High‐ and low‐leukemogenic variants of the radiation leukemia virus (RadLV): Immunogenic, suppressive and genetic properties in relation to leukemogenic activity

C57BL/6 (B6) mice inoculated with the highly leukemogenic variant of the radiation leukemia virus (A‐RadLV) develop suppressor cells capable of abrogating potential anti‐tumor immunity in vitro and in vivo, Inoculation of B6 animals with the low‐leukemogenic D‐RadLV variant does not result in suppressor cell generation but induces antitumor reactive lymphocytes. A‐RadLV and D‐RadLV are not leukemogenic in BALB/c or (B6 × BALB/c)F₁ (F₁) mice, and reactive but not suppressor lymphocytes could be demonstrated in F₁ animals inoculated with either virus. Infectivity assays and fingerprint analysis revealed that A‐RadLV and D‐RadLV contain viruses with N and B tropism. In addition, thymoma cells induced by A‐RadLV produced another virus with a fingerprint pattern containing X‐MuLV elements. The possible implications of the different virus types on the immunogenic and leukemogenic properties of the RadLV variants are discussed.