PROTECTION BY GRAFTS OF EMBRYONAL RAT-TISSUES (TERATOMAS) AGAINST INDUCTION AND TRANSPLANTATION OF MALIGNANT-TUMORS

Clinical observations and experimental studies have shown that pregnan cy may have inhibitory effects on tumor growth rather than invariably aggravate neoplastic disease as believed previously. It has been sugge sted that circulating factors of maternal or fetal origin may protect against tumor growth during pregnancy. The previously created experime ntal model of teratomas provides the means of having an adult animal b earing a permanent graft of embryonal tissues. To investigate the pote ntial effects of embryonal factors on the growth of malignant neoplasm s, rats carrying grafts of embryonal tissues were subjected to the ind uction or transplantation of carcinomas and lymphomas. Finely minced e mbryo tissues or cell suspensions injected in homologous rat recipient s formed permanent benign teratomas composed of a variety of well diff erentiated tissues. One injection of N-methyl-N-nitrosourea, a potent carcinogen administered to all rats, induced fatal mammary adenocarcin oma in 50-60% of control rats but in none of the rats bearing a grafte d teratoma. Transplantation of N-methyl-N-nitrosourea-induced mammary adenocarcinoma or Gross virus-induced lymphoma killed 100% of control rats but resulted in smaller, later appearing tumors in only 25-61% of teratoma-bearing rats. The present experiments showed that rats beari ng grafts of embryonal tissues in the form of teratomas were partially or totally protected against the induction and transplantation of mal ignant tumors that killed 100% of controls. These results suggest that the embryonal tissues are a source of tumor-inhibitory factors, which may be a part of mechanisms controlling the growth and detecting the aberrations of embryonal tissues. Their identification and analysis ma y provide knowledge about embryonal growth and possibly about new subs tances with antineoplastic activity.