Inhibition of mammary tumorigenesis in virgin rats by adoptive transfer of splenocytes from parous donors.

Splenocytes from parous rats have been previously found to have cytotoxic activity against mammary tumor cells in vitro. Experiments were carried out to determine if this pregnancy-induced cytotoxic nature of the splenocytes is inherent and transferable. Splenocytes from parous rats wer adoptively transferred to a group of virgin rats. Another group of age-matched, virgin rats received splenocytes from virgin donors in a similar way. After a period of rest, at the age of 55 days, the rats belonging to both of the groups, received 7,12-dimethylbenz(a)anthracene (DMBA) intragastrically. A third group of untreated virgin rats were also given the chemical carcinogen the same way as above and were considered as intact controls. The rats were monitored for development and growth of mammary tumor from 60 days of DMBA administration. After 4 months of DMBA administration the rats were sacrificed and mammary glands were examined for tumors. Mammary glands with no visible tumors were taken for whole mount preparation, to be examined for microscopic lesions. The results showed that 33 of 41 intact control rats, developed tumor and 27 of the 34 rats that received spleen cells from virgin rats developed tumors. Of the rats that received spleen cells from parous rats, only 18 out of 37 rats developed tumors, indicating an inhibition of tumor induction in these rats. Growth rate of the tumors in this group was also slower than in the control groups.