IMPROVEMENT OF RETROVIRAL RETARGETING BY USING AMINO-ACID SPACERS BETWEEN AN ADDITIONAL BINDING DOMAIN AND THE N-TERMINUS OF MOLONEY MURINELEUKEMIA-VIRUS SU

We previously reported a strategy to redirect the retroviral host rang e by expressing single-chain antibodies (S. J. Russell, R. E. Hawkins, and G. Winter, Nucleic Acids Res, 21:1081-1085, 1993) or ligands (F.- L. Cosset, F. J. Morling, Y. Takeuchi, R. A. Weiss, M. K. L. Collins, and S. J. Russell, J. Virol. 69:6314-6322, 1995) at the N terminus of Moloney marine leukemia virus (MoMLV) surface proteins (SU). Although such chimeric envelopes were able to bind the new receptors, the trans duction efficiency of retargeted viruses was generally low, We hypothe sized that conformational rearrangements of envelope glycoproteins wer e not optimally triggered following binding, and to overcome these pos tbinding blocks, we have generated here a set of chimeric MoMLV-derive d envelopes targeted to the Ram-1 phosphate transporter in which we ha ve varied the spacing between the Ram-1-binding domain and the MoMLV S U, All of the recombinant envelopes were correctly expressed on virion s, and all bound efficiently to Ram-1. However, the interdomain spacin g greatly affected the efficiency of gene transfer by retroviral vecto rs that had bound to Ram-1 via their chimeric envelopes, Optimal inter domain spacing allowed a 100-fold-increased viral transduction via Ram -1 compared to our previous results.