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Assessment of the Synaptic Interface of Primary Human T Cells from Peripheral Blood and Lymphoid Tissue

The current understanding of the dynamics and structural features of T-cell synaptic interfaces has been largely determined through the use of ...

Perelman School of Medicine, University of Pennsylvania

Elimination of lymphoid tissue reservoirs is a key component of HIV eradication strategies. CD8 T cells play a critical role in control of HIV, but their functional attributes in lymph nodes (LNs) remain unclear. Here, we show that memory, follicular CXCR5, and HIV-specific CD8 T cells from LNs do not manifest the properties of cytolytic CD8 T cells. While the frequency of follicular CXCR5 CD8 T cells was strongly inversely associated with peripheral viremia, this association was not dependent on cytolytic CXCR5 CD8 T cells. Moreover, the poor cytolytic activity of LN CD8 T cells was linked to a compartmentalized dissociation between effector programming and the transcription factor T-bet. In line with this, activation of LN CD8 T cells only partially induced the acquisition of cytolytic functions relative to peripheral blood CD8 T cells. These results suggest that a state of immune privilege against CD8 T cell-mediated cytolysis exists in lymphoid tissue, potentially facilitating the persistence of HIV.

HIV-Specific CD8 T Cells Exhibit Reduced and Differentially Regulated Cytolytic Activity in Lymphoid Tissue.

The persistence of HIV reservoirs, including latently infected, resting CD4 T cells, is the major obstacle to cure HIV infection. CD32a expression was recently reported to mark CD4 T cells harboring a replication-competent HIV reservoir during antiretroviral therapy (ART) suppression. We aimed to determine whether CD32 expression marks HIV latently or transcriptionally active infected CD4 T cells. Using peripheral blood and lymphoid tissue of ART-treated HIV or SIV subjects, we found that most of the circulating memory CD32 CD4 T cells expressed markers of activation, including CD69, HLA-DR, CD25, CD38, and Ki67, and bore a T2 phenotype as defined by CXCR3, CCR4, and CCR6. CD32 expression did not selectively enrich for HIV- or SIV-infected CD4 T cells in peripheral blood or lymphoid tissue; isolated CD32 resting CD4 T cells accounted for less than 3% of the total HIV DNA in CD4 T cells. Cell-associated HIV DNA and RNA loads in CD4 T cells positively correlated with the frequency of CD32 CD69 CD4 T cells but not with CD32 expression on resting CD4 T cells. Using RNA fluorescence in situ hybridization, CD32 coexpression with HIV RNA or p24 was detected after in vitro HIV infection (peripheral blood mononuclear cell and tissue) and in vivo within lymph node tissue from HIV-infected individuals. Together, these results indicate that CD32 is not a marker of resting CD4 T cells or of enriched HIV DNA-positive cells after ART; rather, CD32 is predominately expressed on a subset of activated CD4 T cells enriched for transcriptionally active HIV after long-term ART.

CD32 is expressed on cells with transcriptionally active HIV but does not enrich for HIV DNA in resting T cells.

Current paradigms of CD8 T cell-mediated protection in HIV infection center almost exclusively on studies of peripheral blood, which is thought to provide a window into immune activity at the predominant sites of viral replication in lymphoid tissues (LTs). Through extensive comparison of blood, thoracic duct lymph (TDL), and LTs in different species, we show that many LT memory CD8 T cells bear phenotypic, transcriptional, and epigenetic signatures of resident memory T cells (T). Unlike their circulating counterparts in blood or TDL, most of the total and follicular HIV-specific CD8 T cells in LTs also resemble T Moreover, high frequencies of HIV-specific CD8 T with skewed clonotypic profiles relative to matched blood samples are present in LTs of individuals who spontaneously control HIV replication in the absence of antiretroviral therapy (elite controllers). Single-cell RNA sequencing analysis confirmed that HIV-specific T are enriched for effector-related immune genes and signatures compared with HIV-specific non-T in elite controllers. Together, these data indicate that previous studies in blood have largely failed to capture the major component of HIV-specific CD8 T cell responses resident within LTs.

Michael R. Betts

Department of Microbiology and Institute for Immunology

Perelman School of Medicine, University of Pennsylvania

Assessment of the Synaptic Interface of Primary Human T Cells from Peripheral Blood and Lymphoid Tissue

Michael R. Betts

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Department of Microbiology and Institute for Immunology

Perelman School of Medicine, University of Pennsylvania

Assessment of the Synaptic Interface of Primary Human T Cells from Peripheral Blood and Lymphoid Tissue

Department of Microbiology and Institute for Immunology