Previously we have demonstrated that the tumor infiltrating lymphocytes found in SJL/J mice with reticulum cell sarcomas (RCS) are CD4+ T cells which express T cell receptor (TCR) beta chain molecules comprised principally of Vbeta17a encoded variable gene segments. Herein we report both the cellular and molecular characterization of a panel of twenty RCS-specific T cell hybridomas derived from tumor infiltrating T cells of the mesenteric lymph nodes of an SJL/J mouse bearing the transplanted RCS LA-12 tumor. We determined by flow cytometry that all of the RCS reactive T cell hybridomas expressed TCR containing Vbeta17a encoded variable gene segments. Moreover, most of these T cell hybridomas (17 of 20) co-expressed the CD4 molecule, as did the tumor infiltrating T cells from which they were derived. Using Southern blot analysis of beta chain gene rearrangements. we determined that the predominant Vbeta17a gene usage seen in these hybridomas was not the result of the expansion, either in vivo or in vitro, of a single Vbeta17a+ RCS-reactive T cell clone. The hybridization patterns of hybridoma DNA, as revealed by a Jbeta2 probe, were dissimilar and indicated that multiple unique Vbeta17a+ T cells participate in the RCS response. Furthermore, using Northern blot analysis, we were able to determine that the T cell hybridomas used a varied set of TCR Valpha chain gene segments. The T cell hybridomas, for which the Valpha chain gene segments were determined, used Valpha chains comprised of either Valpha1, Valpha4 or Valpha8 family gene segments. Based on these findings we conclude that Valpha chain usage, if not random, is disparate in response to RCS tumors. Furthermore, these data suggest that the important reactivity for the RCS tumor antigen(s) lies with the beta chain (Vbeta17a) but not with the alpha chain used by the T cell. This pattern of alpha and beta chain utilization is consistent with reported TCR usage patterns exhibited by T cells in response to superantigens - where the beta chain and not the a chain dictates antigenic responsiveness. Therefore, our current findings suggest that the tumor antigen(s) presented by this RCS tumor is similar in nature to that of a superantigen.

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