Objective: Conditions,such as congenital anomalies,penile cancer,traumatic penile injury and some types of vasculogenic erectile dysfunction(ED),often require penile reconstruction.For these conditions,various reconstructive procedures have been attempted to achieve functional and cosmetic properties,but these procedures are often limited by a shortage of native penile tissue.The CD133 epitope is a marker of human hematopoietic/endothelial progenitors.Although its function is not clear,this subpopulation of cells has great potential for the repopulation of bone marrow and differentiation into mature endothelial cells in animal models.In this study,we focused on bone-marrow-derived CD 133+ cells,which are very accessible human cells for clinical applications.We hypothesized that the CD133+cells transplanted locally to corpus cavernosa defects in animal models could induce corpus cavernosa regeneration through vasculogenesis and neurogenesis.The objective of this study was to develop an easier regenerating technique of corpus cavernosa through transplanting human bonemarrow-derived CD133+ cells into a rat corpus cavernosa defect model in combination with application of an alginate gel sponge sheet.Methods: The 2×2 mm squares of the right corpus cavernosa of 8-week-old male athymic nude rats were excised.Alginate gel sponge sheets supplemented with 1×104 CD133+ cells derived from human bone marrow were then placed over the gaps on both sides(CD group).The same experiments were conducted on sham-operated rats(SH group),rats with only corpus cavernosa excision(EX group),and rats with alginate gel sheets placed on the injured corpus cavernosa(AL group).Functional and histological evaluations were carried out eight weeks later.The sections of the penises were then stained with hematoxylin-eosin(HE)and observed by light microscopy.We used anti α-smooth muscle actin as a primary antibody to detect vascular smooth muscle.We also used anti-S-100 protein as a primary antibody to detect neuron tissue,especially Schwann cells.In the AL and CD groups,four days after the corpus cavernosa were excised and an alginate gel sheet was placed over the corpus cavernosa stumps,the sheets on the only the right side of the corpus cavernosa were retrieved from three rats in each group.We carried out quantitative reverse transcription polymerase chain reaction(qRT-PCR)analysis of the rat nerve growth factor(NGF)and rat vascular endothelial growth factor(VEGF)in the alginate gel sheets.Results: The mean intracavernous pressure/mean arterial pressure of the CD group(0.34258±0.0831)was significantly higher than that of the EX group(0.0580±0.0831;P=0.0238)and similar to that of the SH group(0.37228±0.1051;P=0.8266).Morphological analysis revealed that the corpus cavernosa tissue was regenerated in the CD rat,based on the determination of appearance in HE-stained tissue.In the EX rat,the structure of the corpus cavernosa tissue disappeared and was replaced with fibrous tissue.In the AL rat,we could not observe the structure of the corpus cavernosa but observed that of the regenerated corpus cavernosa in the horizontal direction.In the CD rat,we observed the tissue of the regenerated corpus cavernosa,the structure resembled that of the SH rat in appearance of HE-stained tissue.Immunohistochemical analysis revealed that,in the SH rat,vascular smooth muscles were detected in the central part of the corpus cavernosum penis,and neuron tissues were detected in the lateral sides of venous sinus.In the EX rat,the regenerated vascular smooth muscles and neuron tissues were hardly detected.In the AL rat,vascular smooth muscles and neuron tissues were regenerated in the horizontal direction,but their constructions were different from those of the SH rat.Similarly,in the CD rat,some vascular smooth muscles were detected.Moreover some venous sinus-like structures without vascular smooth muscles were detected and neuron tissues were regenerated in the lateral sides of the structures.This venous sinus-like stricture was assumed to be an immature venous sinus.The RT-PCR for the extracts from the alginate gel sponge sheets retrieved in the CD group revealed that qRT-PCR helped in determining the amounts of mRNA for rat NGF and rat VEGF to be significantly higher than those in the AL group(NGF: P=0.0309,VEGF: P<0.0001).These results indicate that upregulation of intrinsic growth factors can be derived from rats.Conclusions: Transplantation of CD133+ cells accelerated the functional and histological recovery in this corpus cavernosa defect model.We believe CD133+ cell transplantation will be able to be applied to the treatment of penile regeneration or severe ED that is not responsive to PDE5 inhibitors.The CD133+ cells can be isolated easily from peripheral blood and applied as an autologous therapeutic agent with no limitation due to ethical or technical problems.This advantage will accelerate the progression of cell therapies for penile regeneration from the laboratory to clinical implementation.