Immunomodulatory effects of pretransplant donor blood transfusion on T-cell-independent xenoreactive immunity

Background. Pretransplant blood transfusions have beneficial effects on bot h clinical and experimental allograft survival. In the present study, we ex amined whether pretransplant hamster blood transfusions (pHBT) alone or tog ether with peritransfusion immunosuppressive strategies designed to target B cells and/or natural killer (NK) cells, could modulate T cell-independent (T-I) xenoreactivity in athymic nude rats, Methods. Hamster or mouse hearts were heterotopically xenotransplanted into untreated or treated athymic nude rats receiving either pHBT, anti-B cell. or anti-NK cell therapy alone or their combinations. Xenoreactive antibodi es (xAbs) and the percentage of NK cells were analyzed by FACScan analysis, NK cytotoxicity was measured by a standard 4 hr Cr-51 release assay. Xenog rafts (Xgs) were examined by hematoxylin-eosin (H&E), by light microscopic method with Masson's trichrome and orcein staining, by immunofluorescent st aining for immunoglobulin M and C3 deposition, and by immunohistochemical s taining for infiltration of NK cells and macrophages (M phi s). Results. In 1 of 6 rats given pHBT alone 2 weeks before receiving hamster x enografts, Xg survival was prolonged to 55 days compared with 3.0+/-1.2 day s in the other 5 animals and with 3.0+/-0.6 days in untreated animals. In t he 55 days, surviving Xg infiltration of M phi s and NK cells was seen toge ther with severe signs of chronic rejection, such as fibrosis and obliterat ive vasculopathy, The addition of the anti-B cell immunosuppressant MNA715 (malononitriloamide x920715, 20 mg/kg/day) from day -14 to day +14 or of 10 0 mu L of rabbit anti-asialo GM(1) serum ([anti-ASGM(1)] an NK cell depleti ng antibody) on day -14 resulted in a significant and species-specific prol ongation of the survival of hamster Xgs, respectively 59.8+/-9.6 days and 5 8.2+/-14.7 days (P<0.001 vs. control group), but not of mouse heart Xgs tha t were rejected in a normal tempo, All prolonged hamster Xgs were infiltrat ed with M phi s and NK cells and developed severe lesions of chronic reject ion, such as fibrosis and obliterative vasculopathy. In contrast, MNA715 or anti-ASGM(1) alone had no effect on Xg survival (4.8+/-1.7 days and 2.7+/- 0.6 days, respectively). Combined MNA715/anti-ASGM(1) treatment only modera tely promoted Xg survival (10+/-5.0 days; P<0.001). A simultaneous administ ration of pHBT, MNA715, and anti-ASGM(1) induced indefinite and species-spe cific Xg survival in all recipients. In vivo and in vitro studies demonstra ted that both T-I B cell and NK cell species-specific xenotolerance were ac hieved. Conclusions. Pretransplant blood transfusion may have a species-specific im munomodulatory effect on T-I xenoreactivity. This effect is further enhance d by a temporary co-administration of MNA715 or by a single injection of an ti-ASGM(1) A combination of pHBT, MNA715, and anti-ASGM(1) induces species- specific T-I xenotolerance.