Rapamycin prolongs susceptibility of responding T cells to tolerance induction by CD8+ veto cells

CD8 veto cells are an antigen-specific immunoregulatory cell type that induces tolerance by causing apoptosis in T cells that recognize antigens on the veto cell. However, responding T cells are only susceptible to veto based deletion for a 48-hour window, which represents a severe limitation to the use of veto cells as a cellular therapeutic. Several immunosuppresant drugs inhibit T cell differentiation at distinct points. We hypothesized that immunosuppresants, which arrest T cell differentiation, would maintain responding T cells in a vetoable state.

CD8 veto cells were generated from BALB/c (H-2) mice. The 2C transgenic mouse, which expresses a T cell receptor specific for L was used to visualize responding cells. Veto activity was measured by both visualizing apoptosis of the responding 2C T cells and by measuring a decrease in lysis of H-2 targets. Several immunosuppressant drugs were tested for their effect on veto cell activity.

BALB/c veto cells exhibited a potent and antigen-specific deletion of 2C responder cells, but not mature 2C effectors. The addition of rapamycin significantly extended the window of opportunity to veto based deletion by preventing the responding 2C T cells from differentiating out of a vetoable state.

These findings demonstrate that by utilizing rapamycin, the window of opportunity for veto-based induction of tolerance to transplantation antigens is significantly extended. This approach circumvents a serious obstacle in the development of veto cells as an efficacious cellular therapy to induce allospecific tolerance to transplantation antigens.