Humanized Mouse Model of HIV-1 Latency with Enrichment of Latent Virus in PD-1 ⁺ and TIGIT ⁺ CD4 T Cells

Abstract

Combination anti-retroviral drug therapy (ART) potently suppresses HIV-1 replication but does not result in virus eradication or a cure. A major contributing factor is the long-term persistence of a reservoir of latently infected cells. To study this reservoir, we established a humanized mouse model of HIV-1 infection and ART suppression based on an oral ART regimen. Similar to humans, HIV-1 levels in the blood of ART-treated animals were frequently suppressed below the limits of detection. However, the limited timeframe of the mouse model and the small volume of available samples makes it a challenging model with which to achieve full viral suppression and to investigate the latent reservoir. We therefore used an ex vivo latency reactivation assay that allows a semiquantitative measure of the latent reservoir that establishes in individual animals, regardless of whether they are treated with ART. Using this assay, we found that latently infected human CD4 T cells can be readily detected in mouse lymphoid tissues and that latent HIV-1 was enriched in populations expressing markers of T cell exhaustion, PD-1 and TIGIT. In addition, we were able to use the ex vivo latency reactivation assay to demonstrate that HIV-specific TALENs can reduce the fraction of reactivatable virus in the latently infected cell population that establishes in vivo, supporting the use of targeted nuclease-based approaches for an HIV-1 cure.

Immune Checkpoints in Viral Infections

“…For example, upregulation of PD-1 and CTLA-4 expression is associated with higher plasma viral loads and lower CD4 + T-cell counts. Enhancements in CTLA-4, TIM-3, LAG-3, and TIGIT expression in HIV-infected CD4 + T-cells are also associated with the integration of HIV-DNA in these cells [46,50,51,53,101,102]. Additionally, the upregulation of CTLA-4 in CD4 + T-cells was reported to cause a high level of CCR5 expression on CD4 + T-cells, thereby supporting a vigorous HIV-1 infection [48], which suggests that CTLA-4 upregulation by HIV infection could increase CD4 + T-cell susceptibility to HIV infection.…”

“…Therapy targeting immune checkpoint proteins shows potential for eliminating HIV reservoirs. Multiple immune checkpoint receptors were found to be expressed on latent HIV-1 reservoir cells and associated with the amount of integrated HIV-DNA [102,124,125]. During ART, the CD4 + T-cells expressing PD-1, TIGIT, and LAG-3 alone or in combination were highly enriched for integrated viral genomes as compared with immune checkpoint receptor-negative CD4 + memory T-cells isolated from HIV-infected individuals [101].…”

“…During ART, the CD4 + T-cells expressing PD-1, TIGIT, and LAG-3 alone or in combination were highly enriched for integrated viral genomes as compared with immune checkpoint receptor-negative CD4 + memory T-cells isolated from HIV-infected individuals [101]. The number of simultaneously co-expressed immune checkpoint receptors on CD4 + T-cells was closely related to the reservoir size and CD4 + T-cell counts [45,102,126]. These findings suggest that immune checkpoints might help to establish latent HIV reservoirs.…”

Tracking HIV Rebound following Latency Reversal Using Barcoded HIV

“… 8 , 9 We and others have shown that the BLT mouse model can be efficiently infected with HIV and forms authentic post-integration latency in resting CD4 + T cells. 9 , 10 , 11 , 12 , 13 Viral loads can be suppressed using clinically relevant ART, and if ART is stopped, then viral replication quickly rebounds, as occurs with infected patients.…”

TIGIT is upregulated by HIV-1 infection and marks a highly functional adaptive and mature subset of natural killer cells

“…Early initiation of antiretroviral treatment (ART) in HIV infected individuals does not return TIGIT/CD115 to normal levels on CD8 + T cells [37]. Additionally, the co-expression of TIGIT with immune checkpoint inhibitor PD-1 marks CD4 + T cells harboring latent virus [45][46][47]. These data suggest that the TIGIT/CD155/CD112 pathway in T cells could contribute to HIV pathogenesis.…”