767. A Novel Humanized Mouse Model for Testing Anti-HIV T-Cell Gene Therapy Strategies

Abstract

Despite major advances in the therapeutic treatment of individuals infected with HIV using anti-retroviral therapies (ART), patients are not cured. Deviation from standard drug administration can lead to rapid rebound of viremia, and the emergence of drug-resistant variants. New approaches for treatment of HIV include a range of techniques from gene therapies to vaccine studies. Many of these methods utilize animal models to test the efficacy of treatment prior to advancing to clinical settings. Humanized mouse models have been invaluable for such strategies. Immune compromised mice can engraft with human hematopoietic stem cells (HSC), give rise to a functional human immune system, and maintain an HIV infection. A novel concept for treatment involves engineering a specific immune response against infected cells using chimeric antigen receptors (CAR) to viral epitopes on infected cells. These CAR modified T cells have been used in the preliminary treatment of some cancers, where modified cells lead to the elimination of target cancer cells. A similar approach is being investigated now for HIV. While progress has been made on creating engineered receptors, there has not been a good pre-clinical animal model to test them in. We address this problem by building on the well characterized NOD-scid-gamma (NSG) animal model of HIV treatment, and adapted it to test the functionality of T cell-based immunotherapies. To better model the clinical setting, we use adult apheresis HSCs from healthy mobilized donors as the source for engraftment instead of cord blood or fetal tissue. Neonatal NSG mice injected with these harvested HSCs give rise to over 90% CD3 T-cells in the human fraction circulating in the blood unlike other models which don't readily develop T-cells. Instead of using additional sources for T-cell collection, we harvested CD3 cells directly from the mice, cultured, expanded, and transduced them using GFP expressing lentiviral vectors, and re-infused them back into the mice. The modified CD3 cells were detected in the peripheral blood with frequencies reaching 50% of total CD3 cells without the symptoms of graft-vs-host disease. These cells persisted for over two months and were also found in all lymphoid tissues analyzed at necropsy. To assess safety of vector modified cells, we utilized integration site (IS) analysis to measure the clonal repertoire of injected cells. While over 500 unique clones were detected, we did not observe indications of clonal outgrowth in animals over the course of the experiment. Mice receiving the engrafted HSCs and transduced CD3 cells were capable of sustaining HIV infection with titers between 105-107 viral copies/mL and demonstrated significant CD4 depletion in both blood and lymphoid tissues. With the establishment of this clinically relevant model for testing the effectiveness of T-cell based therapies to treat HIV, we are beginning to test anti-HIV engineered cells. By building upon the existing animal models and combining T-cell gene therapy approaches with IS to monitor for vector safety, we have established a novel method for testing new anti-HIV cure therapies.