Tumor-associated transplantation antigens in immune rejection of mouse malignant cell hybrids

The inability of mouse cell hybrids derived from two malignant parental cells to produce tumors in syngeneic F1 hosts was analyzed. YC hybrids, derived from the fusion of C1.1D and L1210 clls, failed to induce any tumor in adult mice, while 91% of x-irradiated newborn mice developed tumors and died. Some telocentric chromosomes were lacking in hybrid tumors; however, none of the immunologically intact adult mice developed tumors when grafted with tumors grown in x-irradiated newborn mice. This indicates that histocompatibility factors interfered in the failure of YC tumors to grow to adult hosts. Syngeneic F1 mice immunized with Y2C hybrid cells had cytotoxic antibodies against Y2C hybrids and C1.1D and L1210 parental cells. Complete absorption of cytotoxic antibodies directed against hybrid cells by mixtures of both parental cell lines demonstrates the absence of any new antigen on hybrid cells.Hyb rid cells had a higher density of C1.1D-tumor antigenic sites, as compared to C1.1D parental cells. This possibly explains the higher antigenicity and/or the higher sensitivity to immune lysis of hybrid cells.