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Background: HIV-1 specific cytotoxic T lymphocytes are crucial for the elimination of HIV infected cells. We have previously demonstrated using humanized mice that hematopoietic stem cells (HSCs) modified with a protective CD4 chimeric antigen receptor (CD4CAR) successfully differentiated into CD4CAR expressing T cells that significantly suppressed HIV replication. These results demonstrated the feasibility of engineering HIV-specific T cell immunity with a HSC based approach.
Methods: We tested the safety and feasibility of engineering T cell immunity via HSC in a non-human primate (NHP) model of SHIV infection. We utilized CD4CAR vectors that also carry an anti-HIV protective gene (C46) that would inhibit infection. 2 pigtailed macaques (Macaca nemestrina) were transplanted with C46CD4CAR modified autologous HSC and 2 were transplanted with HSC modified with control vector C46CD4CARdeltaZeta that lacks the signaling Zeta chain. After hematopoietic recovery, the animals were challenged with SHIV and went through combined anti-retroviral drug (cART) treatment and withdrawal. Animals were monitored for viral load, CAR cell detection, and immune function for over a year.
Results: We determined that engraftment of pigtailed macaques with C46CD4CAR-modified HSCs was safe and the animals had normal transplant recovery. We observed long-term engraftment and stable production of C46CD4CAR expressing cells without any significant toxicities and found that C46CD4CAR modified HSCs could differentiate into multiple hematopoietic lineages. Following challenge of the animals with SHIV, we observed significant expansion of C46CD4CAR expressing cells after infection and wide distribution of CAR expressing cells in multiple lymphoid tissues. Importantly, we found lower viral loads in lymphoid tissues in C46CD4CAR containing animals than in control animals, suggesting viral suppression by C46CD4CAR expressing cells.
Conclusions: This study in NHPs demonstrates the safety and feasibility of a HSC based therapy utilizing a HIV-specific chimeric antigen receptor for treating chronic HIV infection. These results set the stage for future investigational new drug (IND) development to eradicate viral infection and provide more effective immune surveillance of HIV.