Immunotherapy of lymphoid and nonlymphoid tumors with monoclonal anti-Lyt-1 antibodies

Monoclonal antibodies against the T cell differentiation antigen Lyt-1 were effective in the therapy of transplanted mouse tumors. A possible mechanism whereby anti-Lyt-1 antibodies directly bind and affect the tumor cells was excluded by the following findings: a) growth of lymphoid and nonlymphoid tumors (which lack Lyt-1 antigen) was affected by anti-Lyt-1 antibodies; and b) the curative effect of passively administered anti-Lyt-1 antibodies was abrogated in mice depleted of T cells, supporting a mechanism whereby host Lyt-1⁺ cells were involved in tumor therapy. Treatment with anti-Lyt-1 antibodies was not accompanied by depletion of Lyt-1⁺ cells from lymphoid organs, indicating that the administered antibodies altered Lyt-1⁺ cell functions without affecting their frequency. In view of the in vitro enhancing effects of anti-Lyt-1 antibodies on a variety of immune responses (including lymphokine secretion and generation of cytotoxic T cell), it is suggested that the potentiation of Lyt-1⁺ cell activity by passively administered anti-Lyt-1 antibodies results in tumor rejection.