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HIV-1 causes CD4 + T-cell death through viral integration by stimulation of DNA-dependent protein kinase (DNA-PK), a protein known to act in the p53 damage response pathway for double-stranded DNA breaks, in activated cells. How HIV-1 causes cell death It is known that CD4 + helper T cells, key immune regulators, are eliminated by HIV-1 infection, but how the virus causes cell death has been unclear. Here Gary Nabel and colleagues show that HIV-1 integration is both necessary and sufficient to trigger CD4 + T-cell death, and that integration triggers cell death through activation of DNA-dependent protein kinase (DNA-PK), part of the DNA repair mechanism, and phosphorylation of p53. This work may help to explain how reservoirs of virus are established in HIV-infected subjects, and suggests that treatment with integrase or DNA-PK inhibitors might prolong CD4 cell survival and delay the development of AIDS. Human immunodeficiency virus-1 (HIV-1) has infected more than 60 million people and caused nearly 30 million deaths worldwide 1 , ultimately the consequence of cytolytic infection of CD4 + T cells. In humans and in macaque models, most of these cells contain viral DNA and are rapidly eliminated at the peak of viraemia 2 , 3 , 4 , yet the mechanism by which HIV-1 induces helper T-cell death has not been defined. Here we show that virus-induced cell killing is triggered by viral integration. Infection by wild-type HIV-1, but not an integrase-deficient mutant, induced the death of activated primary CD4 lymphocytes. Similarly, raltegravir, a pharmacologic integrase inhibitor, abolished HIV-1-induced cell killing both in cell culture and in CD4 + T cells from acutely infected subjects. The mechanism of killing during viral integration involved the activation of DNA-dependent protein kinase (DNA-PK), a central integrator of the DNA damage response, which caused phosphorylation of p53 and histone H2AX. Pharmacological inhibition of DNA-PK abolished cell death during HIV-1 infection in vitro , suggesting that processes which reduce DNA-PK activation in CD4 cells could facilitate the formation of latently infected cells that give rise to reservoirs in vivo . We propose that activation of DNA-PK during viral integration has a central role in CD4 + T-cell depletion, raising the possibility that integrase inhibitors and interventions directed towards DNA-PK may improve T-cell survival and immune function in infected individuals.

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.

Follicles (Fs)/Germinal Centers (GCs) in tonsils and lymph nodes are dynamic microenvironments where diverse immune cell populations interact for the development of antibody responses against pathogens. The accurate in situ phenotypic analysis of these immune cells is a prerequisite for the comphehensive understanding of GC development. In this study, we explore unsupervised clustering approaches for distinguishing cell populations within F/GCs using marker expression data. We evaluate multiple clustering algorithms and find that k-means clustering provides the most effective separation of distinct cell subsets. Additionally, we investigate the predictive potential of common GC markers (CD3, CD4, CD20 and BCL6) for PD-1 expression, an important immune checkpoint regulator. Our analysis demonstrates that PD-1 expression can be reliably inferred using these markers, suggesting potential applications for automated cell classification in immunological studies. This approach enhances our ability to analyze immune cell heterogeneity and may contribute to improved understanding of GC dynamics in health and disease. Our findings support the use of computational clustering for high-dimensional immune profiling.

The interaction between follicular T helper cells (TFH) and B cells in the lymph nodes and spleen has a major impact on the development of antigen-specific B cell responses during infection or vaccination. Recent studies described a functional equivalent of these cells among circulating CD4 T cells, referred to as peripheral TFH cells. Here, we characterize the phenotype and in vitro B cell helper activity of peripheral TFH populations, as well as the effect of HIV infection on these populations. In co-culture experiments we confirmed CXCR5+ cells from HIV-uninfected donors provide help to B cells and more specifically, we identified a CCR7(high)CXCR5(high)CCR6(high)PD-1(high) CD4 T cell population that secretes IL-21 and enhances isotype-switched immunoglobulin production. This population is significantly decreased in treatment-naïve, HIV-infected individuals and can be recovered after anti-retroviral therapy. We found impaired immunoglobulin production in co-cultures from HIV-infected individuals and found no correlation between the frequency of peripheral TFH cells and memory B cells, or with neutralization activity in untreated HIV infection in our cohort. Furthermore, we found that within the peripheral TFH population, the expression level of TFH-associated genes more closely resembles a memory, non-TFH population, as opposed to a TFH population. Overall, our data identify a heterogeneous population of circulating CD4 T cells that provides in vitro help to B cells, and challenges the origin of these cells as memory TFH cells.

The continuous development of molecular biology and protein engineering technologies enables the expansion of the breadth and complexity of protein therapeutics for administration. However, the immunogenicity and associated development of antibodies against therapeutics are a major restriction factor for their usage. The B cell follicular and particularly germinal center areas in secondary lymphoid organs are the anatomical sites where the development of antibody responses against pathogens and immunogens takes place. A growing body of data has revealed the importance of the orchestrated function of highly differentiated adaptive immunity cells, including follicular helper CD4 T cells and germinal center B cells, for the optimal generation of these antibody responses. Understanding the cellular and molecular mechanisms mediating the antibody responses against therapeutics could lead to novel strategies to reduce their immunogenicity and increase their efficacy.

Therapeutic monoclonal antibodies (mAb) targeting the immune checkpoint inhibitor programmed cell death protein 1 (PD-1) have achieved considerable clinical success in anti-cancer therapy through relieving T cell exhaustion. Blockade of PD-1 interaction with its ligands PD-L1 and PD-L2 is an important determinant in promoting the functional recovery of exhausted T cells. Here, we show that anti-PD-1 mAbs act through an alternative mechanism leading to the downregulation of PD-1 surface expression on memory CD4 + and CD8 + T cells. PD-1 receptor downregulation is a distinct process from receptor endocytosis and occurs in a CD14 + monocyte dependent manner with the CD64/Fcγ receptor I acting as the primary factor for this T cell extrinsic process. Importantly, downregulation of surface PD-1 strongly enhances antigen-specific functional recovery of exhausted PD-1 + CD8 + T cells. Our study demonstrates a novel mechanism for reducing cell surface levels of PD-1 and limiting the inhibitory targeting by PD-L1/2 and thereby enhancing the efficacy of anti-PD-1 Ab in restoring T cell functionality.

Agents that can simultaneously activate latent HIV, increase immune activation and enhance the killing of latently-infected cells represent promising approaches for HIV cure. Here, we develop and evaluate a trispecific antibody (Ab), N6/αCD3-αCD28, that targets three independent proteins: (1) the HIV envelope via the broadly reactive CD4-binding site Ab, N6; (2) the T cell antigen CD3; and (3) the co-stimulatory molecule CD28. We find that the trispecific significantly increases antigen-specific T-cell activation and cytokine release in both CD4 + and CD8 + T cells. Co-culturing CD4 + with autologous CD8 + T cells from ART-suppressed HIV + donors with N6/αCD3-αCD28, results in activation of latently-infected cells and their elimination by activated CD8 + T cells. This trispecific antibody mediates CD4 + and CD8 + T-cell activation in non-human primates and is well tolerated in vivo. This HIV-directed antibody therefore merits further development as a potential intervention for the eradication of latent HIV infection. One of the main hurdles to curing HIV infection are viral reservoirs. Here, the authors develop a trispecific antibody and demonstrate its ability to simultaneously activate and target latently HIV−1 infected cells for elimination by T cells as an alternative strategy for HIV cure.

Anti-HIV-1 broadly neutralizing antibodies (bNAbs) have the dual potential of mediating virus neutralization and antiviral effector functions through their Fab and Fc domains, respectively. So far, bNAbs with enhanced Fc effector functions in vitro have only been tested in NHPs during chronic simian-HIV (SHIV) infection. Here, we investigate the effects of administering in acute SHIV AD8-EO infection either wild-type (WT) bNAbs or bNAbs carrying the S239D/I332E/A330L (DEL) mutation, which increases binding to FcγRs. Emergence of virus in plasma and lymph nodes (LNs) was delayed by bNAb treatment and occurred earlier in monkeys given DEL bNAbs than in those given WT bNAbs, consistent with faster clearance of DEL bNAbs from plasma. DEL bNAb-treated monkeys had higher levels of circulating virus-specific IFNγ single-producing CD8 + CD69 + T cells than the other groups. In LNs, WT bNAbs were evenly distributed between follicular and extrafollicular areas, but DEL bNAbs predominated in the latter. At week 8 post-challenge, LN monocytes and NK cells from DEL bNAb-treated monkeys upregulated proinflammatory signaling pathways and LN T cells downregulated TNF signaling via NF-κB. Overall, bNAbs with increased affinity to FcγRs shape innate and adaptive cellular immunity, which may be important to consider in future strategies of passive bNAb therapy. In this work, the authors study the immunological and virological effects of administering either wild-type anti-HIV-1 broadly neutralizing antibodies (bNAbs) or bNAbs with a mutation that increases binding to Fc-gamma receptors (FcγRs) to rhesus macaques in the acute phase of SHIV AD8-EO infection.