The Epo-dependent erythroleukemia cell line HCD-57 can grow in the absence of Epo after infection with either SFFV-P or SFFV-A [29], but only SFFV-P can confer factor-independence to BaF3-EpoR cells, an IL-3 dependent hematopoietic cell line that has been engineered to express the Epo receptor (EpoR) [27,28,30]. This evidence concerns the gene EPOR and infection.