MECHANISMS OF IMMUNOLOGICAL ERADICATION OF A SYNGENEIC GUINEA PIG TUMOR

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Abstract
The influence of methotrexate on the development of immunity to the line 10 hepatoma was studied in guinea pigs. Chronic methotrexate treatment had no apparent effect on the ability of immune guinea pigs to suppress the growth of inoculated tumor cells. In contrast, the same methotrexate regimen inhibited the development of tumor immunity if started before the 8th day after immunization with a vaccine containing viable line 10 cells admixed with Bacillus Calmette-Guérin (BCG) cell walls. Thus, methotrexate selectively inhibited the afferent limb of the immune response. In adoptive transfer experiments, methotrexate-treated recipient guinea pigs were capable of being passively sensitized with immune spleen cells, indicating that the primary cell-mediated immune response of the recipient was not required for adoptive immunity. The contribution of recipient T cells in adoptive immunity was further investigated in guinea pigs depleted of T cells by thymectomy, irradiation, and bone marrow reconstitution. Despite demonstrable deficiency in T lymphocyte reactions, “B” animals were fully capable of rejecting tumors after transfer of immune cells. These results suggest that the expression of adoptive immunity was independent of recipient T cell participation. In addition, sublethal irradiation of immune spleen cells prior to adoptive transfer abolished their efficacy. Proliferation of transferred immune cells in the recipient may be essential for expression of adoptive immunity.