Immune responses to weakly immunogenic virally induced tumors. V. Short in vitro cultivation of YAC changes its antigenic properties.

YAC tumor, a Moloney virus-induced lymphoma of A mice, considerably changes its immunogenic properties following cultivation for 12 to 14 hr in vitro. The cultivated tumor, designated YAC-1, generates anti-YAC and anti-YAC-1 reactive cells, while the original YAC tumor generates suppressor cells with abrogate anti-YAC and anti-YAC-1 cytotoxic responses. In this report, we demonstrate by cold target competition experiments that YAC-1 and YAC tumors have distinctive antigenic structures on their surfaces. We have also found that RBL5, a Rauscher virus-induced lymphoma of C57BL/6 mice, generates anti-YAC, anti-YAC-1, and anti-RBL5 reactive cells in A mice. YAC-1 also generates reactive cells against the allogeneic RBL5 tumor. The total population of antitumor reactive cells was found to contain separate subpopulations directed maximally toward each of the three target tumors. The subpopulation directed toward each tumor was shown to be partially, but not completely, cross-reactive with the other tumors. Further, RBL5 priming and YAC-1 priming were shown to stimulate separate populations of antitumor reactive cells.