Growth and antigenic properties of a spontaneously regressing subline of leukemia L1210

A subline (1210/MR) of the lethal parental L1210 leukemia cell line has been demonstrated to undergo dose-dependent spontaneous regression in both syngeneic and hybrid mice, although the regressing and non-regressing cells differed only slightly in growth rate. The regressed mice, like those actively immunized, were specifically protected from the subsequent challenge with L1210 cells. In addition, L1210/MR cells when coinjected could protect CD2F1 mice from low but lethal doses of L1210 cells. These two cell lines shared at least one cross-reacting cell surface antigen as determined by an isologous anti-L1210/MR immune serum. Such immune serum after being absorbed by L1210 cells still retained its in vitro complement-dependent cytotoxicity against L1210/MR cells. We conclude that the cell lines are antigenically related but L1210/MR cells may possess additional novel antigens, and that spontaneous regression of L1210 may be an L1210-specific immunological phenomenon.