"Unlike bacteria, viruses do not replicate on their own. To make viral vaccines, large numbers of viruses must be grown in cell cultures specific to each virus. Some licensed viral vaccines (i.e., some formulations ofhepatitisA, poliovirus, rabies, rubella, and varicellazoster viruses or combination vaccines containing such component viruses) are produced by growing viruses that infect humans in WI-38 or MRC-5 cell cultures. WI-38 and MRC-5 represent two commonly used lineages of human diploid cell cultures, batches of immature cells with twice as many chromosomes as sperm or egg cells. Embryonic diploid cells are valuable in vaccine manufacture, because each aliquot ofthese cells can propagate several dozen times before senescence. Each of these cell lines started with cells harvested from a deliberately aborted fetus. The cell lines are used to grow the viruses, then discarded and not included in vaccine formulations. These cell lines cannot form a human being. TheWI-38 line was developed attheWistar Institute in Philadelphia in 1961, with lung cells from a female fetus of 3 months gestation aborted in Sweden, whose parents feltthey had too many children. Similarly, British scientists funded by the Medical Research Council developed the MRC-5 line in September 1966 with fetal lung fibroblasts “taken from a 14-weekold male fetus removed for psychiatric reasons from a 27-year-old woman. . .”. These cell lines, still in use today, gradually replaced primary cultures of monkey, duck, rabbit, chicken, dog, or mouse tissue, an approach vulnerable to contamination with viruses and bacteria."