NIH/3T3 cells were infected with a cell-free extract from the mouse SRS ascitic tumor and propagated
in vitro. Experimental results showed that type A and type C virus particles were observed in the cytoplasm of infected NIH/ 3T3 cells
by electron-microscopy, X-C assay and reverse transcriptase were both positive. Free proviral-DNA of the leukemia virus was
found in the infected NIH/3T3 cell by Southern blot hybridization.
Morphologically, the NIH/3T3 cells infectedin vitro appeared spherical and formed monolayer cell colonies of various sizes after 24–48 hours. When the cultured cells were inoculated
into nude mice (BALB/ c, nu nu) subcutaneously, fibrosarcoma was induced, 100%. Inoculation of the cell-free extract of the
same cultured cells into inbred SW-1 newborn mice, resulted in the production of lymphocytic leukemia and lymphoma in 52.3%
within 191 days.