T-cell (CAR-T) therapies, to address the enduring challenge of immune rejection in cell replacement therapies for chronic metabolic diseases, including diabetes mellitus.

Hepatic portal vein transplantation strategy for autologous iPSC-induced differentiation and regeneration of islets

Wu et al[15] and Shi et al[46] has established a strong scientific foundation in stem cell-directed differentiation and endodermal organ regeneration. In 2012, Cheng et al[45] reported the generation of self-renewing endodermal progenitor (EP) cell lines derived from human PSCs in Cell Stem Cell. These EP cells exhibit extensive proliferative capacity, stable expression of definitive endodermal markers, and the ability to differentiate into multiple endoderm-derived lineages, including hepatic, pancreatic, and intestinal cell types. Importantly, EP cells demonstrated anon-tumorigenic phenotype in vivo and were capable of generating single-hormone, glucose-responsive pancreatic β-cells, thereby providing a critical theoretical and experimental framework for the development of safe stem cell-based replacement therapies.

Building upon this foundational work, the group subsequently advanced a personalized regenerative strategy based on autologous iPSC technology. In this approach, patient-derived peripheral blood mononuclear cells (PBMCs) were reprogrammed into iPSCs, followed by stepwise directed differentiation into endoderm stem cells (EnSCs) and the assembly of 3D, organoid-like islet tissues (E-islets) in vitro. These engineered islets were designed to recapitulate key architectural and functional features of native pancreatic islets prior to transplantation.

Clinical translation of this strategy was reported in a first-in-human autologous Ipsc-derived regenerative islet transplantation completed in 2023 (ClinicalTrials.gov identifier: NCT07126873). A 58-year-old patient with T2D underwent hepatic portal vein transplantation of autologous E-islets. At 6 months post-transplantation, fasting plasma glucose level declined from 13.2 mmol/L at baseline to 8.5 mmol/L, accompanied by a reduction in HbA1c from 9.1% to 7.2%. Notably, the autologous nature of the therapy obviated the need for systemic immunosuppressive agents throughout the treatment course, thereby significantly reducing the risks typically associated with long-term immunosuppression[15].

Collectively, the major stem cell-based islet replacement strategies currently under investigation exhibit distinct strengths and inherent limitations. Autologous approaches, including chemical reprogramming strategies developed by Guan et al[27] and Wang et al[28] and iPSC-based regenerative platforms advanced by Wu et al[15] and Shi et al[46], effectively eliminate immune rejection and avoid the need for immunosuppressive therapy. However, these personalized strategies are constrained by prolonged manufacturing timelines, high production costs, and limited scalability, collectively impeding rapid and widespread clinical deployment. In contrast, allogeneic strategies exemplified by Vertex Pharmaceuticals prioritize standardization and large-scale manufacturing of “off-the-shelf” cellular products, thereby presenting a potentially more practical route toward broad patient access. Nevertheless, reliance on long-term systemic immunosuppression remains a significant safety concern. Immunoisolation-based approaches pioneered by ViaCyte aim to reconcile these competing challenges, while continue to face unresolved technical barriers, including foreign-body fibrosis and inconsistent in vivo maturation of transplanted progenitor cells.

Although no single strategy currently achieves an optimal balance among immunological safety, functional durability, scalability, and cost-effectiveness, the coexistence of these diverse technological pathways reflects a rapidly evolving and highly innovative research landscape. Together, these complementary approaches highlight the multifaceted progress toward curative cell-based therapies for diabetes, presenting multiple, convergent directions for overcoming the longstanding challenges of immune rejection, donor scarcity, and durable glycemic control.

Recently, our team published the first application of this technology in the treatment of T1D[46], showing its clinical potential and the necessity of immunosuppression therapy. The first patient received twice autologous E-islet transplantation due to maintaining a weak immunosuppression regimen (basiliximab and mycophenolate mofetil) and was ineffective; after secondary E-islet transplants with a full-dose immunosuppression regimen (tacrolimus and mycophenolate mofetil), the patient’s TIR increased from 48% to 97%, with HbA1c decreased to 6.8%, fasting C-peptide recovered to 0.33 nmol/L, and without severe hypoglycemic events. Meanwhile, the other two recipients received allogeneic E-islet transplants with long-term full-dose immunosuppression. Both achieved stable HbA1c levels (5.7%-6.7%) and maintained a TIR of 94%-100%. Fasting and peak postprandial C-peptide levels recovered to approximately normal ranges, accompanied by substantial reductions in insulin dosage, with some patients achieving insulin independence.

This study is the first to clearly document the risk of recurrent autoimmunity in autologous E-islet transplantation, confirming that even patients with T1D receiving autologous transplants require sufficient immunosuppression to protect the graft. Furthermore, continuous glucose monitoring system-derived metrics, including TIR and measures of glycemic variability, together with mixed-meal tolerance test-assessed C-peptide and insulin secretion dynamics and the absence of severe hypoglycemic events, collectively constitute a core set of efficacy indicators for E-islet transplantation. These parameters provide critical clinical evidence for optimizing immunomodulatory strategies in stem cell-based therapies for T1D.

The quality control (QC) framework, described in this study, has been discussed and acknowledged in recent publications from multiple international groups. Yoshihara[47] provided an independent commentary on our autologous EnSC-derived islet transplantation, recognizing its transformative potential while noting remaining challenges in scalability and long-term safety. Licht et al[48] comprehensively reviewed genetic engineering strategies for hypoimmune stem cells-derived β cells and cited our QC measures as part of the broader technical context. Lu et al[49] analyzed global clinical trial trends in stem cell therapy for diabetes, emphasizing the need for standardized manufacturing and quality assessment frameworks, aligning with our institutional experience. Nakayama et al[50] developed a standardized biodistribution protocol for iPSC-derived islets, demonstrating long-term graft survival without migration, thereby providing independent validation being consistent with our findings on safety and persistence. A Nature news article by Mallapaty[51] highlighted our first-in-human CiPSC-derived islet transplantation, describing it as a groundbreaking achievement in the field. Collectively, these external perspectives reinforce the relevance of the QC approach and situate our institutional experience in the broader international research landscape.

Collectively, the four representative strategies detailed above, including autologous chemical reprogramming (Wang et al[30]), allogeneic iPSC-derived islets with systemic immunosuppression (Vertex)[33], gene-edited immunoisolation devices (ViaCyte/CRISPR)[9], and autologous iPSC-derived endodermal stem cell approaches (Wu et al[15]/Cheng et al[45]), illustrate diverse translational pathways that are currently under investigation. Each strategy embodies a distinct trade-off among three core translational pillars: Immune compatibility, manufacturing scalability, and functional durability. Autologous approaches possess the unique advantage of immunosuppression-free transplantation, while facing inherent limitations in terms of scalability, cost, and production timelines. Conversely, allogeneic “off-the-shelf” strategies enable standardized, large-scale manufacturing, whereas remain dependent on systemic immunosuppression, with attendant long-term safety risks. Immunoisolation and gene-editing technologies represent intermediate pathways aimed at reconciling these competing demands, yet they continue to encounter unresolved technical hurdles, including fibrotic overgrowth, inconsistent in vivo maturation, and residual immunogenicity. The coexistence of these divergent strategies, rather than signaling fragmentation, reflects a dynamic and innovative research landscape wherein multiple convergent objectives-durable glycemic control, immune tolerance, and broad patient accessibility are pursued through complementary technologies. This strategic diversity highlights the multifaceted nature of the challenges remaining and provides a robust foundation for future integrative approaches that may ultimately harmonize safety, efficacy, and scalability.

CURRENT CHALLENGES AND INSTITUTIONAL EXPERIENCE IN STEM CELLS--DERIVED ISLET TRANSPLANTATION

While the following subsections draw partly on cumulative clinical experience at Shanghai Changzheng Hospital, this institutional perspective is presented as a case example to illustrate the practical implementation of the principles discussed. Where appropriate, findings and protocols from other leading centers worldwide have been incorporated to provide a more comprehensive and balanced overview of current practices.

Preoperative phase: Immunological assessment and QC

Pre-transplant immunological assessment is critical to the success of the transplant. Current clinical protocols include quantitative assessment of peripheral CD4⁺ and CD8⁺ T-cell counts, calculation of the CD4/CD8 ratio, screening for insulin-specific autoantibodies, and therapeutic drug monitoring of tacrolimus (FK506) blood concentrations in relevant clinical contexts[15]. These parameters provide an initial framework for assessing baseline immune competence and the potential risk of immune-mediated graft dysfunction.

For future applications involving standardized or broadly applicable regenerative islet products, a more comprehensive immunological stratification strategy is under development. This approach integrates high-resolution HLA typing with detailed phenotypic analysis of PBMC subpopulations. HLA typing encompasses loci HLA-A, HLA-B, HLA-C, HLA-DR, HLA-DQ, and HLA-DP, with particular emphasis on HLA-DQ8 and HLA-DR4 alleles, which are strongly associated with T1D susceptibility[52,53]. In parallel, flow cytometric profiling of PBMCs is employed to quantify the proportional composition of T-cell, B-cell, dendritic cell, NK cell, and monocyte subsets. Together, these data enable a multidimensional evaluation of immune status, facilitating prediction of post-transplant immune rejection risk and informing the design of individualized immunomodulatory or immunosuppressive regimens.

Within this immunological assessment framework, a stringent, end-to-end QC system has been established to govern the entire regenerative islet manufacturing process. At the initial PBMC procurement stage, comprehensive pathogen screening is performed, encompassing bacterial, fungal, mycoplasma, and multi-viral testing. During EnSC line establishment (EnSC stage), QC parameters focus on cellular morphology, expression of definitive endodermal markers (notably FOXA1), genomic stability, and tumorigenic potential. EnSCs are required to exhibit a uniform epithelioid morphology, a FOXA1 positivity rate exceeding 90%, a normal karyotype, and the absence of newly acquired cancer-associated mutations.

During directed differentiation, stage-specific QC criteria are applied. At the PP stage, the proportion of PDX1-positive cells must exceed 60%, with overall cell viability maintained above 90%. Upon progression to the EP stage, the combined PDX1/NKX6-1 double-positive population is required to surpass 60%, while cell survival rates must remain above 90%.

At the final regenerative islet stage, quality assessment encompasses three core dimensions: Morphology, cellular composition, and functional competence. Morphologically, regenerated islets must form compact, spherical aggregates with an approximate diameter of 150 μm. Cellular composition analysis requires a PDX1 positivity rate greater than 85% and chromogranin A expression exceeding 60%, with β-cells constituting more than 40% of the total cell population, α-cells more than 20%, and δ-cells less than 15%. Functional validation is performed using GSIS assays to confirm appropriate dynamic insulin responsiveness. Sterility testing and endotoxin assays are mandatory at each manufacturing stage. Collectively, this multilayered immunological evaluation and QC framework provides a robust safeguard for the safety, reproducibility, and clinical efficacy of regenerative islet transplantation, thereby supporting its continued advancement toward broader clinical application. This QC framework is broadly consistent with that reported by Al-Hasani et al[54] from the Baker Heart and Diabetes Institute for their clinical program.

Intraoperative phase: Transplantation sites and strategies

At present, the most widely adopted clinical approach for islet transplantation is percutaneous infusion via the hepatic portal vein. The number of transplanted islets is determined by an integrated assessment of several factors, including the estimated functional islet mass in healthy individuals, the recipient’s residual endogenous islet function, and the anticipated post-transplant survival rate of the infused islets[55,56]. Under local anesthesia, percutaneous hepatic puncture is performed with real-time ultrasound guidance, followed by intraportal islet infusion. Continuous monitoring of portal venous pressure and Doppler ultrasonography is required throughout the procedure to minimize the risks of portal vein thrombosis, embolism, and portal hypertension.

Despite its widespread clinical use, intrahepatic portal vein transplantation presents inherent limitations, most notably the risk of portal vein embolization and early inflammatory injury to transplanted islets[57]. Consequently, alternative transplantation sites are being actively investigated to improve graft survival, engraftment efficiency, and long-term functional outcomes.

Transplantation beneath the rectus abdominis muscle sheath has emerged as a promising extrahepatic site. This anatomical location offers several advantages, including surgical accessibility, minimal interference with vital organs, and a comparatively low incidence of procedure-related complications such as postoperative pain and infection[58,59]. Moreover, the rectus abdominis sheath is characterized by a rich vascular network, which supports adequate blood perfusion and nutrient delivery to transplanted tissues[60]. Favorable outcomes using this transplantation site have been reported, including studies conducted by Wang et al[30].

The greater omentum represents another attractive transplantation site, owing to its pronounced angiogenic capacity and ability to rapidly restore vascularization and oxygenation of transplanted islets. In murine models, pancreatic islets transplanted into the greater omentum regained vascularization and reinnervation within one month, with blood perfusion and oxygenation levels comparable to those of endogenous islets[61]. In addition, the omentum has been shown to provide a supportive microenvironment for islet survival and function, particularly when hydrogels are employed as islet carriers. Using this approach, transplanted islets demonstrated improved glycemic control, reduced blood glucose levels, and increased circulating C-peptide concentrations[62].

Pre-vascularized subcutaneous sites have also demonstrated potential as alternative islet transplantation locations. A recent study reported that a novel pre-vascularized, recyclable poly (D,L-lactide-co-ε-caprolactone) scaffold functioned effectively as an islet graft site in a diabetic mouse model, supporting islet survival and restoring glycemic control[63]. Such engineered subcutaneous platforms offer the advantages of procedural simplicity, ease of graft monitoring, and potential graft retrievability.

Finally, intramuscular transplantation has been explored as an additional alternative. Experimental evidence indicates that islets transplanted into skeletal muscle exhibit higher vascular density and improved oxygenation compared with certain other sites, factors that may contribute to enhanced graft survival and functional performance.

It is worth noting that research into alternative transplantation sites is being pursued actively across multiple international centers, each with distinct methodological emphases. For instance, the Diabetes Research Institute (Miami) has pioneered the development of subcutaneous device-based approaches, reporting promising preclinical outcomes with pre-vascularized scaffolds that support long-term islet survival. Similarly, the Uppsala University group in Sweden has conducted extensive comparative analyses of omental transplantation vs intraportal transplantation, demonstrating superior vascularization rates and oxygen tension in omental grafts[61]. These complementary efforts indicate that no single extrahepatic site has yet emerged as universally optimal; rather, site selection may ultimately need to be tailored to product characteristics, patient factors, and institutional expertise.

Postoperative phase: Dynamic and predictive long-term management strategies

After transplantation, comprehensive and systematic postoperative monitoring and intervention are essential to ensure graft survival, functional durability, and overall clinical efficacy. A dynamic, longitudinal management framework is therefore required to integrate functional assessment, safety surveillance, pharmacological optimization, and contingency planning.

Post-transplant graft function is monitored using continuous glucose monitoring (CGM), which enables real-time assessment of glycemic variability and glucose responsiveness of the transplanted islets. CGM data are complemented by periodic mixed-meal tolerance tests, providing an integrated evaluation of GSIS and overall endocrine function. This combined dynamic monitoring strategy facilitates early detection of functional decline or instability, allowing timely clinical intervention before irreversible graft damage occurs.

Comprehensive safety monitoring constitutes an indispensable component of long-term postoperative management. Particular attention is directed toward procedure-related and site-specific complications, including hepatic portal vein thrombosis, graft-site infection, and localized inflammatory responses[64]. Surveillance protocols include contrast-enhanced magnetic resonance imaging of the upper abdomen at 3-month intervals to evaluate graft morphology and assess potential tumorigenic risk, as well as periodic measurement of serum tumor-associated antigens. Portal venography and portal vein pressure monitoring are employed to assess portal vein patency and to identify early signs of portal hypertension or embolic events.

Pharmacological management is individualized according to patient-specific immune status, metabolic control, and graft performance. Immunosuppressive regimens are optimized using agents such as tacrolimus and mycophenolate mofetil, with dosing adjustments guided by dynamic therapeutic drug monitoring. Notably, glucocorticoids are avoided to minimize metabolic burden and β-cell toxicity, while tacrolimus blood concentrations are closely monitored to balance immunosuppressive efficacy with toxicity risk[15]. Concomitant adjustment of antidiabetic medications is performed as graft function evolves, and routine clinical assessments, including body weight and metabolic parameters, are conducted as part of standard follow-up. In selected cases, secondary transplantation may be required to achieve durable metabolic control. Causes of primary graft failure are multifactorial and include early hypoxia- and inflammation-induced cell loss, insufficient transplanted cell mass, immune-mediated rejection or recurrent autoimmunity, and progression or recurrence of the underlying disease[65,66]. Accordingly, a comprehensive prevention and management framework is essential. This includes individualized optimization of transplanted cell dosage based on recipient body size and residual islet function, as well as early identification of functional deterioration through dynamic metabolic monitoring.

When secondary transplantation is indicated, the underlying causes of initial graft failure must first be clearly delineated, followed by the formulation of a personalized secondary intervention strategy. Adjunctive cellular therapies represent a promising option in this context. MSCs, for example, exhibit pro-regenerative, immunomodulatory, and anti-inflammatory properties that may improve the local immune microenvironment and enhance graft survival[67-69]. In addition, alternative transplantation sites may be selected to optimize vascularization and oxygen delivery, such as the greater omentum or the rectus abdominis muscle sheath[70].

Emerging biomaterial-based and genetic approaches further expand the therapeutic landscape for secondary transplantation. The use of bioscaffolds, including dexamethasone-loaded microplate-enriched collagen-coated polydimethylsiloxane scaffolds, has been shown to enhance islet function and prolong graft survival[71]. In parallel, HLA gene-silencing strategies[72] and bioencapsulation technologies[73] hold promise for reducing graft immunogenicity. Immunosuppressive protocols may also be refined, for example by implementing short-term intensive immunosuppression followed by low-dose maintenance therapy. Metabolic support strategies, such as the adjunctive use of glucagon-like peptide-1 receptor agonists, may further reduce early graft loss and support long-term graft function[73].

These systematic postoperative management measures are critical for maximizing transplantation success and improving long-term patient outcomes. Individualized, multilevel, and dynamically adaptive postoperative strategies represent a cornerstone for achieving sustained graft survival and functional stability following E-islet transplantation.

Establishment of a framework for standardizing and safely advancing E-islet transplantation

On the basis of cumulative experience across the preoperative, intraoperative, and postoperative phases, a structured framework can be proposed to facilitate the standardization and safe clinical advancement of stem cells-derived islet (E-islet) transplantation. This framework integrates patient stratification, process-level QC, and long-term outcome-oriented management, with the aim of supporting both individualized therapy and scalable clinical implementation.

Establishment of individualized patient-centered decision pathways

Future clinical practice should adopt precision-based decision pathways that align transplantation strategies with individual patient characteristics, immunological profiles, and therapeutic objectives. Allogeneic, standardized “off-the-shelf” E-islet products are particularly suitable for patients who prioritize rapid availability and can tolerate long-term immunosuppression. In contrast, autologous E-islet approaches represent the optimal strategy for achieving immunosuppression-free therapy and may be especially advantageous for high-risk or immunologically sensitized populations. Intermediate strategies, including chemically reprogrammed cells or gene-edited hypoimmunogenic E-islets, offer a pragmatic balance between safety, accessibility, and immune compatibility. Preoperative precision assessment forms the cornerstone of this individualized framework. High-resolution HLA typing, combined with comprehensive immune cell subset profiling, provides a rational basis for donor-recipient matching, immunological risk stratification, and selection of the most appropriate transplantation modality.

Implementation of an integrated, end-to-end QC system

Ensuring the safety and consistency of E-islet transplantation requires a comprehensive QC system that extends across the entire production and clinical workflow. Safety assurance should not be limited to terminal product testing but instead encompass all critical stages, including donor screening, stem cell line derivation, differentiation and maturation processes, and final pre-release functional validation. A standardized set of critical quality attributes is recommended, encompassing genomic stability, cellular identity and purity, viability, sterility, endotoxin levels, and in vitro and in vivo functional performance. Clear, stage-specific release criteria should be defined for key molecular and phenotypic markers at each differentiation milestone, thereby minimizing batch-to-batch variability and reducing the risk of adverse clinical outcomes. Such an integrated QC framework is essential for regulatory compliance, multicenter reproducibility, and eventual large-scale clinical translation.

Adoption of a dynamic and predictive long-term postoperative management strategy

Successful E-islet transplantation represents a transition rather than a conclusion of clinical management. Long-term therapeutic success depends on the establishment of a structured, predictive postoperative monitoring program centered on continuous functional assessment and proactive risk mitigation. Real-time evaluation of graft performance using technologies such as CGM should be combined with periodic functional testing to detect early signs of graft instability. In parallel, regular imaging surveillance and serological screening are required to prevent and manage potential neoplastic, vascular, and inflammatory complications. Importantly, predefined, evidence-based intervention pathways should be established to address complex clinical scenarios, including progressive graft dysfunction, immune-mediated injury, or indications for secondary transplantation. Individualized adjustment of immunosuppressive regimens, metabolic support strategies, and site- or dose-specific re-intervention plans should be incorporated into this long-term management framework.

Clinical data from leading research groups have begun to inform the long-term safety profile of stem cells-derived islet transplantation. Wu et al[15] reported that autologous E-islet transplantation in a patient with T2D achieved sustained graft function for more than one year without immunosuppression, with no evidence of tumor formation or off-target differentiation during follow-up. Similarly, Guan et al[27] reported the first-in-human transplantation of chemically iPSC-derived islets (CiPSC-islets), in which a patient with T1D achieved insulin independence at one-year follow-up; imaging and serological surveillance confirmed the absence of graft-derived neoplasms or ectopic tissue formation. These early clinical validations are complemented by allogeneic approaches: Vertex Pharmaceuticals’ VX-880 program has reported engraftment and insulin production in multiple patients with T1D in ongoing phase 1/2 trials, with preliminary safety data showing no unexpected proliferative or tumorigenic events[35]. Collectively, these emerging clinical experiences, although still limited in follow-up duration and patient numbers, provide preliminary evidence supporting the long-term safety and feasibility of stem cells-derived islet products across different manufacturing platforms and immune management strategies.

Collectively, the challenges outlined across the preoperative, intraoperative, and postoperative phases highlight the multifaceted nature of barriers that must be addressed before stem cells-derived islet transplantation can achieve widespread clinical adoption. Immunological incompatibility remains the overarching obstacle, manifesting as allogeneic rejection, recurrent autoimmunity, and innate immune-mediated graft injury, each requiring distinct mitigation strategies ranging from rigorous HLA matching and immune profiling to gene-edited hypoimmune engineering. Moreover, the establishment of stringent, stage-specific QC systems has proven indispensable for ensuring the safety, consistency, and functional potency of regenerative islet products, thereby minimizing batch-to-batch variability and reducing the risk of adverse clinical outcomes. In the intraoperative context, the selection of an optimal transplantation site, balancing surgical accessibility, vascularization potential, and graft retrievability, represents a critical determinant of early engraftment success and long-term functional durability. The hepatic portal vein, despite its historical precedence, is increasingly complemented by extrahepatic alternatives, such as the rectus abdominis sheath, greater omentum, and pre-vascularized subcutaneous scaffolds, each possessing distinct advantages in specific clinical scenarios. Postoperatively, emphasis shifts toward dynamic, predictive, and individualized long-term management, integrating real-time functional monitoring (e.g., CGM), regular safety surveillance (e.g., imaging and tumor marker assessment), and pharmacologic optimization tailored to evolving graft performance and host immune status. Notably, the framework proposed in “Establishment of a framework for standardizing and safely advancing E-islet transplantation” integrates these preoperative, intraoperative, and postoperative considerations into a cohesive, patient-centered paradigm that aligns individualized decision pathways, end-to-end QC, and adaptive long-term follow-up. This integrative approach addresses current translational bottlenecks while providing a scalable blueprint for advancing stem cells-derived islet transplantation from experimental therapy toward routine clinical practice. Collectively, these coordinated strategies indicate that successful clinical translation is unlikely to result from addressing any single barrier in isolation; rather, it requires the implementation of an integrated, multilayered framework spanning the entire therapeutic lifecycle to ensure immunological safety, sustained functional performance, and reproducible efficacy across diverse patient populations.

FUTURE PROSPECTS

With the continuous advancement of stem cell biology, biomaterials, and immunomodulatory strategies, β-cell replacement therapy has emerged as one of the most promising curative approaches for diabetes. Despite substantial progress in the generation of functional E-islets, immune rejection remains the principal barrier to durable clinical translation, particularly for allogeneic and xenogeneic applications. Future developments are therefore expected to focus on immune-evasive cell engineering and alternative strategies that fundamentally address immunogenicity.

Gene-editing based immune evasion strategies

Gene-editing technologies, particularly those based on CRISPR/Cas systems, have introduced transformative opportunities to reduce the immunogenicity of transplanted cells. By disrupting HLA-I expression and concomitantly overexpressing immune checkpoint molecules such as PD-L1, prolonged graft survival has been achieved in non-human primate models without continuous systemic immunosuppression[42,74]. These findings provide compelling pre-clinical evidence supporting the feasibility of immune-evasive β-cell replacement strategies.

In parallel, CRISPR/Cas9-engineered, low-immunogenic iPSC-derived pancreatic endoderm products-exemplified by VCTX210-have demonstrated encouraging translational potential and are currently undergoing clinical evaluation[44]. Such gene-edited platforms aim to generate standardized, “off-the-shelf” cellular products capable of broad clinical deployment while minimizing immune rejection.

Nevertheless, successful clinical translation of gene-editing based strategies critically depends on robust assessment and mitigation of off-target risks. Unintended genomic alterations can be systematically evaluated through integrated approaches combining in silico bioinformatic prediction, genome-wide off-target screening, and long-term safety validation in relevant animal transplantation models. Despite these advances, potential intrinsic risks associated with permanent genome modification, particularly genotoxicity, chromosomal instability, and tumorigenicity, remain incompletely defined and will require continued refinement of detection technologies and extended clinical follow-up to achieve regulatory confidence.

Immune modulation

In terms of humoral immune modulation, the application of anti-inflammatory agents, such as etanercept (a tumor necrosis factor-α antagonist) and anakinra (an interleukin-1 receptor antagonist) has been shown to effectively reduce early graft loss following transplantation[75]. These agents mitigate inflammatory cytokine-mediated damage during the critical early post-transplant period, thereby improving initial graft survival. Local immunomodulation strategies have also attracted increasing attention. The co-transplantation of MSCs, combined with sodium alginate microencapsulation, and supplemented with chemokine delivery systems such as CXCL12, has demonstrated promising outcomes in animal models. This approach not only supports long-term graft function but also creates a localized immunoprotective microenvironment that attenuates immune cell infiltration and inflammatory responses. Collectively, these strategies provide a novel framework for achieving sustained local immune regulation without systemic immunosuppression[76,77].

The integration of multiple immunomodulatory approaches may further enhance therapeutic efficacy. For example, antibody containment combined with plasma exchange has proven effective in preventing acute rejection by removing circulating donor-specific antibodies, thereby reducing immune-mediated graft injury and improving transplantation success rates[78]. In parallel, the application of immunoglobulin G (IgG) silencing technologies offers a promising strategy for inducing long-term immune tolerance. By suppressing IgG activity, these approaches diminish antibody-mediated immune attacks on the graft, prolong graft survival, and significantly reduce the risk of antibody-mediated rejection[79].

Chimeric antigen receptor-based cell-mediated local immune tolerance induction represents another promising avenue for immunomodulation in islet transplantation. Fourth-generation CAR-T cells have demonstrated the feasibility of local immunomodulation through activation-induced interleukin-12 release[80]. Although primarily explored in oncology, the application of chimeric antigen receptor-based cells for targeted immune regulation in transplantation represents an emerging frontier that may synergize with existing islet protective strategies.

Moreover, the synergistic effects of multi-target immunomodulatory molecules are currently under intensive investigation. By simultaneously acting on multiple immune pathways, these strategies enable a more comprehensive suppression of immune responses, ultimately improving graft survival and paving the way for more durable and effective transplantation outcomes. Recent clinical evidence from our IIT study involving three recipients with T1D and complete loss of endogenous pancreatic β-cell function pretransplant demonstrated that both autologous and allogeneic stem cells-derived islet therapy can successfully restore durable normoglycaemic islet function[46]. While autologous approaches eliminate the need for immunosuppression, allogeneic strategies require careful immunological matching and postoperative management to achieve comparable outcomes. These findings emphasize the importance of individualized immunomodulatory approaches based on donor-host compatibility.

Among the diverse immune-evasion strategies under investigation, three approaches have emerged as particularly promising based on accumulating evidence.

Firstly, gene-edited hypoimmune platforms (e.g., VCTX210) disrupt HLA class I/II expression while upregulating immune checkpoint molecules (HLA-E, CD47, PD-L1), enabling evasion of both adaptive and innate immunity. VCTX210 has advanced to clinical trials (NCT05791201); however, long-term safety data remain pending.

Secondly, local immunomodulation strategies combining MSC co-transplantation with biomaterial encapsulation (e.g., CXCL12-loaded alginate devices) provide localized immunoprotective niches, supporting long-term graft survival without systemic immunosuppression in preclinical models[76,77]. However, fibrotic overgrowth and device retrievability remain challenges.

Thirdly, pharmacologic immunomodulation targeting early post-transplant inflammation (etanercept, anakinra) has established clinical utility in terms of reducing early graft loss by mitigating instant blood-mediated inflammatory reaction[74], although these agents do not prevent late rejection.

Significant uncertainties remain, including potential off-target effects and genotoxicity associated with gene-editing approaches, variability in fibrotic responses affecting encapsulation systems, and the limited capacity of pharmacologic strategies to prevent late-stage graft rejection. In summary, although gene-edited hypoimmune platforms may be among the most promising strategies for enabling immunosuppression-free allogeneic islet transplantation, no single approach has yet achieved an optimal balance of safety, efficacy, and scalability. Overcoming these remaining challenges will require coordinated advances across multiple disciplines[74,76,77].

Optimizing pancreatic islet cryopreservation techniques

At the technical level, the optimization of pancreatic islet cryopreservation is essential for improving treatment accessibility and scalability. Current cryopreservation approaches, particularly vitrification-based freezing techniques, have demonstrated the ability to preserve high levels of islet viability and functional integrity when applied to small quantities of islets. In 2022, Zhan et al[81] developed an optimized vitrification and rapid rewarming (VR) technology based on the cryomesh system. By increasing the cooling and rewarming rates (up to 5.4 × 10⁴ C/minute and 30.9 × 10⁴ °C/minute, respectively), this technique effectively prevents ice crystal formation and enables large-scale islet preservation. This method can process 2500 islets, achieving a recovery rate of above 95% and a post-thaw viability of higher than 89%. Furthermore, in a diabetic mouse model, transplantation of VR-preserved islets restored normoglycemia in 92% of recipients within 24-48 hours, with functional maintenance lasting up to 150 days[81]. These methods represent a critical step toward enabling long-term storage, flexible transportation, and centralized manufacturing of islet products. Nevertheless, their safety, reproducibility, and functional stability must be robustly validated through large-scale animal studies and well-designed clinical trials before widespread clinical implementation.

The standardization of cell preparation, QC, and functional characterization, when combined with robust cryopreservation protocols, has the potential to remarkably reduce production costs and logistical barriers. Such advances would facilitate the establishment of islet cell banks and broaden patient access to stem cells-derived islet transplantation therapies, ultimately allowing a larger population of diabetics to benefit from these treatments (Figure 2).

Figure 2 Roadmap for future development of stem cells-based diabetes therapy. This figure illustrates four key strategic directions aimed at advancing the clinical translation and efficacy of stem cell-derived islet (E-islet) transplantation. Gene editing strategies and related technologies to modify E-islets, reducing immunogenicity and enhancing immune compatibility. Microenvironment modulation creates a supportive niche, improving graft survival, vascularization, and long-term function. Establishment of standardized manufacturing process includes procedures, such as cell culture, differentiation, purification, and final formulation for clinical administration. Advanced cryopreservation techniques develop optimized freezing and rewarming protocols to ensure stable preservation, facilitate logistics, and improve the accessibility of islet products. Gene editing: Genetic modification of E-islets to reduce immunogenicity and enhance immune compatibility. Key approaches include CRISPR/Cas9-mediated gene editing, human leukocyte antigen-I knockout to evade CD8⁺ T cell recognition, and programmed death-ligand 1 overexpression to induce local immune tolerance. The goal is to create “immune-evasive” islet cells that survive without systemic immunosuppression. Microenvironment modulation: Creation of a supportive niche at the transplantation site to improve graft survival and function. Key approaches include anti-inflammatory agents, IgG silencing technology to prevent humoral rejection, biomaterial scaffolds, and mesenchymal stem cell co-transplantation to provide immunomodulatory and pro-angiogenic support. The goal is to protect islets during the critical early post-transplant period. Standardized production: Establishment of robust manufacturing processes for scalable clinical deployment. Key components include optimized cell culture, directed differentiation with QC checkpoints, purification, final formulation, and comprehensive quality testing. The goal is to enable “off-the-shelf” availability through reproducible and cost-effective manufacturing. Cryopreservation techniques: Development of optimized protocols for long-term storage and transportation of islet products. Key approaches include vitrification, optimized rewarming protocols, cell isolation and retrieval methods, and specialized injection solutions. The goal is to enable centralized manufacturing, global distribution, and on-demand availability. Created in BioRender (Supplementary material). HLA: Human leukocyte antigen; KO: Knockout; PD-L1: Programmed death-ligand 1; OE: Overexpression; TNF: Tumor necrosis factor; IL-1Ra: Interleukin-1 receptor antagonist; IgG: Immunoglobulin G.

In summary, while gene-edited hypoimmune platforms currently appear to represent the most promising strategy for achieving durable, immunosuppression-free allogeneic islet transplantation (supported by their rapid clinical translation and multilayered immune-evasion design), no single approach has yet demonstrated an optimal balance of safety, efficacy, and scalability. Continued progress will depend on the convergence of advances in genetic engineering, materials science, and immunomodulatory pharmacology to overcome the remaining challenges and fully realize the therapeutic potential of stem cells-derived islet transplantation.

Looking forward, future progress will not depend on the isolated optimization of individual technologies, while will rely on the integration of a multimodal, collaborative therapeutic paradigm. Although significant advances are being made independently in gene editing, immune modulation, cryopreservation, and biomaterials, no single strategy can fully address the complex challenges of stem cells-derived islet transplantation. These challenges include immune rejection, long-term functional maintenance, scalability, and clinical accessibility. Achieving a deep and coordinated integration of genetic engineering, materials science, and cell engineering through interdisciplinary collaboration will be essential for overcoming these bottlenecks and driving substantive progress toward the ultimate goal of a durable and widely accessible cure for diabetes.

CONCLUSION

Stem cells-derived islet transplantation represents a transformative paradigm in diabetes therapy, shifting the therapeutic goal from long-term glycemic control toward the restoration of endogenous insulin-secreting function. This review provided a systematic comparison of clinical strategies developed across different research groups, highlighting both shared progress and divergent translational approaches. Despite noteworthy advances, remarkable challenges remain, particularly in terms of immune rejection, long-term safety, and sustained graft functionality. Successful clinical translation will require the achievement of durable graft survival, the establishment of standardized and scalable manufacturing protocols, and the development of robust postoperative monitoring and follow-up systems. As innovations in stem cell biology, gene editing, immunomodulation, biomaterials, and cryopreservation continue to converge, the realization of a functional and durable cure for diabetes is becoming an increasingly attainable goal.