Involvement of TCR-V beta 8.3+ cells in the cure of mice bearing a large MOPC-315 tumor by low dose melphalan.

We have previously shown that the curative efficacy of low dose melphalan (L-phenylalanine mustard; L-PAM) for mice bearing a large s.c. MOPC-315 tumor requires the participation of CD8+ (but not CD4+) T cell-dependent antitumor immunity. Here we show that CD8+ T cells obtained from regressing tumors on day 4 or 5 after low dose L-PAM therapy of MOPC-315 tumor bearers (L-PAM TuB mice) display a preferential enhancement in the utilization of the TCR-V beta 8.3 gene segment as compared to CD8+ T cells from normal lymph nodes. Treatment of L-PAM TuB mice with mAb F23.1, which leads to the depletion of V beta 8.3+ cells, as well as V beta 8.1 and 8.2+ cells, led to a significant reduction in the ability of their tumor-infiltrating lymphocytes as well as their spleen cells to lyse MOPC-315 tumor cells in vitro in a short term assay. In addition, the mAb F23.1 treatment almost completely abrogated the lytic activity of the tumor-infiltrating lymphocytes against another syngeneic, antigenically related plasmacytoma (the MOPC-104E). Moreover, the mAb F23.1 treatment significantly reduced the curative effectiveness of low dose L-PAM for mice bearing a large MOPC-315 tumor. In contrast, mAb KJ16 treatment, which leads to the depletion of V beta 8.1 and 8.2+ cells (but not V beta 8.3+ cells), did not reduce significantly the curative effectiveness of low dose L-PAM for such MOPC-315 tumor bearers. Thus, V beta 8.3+ T cells are important for the curative effectiveness of low dose L-PAM therapy for MOPC-315 tumor bearers, and it is conceivable that the V beta 8.3+ cells mediate their effect (at least in part) by contributing to the acquisition of CTL activity against plasmacytoma-shared Ag.