# Gut Cytotoxic CD4 T cells in HIV-1 Pathogenesis

> **NIH NIH R01** · UNIVERSITY OF COLORADO DENVER · 2022 · $445,694

## Abstract

ABSTRACT
HIV-1-associated inflammation and chronic immune activation persist despite suppressive antiretroviral
therapy and are strongly linked to the development of comorbidities and increased mortality. The
gastrointestinal (GI) tract is likely a major source of chronic inflammation, as early HIV-1 replication and CD4 T
cell depletion in the gut results in mucosal inflammation and barrier dysfunction, leading to the translocation of
enteric microbes/microbial products into the lamina propria and the systemic circulation. To gain insights into
the molecular processes that drive gut-focused chronic immune activation, we profiled the transcriptome of gut
CD4+CD8α- T cells exposed to gram-negative enteric bacteria and then infected with HIV-1 ex vivo. Multiple
granzyme genes were upregulated following microbe exposure that was further enhanced with HIV-1 infection,
suggesting the synergistic induction of CD4 cytotoxic T lymphocyte (CTL) activity. In pilot ex vivo studies, the
human gut CD4 CTL phenotype was associated with granzyme (GZ) B expression, TCR signaling, Th1/17
polyfunctionality, reactivity to commensal bacteria and subsets expressing GZA, perforin and/or CD107a. The
CD4 CTL phenotype was expressed in CD4 T cells from the gut to a much greater extent than from peripheral
blood and lymphoid tissue. Importantly, HIV-1 replicated to a greater extent in gut CD4 CTLs ex vivo. Here, we
hypothesize that gut CD4 CTLs are uniquely primed to respond to enteric microbes, are highly
susceptible to HIV-1 mediated killing, and play critical roles in mucosal HIV-1 pathogenesis via
cytolytic and pro-inflammatory mechanisms. To gain insights on the role of gut CD4 CTLs in HIV-1
pathogenesis, we propose 3 aims. In Aim 1, we will determine if microbiome species and ligands induce gut
CD4 CTLs in an MHC-II-dependent manner, obtain insights into gut CD4 CTL origin and function by single-cell
transcriptomics, and investigate the stability and fate of these cells ex vivo. In Aim 2, we will determine how
HIV-1 infection further augments GZB production in gut CD4 T cells and using our ex vivo lamina propria
aggregate culture (LPAC) model, determine if gut CD4 CTLs exacerbate direct and bystander HIV-1-mediated
CD4 T cell death via cytolytic mechanisms. In Aim 3, we will evaluate the triggers for GZ secretion and dissect
the non-cytolytic, pro-inflammatory properties of GZs secreted by microbe-exposed gut CD4 T cells ex vivo.
Importantly, we will explore the in vivo relationship between CD4 CTL frequencies and markers of mucosal and
systemic inflammation in archived plasma and gut biopsies from well-characterized cohorts of both untreated
and treated persons with chronic HIV-1 infection. Altogether, these studies should provide critical
information on this striking gut immune cell subpopulation and its contribution to mucosal
inflammation and disease.

## Key facts

- **NIH application ID:** 10318604
- **Project number:** 5R01AI145428-03
- **Recipient organization:** UNIVERSITY OF COLORADO DENVER
- **Principal Investigator:** Mario Luis Santiago
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $445,694
- **Award type:** 5
- **Project period:** 2020-01-07 → 2024-12-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10318604

## Citation

> US National Institutes of Health, RePORTER application 10318604, Gut Cytotoxic CD4 T cells in HIV-1 Pathogenesis (5R01AI145428-03). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10318604. Licensed CC0.

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