Establishment of an immortalized human erythroid cell line sustaining differentiation potential without inducible gene expression system

Ex vivo manufactured red blood cells (RBC) generated from immortalized erythroid cell lines which can continuously grow are expected to become a significant alternative in future transfusion therapies. The ectopic expression of human papilloma virus (HPV) E6/E7 gene has successfully been employed to establish these cell lines. To induce differentiation and maturation of the immortalized cell lines, terminating the HPV-E6/E7 expression through a gene induction system has been believed to be essential. Here, we report that erythroid cell lines established from human bone marrow using simple expression of HPV-E6/E7 are capable of normal erythroid differentiation, without turning gene expression off. Through simply changing cell culture conditions, a newly established cell line, Erythroid Line from Lund University (ELLU), is able to differentiate toward mature cells, including enucleated reticulocytes. ELLU is heterogeneous and, unexpectedly, clones expressing adult hemoglobin rapidly differentiate and produce fragile cells. Upon differentiation, other ELLU clones shift from fetal to adult hemoglobin expression, giving rise to more mature cells. Our findings propose that it is not necessary to employ gene induction systems to establish immortalized erythroid cell lines sustaining differentiation potential and describe novel cellular characteristics for desired functionally competent clones.