In Situ Characterization of Human Lymphoid Tissue Immune Cells by Multispectral Confocal Imaging and Quantitative Image Analysis; Implications for HIV Reservoir Characterization

CD4 T cells are key mediators of adaptive immune responses during infection and vaccination. Within secondary lymphoid organs, helper CD4 T cells, particularly those residing in germinal centers known as follicular helper T cells (Tfh), provide critical help to B-cells to promote their survival, isotype switching and selection of high affinity memory B-cells. On the other hand, the important role of Tfh cells for the maintenance of HIV reservoir is well documented. Thus, interrogating and better understanding the tissue specific micro-environment and immune subsets that contribute to optimal Tfh cell differentiation and function is important for designing successful prevention and cure strategies. Here, we describe the development and optimization of eight multispectral confocal microscopy immunofluorescence panels designed for in depth characterization and immune-profiling of relevant immune cells in formalin-fixed paraffin-embedded human lymphoid tissue samples. We provide a comprehensive library of antibodies to use for the characterization of CD4+ T-cells -including Tfh and regulatory T-cells- as well as CD8 T-cells, B-cells, macrophages and dendritic cells and discuss how the resulting multispectral confocal datasets can be quantitatively dissected using the HistoCytometry pipeline to collect information about relative frequencies and immune cell spatial distributions. Cells harboring actively transcribed virus are analyzed using an in-situ hybridization assay for the characterization of HIV mRNA positive cells in combination with additional protein markers (multispectral RNAscope). The application of this methodology to lymphoid tissues offers a means to interrogate multiple relevant immune cell targets simultaneously at increased resolution in a reproducible manner to guide CD4 T-cell studies in infection and vaccination

Follicular CD4 T Helper Cells As a Major HIV Reservoir Compartment: A Molecular Perspective

Effective antiretroviral therapy (ART) has prevented the progression to AIDS and reduced HIV-related morbidities and mortality for the majority of infected individuals. However, a lifelong administration of ART is necessary, placing an inordinate burden on individuals and public health systems. Therefore, discovering therapeutic regimens able to eradicate or functionally cure HIV infection is of great importance. ART interruption leads to viral rebound highlighting the establishment and maintenance of a latent viral reservoir compartment even under long-term treatment. Follicular helper CD4 T cells (TFH) have been reported as a major cell compartment contributing to viral persistence, consequent to their susceptibility to infection and ability to release replication-competent new virions. Here, we discuss the molecular profiles and potential mechanisms that support the role of TFH cells as one of the major HIV reservoirs

T-cell receptor (TCR) usage in HIV-2 infection

Long-term non-progressors (LTPNs) in HIV infection target the structural protein Gag more frequently than individuals who progress to disease. However, the targeting of Gag per se does not always distinguish these two groups. Various factors have been put forth as likely explanations for this discrepancy including differences in the breadth and magnitude of observed responses, the HLA type of the host, the nature of the individual epitopes targeted and the ability of the virus to mutate these antigenic regions. The purpose of this thesis was to examine, using PBMCs isolated from HIV-2 infected LTNPs and CTL clones established in vitro, the clonotypic architecture and quality of an immunodominant HIV-2 Gag-specific response directed towards the HLA-B*3501-restricted epitope NPVPVGNIY (NY9: Gag245-253). The data presented in this thesis show that in spite of the expression of multiple inhibitory receptors on the surface of NY9-specific CD8+ T-cells, the NY9-response, which is a clonotypically 'private' response, bears a signature characterised by an increased cytotoxic sensitivity and the production of an array of cytokines, most notably IFN-γ and MIP-1β. Moreover, the results of this thesis indicate that the NY9-specific CD8+ T-cells are able to cross-recognise and lyse target B-cells pulsed with the corresponding HIV epitope PY9 and its variants at functional avidities (EC50) that are close to those exhibited by PY9-specific T-cells. However, not all mobilised TCR clonotypes are equally sensitive or equally cross-reactive. When individual CTL clones were studied it emerged that dominant clonotypes within the NY9-specific CD8+ T-cell memory pool possessed a higher avidity for tetramer and sensitivity for antigen than subdominant ones and demonstrated a better cross-reactive potential towards variants of the HIV-2 epitope. Hence, future HIV vaccine strategies may benefit from the inclusion of epitopes like NY9, the presentation of which appears to mobilise CD8+ T-cells with superior functional profiles.</p

The role of follicular helper CD4 T cells in the development of HIV-1 specific broadly neutralizing antibody responses

Abstract The induction of HIV-1-specific antibodies that can neutralize a broad number of isolates is a major goal of HIV-1 vaccination strategies. However, to date no candidate HIV-1 vaccine has successfully elicited broadly neutralizing antibodies of sufficient quality and breadth for protection. In this review, we focus on the role of follicular helper CD4 T-cells (Tfh) in the development of such cross-reactive protective antibodies. We discuss germinal center (GC) formation and the dynamics of Tfh and GC B cells during HIV-1/SIV infection and vaccination. Finally, we consider future directions for the study of Tfh and offer perspective on factors that could be modulated to enhance Tfh function in the context of prophylactic vaccination

T-cell receptor (TCR) usage in HIV-2 infection

Long-term non-progressors (LTPNs) in HIV infection target the structural protein Gag more frequently than individuals who progress to disease. However, the targeting of Gag per se does not always distinguish these two groups. Various factors have been put forth as likely explanations for this discrepancy including differences in the breadth and magnitude of observed responses, the HLA type of the host, the nature of the individual epitopes targeted and the ability of the virus to mutate these antigenic regions. The purpose of this thesis was to examine, using PBMCs isolated from HIV-2 infected LTNPs and CTL clones established in vitro, the clonotypic architecture and quality of an immunodominant HIV-2 Gag-specific response directed towards the HLA-B*3501-restricted epitope NPVPVGNIY (NY9: Gag245-253). The data presented in this thesis show that in spite of the expression of multiple inhibitory receptors on the surface of NY9-specific CD8+ T-cells, the NY9-response, which is a clonotypically 'private' response, bears a signature characterised by an increased cytotoxic sensitivity and the production of an array of cytokines, most notably IFN-γ and MIP-1β. Moreover, the results of this thesis indicate that the NY9-specific CD8+ T-cells are able to cross-recognise and lyse target B-cells pulsed with the corresponding HIV epitope PY9 and its variants at functional avidities (EC50) that are close to those exhibited by PY9-specific T-cells. However, not all mobilised TCR clonotypes are equally sensitive or equally cross-reactive. When individual CTL clones were studied it emerged that dominant clonotypes within the NY9-specific CD8+ T-cell memory pool possessed a higher avidity for tetramer and sensitivity for antigen than subdominant ones and demonstrated a better cross-reactive potential towards variants of the HIV-2 epitope. Hence, future HIV vaccine strategies may benefit from the inclusion of epitopes like NY9, the presentation of which appears to mobilise CD8+ T-cells with superior functional profiles.This thesis is not currently available in ORA

Functional differences exist between TNFα promoters encoding the common -237G SNP and the rarer HLA-B*5701-linked A variant.

A large body of functional and epidemiological evidence have previously illustrated the impact of specific MHC class I subtypes on clinical outcome during HIV-1 infection, and these observations have recently been re-iterated in genome wide association studies (GWAS). Yet because of the complexities surrounding GWAS-based approaches and the lack of knowledge relating to the identity of rarer single nucleotide polymorphism (SNP) variants, it has proved difficult to discover independent causal variants associated with favourable immune control. This is especially true of the candidate variants within the HLA region where many of the recently proposed disease influencing SNPs appear to reflect linkage with 'protective' MHC class I alleles. Yet causal MHC-linked SNPs may exist but remain overlooked owing to the complexities associated with their identification. Here we focus on the ancestral TNFα promoter -237A variant (rs361525), shown historically to be in complete linkage disequilibrium with the 'protective' HLA-B*5701 allele. Many of the ancestral SNPs within the extended TNFα promoter have been associated with both autoimmune conditions and disease outcomes, however, the direct role of these variants on TNFα expression remains controversial. Yet, because of the important role played by TNFα in HIV-1 infection, and given the proximity of the -237 SNP to the core promoter, its location within a putative repressor region previously characterized in mice, and its disruption of a methylation-susceptible CpG dinucleotide motif, we chose to carefully evaluate its impact on TNFα production. Using a variety of approaches we now demonstrate that carriage of the A SNP is associated with lower TNFα production, via a mechanism not readily explained by promoter methylation nor the binding of transcription factors or repressors. We propose that the -237A variant could represent a minor causal SNP that additionally contributes to the HLA-B*5701-mediated 'protective' effect during HIV-1 infection

Altered immune cell follicular dynamics in HIV infection following influenza vaccination

HIV infection changes the lymph node (LN) tissue architecture, potentially impairing the immunologic response to antigenic challenge. The tissue-resident immune cell dynamics in virologically suppressed HIV+ patients on combination antiretroviral therapy (cART) are not clear. We obtained LN biopsies before and 10 to 14 days after trivalent seasonal influenza immunization from healthy controls (HCs) and HIV+ volunteers on cART to investigate CD4+ T follicular helper (Tfh) and B cell dynamics by flow cytometry and quantitative imaging analysis. Prior to vaccination, compared with those in HCs, HIV+ LNs exhibited an altered follicular architecture, but harbored higher numbers of Tfh cells and increased IgG+ follicular memory B cells. Moreover, Tfh cell numbers were dependent upon preservation of the follicular dendritic cell (FDC) network and were predictive of the magnitude of the vaccine-induced IgG responses. Interestingly, postvaccination LN samples in HIV+ participants had significantly (P = 0.0179) reduced Tfh cell numbers compared with prevaccination samples, without evidence for peripheral Tfh (pTfh) cell reduction. We conclude that influenza vaccination alters the cellularity of draining LNs of HIV+ persons in conjunction with development of antigen-specific humoral responses. The underlying mechanism of Tfh cell decline warrants further investigation, as it could bear implications for the rational design of HIV vaccines

TNFα promoters encoding the −237A SNP display reduced activity following stimulation in a luciferase reporter assay system.

<p>Jurkat cells were transfected with reporter luciferase plasmids under the control of TNFα promoters carrying either the −237A or G variant. Following 24 hours, transfected cells were stimulated for 4 hours with PMA/ionomycin or left untreated following which reporter gene activity was measured. The data is presented as fold change (in relative light units (RLU)), and represents differences in RLU between stimulated and non-stimulated cells for each of the transfected variants. The cat whisker plots illustrate pooled results obtained from 4 independent transfection assays, where each transfection included 5 replicas, and denotes median luciferase induction, standard deviation, the upper and lower quartiles and the data range. Wilcoxon-Mann-Whitney tests were used for statistical comparisons, and two-tailed P values are indicated.</p

−237A homozygosity associates with reduced TNFα production in PMA-activated B cell lines.

<p>(a) Immortalised BCL lines generated from healthy donors who were −237 AA homozygous (n = 4), −237GG homozygous (n = 11) or GA heterozygous (n = 4) were stimulated for 4 hours with PMA, or left untreated, following which mRNA was isolated for qPCR analysis. TNFα mRNA fold induction (stimulated/non-stimulated) is reported. (b) One million BCLs from −237GG homozygous (n = 11) and GA heterozygous (n = 4) donors were stimulated with PMA for 4 hours, following which soluble TNFα (sTNFα) levels were measured by ELISA. The data is presented as absolute differences in sTNFα secretion in the −237 homozygous versus heterozygous group. (c) Stimulation of TNFα production on a −237AA background was reduced relative to −237GG in the presence of different stimuli. The data is presented as absolute differences in soluble TNFα secretion (pg/ml) for a single −237GG and −237AA homozygous BCL line. Wilcoxon-Mann-Whitney tests were used for statistical comparisons, and two-tailed P values are indicated in (a) and (b).</p