Analysis of neoplasms induced by Cas-Br-M MuLV tumor extracts

Cas-Br-M is an ecotropic murine leukemia virus isolated from wild mice that induces a wide spectrum of hematopoietic neoplasms, including T and B cell lymphomas, myelogenous leukemias, and erythroleukemias. The purpose of this study was to determine if the induction of neoplasms belonging to multiple lineages was due to the ecotropic virus itself or to the generation of cell lineage-specific recombinant viruses. The results demonstrate that in some instances (two of 12 tumor extracts tested), recombinant viruses can be recovered from primary Cas-Br-M-induced tumors that will induce lymphomas of single lineages in mice inoculated as newborns. One of these viruses is a recombinant mink cell focus-forming virus that induces T cell lymphomas, and the other is a replication-defective, fibroblast-transforming virus that induces early B lineage lymphomas in mice. Histologic and flow microfluorometric cell surface antigen analyses of primary and in vitro adapted tumors are presented in support of a modified scheme of hematopoietic cell development.