Immune responses to weakly immunogenic virally induced tumors I. Overcoming low responsiveness by priming mice with a syngeneic in vitro tumor line or allogeneic cross‐reactive tumor

This report describes model systems which show low primary in vitro syngeneic cytotoxic responses to a Moloney‐induced YAC tumor (syngeneic in A mice) and a Rauscher‐induced RBL5 tumor (syngeneic in C57BL/6 mice) and examines different approaches to overcome these defects. Two major findings were obtained: (a) spleen cells from A mice, injected with tumor cells from an in vitro tumor line YAC‐1, derived from YACL, could generate a significant syngeneic cytotoxic response. In contrast, spleen cells from A mice injected with tumor cells from the in vivo tumor line failed to generate a syngeneic cytotoxic response. Thus, tumor cells from the in vitro line were more immunogeneic that those from the in vivo line. (b) Spleen cells from A mice which were injected with the crossreactive allogeneic tumor RBL5, could generate significant cytotoxic responses to the syngeneic tumors YAC and YAC‐1. Similarly, spleen cells from C57BL/6 mice injected with the cross‐reactive allogeneic tumor YAC‐1, could generate a significant cytotoxic response to the syngeneic tumor RBL5. Thus, cross‐reactive allogeneic tumors could stimulate syngeneic cytotoxicity. The theoretical and the practical implications of these studies are discussed.