Abstract
Leukemia induction by culture-grown thymotropic radiation leukemia virus or by tumor-derived virus present in cell-free tumor extracts was abrogated by incubation of either virus with anti-thymotropoc virus serum, but not by antiserum raised against ecotropic or dual-tropic (mink cell focus-inducing type) viruses that were isolated from radiation leukemia virus-induced thymic leukemias. Thus, virus similar or identical to the cultured thymotropic leukemogenic species may also be the major biologically active principle in tumor-derived extracts, even though the latter also contain viruses of the dual-tropic, mink cell focus-inducing type class.