Following the introduction of penile transplantation, important questions remain regarding the effects of transplant rejection on cavernous tissue function. Now, researchers have developed an ex vivo model of penile transplantation and rejection: tissue samples from patients undergoing penile prosthesis operations were maintained in culture with autologous peripheral blood mononuclear cells (PBMCs). Activation of allogenic PBMCs was used as a surrogate marker of rejection, and could be inhibited by various immunosuppressive agents, potentially enabling the optimal immunosuppression strategy to be identified.