A Novel Gene Therapy Approach Based on Secreted Antiviral Proteins for the Control of HIV Replication

HIV entry into target cells requires the interaction of the HIV envelope glycoprotein (Env) with a primary receptor (CD4) and a co-receptor (most commonly CCR5 or CXCR4). Protein-based HIV entry inhibitors are highly effective in protecting cells from infection. However, their clinical application is limited because their use requires the frequent injection of highly purified proteins. This study focuses on the development of a gene therapy strategy for the delivery of protein-based HIV entry inhibitors. In Chapter 2 we show that an antibody fragment targeting CCR5 (sscFvPRO140) is secreted from gene-modified human cells and can protect unmodified cells from infection. Chapter 3 describes the secretion and antiviral effect of entry inhibitors targeting HIV Env. A soluble receptor (sCD4), sCD4 covalently linked to a fusion inhibitor (sCD4-FIT45) and sCD4 linked to an antibody fragment targeting the co-receptor-binding site (sCD4-scFv17b) were secreted in significant quantities and protected primary HIV target cells from infection. In Chapter 4 we examine the secretion of sCD4 in a mouse model of HIV infection. sCD4 was present in the blood (~100 ng/ml) of mice engrafted with gene-modified hematopoietic stem cells, reduced viral load over time and protected CD4+ T cells from depletion. Chapter 5 describes the use of gene-modified cell lines for the production of secreted human proteins and their small-scale purification from the culture media. In Chapter 6 we further investigate the antiviral potency of sCD4-FIT45. The bifunctional protein inhibited HIV Env-mediated cell fusion and HIV entry of several primary isolates more potently than VRC01, sCD4, or sCD4-scFv17b. Taken together, we have shown that human cells can be engineered to secrete HIV inhibitors. Furthermore, our results highlight the benefit of combining inhibitors that target receptor-binding and membrane fusion.Ph.D