Leukemias Induced in Rats by Mammary Tumor Extracts23

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Abstract
Leukemia was infrequently but repeatedly produced in randombred Sprague-Dawley rats given injections at birth of cell-free and filtered extracts of materials derived from mammary carcinomas induced by 7,12-dimethylbenz[a]anthracene (DMBA) in the same strain of rats. Twelve of the fifty extracts tested were leukemogenic. Extracts of tumor cell cultures and phenol extracts of tumor tissue produced the highest incidence of leukemia in the recipients. This leukemia, designated RMTDL, was serially transplantable to randombred rats, which resulted in a 100% incidence. The transplantation success depended on the age of the recipient, number of cells transplanted, and route of inoculation. Three of seven leukemias, produced with DMBA tumor-derived extracts, were further transmitted in low incidence by filtered extracts of leukemic tissues. Transmission by this method was not achieved beyond the second passage, but a hemag-glutinating virus, designated 9H, was isolated in tissue culture from two extracts of the second passage and from one extract of the first passage. All the leukemias were lymphocytic or lymphoblastic and were uniformly characterized by hepatosplenomegaly. These findings suggest that either a virus or residual cell-bound DMBA was responsible for the partial success in the cell-free induction and passage of this leukemia. The significance, if any, of the involvement of the 9H virus remains to be determined.