Secondary in vitro lymphocyte-proliferative responses to syngeneic plasma cell tumors.

Two characteristics of immune responses to weakly immunogenic plasma cell tumors were demonstrated in this study. (a) Elevated lymphoproliferative responses following in vivo inoculation of sublethal doses of plasma cell tumors were detected by a mixed lymphocyte-tumor interaction (MLTI) assay. Specificity of elevated MLTI responses correlated with resistance to in vivo tumor challenge. These responses were dependent upon the presence of thymus-derived cells. (b) Spleen and lymph node cells showed markedly different patterns of MLTI activity following plasma cell tumor immunization. Spleen cell responses were depressed for the first 30 days postimmunization, whereas lymph node cells showed augmented MLTI reactivity immediately after immunization. These observations indicated that lymphocyte populations from different lymphoid organs may show widely dissimilar responses in vitro at the same point in the in vivo development of tumor resistance.