Friend spleen focus-forming virus induces factor independence in an erythropoietin-dependent erythroleukemia cell line.

Erythroid cells from mice infected with the polycythemia-inducing strain of Friend spleen focus-forming virus (SFFVP), unlike normal erythroid cells, can proliferate and differentiate in apparent absence of the erythroid hormone erythropoietin (Epo). The unique envelope glycoprotein encoded by SFFV has been shown to be responsible for this biological effect. The recent isolation of an Epo-dependent erythroleukemia cell line, HCD-57, derived from a mouse infected at birth with Friend murine leukemia virus, afforded us the opportunity to study the direct effect of SFFVP on a homogeneous population of factor-dependent cells. The introduction of SFFVP in complex with various helper viruses into these Epo-dependent cells efficiently and reproducibly gave rise to lines which expressed high levels of SFFV and were factor independent. SFFV appears to be unique in its ability to abrogate the factor dependence of Epo-dependent HCD-57 cells, since infection of these cells with retroviruses carrying a variety of different oncogenes had no effect. The induction of Epo independence by SFFV does not appear to involve a classical autocrine mechanism, since there is no evidence that the factor-independent cells synthesize or secrete Epo or depend on it for their growth. However, the SFFV-infected, factor-independent cells had significantly fewer receptors available for binding Epo than their factor-dependent counterparts had, raising the possibility that the induction of factor independence by the virus may be due to the interaction of an SFFV-encoded protein with the Epo receptor.

Generation of tumor cell-reactive human monoclonal antibodies using peripheral blood lymphocytes from actively immunized colorectal carcinoma patients.

The use of human monoclonal antibodies (MCA) in the detection and treatment of human cancer has been limited by the apparent scarcity of MCA to tumor cell surface antigens. Using peripheral blood lymphocytes from autologous tumor-immunized patients, we isolated 36 MCA that react to sections of colorectal carcinoma. Twenty of these human MCA appear to be directed against cell surface antigens. Two-thirds of the human MCA-producing cell lines were diploid human B-cells rather than human-mouse heterohybridomas. Direct antibody-binding assays performed with the MCA indicated that they recognized antigenic determinants preferentially expressed on tumor cells. Experiments with paired specimens of air-dried, dissociated colon tumor cells and normal colonic mucosa cells suggested that the MCA bound significantly more to the cell surfaces of tumor cells than to the surfaces of normal colonic mucosa cells. Similarly, tests with a panel of cryostat sections of paired colon tumor and normal colonic mucosa showed that MCA bound to the tumor cells and not to the normal colonic mucosa. None of the MCA bound to cells from frozen sections of normal breast, stomach, liver, skeletal muscle, or skin. Furthermore, the human MCA did not react with carcinoembryonic antigen and human erythrocyte antigens as measured by various techniques. Our data also demonstrated that these transformed B-cells and hybridomas were stable producers of human MCA. Thus, our studies show that these tumor-specific human MCA may have the specificity and stability necessary for in vivo evaluation of their use in the detection and treatment of cancer.