Background: COVID-19 has caused millions of deaths and continues to burden individuals and the healthcare system. Antibodies that neutralize SARS-CoV-2 have proven to be the most reliable markers of immune protection, targets for vaccine development, and approaches for anti-viral antibody-based therapies. Measuring neutralizing antibody (NAb) titers at the bedside could inform individualized shared decision-making with patients regarding the potential benefits of repeating vaccines, use of preventative or therapeutic antibody-based therapies, and, where relevant, collection of COVID-19 convalescent plasma (CCP) with greater efficacy, especially as NAb-escape mutations have guided SARS-CoV-2 variant emergence. However, specific and accessible assays to quantify NAb levels in individuals, including the identification of potential antibody donors at the time of donation, remain unavailable. Therefore, there is a need for platforms that can be rapidly adapted to quantify serum antibody responses with known or expected correlates of protection. Methods: In this report, we apply a novel semi-quantitative method to an established antibody lateral flow assay (sqLFA) and analyze its ability to detect the presence of functional NAbs in the serum of COVID-19-recovered individuals early in the pandemic. Results: We found that the sqLFA has a strong positive correlation with the gold-standard microneutralization assay (specificity 80% and sensitivity 90% at a microneutralization cutoff of 1:40). Conclusions: Taken together, the sqLFA provides a novel point-of-care-based platform for rapid readout of NAb-based immune protection to SARS-CoV-2.

HIV-1 persists in CD4⁺ T cells and brain microglia through host factors that enforce viral latency, yet the mechanisms that stabilize key transcriptional regulators remain incompletely understood. Here, we identify the YEATS domain-containing protein ENL and its associated deubiquitinase USP7 as a host complex that maintains HIV-1 latency. USP7 stabilizes BRD4 by deubiquitination, suppressing HIV transcription and sustaining viral quiescence. Disruption of the ENL-USP7 complex using selective PROTACs reactivates latent HIV in cell line models, as well as in resting CD4⁺ T cells and microglia isolated from people with HIV on antiretroviral therapy. These findings uncover a critical ENL-USP7-BRD4 axis that enforces HIV-1 latency and highlight USP7 as a potential target for latency-reversing strategies. Highlights:ENL, a YEATS domain-containing crotonylation reader, acts as a suppressor rather than an activator of HIV-1 transcription.ENL recruits USP7 to stabilize BRD4 and enforce viral latency.Disruption of the ENL-USP7-BRD4 axis reactivates latent HIV in T cells and microglia.Targeting USP7 or ENL reveals a therapeutic vulnerability in HIV reservoirs.

The estrogen receptor (ER) is hypothesized to directly influence HIV transcription and latency but is also critical for immune signaling. However, the mechanisms of action of the ER in immune cells in the context of HIV are limited, and relevant to HIV cure strategies, the influence of latency reversal agents (LRAs) on the ER pathway are unknown. We evaluated (a) the effect of estrogen (E2) on the nuclear translocation of ERα in CD4+ T cells; (b) the ability of Fulvestrant, a selective estrogen receptor degrader (SERD), and ARV-471, a potent, PROteolysis TArgeting Chimera (PROTAC) selective ERα degrader to modulate ERα; and c) the effect of different classes of LRAs on ERα signaling. In contrast to what has been demonstrated in oncology, E2 did not induce ERα nuclear translocation in CD4+ T cells. Similarly, neither Fulvestrant nor ARV-471 induced degradation of ERα in CD4+ T cells. LRAs significantly downregulated ERα gene and protein expression in both PBMCs and CD4+ T cells. Collectively, our results suggest that estrogen influences on HIV transcription are not likely a consequence of canonical nuclear ERα mechanisms. The consequences of LRA downregulation of ERα, a protein important for immune signaling, warrant further investigation.

BACKGROUND Approaches to achieving antiretroviral therapy–free (ART-free) remission from HIV-1 must consider that people over 50 years now comprise the majority of people with HIV (PWH) on ART in various regions, including the United States. METHODS We report a double-blind, randomized trial in which PWH on ART, aged 21–60 years, received modified vaccinia Ankara–vectored (MVA-vectored) vaccines, MVA.tHIVconsv3 (M3) and MVA.tHIVconsv4 (M4), either alone or in combination ( n = 7/group), or saline placebo ( n = 3). M3 and M4 contain complementary HIVconsvX immunogens that each span the same regions in HIV-1 Gag and Pol but differ by approximately 8% at the amino acid level. RESULTS M3, M4, and M3M4 regimens were well tolerated and all significantly increased both the frequency (peak median increase ~3-fold) and breadth of the HIVconsvX-specific T cell response while redirecting T cells to target conserved regions in HIV-1 for up to 10 weeks after vaccination. We also demonstrated that vaccination increased frequencies of T cells targeting participant autologous HIV-1 sequences. Vaccination mostly expanded preexisting HIV-1–specific T cells and did not impact CD4 + T cell activation, low-level viremia, or integrated HIV-1 provirus. Linear regression indicated that age was independently and negatively associated with the change in T cell frequency at 1, 2, and 10 weeks after vaccination (~1.41-fold decrease per 10 years older). After adjusting for age, years on ART was positively associated with HIVconsvX-specific T cell frequencies at 1 and 2 weeks following vaccination. CONCLUSION In PWH receiving ART, MVA.HIVconsvX vaccines significantly increased T cells targeting conserved regions of HIV-1. Novel strategies may be required to enhance anti–HIV-1 immunity in older adults. TRIAL REGISTRATION ClinicalTrials.gov NCT03844386 FUNDING NIH National Institute of Allergy and Infectious Diseases (NIAID) grants U01AI131310, HHSN272201100021I/HHSN27200037 (subcontract OX-14007.004.0037-212), UM1TR004406, P30AI050410, and P30CA016086; International AIDS Vaccine Initiative; European and Developing Countries Clinical Trials Partnership SRIA2015-1066; European Commission’s Horizon 2020 Research and Innovation Programme 681137.

Abstract Activation of the non-canonical NF-κB pathway via RelB/p52 signaling by SMAC mimetics such as AZD5582 is a promising strategy to induce HIV expression from latency, but the chromatin mechanisms linking RelB/p52 to proviral regulation remain poorly defined. Here, we combine RelB BioID proteomics, targeted HIV-CRISPR screening, and pharmacologic validation to identify ncNF-κB-associated regulators of HIV expression. RelB BioID revealed an extensive interaction network of chromatin and transcriptional regulators in basal and AZD5582-activated states. Basally associated RelB proteins included NSD2, SWI/SNF components, UHRF1, and DNMT1, while AZD5582-enriched proteins included p300, USP7, LSD1/KDM1A, NuRD components, SIN3A, and HBO1/KAT7. Functional screening using a custom guide RNA library targeting all BioID-identified factors identified regulators that promote HIV reactivation, including HBO1/KAT7, NSD2, and SIN3A, and regulators that restrict HIV expression, including p300, CHD4, and USP7. Because KAT7/HBO1 and p300 encode acetyltransferases with opposing screen phenotypes, we tested whether their catalytic activities contribute to HIV transcriptional regulation and found that, consistent with the CRISPR screen, KAT7/HBO1 inhibition reduced AZD5582-induced reactivation, whereas p300 inhibition enhanced it. Together, these data define a resource linking the RelB-associated chromatin landscape to HIV latency and reactivation.

OBJECTIVE:Despite effective antiretroviral therapy (ART), people with HIV (PWH) continue to experience elevated morbidity, potentially driven by persistent immune dysregulation. This study aimed to define transcriptomic heterogeneity in peripheral CD4+ T cells and identify immune signatures associated with clinical stratification in ART-treated PWH. DESIGN:We analyzed transcriptomic and immunologic (plasma cytokine) data from a well-characterized cohort of ART-suppressed PWH to identify biologically meaningful subgroups. METHODS:Bulk RNA sequencing was performed on peripheral CD4+ T cells from 154 ART-treated PWH. Plasma levels of immune mediators were also quantified. We applied Pairwise Controlled Manifold Approximation (PaCMAP), a novel dimensionality reduction technique, to identify transcriptomic clusters and assessed their associations with clinical and immunological parameters, including CD4:CD8 ratio and cell-associated HIV DNA/RNA. RESULTS:PaCMAP identified three distinct transcriptomic clusters among PWH. These clusters were enriched for differential expression of genes regulated by NF-κB, suggesting a role for chronic immune activation and inflammation. While clustering was not associated with HIV reservoir size, there was a modest association with CD4:CD8 ratio, a key marker of immune recovery. Additionally, plasma levels of IL-1β, TNF-α, and G-CSF differed across clusters, supporting a link between plasma cytokines and CD4+ T cell transcriptomic diversity. CONCLUSIONS:Our findings define transcriptomic subgroups in ART-treated PWH that are characterized by NF-κB-driven gene expression and distinct inflammatory cytokine profiles. These immune signatures may serve as biomarkers for immunological stratification and provide insight into persistent immune dysfunction despite viral suppression.

Cannabis use is prevalent among individuals living with HIV in the United States, but the impact of cannabis exposure on the reservoir of latently infected cells that persists during antiretroviral therapy (ART) remains unclear. To address this gap, we analyzed the effect of Δ-9-tetrahydrocannabinol (THC) on primary CD4 T cells that were latently infected with HIV. We found that THC did not have a strong effect on baseline or latency reversing agent (LRA) stimulated HIV expression, or on expression of an activation marker (CD38). However, using an integrated multiomic single-cell analysis of genome-wide chromatin accessibility and gene expression, we observed altered expression of several hundred genes in HIV infected CD4 T cells after THC exposure, including transcriptional downregulation of genes involved in protein translation and antiviral pathways, indicating that THC suppresses innate immune activation in infected cells. Additionally, chromatin accessibility analysis demonstrated upregulated chromatin binding activity for the transcriptional regulator CTCF, and reduced activity for members of the ETS transcription factor family in infected cells after THC exposure. These findings provide insights into the mechanisms by which cannabis use could influence the persistence of HIV within cellular reservoirs and the molecular phenotype of latently infected cells. Further elucidation of the underlying mechanisms involved in THC-mediated changes to HIV infected cells, will lead to an improved understanding of the impact of cannabis use on the HIV reservoir.

The role of epigenetic regulation in HIV latency remains incompletely understood. We show that histone deacetylase 3 (HDAC3) inhibits trans-activator of transcription (Tat)-mediated HIV transcription through histone decrotonylation (HDCR), independent of deacetylase activity. Chemical biology approaches identified selective HDCR inhibitors (HDCRis) that reverse HIV latency with minimal impact on other histone acylations. Although HDAC2, HDAC3, and HDAC8 exhibit HDCR activity, genetic and chemical studies reveal that the HDCRi citarinostat is selective for HDAC3 and HDAC8. Molecular docking suggests that HDCRi binds outside the zinc-binding pocket, distinct from the classical HDAC inhibitor vorinostat (SAHA, suberoylanilide hydroxamic acid). Key residues (arginine-265, arginine-301, glutamine-113, and aspartic acid-57) are essential for HDCR selectivity, as their mutation abolishes HDCR activity and increases histone crotonylation without altering other acylation marks. Citarinostat increases histone crotonylation at the HIV long terminal repeat, robustly activating HIV transcription in cell lines, primary CD4+ T cells, and brain microglia from simian immunodeficiency virus-infected nonhuman primates and participants enrolled in the Last Gift rapid research autopsy cohort, highlighting HDCR as a promising therapeutic target for HIV latency.

Entry of HIV into latency is determined by a combination of factors, including fluctuations in the viral Tat protein, as well as the transcriptomic phenotype of the host cell. Determining the impact of the proviral integration site on viral expression has been challenging due to difficulty in measuring integration site and viral expression from the same cell. To investigate the influence of the HIV integration site on HIV expression, we analyzed a combined scRNAseq/scATACseq dataset from 117,610 HIV infected primary CD4 T cells. We used the scATACseq data to recover HIV integration site information from 1530 cells, and correlated this information with viral RNA reads in the scRNAseq data. We observed that, overall, HIV expression did not differ depending on the genomic features of viral integration, such as genic vs non genic, intron vs exon and forward versus reverse orientation. Furthermore, we found that there was no significant difference in HIV expression across 15 distinct chromatin compartments. Additionally, analysis of expression for host genes that were the target of proviral integration revealed strong upregulation of expression of the targeted host gene in ∼5% of the infected cells. This insertional activation occurred almost exclusively when HIV was integrated in the same orientation as the host cell gene and occurred as a result of integration within diverse positions across a gene. These findings suggest that HIV expression is relatively robust to the genomic context of the HIV integration site, and that HIV can strongly upregulate expression of integration site genes during infection.

Abstract Antiretroviral therapy (ART) effectively suppresses systemic HIV replication but does not eradicate viral reservoirs in the brain, where their identity and contribution to neurological injury remain poorly defined. Using bulk, single-cell, and single-nucleus transcriptomics of postmortem human brain tissue, we identify an activated SPP1⁺ microglial population that expands 5.8-fold during ART and serves as the primary central nervous system (CNS) reservoir, preferentially harboring HIV transcripts. These reservoir microglia adopt a distinct, immune-evasive reprogramming state marked by chronic type I interferon signaling and inflammasome activation, which we recapitulate in primary human microglia via prolonged interferon-β exposure. We show that viral transcription in ART-suppressed brains is dominated by nef, which may sustain the viral reservoir by disrupting host HLA-A and HLA-E presentation machinery. This persistent, immune-evasive state is associated with TREM2-C1QC complement-mediated synaptic pruning and severe DNA damage response dysregulation, culminating in a profound loss of VGLUT1⁺ and GAD67⁺ glutamatergic neurons that persists despite viral suppression. Our findings establish SPP1⁺ microglia as an active, pathogenic CNS reservoir, identifying the SPP1, MHC-I, and complement pathways as therapeutic targets to eliminate viral persistence and reverse HIV-associated neurocognitive dysfunction.

Antiretroviral therapy suppresses HIV replication but fails to eliminate the virus due to the persistence of a transcriptionally silent reservoir, which remains the primary barrier to a cure. HIV latency is maintained through chromatin-mediated repression, making epigenetic regulators attractive therapeutic targets. To identify new modulators of latency, we screened a focused library of 84 chromatin-targeting small molecules. This screen identified BAY-299, a bromodomain inhibitor selective for TAF1 and BRD1, as a latency-modulating compound. BAY-299 reactivated HIV expression and enhanced the efficacy of established latency-reversing agents, including vorinostat, prostratin, and iBET-151, in cell line models. CRISPR/Cas9-mediated knockout experiments demonstrated that TAF1, but not BRD1, is essential for maintaining HIV latency and that TAF1 depletion selectively increases HIV transcription with minimal effects on host gene expression. Dual knockout of TAF1 and Tat revealed that reactivation of HIV in the absence of TAF1 is partially Tat-dependent. Cleavage Under Targets and Release Using Nuclease analysis further showed that TAF1 depletion increased histone acetylation at the viral promoter and across the HIV gene body, suggesting a chromatin-based mechanism. These findings identify TAF1 as a novel regulator of HIV latency and demonstrate the utility of targeted chemical screening to uncover therapeutic vulnerabilities within the latent reservoir. IMPORTANCE:HIV remains incurable due to the persistence of a transcriptionally silent reservoir in infected cells that is not eliminated by antiretroviral therapy. This transcriptionally silent state, known as latency, is controlled by host cell factors that regulate access to the viral genome. In this study, we identified the host protein TAF1 as a key regulator that maintains HIV in a latent state in cell line models of latency. Using both genetic and chemical approaches, we demonstrate that reducing TAF1 levels selectively increases HIV gene expression without broadly disrupting host gene transcription. These findings highlight a previously unrecognized mechanism of HIV latency control and identify TAF1 as a potential therapeutic target for HIV. Understanding how host chromatin regulators contribute to latency is essential for developing strategies that aim to eliminate the persistent HIV reservoir.

ABSTRACT HIV cure strategies that aim to induce viral reactivation for immune clearance leverage latency reversal agents to modulate host pathways which directly or indirectly facilitate viral reactivation. Inhibition of bromo and extra-terminal domain (BET) family member BRD4 reverses HIV latency, but enthusiasm for the use of BET inhibitors in HIV cure studies is tempered by concerns over inhibition of other BET family members and dose-limiting toxicities in oncology trials. Here, we evaluated the potential for bivalent chemical degraders targeted to the BET family as alternative latency reversal agents. We observed that despite highly potent and selective BRD4 degradation in primary CD4+ T-cells from ART-suppressed donors, BRD4 degraders failed to induce latency reversal as compared to BET inhibitors. Furthermore, BRD4 degraders failed to mimic previously observed synergistic HIV reactivation between BET inhibitors and an activator of the non-canonical NF-κB pathway. Mechanistic investigation of this discrepancy revealed that latency reversal by BET inhibitors is not related to the abatement of competition between Tat and BRD4 for P-TEFb, but rather the ability of BRD4 to disrupt 7SK and increase the levels of free P-TEFb. This activity is dependent on the shift of BRD4 from chromatin-bound to soluble and retargeting of P-TEFb to chromatin, which is dependent on intact BRD4 but independent of the bromodomains. IMPORTANCE Multiple factors and pathways contribute to the maintenance of HIV latency, including bromo and extra-terminal domain (BET) family member BRD4. While small molecule inhibitors of the BET family result in latency reversal, enthusiasm for the use of BET inhibitors in HIV cure is limited due to toxicity concerns. We examined BRD4-selective chemical degraders as alternatives to BET inhibitors but found two robust degraders failed to induce latency reversal. We observed key differences in the ability of BET inhibitors versus BET degraders to disrupt P-TEFb, a key cellular activator of transcription and a complex required for HIV reactivation. We present a new model for the role of BRD4 in HIV latency and propose that BRD4 be reconsidered as an activator rather than a repressor of HIV transcription in the context of HIV cure strategies.

To better understand the molecular mechanism that drives neuroinflammation, we analyzed the protein profiles of 27 brains from HIV with HIV (PWH) on antiretroviral therapy (ART), including various stages of HIV-associated neurocognitive disorders (HAND), and compared them to 9 HAND-negative controls. We found that most of the proteins that were increased-about 66.7%-were involved in immune response pathways. Of these, 23.3% were specifically related to type I interferon (IFN-I) signaling, which remains active in the brain through both HIV-related and unrelated mechanisms. Using single-cell RNA sequencing (scRNA-seq) on brain tissues collected during rapid autopsies from participants in the Last Gift cohort, we found that IFN-I signaling was especially strong in astrocytes, microglia (MG), and endothelial cells. In a mini-brain organoid model of acute HIV infection, IFN-I signaling was also highly active in astrocytes but less so in MG. Interestingly, IFN-I activation can happen without HIV being present-expression of human endogenous retrovirus-W1 (HERV-W1) Env can directly trigger this response in astrocytes, and it continues in glial cells even with effective ART. Together, our findings point to persistent IFN-I activation in glial and endothelial cells in the brain, which may contribute to neuroinflammation and cognitive disorders in PWH on ART.

Human Immunodeficiency virus (HIV) infection is regulated by a wide array of host cell factors that combine to influence viral transcription and latency. To understand the complex relationship between the host cell and HIV-1 latency, we performed a lentiviral CRISPR screen that targeted a set of host cell genes whose expression or activity correlates with HIV-1 expression. We further investigated one of the identified factors - the transcription factor ETS1, and found that it is required for maintenance of HIV-1 latency in both latently infected cell lines and in a primary CD4 T cell latency model. Interestingly, ETS1 played divergent roles in actively infected and latently infected CD4 T cells, with knockout of ETS1 leading to reduced HIV-1 expression in actively infected cells, but increased HIV-1 expression in latently infected cells, indicating that ETS1 can play both a positive and negative role in HIV-1 expression. CRISPR/Cas9 knockout of ETS1 in CD4 T cells from ART-suppressed people with HIV-1 (PWH) confirmed that ETS1 maintains transcriptional repression of the clinical HIV-1 reservoir. Transcriptomic profiling of ETS1-depleted cells from PWH identified a set of host cell pathways involved in viral transcription that are controlled by ETS1 in resting CD4 T cells. In particular, we observed that ETS1 knockout increased expression of the long non-coding RNA MALAT1 that has been previously identified as a positive regulator of HIV-1 expression. Furthermore, the impact of ETS1 depletion on HIV-1 expression in latently infected cells was partially dependent on MALAT1. Additionally, we demonstrate that ETS1 knockout resulted in enhanced abundance of activating modifications (H3K9Ac, H3K27Ac, H3K4me3) on histones located at the HIV-1 long terminal repeat (LTR), indicating that ETS1 regulates the activity of chromatin-targeting complexes at the HIV-1 LTR. Overall, these data demonstrate that ETS1 is an important regulator of HIV-1 latency that impacts HIV-1 expression through repressing MALAT1 expression and by regulating modification of proviral histones.

Antiretroviral therapy (ART) has dramatically improved the clinical prognosis for people with HIV and prevents HIV transmission. However, ART does not cure HIV infection because of a persistent, latent viral reservoir in long-lived cells such as central memory CD4+ T (TCM) cells. Eliminating or preventing reservoir formation will require a better understanding of HIV-1 latency establishment. We and others have recently shown that host cell factors such as histone deacetylases (HDACs) are critical cellular factors that allow HIV-1 entry into latency. Whether HDACs interact with specific viral factors to regulate latency establishment, however, is unknown. To examine the role of individual HIV-1 accessory proteins, we constructed a panel of HIV-1 reporter strains, each expressing a single HIV-1 accessory protein, and examined them in a primary CD4+ T-cell latency model. Interestingly, we found that the HDAC inhibitor (HDACi) vorinostat potently enhances the effect of the HIV-1 protein Vpr in promoting HIV expression in infected cells, suggesting that Vpr possesses a cryptic transcription-promoting activity that is restricted by HDACs. This activity was dependent on a p300-binding domain of Vpr and inhibited by a selective p300 histone acetyltransferase inhibitor. Interestingly, Vpr expression also resulted in a significant increase in the proportion of infected cells with a central memory (TCM) phenotype. Furthermore, we observed that TCM cells were more resistant to Vpr-induced apoptosis/cell death than other CD4+ T-cell subtypes, indicating that Vpr expression during reservoir formation selects for latent proviruses in TCM cells. Overall, these findings suggest that Vpr plays an important role in shaping the latent reservoir and that HIV-1 latency results, in part, from an HDAC-mediated restriction of Vpr's transcription-promoting activity. Understanding how viral factors shape the latent reservoir and how host and viral factors interact during HIV-1 latency establishment in CD4+ T cells will aid in the development of new latency-targeting therapies.

The primary obstacle to HIV-1 cure is the persistence of a long-lived latent reservoir, best characterized in memory CD4+ T cells. New research supports latency prevention as a therapeutic strategy. However, this approach will require a better understanding of how HIV-1 establishes latency. We recently showed using a primary CD4+ T-cell model that histone deacetylases (HDACs) are critical for latency entry. The role of viral factors, however, is unknown. We sought to determine how the cytotoxic HIV-1 protein Vpr, both alone and in combination with the HDAC inhibitor vorinostat (VOR), regulates HIV-1 latency establishment. In a primary CD4+ T-cell model, we observed a p300-dependent synergy between Vpr and VOR in maintaining viral gene expression. Using a selective p300 histone acetyltransferase (HAT) inhibitor, we observed that p300 HAT activity may be required. Interestingly, Vpr expression also resulted in an increased relative frequency of central memory T cells (TCM), the cell type in which the latent HIV-1 reservoir is enriched. Our preliminary results provide evidence that the increased proportion of TCM-like cells may be due to relatively lower levels of Vpr-induced apoptosis in these cells compared with other compartments. Vpr may therefore play an important role in shaping the latent reservoir. An improved understanding of how both viral and host factors affect latent reservoir formation will aid in the development of new latent HIV-1 reservoir-targeting therapies. Supported by NIH CARE Collaboratory 1UM1AI126619 and NIH 1R01AI143381-01A1 Viral Immunology (VIR)

Human gastrointestinal (GI) tissues are a major site of HIV-1 viral persistence, but the nature of the GI reservoir remains poorly described. To characterize the GI HIV reservoir, we profiled cells from GI tissue and matched PBMCs from 10 people with HIV on antiretroviral therapy using single-cell RNA sequencing. We identified distinct compartment-specific patterns of gene expression, highlighting key differences between blood and colon CD4+ T cell populations. vRNA+ cells from both blood and GI tissue were heterogeneous and found in multiple subtypes of CD4+ T cells, although vRNA+ cells were particularly enriched in cells with Th17 or Treg17 phenotypes. Transcriptomic comparison of HIV vRNA+ and vRNA- T cells revealed 116 differentially expressed genes that were associated with HIV infection, including ZBED2, MAF, and IL17F. These data provide what we believe to be new information regarding the GI-resident HIV reservoir and suggest that compartment-specific patterns of gene expression are associated with HIV infection.

HIV persists during therapy due the existence of a latently infected reservoir in which viral gene expression is silenced. This reservoir thus represents the primary barrier to a cure for HIV. To eliminate latently infected cells from people with HIV (PWH) on antiretroviral therapy (ART), small molecules that reverse HIV latency (Latency reversing agents – LRAs) have been previously developed and tested, but these lack specificity for HIV and are typically inefficient at promoting broad reservoir reactivation. As such, more potent and selective tools for latency reversal are needed. Recently, delivery of mRNA encoding the viral protein Tat, which promotes transcriptional elongation, has attracted interest as a possible HIV-specific approach to inducing latency reversal. This review will cover the evidence that Tat plays a key role in both establishment of HIV latency and latency reversal, as well as recent developments in which Tat mRNA delivery has been used to enhance latency reversal approaches. Delivery of Tat to infected cells represents a promising avenue to bypass the limitations of small molecule LRAs and achieve broad reactivation of the clinical reservoir.