CD16+ monocytes give rise to CD103+RALDH2+TCF4+ dendritic cells with unique transcriptional and immunological features

Integration of single-cell and bulk RNA sequencing revealed immune heterogeneity and its association with disease activity in rheumatoid arthritis patients

Rheumatoid arthritis (RA) is a chronic, inflammatory, systemic autoimmune disease characterized by cartilage, bone damage, synovial inflammation, hyperplasia, autoantibody production, and systemic features. To obtain an overall profile of the immune environment in RA patients and its association with clinical features, we performed single-cell transcriptome and T-cell receptor sequencing of mononuclear cells from peripheral blood (PBMC) and synovial fluid (SF) from RA patients, integrated with two large cohorts with bulk RNA sequencing for further validation and investigation. Dendritic cells (DCs) exhibited relatively high functional heterogeneity and tissue specificity in relation to both antigen presentation and proinflammatory functions. Peripheral helper T cells (TPHs) are likely to originate from synovial tissue, undergo activation and exhaustion, and are subsequently released into the peripheral blood. Notably, among all immune cell types, TPHs were found to have the most intense associations with disease activity. In addition, CD8 effector T cells could be clustered into two groups with different cytokine expressions and play distinct roles in RA development. By integrating single-cell data with bulk sequencing from two large cohorts, we identified interactions among TPHs, CD8 cells, CD16 monocytes, and DCs that strongly contribute to the proinflammatory local environment in RA joints. Of note, the swollen 28-joint counts exhibited a more pronounced association with this immune environment compared to other disease activity indexes. The immune environment alternated significantly from PBMCs to SF, which indicated that a series of immune cells was involved in proinflammatory responses in the local joints of RA patients. By integrating single-cell data with two large cohorts, we have uncovered associations between specific immune cell populations and clinical features. This integration provides a rapid and precise methodology for assessing local immune activation, offering valuable insights into the pathophysiological mechanisms at play in RA.

Flexible modeling of regulatory networks improves transcription factor activity estimation

Transcriptional regulation plays a crucial role in determining cell fate and disease, yet inferring the key regulators from gene expression data remains a significant challenge. Existing methods for estimating transcription factor (TF) activity often rely on static TF-gene interaction databases and cannot adapt to changes in regulatory mechanisms across different cell types and disease conditions. Here, we present a new algorithm - Transcriptional Inference using Gene Expression and Regulatory data (TIGER) - that overcomes these limitations by flexibly modeling activation and inhibition events, up-weighting essential edges, shrinking irrelevant edges towards zero through a sparse Bayesian prior, and simultaneously estimating both TF activity levels and changes in the underlying regulatory network. When applied to yeast and cancer TF knock-out datasets, TIGER outperforms comparable methods in terms of prediction accuracy. Moreover, our application of TIGER to tissue- and cell-type-specific RNA-seq data demonstrates its ability to uncover differences in regulatory mechanisms. Collectively, our findings highlight the utility of modeling context-specific regulation when inferring transcription factor activities.

Hematopoietic growth factors Regulate Entry of Monocytes into the Adult Brain via Chemokine Receptor CCR5

Monocytes are circulating macrophage precursors and are generated from bone marrow hematopoietic stem cells. In the adults, monocytes continuously replenish cerebral border-associated macrophages under a physiological condition. Monocytes also rapidly infiltrate into the brain in the settings of pathological conditions. The mechanisms of recruiting monocyte-derived macrophages into the brain under pathological conditions have been extensively studied. However, it remains unclear how monocytes enter the brain for renewal of border-associated macrophages under the physiological condition. Using both in vitro and in vivo approaches, this study reveals that the combination of two hematopoietic growth factors, stem cell factor (SCF) and granulocyte colony-stimulating factor (G-CSF), complementarily and synergistically enhances adhesion of monocytes to cerebral endothelial cells in a dose dependent manner. Cysteine-cysteine chemokine receptor 5 (CCR5) in brain endothelial cells, but not cell adhesion molecules mediating neuroinflammation-related infiltration of monocyte-derived macrophages, modulates the SCF+G-CSF-enhanced monocyte-endothelial cell adhesion. Blocking CCR5 or genetically deleting CCR5 reduces monocyte-endothelial cell adhesion induced by SCF+G-CSF. SCF+G-CSF-enhanced recruitment of bone marrow-derived monocytes/macrophages in cerebral perivascular space is also reduced in adult CCR5 knockout mice. This study demonstrates the contribution of SCF and G-CSF in regulating the entry of monocytes into the adult brain to replenish perivascular macrophages.

A Blood Immunological Signature of Subclinical Coronary Artery Atherosclerosis in People Living with HIV-1 Receiving Antiretroviral Therapy

Cardiovascular disease (CVD) remains an important co-morbidity in people living with HIV-1 (PLWH) receiving antiretroviral therapy (ART). Our previous studies performed on the Canadian HIV/Aging Cohort Study (CHACS) (>40 years-old; Framingham Risk Score (FRS) >5%), revealed a 2-3-fold increase in non-calcified coronary artery atherosclerosis (CAA) plaque burden, measured by Computed tomography angiography scan (CTAScan) as total (TPV) and low attenuated plaque volume (LAPV) in ART-treated PLWH (HIV+) versus uninfected controls (HIV-). In an effort to identify novel correlates of subclinical CAA, markers of intestinal damage (sCD14, LBP, FABP2); cell trafficking/inflammation (CCL20, CX3CL1, MIF, CCL25); subsets of Th17-polarized and regulatory (Tregs) CD4 + T-cells, classical/intermediate/non-classical monocytes, and myeloid/plasmacytoid dendritic cells, were studied in relationship with HIV and TPV/LAPV status. The TPV detection/values coincided with higher plasma sCD14, FABP2, CCL20, MIF, CX3CL1 and triglyceride levels, lower Th17/Treg ratios, and classical monocyte expansion. Among HIV + , TPV + versus TPV - exhibited lower Th17 frequencies, reduced Th17/Treg ratios, higher frequencies of non-classical CCR9 low HLADR high monocyte, and increased plasma fibrinogen levels. Finally, Th17/Treg ratios and non-classical CCR9 low HLADR high monocyte frequencies remained associated with TPV/LAPV after adjusting for FRS and HIV/ART duration in a logistic regression model. These findings point to Th17 paucity and non-classical monocyte abundance as novel immunological correlates of subclinical CAA that may fuel the CVD risk in ART-treated PLWH.

Inflammatory and tolerogenic myeloid cells determine outcome following human allergen challenge

Innate mononuclear phagocytic system (MPS) cells preserve mucosal immune homeostasis. We investigated their role at nasal mucosa following allergen challenge with house dust mite. We combined single-cell proteome and transcriptome profiling on nasal immune cells from nasal biopsies cells from 30 allergic rhinitis and 27 non-allergic subjects before and after repeated nasal allergen challenge. Biopsies of patients showed infiltrating inflammatory HLA-DRhi/CD14+ and CD16+ monocytes and proallergic transcriptional changes in resident CD1C+/CD1A+ conventional dendritic cells (cDC)2 following challenge. In contrast, non-allergic individuals displayed distinct innate MPS responses to allergen challenge: predominant infiltration of myeloid-derived suppressor cells (MDSC: HLA-DRlow/CD14+ monocytes) and cDC2 expressing inhibitory/tolerogenic transcripts. These divergent patterns were confirmed in ex vivo stimulated MPS nasal biopsy cells. Thus, we identified not only MPS cell clusters involved in airway allergic inflammation but also highlight novel roles for non-inflammatory innate MPS responses by MDSC to allergens in non-allergic individuals. Future therapies should address MDSC activity as treatment for inflammatory airway diseases.

A novel 3D cell culture model to study the human small intestinal immune landscape

Several subsets of mononuclear phagocytes and DCs (MDC) populate the small intestine (SI), and these cells reportedly exert specialized functions in anti-microbial immunity and tolerance. Given the specialized phenotype of these cells, differing from other MDC family members, including their putative circulating blood precursors, local intestinal factors play key instructive roles in their differentiation. We designed an SI cell culture model composed of three intestinal epithelial cell (IEC) types, including absorptive enterocytes (E cells), antigen delivering microfold (M) cells, and mucus-producing goblet (G) cells plus T lymphocytes and soluble B cell-derived factors. This model was used to study the differentiation fate of CD34⁺ hematopoietic progenitor cell-derived monocyte/DC precursors. Progeny cells can be analyzed after a 3-week co-culture period, mimicking the physiologic turn-over time of intestinal MDC. A dominant monocyte differentiation pathway was suppressed, in favor of partial differentiation along DC and macrophage pathways, with low percentages of cells acquired DC or macrophage markers. Moreover, E and G cells play opposing roles in CX3CR1⁺ vs CD103^dim cell differentiation, indicating that both together might counter-balance M/DC differentiation. Thus, SI epithelial cells suppress M/DC differentiation, supporting a key role for exogenous factors in M/DC differentiation.

Exosome-derived FGD5-AS1 promotes tumor-associated macrophage M2 polarization-mediated pancreatic cancer cell proliferation and metastasis

Inflammatory molecules and exosomes are crucial for signal transduction between tumor-associated macrophages and tumor cells. IL-6, a key inflammatory molecule secreted by M2 macrophages after polarization, can mediate malignant progression of pancreatic cancer (PC). However, the functions and mechanisms of IL-6 and tumor-derived exosomes in tumor-associated macrophages and PC remain unclear. Transcriptome chip and quantitative reverse transcription PCR experiments indicated that FGD5-AS1 induced IL-6 and high FGD5-AS1 expression correlated with the poor prognosis in PC patients. RNA pulldown, mass spectrometry, and dual luciferase reporter assays were used to identify the mechanism of exosomal FGD5-AS1 in promoting PC progression and M2 macrophage polarization. FGD5-AS1 exerted cancer-promoting functions when co-cultured with M2 macrophages. PC-derived exosomal FGD5-AS1 stimulated M2 macrophage polarization by activating STAT3/NF-κB pathway. FGD5-AS1 interacts with p300, resulting in STAT3 acetylation, thus promoting nuclear localization and transcriptional activity of STAT3/NF-κB. These data indicated that PC cells generate FGD5-AS1-rich exosomes, which cause M2 macrophage polarization to promote the malignant behaviors of PC cells. Targeting exosomal FGD5-AS1 may provide a potential diagnosis and treatment strategy for PC.

Recapitulation of pro-inflammatory signature of monocytes with ACVR1A mutation using FOP patient-derived iPSCs

BACKGROUND

Fibrodysplasia ossificans progressiva (FOP) is a rare genetic disease characterized by progressive heterotopic ossification (HO) in soft tissues due to a heterozygous mutation of the ACVR1A gene (FOP-ACVR1A), which erroneously transduces the BMP signal by Activin-A. Although inflammation is known to trigger HO in FOP, the role of FOP-ACVR1A on inflammatory cells remains to be elucidated.

RESULTS

We generated immortalized monocytic cell lines from FOP-iPSCs (FOP-ML) and mutation rescued iPSCs (resFOP-ML). Cell morphology was evaluated during the monocyte induction and after immortalization. Fluorescence-activated cell sorting (FACS) was performed to evaluate the cell surface markers CD14 and CD16 on MLs. MLs were stimulated with lipopolysaccharide or Activin-A and the gene expression was evaluated by quantitative PCR and microarray analysis. Histological analysis was performed for HO tissue obtained from wild type mice and FOP-ACVR1A mice which conditionally express human mutant ACVR1A gene by doxycycline administration. Without any stimulation, FOP-ML showed the pro-inflammatory signature of CD16+ monocytes with an upregulation of INHBA gene, and treatment of resFOP-ML with Activin-A induced an expression profile mimicking that of FOP-ML at baseline. Treatment of FOP-ML with Activin-A further induced the inflammatory profile with an up-regulation of inflammation-associated genes, of which some, but not all, of which were suppressed by corticosteroid. Experiments using an inhibitor for TGFβ or BMP signal demonstrated that Activin-A-induced genes such as CD16 and CCL7, were regulated by both signals, indicating Activin-A transduced dual signals in FOP-ML. A comparison with resFOP-ML identified several down-regulated genes in FOP-ML including LYVE-1, which is known to suppress matrix-formation in vivo. The down-regulation of LYVE-1 in HO tissues was confirmed in FOP model mice, verifying the significance of the in vitro experiments.

CONCLUSION

These results indicate that FOP-ML faithfully recapitulated the phenotype of primary monocytes of FOP and the combination with resFOP-ML is a useful tool to investigate molecular events at the initial inflammation stage of HO in FOP.

CD169 (Siglec-1) as a Robust Human Cell Biomarker of Toll-Like Receptor 9 Agonist Immunotherapy

Immunotherapy is a promising therapeutic area in cancer and chronic viral infections. An important component of immunotherapy in these contexts is the activation of innate immunity. Here we investigate the potential for CD169 (Siglec 1) expression on monocytes to serve as a robust biomarker for activation of innate immunity and, particular, as a proxy for IFN-α production. Specifically, we investigated the effects of Toll-like receptor 9 agonism with MGN1703 (lefitolimod) across experimental conditions ex vivo, in humanized mice, and in clinical trial participants. Ex vivo we observed that the percentage of classical monocytes expressing CD169 increased dramatically from 10% pre-stimulation to 97% 24 hrs after MGN1703 stimulation (p<0.0001). In humanized NOG mice, we observed prominent upregulation of the proportions of monocytes expressing CD169 after two doses of MGN1703 where 73% of classical monocytes were CD169 positive in bone marrow following MGN1703 treatment vs 19% in vehicle treated mice (p=0.0159). Finally, in a clinical trial in HIV-infected individuals receiving immunotherapy treatment with MGN1703, we observed a uniform upregulation of CD169 on monocytes after dosing with 97% of classical monocytes positive for CD169 (p=0.002). Hence, in this comprehensive evaluation ex vivo, in an animal model, and in a clinical trial, we find increases in the percentage of CD169 positive monocytes to be a reliable and robust biomarker of immune activation following TLR9 agonist treatment.

Monocyte Gene and Molecular Expression Profiles Suggest Distinct Effector and Regulatory Functions in Beninese HIV Highly Exposed Seronegative Female Commercial Sex Workers

We have previously reported that the female genital tract (FGT) of Beninese HIV highly-exposed seronegative (HESN) commercial sex workers (CSWs), presented elevated frequencies of a myeloid HLA-DR+CD14+CD11c+ population presenting “tolerogenic” monocyte derived dendritic cells (MoDC) features. In order to assess whether a differential profile of monocytes may be involved in the generation of these genital MoDCs, we have herein characterized the blood monocyte compartment of Beninese HESNs (HIV-uninfected ≥ 10 years CSWs) and relevant controls (HIV-uninfected 2.5–5 years CSWs herein termed “early HESNs”), HIV-infected CSWs, and low-risk HIV-uninfected women from the general population. Transcriptomic analyses by RNA-Seq of total sorted blood monocytes demonstrate that in comparison to the control groups, HESNs present increased expression levels of FCGR2C, FCAR, ITGAX, ITGAM, CR2, CD68, and CD163 genes, associated with effector functions. Moreover, we found increased expression levels of genes associated with protection/control against SHIV/HIV such as CCL3, CCL4, CCL5, BHLHE40, and TNFSF13, as well as with immune regulation such as IL-10, Ahr, CD83, and the orphan nuclear receptor (NR)4A1, NR4A2, and NR4A3. Through multicolor flow cytometry analyses, we noticed that the frequencies of intermediate and non-classical monocyte populations tended to be elevated in the blood of HESNs, and exhibited increased expression levels of effector CD16, CD11c, CD11b, as well as regulatory HLA-G, IL-10, and IFN-α markers when compared to HIV-uninfected women and/or HIV-infected CSWs. This profile is compatible with that previously reported in the FGT of HESNs, and likely confers an enormous advantage in their resistance to HIV infection.

Emerging role of non-coding RNAs in the course of HIV infection

Recent studies have shown that non-coding region of the human genome can exert important regulatory roles on critical biological functions, including response to viral infections, among them is human immunodeficiency virus (HIV). HIV/AIDS is characterized by a gradual diminution of CD4 + T cells resulting in progressive deterioration of host immune responses and eventually high vulnerability to opportunistic infections and cancer. T cells functions have been shown to be delicately regulated by an active functional network of non-coding RNAs. Several lncRNAs such as MALAT1, NEAT1, GAS5, LOC102549805, NKILA, BACE1-AS, LINC00313, RP11-539L10.2, PVT1, LINC00173, NRON and AK130181 have been found to affect response of immune system to HIV or its pathological consequences. Moreover, numerous miRNAs such as hsa-miR-191-5p, miR-155, miR-103, miR-107, miR-150, miR-144, miR-125b, miR-146a, miR-146b-5p and miR-15a are involved in this process. In the current manuscript, we explain the role of lncRNAs and miRNAs in the regulation of response to HIV infection, apoptosis and activity of T cells, reactivation or latency of this virus and even pathological manifestations such as Tat-mediated induction of astrocytic amyloidosis.

Antiretroviral Drug Transporters and Metabolic Enzymes in Circulating Monocytes and Monocyte-Derived Macrophages of ART-Treated People Living With HIV and HIV-Uninfected Individuals

ABSTRACT

Membrane-associated drug transport proteins and drug metabolic enzymes could regulate intracellular antiretroviral (ARV) drug concentrations in HIV-1 target cells such as myeloid cells. We investigated the expression of these transporters and enzymes in monocyte subsets and monocyte-derived macrophages (MDMs) isolated from peripheral blood mononuclear cells (PBMCs) of HIV-uninfected individuals (HIV-negative) and people living with HIV receiving viral suppressive antiretroviral therapy (ART; HIV+ART) and examined plasma and intracellular ARV concentrations. Monocytes were isolated from PBMCs of 12 HIV-negative and 12 HIV+ART donors and differentiated into MDMs. The mRNA and protein expression of drug transporters and metabolic enzymes were analyzed by quantitative real-time polymerase chain reaction and flow cytometry, respectively. ARV drug concentrations were quantified in plasma, PBMCs, monocytes, and MDMs by LC-MS/MS. The mRNA expression of relevant ARV transporters or metabolic enzymes, ABCB1/P-gp, ABCG2/BCRP, ABCC1/MRP1, ABCC4/MRP4, SLC22A1/OCT1, SLC29A2/ENT2, CYP2B6, CYP2D6, and UGT1A1, was demonstrated in monocytes and MDMs of 2 to 4 HIV-negative donors. P-gp, BCRP, and MRP1 proteins were differentially expressed in classical, intermediate, and nonclassical monocytes and MDMs of both HIV+ART and HIV-negative donors. Intracellular concentrations of ARVs known to be substrates of these transporters and metabolic enzymes were detected in monocytes of HIV+ART donors but were undetectable in MDMs. In this study, we demonstrated the expression of drug transporters and metabolic enzymes in monocytes and MDMs of HIV-negative and HIV+ART individuals, which could potentially limit intracellular concentrations of ARVs and contribute to residual HIV replication. Further work is needed to assess the role of these transporters in the penetration of ARVs in tissue macrophages.

ILF3 Is a Negative Transcriptional Regulator of Innate Immune Responses and Myeloid Dendritic Cell Maturation

APCs such as myeloid dendritic cells (DCs) are key sentinels of the innate immune system. In response to pathogen recognition and innate immune stimulation, DCs transition from an immature to a mature state that is characterized by widespread changes in host gene expression, which include the upregulation of cytokines, chemokines, and costimulatory factors to protect against infection. Several transcription factors are known to drive these gene expression changes, but the mechanisms that negatively regulate DC maturation are less well understood. In this study, we identify the transcription factor IL enhancer binding factor 3 (ILF3) as a negative regulator of innate immune responses and DC maturation. Depletion of ILF3 in primary human monocyte-derived DCs led to increased expression of maturation markers and potentiated innate responses during stimulation with viral mimetics or classic innate agonists. Conversely, overexpression of short or long ILF3 isoforms (NF90 and NF110) suppressed DC maturation and innate immune responses. Through mutagenesis experiments, we found that a nuclear localization sequence in ILF3, and not its dual dsRNA-binding domains, was required for this function. Mutation of the domain associated with zinc finger motif of ILF3's NF110 isoform blocked its ability to suppress DC maturation. Moreover, RNA-sequencing analysis indicated that ILF3 regulates genes associated with cholesterol homeostasis in addition to genes associated with DC maturation. Together, our data establish ILF3 as a transcriptional regulator that restrains DC maturation and limits innate immune responses through a mechanism that may intersect with lipid metabolism.

RALDH Activity Induced by Bacterial/Fungal Pathogens in CD16+ Monocyte-Derived Dendritic Cells Boosts HIV Infection and Outgrowth in CD4+ T Cells

HIV reservoirs persist in gut-homing CD4⁺ T cells of people living with HIV and receiving antiretroviral therapy, but the antigenic specificity of such reservoirs remains poorly documented. The imprinting for gut homing is mediated by retinoic acid (RA), a vitamin A-derived metabolite produced by dendritic cells (DCs) exhibiting RA-synthesizing (RALDH) activity. RALDH activity in DCs can be induced by TLR2 ligands, such as bacterial peptidoglycans and fungal zymosan. Thus, we hypothesized that bacterial/fungal pathogens triggering RALDH activity in DCs fuel HIV reservoir establishment/outgrowth in pathogen-reactive CD4⁺ T cells. Our results demonstrate that DCs derived from intermediate/nonclassical CD16⁺ compared with classical CD16^- monocytes exhibited superior RALDH activity and higher capacity to transmit HIV infection to autologous Staphylococcus aureus-reactive T cells. Exposure of total monocyte-derived DCs (MDDCs) to S. aureus lysates as well as TLR2 (zymosan and heat-killed preparation of Listeria monocytogenes) and TLR4 (LPS) agonists but not CMV lysates resulted in a robust upregulation of RALDH activity. MDDCs loaded with S. aureus or zymosan induced the proliferation of T cells with a CCR5⁺integrin β7⁺CCR6⁺ phenotype and efficiently transmitted HIV infection to these T cells via RALDH/RA-dependent mechanisms. Finally, S. aureus- and zymosan-reactive CD4⁺ T cells of antiretroviral therapy-treated people living with HIV carried replication-competent integrated HIV-DNA, as demonstrated by an MDDC-based viral outgrowth assay. Together, these results support a model in which bacterial/fungal pathogens in the gut promote RALDH activity in MDDCs, especially in CD16⁺ MDDCs, and subsequently imprint CD4⁺ T cells with gut-homing potential and HIV permissiveness. Thus, nonviral pathogens play key roles in fueling HIV reservoir establishment/outgrowth via RALDH/RA-dependent mechanisms that may be therapeutically targeted.

The Importance of Regulation in Natural Immunity to HIV

Worldwide, most Human Immunodeficiency Virus (HIV) infections are acquired through heterosexual intercourse, and in sub-Saharan Africa, 59% of new HIV infections affect women. Vaccines and microbicides hold promise for preventing the acquisition of HIV. To this end, the study of HIV highly exposed seronegative (HESN) female commercial sex workers (CSWs), who constitute a model of natural immunity to HIV, provides an exceptional opportunity to determine important clues for the development of preventive strategies. Studies using both female genital tract (FGT) and peripheral blood samples of HESN CSWs, have allowed identifying distinct features, notably low-inflammatory patterns associated with resistance to infection. How this seemingly regulated response is achieved at the initial site of HIV infection remains unknown. One hypothesis is that populations presenting regulatory profiles contribute to the orchestration of potent anti-viral and low-inflammatory responses at the initial site of HIV transmission. Here, we view to update our knowledge regarding this issue.

6-Sulfo LacNAc (Slan) as a Marker for Non-classical Monocytes

Monocytes are subdivided into three subsets, which have different phenotypic and functional characteristics and different roles in inflammation and malignancy. When in man CD14 and CD16 monoclonal antibodies are used to define these subsets, then the distinction of non-classical CD14low and intermediate CD14high monocytes requires setting a gate in what is a gradually changing level of CD14 expression. In the search for an additional marker to better dissect the two subsets we have explored the marker 6-sulfo LacNAc (slan). Slan is a carbohydrate residue originally described to be expressed on the cell surface of a type of dendritic cell in human blood. We elaborate herein that the features of slan+ cells are congruent with the features of CD16+ non-classical monocytes and that slan is a candidate marker for definition of non-classical monocytes. The use of this marker may help in studying the role of non-classical monocytes in health and in diagnosis and monitoring of disease.

HIV-1 is rarely detected in blood and colon myeloid cells during viral-suppressive antiretroviral therapy

OBJECTIVE

The aim of this study was to explore the contribution of blood and colon myeloid cells to HIV persistence during antiretroviral therapy (ART).

DESIGN

Leukapheresis was collected from HIV-infected individuals with undetectable plasma viral load during ART (HIV + ART; n = 15) and viremics untreated (HIV+; n = 6). Rectal sigmoid biopsies were collected from n = 8 HIV+ART.

METHODS

Myeloid cells (total monocytes (Mo), CD16/CD16 Mo, CD1c dendritic cells) and CD4 T cells were isolated by magnetic-activated cell sorting (MACS) and/or fluorescence-activated cell sorting (FACS) from peripheral blood. Matched myeloid and CCR6CD4 T cells were isolated from blood and rectal biopsies by FACS. Levels of early (RU5 primers), late (Gag primers) and/or integrated HIV-DNA (Alu/HIV primers) were quantified by nested real-time PCR. Replication-competent HIV was amplified by co-culturing cells from HIV-positive individuals with CD3/CD28-activated CD4 T cells from uninfected donors.

RESULTS

Early/late but not integrated HIV reverse transcripts were detected in blood myeloid subsets of four out of 10 HIV+ART; in contrast, integrated HIV-DNA was exclusively detected in CD4 T cells. In rectal biopsies, late HIV reverse transcripts were detected in myeloid cells and CCR6CD4 T cells from one out of eight and seven out of eight HIV+ART individuals, respectively. Replication-competent HIV was outgrown from CD4 T cells but not from myeloid of untreated/ART-treated HIV-positive individuals.

CONCLUSION

In contrast to CD4 T cells, blood and colon myeloid cells carry detectable HIV only in a small fraction of HIV+ART individuals. This is consistent with the documented resistance of Mo to HIV infection and the rapid turnover of Mo-derived macrophages in the colon. Future assessment of multiple lymphoid and nonlymphoid tissues is required to include/exclude myeloid cells as relevant HIV reservoirs during ART.

Human Dendritic Cell Subsets, Ontogeny, and Impact on HIV Infection

Dendritic cells (DCs) play important roles in orchestrating host immunity against invading pathogens, representing one of the first responders to infection by mucosal invaders. From their discovery by Ralph Steinman in the 1970s followed shortly after with descriptions of their in vivo diversity and distribution by Derek Hart, we are still continuing to progressively elucidate the spectrum of DCs present in various anatomical compartments. With the power of high-dimensional approaches such as single-cell sequencing and multiparameter cytometry, recent studies have shed new light on the identities and functions of DC subtypes. Notable examples include the reclassification of plasmacytoid DCs as purely interferon-producing cells and re-evaluation of intestinal conventional DCs and macrophages as derived from monocyte precursors. Collectively, these observations have changed how we view these cells not only in steady-state immunity but also during disease and infection. In this review, we will discuss the current landscape of DCs and their ontogeny, and how this influences our understanding of their roles during HIV infection.