Identification of a novel tumor-specific CTL epitope presented by RMA, EL-4, and MBL-2 lymphomas reveals their common origin

C57BL/6 mice generate a vigorous H-2D(b)-restricted CTL response against mu rine leukemia virus (MuLV)-induced tumors. For many years it has been sugge sted that this response is directed to an MuLV-encoded peptide as well as t o a nonviral tumor-associated peptide, Recently, a peptide from the leader sequence of gag was demonstrated to be the MuLV-derived epitope, Here we de scribe the molecular identification of the tumor-associated epitope, Furthe rmore, we show that the CTL response against this epitope can restrict the outgrowth of MuLV-induced tumors in vivo, The epitope is selectively presen ted by the MuLV-induced T cell tumors RBL-5, RMA, and MBL-2 as well as by t he chemically induced T cell lymphoma EL-4, Intriguingly, these tumors shar e expression of the newly identified epitope because they represent variant s of the same clonal tumor cell line, as evident from sequencing of the TCR alpha- and beta-chains, which proved to be identical. Our research shows t hat all sources of RBL-5, RMA, RMA-S, MBL-2, and EL-4 tumors are derived fr om a single tumor line, most likely EL-4.