Abstract
Hematopoietic stem cell gene therapy for HIV/AIDS is a promising alternative to lifelong antiretroviral therapy. One of the limitations of this approach is the number and quality of stem cells available for transplant following in vitro manipulations associated with stem cell isolation and genetic modification. The development of methods to increase the number of autologous, gene-modified stem cells available for transplantation would overcome this barrier. Hematopoietic stem and progenitor cells (HSPC) from adult growth factor-mobilized peripheral blood were cultured in the presence of an aryl hydrocarbon receptor antagonist (AhRA) previously shown to expand HSPC from umbilical cord blood. Qualitative and quantitative assessment of the hematopoietic potential of minimally cultured (MC-HSPC) or expanded HSPC (Exp-HSPC) was performed using an immunodeficient mouse model of transplantation. Our results demonstrate robust, multilineage engraftment of both MC-HSPC and Exp-HSPC although estimates of expansion based on stem cell phenotype were not supported by a corresponding increase in in vivo engrafting units. Bone marrow of animals transplanted with either MC-HSPC or Exp-HSPC contained secondary engrafting cells verifying the presence of primitive stem cells in both populations. However, the frequency of in vivo engrafting units among the more primitive CD34+/CD90+ HSPC population was significantly lower in Exp-HSPC compared with MC-HSPC. Exp-HSPC also produced fewer lymphoid progeny and more myeloid progeny than MC-HSPC. These results reveal that in vitro culture of adult HSPC in AhRA maintains but does not increase the number of in vivo engrafting cells and that HSPC expanded in vitro contain defects in lymphopoiesis as assessed in this model system. Further investigation is required before implementation of this approach in the clinical setting.