Enhanced cardiac allograft survival by Vav1-Rac signaling blockade in a mouse model

BackgroundVav1-Rac signaling plays a pivotal role in TCR/antigen and CD28 signals for T cell activation. However, pharmacological interference of this signaling has not been tested in the prevention of alloimmune-mediated allograft rejection. It has been demonstrated that 6-thio-GTP, a metabolite of azathioprine, specifically inhibits Vav1-Rac activity in T lymphocytes. Here we show the immunosuppressive efficacy of 6-thio-GTP in the prevention of cardiac allograft rejection.MethodsT cell proliferations were measured by 3H-thymidine uptake. The immunosuppressive activities of 6-thio-GTP were tested in the cardiac allograft model of C57BL/6 (H-2b) to Balb/c (H-2d) mice.Results6-Thio-GTP inhibited TCR/alloantigen stimulated T cell proliferation and CD28-dependent T cell survival. Administration of 6-thio-GTP (0.5 mg/kg) prolonged graft survival to 13.8 ± 2.39 days compared to 8.3 ± 0.48 days in PBS controls (p < 0.0001). Combination of 6-thio-GTP (0.5 mg/kg) with CsA (15 mg/kg) enhanced graft survival from 15.0 ± 1.61 days in CsA treated recipients to 36.8 ± 2.17 days in those received 20 days of combination therapy of CsA and 6-thio-GTP (p < 0.0001), or to 42.7 ± 16.63 days in the group treated with 20 days of CsA and 60 days of 6-thio-GTP (p < 0.0001). Lymphocytes from 6-thio-GTP treated recipients with long-term surviving grafts (> 60 days) displayed reduced proliferative response to alloantigen and higher frequencies of regulatory T cells (Treg).ConclusionVav1-Rac inhibitor 6-thio-GTP prolongs allograft survival alone or in combination with CsA by suppression of alloreactive T cell activation. Our findings suggest the therapeutic potential of pharmacological interference of Vav1-Rac signaling for transplantation.