LSTRA murine leukemia injected s.c. or intradermally was uniformly lethal for BALB/c × DBA/2 F1 mice at doses of 103 cells or greater. Mice that survived after injection of near-threshold tumor cell doses usually were not immune to the tumor. Few mice were cured by excision of the injection site tumor ≥6 days after injection, but those that were cured developed tumor immunity. Irradiation of the tumor cells with 8000 rads reliably prevented growth. Injection of 106 LSTRA cells exposed to 8000 rads (Lx) immunized few animals to LSTRA challenge while 107 Lx protected most of the mice against challenge with 105 or 106 tumor cells. LSTRA-induced immunity was effective against a tumor line induced by the murine sarcoma virus (Moloney) but not against a spontaneous mammary carcinoma or an antigenic, chemically-induced sarcoma. Lymphoid cells from immune mice were effective in the local passive transfer (Winn) test. The low level of immunity induced by 106 Lx was significantly potentiated by admixture of 5 × 103 or 5 × 105 colony-forming units Bacillus Calmette-Guérin in the tumor cell vaccine. Bacillus Calmette-Guérin given alone did not protect mice against LSTRA, and admixture of a higher dose of Bacillus Calmette-Guérin (5 × 107 colony-forming units) did not alter the weak immunity induced by the 106 Lx. Thus, potentiation of tumor immunity by an immune stimulant may occur with a relatively low optimum dose; higher doses may evoke lesser effects.
Supported by Contract N01-CB-33891, Grant P30-CA-18450, and Research Career Development Award K04-CA-70948 [G. L. B.], all from the National Cancer Institute and by funds from the Jake Gittlen Memorial Golf Tournament.