文摘
Graft rejection remains an obstacle to successful outcome sin MHC-mismatched allogeneic marrow transplants. In preclinical canine studies of transplants of MHC-mismatched unrelated marrow, mAb S5, directed to the cellular adhesion molecule CD44, was found effective in enhancing engraftment. This effect could be mediated by inhibitory action(s) of S5 on residual host immunologic effector cells, including apoptosis of immunocompetent cells. S5 was shown to interfere with the function of NK cells, which are known to contribute to rejection of MHC-mismatched marrow. Therefore, we tested the ability of S5 to induce apoptosis in PBMCs from healthy human donors. In this study, normal PBMC were incubated with the anti-CD44 mAb S5, control mAb 31A or medium. Early apoptotic cells were measured as percent Annexin V+/propidium iodide− cells by FACS analysis. Time course analysis from PBMCs (n=10) after 12/18h revealed a significant increase in apoptotic cells when incubated with S5 as compared to 31A (p=.002 and .002 at 12 and 18h, respectively) or S5 compared to medium (p=.002 and .002 at 12 and 18h, respectively). At 24h, the S5-induced apoptosis continued to be higher than with 31A or medium, though this was no longer significant (p=.15 and .20, respectively). PBMCs were sorted for CD3+ T cells and CD56+/CD3− NK cells via a cell sorter or autoMACS®. The incubation of CD3+ cells with S5 significantly increased the median difference (Δ) in percent of apoptosis compared to 31A (median Δ 16 % , p=.02), or medium (median Δ 16 % , p=.02). Similarly, CD56+/CD3− cells were highly sensitive to S5-induced apoptosis as compared to 31A (median Δ 11 % , p=.02) or medium (median Δ 8 % , p=.02). Taken together, these data indicate that anti-CD44 antibody S5 induces apoptosis in human T cells and NK cells by a yet unidentified mechanism. Reducing the number of immunocompetent cells inthe host before TBI could be one mechanism whereby S5 exerts its effect on facilitating engraftment in the MHC-nonidentical transplant setting.
