Antibody-Mediated In Vivo Suppression of EL4 Leukemia in a Syngeneic Hos2

Abstract

C57BL/6 mice given a lethal dose (10⁵) of EL4 leukemia cells showed survival and tumor rejection when the tumor cells were pretreated in vitro with xenogeneic (rabbit) or allogeneic (BALB/c) anti-EL4 sera at relatively high dilutions (up to 1:100). The IgG fraction of the rabbit anti-EL4 serum effectively mediated protection. The protection was specific and not abrogated by sublethal irradiation (500 R) of mice 24 hours before tumor grafting. Injection of thioglycolate intraperitoneally before tumor inoculation enabled these mice to reject 5 times as many (5 × 10⁵) antiserum-treated tumor cells. Thus specific antiserum in the presence of host factors was important in tumor graft rejection. Antibody attached to the tumor cells probably activated normal host cells which led to tumor destruction. Such observations may represent the in vivo parallel of the antibody-dependent cellular cytotoxicity phenomenon detected in vitro.