DEFINITION OF A UNIQUE CELL-SURFACE ANTIGEN OF MOUSE LEUKEMIA RL-MALE-1 BY CELL-MEDIATED CYTOTOXICITY

BALB/c x-ray-induced leukemia RLmale1 is strongly immunogenic for (BALB/c x C57BL/6)F 1 mice. Transplants of RLmale1 regressed after initial growth, and after tumor regression mice could resist repeated inocula of 10 7 RLmale1 cells. Spleen cells from immunized mice after in vitro stimulation with RLmale1 were cytotoxic for RLmale1 cells in 3-hr 51Cr assays. Pretreatment of immune spleen cells with Thy-1, Lyt-2, or Lyt-3 antisera and complement eliminated cytotoxic activity, indicating that effector cells for RLmale1 lysis are T cells. Tests with other target cells showed little or no cytotoxicity. Analysis of the specificity of T-cell killing of RLmale1 by competitive inhibition assays with unlabeled cells indicated that only RLmale1 could inhibit killing; other BALB/c tumors (13 x-ray or murine leukemia virus-induced leukemias and three myelomas) failed to inhibit lysis of RLmale1. A range of alloantisera and heteroantisera were tested for their capacity to block lytic activity in the absence of added complement. H-2(d) antisera and Lyt-2 and -3 antisera blocked lysis, the latter at the level of the effector cell. Antisera to other cell surface alloantigens, murine leukemia virus-related antigens, and immunoglobulins did not bloc RLmale1 lysis. Thus, T cells from mice immunized against RLmale1 recognize an individually distinct or unique antigen that does not appear to be related to any of the serologically defined cell surface determinants of RLmale1. In its restriction to a single leukemia, the RLmale1 antigen resembles the individually distinct antigens of chemically induced tumors and other tumor types of rodents.