Improving Gene Therapy Efficiency through the Enrichment of Human Hematopoietic Stem Cells

Abstract

Lentiviral vector (LV)-based hematopoietic stem cell (HSC) gene therapy is becoming a promising clinical strategy for the treatment of genetic blood diseases. However, the current approach of modifying 1× 108 to 1× 109 CD34+ cells per patient requires large amounts of LV, which is expensive and technically challenging to produce at clinical scale. Modification of bulk CD34+ cells uses LV inefficiently, because the majority of CD34+ cells are short-term progenitors with a limited post-transplant lifespan. Here, we utilized a clinically relevant, immunomagnetic bead (IB)-based method to purify CD34+CD38- cells from human bone marrow (BM) and mobilized peripheral blood (mPB). IB purification of CD34+CD38- cells enriched severe combined immune deficiency (SCID) repopulating cell (SRC) frequency an additional 12-fold beyond standard CD34+ purification and did not affect gene marking of long-term HSCs. Transplant of purified CD34+CD38- cells led to delayed myeloid reconstitution, which could be rescued by the addition of non-transduced CD38+ cells. Importantly, LV modification and transplantation of IB-purified CD34+CD38- cells/non-modified CD38+ cells into immune-deficient mice achieved long-term gene-marked engraftment comparable with modification of bulk CD34+ cells, while utilizing ∼7-fold less LV. Thus, we demonstrate a translatable method to improve the clinical and commercial viability of gene therapy for genetic blood cell diseases.