Demonstration and characterization of virus released by murine B cell leukemia cells (BCL₁)

LPS-stimulated leukemia cells derived from BALB/c mice bearing transplantable B-lymphocytic leukemia (BCL₁) which arose spontaneously in a female BALB/c mouse, contained viral particles as suggested by electron microscopy as well as by tissue cultures using the XC assay. Some cell free extracts prepared from BCL₁ cells were capable of transforming normal B-lymphocytes when inoculated into untreated syngeneic recipients. Cytogenetic analysis of spleen cells obtained from a splenomegalic male mouse neonatally inoculated with cell-free extract indicated that the tumor cells had a male karyotype with 42 chromosomes as compared to 37 chromosomes and a female karyotype in original BCL₁ cells, thus excluding the possibility of tumor propagation by transplantation of intact BCL₁ cells. These findings suggest viral involvement in the etiology of BCL₁.