A Point-of-Care Platform for Hematopoietic Stem Cell Gene Therapy

Hematopoietic stem and progenitor cell (HSPC) gene therapy holds great promise but requires highly technical and dedicated facilities. Current state-of-the-art requires ex vivo HSPC gene transfer in dedicated Good Manufacturing Practices (GMP) facility infrastructure, limiting treatment to highly developed countries. A patient point-of-care strategy would therefore make HSPC gene therapy available to patients worldwide. We developed a short, semi-automated, mostly-closed platform for ex vivo isolation and lentivirus (LV) gene modification of CD34⁺ HSPCs from either bone marrow or mobilized peripheral blood sources using the CliniMACS Prodigy^® (Figure 1). Experiments were performed with a biosafety cabinet and personal protective equipment to simulate anticipated conditions in clinical facilities of underdeveloped countries. A total of 7 custom programs were developed for bone marrow or mobilized peripheral blood CD34⁺ cell isolation and LV transduction. Addition of a pyrimidoindole derivative, UM 729, permitted efficient transduction of CD34⁺ HSPCs in <18 hours. Complete semi-automated production took <34 hours from collection to infusion of the gene modified cell product, requiring very little operator hands-on time. Autologous, LV gene-modified CD34⁺ HSPCs from two nonhuman primates produced using this platform engrafted and supported multilineage hematopoietic repopulation after myeloablative total body irradiation at 1020 cGy. Total cell doses achieved were 27 x 10⁶ and 5.4 x 10⁶ CD34⁺ cells/kg body weight, respectively. We observed stable, persistent and polyclonal gene marking in peripheral blood granulocytes up to 40% and lymphocytes up to 15% within 4 months after infusion. Neither animal displayed evidence for increased toxicity, including potential contamination from the cell products. We then validated processing of human bone marrow and mobilized apheresis products from healthy adult donors. We demonstrate efficient isolation of human CD34⁺ HSPCs and up to 60% transduction efficiency with a clinical-grade LV currently being tested in a phase I clinical trial for treatment of HIV-associated lymphoma. Products tested met current FDA approved specifications for infusion. Xenotransplantation of these products into immunodeficient mice resulted in polyclonal engraftment over 12 weeks. These data demonstrate preclinical safety and feasibility of a patient point-of-care strategy for ex vivo LV gene transfer into HSPCs. This platform represents a major advance in global portability of LV mediated HSPC gene therapy.

Figure 1.

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Figure 1.

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