Use of syngeneic monoclonal antibodies in the therapy of disseminated myeloid leukemic cells

A syngeneic monoclonal antibody (MAb) (IC5F5) was successfully used in the immunotherapy of Rauscher-virus-induced myeloid leukemic RMB-I cells. It is directed to a virus-encoded, but aberrantly processed protein, which is expressed on the cell membrane. When applied in vivo, it binds only to RMB-I tumor cells. BALB/c mice were inoculated i.p. or i.v. with 10(7) RMB-I cells and died within 2-3 weeks due to increasing tumor load. Mice inoculated i.p. were completely cured by daily injections of ascites containing IC5F5. Disseminated tumor cells in liver and hemopoietic organs were observed after i.v. inoculation. Daily treatment with MAbs resulted in survival beyond 90 days. No antigenic modulation was observed when tumor tissue was analyzed 2-10 days after treatment. Treatment was successful even when therapy was postponed until day 5 following inoculation of tumor cells. When the number of ascites injections was reduced, survival was identical to that observed among repeatedly treated mice. Ten- and 100-fold dilution of ascites fluid diminished the number of survivors, but still resulted in a median survival time of 38 and 20 days, respectively, as compared to 14 days for untreated mice.