Prolonged rat heart allograft survival and reduced graft immunogenicity after photochemical donor and transplant pretreatment.

The purpose of these experiments was to evaluate the influence of pretreatment of the heart donor with the photosensitizer 8-methoxypsoralen plus ex vivo longwave ultraviolet irradiation of the graft (PUVA) on survival time and immunogenicity of rat heart allografts in a donor-recipient combination that was different at the major histocompatibility complex (MHC). PUVA treatment of the donor hearts significantly prolonged their survival in allogeneic recipients. The efficacy of this therapy was dependent on the time of ultraviolet irradiation. Immunohistological studies using monoclonal antibodies to rat MHC class I and II antigens showed a significant reduction of class II antigen expression in heart cryostat sections after PUVA treatment. No differences were seen in the tissue distribution of class I antigen. This reduction of donor MHC class II antigens may influence the antigen presentation as well as the activation of T helper cells. In conclusion, PUVA treatment is effective to reduce the immunogenicity and to improve the graft survival time of rat heart allografts. These experimental findings are new and suggest a possible clinical application of photochemical pretreatment.