Reduced immunogenicity of rat renal allografts after photochemical donor pretreatment and passive transfer of graft protection.

Photochemical pretreatment of the kidney donor (Sprague-Dawley rats/SD) with 8-methoxypsoralen (8-MOP) and ex vivo longwave ultraviolet (UVA) irradiation of the kidney graft (PUVA therapy) significantly prolonged survival in allogeneic recipients (BD IX rats). After more than 100 days 7 long-term surviving PUVA-pretreated SD kidneys were retransplanted into BD IX rats. Seven out of 7 secondary recipients survived for more than 100 days. Twenty BD IX recipients of normal SD kidneys were treated at the time of transplantation with serum (1 ml i.v.) and/or spleen lymphocytes (1 X 10(7) i.v.) obtained from the PUVA-treated long-term survivors. A prolonged graft survival was achieved in 7 out of 20 rats, among them 4 out of 8 recipients of the serum-treated group. In conclusion, the long-term survival of PUVA-treated rat renal allografts is associated with a strong reduction of graft immunogenicity and the development of graft protecting humoral as well as cellular effectors.