Efforts to design an HIV vaccine often focus on eliciting powerful immune responses that thwart the virus before it can infect CD4+ T cells and establish latency. However, increased inflammation, including T cell responses, could counterproductively create more target cells for HIV infection. This inflammatory axis must be considered in HIV vaccine design to avoid the development of vaccines that may backfire by increasing the availability of HIV-suceptible cells.
The development of an efficacious HIV vaccine relies on understanding what constitutes a protective immune response against the virus. Conversely, identifying the characteristics of a poor anti-HIV immune response is equally important. Previous work by Dr. Jai Lingappa (University of Washington) and the Partners in Prevention HSV/HIV Transmission Study and the Partners PrEP Study Teams found that individuals with genetic variations in CD101 were more likely to acquire HIV infection. CD101 is a transmembrane surface protein expressed on T cells, monocytes, and dendritic cells. Although its function on T cells isn’t fully clear, earlier work has suggested CD101 to play a role in T cell receptor (TCR)-dependent T cell activation and increase suppressive ability on regulatory T cells (Treg), a subset of CD4+ T cells that restrain other T and immune cells. Based on the increased HIV acquisition risk associated with CD101 variation, Dr. Laura Richert-Spuhler (Lund lab; Vaccine and Infectious Disease Division), along with colleagues from the University of Washington and the Partners in Prevention HSV/HIV Transmission Study and the Partners PrEP Study Teams, followed up on these findings. The results of their investigation of the role of CD101 on CD4+ T cells were recently published in Cell Reports Medicine.
Given the putative immunoregulatory functions of CD101, the authors hypothesized that missense mutations in CD101 decrease the suppressive ability of Tregs, leading to a heightened baseline T cell inflammatory environment which may increase HIV acquisition risk through. To test this hypothesis, the authors first obtained peripheral blood mononuclear cells (PBMCs) from HIV-negative African individuals with and without confirmed CD101 genetic variations enrolled in the Partners in Prevention HSV/HIV Transmission Study and the Partners PrEP Study. Using flow cytometry, they assessed the immune landscapes in the blood. From this initial screen, they found that variants contained higher proportions of CD8 and Tregs expressing CD101, while antigen presenting cells such as dendritic cells, monocytes, and B cells expressing CD101 were decreased, highlighting an altered immune baseline in individuals with CD101 variations.
To next interrogate the functional capabilities of CD101-variant immune cells, the authors cultured either variant or control PBMC with lysate from Epstein-Barr virus (EBV)—a common virus that most adults in Africa have been infected with—to test the ability of EBV-specific T cells to respond to cognate antigen. They found that in response to stimulation with EBV antigen, CD101 variants had increased frequencies of CD4+ and CD8+ T cells producing pro-inflammatory cytokines interferon-gamma (IFNg) and tumor necrosis factor alpha (TNF-a), especially among CD101+ T cells. This suggests that variants are associated with increased T cell proinflammatory potential at homeostasis.
The responses of conventional T cells are normally controlled by Tregs; therefore, the authors hypothesized that the increased proinflammatory potential observed in the T cells with CD101 variants was due to functional impairment in CD101-variant Tregs. To test this, they separately stimulated either whole PBMCs or PBMCs with Tregs removed through fluorescence-activated cell sorting (FACS) from CD101-variant and non-variant individuals with an EBV lysate. In support of their hypothesis, a loss of Tregs in PBMC cultures with non-variant CD101 greatly increased the proinflammatory cytokines produced by other CD4+ T cells, while a loss of CD101-variant Tregs only slightly increased cytokine production. This discrepancy in cytokine production suggests that variant Tregs exert less suppressive control over conventional CD4+ T cells. Further supporting this finding, RNA-sequencing of CD4+ and CD8+ conventional T cells in CD101-variant versus functional individuals found that variant T cells expressed fewer transcripts for genes associated with antiviral activity, suggesting that HIV acquisition risk could be increased in individuals with CD101 variation due to a two-fold factor: an increase in the activation status of target CD4+ T cells that are also less able to resist viral infection.
“Functional variation in the gene CD101 is associated with an increased risk of HIV acquisition. Here we assessed the immunologic effect of these specific variants including T cell activation status, phenotype, and transcriptional signature. We found that as compared to individuals with no functional CD101 variants, individuals with missense mutations in CD101 demonstrated a heightened pro-inflammatory setpoint, including a reduced capacity of regulatory T cells to appropriately suppress effector responses, and an altered transcriptional profile,” explained Dr. Richert-Spuhler. Together, this work further supports the existing hypothesis that CD101 is a mediator of bystander T cell activation and baseline immune inflammation, which have consequences for HIV acquisition risk. Going forward, the “public health impact of our findings is highlighted by the notable prevalence of CD101 variants among East Africans,” continued Dr. Richert-Spuhler. “Our understanding of the factors that contribute to an individual’s risk of acquiring HIV remains incomplete, but [these findings regarding CD101] could be leveraged in devising therapeutic and preventative strategies,” said Dr. Richert-Spuhler.
Richert-Spuhler LE, Mar CM, Shinde P, Hong T, Greene E, Hou S, Thomas K, Gottardo R, Mugo N, de Bruyn G, Celum C, Baeten JM, Lingappa JR, Lund JM, Partners in Prevention HSV/HIV Transmission Study. CD101 genetic variants modify regulatory and conventional T cell phenotype and functions. Cell Reports Medicine. 2021 Jun 15;2(6):100322. doi: 10.1016/j.xcrm.2021.100322.
UW/Fred Hutch Cancer Consortium member Raphael Gottardo contributed to this work.
This work was supported by the National Institute of Allergy and Infectious Diseases of the National Institutes of Health and by the Bill and Melinda Gates Foundation.