Poorly metastatic tumor cell variants as primary targets of syngeneic antibody responses against murine melanoma.

Age-matched female C57BL/6 mice given injections i.v. of the syngeneic, poorly metastatic melanomas B16-F1 or JB/RH mount a measurable anti-melanoma antibody (Ab) response. The experiments described here examine the possibility of whether these Ab responses are in fact targeted against metastatically distinct subpopulations of melanoma. Reactivity of antisera and monoclonal antibodies (MoAb) developed by syngeneic immunization were examined by radioimmunoassay, flow cytometry, and Western blot analyses. Anti-melanoma antisera collected at various times after i.v. injection of melanoma cells were tested in radioimmunoassay against C57BL/6 melanoma cell lines and clones of well-characterized experimental metastatic activity. A strong inverse correlation between metastatic activity and Ab binding was observed. Furthermore, i.v. injection of poorly metastatic melanoma lines always resulted in strong Ab response, while highly metastatic clones did not. The relative distribution of Ab-reactive cells in melanoma populations was examined by flow cytometry. Again, the proportion of reactive cells in all melanoma cell lines and clones tested was inversely proportional to the degree of experimental metastatic activity. Hybridoma technology used to capture this selective Ab response yielded monoclonal reagents with distinct anti-melanoma specificity. Monoclonal antibody directed against nonmetastatic melanoma variants defined specific Mr 45,000 and 50,000 bands in Western blot analyses. Finally, melanoma cells nonreactive with the syngeneic Ab response were isolated after immunomagnetic bead plus magnet removal of the positive population. The experimental metastatic potential of these negatively selected cells was then compared with cells similarly fractionated with normal mouse serum or control MoAb. The results of these studies showed a clear increase in metastatic potential of anti-B16-F1 melanoma antiserum or MoAb-depleted cells. These results support the contention that host Ab responses may favor tumor progression and metastasis through selective Ab responses against the poorly metastatic population.