Surface phenotypes in T-cell leukaemia are determined by oncogenic retroviruses

Spontaneous thymic leukaemia in experimental mice is the result of a complex series of genetically controlled events1. An important step in this process involves the production by thymocytes of recombinant polytropic retroviruses (MCF viruses)2,3. These leukaemogenic agents arise by recombination of genes from the env regions of endogenous precursor viruses4,5. Sequences in these regions encode the envelope glycoprotein gp70 (ref. 6). Thus far, each cloned isolate of recombinant virus from AKR and HRS/J mice has been found to possess unique oligonucleotide sequences in its env region, as well as clone-specific peptides in its gp70 (refs 7, 8). Therefore, the polytropic viruses of these leukaemia-susceptible mice are extremely diverse. These findings suggest that random recombination of env genes gives rise to leukaemogenic polytropic viruses. McGrath and Weissman9 have proposed that thymocytes with cell surface receptors for the gp70 of a particular leukaemogenic virus are the target cells for malignant transformation by that specific virus. In view of the diversity of polytropic viral gp70, their hypothesis would predict extensive phenotypic diversity among spontaneous thymic leukaemias. In contrast, leukaemias induced by a particular leukaemogenic recombinant virus would always have the same phenotype. Here we verify these predictions experimentally.