Simultaneous infection with retroviruses pseudotyped with different envelope proteins bypasses viral receptor interference associated with colocalization of gp70 and target cells on fibronectin CH-296

Several factors are thought to limit the efficiency of retroviral transduct ion in clinical gene therapy protocols that target hematopoietic stem cells . For example, the level of expression of the amphotropic receptor Pit-2, a phosphate symporter, appears to be low in human and murine hematopoietic s tem cells, We have previously demonstrated that transduction of hematopoiet ic cells in the presence of the fibronectin (FN) fragment CH-296 is extreme ly efficient (H. Hanenberg, X. L. Xiao, D. Dilloo, It. Hashino, I. Kato, an d D. A. Williams, Nat, Med, 2:876-882, 1996), To examine functionally wheth er the retrovirus receptor is a limiting factor In transduction of hematopo ietic cells, we performed competition experiments in the presence of FN CH- 296 with retrovirus vectors pseudotyped with the same or a different envelo pe protein. We demonstrate in both human erythroleukemia (HEL) cells and pr imary human CD34(+) hematopoietic cells inhibition of efficient infection d ue to receptor interference when two vectors targeting the amphotropic rece ptor are used simultaneously. Receptor interference lasted up to 24 h, No i nterference was demonstrated when vectors targeting the amphotropic recepto r and the gibbon ape leukemia virus (GALV) receptor Pit-1 were used concurr ently. In contrast, simultaneous infection with vectors targeting both Pit- 1 and Pit-2 yielded transduction efficiencies consistently higher than with either vector alone in both HEL cells and human CD34(+) hematopoietic cell s. These data demonstrate that the use of FN CH-296 leads to amphotropic re ceptor saturation in these cells. Simultaneous infection with vectors targe ting both amphotropic and GALV receptors may prove to be of additional bene fit in the design of gene therapy protocols.