Peripheral blood lymphocytes in chimeric pigs resist lysis by antibody and complement C
Background A possible technology for preventing xenograft rejection without severe immune suppression is accommodation. Generally graft accommodation is appreciated in the sensitized recipient, after the transplant. By inducing accommodation in chimeric donors, however, much of the cost and risk of inducing accommodation in the recipient might be avoided. An indirect assay of accommodation in the donor pig is needed for screening donors. The resistance of peripheral blood lymphocytes to cytolysis by antibody and complement is assessed.
Materials and methods Chimerism was induced in pigs by infusing sheep marrow into preimmune fetal pigs. The newborn pigs were assessed for chimerism. Peripheral blood lymphocytes (PBL) were tested with a complement dependent lymphocytotoxicity assay using anti-serum from highly sensitized sheep and fresh rabbit complement. At a titer of anti-serum causing lysis of 95-100% lysis of normal pig lymphocytes, the cytolysis of the test cells was determined. Heterotopic heart transplants were performed with some test subjects. A longitudinal assessment of lymphocyte accommodation was done.
Results The PBL from chimeric pigs resisted cytolysis by antibody and complement. The reduction in cytolysis was proportional to the cellular chimerism. Heart transplants were performed with 8 chimeric donors and 4 controls assessed in this manner. The lymphocyte cytolysis in the chimeric donors averaged 9% (range 1-28%) compared with 97% cytolysis of control PBL. The mean graft survival of the chimeric grafts was 28 days (range 4-63 days). The control grafts survived 6 days (range 5-7). The reduction in cytolysis was not due to circulating sheep lymphocytes as chimerism averaged just 8%. PBL from 5 chimeric pigs were assessed for 84 days. The resistance to cytolysis was consistent throughout this period, averaging 12% at 14 and 42 days, 16% at 84 days. The controls averaged 96% lysis. The swine then averaged 78 kg in weight.
Conclusions The resistance of PBL to cytolysis may provide an indirect method to assess xenograft accommodation. Accommodation apparently persists for at least 12 weeks, long enough to provide organs for adult recipients.