Treatment of acute kidney allograft rejection with the nonmitogenic CD3 mAb CLB T3/4.A (IgA-CD3): absence of a correlation of clinical responsiveness with inhibition of lymphocyte reactivity in vitro.

CLB T3/4.A (IgA-CD3) is a nonmitogenic, murine IgA monoclonal antibody (mAb) to human CD3 selected for clinical studies to provide an alternative for the mitogenic therapeutic mAb OKT3. The use of OKT3 is hampered by severe first dose side effects. Previously, we reported that IgA-CD3 is better tolerated than the murine IgG2a CD3 mAb CLB T3/4.2a (IgG2a-CD3). We concluded that the heavy chain isotype of the mAb largely determines the side effects of CD3 mAb therapy. In comparison to murine IgG2a (which is the isotype of OKT3), murine IgA has the advantage that it does not bind to human Fc-receptors and that it is a poor activator of the human complement system. Here we try to relate the results of in vitro lymphocyte reactivity during treatment of a first rejection episode after renal transplantation with clinical responsiveness.