Pseudotyped recombinant adeno-associated viral vectors mediate efficient gene transfer into primary human CD34+ peripheral blood progenitor cells

Background and aims. Because of their pluripotency, human CD34(+) peripheral blood progenitor cells (PBPC) are targets of interest for the treatment of many acquired and inherited disorders using gene therapeutic approaches. Unfortunately, most current vector systems lack either sufficient transduction efficiency or an appropriate safety profile. Standard single-stranded recombinant adeno-associated virus 2 (AAV2)-based vectors offer an advantageous safety profile, yet lack the required efficiency in human PBPC. Methods. A panel of pseudotyped AAV vectors (designated AAV2/x, containing the vector genome of serotype 2 and capsid of serotype x, AAV2/1-AAV2/6) was screened on primary human granulocyte-colony-stimulating factor (G-C SF)-mobilized CD34(+) PBPC to determine their gene transfer efficacy. Additionally, double-stranded self-complementary AAV (dsAAV) were used to determine possible second-strand synthesis limitations. Results. AAV2/6 vectors proved to be the most efficient [12.8% (1.8-25.4%) transgene-expressing PBPC after a single transduction], being significantly more efficient (all P<0.005) than the other vectors [AAV2/2, 2.0% (0.2-7.3%); AAV2/1, 1.3% (0.1-2.9%); others, <1% transgene-expressing PBPC]. In addition, the relevance of the single-to-double-strand conversion block in transduction of human PBPC could be shown using pseudotyped dsAAV vectors: for dsAAV2/2 [9.3% (8.3-20.3%); P<0.001] and dsAAV2/6 [37.7% (23.6-61.0%); P<0.001) significantly more PBPC expressed the transgene compared with their single-stranded counterparts;, for dsAAV2/1, no significant increase could be observed. Conclusions. We have shown that clinically relevant transduction efficiency levels using AAV-based vectors in human CD34(+) PBPC are feasible, thereby offering an efficient alternative vector system for gene transfer into this important target cell population.