Constitutive active p21^ras enhances primary T cell responsiveness to Ca²⁺ signals without interfering with the induction of clonal anergy

Chronic engagement of the T cell receptor mediates the induction of T lymphocyte unresponsiveness called clonal anergy. The development of such unresponsiveness has been suggested as one of the mechanisms that regulate peripheral tolerance to self-antigens and hamper the capacity of tumor antigen-specific T cells to eliminate cancerous cells. In the attempt to enhance the effector function of CD4⁺ T lymphocytes and their resistance to clonal anergy induction, we have transduced primary T cells with a retroviral vector encoding active p21^ras (Ras^Leu61). Here we show that Ras^Leu61 elicited TCR-independent activation of the Ras-Raf-ERK pathway and conferred primary T cells with the ability to secrete IL-2 in response to stimulation with a Ca²⁺ ionophore alone, without altering antigen-, CD3/CD28- and PMA/ionomycin-driven IL-2 secretion and T cell proliferation in vitro. However, chronic engagement of the TCR on the surface of Ras^Leu61 T cells still led to an inability of the cells to produce IL-2 upon restimulation. These results indicate that enforced p21^ras functionality enhances primary T cells responses to calcium-generated signals, but is insufficient to prevent TCR-driven T cell unresponsiveness and suggest that additional biochemical mechanisms, independent of p21^ras, negatively regulate IL-2 production in unresponsive T cells.