The monoclonal antibodies ipilimumab (anti-CTLA-4) and nivolumab (anti-PD-1) have shown remarkable antitumor activity in an increasing number of cancers. When combined, ipilimumab and nivolumab have demonstrated superior activity in patients with metastatic melanoma (CHECKMATE-067). Here we describe the preclinical development strategy that predicted these clinical results. Synergistic antitumor activity in mouse MC38 and CT26 colorectal tumor models was observed with concurrent, but not sequential CTLA-4 and PD-1 blockade. Significant antitumor activity was maintained using a fixed dose of anti-CTLA-4 antibody with decreasing doses of anti-PD-1 antibody in the MC38 model. Immunohistochemical and flow cytometric analyses confirmed that CD3+ T cells accumulated at the tumor margin and infiltrated the tumor mass in response to the combination therapy, resulting in favorable effector and regulatory T-cell ratios, increased pro-inflammatory cytokine secretion, and activation of tumor-specific T cells. Similarly, in vitro studies with combined ipilimumab and nivolumab showed enhanced cytokine secretion in superantigen stimulation of human peripheral blood lymphocytes and in mixed lymphocyte response assays. In a cynomolgus macaque toxicology study, dose-dependent immune-related gastrointestinal inflammation was observed with the combination therapy; this response had not been observed in previous single agent cynomolgus studies. Together, these in vitro assays and in vivo models comprise a preclinical strategy for the identification and development of highly effective antitumor combination immunotherapies.

The immune system influences the fate of developing cancers by not only functioning as a tumour promoter that facilitates cellular transformation, promotes tumour growth and sculpts tumour cell immunogenicity, but also as an extrinsic tumour suppressor that either destroys developing tumours or restrains their expansion. Yet, clinically apparent cancers still arise in immunocompetent individuals in part as a consequence of cancer-induced immunosuppression. In many individuals, immunosuppression is mediated by cytotoxic T-lymphocyte associated antigen-4 (CTLA-4) and programmed death-1 (PD-1), two immunomodulatory receptors expressed on T cells. Monoclonal-antibody-based therapies targeting CTLA-4 and/or PD-1 (checkpoint blockade) have yielded significant clinical benefits-including durable responses--to patients with different malignancies. However, little is known about the identity of the tumour antigens that function as the targets of T cells activated by checkpoint blockade immunotherapy and whether these antigens can be used to generate vaccines that are highly tumour-specific. Here we use genomics and bioinformatics approaches to identify tumour-specific mutant proteins as a major class of T-cell rejection antigens following anti-PD-1 and/or anti-CTLA-4 therapy of mice bearing progressively growing sarcomas, and we show that therapeutic synthetic long-peptide vaccines incorporating these mutant epitopes induce tumour rejection comparably to checkpoint blockade immunotherapy. Although mutant tumour-antigen-specific T cells are present in progressively growing tumours, they are reactivated following treatment with anti-PD-1 and/or anti-CTLA-4 and display some overlapping but mostly treatment-specific transcriptional profiles, rendering them capable of mediating tumour rejection. These results reveal that tumour-specific mutant antigens are not only important targets of checkpoint blockade therapy, but they can also be used to develop personalized cancer-specific vaccines and to probe the mechanistic underpinnings of different checkpoint blockade treatments.

While a fraction of cancer patients treated with anti-PD-1 show durable therapeutic responses, most remain unresponsive, highlighting the need to better understand and improve these therapies. Using an in vivo screening approach with a customized shRNA pooled library, we identified DDR2 as a leading target for the enhancement of response to anti-PD-1 immunotherapy. Using isogenic in vivo murine models across five different tumor histologies-bladder, breast, colon, sarcoma, and melanoma-we show that DDR2 depletion increases sensitivity to anti-PD-1 treatment compared to monotherapy. Combination treatment of tumor-bearing mice with anti-PD-1 and dasatinib, a tyrosine kinase inhibitor of DDR2, led to tumor load reduction. RNA-seq and CyTOF analysis revealed higher CD8+ T cell populations in tumors with DDR2 depletion and those treated with dasatinib when either was combined with anti-PD-1 treatment. Our work provides strong scientific rationale for targeting DDR2 in combination with PD-1 inhibitors.

Triple-negative breast cancer (TNBC) is an aggressive and molecularly diverse breast cancer subtype typified by the presence of p53 mutations (∼80%), elevated immune gene signatures and neoantigen expression, as well as the presence of tumor infiltrating lymphocytes (TILs). As these factors are hypothesized to be strong immunologic prerequisites for the use of immune checkpoint blockade (ICB) antibodies, multiple clinical trials testing single ICBs have advanced to Phase III, with early indications of heterogeneous response rates of <20% to anti-PD1 and anti-PDL1 ICB. While promising, these modest response rates highlight the need for mechanistic studies to understand how different ICBs function, how their combination impacts functionality and efficacy, as well as what immunologic parameters predict efficacy to different ICBs regimens in TNBC. To address these issues, we tested anti-PD1 and anti-CTLA4 in multiple models of TNBC and found that their combination profoundly enhanced the efficacy of either treatment alone. We demonstrate that this efficacy is due to anti-CTLA4-driven expansion of an individually unique T-cell receptor (TCR) repertoire whose functionality is enhanced by both intratumoral Treg suppression and anti-PD1 blockade of tumor expressed PDL1. Notably, the individuality of the TCR repertoire was observed regardless of whether the tumor cells expressed a nonself antigen (ovalbumin) or if tumor-specific transgenic T-cells were transferred prior to sequencing. However, responsiveness was strongly correlated with systemic measures of tumor-specific T-cell and B-cell responses, which along with systemic assessment of TCR expansion, may serve as the most useful predictors for clinical responsiveness in future clinical trials of TNBC utilizing anti-PD1/anti-CTLA4 ICB.

Expression of cytotoxic T-lymphocyte antigen 4 (CTLA-4), a negative regulator of T-cell function, is increased in chronic HIV-1 infection. It was hypothesized that CTLA-4 blockade may enhance immune response to HIV-1 and result in better control of viremia. This open-label, multiple ascending dose study (NCT03407105)-the first to examine ipilimumab in participants with HIV-1 infection-assessed the safety, tolerability, and pharmacokinetics of ipilimumab, as well as whether ipilimumab enhanced immune response to HIV-1 and improved control of viremia. Twenty-four participants received 2 or 4 doses of ipilimumab (0.1, 1, 3, or 5 mg/kg) every 28 days. No serious adverse events (AEs) or dose-limiting toxicities were reported; one participant discontinued ipilimumab for an AE of grade 2 facial palsy. Twenty participants (83.3%) had ≥1 AE; all but 1 were grade 1 or 2. Eight participants (33.3%) had potentially immune-related AEs (7 had grade 1 diarrhea not requiring corticosteroids; 1 who had diarrhea also had transient antinuclear antibody positivity; 1 had grade 2 facial palsy requiring corticosteroids). Two participants (8.3%), one each in the 0.1- and 1-mg/kg dose groups, had a decrease from baseline HIV-1 RNA of 0.85 and 1.36 log10 copies/mL. Fourteen participants (58.3%) had an increase from baseline HIV-1 RNA (mean, 0.87 log10 copies/mL; range, 0.59-1.29). Of these 14 participants, all but 1 were in the higher ipilimumab dose groups (3 or 5 mg/kg). No pattern was noted regarding change from baseline in CD4 or CD8 T cells; ex vivo assessments of immune response were precluded because of inadequate cell viability. Serum concentration data for ipilimumab showed biphasic disposition, with steady state reached by dose 3. Ipilimumab treatment was well tolerated and was associated with variations in HIV-1 RNA in excess of expected repeat measures in most participants, but these were not related to combination antiretroviral therapy status or CD4 counts. The mechanism(s) underlying the increased variation in HIV-1 RNA is unclear and needs further study.

Expression of the programmed death 1 (PD-1) receptor and its ligands are implicated in the T cell exhaustion phenotype which contributes to the persistence of several chronic viral infections, including human hepatitis C virus (HCV). The antiviral potential of BMS-936558 (MDX-1106) - a fully human anti-PD-1 monoclonal immunoglobulin-G4 that blocks ligand binding - was explored in a proof-of-concept, placebo-controlled single-ascending-dose study in patients (N = 54) with chronic HCV infection. Interferon-alfa treatment-experienced patients (n = 42) were randomized 5∶1 to receive a single infusion of BMS-936558 (0.03, 0.1, 0.3, 1.0, 3.0 mg/kg [n = 5 each] or 10 mg/kg [n = 10]) or of placebo (n = 7). An additional 12 HCV treatment-naïve patients were randomized to receive 10 mg/kg BMS-936558 (n = 10) or placebo (n = 2). Patients were followed for 85 days post-dose. Five patients who received BMS-936558 (0.1 [n = 1] or 10 mg/kg) and one placebo patient achieved the primary study endpoint of a reduction in HCV RNA ≥0.5 log10 IU/mL on at least 2 consecutive visits; 3 (10 mg/kg) achieved a >4 log10 reduction. Two patients (10 mg/kg) achieved HCV RNA below the lower limit of quantitation (25 IU/mL), one of whom (a prior null-responder) remained RNA-undetectable 1 year post-study. Transient reductions in CD4(+), CD8(+) and CD19(+) cells, including both naïve and memory CD4(+) and CD8(+) subsets, were observed at Day 2 without evidence of immune deficit. No clinically relevant changes in immunoglobulin subsets or treatment-related trends in circulating cytokines were noted. BMS-936558 exhibited dose-related exposure increases, with a half-life of 20-24 days. BMS-936558 was mostly well tolerated. One patient (10 mg/kg) experienced an asymptomatic grade 4 ALT elevation coincident with the onset of a 4-log viral load reduction. Six patients exhibited immune-related adverse events of mild-to-moderate intensity, including two cases of hyperthyroidism consistent with autoimmune thyroiditis. Further investigation of PD-1 pathway blockade in chronic viral disease is warranted.

Cyclin D1 overexpression is associated with mantle cell lymphoma and multiple myeloma. In myeloma, it often results from chromosomal translocations linking the CCND1 gene to the 3' part of the IgH locus constant region. This region includes a single and potent transcriptional regulatory region (RR) 3' of the Calpha gene mostly active in mature B-cells. To check whether this RR alone was sufficient to deregulate CCND1, we generated mice carrying a 3'IgH RR-driven human CCND1 transgene and specifically up-regulating cyclin D1 expression in B-cells. In transgenic B-cells, cyclin D1 enforced cell cycle entry in response to various stimuli (LPS, anti-IgM, anti-CD40) but also increased cell death, so that exaggerated proliferation did not result in peripheral lymphocytosis. Despite exaggerated B-cell entry into G(1) phase, malignant lymphoproliferation did not occur either. Crossing of CCND1-3'IgH RR mice with c-myc-3'IgH RR mice did not reveal accelerated tumorigenesis as compared with c-myc-3'IgH RR mice alone. The data presented here demonstrate that the 3'IgH RR-mediated deregulation of CCND1 in mature B-cells cannot by itself trigger the development of lymphomas and strengthen the concept that cyclin D1 per se is not an armful proto-oncogene. Rather its overexpression in several malignancies might be only a stigma of lymphomagenesis or represent a single hit within a multiple hit process.

The HVEM (TNFRSF14) receptor gene is among the most frequently mutated genes in germinal center lymphomas. We report that loss of HVEM leads to cell-autonomous activation of B cell proliferation and drives the development of GC lymphomas in vivo. HVEM-deficient lymphoma B cells also induce a tumor-supportive microenvironment marked by exacerbated lymphoid stroma activation and increased recruitment of T follicular helper (TFH) cells. These changes result from the disruption of inhibitory cell-cell interactions between the HVEM and BTLA (B and T lymphocyte attenuator) receptors. Accordingly, administration of the HVEM ectodomain protein (solHVEM(P37-V202)) binds BTLA and restores tumor suppression. To deliver solHVEM to lymphomas in vivo, we engineered CD19-targeted chimeric antigen receptor (CAR) T cells that produce solHVEM locally and continuously. These modified CAR-T cells show enhanced therapeutic activity against xenografted lymphomas. Hence, the HVEM-BTLA axis opposes lymphoma development, and our study illustrates the use of CAR-T cells as "micro-pharmacies" able to deliver an anti-cancer protein.

Heparanase (HPSE) is an endoglycosidase that cleaves heparan sulfate and has been shown in various cancers to promote metastasis, angiogenesis, osteolysis, and chemoresistance. Although heparanase is thought to act predominantly extracellularly or within the cytoplasm, it is also present in the nucleus, where it may function in regulating gene transcription. Using myeloma cell lines, we report here that heparanase enhances chromatin accessibility and confirm a previous report that it also upregulates the acetylation of histones. Employing the Multiple Myeloma Research Foundation CoMMpass database, we demonstrate that patients expressing high levels of heparanase display elevated expression of proteins involved in chromatin remodeling and several oncogenic factors compared to patients expressing low levels of heparanase. These signatures were consistent with the known function of heparanase in driving tumor progression. Chromatin opening and downstream target genes were abrogated by inhibition of heparanase. Enhanced levels of heparanase in myeloma cells led to a dramatic increase in phosphorylation of PTEN, an event known to stabilize PTEN, leading to its inactivity and loss of tumor suppressor function. Collectively, this study demonstrates that heparanase promotes chromatin opening and transcriptional activity, some of which likely is through its impact on diminishing PTEN tumor suppressor activity.

Advanced ovarian cancer (OC) patients have a poor 5-year survival of only 28%, emphasizing the medical need for improved therapies. Adjuvant immunotherapy could be an attractive approach since OC is an immunogenic disease and the presence of tumor-infiltrating lymphocytes has shown to positively correlate with patient survival. Among these infiltrating lymphocytes are natural killer (NK) cells, key players involved in tumor targeting, initiated by signaling via activating and inhibitory receptors. Here, we investigated the role of the DNAM-1/TIGIT/CD96 axis in the anti-tumor response of NK cells toward OC. Ascites-derived NK cells from advanced OC patients showed lower expression of activating receptor DNAM-1 compared to healthy donor peripheral blood NK cells, while inhibitory receptor TIGIT and CD96 expression was equal or higher, respectively. This shift to a more inhibitory phenotype could also be induced in vitro by co-culturing healthy donor NK cells with OC tumor spheroids, and in vivo on intraperitoneally infused NK cells in SKOV-3 OC bearing NOD/SCID-IL2Rγnull (NSG) mice. Interestingly, TIGIT blockade enhanced degranulation and interferon gamma (IFNγ) production of healthy donor CD56dim NK cells in response to OC tumor cells, especially when DNAM-1/CD155 interactions were in place. Importantly, TIGIT blockade boosted functional responsiveness of CD56dim NK cells of OC patients with a baseline reactivity against SKOV-3 cells. Overall, our data show for the first time that checkpoint molecules TIGIT/DNAM-1/CD96 play an important role in NK cell responsiveness against OC, and provides rationale for incorporating TIGIT interference in NK cell-based immunotherapy in OC patients.

Lymphoid stromal cells (LSCs) are essential organizers of immune responses. We analyzed tonsillar tissue by combining flow cytometry, in situ imaging, RNA sequencing, and functional assays, defining three distinct human LSC subsets. The integrin CD49a designated perivascular stromal cells exhibiting features of local committed LSC precursors and segregated cytokine and chemokine-producing fibroblastic reticular cells (FRCs) supporting B and T cell survival. The follicular dendritic cell transcriptional profile reflected active responses to B cell and non-B cell stimuli. We therefore examined the effect of B cell stimuli on LSCs in follicular lymphoma (FL). FL B cells interacted primarily with CD49a+ FRCs. Transcriptional analyses revealed LSC reprogramming in situ downstream of the cytokines tumor necrosis factor (TNF) and transforming growth factor β (TGF-β), including increased expression of the chemokines CCL19 and CCL21. Our findings define human LSC populations in healthy tissue and reveal bidirectional crosstalk between LSCs and malignant B cells that may present a targetable axis in lymphoma.

Novel therapeutic approaches combining immune-checkpoint inhibitors are needed to improve clinical outcomes for patients with cancer. Lymphocyte-activation gene 3 (LAG-3) is an immune-checkpoint molecule that inhibits T-cell activity and antitumor immune responses, acting through an independent mechanism from that of programmed death-1 (PD-1) and cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4). Here, we describe the development and preclinical characterization of relatlimab, a human antibody that binds to human LAG-3 with high affinity and specificity to block the interaction of LAG-3 with the ligands MHC II and fibrinogen-like protein-1, and to reverse LAG-3-mediated inhibition of T-cell function in vitro. Consistent with previous reports, in mouse models, the combined blockade of LAG-3 and PD-1 with surrogate antibodies resulted in enhanced antitumor activity greater than the individual blockade of either receptor. In toxicity studies in cynomolgus monkeys, relatlimab was generally well tolerated when combined with nivolumab. These results are consistent with findings from the RELATIVITY-047 phase II/III trial showing that relatlimab combined with nivolumab is a well-tolerated regimen that demonstrates superior progression-free survival compared with nivolumab monotherapy in patients with unresectable or metastatic melanoma.

While engagement of the inhibitory Fcγ-receptor (FcγR) IIB is an absolute requirement for in vivo antitumor activity of agonistic mouse anti-CD40 monoclonal antibodies (mAbs), a similar requirement for human mAbs has been disputed. By using a mouse model humanized for its FcγRs and CD40, we revealed that FcγRIIB engagement is essential for the activity of human CD40 mAbs, while engagement of the activating FcγRIIA inhibits this activity. By engineering Fc variants with selective enhanced binding to FcγRIIB, but not to FcγRIIA, significantly improved antitumor immunity was observed. These findings highlight the necessity of optimizing the Fc domain for this class of therapeutic antibodies by using appropriate preclinical models that accurately reflect the unique affinities and cellular expression of human FcγR.

Despite advancements in targeting the immune checkpoints program cell death protein 1 (PD-1), programmed death ligand 1 (PD-L1), and cytotoxic T lymphocyte-associated protein 4 (CTLA-4) for cancer immunotherapy, a large number of patients and cancer types remain unresponsive. Current immunotherapies focus on modulating an antitumor immune response by directly or indirectly expanding antitumor CD8 T cells. A complementary strategy might involve inhibition of Tregs that otherwise suppress antitumor immune responses. Here, we sought to identify functional immune molecules preferentially expressed on tumor-infiltrating Tregs. Using genome-wide RNA-Seq analysis of purified Tregs sorted from multiple human cancer types, we identified a conserved Treg immune checkpoint signature. Using immunocompetent murine tumor models, we found that antibody-mediated depletion of 4-1BB-expressing cells (4-1BB is also known as TNFRSF9 or CD137) decreased tumor growth without negatively affecting CD8 T cell function. Furthermore, we found that the immune checkpoint 4-1BB had a high selectivity for human tumor Tregs and was associated with worse survival outcomes in patients with multiple tumor types. Thus, antibody-mediated depletion of 4-1BB-expressing Tregs represents a strategy with potential activity across cancer types.

CD4+ T cells provide adaptive immunity against pathogens and abnormal cells, and they are also associated with various immune-related diseases. CD4+ T cells' metabolism is dysregulated in these pathologies and represents an opportunity for drug discovery and development. Genome-scale metabolic modeling offers an opportunity to accelerate drug discovery by providing high-quality information about possible target space in the context of a modeled disease. Here, we develop genome-scale models of naïve, Th1, Th2, and Th17 CD4+ T-cell subtypes to map metabolic perturbations in rheumatoid arthritis, multiple sclerosis, and primary biliary cholangitis. We subjected these models to in silico simulations for drug response analysis of existing FDA-approved drugs and compounds. Integration of disease-specific differentially expressed genes with altered reactions in response to metabolic perturbations identified 68 drug targets for the three autoimmune diseases. In vitro experimental validation, together with literature-based evidence, showed that modulation of fifty percent of identified drug targets suppressed CD4+ T cells, further increasing their potential impact as therapeutic interventions. Our approach can be generalized in the context of other diseases, and the metabolic models can be further used to dissect CD4+ T-cell metabolism.

Although recent FDA approvals on ipilimumab and sipuleucel-T represent major milestones, the ultimate success of immunotherapy approaches will likely benefit from appropriate combinations with other immunotherapeutic and/or non-immunotherapeutic approaches. However, implementation of ideal combinations in the clinic may still face formidable challenges in regulatory, drug-availability and intellectual property aspects. The 2011 SITC annual meeting hosted a workshop on combination immunotherapy to discuss: 1) the most promising combinations found in the laboratory; 2) early success of combination immunotherapy in clinical trials; 3) industry perspectives on combination approaches, and 4) relevant regulatory issues. The integrated theme was how to accelerate the implementation of efficacious combined immunotherapies for cancer patients. Rodent animal models are providing many examples of synergistic combinations that typically include more than two agents. However, mouse and human immunology differ in a significant number of mechanisms and hence we might be missing opportunities peculiar to humans. Nonetheless, incisive animal experimentation with deep mechanistic insight remains the best compass that we can use to guide our paths in combinatorial immunotherapy. Combination immunotherapy clinical trials are already in progress and preliminary results are extremely promising. As a key to translate promising combinations into clinic, real and "perceived" business and regulatory hurdles were debated. A formidable step forward would be to be able to test combinations of investigational agents prior to individual approval. Taking together the FDA and the industrial perspective on combinatorial immunotherapy, the audience was left with the clear message that this is by no means an impossible task. The general perception is that the road ahead of us is full of combination clinical trials which hopefully will bring clinical benefit to our cancer patients at a fast pace.

Immune checkpoint blockade has shown promising antitumor activity against a variety of tumor types. However, responses in castration-resistant prostate cancer remain relatively rare-potentially due to low baseline levels of infiltration. Using an immunocompetent cMyc-driven model (Myc-CaP), we sought to understand the immune infiltrate induced by androgen deprivation therapy (ADT) and to leverage that infiltration toward therapeutic benefit.

Recent advances in cancer treatment with checkpoint blockade of receptors such as CTLA-4 and PD-1 have demonstrated that combinations of agents with complementary immunomodulatory effects have the potential to enhance antitumor activity as compared to single agents. We investigated the efficacy of immune-modulatory interleukin-21 (IL-21) combined with checkpoint blockade in several syngeneic mouse tumor models. After tumor establishment, mice were administered recombinant mouse IL-21 (mIL-21) alone or in combination with blocking monoclonal antibodies against mouse PD-1 or CTLA-4. In contrast to monotherapy, IL-21 enhanced antitumor activity of mCTLA-4 mAb in four models and anti-PD-1 mAb in two models, with evidence of synergy for one or both of the combination treatments in the EMT-6 and MC38 models. The enhanced efficacy was associated with increased intratumoral CD8+ T cell infiltrates, CD8+ T cell proliferation, and increased effector memory T cells, along with decreased frequency of central memory CD8+ T cells. In vivo depletion of CD8+ T cells abolished the antitumor activities observed for both combination and monotherapy treatments, further supporting a beneficial role for CD8+ T cells. In all studies, the combination therapies were well tolerated. These results support the hypothesis that the combination of recombinant human IL-21 with CTLA-4 or PD-1 monoclonal antibodies could lead to improved outcomes in cancer patients.

Brain glioma treatment with checkpoint inhibitor antibodies to cytotoxic T-lymphocyte-associated antigen 4 (a-CTLA-4) and programmed cell death-1 (a-PD-1) was largely unsuccessful due to their inability to cross blood-brain barrier (BBB). Here we describe targeted nanoscale immunoconjugates (NICs) on natural biopolymer scaffold, poly(β-L-malic acid), with covalently attached a-CTLA-4 or a-PD-1 for systemic delivery across the BBB and activation of local brain anti-tumor immune response. NIC treatment of mice bearing intracranial GL261 glioblastoma (GBM) results in an increase of CD8+ T cells, NK cells and macrophages with a decrease of regulatory T cells (Tregs) in the brain tumor area. Survival of GBM-bearing mice treated with NIC combination is significantly longer compared to animals treated with single checkpoint inhibitor-bearing NICs or free a-CTLA-4 and a-PD-1. Our study demonstrates trans-BBB delivery of tumor-targeted polymer-conjugated checkpoint inhibitors as an effective GBM treatment via activation of both systemic and local privileged brain tumor immune response.

HIV infection induces phenotypic and functional changes to CD8+ T cells defined by the coordinated upregulation of a series of negative checkpoint receptors that eventually result in T cell exhaustion and failure to control viral replication. We report that effector CD8+ T cells during HIV infection in blood and SIV infection in lymphoid tissue exhibit higher levels of the negative checkpoint receptor TIGIT. Increased frequencies of TIGIT+ and TIGIT+ PD-1+ CD8+ T cells correlated with parameters of HIV and SIV disease progression. TIGIT remained elevated despite viral suppression in those with either pharmacological antiretroviral control or immunologically in elite controllers. HIV and SIV-specific CD8+ T cells were dysfunctional and expressed high levels of TIGIT and PD-1. Ex-vivo single or combinational antibody blockade of TIGIT and/or PD-L1 restored viral-specific CD8+ T cell effector responses. The frequency of TIGIT+ CD4+ T cells correlated with the CD4+ T cell total HIV DNA. These findings identify TIGIT as a novel marker of dysfunctional HIV-specific T cells and suggest TIGIT along with other checkpoint receptors may be novel curative HIV targets to reverse T cell exhaustion.