Persistence of SIV in the brain of SIV-infected Chinese rhesus macaques with or without antiretroviral therapy

Regional Analysis of Intact and Defective HIV Proviruses in the Brain of Viremic and Virally Suppressed People with HIV

Here, we provide the first regional analysis of intact and defective HIV reservoirs within the brain. Brain tissue from both viremic and virally suppressed people with HIV (PWH) harbored HIV pol DNA in all regions tested, with lower levels present in basal ganglia and cerebellum relative to frontal white matter. Intact proviruses were primarily found in the frontal white matter but also detected in other brain regions of PWH, demonstrating frontal white matter as a major brain reservoir of intact, potentially replication competent HIV DNA that persists despite antiretroviral therapy. ANN NEUROL 2023;94:798-802.

Advancing the preclinical study of comorbid neuroHIV and substance use disorders: Current perspectives and future directions

Human immunodeficiency virus (HIV) remains a persistent public health concern throughout the world. Substance use disorders (SUDs) are a common comorbidity that can worsen treatment outcomes for people living with HIV. The relationship between HIV infection and SUD outcomes is likely bidirectional, making clear interrogation of neurobehavioral outcomes challenging in clinical populations. Importantly, the mechanisms through which HIV and addictive drugs disrupt homeostatic immune and CNS function appear to be highly overlapping and synergistic within HIV-susceptible reward and motivation circuitry in the central nervous system. Decades of animal research have revealed invaluable insights into mechanisms underlying the pathophysiology SUDs and HIV, although translational studies examining comorbid SUDs and HIV are very limited due to the technical challenges of modeling HIV infection preclinically. In this review, we discuss preclinical animal models of HIV and highlight key pathophysiological characteristics of each model, with a particular emphasis on rodent models of HIV. We then review the implementation of these models in preclinical SUD research and identify key gaps in knowledge in the field. Finally, we discuss how cutting-edge behavioral neuroscience tools, which have revealed key insights into the neurobehavioral mechanisms of SUDs, can be applied to preclinical animal models of HIV to reveal potential, novel treatment avenues for comorbid HIV and SUDs. Here, we argue that future preclinical SUD research would benefit from incorporating comorbidities such as HIV into animal models and would facilitate the discovery of more refined, subpopulation-specific mechanisms and effective SUD prevention and treatment targets.

Advances in HIV therapeutics and cure strategies: findings obtained through non-human primate studies

Human immunodeficiency virus (HIV), the main contributor of the ongoing AIDS epidemic, remains one of the most challenging and complex viruses to target and eradicate due to frequent genome mutation and immune evasion. Despite the development of potent antiretroviral therapies, HIV remains an incurable infection as the virus persists in latent reservoirs throughout the body. To innovate a safe and effective cure strategy for HIV in humans, animal models are needed to better understand viral proliferation, disease progression, and therapeutic response. Nonhuman primates infected with simian immunodeficiency virus (SIV) provide an ideal model to study HIV infection and pathogenesis as they are closely related to humans genetically and express phenotypically similar immune systems. Examining the clinical outcomes of novel treatment strategies within nonhuman primates facilitates our understanding of HIV latency and advances the development of a true cure to HIV.

Myelin regulatory factor is a target of individual and interactive effects of HIV-1 Tat and morphine in the striatum and pre-frontal cortex

HIV-associated neurocognitive disorders (HAND) remain pervasive even with increased efficacy/use of antiretroviral therapies. Opioid use/abuse among HIV + individuals is documented to exacerbate CNS deficits. White matter (WM) alterations, including myelin pallor, and volume/structural alterations detected by diffusion tensor imaging are common observations in HIV + individuals, and studies in non-human primates suggest that WM may harbor virus. Using transgenic mice that express the HIV-1 Tat protein, we examined in vivo effects of 2-6 weeks of Tat and morphine exposure on WM using genomic and biochemical methods. RNA sequencing of striatal tissue at 2 weeks revealed robust changes in mRNAs associated with oligodendrocyte precursor populations and myelin integrity, including those for transferrin, the atypical oligodendrocyte marker N-myc downstream regulated 1 (Ndrg1), and myelin regulatory factor (Myrf/Mrf), an oligodendrocyte-specific transcription factor with a significant role in oligodendrocyte differentiation/maturation. Western blots conducted after 6-weeks exposure in 3 brain regions (striatum, corpus callosum, pre-frontal cortex) revealed regional differences in the effect of Tat and morphine on Myrf levels, and on levels of myelin basic protein (MBP), whose transcription is regulated by Myrf. Responses included individual and interactive effects. Although baseline and post-treatment levels of Myrf and MBP differed between brain regions, post-treatment MBP levels in striatum and pre-frontal cortex were compatible with changes in Myrf activity. Additionally, the Myrf regulatory ubiquitin ligase Fbxw7 was identified as a novel target in our model. These results suggest that Myrf and Fbxw7 contribute to altered myelin gene regulation in HIV.

Machine Learning Prediction and Phyloanatomic Modeling of Viral Neuroadaptive Signatures in the Macaque Model of HIV-Mediated Neuropathology

In human immunodeficiency virus (HIV) infection, virus replication in and adaptation to the central nervous system (CNS) can result in neurocognitive deficits in approximately 25% of patients with unsuppressed viremia. While no single viral mutation can be agreed upon as distinguishing the neuroadapted population, earlier studies have demonstrated that a machine learning (ML) approach could be applied to identify a collection of mutational signatures within the virus envelope glycoprotein (Gp120) predictive of disease. The S[imian]IV-infected macaque is a widely used animal model of HIV neuropathology, allowing in-depth tissue sampling infeasible for human patients. Yet, translational impact of the ML approach within the context of the macaque model has not been tested, much less the capacity for early prediction in other, noninvasive tissues. We applied the previously described ML approach to prediction of SIV-mediated encephalitis (SIVE) using gp120 sequences obtained from the CNS of animals with and without SIVE with 97% accuracy. The presence of SIVE signatures at earlier time points of infection in non-CNS tissues indicated these signatures cannot be used in a clinical setting; however, combined with protein structural mapping and statistical phylogenetic inference, results revealed common denominators associated with these signatures, including 2-acetamido-2-deoxy-beta-d-glucopyranose structural interactions and high rate of alveolar macrophage (AM) infection. AMs were also determined to be the phyloanatomic source of cranial virus in SIVE animals, but not in animals that did not develop SIVE, implicating a role for these cells in the evolution of the signatures identified as predictive of both HIV and SIV neuropathology. IMPORTANCE HIV-associated neurocognitive disorders remain prevalent among persons living with HIV (PLWH) owing to our limited understanding of the contributing viral mechanisms and ability to predict disease onset. We have expanded on a machine learning method previously used on HIV genetic sequence data to predict neurocognitive impairment in PLWH to the more extensively sampled SIV-infected macaque model in order to (i) determine the translatability of the animal model and (ii) more accurately characterize the predictive capacity of the method. We identified eight amino acid and/or biochemical signatures in the SIV envelope glycoprotein, the most predominant of which demonstrated the potential for aminoglycan interaction characteristic of previously identified HIV signatures. These signatures were not isolated to specific points in time or to the central nervous system, limiting their use as an accurate clinical predictor of neuropathogenesis; however, statistical phylogenetic and signature pattern analyses implicate the lungs as a key player in the emergence of neuroadapted viruses.

Longitudinal white matter alterations in SIVmac239-infected rhesus monkeys with and without regular cART treatment

Objective

To use SIV-mac239-infected Chinese rhesus monkeys to study white matter changes with and without regular combined antiretroviral therapy (cART) and the relationships between the changes and clinical results.

Methods

Diffusion tensor imaging (DTI) data were collected at baseline and 10 days, 4 weeks, 12 weeks, 24 weeks, and 36 weeks after viral inoculation. Plasma CD4 T cell counts, CD4/CD8 ratio, plasma viral load, and cerebrospinal fluid (CSF) viral load were collected at baseline and 1 week, 5 weeks, 12 weeks, 24 weeks, and 36 weeks after viral inoculation. Microstructural characteristics were examined within 76 white matter areas defined by the DTI-white matter (WM) atlas for rhesus macaques. Corrections for multiple comparisons were performed using a false discovery rate (p < 0.05, FDR). Correlation analyzes between imaging markers and clinical markers (plasma CD4 T cell counts, CD4/CD8 ratio, plasma viral load, and cerebral spinal fluid viral load) were performed using Pearson correlations.

Results

White matter changes in SIV-infected macaques were detected in different brain regions as early as 4 weeks after inoculation. As time progressed, cART reversed, ameliorated, or even enhanced the effects. The CD4 T cell count was mainly associated with DTI metrics before cART, while the CD4/CD8 ratio was associated with white matter changes with and without cART. Viral load was positively associated with mean diffusivity in HIV patients without cART, and the opposite results were seen in HIV patients with cART.

Conclusion

SIV-mac239 infection may be an ideal tool for studying HIV-induced changes in the brain. The first white matter changes appeared in a structure adjacent to the periventricular area as early as 4 weeks after inoculation. As time progressed, cART had different effects on different regions, reversing, attenuating, or even progressing the pathology. Moreover, these changes were closely related to the CD4/CD8 ratio and viral load, even after cART.

Duration of antiretroviral therapy impacts the degree of residual SIV infection in the gut in long-term non-progressing Chinese rhesus macaques

The gut is a major reservoir in HIV-infected individuals on antiretroviral therapy (ART) and in long-term non-progressors (LTNPs). Whether ART reduces gut infection and reservoirs in LTNPs is unknown. Herein, SIV-infected LTNP Rhesus macaques were treated with short- or long-term ART, and SIV envelope gp120 sequences obtained from single genome amplification were analyzed before and after ART in peripheral blood and the intestine. Although ART does not eliminate SIV in these LTNPs, a longer ART period dramatically reduces SIV infection in the gut. This study highlights the importance of long-term ART in LTNPs to minimize gut infection and prolong remission.

Systems biology analyses reveal enhanced chronic morphine distortion of gut-brain interrelationships in simian human immunodeficiency virus infected rhesus macaques

Background

Commonly used opioids, such as morphine have been implicated in augmented SIV/HIV persistence within the central nervous system (CNS). However, the extent of myeloid cell polarization and viral persistence in different brain regions remains unclear. Additionally, the additive effects of morphine on SIV/HIV dysregulation of gut-brain crosstalk remain underexplored. Therefore, studies focused on understanding how drugs of abuse such as morphine affect immune dynamics, viral persistence and gut-brain interrelationships are warranted.

Materials and methods

For a total of 9 weeks, rhesus macaques were ramped-up, and twice daily injections of either morphine (n = 4) or saline (n = 4) administered. This was later followed with infection with SHIVAD8EO variants. At necropsy, mononuclear cells were isolated from diverse brain [frontal lobe, cerebellum, medulla, putamen, hippocampus (HIP) and subventricular zone (SVZ)] and gut [lamina propria (LP) and muscularis (MUSC) of ascending colon, duodenum, and ileum] regions. Multiparametric flow cytometry was used to were profile for myeloid cell polarity/activation and results corroborated with indirect immunofluorescence assays. Simian human immunodeficiency virus (SHIV) DNA levels were measured with aid of the digital droplet polymerase chain reaction (PCR) assay. Luminex assays were then used to evaluate soluble plasma/CSF biomarker levels. Finally, changes in the fecal microbiome were evaluated using 16S rRNA on the Illumina NovaSeq platform.

Results

Flow Cytometry-based semi-supervised analysis revealed that morphine exposure led to exacerbated M1 (CD14/CD16)/M2 (CD163/CD206) polarization in activated microglia that spanned across diverse brain regions. This was accompanied by elevated SHIV DNA within the sites of neurogenesis-HIP and SVZ. HIP/SVZ CD16+ activated microglia positively correlated with SHIV DNA levels in the brain (r = 0.548, p = 0.042). Simultaneously, morphine dependence depleted butyrate-producing bacteria, including Ruminococcus (p = 0.05), Lachnospira (p = 0.068) genera and Roseburia_sp_831b (p = 0.068). Finally, morphine also altered the regulation of CNS inflammation by reducing the levels of IL1 Receptor antagonist (IL1Ra).

Conclusion

These findings are suggestive that morphine promotes CNS inflammation by altering receptor modulation, increasing myeloid brain activation, distorting gut-brain crosstalk, and causing selective enhancement of SHIV persistence in sites of neurogenesis.

Intact HIV Proviruses Persist in the Brain Despite Viral Suppression with ART

OBJECTIVE

Human immunodeficiency virus (HIV) persistence in blood and tissue reservoirs, including the brain, is a major barrier to HIV cure and possible cause of comorbid disease. However, the size and replication competent nature of the central nervous system (CNS) reservoir is unclear. Here, we used the intact proviral DNA assay (IPDA) to provide the first quantitative assessment of the intact and defective HIV reservoir in the brain of people with HIV (PWH).

METHODS

Total, intact, and defective HIV proviruses were measured in autopsy frontal lobe tissue from viremic (n = 18) or virologically suppressed (n = 12) PWH. Total or intact/defective proviruses were measured by detection of HIV pol or the IPDA, respectively, through use of droplet digital polymerase chain reaction (ddPCR). HIV-seronegative individuals were included as controls (n = 6).

RESULTS

Total HIV DNA was present at similar levels in brain tissues from untreated viremic and antiretroviral (ART)-suppressed individuals (median = 22.3 vs 26.2 HIV pol copies/10⁶ cells), reflecting a stable CNS reservoir of HIV that persists despite therapy. Furthermore, 8 of 10 viremic and 6 of 9 virally suppressed PWH also harbored intact proviruses in the CNS (4.63 vs 12.7 intact copies/10⁶ cells). Viral reservoirs in CNS and matched lymphoid tissue were similar in the composition of intact and/or defective proviruses, albeit at lower levels in the brain. Importantly, CNS resident CD68+ myeloid cells in virally suppressed individuals harbored HIV DNA, directly showing the presence of a CNS resident HIV reservoir.

INTERPRETATION

Our results demonstrate the first evidence for an intact, potentially replication competent HIV reservoir in the CNS of virally suppressed PWH. ANN NEUROL 2022;92:532-544.

Neuroinflammatory Profiling in SIV-Infected Chinese-Origin Rhesus Macaques on Antiretroviral Therapy

The central nervous system (CNS) HIV reservoir is an obstacle to achieving an HIV cure. The basal ganglia harbor a higher frequency of SIV than other brain regions in the SIV-infected rhesus macaques of Chinese-origin (chRMs) even on suppressive combination antiretroviral therapy (ART). Since residual HIV/SIV reservoir is associated with inflammation, we characterized the neuroinflammation by gene expression and systemic levels of inflammatory molecules in healthy controls and SIV-infected chRMs with or without ART. CCL2, IL-6, and IFN-γ were significantly reduced in the cerebrospinal fluid (CSF) of animals receiving ART. Moreover, there was a correlation between levels of CCL2 in plasma and CSF, suggesting the potential use of plasma CCL2 as a neuroinflammation biomarker. With higher SIV frequency, the basal ganglia of untreated SIV-infected chRMs showed an upregulation of secreted phosphoprotein 1 (SPP1), which could be an indicator of ongoing neuroinflammation. While ART greatly reduced neuroinflammation in general, proinflammatory genes, such as IL-9, were still significantly upregulated. These results expand our understanding of neuroinflammation and signaling in SIV-infected chRMs on ART, an excellent model to study HIV/SIV persistence in the CNS.

Lentiviral Infections Persist in Brain despite Effective Antiretroviral Therapy and Neuroimmune Activation

HIV infection persists in different tissue reservoirs among people with HIV (PWH) despite effective antiretroviral therapy (ART). In the brain, lentiviruses replicate principally in microglia and trafficking macrophages. The impact of ART on this viral reservoir is unknown. We investigated the activity of contemporary ART in various models of lentivirus brain infection. HIV-1 RNA and total and integrated DNA were detected in cerebral cortex from all PWH (n = 15), regardless of ART duration or concurrent plasma viral quantity and, interestingly, integrated proviral DNA levels in brain were significantly higher in the aviremic ART-treated group (P < 0.005). Most ART drugs tested (dolutegravir, ritonavir, raltegravir, and emtricitabine) displayed significantly lower 50% effective concentration (EC₅₀) values in lymphocytes than in microglia, except tenofovir, which showed 1.5-fold greater activity in microglia (P < 0.05). In SIV-infected Chinese rhesus macaques, despite receiving suppressive (n = 7) or interrupted (n = 8) ART, brain tissues had similar SIV-encoded RNA and total and integrated DNA levels compared to brains from infected animals without ART (n = 3). SIV and HIV-1 capsid antigens were immunodetected in brain, principally in microglia/macrophages, regardless of ART duration and outcome. Antiviral immune responses were comparable in the brains of ART-treated and untreated HIV- and SIV-infected hosts. Both HIV-1 and SIV persist in brain tissues despite contemporary ART, with undetectable virus in blood. ART interruption exerted minimal effect on the SIV brain reservoir and did not alter the neuroimmune response profile. These studies underscore the importance of augmenting ART potency in different tissue compartments. IMPORTANCE Antiretroviral therapy (ART) suppresses HIV-1 in plasma and CSF to undetectable levels. However, the impact of contemporary ART on HIV-1 brain reservoirs remains uncertain. An active viral reservoir in the brain during ART could lead to rebound systemic infection after cessation of therapy, development of drug resistance mutations, and neurological disease. ART's impact, including its interruption, on brain proviral DNA remains unclear. The present studies show that in different experimental platforms, contemporary ART did not suppress viral burden in the brain, regardless of ART component regimen, the duration of therapy, and its interruption. Thus, new strategies for effective HIV-1 suppression in the brain are imperative to achieve sustained HIV suppression.

Advances in SIV/SHIV Non-Human Primate Models of NeuroAIDS

Non-human primates (NHPs) are the most relevant model of Acquired Immunodeficiency Syndrome (AIDS) and neuroAIDS, being of great importance in explaining the pathogenesis of HIV-induced nervous system damage. Simian Immunodeficiency Virus (SIV)/ Simian-Human Immunodeficiency Virus (SHIV)-infected monkeys have provided evidence of complex interactions between the virus and host that include host immune response, viral genetic diversity, and genetic susceptibility, which may explain virus-associated central nervous system (CNS) pathology and HIV-associated neurocognitive disorders (HAND). In this article, we review the recent progress contributions obtained using monkey models of HIV infection of the CNS, neuropathogenesis and SIV encephalitis (SIVE), with an emphasis on pharmacologic therapies and dependable markers that predict development of CNS AIDS.

Early prediction of putamen imaging features in HIV-associated neurocognitive impairment syndrome

Background

To explore the correlation between the volume of putamen and brain cognitive impairment in patients with HIV and to predict the feasibility of early-stage HIV brain cognitive impairment through radiomics.

Method

Retrospective selection of 90 patients with HIV infection, including 36 asymptomatic neurocognitive impairment (ANI) patients and 54 pre-clinical ANI patients in Beijing YouAn Hospital. All patients received comprehensive neuropsychological assessment and MRI scanning. 3D Slicer software was used to acquire volume of interest (VOI) and radiomics features. Clinical variables and volume of putamen were compared between patients with ANI and pre-clinical ANI. The Kruskal Wallis test was used to analysis multiple comparisons between groups. The relationship between cognitive scores and VOI was compared using linear regression. For radiomics, principal component analysis (PCA) was used to reduce model overfitting and calculations and then a support vector machine (SVM) was used to build a binary classification model. For model performance evaluation, we used an accuracy, sensitivity, specificity and receiver operating characteristic curve (ROC).

Result

There were no significant differences in clinical variables between ANI group and pre-clinical-ANI group (P>0.05). The volume of bilateral putamen was significantly different between AHI group and pre-clinical group (P<0.05), but there was only a trend in the left putamen between ANI-treatment group and pre-clinical treatment group(P = 0.063). Reduced cognitive scores in Verbal Fluency, Attention/Working Memory, Executive Functioning, memory and Speed of Information Processing were negatively correlated with the increased VOI (P<0.05), but the correlation was relatively low. In diagnosing the ANI from pre-clinical ANI, the mean area under the ROC curves (AUC) were 0.85 ± 0.22, the mean sensitivity and specificity were 63.12 ± 5.51 and 94.25% ± 3.08%.

Conclusion

The volumes of putamen in patients with ANI may be larger than patients with pre-clinical ANI, the change of the volume of the putamen may have a certain process; there is a relationship between putamen and cognitive impairment, but the exact mechanism is unclear. Radiomics may be a useful tool for predicting early stage HAND in patients with HIV.

The Brain Retains: Nonhuman Primate Models for Pediatric HIV-1 in the CNS

PURPOSE OF REVIEW

Perinatal HIV-1 infection is associated with an increased risk for neurologic impairments. With limited access to clinical specimens, animal models could advance our understanding of pediatric central nervous system (CNS) disease and viral persistence. Here, we summarize current findings on HIV-1 CNS infection from nonhuman primate (NHP) models and discuss their implications for improving pediatric clinical outcomes.

RECENT FINDINGS

SIV/SHIV can be found in the CNS of infant macaques within 48 h of challenge. Recent studies show an impermeable BBB during SIV infection, suggesting neuroinvasion in post-partum infection is likely not wholly attributed to barrier dysfunction. Histopathological findings reveal dramatic reductions in hippocampal neuronal populations and myelination in infected infant macaques, providing a link for cognitive impairments seen in pediatric cases. Evidence from humans and NHPs support the CNS as a functional latent reservoir, harbored in myeloid cells that may require unique eradication strategies. Studies in NHP models are uncovering early events, causes, and therapeutic targets of CNS disease as well as highlighting the importance of age-specific studies that capture the distinct features of pediatric HIV-1 infection.

Different roles of frontal versus striatal atrophy in HIV-associated neurocognitive disorders

Gray matter (GM) atrophy is frequently detected in persons living with HIV, even in the era of combination antiretroviral therapy (cART), but the specificity of regions affected remains elusive. For instance, which regions are consistently affected in HIV? In addition, atrophy at which regions is frequently associated with neurocognitive impairment in HIV? Resolving these questions can potentially help to establish the possible neural profiles of HIV-associated neurocognitive disorders (HAND) severity, which currently is solely defined by neurobehavioral assessments. Here, we addressed these questions using a novel meta-analysis technique, the colocalization-likelihood estimation (CLE) technique, to quantitatively synthesize the findings of GM atrophy in HIV+ adults. Twenty-one of 386 studies published between 1988 and November 2017 and identified in PubMed were selected, plus four identified in other resources. In the end, 25 studies (1,370 HIV+ adults, 889 HIV- controls) were included in the meta-analysis. This technique revealed that GM atrophy in HIV+ adults was dominated by two distinct but nonexclusive profiles: frontal (including anterior cingulate cortex, [ACC]) atrophy, which was associated withHIV-disease and consistently differentiated HIV+ adults from HIV- controls; and caudate/striatum atrophy, which was associated with neurocognitive impairment. The critical role of caudate/striatum atrophy in neurocognitive impairment was further supported by a separate data analysis, which examined the findings of correlation analyses between GM and neurocognitive performance. These results suggest that the frontal lobe and the striatum play critical but differential roles in HAND. A neural model of HAND severity was proposed with several testable predictions.

Persistent Viral Reservoirs in Lymphoid Tissues in SIV-Infected Rhesus Macaques of Chinese-Origin on Suppressive Antiretroviral Therapy

Understanding HIV latent reservoirs in tissues is essential for the development of new strategies targeting these sites for eradication. Here, we assessed the size of latent reservoirs and the source of residual viruses in multiple lymphoid tissues of SIV-infected and fully suppressed rhesus macaques of Chinese-origin (cRMs). Eight cRMs were infected with SIVmac251 and treated with tenofovir and emtricitabine daily for 24 weeks initiated 4 weeks post-infection. Four of the eight animals reached sustained full viral suppression with undetectable viremia. The levels of cell-associated SIV DNA varied in peripheral blood mononuclear cells (PBMCs) and multiple lymphoid tissues, but with higher levels in the mesenteric lymph nodes (MesLNs). The levels of cell-associated SIV RNA also varied in different tissues. The higher frequency of viral RNA detection in the MesLNs was also observed by in situ hybridization. Consistently, the infection unit per million cells (IUPM) in the MesLNs was higher than in PBMCs and other tested lymphoid tissues by quantitative viral outgrowth assay (QVOA). Furthermore, env gp120 from tissue SIV RNA was amplified by single genome amplification. Phylogenetic analysis revealed diverse variants from tissues parallel to the viral inoculum in all viral suppressed animals. These results demonstrate that the latency and viral reservoirs in the lymphoid tissues still exist in aviremic macaques under full suppressive therapy. Moreover, the size of viral latent reservoirs differs in various lymphoid tissues with a relatively larger size in the MesLNs.

BCL6 Inhibitor-Mediated Downregulation of Phosphorylated SAMHD1 and T Cell Activation Are Associated with Decreased HIV Infection and Reactivation

Clearance of HIV-infected germinal center (GC) CD4⁺ follicular helper T cells (Tfh) after combination antiretroviral therapy (ART) is essential to an HIV cure. Blocking B cell lymphoma 6 (BCL6; the master transcription factor for Tfh cells) represses HIV infection of tonsillar CD4⁺ Tfh ex vivo, reduces GC formation, and limits immune activation in vivo We assessed the anti-HIV activity of a novel BCL6 inhibitor, FX1, in Tfh/non-Tfh CD4⁺ T cells and its impact on T cell activation and SAMHD1 phosphorylation (Thr592). FX1 repressed HIV-1 infection of peripheral CD4⁺ T cells and tonsillar Tfh/non-Tfh CD4⁺ T cells (P < 0.05) and total elongated and multispliced HIV-1 RNA production during the first round of viral life cycle (P < 0.01). Using purified circulating CD4⁺ T cells from uninfected donors, we demonstrate that FX1 treatment resulted in downregulation pSAMHD1 expression (P < 0.05) and T cell activation (HLA-DR, CD25, and Ki67; P < 0.01) ex vivo corresponding with inhibition of HIV-1 and HIV-2 replication. Ex vivo HIV-1 reactivation using purified peripheral CD4⁺ T cells from HIV-infected ART-suppressed donors was also blocked by FX1 treatment (P < 0.01). Our results indicate that BCL6 function contributes to Tfh/non-Tfh CD4⁺ T cell activation and cellular susceptibility to HIV infection. BCL6 inhibition represents a novel therapeutic strategy to potentiate HIV suppression in Tfh/non-Tfh CD4⁺ T cells without reactivation of latent virus.IMPORTANCE The expansion and accumulation of HIV-infected BCL6⁺ Tfh CD4⁺ T cells are thought to contribute to the persistence of viral reservoirs in infected subjects undergoing ART. Two mechanisms have been raised for the preferential retention of HIV within Tfh CD4⁺ T cells: (i) antiretroviral drugs have limited tissue distribution, resulting in insufficient tissue concentration and lower efficacy in controlling HIV replication in lymphoid tissues, and (ii) cytotoxic CD8⁺ T cells within lymphoid tissues express low levels of chemokine receptor (CXCR5), thus limiting their ability to enter the GCs to control/eliminate HIV-infected Tfh cells. Our results indicate that the BCL6 inhibitor FX1 can not only repress HIV infection of tonsillar Tfh ex vivo but also suppress HIV infection and reactivation in primary, non-Tfh CD4⁺ T cells. Our study provides a rationale for targeting BCL6 protein to extend ART-mediated reduction of persistent HIV and/or support strategies toward HIV remission beyond ART cessation.