The improved lytic function and in vivo efficacy of monovalent monoclonal CD3 antibodies.

A series of hybrid-hybridomas were derived by the cell fusion of a CD3 antibody-secreting hybridoma with other Ig-producing cell lines. The Ig molecules secreted by these hybrid-hybridomas were fractionated by ion-exchange chromatography, and fractions containing monovalent CD3 antibodies were tested for complement-mediated lysis of T cells. Two monovalent CD3 antibodies with mixed heavy chain isotypes were very poor in lysis but, in contrast, a monovalent antibody possessing two identical rat gamma 2b heavy chains but two non-identical light chains was found to be more lytic with human complement than the parental bivalent CD3 antibody. The difference in lysis was not readily explicable in terms of a difference in complement activation at the level of C1q binding or cell-associated C3. A highly purified batch of this lytic monovalent CD3 antibody was prepared in a form suitable for in vivo therapy. In a preliminary clinical study in one patient with a T lymphoma in leukemic phase this monovalent CD3 antibody was found to be very effective in depleting CD3+ tumor cells in the peripheral blood and bone marrow. The cells in the peripheral blood were completely cleared and there was no evidence for antigenic modulation. In addition the antibody was able to reverse cell-mediated kidney rejection in three kidney graft patients. These results suggest that monovalent antibody may be effective in vivo as well as in vitro and that a fuller clinical evaluation is justified.