Robust, but transient expression of adeno-associated virus-transduced genes during human T lymphopoiesis

Recombinant adeno-associated viruses (rAAV) have been proposed to be gene transfer vehicles for hematopoietic stem cells with advantages over other virus-based systems due to their high titers and relative lack of dependence on cell cycle for target cell integration. We evaluated rAAV vector containing a LacZ reporter gene under the control of a cytomegalovirus (CMV) promoter in the context of primary human CD34+CD2- progenitor cells induced to undergo T-cell differentiation using an in vitro T-lymphopoiesis system. Target cells from either adult bone marrow or umbilical cord blood were efficiently transduced, and 71% to 79% CD2+ cells expressed a LacZ marker gene mRNA and produced LacZ-encoded protein after exposure to rAAV-CMV-LacZ. The impact of transgene expression on the differentiation of T cells was assessed by sequential quantitation of immunophenotypic subsets of virus-exposed cells and no alteration was noted compared with control. The durability of transgene expression was assessed and found to decay by day 35 with kinetics dependent on the multiplicity of infection. In addition, vector DNA was absent from CD4 or CD8 subselected CD3+ cells by DNA-polymerase chain reaction. These data suggest that rAAV vectors may result in robust transgene expression in primitive cells undergoing T-cell lineage commitment without toxicity or alteration in the pattern of T-cell differentiation. However, expression is transient and integration of the transgene unlikely. Recombinant AAV vectors are potentially valuable gene transfer tools for the genetic manipulation of events during T-cell ontogony but their potential in gene therapy strategies for diseases such as acquired immunodeficiency syndrome is limited.