A syngeneic monoclonal antibody (MAb) (IC5F5) was SUC-in RPMI 1640 + 10% fetal calf serum (Seromed, Miles, Brus-cessfully used in the immunotherapy of Rauxher-virus-in-sels). duced myeloid leukemic RMB-I cells. It is directed to a virusencoded, but aberrantly processed protein, which is expressed Mice and tUmr on the cell membrane. When applied in vivo, it binds Only to Male and female BALB/c mice, 8-12 weeks old, were ob-RMB-I tumor cells. BALBlc mice were inoculated i.p. or i.v. tained from TNO, zeist (The Netherlands). Intra-abdominal with lo' RMB-I cells and died within 2-3 weeks due to increasing load. Mice inoculated i.p. were completely cured and disseminated tumors were obtained by i.p. or i.v. injection by daily injections of ascites containing IC5F5. Disseminated Of lo7 RMB-l tumor cells in liver and hemopoietic organs were observed ~~~~~l ~ antibody after i.v. inoculation. Daily treatment with MAbs resulted in suwjval beyond 90 days. No antigenic modulation was ob-
Ascites fluid containing MAb IC5F5 was obtained after served when tumor tisue was analyzed 2-10 days after treat-injection of 15 X lo6 hybridoma cells i.p. in BALB/c mice ment. Treatment was successful even when therapy was pre-treated 10-21 days earlier with 0.5 ml Pristane (Janssen, ostponed until day 5 following inoculation of tumor cells. Beerse, Belgium). Ascites fluid of mice bearing the nonhhen the number of w i t e s injections was reduced, survival binding hybridoma 4E3 was used as control.
was identical to that observed among repeatedly treated mice.
Ten-and 100-fold dilution of ascites fluid diminished the num-In vitro modulation ber of survivors, but still resulted in a median survival time of RMB-l cells were co-cu~tured with or without 1 % IC5F5 or 4E3 ascites. After 2 days, the cultures were centrifuged and 38 and 20 days, respectively, as compared to 14 days for un-'To whom reprint requests should be sent.