Isolation of a myelogenous leukemia‐inducing virus from mice infected with the friend virus complex

A myelogenous leukemia‐inducing virus (MyLV) has been isolated from a chloroleukemic C57Bl mouse, injected neonatally with the lymphatic leukemia virus (LLV)‐containing helper component of the Friend virus (FV) complex. MyLV, free of detectable spleen focus‐forming virus (SFFV), consistently induced only myelogenous leukemia in neonatally infected C57Bl, Ha/ICR, C3H and BALB/c mice, within 5 months (including chloroleukemias in C57Bl and Ha/ICR). The leukemia involved chiefly the spleen, liver, lymph nodes and bone marrow, and tumor cells could be recovered from the marrow to grow in the solid (subcutaneous) or ascites (intraperitoneal) form. MyLV preparations had ample helper activity for SFFV in restrictive hosts, and could be used to prepare a MyLV pseudotype of SFFV which was antigenically indistinguishable from native FV complex. MyLV could have arisen by selection of a pre‐existing variant in the LLV population, by a genetic interaction between LLV and the C57Bl chloroleukemic host cell, or could have arisen from the original host C57Bl mice as a result of activation following the infection with LLV.