In vitro malignant progression of cells derived from Abelson murine leukaemia virus-induced thymic lymphomas

Cell lines derived from A-MuLV induced thymic lymphomas in BALB/c and C57BL/6 mice were analysed for their in vivo and in vitro potential of growth. Despite their immunogenicity, cell lines of BALB/c origin readily grew in syngeneic recipients. On the contrary, all cell lines of C57BL/6 origin failed to grow in immunocompetent hosts even though they were able to form tumours in immunosuppressed syngeneic mice. Among C57BL/6 lymphoma cells progression toward a more malignant phenotype was observed in TB6-3 cells, and in their derived clones, after several in vitro passages. This event was accompanied by the in vitro loss of requirement for exogenous growth factor(s) when tumorigenic TB6-3 cells were plated at high density. Moreover, culture medium from fully malignant TB-3 cells was mitogenic for mature T-lymphoma cells suggesting the involvement of an autocrine mechanism in the control of cell proliferation. Apparently, the viral oncogene (v-abl) is not directly involved in malignant progression since no differences between non-tumorigenic and tumorigenic cells could be detected in A-MuLV integration patterns, v-abl specific mRNA expression, and P160(gag-abl) production.