Process for the in vitro culture of cells infected by a multiple sclerosis associated virus, and infected cell lines so produced. According to the invention, the process consists: a) in cultivating human cells infected by a viral strain, obtaining at least one primary cell culture infected by said viral strain, b) cultivating non-infected human cells permissive to said viral strain, obtaining at least one permissive culture, c) cultivating together at least one sample of an infected primary cell culture and one sample of the permissive culture to obtain a first infected derived culture, d) cultivating in series the first infected derived culture. Application in the pharmaceutical diagnostic industry.