Here, we evaluated two different strategies to inhibit the undesirable immune activation that follows muscle gene transfer by acting at two different checkpoints of the immune response, i.e., on T cell priming or on the functions of activated T cells that may escape such priming blockade. We used the administration of CTLA-4/Ig to inhibit the substantial immune priming that immediately follow vector injection. Indeed, CTLA-4/Ig represent a potent immunosuppressive fusion protein that reversibly prevents T cell activation (Wallace et al., 1995) and is now used in the clinic to treat inflammatory diseases such as rheumatoid arthritis (Bluestone et al., 2006) . Its immunomodulatory action depends on its competitive inhibitory effect on the CD28/B7 pathway thereby preventing the pivotal CD28-dependent costimulation required to fully activate T lymphocytes (Salomon and Bluestone, 2001) . As a second strategy, we turned to immunomodulatory molecules that could protect transduced muscle fibers from immune attacks by activated T cells. For that, we aimed at stimulating the inhibitory PD-1 molecule expressed on T cells upon activation, by the gene transfer of its ligands PD-L1 or PD-L2 to muscle cells (Freeman et al., 2000; Latchman et al., 2001; Ishida et al., 2002) . We show herein that acting on these two non-redundant mechanisms of tolerance provides synergistic effects that prolong transgene expression in muscle even in the presence of circulating cytotoxic T cells directed against the transgene product.