TIGIT blockade enhances NK cell activity against autologous HIV-1-infected CD4+ T cells

Immune restoration by TIGIT blockade is insufficient to control chronic SIV infection

TIGIT is a negative immune checkpoint receptor associated with T cell exhaustion in cancer and HIV. TIGIT upregulation in virus-specific CD8+ T cells and NK cells during HIV/SIV infection results in dysfunctional effector capabilities. In vitro studies targeting TIGIT on CD8+ T cells suggest TIGIT blockade as a viable strategy to restore SIV-specific T cell responses. Here, we extend these studies in vivo using TIGIT blockage in nonhuman primates in an effort to reverse T cell and NK cell exhaustion in the setting of SIV infection. We demonstrate that in vivo administration of a humanized anti-TIGIT monoclonal antibody (mAb) is well tolerated in both cynomolgus macaques and rhesus macaques. Despite sustained plasma concentrations of anti-TIGIT mAb, we observed no consistent improvement in NK or T cell cytolytic capacity. TIGIT blockade minimally enhanced T cell proliferation and virus-specific T cell responses in both magnitude and breadth though plasma viral loads in treated animals remained stable indicating that anti-TIGIT mAb treatment alone was insufficient to increase anti-SIV CD8+ T cell function. The enhancement of virus-specific T cell proliferative responses observed in vitro with single or dual blockade of TIGIT and/or PD-1 highlights TIGIT as a potential target to reverse T cell dysfunction. Our studies, however, reveal that targeting the TIGIT pathway alone may be insufficient in the setting of viremia and that combining immune checkpoint blockade with other immunotherapeutics may be a future path forward for improved viral control or elimination of HIV.IMPORTANCEUpregulation of the immune checkpoint receptor TIGIT is associated with HIV-mediated T cell dysfunction and correlates with HIV disease progression. Compelling evidence exists for targeting immune checkpoint receptor pathways that would potentially enhance immunity and refocus effector cell efforts toward viral clearance. In this report, we investigate TIGIT blockade as an immunotherapeutic approach to reverse immune exhaustion during chronic SIV/SHIV infection in a nonhuman primate model of HIV infection. We show that interfering with the TIGIT signaling axis alone is insufficient to improve viral control despite modest improvement in T cell immunity. Our data substantiate the use of targeting multiple immune checkpoint receptors to promote synergy and ultimately eliminate HIV-infected cells.

Weak SARS-CoV-2-specific responses of TIGIT-expressing CD8 + T cells in people living with HIV after a third dose of a SARS-CoV-2 inactivated vaccine

BACKGROUND

T-cell immunoreceptor with immunoglobulin and immunoreceptor tyrosine-based inhibition motif domains (TIGIT), an inhibitory receptor expressed on T cells, plays a dysfunctional role in antiviral infection and antitumor activity. However, it is unknown whether TIGIT expression on T cells influences the immunological effects of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) inactivated vaccines.

METHODS

Forty-five people living with HIV (PLWH) on antiretroviral therapy (ART) for more than two years and 31 healthy controls (HCs), all received a third dose of a SARS-CoV-2 inactivated vaccine, were enrolled in this study. The amounts, activation, proportion of cell subsets, and magnitude of the SARS-CoV-2-specific immune response of TIGIT + CD4 + and TIGIT + CD8 + T cells were investigated before the third dose but 6 months after the second vaccine dose (0W), 4 weeks (4W) and 12 weeks (12W) after the third dose.

RESULTS

Compared to that in HCs, the frequency of TIGIT + CD8 + T cells in the peripheral blood of PLWH increased at 12W after the third dose of the inactivated vaccine, and the immune activation of TIGIT + CD8 + T cells also increased. A decrease in the ratio of both T naïve (T N ) and central memory (T CM ) cells among TIGIT + CD8 + T cells and an increase in the ratio of the effector memory (T EM ) subpopulation were observed at 12W in PLWH. Interestingly, particularly at 12W, a higher proportion of TIGIT + CD8 + T cells expressing CD137 and CD69 simultaneously was observed in HCs than in PLWH based on the activation-induced marker assay. Compared with 0W, SARS-CoV-2-specific TIGIT + CD8 + T-cell responses in PLWH were not enhanced at 12W but were enhanced in HCs. Additionally, at all time points, the SARS-CoV-2-specific responses of TIGIT + CD8 + T cells in PLWH were significantly weaker than those of TIGIT - CD8 + T cells. However, in HCs, the difference in the SARS-CoV-2-specific responses induced between TIGIT + CD8 + T cells and TIGIT - CD8 + T cells was insignificant at 4W and 12W, except at 0W.

CONCLUSIONS

TIGIT expression on CD8 + T cells may hinder the T-cell immune response to a booster dose of an inactivated SARS-CoV-2 vaccine, suggesting weakened resistance to SARS-CoV-2 infection, especially in PLWH. Furthermore, TIGIT may be used as a potential target to increase the production of SARS-CoV-2-specific CD8 + T cells, thereby enhancing the effectiveness of vaccination.

Virus-Host Protein Interaction Network of the Hepatitis E Virus ORF2-4 by Mammalian Two-Hybrid Assays

Throughout their life cycle, viruses interact with cellular host factors, thereby influencing propagation, host range, cell tropism and pathogenesis. The hepatitis E virus (HEV) is an underestimated RNA virus in which knowledge of the virus-host interaction network to date is limited. Here, two related high-throughput mammalian two-hybrid approaches (MAPPIT and KISS) were used to screen for HEV-interacting host proteins. Promising hits were examined on protein function, involved pathway(s), and their relation to other viruses. We identified 37 ORF2 hits, 187 for ORF3 and 91 for ORF4. Several hits had functions in the life cycle of distinct viruses. We focused on SHARPIN and RNF5 as candidate hits for ORF3, as they are involved in the RLR-MAVS pathway and interferon (IFN) induction during viral infections. Knocking out (KO) SHARPIN and RNF5 resulted in a different IFN response upon ORF3 transfection, compared to wild-type cells. Moreover, infection was increased in SHARPIN KO cells and decreased in RNF5 KO cells. In conclusion, MAPPIT and KISS are valuable tools to study virus-host interactions, providing insights into the poorly understood HEV life cycle. We further provide evidence for two identified hits as new host factors in the HEV life cycle.

Knockout of the inhibitory receptor TIGIT enhances the antitumor response of ex vivo expanded NK cells and prevents fratricide with therapeutic Fc-active TIGIT antibodies

BACKGROUND

Inhibitory receptor T-cell Immunoreceptor with Ig and ITIM domains (TIGIT) expressed by Natural Killer (NK) and T cells regulates cancer immunity and has been touted as the next frontier in the development of cancer immunotherapeutics. Although early results of anti-TIGIT and its combinations with antiprogrammed death-ligand 1 were highly exciting, results from an interim analysis of phase III trials are disappointing. With mixed results, there is a need to understand the effects of therapeutic anti-TIGIT on the TIGIT+ immune cells to support its clinical use. Most of the TIGIT antibodies in development have an Fc-active domain, which binds to Fc receptors on effector cells. In mouse models, Fc-active anti-TIGIT induced superior immunity, while Fc receptor engagement was required for its efficacy. NK-cell depletion compromised the antitumor immunity of anti-TIGIT indicating the essential role of NK cells in the efficacy of anti-TIGIT. Since NK cells express TIGIT and Fc-receptor CD16, Fc-active anti-TIGIT may deplete NK cells via fratricide, which has not been studied.

METHODS

CRISPR-Cas9-based TIGIT knockout (KO) was performed in expanded NK cells. Phenotypic and transcriptomic properties of TIGIT KO and wild-type (WT) NK cells were compared with flow cytometry, CyTOF, and RNA sequencing. The effect of TIGIT KO on NK-cell cytotoxicity was determined by calcein-AM release and live cell imaging-based cytotoxicity assays. The metabolic properties of TIGIT KO and WT NK cells were compared with a Seahorse analyzer. The effect of the Fc-component of anti-TIGIT on NK-cell fratricide was determined by co-culturing WT and TIGIT KO NK cells with Fc-active and Fc-inactive anti-TIGIT.

RESULTS

TIGIT KO increased the cytotoxicity of NK cells against multiple cancer cell lines including spheroids. TIGIT KO NK cells upregulated mTOR complex 1 (mTORC1) signaling and had better metabolic fitness with an increased basal glycolytic rate when co-cultured with cancer cells compared with WT NK cells. Importantly, TIGIT KO prevented NK-cell fratricide when combined with Fc-active anti-TIGIT.

CONCLUSIONS

TIGIT KO in ex vivo expanded NK cells increased their cytotoxicity and metabolic fitness and prevented NK-cell fratricide when combined with Fc-active anti-TIGIT antibodies. These fratricide-resistant TIGIT KO NK cells have therapeutic potential alone or in combination with Fc-active anti-TIGIT antibodies to enhance their efficacy.

Immune checkpoint inhibitors as potential therapy for reverting T-cell exhaustion and reverting HIV latency in people living with HIV

The immune system of people living with HIV (PLWH) is persistently exposed to antigens leading to systemic inflammation despite combination antiretroviral treatment (cART). This inflammatory milieu promotes T-cell activation and exhaustion. Furthermore, it produces diminished effector functions including loss of cytokine production, cytotoxicity, and proliferation, leading to disease progression. Exhausted T cells show overexpression of immune checkpoint molecules (ICs) on the cell surface, including programmed cell death protein 1 (PD-1), cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4), T-cell immunoglobulin and mucin-domain containing-3 (TIM-3), T-cell immunoglobulin and immunoreceptor tyrosine-based inhibitory motif domain (TIGIT), and lymphocyte activation gene-3 (LAG-3). The ICs also play a crucial role in T-cell exhaustion by reducing the immune response to cancer antigens. Immunotherapy based on immune checkpoint inhibitors (ICIs) has changed the management of a diversity of cancers. Additionally, the interest in exploring this approach in the setting of HIV infection has increased, including AIDS-defining cancers and non-AIDS-defining cancers in PLWH. To date, research on this topic suggests that ICI-based therapies in PLWH could be a safe and effective approach. In this review, we provide an overview of the current literature on the potential role of ICI-based immunotherapy not only in cancer remission in PLWH but also as a therapeutic intervention to restore immune response against HIV, revert HIV latency, and attain a functional cure for HIV infection.

Vaccinal effect of HIV-1 antibody therapy: dream or reality?

PURPOSE OF REVIEW

This review summarizes recent studies reporting the induction of vaccinal effects by human immunodeficiency virus (HIV-1) antibody therapy. It also puts into perspective preclinical studies that have identified mechanisms involved in the immunomodulatory properties of antiviral antibodies. Finally, it discusses potential therapeutic interventions to enhance host adaptive immune responses in people living with HIV (PLWH) treated with broadly neutralizing antibodies (bNAbs).

RECENT FINDINGS

Recent studies in promising clinical trials have shown that, in addition to controlling viremia, anti-HIV-1 bNAbs are able to enhance the host's humoral and cellular immune response. Such vaccinal effects, in particular the induction of HIV-1-specific CD8 + T-cell responses, have been observed upon treatment with two potent bNAbs (3BNC117 and 10-1074) alone or in combination with latency-reversing agents (LRA). While these studies reinforce the idea that bNAbs can induce protective immunity, the induction of vaccinal effects is not systematic and might depend on both the virological status of the patient as well as the therapeutic strategy chosen.

SUMMARY

HIV-1 bNAbs can enhance adaptive host immune responses in PLWH. The challenge now is to exploit these immunomodulatory properties to design optimized therapeutic interventions to promote and enhance the induction of protective immunity against HIV-1 infection during bNAbs therapy.

TIGIT Expression on Activated NK Cells Correlates with Greater Anti-Tumor Activity but Promotes Functional Decline upon Lung Cancer Exposure: Implications for Adoptive Cell Therapy and TIGIT-Targeted Therapies

Treatments targeting TIGIT have gained a lot of attention due to strong preclinical and early clinical results, particularly with anti-PD-(L)1 therapeutics. However, this combination has failed to meet progression-free survival endpoints in phase III trials. Most of our understanding of TIGIT comes from studies of T cell function. Yet, this inhibitory receptor is often upregulated to the same, or higher, extent on NK cells in cancers. Studies in murine models have demonstrated that TIGIT inhibits NK cells and promotes exhaustion, with its effects on tumor control also being dependent on NK cells. However, there are limited studies assessing the role of TIGIT on the function of human NK cells (hNK), particularly in lung cancer. Most studies used NK cell lines or tested TIGIT blockade to reactivate exhausted cells obtained from cancer patients. For therapeutic advancement, a better understanding of TIGIT in the context of activated hNK cells is crucial, which is different than exhausted NK cells, and critical in the context of adoptive NK cell therapeutics that may be combined with TIGIT blockade. In this study, the effect of TIGIT blockade on the anti-tumor activities of human ex vivo-expanded NK cells was evaluated in vitro in the context of lung cancer. TIGIT expression was higher on activated and/or expanded NK cells compared to resting NK cells. More TIGIT⁺ NK cells expressed major activating receptors and exerted anti-tumor response as compared to TIGIT^- cells, indicating that NK cells with greater anti-tumor function express more TIGIT. However, long-term TIGIT engagement upon exposure to PVR⁺ tumors downregulated the cytotoxic function of expanded NK cells while the inclusion of TIGIT blockade increased cytotoxicity, restored the effector functions against PVR-positive targets, and upregulated immune inflammation-related gene sets. These combined results indicate that TIGIT blockade can preserve the activation state of NK cells during exposure to PVR⁺ tumors. These results support the notion that a functional NK cell compartment is critical for anti-tumor response and anti-TIGIT/adoptive NK cell combinations have the potential to improve outcomes.

Effective innate immune response in natural HIV-1 controllers. Can mimicking lead to novel preventive and cure strategies against HIV-1?

PURPOSE OF REVIEW

HIV-1 controller individuals represents a model that can be useful for the development of novel vaccines and therapies. Initial studies pointed to the involvement of improved adaptive immunity, however, new emerging evidence suggests the contribution of innate cells to effective antiviral responses in spontaneous controllers. Therefore, understanding the alterations on innate cell subsets might be crucial to develop new effective therapeutic strategies.

RECENT FINDINGS

Among different innate immune cells, dendritic cell (DC) and natural killer (NK) cell are essential for effective antiviral responses. DC from controllers display improved innate detection of HIV-1 transcripts, higher induction of interferons, higher antigen presenting capacities and increased metabolism and higher capacities to induce polyfunctional CD8+ T-cell responses. Such properties have been mimicked by Toll-like receptor ligands and applied to DC-based immunotherapies in humans and in animal models. NK cells from controllers display higher expression of activating receptors promoting increased antibody-dependent cellular cytotoxicity (ADCC) and natural cytotoxicity activities. Neutralizing antibodies in combination with interleukin-15 superagonist or interferon-α can increase ADCC and cytotoxicity in NK cells from HIV-1 progressors.

SUMMARY

Mimicking DC and NK cell innate profiles in controllers has become a promising strategy to step forward a novel efficient immunotherapy against the HIV-1 infection.

Navigating the complexity of chronic HIV-1 associated immune dysregulation

Despite successful viral suppression with antiretroviral therapy, chronic HIV-1 infection is associated with ongoing immune dysfunction. Investigation of the complex immune response in treated and untreated individuals with chronic HIV-1 infection is warranted. Immune alterations such as monocyte phenotype and Th-17/Treg ratios often persist years after the reduction in viraemia and predispose many individuals to long-term comorbidities such as cardiovascular disease or cancer. Furthermore, while there has been extensive research on the latent reservoir of treated patients with chronic HIV-1, which prevents the discontinuation of treatment, the mechanism behind this remains elusive and needs further investigation. In this review, we assist in navigating the recent research on these groups of individuals and provide a basis for further investigation.

Negative Regulation and Protective Function of Natural Killer Cells in HIV Infection: Two Sides of a Coin

Natural killer (NK) cells play an important immunologic role, targeting tumors and virus-infected cells; however, NK cells do not impede the progression of human immunodeficiency virus (HIV) infection. In HIV infection, NK cells exhibit impaired functions and negatively regulate other immune cell responses, although NK cells can kill HIV-infected cells and thereby suppress HIV replication. Considerable recent research has emerged regarding NK cells in the areas of immune checkpoints, negative regulation, antibody-dependent cell-mediated cytotoxicity and HIV reservoirs during HIV infection; however, no overall summary of these factors is available. This review focuses on several important aspects of NK cells in relation to HIV infection, including changes in NK cell count, subpopulations, and immune checkpoints, as well as abnormalities in NK cell functions and NK cell negative regulation. The protective function of NK cells in inhibiting HIV replication to reduce the viral reservoir and approaches for enhancing NK cell functions are also summarized.