Stem cell transplantation in immuno-hematologic and infectious diseases

Abstract

Stem cells are pluripotent cells that can divide and differentiate, forming many different types of cells. Stem cells can be obtained from various sources, with embryonic stem cells being the most advantageous as they possess a broad dividing potential. When the standard treatment proves ineffective, stem cells are typically utilized as a final option. Infections and childhood malignancies are among the significant causes of mortality in the pediatric population. Stem cell therapy has shown a decrease in morbidity and mortality when used in patients with favorable conditions like young age and lack of comorbidities. This review discusses how stem cells are prepared and used in treating pediatric diseases like X-linked agammaglobulinemia, diabetes mellitus, aplastic anemia, infections, and leukemia. Technological advancement has played a significant role in producing more specific stem cells using genetic modification methods like clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9, which produce stem cells that target a particular cell type, e.g., myocytes and hematopoietic cells, further increasing the effectiveness of the therapy. We address the obstacles faced when conducting research related to stem cells, including ethical and legal issues, which hinder the use of this therapy in some fields. We also indicate recommendations for increasing the efficacy of stem cell therapy in the pediatric population.

Key Words: Stem cell; Pluripotent; Malignancy; Morbidity; Agammaglobulinemia; Diabetes mellitus; Aplastic anemia; CRISPR-associated protein 9; Leukemia

Core Tip: Treatment of some diseases in the pediatric population can be ineffective with standard therapy. The use of stem cells to treat various diseases in this population has increased over the last few years due to technological and genetic advancements that have allowed more targeted therapies to be used. Ethical and legal issues remain a significant hindrance in research and clinical studies related to stem cells.

INTRODUCTION

Stem cells are pluripotent cells that can regenerate and differentiate into various types of cells. Stem cells can be obtained from bone marrow, fat, dental pulp, blood, amniotic fluid, umbilical cord, and other tissues (Figure 1)[1-5]. Embryonic stem cells are derived from embryos at a specific period, nearly 4 or 5 days after fertilization[6]. Though not as effective in differentiation, adult stem cells can also be used[7,8]. Pluripotent cells can differentiate into many cells, while oligopotent cells can differentiate into a limited number. Oligopotent cells include myeloid cells, which can differentiate into any blood cells found in the body, such as hematopoietic stem cells, lymphoid progenitor cells, and mammary stem cells. Table 1 shows the difference between pluripotent and oligopotent stem cells and the types of pediatric diseases that can be treated[5,8]. The use of stem cells to treat different diseases, especially where the standard treatment is ineffective, has increased over the years.

Figure 1 The figure shows types of stem cells with their respective examples. Adapted from Das and Tyagi[100].

Table 1 The table below shows the difference between pluripotent and oligopotent stem cells, listing various diseases they can treat.

Pluripotent stem cells	Oligopotent stem cells
They can differentiate into any type of cell in the body	They can self-renew and differentiate into hematopoietic stem cells
The functions of the original cells are difficult to achieve	Non-controversial, accepted distinctly by patients
Immunogenicity i.e., immunological mismatch of the stem cells to the body is a major problem	Mainly found in bone marrow
Can be differentiated into endoderm, ectoderm, mesoderm, allowing a wide range of use in treatment. High rates of genetic instability increase tumorigenicity	Differentiate into red and white blood cells and platelets. Can also result in hematopoietic malignancy
Used to treat heart diseases e.g., long QT syndrome, Brugada syndrome, cardiomyopathies etc. muscle disorders, diabetes, kidney diseases, cystic fibrosis, spinal cord injury and many more	Used to treat: Malignancies e.g., leukemia, lymphoma, neuroblastoma, Ewing sarcoma, choriocarcinoma and phagocyte disorders. Congenital diseases e.g., lysosomal storage disorders, mucopolysaccharidoses, glycoproteinoses, ataxia telangiectasia, Di George syndrome, severe combined immunodeficiency, aplastic anemia etc.

Usually, it is not used as the first-line treatment due to the availability of less invasive therapies, but also due to the complicated procedures used and the side effects of the transplantation process. Many studies have shown that many diseases could be treated by using stem cell therapy[9]. Still, ethical and legal issues, expenses, and many other factors hinder more studies. The new 2021 International Society for Stem Cell Research guideline, compared to the previous one, provided a more favorable environment to conduct advanced studies in this field by adding new recommendations that address recent advancements involving embryos, organoids, gene editing, chimeras, and stem cell-based embryo models[10].

In this article, we will review the applications of stem cells and their limitations, which are derived from these technologies, mainly focusing on immunohematologic and infectious diseases. The review consists of various sections, like acquisition of stem cells, where we explain in an orderly manner how stem cells are obtained, prepared, and purified before use. The next section addresses the use of stem cells in diseases such as Bruton’s agammaglobulinemia, Type 1 diabetes mellitus, aplastic anemia, colistin-resistant Acinetobacter baumannii sepsis, Pseudomonas aeruginosa infection, and leukemia. In the discussion section, we discuss the stem cell developments over the years, the stem cell market, the prices, and the complications that occur because of stem cell use. The future expectations section explains the newly developed gene editing methods and discoveries that might cause significant improvements in this field.

The relevant literature was searched in PubMed and Google Scholar using the keywords “stem cells”, “immunology”, “hematology”, “infectious disease”, “Bruton”, “leukemia”, “diabetes”, “aplastic anemia”, and “sepsis” for the last 25 years (published from January 2000 to July 2025). Articles with titles that do not include these keywords are not screened.

Stem cells are acquired through a series of processes. Cells are cultured in isolated conditions to avoid complications resulting from cell overproduction[11]. In vitro stem cells can cause chromosomal abnormalities and mutations[8]. Stem cells undergo asymmetric division, producing slightly larger cells[12]. Stem cells are produced based on the number of cells required for a particular treatment. For example, pancreatic islet transplantation requires about 1 billion cells[13]. Other requirements include bioreactor dimensions for generating multiple cells, medium, and the duration necessary for the production. A culture medium is needed to produce specific cell types. Ongoing studies exist using xeno-free media to culture stem cells[14]. A matrix is required for the produced cells to attach. Bioreactors are necessary to provide a regulated and controlled environment for cell growth. Hematopoietic stem cells have shown the most successful results in producing various progenitor cells[15]. Sources of stem cells include bone marrow, peripheral blood, umbilical cord, etc.[16,17]. The stem cells are expanded and scaled up in vitro. The number of bone marrow cells has increased in the presence of CD34+ cells. The function of CD34+ is not entirely known yet, but experimental studies suggest that CD34+ regulates the proliferation and maintenance of stem cells[18,19]. Transcription markers are added depending on the cells produced[20,21].

The differentiated cells are enriched for safety and purity. The purification process involves both positive and negative selection. For example, in cardiomyocytes, the specific surface marker CD166/activated leukocyte cell adhesion molecule is used to isolate cardiomyocytes from embryonic cultures to produce stem cells, which can be used in cardiac cell damage, like infarction, an irreversible damage to myocytes. These specific cells have also shown a decrease in post-transplant complications like transplant rejection. Cytotoxic monoclonal antibodies eliminate[22,23] undifferentiated cells to reduce complications like teratoma formation[24,25]. All types of stem cells have pros and cons as shown in the table below (Table 2). The stem cells obtained can be implanted after the donor and recipient’s matching human leukocyte antigen (HLA) is confirmed.

Table 2 The table below shows different stem cell types and their pros and cons.

Stem cells	Pros	Cons
Fetal cells	Safe and effective for transplantation	Tissue availability. Ethical issues
Embryonic stem cells	Pluripotent, have stable karyotype and can differentiate into a wide variety of cells. Autologous transplant so less risk of GVHD	Over proliferation can cause tumor formation. Ethical concerns. High rate of rejection. Limited supply and availability
Pluripotent stem cells	Reduces ethical issues. Lower rejection risk since used as specific therapy	High risk of tumor formation i.e., teratoma. High risk due to reprogramming. Hard to make standard therapy
Reprogrammed stem cells	Low tumor formation risk. Lower rejection risk. Reduced ethical issues. Undergoes simple formation process	Low efficiency. Not deeply understood due to lack of enough studies. Hard to standardize
Adult stem cells	No ethical issues	Restricted potentials

Adopted from Pereira et al[101]. GVHD: Graft-vs-host disease.

STEM CELL USES IN BRUTON AGAMMAGLOBULINEMIA

Also known as X-linked agammaglobulinemia, Bruton agammaglobulinemia is an immunodeficiency disease commonly affecting pediatric patients aged 1-5[26]. It is caused by a genetic mutation of the Bruton tyrosine kinase gene[27]. It presents with low immunoglobulin levels due to a significantly reduced or complete lack of B cells in circulation[28,29]. Standard therapy includes gamma globulin therapy and antibiotics[30,31].

The patients undergo hydration therapy before transfusion, then are pretreated with hydrocortisone and antihistamines before the stem cell infusion. Post-transplantation, the patients are followed up at a short interval, especially within the first few days. The follow-up continues at 4 months, 8 months, and 12 months and then at 6-month intervals for 5 years after transplantation. Patients are selected based on eligibility criteria to avoid the procedure’s toxic effects. Patients and donors are chosen based on age because the normal number of B cell precursors decreases with age[32,33], and the risk of graft vs host disease is lower in patients receiving stem cells from young donors[34,35]. According to studies, it is unlikely that patients with X-linked agammaglobulinemia who are not given any pretreatment or anti-rejection therapy will show clinical benefit even if the HLA is matched. This acts as a significant hindrance to the widespread use of stem cells. The use of minimally toxic preparative regimens may be sufficient to permit long-term B-cell engraftment in patients with X-linked agammaglobulinemia[36]. Studies on X-linked agammaglobulinemia and stem cell use are scarce. Still, an example includes a case report in which a pediatric patient presented with X-linked agammaglobulinemia and acute myeloid leukemia (one among the complications of X-linked agammaglobulinemia). The patient was treated with standard treatment, i.e., chemotherapy, and after 7 months, relapse occurred. After two re-induction trials, the patient’s symptoms persisted. The patient was then treated with stem cell therapy, and after two years, the patient’s leukemia remained in remission, and the CD19 and immunoglobulin levels became elevated[37]. This indicates significant benefits and success of stem cell therapy.

STEM CELL USES IN TYPE 1 DIABETES MELLITUS

Pancreatic beta cells produce insulin, an essential regulator of energy metabolism throughout the body, by using carbohydrates, fats, and proteins[38,39]. The amount of insulin in the body varies depending on the energy required and the metabolites available. Type 1 diabetes mellitus is a disease that results from a lack of islet beta cells of the pancreas. In type 1 diabetes, insulin production is lacking because an autoimmune process selectively destroys β cells[40,41]. The lack of insulin causes an increase in blood glucose level, resulting in various metabolic complications due to non-functioning enzymatic reactions and deposition in different organs over the years. Keeping blood glucose levels as close to normal as possible is essential to avoid long-term complications such as cardiovascular, nephrogenic, and ophthalmologic diseases[42,43]. The standard treatment of type 1 diabetes is insulin replacement therapy.

The advancements in stem cell technologies have led to human clinical trials using stem cell-derived pancreatic products. In one study, stem cell-derived pancreatic endoderm cell population known as pancreatic endoderm cells was produced in vivo[44,45]. The Encaptra^® device was designed to immunoprotect the cells using a cell-impermeable membrane[46]. The engraftment was tolerated but halted due to insufficient engraftment materials. Another study demonstrated glucose-responsive C-peptide production 6-9 months post-transplant as the grafted cells matured from pancreatic progenitors into endocrine cells[47,48]. The current differentiation methodologies have challenges, including producing different cell types resembling enterochromaffin cells, which are endocrine[49]. Also, the graft cells do not work exactly as the original cells, requiring a lot of cells to be engrafted. Currently, ongoing studies are developing more advanced islets through a multistep differentiation process that attempts to mimic stages of embryonic development[50]. A triple-blinded, randomized study using mesenchymal stem cells (MSCs) in 21 patients with type 1 diabetes mellitus showed impressive results, including reduction of hypoglycemic episodes, improved glycated hemoglobin levels, and improved quality of life[51].

STEM CELL USES IN APLASTIC ANEMIA

Aplastic anemia is when the bone marrow fails to produce hematopoietic cells, resulting in various complications. It is a rare condition with different etiologies, including benzene, specific animal fertilizers, and pesticide exposure[52]. Infectious agents may cause aplastic anemia, though not commonly, because it usually presents as an immune-mediated disease. HLA-DR2 is over-represented among patients with aplastic anemia, and its presence predicts a better response to cyclosporine[53,54]. Despite an unknown mechanism of action, horse anti-thymocyte globulin is the only drug approved by the Food and Drug Administration for the treatment of aplastic anemia[55].

Hematopoietic stem cell transplantation can offer a cure, especially in the pediatric population. Allogeneic bone marrow transplantation from a histocompatible matched sibling is most curative. Studies have shown a 5-year survival rate of approximately 77%[56]. The most important indications of stem cell transplantation include age and HLA matching to avoid graft-vs-host disease (GVHD)[57]. Evaluation of previous bacterial, viral, and fungal infections should be conducted and eradicated before the transplantation. Prophylaxis for GVHD includes a short course of methotrexate; some protocols add alemtuzumab[58]. Post-transplant cyclosporine levels should be maintained around 200-300 ng/mL, and tacrolimus levels between 10 and 15 ng/mL. This treatment should be continued for 9-12 months, followed by a taper over 3 months[36]. The graft failure rate has been reported to range from 0% to 26%[59]. Chimerism analysis is performed in 1-month, 3-month, 6-month, and 12-month post-transplant intervals. Survival rate has improved rapidly from 48% to 90% over the last 40 years[60,61], making stem cell transplant the most effective treatment for aplastic anemia. A retrospective study reviewed 127 patients with severe aplastic anemia treated with hematopoietic stem cells. The study showed decreased graft rejection and an overall 5-year survival of approximately 91%[62].

STEM CELL USES IN TREATING COLISTIN-RESISTANT ACINETOBACTER BAUMANNII SEPSIS

Sepsis is one of the leading causes of death globally. According to studies, the estimated number of cases ranges from 19.9 million to 48.9 million[63,64]. Colistin-resistant Acinetobacter baumannii, a microorganism with multidrug resistance of approximately 33%[65], is very hard to treat with standard treatment. It has a mortality rate as high as 70%[66]. The standard therapy includes a colistin-fosfomycin combination with no significant side effects[67,68].

Currently, there are studies on using MSCs to treat this drug-resistant sepsis[69]. MSCs have antibacterial and anti-inflammatory properties, and they increase the production of anti-inflammatory cytokines [interleukin (IL)-10, IL-13] while decreasing the production of proinflammatory cytokines (tumor necrosis factor-α, IL-1, IL-6). Although animal models have shown a successful response to MSC, it is not practical to explore findings on sepsis patients by relating them to animal studies[70]. The preliminary data for the Russian clinical trial of MSCs for septic shock (NCT01849237) have been reported[71]. Despite fewer published studies, treating colistin-resistant Acinetobacter baumannii sepsis using MSCs and the colistin-fosfomycin regimen holds significant potential for reducing bacterial load and preventing disease progression. In an experimental model study design of mice, Acinetobacter baumannii was injected into the subjects after administering different treatment modalities, and then the bacterial clearance was observed. The clearance of bacterial load was highest in groups in which MSCs were administered. The study concluded that adding stem cells is essential for clearing bacterial load and preventing histopathologic damage[72].

STEM CELL USES IN PSEUDOMONAS AERUGINOSA INFECTION

Infection is the primary cause of death in the pediatric population[73], partly because the immune system is not fully developed enough to fight the pathogens. Pseudomonas aeruginosa is one of the most difficult microorganisms to treat due to the development of resistance strains even to newly developed treatments. Antibiotic exposure in neonates increases the incidence of superinfection, necrotizing enterocolitis, and death[74].

Studies have shown that using human umbilical cord MSCs extensively treats infectious diseases in neonates. These cells can proliferate and differentiate into various cells[75]. A study showed that human umbilical cord MSCs could be effective against Pseudomonas aeruginosa resistant strains[76]. The study assessed the effects of stem cells on Pseudomonas-resistant bacteria. Stem cells were infected with the bacteria for 6 hours. Then, the ability of stem cells to inhibit bacterial growth was evaluated by incubation. The results showed that the development of Pseudomonas was remarkably inhibited compared to the control medium, proving the effectiveness of the therapy. Stem cells proved to have a more potent antibacterial effect. An animal study was conducted to check the antimicrobial properties of MSCs against various bacteria affecting patients with cystic fibrosis. The study found that the number of Pseudomonas bacteria was decreased in groups where stem cells were administered and further showed additive effects with combination therapy with geneticin[77].

STEM CELL USES IN PATIENTS WITH LEUKEMIA

Leukemia is a condition that occurs due to abnormal proliferation and differentiation of hematopoietic cells. It is the most common malignancy of childhood. Leukemia can be divided into myeloid and lymphoblastic leukemia, subdivided into acute and chronic[78,79]. Leukemia is managed with multi-agent systemic chemotherapy for over 2 years to 3 years. A more targeted therapy has been developed for patients with a positive Philadelphia chromosome[80]. Targeted therapy has much lower side effects than non-targeted therapy, but cannot be used in all types of leukemia.

The production of hematopoietic cells from pluripotent stem cells requires a change from endothelial to hematopoietic progenitor cells[81]. Hematopoietic stem cells can be obtained from various types of cells, including human embryonic stem cells, induced pluripotent stem cells, tiny embryonic-like stem cells, and many others. Transcription factors responsible for hematopoietic cells, i.e., runt-related transcription factor 1, promote the development of the cells by activating the expression of runt-related transcription factor 1a, the primary regulator for hematopoiesis. Spalt-like transcription factor 4 is highly expressed in CD34+, CD38- hematopoietic stem cells and not in CD34+, CD38+ hematopoietic progenitor cells. Downregulating this gene is beneficial in treating leukemia[82]. Auto and allogeneic human stem cell transplantation has significantly improved leukemia treatment. The risk of side effects, e.g., blast crisis and relapse, is much lower. Allogeneic human stem cell transplant is a more commonly used treatment for many classes of leukemia. A case study of an 8-year-old boy showed relapse after 3 months of treatment of leukemia with chemotherapy, complications with organisms like mucormycosis affecting the brain and lungs occurred. Administration of cord blood transplant with liposomal amphotericin B resulted in complete remission. The study concluded that stem cell therapy could reduce the mortality rate in patients with leukemia complicated with mucormycosis[83].

DISCUSSION

In 1998, the first human embryonic stem cell line was derived, creating a significant revolution in the stem cell field. Over the years, research has been conducted, and in 2012, a Nobel Prize was awarded for the discovery of mature cell reprogramming to produce pluripotent cells. This allowed more studies to be undertaken due to the increased sources from which stem cells could be obtained. In 2014, the first clinical trial with human induced pluripotent stem cells was initiated[84]. The primary gene editing methods include clustered regularly interspaced short palindromic repeats, organoids, and chimeric embryos. Clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 is a popular gene editing method involving adding, removing, or changing DNA sections. The preparation process involves the following steps: The CRISPR-associated protein 9 scans for a specific DNA protospacer adjacent motif, the adjacent DNA segment is unwound, and if it matches the sequence in crRNA, then CRISPR-associated protein 9 cuts both strands of the DNA, creating a double-stranded DNA break. The obtained products can then be introduced into the nucleus of various cells, generating multiple outcomes to the added products[85]. This method has the potential to cure genetic diseases, neurodegenerative diseases, and cancer.

Trials have shown outstanding results in hematologic diseases like sickle cell anemia[86,87]. Factors like genetic mismatching and the pre-transplantation treatments impede the use of stem cells. Stem cell therapy is a costly treatment method. Analysis of the global market showed that in 2022, the total budget was approximately US $287 million and is predicted to rise to US $1172 million within 8 years. For each treatment, the cost ranges from 10000$ to 60000$[88]. This prevents many patients from accessing therapy.

Stem cell transplantation leads to severe immune deficiency, thus a high risk of infection. The innate immune system recovers earlier, while the adaptive immune system, especially T-cells, remains impaired for years. Complications of stem cell therapy can be divided into two groups: Early and late complications. Early complications include infections, acute GVHD, transplant failure, pneumonitis, veno-occlusive disease, cardiac failure, hemorrhagic cystitis due to the use of highly cytotoxic agents for pretreatment, etc. Late complications include chronic GVHD, autoimmune disorders, secondary malignancy, infections, etc. Stem cell treatment has shown an increased success in treating different diseases, including drug-resistant infections. Since many studies are not conducted in clinical settings, understanding their effects on human beings is limited. Many clinical studies are limited by one or another factor, making it hard to utilize the therapy effectively[89,90]. Since the process is a multi-procedure and requires an extended follow-up, some studies showed several patients withdrawing from the study[91]. The limitations of performing studies in the pediatric population lead to insufficient information concerning this group. The previous guidelines on stem cell research restricted most studies from being conducted due to ethical and legal issues. The 2021 International Society for Stem Cell Research guideline consists of 3 categories of research: Category one research, exempted from review; category two research, reviewed but with specialized oversight; and category 3, into which research is not allowed. Despite being revised, there are still restrictions, especially on the use of embryonic stem cells, that prevent more trials from being performed[92]. For example, many studies directed to the nervous system are considered high risk, thus not performed clinically despite showing promising results in treating diseases like Parkinson’s disease, stroke, and spinal cord diseases[93]. This gives organoid studies an upper hand, creating the potential to study human development, regenerative medicines, and different diseases in detail[94].

FUTURE EXPECTATIONS

To ensure even more successful future results, scientists are currently studying issues related to donor cells, cell processing, and the therapeutic cell niche. Cytogenetic testing might achieve therapeutic goals, such as comparative genomic hybridization arrays and karyotyping. The newly discovered gene editing methods, including single-cell omics, and the CRISPR gene editing technique, have shown promising results in this field. Using these techniques, genes in stem cells can be activated or silenced depending on the required cell type. Genes can also be modified to produce cells needed for use within a particular period, temporarily and even permanently. Gene editing by the clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 method is handy in diseases that occur due to mutations.

Regarding ethical issues, embryonic stem cells have been established from a more ethical source, i.e., surplus in vitro fertilization embryos[95]. Technological development has allowed studies like molecular regulation of myogenesis to be conducted, creating a new era of treatment of cardiac diseases[96]. Examples of studies conducted were explicitly aimed at myogenesis[97-99]. Genetic modification has also been shown to reduce the side effects and complications of the treatment since it’s more specific.

CONCLUSION

The application of stem cell therapy has been shown to reduce morbidity and mortality in groups of patients with favorable criteria for transplantation, i.e., age, comorbidities, type of stem cells used, etc. Using stem cells to treat diseases in the pediatric population is an emerging technology that still requires further research. The stem cell research guideline should be revised to create a more flexible environment for conducting research. Conditions enabling researchers to conduct studies across various fields and support from the healthcare system should be established. The long-term side effects should be studied comprehensively to establish more thorough pre- and post-transplant management procedures. The high prices prevent many patients from using the therapy. In addition, results obtained from various studies should be shared even if the survey was incomplete. Multiple solutions and study models can be constructed by understanding the weaknesses and strengths of studies. Also, by providing education about the use of embryonic stem cells and solving the ethical issues, stem cell treatment may become one of the best ways to treat drug-resistant and other conditions in pediatric patients.