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Protection against Radiation Leukemogenesis by Repeated Injections of Immune and Nonimmune Foreign Sera¹

Department of Radiology, Stanford University School of Medicine, Stanford, California 94305

Significant inhibition of lymphoid tumor development was observed in X-irradiated strain C57BL mice treated with multiple injections of rat antiserum prepared by immunization of Wistar-Furth or (Wistar-Furth·BN) F₁ rats with histocompatible lymphomas induced by the radiation leukemia virus (RadLV). However, there was also significant inhibition, relative to phosphate-buffered saline controls, in C57BL mice that received injections of normal rat serum. This prompted additional experiments in which fetal calf serum or Freund's complete adjuvant were injected as nonspecific immunostimulants. Strong protection was observed with fetal calf serum, and a slight inhibitory effect (not significant) was also seen with Freund's complete adjuvant. The results are discussed in terms of the following alternative interpretations, which are not mutually incompatible: (a) the inhibitory effect of the rat anti-RadLV serum, as well as that of "normal" serum, which may have contained natural antibody to RadLV, is due to passive immunization by specific antiviral antibody, thus further implicating RadLV in the etiology of radiogenic lymphomas; (b) the protective effect is due to hyperimmunization of the mice against foreign (rat and bovine) sera, leading to nonspecific stimulation of the immune surveillance mechanisms of the host animals; and/or (c) prevention by the foreign sera is due to the radiation leukemia protection factor described by Berenblum et al.

¹ This investigation was supported by Research Grants CA 03552 and CA 10372 and by Training Grant CA 05008 from the National Cancer Institute, NIH; and by Research Grant T-513 from the American Cancer Society.

² Recipient of an Eleanor Roosevelt International Cancer Research Fellowship. Present address: School of Veterinary Medicine, University of Pennsylvania, New Bolton Center, Kennett Square, Pa. 19348.

Received 12/27/72. Accepted 3/14/73.