Transgene-free iPSCs generated from small volume peripheral blood nonmobilized CD34⁺ cells

A variety of somatic cells can be reprogrammed to induced pluripotent stem cells (iPSCs), but CD34⁺ hematopoietic stem cells (HSCs) present in nonmobilized peripheral blood (PB) would be a convenient target. We report a method for deriving iPSC from PB HSCs using immunobead purification and 2- to 4-day culture to enrich CD34⁺ HSCs to 80% 6 9%, followed by reprogramming with loxP-flanked polycistronic (human Oct4, Klf4, Sox2, and c-Myc) STEMCCA-loxP lentivector, or with Sendai vectors. Colonies arising with STEMCCA-loxP were invariably TRA-1-60⁺, yielding 5.3 6 2.8 iPSC colonies per 20 mL PB (n 5 17), where most colonies had single-copy STEMCCA-loxP easily excised by transient Cre expression. Colonies arising with Sendai were variably reprogrammed (10%-80% TRA-1-60⁺), with variable yield (6 to >500 TRA-1-60⁺ iPSC colonies per 10 mL blood; n 5 6). Resultant iPSC clones expressed pluripotent cell markers and generated teratomas. Genomic methylation patterns of STEMCCA-loxP–reprogrammed clones closely matched embryonic stem cells. Furthermore, we showed that iPSCs are derived from the nonmobilized CD34⁺ HSCs enriched from PB rather than from any lymphocyte or monocyte contaminants because they lack somatic rearrangements typical of T or B lymphocytes and because purified CD14⁺ monocytes do not yield iPSC colonies under these reprogramming conditions.