Modulation of cell-mediated alloimmunity by BCG. I. Antagonism and potentiation of immunosuppression caused by cytarabine.

The ability of iv administered BCG to antagonize immunosuppression caused by injection of the antimetabolite cytarabine (beta-cytosine arabinoside; ara-C) was investigated in C57BL/6 mice. Treatment with BCG 10 days before alloimmunization with killed L1210 tumor cells decreased spleen T-cell-mediated cytolysis against allogeneic P815Y tumor cells, as measured by a short-term 51Cr release assay, and potentiated immunosuppression due to ara-C. In contrast, spleen cell-mediated immunity (CMI) that was assayed by a 48-hour microcytotoxicity assay (MCA) was augmented by systemic BCG administered before alloimmunization. Pretreatment with BCG resulted in a complete and long-lasting protection against the immunosuppressive effects of ara-C on this CMI as measured by the MCA. Treatment with BCG after cytoreductive therapy resulted in a significant, although transient, reversal of immunosuppression. Depending on the type of response and thus the type of effector cell measured, BCG acts as a moderate immunosuppressive agent or a strong immunopotentiator of CMI.