Immunogenicity of modified tumor cells in syngenic hosts.

Modified tumor cells were used to immunize three murine hosts against syngenic ascitic lymphomas: C3H-6C3HED, BALB/c-P1798, and DBA/2-L1210. When the host was capable of a significant immune response against the malignant cells during progressive tumor growth (e.g., C3H vs. 6C3HED), protective immunization against a larger challenge tumor dose was achieved after fewer vaccinations. Lipopolysaccharide (LPS) enhanced host response to iodoacetamide (IAd) modified P1798 and L1210 so as to confer resistance after fewer immunizations with these weakly antigenic tumors. Similarities among the three systems were also seen. Modified cells may be stored at 4 degrees C several weeks and are effective when 107-108 are given i.p.; resistance appears maximal about one week after vaccination. In immunotherapy trials, C3H mice implanted with 5 x 104 6C3HED cells and treated at least four times with IAd-6C3HED demonstrated a 25% cure rate. A model was presented for evaluating parameters of response to immunotherapy in conjunction with chemotherapy. Cell-mediated immunity in resistant mice was demonstrated by inhibition of DNA synthesis in cultures of lymphoma cells and sensitized peritoneal cells (PEC) compared to that with nonimmune PEC. This assay system may also provide an opportunity for examining the hypothesis of immunostimulation of tumor growth in vitro. Humoral response to modified cells was established by membrane immunofluorescence. Although anti-6C3HED and anti-L1210 appear specific, anti-P1798 antiserum reacts with BALB/c thymocytes and murine fetal antigen.