Improvement of urethral sphincter deficiency in female rats following autologous skeletal muscle myoblasts grafting

The effect of skeletal muscle-derived cells implantation on stress urinary incontinence and functional urethral properties in female patients

OBJECTIVE

To evaluate improvement of stress urinary incontinence (SUI) and functional status of the urethra after autologous skeletal-muscle derived cell (aSMDC) implantation.

METHODS

Phase I-II, open, non-randomized, single-center study of ultrasound guided aSMDC implantation (dosed at 0.2 × 106  cells/2 mL) into the external urethral sphincter to treat SUI.

RESULTS

A total of 38 patients were treated and followed for 2 years. SUI measured by Incontinence Episode Frequency score, short pad test, quality of life, patient's and clinician's perception significantly improved and remained improved after 2 years. However, urodynamic urethral properties in general did not improve at 1-year after treatment. Subgroup analysis revealed that addition of an adjuvant functional electrical stimulation therapy discontinued 4 weeks after injection in the compliant group, gave better urodynamic values and maintained the long-term SUI improvement at 2 years.

CONCLUSION

The aSMDC injection was safe and well-tolerated by patients. The status of SUI improved and with it the quality of life of patients, even if this was not necessarily reflected in the urodynamic urethral properties. Electrical stimulation, as an adjuvant therapy, could have an essential role in the success of the therapy.

CLINICAL REGISTRATION

Clinical study was registered under Eudra-CT number: 2010-021867-34 at European Clinical Trial Database (EudraCT), accessible at: EudraCT (europa.eu).

Influence of background characteristics in responders of regenerative therapy by periurethral injection of adipose-derived regenerative cells for male stress urinary incontinence

OBJECTIVES

To determine if the male responders with post-prostatectomy incontinence in the ADRESU study, which is a clinical trial of regenerative therapy by periurethral injection of adipose-derived regenerative cells, are influenced by any background characteristics.

METHODS

Briefly, autologous adipose-derived regenerative cells isolated from abdominal adipose tissue and a mixture of adipose-derived regenerative cells with fat tissue were transurethrally injected into the rhabdosphincter and submucosal space of the urethra, respectively. Sixteen out of 43 patients (37.2%) responded to treatment (responders) and exhibited improvement in the urine leakage volume, defined as >50% reduction from baseline determined by the 24-hour pad test at 52 weeks of treatment (or last visit within 52 weeks). Background data such as age, body weight, method of prostatectomy, baseline frequency of leaks, number of leaks, number of pad changes, International Consultation on Incontinence Questionnaire-Short Form, King's Health Questionnaire, urodynamic urethral function including functional profile length and maximum urethral closure pressure, and abdominal leak point pressure were collected and compared between responders and nonresponders.

RESULTS

None of the background factors influenced improvement in the responders as compared with the nonresponders. However, a significant between-group difference in the rates of decrease in urine leakage volume was noted in patients of younger age (<70 years), compared with those of older age (≥70 years) from 2 to 26 weeks of treatment.

CONCLUSION

A greater decrease in urine leakage volume was noted in the younger patient group than in the older patient group.

A double-blind, randomized, placebo-controlled clinical trial evaluating the safety and efficacy of autologous muscle derived cells in female subjects with stress urinary incontinence

PURPOSE

The purpose of the study was to assess safety and efficacy of autologous muscle derived cells for urinary sphincter repair (AMDC-USR) in female subjects with predominant stress urinary incontinence.

METHODS

A randomized, double-blind, multicenter trial examined intra-sphincteric injection of 150 × 10⁶ AMDC-USR versus placebo in female subjects with stress or stress predominant, mixed urinary incontinence. AMDC-USR products were generated from vastus lateralis needle biopsies. Subjects were randomized 2:1 to receive AMDC-USR or placebo and 1:1 to receive 1 or 2 treatments (6 months after the first). Primary outcome was composite of ≥ 50% reduction in stress incontinence episode frequency (IEF), 24-h or in-office pad weight tests at 12 months. Other outcome data included validated subject-recorded questionnaires. Subjects randomized to placebo could elect to receive open-label AMDC-USR treatment after 12 months. Subject follow-up was up to 2 years.

RESULTS

AMDC-USR was safe and well-tolerated with no product-related serious adverse events or discontinuations due to adverse events. Interim analysis revealed an unexpectedly high placebo response rate (90%) using the composite primary outcome which prevented assessment of treatment effect as designed and thus enrollment was halted at 61% of planned subjects. Post hoc analyses suggested that more stringent endpoints lowered placebo response rates and revealed a possible treatment effect.

CONCLUSIONS

Although the primary efficacy finding was inconclusive, these results inform future trial design of AMDC-USR to identify clinically meaningful efficacy endpoints based on IEF reduction, understanding of placebo response rate, and refinement of subject selection criteria to more appropriately align with AMDC-USR's proposed mechanism of action.

Intraurethral co-transplantation of bone marrow mesenchymal stem cells and muscle-derived cells improves the urethral closure

Background

Cell therapy constitutes an attractive alternative to treat stress urinary incontinence. Although promising results have been demonstrated in this field, the procedure requires further optimization. The most commonly proposed cell types for intraurethral injections are muscle derived cells (MDCs) and mesenchymal stem/stromal cell (MSCs). The aim of this study was to evaluate the effects of MDC-MSC co-transplantation into the urethra.

Methods

Autologous transplantation of labeled MDCs, bone marrow MSCs or co-transplantation of MDC-MSC were performed in aged multiparous female goats (n = 6 in each group). The mean number of cells injected per animal was 29.6 × 10⁶(± 4.3 × 10⁶). PBS-injected animals constituted the control group (n = 5). Each animal underwent urethral pressure profile (UPP) measurements before and after the injection procedure. The maximal urethral closure pressure (MUCP) and functional area (FA) of UPPs were calculated. The urethras were collected at the 28th or the 84th day after transplantation. The marker fluorochrome (DID) was visualized and quantified using in vivo imaging system in whole explants. Myogenic differentiation of the graft was immunohistochemically evaluated.

Results

The grafted cells were identified in all urethras collected at day 28 regardless of injected cell type. At this time point the strongest DID-derived signal (normalized to the number of injected cells) was noted in the co-transplanted group. There was a distinct decline in signal intensity between day 28 and day 84 in all types of transplantation. Both MSCs and MDCs contributed to striated muscle formation if transplanted directly to the external urethral sphincter. In the MSC group those events were rare. If cells were injected into the submucosal region they remained undifferentiated usually packed in clearly distinguishable depots. The mean increase in MUCP after transplantation in comparison to the pre-transplantation state in the MDC, MSC and MDC-MSC groups was 12.3% (± 11.2%, not significant (ns)), 8.2% (± 9.6%, ns) and 24.1% (± 3.1%, p = 0.02), respectively. The mean increase in FA after transplantation in the MDC, MSC and MDC-MSC groups amounted to 17.8% (± 15.4%, ns), 15.2% (± 12.9%, ns) and 17.8% (± 2.5%, p = 0.04), respectively.

Conclusions

The results suggest that MDC-MSC co-transplantation provides a greater chance of improvement in urethral closure than transplantation of each population alone.

Modelling human myoblasts survival upon xenotransplantation into immunodeficient mouse muscle

Cell transplantation has been challenged in several clinical indications of genetic or acquired muscular diseases, but therapeutic success were mitigated. To understand and improve the yields of tissue regeneration, we aimed at modelling the fate of CD56-positive human myoblasts after transplantation. Using immunodeficient severe combined immunodeficiency (SCID) mice as recipients, we assessed the survival, integration and satellite cell niche occupancy of human myoblasts by a triple immunohistochemical labelling of laminin, dystrophin and human lamin A/C. The counts were integrated into a classical mathematical decline equation. After injection, human cells were essentially located in the endomysium, then they disappeared progressively from D0 to D28. The final number of integrated human nuclei was grossly determined at D2 after injection, suggesting that no more efficient fusion between donor myoblasts and host fibers occurs after the resolution of the local damages created by needle insertion. Almost 1% of implanted human cells occupied a satellite-like cell niche. Our mathematical model validated by histological counting provided a reliable quantitative estimate of human myoblast survival and/or incorporation into SCID muscle fibers. Informations brought by histological labelling and this mathematical model are complementary.

Design of a single-arm clinical trial of regenerative therapy by periurethral injection of adipose-derived regenerative cells for male stress urinary incontinence in Japan: the ADRESU study protocol

BACKGROUND

Male stress urinary incontinence is a prevalent condition after radical prostatectomy. While the standard recommendation for the management of urine leakage is pelvic floor muscle training, its efficacy is still unsatisfactory. Therefore, we have focused on regenerative therapy, which consists of administering a periurethral injection of autologous regenerative cells from adipose tissue, separated using the Celution® system. Based on an interim data analysis of our exploratory study, we confirmed the efficacy and acceptable safety profile of this treatment. Accordingly, we began discussions with Japanese regulatory authorities regarding the development of this therapy in Japan. The Ministry of Health, Labour and Welfare suggested that we implement a clinical trial of a new medical device based on the Pharmaceutical Affaires Act in Japan. Next, we discussed the design of this investigator-initiated clinical trial (the ADRESU study) aimed at evaluating the efficacy and safety of this therapy, in a consultation meeting with the Pharmaceuticals and Medical Device Agency.

METHODS

The ADRESU study is an open-label, multi-center, single-arm study involving a total of 45 male stress urinary incontinence patients with mild-to-moderate urine leakage persisting more than 1 year after prostatectomy, in spite of behavioral and pharmacological therapies. The primary endpoint is the rate of patients at 52 weeks with improvement of urine leakage volume defined as a reduction from baseline greater than 50% by 24-h pad test. Our specific hypothesis is that the primary endpoint result will be higher than a pre-specified threshold of 10%.

DISCUSSION

The ADRESU study is the first clinical trial of regenerative treatment for stress urinary incontinence by adipose-derived regenerative cells using the Celution® system based on the Japanese Pharmaceutical Affaires Act. We will evaluate the efficacy and safety in this trial to provide an adequate basis for marketing approval with the final objective of making this novel therapy widely available for Japanese patients.

TRIAL REGISTRATION

This trial was registered at the University Hospital Medical information Network Clinical Trial Registry (UMIN-CTR Unique ID: UMIN000017901 ; Registered July 1, 2015) and at ClinicalTrials.gov (ClinicalTrials.gov Identifier: NCT02529865 ; Registered August 18, 2015).

Stem Cell Therapy for Treatment of Stress Urinary Incontinence: The Current Status and Challenges

Stress urinary incontinence (SUI) is a common urinary system disease that mostly affects women. Current treatments still do not solve the critical problem of urethral sphincter dysfunction. In recent years, there have been major developments in techniques to obtain, culture, and characterize autologous stem cells as well as many studies describing their applications for the treatment of SUI. In this paper, we review recent publications and clinical trials investigating the applications of several stem cell types as potential treatments for SUI and the underlying challenges of such therapy.

Stress urinary incontinence animal models as a tool to study cell-based regenerative therapies targeting the urethral sphincter

Urinary incontinence (UI) is a major health problem causing a significant social and economic impact affecting more than 200million people (women and men) worldwide. Over the past few years researchers have been investigating cell therapy as a promising approach for the treatment of stress urinary incontinence (SUI) since such an approach may improve the function of a weakened sphincter. Currently, a diverse collection of SUI animal models is available. We describe the features of the different models of SUI/urethral dysfunction and the pros and cons of these animal models in regard to cell therapy applications. We also discuss different cell therapy approaches and cell types tested in preclinical animal models. Finally, we propose new research approaches and perspectives to ensure the use of cellular therapy becomes a real treatment option for SUI.

Regeneration of degenerated urinary sphincter muscles: improved stem cell-based therapies and novel imaging technologies

Stress urinary incontinence (SUI) is a largely ousted but significant medical, social, and economic problem. Surveys suggest that nowadays approximately 10% of the male and 15% of the female population suffer from urinary incontinence at some stage in their lifetime. In women, two major etiologies contribute to SUI: degeneration of the urethral sphincter muscle controlling the closing mechanism of the bladder outflow and changes in lower pelvic organ position associated with degeneration of connective tissue or with mechanical stress, including obesity and load and tissue injury during pregnancy and delivery. In males, the reduction of the sphincter muscle function is sometimes due to surgical interventions as a consequence of prostate cancer treatment, benign prostate hyperplasia, or of neuropathical origin. Accordingly, for women and men different therapies were developed. In some cases, SUI can be treated by physical exercise, electrophysiological stimulation, and pharmacological interventions. If this fails to improve the situation, surgical interventions are required. In standard procedures, endoprostheses for mechanical support of the weakened tissue or mechanical valves for a bladder outflow control are implanted. In 20% of cases treated, repeat procedures are required as implants yield all sorts of side effects in time. Based on preclinical studies, the application of an advanced therapy medicinal product (ATMP) such as implantation of autologous cells may be a curative and long-lasting therapy for SUI. Cellular therapy could also be an option for men suffering from incontinence caused by injury of the nerves controlling the muscular sphincter system. Here we briefly report on human progenitor cells, especially on mesenchymal stromal cells (MSCs), their expansion and differentiation to smooth muscle or striated muscle cells in vitro, labeling of cells for in vivo imaging, concepts of improved, precise, yet gentle application of cells in muscle tissue, and monitoring of injected cells in situ.

Towards a Treatment of Stress Urinary Incontinence: Application of Mesenchymal Stromal Cells for Regeneration of the Sphincter Muscle

Stress urinary incontinence is a significant social, medical, and economic problem. It is caused, at least in part, by degeneration of the sphincter muscle controlling the tightness of the urinary bladder. This muscular degeneration is characterized by a loss of muscle cells and a surplus of a fibrous connective tissue. In Western countries approximately 15% of all females and 10% of males are affected. The incidence is significantly higher among senior citizens, and more than 25% of the elderly suffer from incontinence. When other therapies, such as physical exercise, pharmacological intervention, or electrophysiological stimulation of the sphincter fail to improve the patient’s conditions, a cell-based therapy may improve the function of the sphincter muscle. Here, we briefly summarize current knowledge on stem cells suitable for therapy of urinary incontinence: mesenchymal stromal cells, urine-derived stem cells, and muscle-derived satellite cells. In addition, we report on ways to improve techniques for surgical navigation, injection of cells in the sphincter muscle, sensors for evaluation of post-treatment therapeutic outcome, and perspectives derived from recent pre-clinical studies.

Regenerative treatment of male stress urinary incontinence by periurethral injection of autologous adipose-derived regenerative cells: 1-year outcomes in 11 patients

OBJECTIVES

To assess the efficacy and safety of a novel cell therapy for male stress urinary incontinence consisting of periurethral injection of autologous adipose-derived regenerative cells, and to determine the 1-year outcomes.

METHODS

A total of 11 male patients with persistent stress urinary incontinence after prostate surgery were included in the study. The Celution system was used to isolate adipose-derived regenerative cells from abdominal adipose tissue obtained by liposuction. Subsequently, these regenerative cells, and a mixture of regenerative cells and adipose tissue were transurethrally injected into the rhabdosphincter and submucosal space of the urethra, respectively. The 1-year outcomes were assessed using a 24-h pad test, a validated patient questionnaire, urethral pressure profile, transrectal ultrasonography and magnetic resonance imaging.

RESULTS

Stress urinary incontinence improved progressively in eight patients during the 1-year follow up, as determined by a 59.8% decrease in the leakage volume in the 24-h pad test, decreased frequency and amount of incontinence, and improved quality of life. One patient achieved total continence. The mean maximum urethral closing pressure and functional profile length increased from 35.5 to 44.7 cmH₂O, and from 20.4 to 26.0 mm, respectively. Magnetic resonance imaging showed the sustained presence of the injected adipose tissue, and enhanced ultrasonography showed a progressive increase in blood flow to the injected area in all patients. No significant adverse events were observed peri- or postoperatively.

CONCLUSION

Periurethral injection of autologous adipose-derived regenerative cells might represent a safe and feasible treatment modality for male stress urinary incontinence.

The effect of endoscopic administration of autologous porcine muscle-derived cells into the urethral sphincter

OBJECTIVE

To verify the fate of autologous porcine myogenic cells after endoscopic administration into the urethral sphincter.

METHODS

This study was performed on pig animal models. The muscle-derived cells (MDCs) were isolated and identified. After the third passage, the 6 × 10(7) of PKH26 labeled cells were injected into the urethral sphincter using a urethrocystoscope. The urethras were collected after 28 days. To analyze the fate of injected cells, the PKH26 presence, the desmin expression, and the distribution of acetylcholine receptors were evaluated in the tissue sections. Moreover, the maximal urethral closure pressure (MUCP) was assessed in experimental and control groups at day 1 and day 28.

RESULTS

The isolated porcine MDCs expressed desmin and were able to differentiate into myotubes in vitro. At day 28 after the transplantation, the depots of PKH26-positive cells were observed in the muscular layer, but also in the submucosa. The staining for desmin revealed that cells located in the muscle layer were integrated with muscle fibers that possessed acetylcholine receptors. However, cells administered into nonmuscle tissue did not express desmin. Urethral pressure profilometry demonstrated no significant differences between MUCP in the transplanted group in comparison to the control group at day 28.

CONCLUSION

The present study demonstrates the successful endoscopic transplantation of myogenic cells into the urethral sphincter. The experiments indicated the key importance of precise cell administration in terms of their fate after the injection.

Autologous muscle derived cell therapy for stress urinary incontinence: a prospective, dose ranging study

PURPOSE

In this feasibility study we assessed the 12-month safety and potential efficacy of autologous muscle derived cells (Cook MyoSite Incorporated, Pittsburgh, Pennsylvania) as therapy for stress urinary incontinence.

MATERIALS AND METHODS

A total of 38 women in whom stress urinary incontinence had not improved with conservative therapy for 12 or more months underwent intrasphincter injection of low doses (1, 2, 4, 8 or 16 × 10(6)) or high doses (32, 64 or 128 × 10(6)) of autologous muscle derived cells, which were derived from biopsies of their quadriceps femoris. All patients could elect a second treatment of the same dose after 3-month followup. Assessments were made at 1, 3, 6 and 12 months after the last treatment. The primary end point was the incidence and severity of adverse events. In addition, changes in stress urinary incontinence severity were evaluated by pad test, diary of incontinence episodes and quality of life surveys.

RESULTS

Of the 38 patients 33 completed the study. Treatment related complications were limited to minor events such as pain/bruising at the biopsy and injection sites. Of patients who received 2 treatments of autologous muscle derived cells who were eligible for analysis, a higher percentage of those in the high dose vs the low dose group experienced a 50% or greater reduction in pad weight (88.9%, 8 of 9 vs 61.5%, 8 of 13), had a 50% or greater reduction in diary reported stress leaks (77.8%, 7 of 9 vs 53.3%, 8 of 15) and had 0 to 1 leaks during 3 days (88.9%, 8 of 9 vs 33.3%, 5 of 15) at final followup.

CONCLUSIONS

Injection of autologous muscle derived cells in a wide range of doses appears safe with no major treatment related adverse events reported. In addition, treatment with autologous muscle derived cells shows promise for relieving stress urinary incontinence symptoms and improving quality of life.

Is tissue engineering and biomaterials the future for lower urinary tract dysfunction (LUTD)/pelvic organ prolapse (POP)?

The fields of tissue engineering and regenerative medicine have seen major advances over the span of the past two decades, with biomaterials playing a central role. Although the term "regenerative medicine" has been applied to encompass most fields of medicine, in fact urology has been one of the most progressive. Many urological applications have been investigated over the past decades, with the culmination of these technologies in the introduction of the first laboratory-produced organ to be placed in a human body.1 With the quality of life issues associated with urinary incontinence, there is a strong driver to identify and introduce new technologies and the potential exists for further major advancements from regenerative medicine approaches using biomaterials, cells or a combination of both. A central question is why use biomaterials? The answer rests on the need to make up for inadequate or lack of autologous tissue, to decrease morbidity and to improve long-term efficacy. Thus, the ideal biomaterial needs to meet the following criteria: (1) Provide mechanical and structural support, (2) Maintain compliance and be biocompatible with surrounding tissues, and (3) Be "fit for purpose" by meeting specific application needs ranging from static support to bioactive cell signaling. In essence, this represents a wide range of biomaterials with a spectrum of potential applications, from use as a supportive or bulking implant alone, to implanted biomaterials that promote integration and eventual replacement by infiltrating host cells, or scaffolds pre-seeded with cells prior to implant. In this review we shall discuss the structural versus the integrative uses of biomaterials by referring to two key areas in urology of (1) pelvic organ support for prolapse and stress urinary incontinence, and (2) bladder replacement/augmentation.

Regenerative medicine in urology

The term 'regenerative medicine' encompasses strategies for restoring or renewing tissue or organ function by: (i) in vivo tissue repair by in-growth of host cells into an acellular natural or synthetic biomaterial, (ii) implantation of tissue 'engineered'in vitro by seeding cultured cells into a biomaterial scaffold, and (iii) therapeutic cloning and stem cell-based tissue regeneration. In this article, we review recent developments underpinning the emerging science of regenerative medicine and critically assess where successful implementation of novel regenerative medicine approaches into urology practice might genuinely transform the quality of life of affected individuals. We advocate the need for an evidence-based approach supported by strong science and clinical objectivity.

The clinical relevance of cell-based therapy for the treatment of stress urinary incontinence

Stress urinary incontinence is a common disorder affecting the quality of life for millions of women worldwide. Effective surgical procedures involving synthetic permanent meshes exist, but significant short- and long-term complications occur. Cell-based therapy using autologous stem cells or progenitor cells presents an alternative approach, which aims at repairing the anatomical components of the urethral continence mechanism. In vitro expanded progenitor cells isolated from muscle biopsies have been most intensely investigated, and both preclinical trials and a few clinical trials have provided proof of concept for the idea. An initial enthusiasm caused by positive results from early clinical trials has been dampened by the recognition of scientific irregularities. At the same time, the safety issue for cell-based therapy has been highlighted by the appearance of new and comprehensive regulatory demands. The influence on the cost effectiveness, the clinical relevance and the future perspectives of the present clinical approach are discussed.

Intrasphincteric injections of autologous muscular cells in women with refractory stress urinary incontinence: a prospective study

INTRODUCTION AND HYPOTHESIS

Cell therapy for stress urinary incontinence (SUI) management has been experienced with encouraging results.

METHODS

We conducted an open prospective study on 12 women presenting severe SUI with fixed urethra, after previous failed surgical management. Patients underwent intrasphincteric injections of autologous progenitor muscular cells isolated from a biopsy of deltoid muscle. Primary endpoint focused on safety (measurement of Q(max) variation after 3 months). Secondary endpoints assessed side effects and efficacy.

RESULTS

No variation was diagnosed on Q(max) measurements. Efficacy data show that three of 12 patients are dry at 12 months, seven other patients are improved on pad test but not on voiding diary, and two patients were slightly worsened by the procedure. Quality of life was improved in half of patients.

CONCLUSIONS

Cell therapy for severe multioperated cases of SUI is a mini-invasive, feasible, and safe procedure that can improve urinary condition in as a second line therapy.

Myoblast transplantation to defecation muscles in a rat model: a possible treatment strategy for fecal incontinence after the repair of imperforate anus

PURPOSE

Infants with higher anorectal anomalies often develop fecal incontinence after surgical reconstruction mainly due to the incomplete development of defecation muscles. We investigated the possibility of defecation muscle regeneration by myoblast transplantation to improve fecal continence.

METHODS

Myoblasts from F344 female rats at ages of 1 day, 1, 2, 3, 4, 8, and 12 weeks were prepared by a preplating method. In vivo muscle differentiation of myoblasts was evaluated using immunofluorescence after transplantation of GFP-positive myoblasts into nude mice, the damaged thigh muscles, and the levator ani muscle of GFP-negative rats.

RESULTS

The ratios of myoblasts obtained from 1 day, 1, 2, 3, 4, 8, and 12-week-old rats were 35, 71, 65, 61, 52, 44, and 23%, respectively. Myotube formation by transplanted myoblasts was observed in the back of nude mice. Myoblasts transplanted into damaged thigh muscles were integrated into recipient muscles with myofiber formation. Transferred myoblasts formed myotubes surrounding the levator ani muscle, although myofiber formation was not observed.

CONCLUSION

Myoblasts were most efficiently obtained from juvenile rats. Myoblast transplantation may provide a novel treatment strategy for improving fecal continence after repair of anorectal anomalies in infants.

The Fate of Implanted Syngenic Muscle Precursor Cells in Injured Striated Urethral Sphincter of Female Rats

We studied the outcome of syngenic skeletal muscle precursor cells (MPCs) implanted in the striated urethral sphincter of the female rat. These cells were injected at the site of a longitudinal sphincterotomy performed 21 days before implantation. MPCs were isolated from the striated hindlimb muscles of syngenic adult rats and were infected with a retrovirus carrying the gene for either the green fluorescent protein (GFP) or the β-galactosidase enzyme (β-gal). MPCs (2 × 105) were injected longitudinally at the site of the lesion in 48 animals using a 10-μl Hamilton syringe. Then the whole urethras were excised from 2 h up to 90 days for cross section immunocytochemistry analysis. All the urethras exhibited connective tissue in place of the injury of the striated fibers. Two hours after injection a cluster of small round basophilic cells was observable at the site of injection and some of them expressed GFP or β-gal. A few GFP- and β-gal-positive cells were already detectable 7 days after injection. A large amount of injected cells probably died after injection. Many striated fibers of the urethra became GFP positive from day 7 until day 21, suggesting that few MPCs were allowed to incorporate the divided extremities of the striated fibers from day 7. Unfortunately, we did not observe centronucleated regenerated fibers in this experiment.