In Vitro Transformation of Fetal Brain Cells From CDF Rats Exposed In Utero to N-Ethyl-N-nitrosourea: Morphologic and Immunologic Studies234

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Abstract
Inbred CDF rats received 250 mg N-ethyl-N-nitrosourea (ENU)/kg body weight in monosodium phosphate buffer (pH 5.5) during late pregnancy (18–21 days). Control rats received only buffer. One hour after ENU or buffer administration, the fetuses were delivered and fetal brain cells (FBC) were put in longterm tissue culture. Cell growth consisted of monolayers of glial, fibroblastic, and epithelial-like cells. FBC from buffer-treated rats could not be subcultured for more than 13–15 passages; only one culture was maintained up to the 26th passage. FBC from ENU-treated rats showed in vitro malignant transformation beginning at the 8th passage (100 days). Injection of these cells sc into Irradiated or neonatally thymectomized syngeneic rats induced small palpable tumors that regressed completely by 15–28 days. Small nonprogressively growing subcutaneous tumors in normal rats, however, were obtained only after the 19th in vitro passage (200 days). These transformed FBC appeared highly antigenic. Tumor-associated antibody was demonstrated in the sera of tumor-bearing rats with anti-C3-mixed hemadsorption and immune adherence assays. Rats immunized with irradiated malignant FBC showed rising tumor antibody titers. The antibody was absorbed by ENU-exposed FBC but not by normal fetal or adult syngeneic brain cells. We concluded that ENU-exposed cells become malignant when grown in vitro for at least 8 passages (100 days) but grow in vivo in X-irradiated or neonatally thymectomized rats only. These antigenic and tumorigenic clones may be selected in vitro, where they grow readily in the absence of immune resistance.