Specific recognition of tumors induced by homeostatic proliferation. (a) Sublethally irradiated C57BL/6 mice were transfused with 5 × 10⁶ LN cells prior to challenge with B78D14 melanoma cells (n = 4). Ten days after challenge, splenocytes were coincubated with either irradiated B78D14 melanoma cells (filled squares) or irradiated MC-38 colon carcinoma cells (open squares) for 48 hours; a standard 4-hour ⁵¹Cr-release assay was performed at three effector-to-target cell ratios. Results indicate percentage of specific lysis from a pool of four mice assessed in triplicate. (b) Sublethally irradiated C57BL/6 mice were transfused with 5 × 10⁶ LN cells prior to challenge with B78D14 melanoma cells. Thirty-five days after challenge, splenocytes were cultured for 72 hours with either B78D14 melanoma cells (black bars) or MC-38 colon carcinoma cells (white bars). Similarly cultured control lymphocytes were derived from nonirradiated, nontransfused, and melanoma-challenged mice. Results indicate IFN-γ levels in the supernatants from a pool of four mice assessed in quadruplicate.