Facilitation and inhibition of B16 melanoma by BCG in vivo and by lymphoid cells from BCG‐treated mice in vitro

Groups of mice were pretreated with varying dosages of BCG, then injected with B16 melanoma cells. In mice pretreated with high‐dose (0.5 mg) BCG, the tumor grew at an accelerated rate, whereas with low‐dose (0.005 mg) BCG, the tumor grew at a reduced rate when compared to growth in control mice. These data show that BCG could, depending upon dosage, either facilitate or inhibit tumor growth in vivo. Furthermore, lymphoid cells from high‐dose BCG‐treated tumor‐bearing mice were stimulatory to target B16 melanoma cells in vitro if the ratio of lymphoid cells to target tumor cells was sufficiently low (25:1‐200:1), but were inhibitory when the ratio was high (400:1‐1,000:1).