Gene transfer into human cord blood-derived CD34⁺ cells by adeno-associated viral vectors

Objective: Bone marrow-derived CD34⁺ cells are currently used in clinical trials in patients with ischemic heart disease. An option to enhance activity of injected progenitors may be offered by genetic engineering of progenitor cells with angiogenic growth factors. Recombinant adeno-associated viral vectors (rAAV) have emerged as a leading gene transfer systems. In contrast to other vector systems in use for genetic engineering of CD34⁺ cells, rAAV-mediated gene expression does not depend on vector integration. This is relevant for application in regenerative medicine of ischemic tissues, where transient transgene expression is likely sufficient to achieve therapeutic benefits. Materials and Methods: We compared three different human AAV serotypes, packaged as pseudotypes by a helper virus-free production method, for their transduction efficiency in human cord blood-derived CD34⁺ cells. We further assessed the impact of vector genome conformation, of α_vβ₅ and α₅β₁ integrin availability and of the transcription-modulating drugs retinoic acid and Trichostatin A on rAAV-mediated human CD34⁺ cell transduction. Results: We provide, for the first time, evidence that hCD34⁺ cells can be reproducibly transduced with high efficiency by self-complementary rAAV2 without inducing cytotoxicity or interfering with their differentiation potential. We further show the involvement of α₅β₁ integrin as a crucial AAV2 internalization receptor and a function for transcription-modulating drugs in enhancing rAAV-mediated transgene expression. Conclusion: This study represents a first step toward translation of a combined cellular/rAAV-based therapy of ischemic disease.