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SUMMARYSpontaneous osteomas in strain 101 mice, a strain which has a high incidence of benign bone tumours, harbour numerous C-type virus-like particles with pleomorphic characteristics. A cell-free extract from osteomas from two mice induced bone tumours, together with osteopetrosis and lymphomas, in newborn mice of the low incidence NMRI strain after a latent period of 12 to 15 months. When C3H embryo fibroblasts were infected with the osteoma extract, the resulting cell line produced virus (OA MuLVc) with a high titre. OA MuLV c was cloned by serial endpoint dilution and NIH 3T3 cells were productively infected. The resulting virus was named OA MuLVN. OA MuLV c and OA MuLVN also induced bone tumours, osteopetrosis and lymphomas 12 to 15 months after injection into newborn NMRI mice. The isolated virus showed typical characteristics of the murine retrovirus group. Fv-1 host range restriction assays classified the viruses as N-ecotropic and XC-positive. Tryptic p30 peptide analysis and RNase T1 fingerprint analysis of OA MuLVc and OA MuLVy indicated that OA MuLVc contains an Akv-like virus as well as additional components, whereas OA MuLVN is closely related to Akv, but not identical to it. Serological analysis of the envelope proteins using monoclonal antibodies also showed the virus to be similar, but not identical, to Akv virus.

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Human sera contain antigens and also circulating immune complexes that are related to the primate retroviral envelope glycoprotein gp70 of simian sarcoma/simian sarcoma associated virus (SiSV) and of gibbon ape leukemia virus (GaLV). SiSVgp70 related antigens (AG) and immune complexes (IC) are detected both in leukemic and in nonleukemic sera.23 In a further analysis of these data, the prognostic significance of SiSVgp70 related AG and IC indicates an unfavorable clinical course and a shorter survival time in acute leukemias (AL) and in chronic myelogenous leukemia in blast crisis (CML‐BC). Survival data of 56 of 64 patients tested were analyzed (38 patients with AL and 18 patients with CML‐BC). Patients with AL whose sera were positive for SiSVgp70 realted AG and IC had a median survival time of 9.5 months after diagnosis versus 16 months for patients negative for such AG and IC. This difference in survival time was more pronounced for patients with acute nonlymphocytic leukemia (ANLL) (6.5 versus 19 months). The difference in survival between SiSVgp70 related AG‐ and IC‐negative and positive groups as tested by life table analysis (log‐rank test) is significant (P < 0.05). Patients with AL of the AG‐ and/or IC‐positive group had fewer complete remissions. Patients who had no remissions belong to the AG‐ and/or IC‐positive group (P = 0.06). Patients with CML‐BC whose sera were positive for SiSVgp70 related AG and/or IC had a median survival time of 2 months after diagnosis versus 7 months for patients with sera negative for such AG and IC. As tested by long‐rank test, survival curves between the two groups are significantly different (P < 0.05). These findings suggest that SiSVgp70 related AG and IC may play an important role in the course of acute leukemia and can provide useful prognostic information.