THERAPEUTIC EFFECTIVENESS OF NEURAMINIDASE‐TREATED TUMOR CELLS AS AN IMMUNOGEN IN MAN AND EXPERIMENTAL ANIMALS WITH LEUKEMIA*

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Abstract
The immunogenicity of leukemia L1210 in DBA/2 Ha and 6C3HED lymphosarcoma tumor cells in C3H/f mice was significantly increased after treatment with V. cholerae neuraminidase. DBA/2 Ha and C3H/f mice repeatedly immunized with neuraminidase-treated tumor cells rejected subsequent challenge of 10(7) or 10(6) untreated tumor cells, respectively. Based on the 51Cr microcytotoxicity assay, both strains of mice showed strong complement-dependent antibody titers and cell-mediated immunity. Sera and splenic lymphocytes from immunized C3H/f mice neutralized the tumorigenicity of 6C3HED lymphosarcoma and protected the recipient C3H/f mice against the disease. Immune lymphocytes pretreated with anti-theta sera lost their ability to neutralize the tumorigenicity of lymphosarcoma, and they failed to be stimulated by T-cell mitogens. We studied the effectiveness of chemoimmunotherapy in DBA/2 Ha mice with leukemia L1210. A single near optimal dose of BCNU 2 days after implantation of 10(6) tumor cells increased the survival time. A single immunization with 2 X 10(7) neuraminidase-treated L1210 tumor cells 4 days after cytoreductive therapy increased survival and resulted in cures for 50% of animals. Immunization of mice with neuraminidase-treated tumor cells and MER produced indefinite survival in a larger percentage of mice than did either treatment alone. AKR mice with spontaneous leukemia treated with combination chemotherapy sustained an 180% increase in life-span. Combination chemotherapy plus immunization with neuraminidase-treated syngeneic or allogeneic (Gross virus-induced) E2G leukemia cells were highly effective in prolonging the life-span of the immunized leukemic AKR mice. The experimental data led to clinical trials in acute myelocytic leukemia with neuraminidase-treated a-logeneic myeloblasts. Patients with acute myelocytic leukemia were randomized into two groups after remission induction. The median remission duration of patients on sustaining chemotherapy alone was 19 weeks (8 patients), whereas six of nine patients who received neuraminidase-treated allogeneic myeloblasts remain in remission 79-132 weeks. Statistical analysis of the remission duration and survival of patients who received chemoimmunotherapy versus the control group shows highly significant differences.

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