CD4 T Follicular Helper and Regulatory Cell Dynamics and Function in HIV Infection

Safety and protective efficacy of PfSPZ Vaccine administered to HIV-negative and -positive Tanzanian adults

BACKGROUNDSanaria PfSPZ Vaccine, composed of attenuated Plasmodium falciparum (Pf) sporozoites (SPZ), protects against malaria. We conducted this clinical trial to assess the safety and efficacy of PfSPZ Vaccine in HIV-positive (HIV+) individuals, since the HIV-infection status of participants in mass vaccination programs may be unknown.METHODSThis randomized, double-blind, placebo-controlled trial enrolled 18- to 45-year-old HIV-negative (HIV-) and well-controlled HIV+ Tanzanians (HIV viral load <40 copies/mL, CD4 counts >500 cells/μL). Participants received 5 doses of PfSPZ Vaccine or normal saline (NS) over 28 days, followed by controlled human malaria infection (CHMI) 3 weeks later.RESULTSThere were no solicited adverse events in the 9 HIV- and 12 HIV+ participants. After CHMI, 6 of 6 NS controls, 1 of 5 HIV- vaccinees, and 4 of 4 HIV+ vaccinees were Pf positive by quantitative PCR (qPCR). After immunization, anti-Pf circumsporozoite protein (anti-PfCSP) (isotype and IgG subclass) and anti-PfSPZ antibodies, anti-PfSPZ CD4+ T cell responses, and Vδ2+ γδ CD3+ T cells were nonsignificantly higher in HIV- than in HIV+ vaccinees. Sera from HIV- vaccinees had significantly higher inhibition of PfSPZ invasion of hepatocytes in vitro and antibody-dependent complement deposition (ADCD) and Fcγ3B binding by anti-PfCSP and ADCD by anti-cell-traversal protein for ookinetes and SPZ (anti-PfCelTOS) antibodies.CONCLUSIONSPfSPZ Vaccine was safe and well tolerated in HIV+ vaccinees, but not protective. Vaccine efficacy was 80% in HIV- vaccinees (P = 0.012), whose sera had significantly higher inhibition of PfSPZ invasion of hepatocytes and enrichment of multifunctional PfCSP antibodies. A more potent PfSPZ vaccine or regimen is needed to protect those living with HIV against Pf infection in Africa.TRIAL REGISTRATIONClinicalTrials.gov NCT03420053.FUNDINGEquatorial Guinea Malaria Vaccine Initiative (EGMVI), made up of the Government of Equatorial Guinea Ministries of Mines and Hydrocarbons, and Health and Social Welfare, Marathon Equatorial Guinea Production Limited, Noble Energy, Atlantic Methanol Production Company, and EG LNG; Swiss government, through ESKAS scholarship grant no. 2016.0056; Intramural Research Program of the National Institute of Allergy and Infectious Diseases, NIH; NIH grant 1U01AI155354-01.

The regulation of Tfh cell differentiation by β-hydroxybutyrylation modification of transcription factor Bcl6

Transcriptional repressor B cell lymphoma 6 (Bcl6) is a major transcription factor involved in Tfh cell differentiation and germinal center response, which is regulated by a variety of biological processes. However, the functional impact of post-translational modifications, particularly lysine β-hydroxybutyrylation (Kbhb), on Bcl6 remains elusive. In this study, we revealed that Bcl6 is modified by Kbhb to affect Tfh cell differentiation, resulting in the decrease of cell population and cytokine IL-21. Furthermore, the modification sites are identified from enzymatic reactions to be lysine residues at positions 376, 377, and 379 by mass spectrometry, which is confirmed by site-directed mutagenesis and functional analyses. Collectively, our present study provides evidence on the Kbhb modification of Bcl6 and also generates new insights into the regulation of Tfh cell differentiation, which is a starting point for a thorough understanding of the functional involvement of Kbhb modification in the differentiations of Tfh and other T cells.

Characterization of T Follicular Helper Cells and T Follicular Regulatory Cells in HIV-Infected and Sero-Negative Individuals

Humoral immune response is important in fighting pathogens by the production of specific antibodies by B cells. In germinal centers, T follicular helper (TFH) cells provide important help to B-cell antibody production but also contribute to HIV persistence. T follicular regulatory (TFR) cells, which inhibit the function of TFH cells, express similar surface markers. Since FOXP3 is the only marker that distinguishes TFR from TFH cells it is unknown whether the increase in TFH cells observed in HIV infection and HIV persistence may be partly due to an increase in TFR cells. Using multicolor flow cytometry to detect TFH and TFR cells in cryopreserved peripheral blood mononuclear cells from HIV-infected and non-infected participants in the UCLA Multicenter AIDS Cohort Study (MACS), we identified CD3⁺CXCR5⁺CD4⁺CD8^-BCL6⁺ peripheral blood TFH (pTFH) cells and CD3⁺CXCR5⁺CD4⁺CD8^-FOXP3⁺ peripheral blood TFR (pTFR) cells. Unlike TFR cells in germinal centers, pTFR cells do not express B cell lymphoma 6 (BCL6), a TFH cell master transcriptional regulator. Our major findings are that the frequency of pTFH cells, but not pTFR cells was higher in HIV-infected participants of the MACS and that pTFH cells expressed less CCR5 in HIV-infected MACS participants. Constitutive expression of CCR5 in TFR cells supports their potential to contribute to HIV persistence.

HCV Cure With Direct-Acting Antivirals Improves Liver and Immunological Markers in HIV/HCV-Coinfected Patients

Hepatitis C virus (HCV) cure after all-oral direct-acting antiviral (DAA) therapy greatly improves the liver and immune system. We aimed to assess the impact of this HCV clearance on immune system-related markers in plasma and the gene expression profile in human immunodeficiency virus (HIV)/HCV-coinfected patients with advanced cirrhosis. We performed a prospective study on 33 HIV/HCV-coinfected patients at baseline and 36 weeks after the sustained virological response. Gene expression was evaluated by RNA-seq analysis on peripheral blood mononuclear cells (PBMCs) and plasma biomarkers by multiplex immunoassays. We found a decrease in plasma biomarkers (PD1, PDL1, CXCL10, CXCL8, IL12p70, IL10, and TGFβ) and liver disease markers (stiffness measurement (LSM), hepatic venous pressure gradient (HVPG), and transaminases, among others). Furthermore, decreased plasma levels of CXCL8, CXCL10, IL10, and PD1 were associated with reduced LSM values. We also found two upregulated (HAS1 and IRG1) and 15 downregulated (CXCL11, CCL8, CCL7, CCL2, ADARB2, RRAD, MX1, SIGLEC1, IFI44L, IFI44, IFI27, IFI6, IFIT3, IFIT1B, and IFIT1) genes at the end of follow-up, all interferon-stimulated genes (ISGs) grouped into four pathways (“cytokine-cytokine receptor interaction”, “viral protein interaction with cytokine and cytokine receptor”, “chemokine signaling pathway”, and “hepatitis C”). Additionally, the decrease in most of these ISGs was significantly related to reduced LSM and HVPG values. In conclusion, HIV/HCV-coinfected patients with advanced-HCV-related cirrhosis who eradicated HCV following DAA therapy exhibited an improvement in liver disease markers and a significant decrease in plasma biomarkers and gene expression related to antiviral/inflammatory response, particularly in levels of several chemokines and ISGs.

HCV eradication with IFN-based therapy does not completely restore gene expression in PBMCs from HIV/HCV-coinfected patients

Objective

To evaluate the impact of hepatitis C virus (HCV) elimination via interferon (IFN)-based therapy on gene expression profiles related to the immune system in HIV/HCV-coinfected patients.

Methods

We conducted a prospective study in 28 HIV/HCV-coinfected patients receiving IFN-based therapy at baseline (HIV/HCV-b) and week 24 after sustained virological response (HIV/HCV-f). Twenty-seven HIV-monoinfected patients (HIV-mono) were included as a control. RNA-seq analysis was performed on peripheral blood mononuclear cells (PBMCs). Genes with a fold-change (FC) ≥ 1.5 (in either direction) and false discovery rate (FDR) ≤ 0.05 were identified as significantly differentially expressed (SDE).

Results

HIV/HCV-b showed six SDE genes compared to HIV-mono group, but no significantly enriched pathways were observed. For HIV/HCV-f vs. HIV/HCV-b, we found 58 SDE genes, 34 upregulated and 24 downregulated in the HIV/HCV-f group. Of these, the most overexpressed were CXCL2, PDCD6IP, ATP5B, IGSF9, RAB26, and CSRNP1, and the most downregulated were IFI44 and IFI44L. These 58 SDE genes revealed two significantly enriched pathways (FDR < 0.05), one linked to Epstein-Barr virus infection and another related to p53 signaling. For HIV/HCV-f vs. HIV-mono group, we found 44 SDE genes that revealed 31 enriched pathways (FDR < 0.05) related to inflammation, cancer/cell cycle alteration, viral and bacterial infection, and comorbidities associated with HIV/HCV-coinfection. Five genes were overrepresented in most pathways (JUN, NFKBIA, PIK3R2, CDC42, and STAT3).

Conclusion

HIV/HCV-coinfected patients who eradicated hepatitis C with IFN-based therapy showed profound gene expression changes after achieving sustained virological response. The altered pathways were related to inflammation and liver-related complications, such as non-alcoholic fatty liver disease and hepatocellular carcinoma, underscoring the need for active surveillance for these patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12929-021-00718-6.

Distinct Features of Germinal Center Reactions in Macaques Infected by SIV or Vaccinated with a T-Dependent Model Antigen

B-cell follicles constitute large reservoirs of infectious HIV/SIV associated to follicular dendritic cells and infecting follicular helper (T_FH) and regulatory (T_FR) T-cells in germinal centers (GCs). Thus, follicular and GC B-cells are persistently exposed to viral antigens. Despite recent development of potent HIV immunogens, numerous questions are still open regarding GC reaction during early HIV/SIV infection. Here, we dissect the dynamics of B- and T-cells in GCs of macaques acutely infected by SIV (Group SIV⁺) or vaccinated with Tetanus Toxoid (Group TT), a T-dependent model antigen. Systemic inflammation and mobilization of antigen-presenting cells in inguinal lymph nodes and spleen are lower in Group TT than in Group SIV⁺. Despite spleen GC reaction of higher magnitude in Group SIV^+, the development of protective immunity could be limited by abnormal helper functions of T_FH massively polarized into T_FH1-like cells, by inflammation-induced recruitment of fCD8 (either regulatory or cytotoxic) and by low numbers of T_FR limiting T_FH/T_FR competition for high affinity B-cells. Increased GC B-cells apoptosis and accumulation of CD21^lo memory B-cells, unable to further participate to GC reaction, likely contribute to eliminate SIV-specific B-cells and decrease antibody affinity maturation. Surprisingly, functional GCs and potent TT-specific antibodies develop despite low levels of CXCL13.

Near normalization of peripheral blood markers in HIV-infected patients on long-term suppressive antiretroviral therapy: a case-control study

OBJECTIVE

To explore the differences in peripheral blood markers between HIV well controlled patients on long-term suppressive antiretroviral therapy (HIV-group) and age-matched healthy controls, to evaluate the benefits of virological suppression in those patients.

METHODS

We performed a case-control study in 22 individuals in the HIV-group and 14 in the healthy control-group. RNA-seq analysis was performed from peripheral blood mononuclear cells. Peripheral blood T-cell subsets were evaluated by flow cytometry and plasma biomarkers by immunoassays. All P values were corrected by the false discovery rate (q values).

RESULTS

Only the serine/arginine repetitive matrix 4 gene, which is involved in alternative RNA splicing events, was differentially expressed between HIV and healthy control groups (q value ≤0.05 and fold-change ≥2). However, 147 differentially expressed genes were found with a more relaxed threshold (P value ≤0.05 and fold-change ≥1.5), of which 67 genes with values of variable importance in projection at least one were selected for pathway analysis. We found that six ribosomal genes represented significant ribosome-related pathways, all of them downregulated in the HIV-group, which may be a strategy to facilitate viral production. T cells subset and plasma biomarkers did not show significant differences after false discovery rate correction (q value >0.05), but a noncorrected analysis showed higher values of regulatory CD4 T cells (CD4CD25CD127), MCP-1, and sVEGF-R1 in the HIV-group (P value ≤0.05).

CONCLUSION

T-cell subsets, plasma biomarkers, and gene expression were close to normalization in HIV-infected patients on long-term suppressive combination antiretroviral therapy compared with healthy controls. However, residual alterations remain, mainly at the gene expression, which still reveals the impact of HIV infection in these patients.

Alterations of the frequency and functions of follicular regulatory T cells and related mechanisms in HIV infection

Human immunodeficiency virus (HIV) infection impairs both cellular and humoral immune system. Follicular regulatory T (Tfr) cells are a recently characterised subset of CD4⁺T cells. Tfr also exerts an immunosuppressive effect on humoral immune system through interaction with follicular helper T (Tfh) cells, but the role of Tfr in HIV infection needs to be further elucidated. 20 treatment-naïve and 20 antiretroviral therapy (ART)-treated HIV-infected individuals were enrolled for cross-sectional study and nine complete responders (CRs) and eight immune non-responders (INRs) after ART were collected for retrospective cohort study. Tfr phenotypes, cytokine secretions, and apoptosis of those subjects were evaluated by flow cytometry. HIV DNA was measured by reverse transcription-quantitative PCR (RT-qPCR). Significantly increased circulating Tfr was observed in chronic HIV⁺ patients and the imbalance between Tfr and Tfh17 was associated with CD4⁺T counts. In addition, an elevated proportion of Tfr was associated with immune reconstruction failure of patients after ART. The IL-10 and CTLA-4 expressions of Tfr cells were up-regulated in treatment-naïve HIV⁺ patients. Ex vivo experiments showed IL-10 and CTLA-4 expressed by Tfr inhibited IL-21 secretion of Tfh. Tfr harboured a comparable HIV-1 DNA level with Tfh in HIV⁺ patients. Compared to Tfr of HCs, Tfr cells of HIV⁺ patients were more insensitive to CD95 and IFN-α induced apoptosis, had a higher proliferation rate, and had more stem-like T cell (Tscm) phenotype. The anti-apoptosis feature, higher proliferation rate, and Tscm-like features of Tfr in HIV⁺ patients, led to the expansion of Tfr which in turn resulted in dysfunction of Tfh. Tfr cells were also involved in immune reconstruction failure and latent infection of HIV. Tfr cells were a novel, and potentially therapeutic, target for the cure of HIV infection, especially for HIV vaccine development and HIV reservoir elimination.

Impact of BAFF Blockade on Inflammation, Germinal Center Reaction and Effector B-Cells During Acute SIV Infection

Memory B-cell dysfunctions and inefficient antibody response suggest germinal center (GC) impairments during HIV/SIV infection with possible contribution of overproduced B-cell activating factor (BAFF). To address this question, we compared proportions and functions of various B-cell subsets and follicular helper T-cells (T_FH) in untreated (Placebo) and BR3-Fc treated (Treated) SIV-infected macaques. From day 2 post-infection (dpi), Treated macaques received one weekly injection of BR3-Fc molecule, a soluble BAFF antagonist, for 4 weeks. Whereas, the kinetics of CD4⁺ T-cell loss and plasma viral loads were comparable in both groups, BAFF blockade delayed the peak of inflammatory cytokines (CXCL10, IFNα), impaired the renewal of plasmacytoid dendritic cells and fostered the decline of plasma CXCL13 titers after 14 dpi. In Treated macaques, proportions of total and naïve B-cells were reduced in blood and spleen whereas SIV-induced loss of marginal zone (MZ) B-cells was only accentuated in blood and terminal ileum. Proportions of spleen GC B-cells and T_FH were similar in both groups, with CD8⁺ T-cells and rare Foxp3⁺ being present in spleen GC. Regardless of treatment, sorted T_FH produced similar levels of IL21, CXCL13, and IFNγ but no IL2, IL4, or BAFF and exhibited similar capacities to support IgG production by autologous or heterologous B-cells. Consistently, most T_FH were negative for BAFF-R and TACI. Higher proportions of resting and atypical (CD21^lo) memory B-cells were present in Treated macaques compared to Placebo. In both groups, we found higher levels of BAFF-R expression on MZ and resting memory B-cells but low levels on atypical memory B-cells. TACI was present on 20-30% of MZ, resting and atypical memory B-cells in Placebo macaques. BAFF blockade decreased TACI expression on these B-cell subsets as well as titers of SIV-specific and vaccine-specific antibodies arguing for BAFF being mandatory for plasma cell survival. Irrespective of treatment, GC B-cells expressed BAFF-R at low level and were negative for TACI. In addition to key information on spleen BAFF-R and TACI expression, our data argue for BAFF contributing to the GC reaction in terminal ileum but being dispensable for the generation of atypical memory B-cells and GC reaction in spleen during T-dependent response against SIV.

Mild profile improvement of immune biomarkers in HIV/HCV-coinfected patients who removed hepatitis C after HCV treatment: A prospective study

OBJECTIVE

There are a lack of consistency among articles in regards to the evolution of peripheral immune biomarkers after HCV therapy. We aimed to detect the most relevant changes in peripheral immune biomarkers among HIV/HCV-coinfected patients who achieved sustained virologic response (SVR) following peg-IFN-α/ribavirin therapy and to evaluate its normalization with respect to an HIV-monoinfected control group.

METHODS

We performed a prospective cohort study in 99 HIV/HCV-coinfected patients with samples at baseline (HIV/HCV-b-group) and at week 24 after SVR (HIV/HCV-f-group). We also used a control group of 39 HIV-monoinfected patients (HIV-group) negative for HCV and HBV infections, and who had undetectable HIV viral load and CD4⁺ >500 cells/mm³. Peripheral T cell subsets were assessed by flow cytometry and plasma biomarkers by immunoassays.

RESULTS

HIV/HCV-coinfected patients had higher values of in IL-10, IL-4, IP-10, IL-8, IL-1β, IL-18, IL-6, IFN-γ, IL-12p70, TNF-α, sVCAM-1, sICAM-1, and sTNFR-1 than HIV control subjects, both at the beginning and at the end of follow-up. Moreover, three biomarkers (CD4⁺CD38⁺, telomere length, and IL-1RA) were normalized in relation to the control group at the end of follow-up (the HIV/HCV-b group had higher values and the HIV/HCV-f group had similar values as the HIV-group). Additionally, LPS, IL-2, and IL-17A levels were higher in the HIV/HCV-f group than the HIV-group (24 weeks after SVR). During the follow-up, HIV/HCV-coinfected patients had a significant decrease by the end of follow-up in CD8⁺CD45RA^-CD28⁺, CD4⁺CD38⁺, CD4⁺CD25⁺CD127^-/low, CD4⁺CD25⁺CD127^-/low CD45RA^-, FABP2, LBP, IP-10, sVCAM1. Only CD4⁺CD38⁺ was normalized.

CONCLUSION

HIV/HCV-patients showed a slight improvement in the overall profile of immune biomarkers after achieving SVR.

A rare case of an HIV-seronegative AIDS patient with Pneumocystis jirovecii pneumonia

Background

As technology progresses, several highly sensitive human immunodeficiency virus (HIV) screening kits are being researched and developed to quickly and efficiently identify serum HIV antibodies within the non-window period. In individuals who are HIV-seronegative, HIV infections that are not within a window period are rare. In such cases, all antibody detection methods will fail, and misdiagnosing these patients will have catastrophic consequences.

Case presentation

A 22-year-old male Chinese patient with diffuse exudative lesions in both lungs and initial symptoms of cough and dyspnoea was diagnosed with Pneumocystis jirovecii pneumonia (PJP) by aetiological examination, and the patient’s plasma CD4⁺ T-cell count was extremely low. In China, PJP is prevalent in HIV-infected individuals. Pneumocystis jirovecii (P. jirovecii) has a high colonisation rate in patients with HIV infections. This patient was naturally suspected of being an HIV patient; however, serum HIV antibody tests were negative using both an enzyme-linked immunosorbent assay (ELISA) and a latex agglutination assay, and HIV was not detected by western blotting. Subsequently, the plasma HIV viral load was found to be extremely high on two repeated plasma HIV RNA tests, thus confirming HIV-seronegative acquired immunodeficiency syndrome (AIDS) in this patient. With administration of effective anti-P. jirovecii treatment and highly active antiretroviral therapy (HAART) after diagnosis, the patient’s disease condition was rapidly controlled.

Conclusion

This is the second reported case in China of an HIV-seronegative AIDS patient. Such cases are also rare worldwide. Although HIV-seronegative HIV infections are rare, AIDS should be considered in immunodeficient patients with opportunistic infections, even if the test results are HIV-seronegative. Plasma HIV RNA testing is important for such patients.

Electronic supplementary material

The online version of this article (10.1186/s12879-019-4143-8) contains supplementary material, which is available to authorized users.

Early T Follicular Helper Cell Responses and Germinal Center Reactions Are Associated with Viremia Control in Immunized Rhesus Macaques

T follicular helper (T_FH) cells are fundamental in germinal center (GC) maturation and selection of antigen-specific B cells within secondary lymphoid organs. GC-resident T_FH cells have been fully characterized in human immunodeficiency virus (HIV) infection. However, the role of GC T_FH cells in GC B cell responses following various simian immunodeficiency virus (SIV) vaccine regimens in rhesus macaques (RMs) has not been fully investigated. We characterized GC T_FH cells of RMs over the course of a mucosal/systemic vaccination regimen to elucidate GC formation and SIV humoral response generation. Animals were mucosally primed twice with replicating adenovirus type 5 host range mutant (Ad5hr)-SIV recombinants and systemically boosted with ALVAC-SIV_M766Gag/Pro/gp120-TM and SIV_M766&CG7V gD-gp120 proteins formulated in alum hydroxide (ALVAC/Env) or DNA encoding SIVenv/SIVGag/rhesus interleukin 12 (IL-12) plus SIV_M766&CG7V gD-gp120 proteins formulated in alum phosphate (DNA&Env). Lymph nodes were biopsied in macaque subgroups prevaccination and at day 3, 7, or 14 after the 2nd Ad5hr-SIV prime and the 2nd vector/Env boost. Evaluations of GC T_FH and GC B cell dynamics including correlation analyses supported a significant role for early GC T_FH cells in providing B cell help during initial phases of GC formation. GC T_FH responses at day 3 post-mucosal priming were consistent with generation of Env-specific memory B cells in GCs and elicitation of prolonged Env-specific humoral immunity in the rectal mucosa. GC Env-specific memory B cell responses elicited early post-systemic boosting correlated significantly with decreased viremia postinfection. Our results highlight the importance of early GC T_FH cell responses for robust GC maturation and generation of long-lasting SIV-specific humoral responses at mucosal and systemic sites. Further investigation of GC T_FH cell dynamics should facilitate development of an efficacious HIV vaccine.IMPORTANCE The modest HIV protection observed in the human RV144 vaccine trial associated antibody responses with vaccine efficacy. T follicular helper (T_FH) cells are CD4⁺ T cells that select antibody secreting cells with high antigenic affinity in germinal centers (GCs) within secondary lymphoid organs. To evaluate the role of T_FH cells in eliciting prolonged virus-specific humoral responses, we vaccinated rhesus macaques with a combined mucosal prime/systemic boost regimen followed by repeated low-dose intrarectal challenges with SIV, mimicking human exposure to HIV-1. Although the vaccine regimen did not prevent SIV infection, decreased viremia was observed in the immunized macaques. Importantly, vaccine-induced T_FH responses elicited at day 3 postimmunization and robust GC maturation were strongly associated. Further, early T_FH-dependent SIV-specific B cell responses were also correlated with decreased viremia. Our findings highlight the contribution of early vaccine-induced GC T_FH responses to elicitation of SIV-specific humoral immunity and implicate their participation in SIV control.

Toxoplasma: Immunity and Pathogenesis

Toxoplasma gondii infection induces a strong immunity in the host. Although the response is manifested by innate response during early infection, adaptive immunity is critical for long-term protection. Amongst the adaptive immune response CD4 T cells play an important helper role for CD8 T cells which are the primary effector cells responsible for controlling the infection. Notwithstanding the induction of robust CD8 T immunity during acute infection, the parasite is not eradicated. One of the reasons for this is the functional exhaustion of CD8 T cells during latent infection. Recent studies from our laboratory have reported that primary cause of CD8 T cell exhaustion is compromised CD4 T cell help during latent toxoplasmosis. CD8 T cell dysfunctionality is preceded by CD4 exhaustion and effector immunity is severely compromised.

Effective B cell activation in vitro during viremic HIV-1 infection with surrogate T cell stimulation

Identifying HIV-1-associated B cell defects and responses to activation may direct interventions to circumvent their impaired antibody responses to infection and vaccines. Among 34 viremic HIV-1-infected and 20 seronegative control adults, we measured baseline frequencies and activation of B and T cell subsets, expression of activation-induced cytidine deaminase (AID), potential determinants of B cell activation in vivo and B and T cell responses in vitro. At baseline, HIV-1 infection was associated with increased IgM memory and decreased anergic cell frequencies, as well as increased activation in all 10 B cell subsets compared with controls. HIV-1 status, TFH activation, and BAFF were significant potential drivers of B cell activation. Despite high baseline activation among HIV-1-infected subjects, stimulation in vitro with combined surrogates for antigen (anti-IgM), cognate (CD40 ligand) and soluble T cell factors (IL-4) elicited comparable B cell activation, transitions from naïve to class-switched memory cells and AID expression in both groups. In summary, viremic HIV-1 infection perturbs circulating B cell subsets and activation at each stage of B cell maturation. However, that appropriate stimulation of B cells elicits effective activation and maturation provides impetus for advancing vaccine development to prevent secondary infections by circumventing early B cell defects.

Dysregulation of the Immune System in HIV/HCV-Coinfected Patients According to Liver Stiffness Status

Background: Advanced cirrhosis is related to alterations in immunity. We aimed to evaluate the levels of peripheral CD4⁺ T cells (Tregs) and plasma cytokine in patients coinfected with human immunodeficiency virus and hepatitis C virus (HIV/HCV) according to liver fibrosis stages [evaluated as liver stiffness measure (LSM)] and their linear relationship. Methods: We performed a cross-sectional study on 238 HIV/HCV-coinfected patients (119 had <12.5 kPa, 73 had 12.5–25 kPa, and 46 had >25 kPa). Peripheral T-cell subsets were phenotyped by flow cytometry, plasma biomarkers were assessed by multiplex immunoassays, and LSM was assessed by transient elastography. Results: We found HIV/HCV-coinfected patients had higher values of CD4⁺ Tregs (p < 0.001), memory Tregs (p ≤ 0.001), and plasma cytokine levels [IFN-γ (p ≤ 0.05) and IL-10 (p ≤ 0.01)] compared with healthy donors and HIV-monoinfected patients. In the multivariate analysis, higher LSM values were associated with reduced levels of IL-10 (adjusted arithmetic mean ratio (aAMR) = 0.83; p = 0.019), IL-2 (aAMR = 0.78; p = 0.017), TNF-α (aAMR = 0.67; p < 0.001), and IL-17A (aAMR = 0.75; p = 0.006). When we focus on HIV/HCV-coinfected patients analyzed by LSM strata, patients with ≥25 kPa had lower values of IL-2 (aAMR = 0.66; p = 0.021), TNF-α (aAMR = 0.565; p = 0.003), and IL-17A (aAMR = 0.58; p = 0.003) than patients with <12.5 kPa. Conclusion: HIV/HCV-coinfected patients showed an immunosuppressive profile compared to healthy controls and HIV-monoinfected patients. Additionally, HIV/HCV-coinfected patients with advanced cirrhosis (LSM ≥ 25 kPa) had the lowest plasma values of cytokines related to Th1 (IL-2 and TNF-α) and Th17 (IL-17A) response.

T follicular helper cell development and functionality in immune ageing

By 2050, there will be over 1.6 billion adults aged 65 years and older, making age-related diseases and conditions a growing public health concern. One of the leading causes of death in the ageing population is pathogenic infections (e.g. influenza, Streptococcus pneumoniae). This age-dependent susceptibility to infection has been linked to a reduced ability of the ageing immune system to mount protective responses against infectious pathogens, as well as to vaccines against these pathogens. The primary immune response that promotes protection is the production of antibodies by B cells - a response that is directly mediated by T follicular helper (T_FH) cells within germinal centers (GCs) in secondary lymphoid tissues. In this review, we will summarize the current knowledge on the development and functionality of T_FH cells, the use of circulating T_FH (cT_FH) cells as vaccine biomarkers, and the influence of age on these processes. Moreover, we will discuss the strategies for overcoming T_FH cell dysfunction to improve protective antibody responses in the ageing human population.

The Janus Face of Follicular T Helper Cells in Chronic Viral Infections

Chronic infections with non-cytopathic viruses constitutively expose virus-specific adaptive immune cells to cognate antigen, requiring their numeric and functional adaptation. Virus-specific CD8 T cells are compromised by various means in their effector functions, collectively termed T cell exhaustion. Alike CD8 T cells, virus-specific CD4 Th1 cell responses are gradually downregulated but instead, follicular T helper (T_FH) cell differentiation and maintenance is strongly promoted during chronic infection. Thereby, the immune system promotes antibody responses, which bear less immune-pathological risk compared to cytotoxic and pro-inflammatory T cell responses. This emphasis on T_FH cells contributes to tolerance of the chronic infection and is pivotal for the continued maturation and adaptation of the antibody response, leading eventually to the emergence of virus-neutralizing antibodies, which possess the potential to control the established chronic infection. However, sustained high levels of T_FH cells can also result in a less stringent B cell selection process in active germinal center reactions, leading to the activation of virus-unspecific B cells, including self-reactive B cells, and to hypergammaglobulinemia. This dispersal of B cell help comes at the expense of a stringently selected virus-specific antibody response, thereby contributing to its delayed maturation. Here, we discuss these opposing facets of T_FH cells in chronic viral infections.

Helios + Regulatory T cell frequencies are correlated with control of viral replication and recovery of absolute CD4 T cells counts in early HIV-1 infection

BACKGROUND

The acute phase of HIV infection is characterized by massive depletion of CD4 T cells, high viral plasma levels and pronounced systemic immune activation. Regulatory T cells (Tregs) have the potential to control systemic immune activation but also to suppress antigen specific T and B cell response. The co-expression of FoxP3 and Helios transcription factors, has been described for identification of highly suppressive Tregs. The aim of this study was to characterize the phenotype of classic Tregs during early HIV infection, and to assess the correlations between the frequencies and phenotype of Tregs with the plasma viral load, CD4 counts, immune activation and the frequency of antibodies reactive to HIV-1 proteins, measured by an immunochromatographic test.

RESULTS

The relative frequency of classic Tregs cells in peripheral blood correlated positively with HIV viral load and immune activation of CD8 T cells, and inversely with absolute CD4 counts and development of anti-HIV antibodies in subjects with early HIV infection. However, the expression of Helios in classic Tregs was inversely correlated with viral replication and immune activation, and positively with recovery of CD4 T cell counts and appearance of antibodies reactive to HIV-1 proteins.

CONCLUSION

These results raise the hypothesis that classic Tregs are inefficient at controlling systemic immune activation in subjects with early HIV infection and may be associated with delayed production of antibodies against HIV proteins, delaying the control of viral replication. Conversely, Helios expressing Tregs might contribute to control of viral replication by mechanisms involving the limitation of systemic immune activation.

CD4+ T Cell Differentiation in Chronic Viral Infections: The Tfh Perspective

CD4+ T cells play a critical role in the response to chronic viral infections during the acute phase and in the partial containment of infections once chronic infection is established. As infection persists, the virus-specific CD4+ T cell response begins to shift in phenotype. The predominant change described in both mouse and human studies of chronic viral infection is a decrease in detectable T helper type (Th)1 responses. Some Th1 loss is due to decreased proliferative potential and decreased cytokine production in the setting of chronic antigen exposure. However, recent data suggest that Th1 dysfunction is accompanied by a shift in the differentiation pathway of virus-specific CD4+ T cells, with enrichment for cells with a T follicular helper cell (Tfh) phenotype. A Tfh-like program during chronic infection has now been identified in virus-specific CD8+ T cells as well. In this review, we discuss what is known about CD4+ T cell differentiation in chronic viral infections, with a focus on the emergence of the Tfh program and the implications of this shift with respect to Tfh function and the host-pathogen interaction.

Pathogenesis of infections in HIV-infected individuals: insights from primary immunodeficiencies

Following infection with almost any given microorganism other than an emerging pathogen, only a minority of individuals develop life-threatening clinical disease, implying that these individuals have some form of immunodeficiency. A growing number of inherited and acquired immunodeficiencies have been deciphered over the last 50 years. HIV infection is probably the best-known acquired immunodeficiency. It emerged about 40 years ago and precipitates various severe infections, the occurrence of which is associated with a fall in circulating CD4⁺ T cells. However, despite the strength of this correlation, infection rates differ between patients with similar levels and durations of CD4⁺ T lymphopenia in the presence or absence of antiretroviral treatment. Moreover, a few infections seem to be less dependent on total CD4⁺ T-cell levels. The fine detail of the mechanisms underlying these infections is unknown. We discuss here how studies of the human genetics and immunology of some of these infections in patients with primary immunodeficiencies (PIDs) have provided unique insights into their molecular and cellular basis. Defects of specific CD4⁺ Th-cell subsets account for some of these infections, as best exemplified by Th1* for mycobacteriosis and Th17 for candidiasis. PIDs are individually rare, but collectively much more common than initially thought, with new disorders being discovered at an ever-increasing pace and a global prevalence worldwide approaching that of HIV infection. Studies of known and new PIDs should make it possible to dissect the pathogenesis of most human infections at an unprecedented level of molecular and cellular precision. The predictive, preventive, and therapeutic implications of studies of immunity to infection in PIDs may extend to HIV-infected patients and patients with infectious diseases in other settings.