Immunotherapy in Friend Virus Leukemia. II. Prevention of Friend Leukemia by Passive Administration of Immune Serum and Cells to Young Mice

Summary

Different ways of imparting passive immunity to primary Friend virus-induced leukemia were compared. Antiserum produced by immunizing semisyngeneic mice with DBA/2 Friend leukemic spleen cells or formalin-inactivated leukemic spleen homogenate was shown to neutralize virus and to be cytotoxic to Friend leukemia cells. Inoculation of such sera to newborn litters effectively prevented the induction of Friend leukemia. This effect was seen when antiserum was given as late as 6 days after the Friend virus. Virus titrations showed that the best protection was achieved by a combination of immunization of the mother and inoculation of hyperimmune serum to the newborns. Cytotoxic antibodies in the sera of immunized females decreased during lactation. Significant amounts of cytotoxic antibodies were found in litters suckling immunized females but not in litters from immunized mothers suckling untreated nurses. Furthermore, the spleen weights of the infected litters were inversely related to the presence of cytotoxic antibodies in the mother's serum. Immune lymph node cells had to be given 7–14 days before Friend virus challenge for maximum protection. This implies that humoral antibodies are synthesized and that they are responsible for an early virus neutralization giving an efficient protection to the Friend leukemia. The protective effect was specific and there was no cross-reaction with the Gross virus-induced leukemia antigen.