Recovery of Murine Xenotropic Type-C Virus from C57L Mice2

Abstract

A type-C virus was isolated from C57L mice, a strain previously considered exceptionally low in expression of these viruses. The recovery was made by the heterotransplantation of human rhabdomyosarcoma (RD) cells in antithymocyte serum-treated mice. Viral reverse transcriptase (RT) activity was detected in supernatants of RD cells recultured from the transplanted tumors; the virus was subsequently seen by electron microscopy. The biologic activity of this virus was demonstrated by its rescue of the sarcoma genome from transformed nonproducer rat cells; it also infected productively various animal cell cultures, but was not infectious for mouse cells and did not produce plaques in the XC test for murine leukemia viruses (MLV). The group-specific protein and the RT of this C57L type-C virus were antigenically like those of all MLV. Its envelope antigen and host range, however, proved distinctive and were like those of isolates previously recovered from NZB, NIH Swiss, and C57BL/6 mice. It is, therefore, a member of the newly recognized group of endogenous xenotropic murine type-C viruses that cannot be propagated in murine cells.