Stem cell therapy for faecal incontinence: Current state and future perspectives

Table 1 Faecal incontinence models employed in published preclinical studies and their types of reparation systems

Surgical injury	Crioinjury	Pudendal nerve crush	No injury
Section	2	1[43]	3
Anterior: 2
Left lateral: 9[43]
Posterior subtotal: 3
Proctoepisiotomy: 1
25% excision: 4
50% excision (IAS: 1) (both: 3)
Total excision EAS: 1
Type of reparations employed
Surgical repair	No repair	Substitution	Not applicable
6	Crioinjury: 2	2	3
Randomized 2[39,64]	Section: 9[39,43,64] Excision: 7

Numbers indicate the number of published studies. EAS: External anal sphincter; IAS: Internal anal sphincter.

Table 2 Origin of stem cells used in published preclinical studies, classified by organ origin and transplant type

Kind of stem cells employed
Muscle progenitors	Bone marrow SCs	ASCs	Enteric neural	USCs
Myoblasts: 6	BM-MSCs: 10[35,38,60]	Aut: 1	Aut: 1	Xenog: 1[38]
Muscle SCs: 9	Mononuclear: 1[60]	Xenog: 1	Xenog: 1
Autologous/syngeneic	Allogeneic	Xenogeneic
11[35]	17[35,38]	3[38]

Numbers indicate the number of published studies. ASCs: Adipose-derived stem cells; USCs: Umbilical cord stem cells; BM-MSCs: Bone marrow-derived mesenchymal stem cells; Aut: Autologous; Xenog: Xenogeneic.

Table 3 Bioengineering strategies used with stem cells in published preclinical studies, and scaffolds employed as stem cell carriers to improve their function

Bioengineering models
[46,55,56]	Polycaprolactone beads
[51]	IAS muscle cells + human ENPC + bilayer collagen and laminin hydrogel
[57]	Polyethylene glycol-based hydrogel matrix scaffold
[58]	Decellularized EAS
[76]	IAS cells + enteric neural progenitor cells (biosphincter)
[65]	Polyacrylamide hydrogel carrier (Bulkamid)
[61,63]	Gelatin scaffold

ENPC: Enteric neural progenitor cells; EAS: External anal sphincter; IAS: Internal anal sphincter.

Table 4 Overview and concise review of different published studies related to faecal incontinence and stem cell therapy in animal models

Ref.	Animal	N	Randomized	Type of SC	Compared to	FI model	Repair?	Treatment	Effect measure	Follow up	Principal Results	Security concerns
[35]	Rats	32	No	AUT/ALLOG BM-MSCs	Sham injury Injury + SSF	Surg section	Surg	Inj IE	Histology In vitro contractility	30 d	↑ muscular area ↑ Electric response and relaxing	No
[36]	Rats	15	No	MDSC AUT	No injury Crioinj/crioinj + SCs	Crioinjury	No	Inj IE	Histology In vitro contractility	7 d	SC survive + myofibre differentiation ↑ contractility (NSS)	No
[37]	Rats	??	No	Myoblast ALLOG	Subcutaneous levator ani thig muscle	No	No	Inj levator ani	Histology	??	SC survivor injury necessary for myofibre formation	No
[38]	Rab-bits	31	No	hUSCs SYNG BM-MSCs ALLOG	Culture medium Saline	Section	No	Inj IE 2 wk later	Clinic EMG Histology	2 wk	BM-MSC: better continence ↑ act SS ↑ muscle	No
[39]	Rats	120	Yes	MDSC ALLOG	Saline	Surg section EAS	Surg	Inj IE	Contractility	13 wk	↑ SS contractility 7/90 d only repaired	No
[40]	Rats	4	No	Myoblasts ALLOG	None	No	No	Inj IE	Histology	10 d	SC survival and integration in sane host tissue	No
[41]	Rabbits	21	No	MDSC AUT	Saline	Surg section EAS	No	Inj IE 3 wk later	Clinic Histology EMG + MAR	2 mo 6 mo (control)	↑ continence since 4w Miotube + myofibre (4wk), SC Survival, ↓ Cd3 and cd34 cells, ↑ proliferate ↑ SS MAR and EMG since 4wk and grew	No
[42]	Rats	224	No	BM-MSCs ALLOG local/systemic	PBS local/Syst	Surg section EAS	Surg	Inj IE/systemic	Mollecular Histology Neurophisiology	21 d	Local: ↑ECM acute phase ↑ fibers SS detected 24-48 h (no later) ↑ activity	↑ mortality nearly SS systemic
[43]	Rats	70	Yes	BM-MSCs ALLOG local/systemic	PBS local/Syst/Sham injuries	Surg section PNC	No	Inj IE/systemic	MAR + EMG	10 d	IM/IV improve MAR, IV MAR non after PNC No SC survivor	No
[46]	Dogs	10	No	Myoblast AUT + bioengineering	SC/nothing	Excision 25% AS	No	Inj IE 3 mo later	CMAP/MAR Histology	3 mo	↑ MAR (non SS) Foreign body reaction	No
[47]	Rats	33	No	MDSCs ALLOG	Sham control (9 vs 24 rats)	Surg section	Surg	Inj IE	Migration lung-liver AS histology	30 d	No migration	2 benign local foci
[48]	Rats	45	No	Myoblast SYNG	Uninjured crioinj + PBS	Crioinjury	No	Inj IE	Histology/MAR	2 mo (histo) 6 mo (function)	Restitutio (60 d), SC integrated ↑ MAR 30 d, SS from 60 d	No
[49]	Rats	33	Yes	MDSC ALLOG	PBS	Surg section (Proctoepisio)	Surg	Inj IE	MAR + EMG Histology	4 wk	Improve SS EMG + MAR 2wk not 4wk No differences in sphincter thickness	No
[50]	Rabbits	12	Yes	MDSC AUT	Saline	Surg section EAS	No	Inj IE 3wk later	MRI/MAR + EMG Histology	4 wk	Labelled cells in MRI + areas, iron + myofibre ↑ ES MAR y EMG	No
[51]	Rats	??	No	Neural enteric progenitors XENOG	No injury/Crio/Crio + SCs	NO	No	BE: NPC + IAS cells + bilayer	Histology/EMG	4 wk	↑ neovascularization normal functioning	No
[53]	Rats	50	Yes	BM-MSCs ALLOG local/systemic	Saline Uninjured	Excision 25% AS	No	Inj IE/serial IV 24 h/3 wk later	MAR Histology (immunofluoresc)	5 wk	-↑ P 10d MSCs, 5wk MSC > Saline but no differences with uninjured Histology: ↓gap, fibrosis, scar/ Delayed 3wk no efficacy	No
[54]	Rats	40	Yes	MDSC ALLOG	PBS	Surg section	Surg	Inj IE	Histology	3 mo	No differences between groups	No
[55]	Dogs	15	No	Myobl AUT + PCL beads	PBS Uninjured	Excision 25% AS	No	Inj IE 1mo later	MAR Histology	3 mo	↑ SS MAR (50% basal) SC survival + differentiation	No
[56]	Dogs	10	Yes	Myoblast AUT (A)	(B) Myob aut + PCL beads with bFGF	Excision 25% AS	No	Inj IE 1 mo later	MAR/CMAP Histology	3 mo	↑ SS MAR + CMAP B > A SC en 40% (A) vs 100% (B)	No
[57]	Rats	80+ 20	Yes	MDSC ALLOG + hidrogel	Nothing PBS-hydrogel Collagen/No injury	Surg Section	No	Inj IE	Contractility Histology	3 mo	↑Contract and ↑ all F-U in SC-Hydrogel ↑ SS Muscle SC-Hydrogel; ↓ inflammation SC-Hydrogel and collagen	No
[58]	Rab-bits	16	No	MDSC AUT	Only EAS scafold	Total EAS excision	No	EAS sustitution	Histol (every 3 mo) EMG 2 yr	2 yr	No inflammation-reject, improve SS 3-6mo Improve EMG (no statistics provided)	No
[59]	Rats	58	Yes	BM-MSC ALLOG + electrostim	No treatment Elecrostimulation	Excision 50%	No	Inj IE + electrostim	Histology/MAR	4 wk	4wk, electrostimulation + 1 dose MSCs: ↑ muscle in injury area ↑ resting P compared with other groups	No
[60]	Rats	32	No	BM-MSCs ALLOG BM mononuclear	Sham surgery SSF	Surg section	Surg	Inj IE	Histol/morphometry/MAR In vitro contractility	30 d	SC ↑ regen and SS contractility No differences between SC SC survive 30 d	No
[61]	Rats	32	Yes	BM-MSCs ALLO + SDF-1 (simult/deferred)	No treatment SDF-1	Excision 50%	No	Inj IE + SDF-1 ± gelatin scaffold	Histology/MAR	4 wk	SDF-1 +/- SCs: ↑ resting P and %muscle and muscle organization and ↓ fibrosis (SS)	No
[76]	Rabbits	20	No	Neural enteric Progenitors AUT	No treatment Sham injury	Excision 50% IAS	No	Sustitution (biosphincter) 6-8 wk later	Histology/MAR	3 mo	Functional improvement since 1mo, SS with others Regeneration, neovascularization and innervation	No
[63]	Rats	56	Yes	BM-MSCs ALLOG + SDF-1 (deferred)	No treatment SDF-1	Excision 50%	No	Inj IE + SDF-1 ± gelatin scaffold	Histology Morphometry MAR Cytoquines	8 wk	Plasmid +/- SCS: ↑ MAR, muscle organization Plasmid: ↑ muscle mass SDF-1 sufficient for repairing without SC+ / -scaffold	No
[64]	Rats	36	Yes	ASCs SYNG	Conventional suture	Surg section	Yes/No	Inj IE biosuture	Histology/MAR	7 d	No functional differences SC survivor and migration to injury	No
[65]	Rats	58	Yes	Human ASCs	SSF Bulkamid (hydrogel)	Surg section	Surg	Inj IE	MAR micro-CT Histology	4 wk	Functional: ↑ SS ASCs and grew: no differences between carriers Morphology: no differences in muscle, > inflammation if ASCs, micro-CT correlation	No
[67]	Rats	60	No	BM-MSCs ALLOG ± electroacupunct	Sham injury Elecroacupunture SSF acupuncture	Surg section	No	Inj IV	Morphology	14 d	SC+EA ↑vessels, fibroplasia and ↓ inflammation ↑ muscle SS and homing growth factors (SS). Electroacupunct promotes homing	No

AUT: Autologous; ALLOG: Allogeneic; SYNG: Syngeneic; XENOG: Xenogeneic; SSF: Saline solution; Surg: Surgical; Inj: Injection; IE: Intrasphincteric; Crioinj: Cryoinjury; NSS: Non-statistically significant; SS: Statistically significant; ??: Unknown; ECM: Extracellular matrix; AS: Anal sphincter; Proctoepisio: Proctoepisiotomy; NPC: Neural progenitor cells; Immunofluoresc: Immunofluorescence; P: Pressure; PCL: Polycaprolactone; F-U: Followup; Histol: Histology; Simult: Simultaneous; Electrostim: Electrostimulation; Electroacupunt: Electroacupuncture.

Table 5 Overview of published clinical experience in stem cell therapy for faecal incontinence

Ref.	Study type	N	Stem cell	Treat-ment	Compared	Other treatments	Effect measure	F-U	Principal results
[102]	Phase II RCT	26	AUT ASCs	Injection fistula	Fibrin glue	No	Subjective	1 yr	Improvement 60% vs 23%
[68]	Obser-vational	10	AUT MB	Injection EAS	No	Anal electrical estimulation 10 + 4 wk	Clinical MAR Morphology	1 yr	↓ Wexner and episodes 1 yr, ↑QoL ↑ Voluntary P 1, 6 mo no at 12 Morphology no changes
[69]	Obser-vational	=						5 yr	↓ Wexner and episodes, ↑QoL ↑ P
[70]	Case report	1	AUT MB	Injection EAS	No	No	Clinical MAR + EMG	1 yr	Improved since 6 wk ↑ P and EMG on scar area
[71]	Obser-vational	10	AUT MB	Injection EAS	No	No	Clinical MAR	1 yr	MAR SS 18 wk Clinical: 66% 18 wk and 44.4% 1 yr EMG improvement all F-U
[72]	RCT double-blind	18	ALLO ASCs	Injection EAS	PBS	Surgery	Wexner US EMG	2 mo	No differences on Wexner ↑ SS muscle area and EMG
[73]	Phase II RCT	24	AUT MB	Injection EAS	Placebo	Biofeedback 15 d	Wexner, FIQL MAR, NPS US, MRI	1 yr	SS improve wexner 1 yr, response 60% Partial improvement FIQL 6-12 mo No morphologic differences at 12 mo Transient placebo effect

AUT: Autologous; ALLO: Allogeneic; RCT: Randomized controlled trial; MB: Myoblast; NPS: Neurophysiology; SS: Statistically significant; QoL: Quality of life; P: Pressure; F-U: Follow-up.