These cells were taken from the lungs of a British baby girl in 1974, about 15 weeks gestation. The cell line name stands for Medical Research Council, cell culture 9.
J.P. Jacobs, who developed MRC-5, also developed this cell line. Note that the harvesting of this child occurred immediately following her abortion.
[T]he cells were derived from the lungs of a female fetus in 1974, whose gestational age was about fifteen weeks. The fetus was of normal development and was delivered of a fourteen-year-old mother whose pregnancy was terminated by therapeutic abortion because she was unmarried. The medical history of the mother and her family indicated nothing abnormal according to information given by the gynecologist who performed the operation. The lungs were dissected from the fetus immediately following the abortion
 J. P. Jacobs, A. J. Garrett, and R. Merton, “Characteristics of a Serially Propagated Human Diploid Cell Designated MRC-9,” Journal of Biological Standardization 7.2 (April 1979): 114. <https://www.sciencedirect.com/science/article/abs/pii/S0092115779800438?via%3Dihub>