Extraction of Immunogenic and Suppressogenic Antigens from Variants of B16 Melanoma Exhibiting Low or High Metastatic Potentials¹

This investigation examined the effect of soluble antigen prophylaxis on s.c. and metastatic growth of B16 variants which demonstrated either a low or high propensity to colonize the lungs (B16-F1 and B16-F10, respectively) of syngeneic C57BL/6J mice. The two variants share a tumor-associated antigen, since immunization with crude butanol extracts (CBEs) of B16-F1 cells protected hosts against s.c. challenge with either B16-F1 or B16-F10 cells. CBE from B16-F10 (CBE-F10) were unable to engender a measurable immune response against s.c. challenge with either tumor variant. Pretreatment with 100 to 300 µg CBE from F1 cells was also effective in reducing the outgrowth of experimentally induced B16-F1 or B16-F10 pulmonary foci. However, mice immunized with 100 µg CBE-F10 bore significantly more pulmonary tumors than did phosphate-buffered saline-treated controls. The enhancing and protective activities were specific for the B16 tumor and could be adoptively transferred 24 hr prior to tumor challenge by i.p. injection of 5 × 10⁷ spleen cells from CBE-immunized mice. The enhancing activity in the CBE-F10 immune spleen cell population was abolished by depletion of adherent cells onto plastic. Adoptive transfer of the CBE-F10-immune adherent cell population did not affect metastatic growth, suggesting that, in this experimental system, the adherent population was not an efferent suppressor and could not recruit host elements to effect suppression. Indeed, spleen cell-mixing experiments demonstrated that only immune adherent cells combined with immune nonadherent cells could partially reconstitute the tumor growth-enhancing potential of the unfractionated CBE-F10-immune spleen cell population.