Immunotherapy and chemotherapy of Moloney sarcoma virus-induced tumors in mice.

Regression of autochthonous (primary) murine sarcoma virus (Moloney) (MSV)-induced tumors was first detectable in 13% of BALB/c mice inoculated with MSV at 3 weeks of age and increased in incidence thereafter. This correlated with the ability to resist transplanted BALB/c Moloney sarcoma (MS) cells. Treatment of young BALB/c mice bearing palpable primary tumors with spleen cells or with serum from adult BALB/c or CDF (BALB/c X DBA)Fj mice whose autochtho nous tumors had regressed resulted in complete tumor regression in 34—40% of the hosts. Such immune cells, in conjunction with cyclophosphamide (CY), were also effective in eradicating palpable transplanted tumors. Primary tumors were moderately sensitive to CY. However, CY given to young mice bearing primary tumors transiently inhibited tumor growth and doubled host survival time, whereas CY given to adult tumor-bearing mice decreased tumor growth but also depressed immunologie reactivity, thereby preventing tumor regression. This illustrates a poten tial danger in treating a host already responding against his tumor with a chemotherapeutic agent possessing potent immunosuppressive activity. Specific immunotherapy pre vented the deleterious effect of CY. Most adult BALB/c mice bearing palpable primary tumors and inoculated with CY were cured by spleen cells or by serum from BALB/c, CDF, or (BALB/c X C57BL/6)F, mice hyperimmunized by MSV, but not by cells from unimmunized mice or by anti-BALB/c serum. The results show that established primary MSV-induced tumors can be cured by lymphoid cells or serum from syngeneic or allogeneic donors specifically sensitized to MSVinduced tumor antigens.