Defective T-cell receptor-induced apoptosis of T cells and rejection of transplanted immunogenic tumors in p53^-/- mice

Mice lacking the tumor suppressor gene p53 spontaneously develop T-cell lymphomas at a high rate, suggesting that in these mice lymphomas arise due to defective apoptosis mechanisms in T cells mediated by p53. However, a role of p53 in regulation of T-cell responses or apoptosis has been poorly defined. TCR-mediated signaling in the absence of CD28 costimulation induces both apoptosis and proliferation of na?̈ve T cells from WT mice. In this report we show that, in response to TCR stimulation, T cells from na?̈ve p53-deficient mice exhibited higher proliferation and drastically reduced apoptosis than WT T cells. CD28 costimulation enhanced the proliferation of TCR-stimulated WTand p53^-/- T cells, suggesting that p53 uncouples CD28-mediated antiapoptotic and proliferative signals. To evaluate the physiological significance of these findings, we transplanted OVA expressing-EG.7 tumor cells into WT and p53^-/- mice. Unlike WT mice, p53^-/- mice exhibited a robust tumor-resistant phenotype and developed cytotoxic T-cell responses against OVA. Collectively, these data support the hypothesis that p53 is an essential factor in negative regulation of T-cell responses and have implication for immunomodulation during treatment of cancers and other inflammatory conditions.