Zeitschrift für antivirale und antiretrovirale Medikamente
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Gene Therapy Using a Secreted Single Chain Variable Fragment Targeting CCR5 to Inhibit HIV Infection

Alexander Falkenhagen, Masoud Ameli, Sabah Asad, Stanley E Read and Sadhna Joshi

Interaction of R5 HIV with cellular CCR5 is mandatory for entry into host cells. The humanized monoclonal antibody PRO 140 masks cell surface CCR5 and efficiently blocks R5 HIV infection. While weekly administrations of PRO 140 have been shown to drastically reduce the viral load in patients, frequent injections of purified antibodies are neither practical nor cost-effective. Engineering gene-modified cells or tissues to secrete therapeutic proteins at sites of viral replication may advantageously replace continued drug administration. We have designed a gene encoding a secreted single chain variable fragment of PRO 140, sscFvPRO140, and have used a lentiviral vector for its delivery and expression. The sscFvPRO140 was effectively secreted from gene-modified cells, remained stable in culture supernatant at 37°C, and specifically bound to CCR5-expressing cells. Single-round infection assays were performed to assess inhibition of HIV infection. sscFvPRO140 reduced R5 HIV entry in unmodified target cells, although with a lower potency compared to what has been reported for the parent monoclonal antibody. Entry of X4 HIV, which utilizes CXCR4 as a co-receptor, remained unaltered. Furthermore, viral entry was substantially reduced when gene-modified HIV target cells expressing sscFvPRO140 were infected. Gene therapy using intracellularly active molecules, such as ribozymes or Zinc finger nucleases, only confers protection to gene-modified target cells. In contrast, the proposed gene therapy strategy based on secreted anti-HIV proteins has the potential to protect the gene-modified as well as unmodified HIV target cell populations.