RD114‐Pseudotyped Oncoretroviral Vectors

Limited functional expression of the viral envelope receptor is a recognized barrier to efficient oncoretroviral mediated gene transfer. To circumvent this barrier we evaluated a number of envelope proteins with respect to gene transfer efficiency into primitive human hematopoietic stem cell populations. We observed that oncoretroviral vectors pseudotyped with the envelope protein of feline endogenous virus (RD114) could efficiently transduce human repopulating cells capable of establishing multilineage hematopoiesis in immunodeficient mice after a single exposure to RD114-pseudotyped vector. Comparable rates of gene transfer with amphotropic and GALV-pseudotyped vectors have been reported, but only after multiple exposures to the viral supernatant. Oncoretroviral vectors pseudotyped with the RD114 or the amphotropic envelopes had similar stability in vitro, indicating that the increased efficiency in gene transfer is at the receptor level likely due to increased receptor expression or an increased receptor affinity for the RD114 envelope. We also found that RD114-pseudotype vectors can be efficiently concentrated, thereby removing any adverse effects of the conditioned media to the long-term repopulating potential of the target human hematopoietic stem cell. These studies demonstrate the potential of RD114-pseudotyped vectors for clinical use.