Studies on the Mechanism of Immunological Enhancement of Tumor Grafts

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Abstract
The mechanism of immunological enhancement of tumor homografts by heteroimmune serum was studied, particularly the immunological properties of the active antiserum and its mode of action. Tumor homografts, enhanced by heteroimmune serum, were shown to elicit an intense homograft reaction, while growing progressively in foreign hosts. This reaction is manifested both by the production of isohemagglutinins with enhanced 6C3HED lymphosarcoma and by the increased resistance of the host, i.e., transplantation immunity produced by enhanced Sarcoma SBL1. The enhancement of tumor homografts was thus attributed to a capacity to resist transplantation immunity induced in the tumor cells and not to suppression of the host's resistance. This implies a direct action of the enhancing antibodies on the tumor cells. The direct action was further supported by the fact that heteroimmune serum enhanced the growth of tumor isografts. Passive transfer of immunity through lymph nodes activated by tumor homografts of Sarcoma MC1M revealed that after a prolonged exposure the same lymph nodes producing transplantation immunity can produce enhancing antibodies. The experimental data obtained in the present study might explain immunological enhancement if it is assumed that the enhancing antibodies stimulate an augmented synthesis of their homologous antigen in the tumor cells. Such an increased production of antigen might explain both the augmented growth of enhanced tumor isografts and the resistance of enhanced tumor homografts to transplantation immunity.