The roles of humoral and cellular antitumor immune responses induced by immunization with
tumor-derived idiotypic
IgM were studied in a syngeneic, transplantable
B cell lymphoma (38C13) of C3H mice. Id vaccination with
keyhole limpet hemocyanin-conjugated Id induced protection against a subsequent lethal
tumor challenge. Such immunizations elicited
anti-idiotypic antibodies that were cytotoxic in in vitro antibody-dependent cellular cytotoxicity assays as well as in vivo passive transfer experiments. L3T4+ T cells, which proliferated in vitro in response to the specific Id
protein, were also induced. However, cells mediating direct cytotoxicity, either in vitro or in vivo, were not observed in the lymph nodes, spleens, or peritoneal cavity of immune mice or at the site of
tumor regression as demonstrated by using a
tumor sponge implantation model. In addition, in vitro sensitization of immune lymphocytes against 38C13
tumor cells failed to induce cytotoxicity. Immunization with
lipid conjugated Id also elicited a T cell proliferative response but failed to induce
anti-idiotypic antibodies and did not confer resistance to
tumor growth. These results suggest that
anti-idiotypic antibodies play the major role in the destruction of 38C13
tumor cells. However, in vivo depletion of L3T4+ or Lyt-2+ cells from 38C-Id-keyhole limpet
hemocyanin-immunized mice resulted in diminished protection against a
tumor challenge. Thus, although humoral responses appear to play the predominant part in
tumor destruction, cellular responses are also required for the full expression of antitumor immunity in this system.