Harnessing Natural Killer Cell Innate and Adaptive Traits in HIV Infection

Mapping the interplay between NK cells and HIV: therapeutic implications

Although highly effective at durably suppressing plasma HIV-1 viremia, combination antiretroviral therapy (ART) treatment regimens do not eradicate the virus, which persists in long-lived CD4+ T cells. This latent viral reservoir serves as a source of plasma viral rebound following treatment interruption, thus requiring lifelong adherence to ART. Additionally, challenges remain related not only to access to therapy but also to a higher prevalence of comorbidities with an inflammatory etiology in treated HIV-1+ individuals, underscoring the need to explore therapeutic alternatives that achieve sustained virologic remission in the absence of ART. Natural killer (NK) cells are uniquely positioned to positively impact antiviral immunity, in part due to the pleiotropic nature of their effector functions, including the acquisition of memory-like features, and, therefore, hold great promise for transforming HIV-1 therapeutic modalities. In addition to defining the ability of NK cells to contribute to HIV-1 control, this review provides a basic immunologic understanding of the impact of HIV-1 infection and ART on the phenotypic and functional character of NK cells. We further delineate the qualities of "memory" NK cell populations, as well as the impact of HCMV on their induction and subsequent expansion in HIV-1 infection. We conclude by highlighting promising avenues for optimizing NK cell responses to improve HIV-1 control and effect a functional cure, including blockade of inhibitory NK receptors, TLR agonists to promote latency reversal and NK cell activation, CAR NK cells, BiKEs/TriKEs, and the role of HIV-1-specific bNAbs in NK cell-mediated ADCC activity against HIV-1-infected cells.

Impact of IL-15 and latency reversing agent combinations in the reactivation and NK cell-mediated suppression of the HIV reservoir

Inhibitors of histone deacetylases (HDACis) are major latency reversing agent (LRA) candidates in 'shock and kill' strategies to eradicate the HIV reservoir in infected patients. The poor achievements of initial HDACi-based trials and subsequent studies have highlighted the need for more efficient approaches such as combinatory and immunostimulating therapies. Here we studied combinations of IL-15 with pan-HDACi (Vorinostat, Romidepsin, Panobinostat) or class I selective-HDACi (Entinostat) with or without a PKC agonist (Prostratin) for their impact on in vitro reactivation and NK cell-mediated suppression of latent HIV. Results showed that pan-HDACis but not Entinostat reduced NK cell viability and function; yet, combined IL-15 reverted the negative effects of pan-HDACis except for Panobinostat. All HDACis were ineffective at reactivating HIV in a CD4⁺ T cell model of latency, with pan-HDACis suppressing spontaneous and IL-15- or Prostratin-induced HIV release, while IL-15 + Prostratin combination showed maximal activity. Moreover, Panobinostat impaired STAT5 and NF-κB activation by IL-15 and Prostratin, respectively. Finally, by using effectors (NK) and targets (latently infected CD4⁺ T cells) equally exposed to drug combinations, we found that IL-15-mediated suppression of HIV reactivation by NK cells was inhibited by Panobinostat. Our data raise concerns and encouragements for therapeutic application of IL-15/LRA combinations.

Emerging therapeutic potential of regulatory T (Treg) cells for rheumatoid arthritis: New insights and challenges

Rheumatoid arthritis (RA) is an autoimmune-related disorder characterized by chronic inflammation. Although the etiopathogenesis of RA still remains to be clarified, it is supposed that the breakdown of immune self-tolerance may contribute to the development of RA. Thus, restoring of immune tolerance at the site of inflammation is the ultimate goal of RA treatment. Regulatory T cells (Treg cells) are the main suppressive cells that maintain tolerance and inhibit immunity against auto-antigen. Of note, recent studies demonstrated the efficacy of adoptive transfer of Treg cells in the modulation of the unwanted immune response, which makes them an ideal candidate to maintain immune homeostasis and restore antigen-specific tolerance in the case of RA and other autoimmune diseases. This review intends to submit recent finding of Treg cells-based therapies in RA with a focus on strategies applied to improve the therapeutic value of Treg cells to restore immune tolerance.

Targeting NK Cells for HIV-1 Treatment and Reservoir Clearance

Combined antiretroviral therapy (cART) can inhibit the replication of human immunodeficiency virus type 1 (HIV-1) and reduce viral loads in the peripheral blood to undetectable levels. However, the presence of latent HIV-1 reservoirs prevents complete HIV-1 eradication. Several drugs and strategies targeting T cells are now in clinical trials, but their effectiveness in reducing viral reservoirs has been mixed. Interestingly, innate immune natural killer (NK) cells, which are promising targets for cancer therapy, also play an important role in HIV-1 infection. NK cells are a unique innate cell population with features of adaptive immunity that can regulate adaptive and innate immune cell populations; therefore, they can be exploited for HIV-1 immunotherapy and reservoir eradication. In this review, we highlight immunotherapy strategies for HIV infection that utilize the beneficial properties of NK cells.

NK cell-based therapies for HIV infection: Investigating current advances and future possibilities

NK cells are well-known for their antiviral functions. Also, their role in HIV has been well established, with rapid responses elicited during early HIV infection. Most immune cells including CD4⁺ T cells, monocytes, Mϕs, and dendritic cells are readily infected by HIV. Recent evidence from multiple studies has suggested that similar to these cells, in chronic conditions like HIV, NK cells also undergo functional exhaustion with impaired cytotoxicity, altered cytokine production, and impaired ADCC. NK-based immunotherapy aims to successfully restore, boost, and modify their activity as has been already demonstrated in the field of cancer immunotherapy. The utilization of NK cell-based strategies for the eradication of HIV from the body provides many advantages over classical ART. The literature search consisted of manually selecting the most relevant studies from databases including PubMed, Embase, Google Scholar, and ClinicalTrial.gov. Some of the treatments currently under consideration are CAR-NK cell therapy, facilitating ADCC, TLR agonists, bNAbs, and BiKEs/TriKEs, blocking inhibitory NK receptors during infection, IL-15 and IL-15 superagonists (eg: ALT-803), and so on. This review aims to discuss the NK cell-based therapies currently under experimentation against HIV infection and finally highlight the challenges associated with NK cell-based immunotherapies.

The CD8+ T Cell Noncytotoxic Antiviral Responses

The CD8+ T cell noncytotoxic antiviral response (CNAR) was discovered during studies of asymptomatic HIV-infected subjects more than 30 years ago. In contrast to CD8+ T cell cytotoxic lymphocyte (CTL) activity, CNAR suppresses HIV replication without target cell killing. This activity has characteristics of innate immunity: it acts on all retroviruses and thus is neither epitope specific nor HLA restricted. The HIV-associated CNAR does not affect other virus families. It is mediated, at least in part, by a CD8+ T cell antiviral factor (CAF) that blocks HIV transcription. A variety of assays used to measure CNAR/CAF and the effects on other retrovirus infections are described. Notably, CD8+ T cell noncytotoxic antiviral responses have now been observed with other virus families but are mediated by different cytokines. Characterizing the protein structure of CAF has been challenging despite many biologic, immunologic, and molecular studies. It represents a low-abundance protein that may be identified by future next-generation sequencing approaches. Since CNAR/CAF is a natural noncytotoxic activity, it could provide promising strategies for HIV/AIDS therapy, cure, and prevention.

The role of donor-unrestricted T-cells, innate lymphoid cells, and NK cells in anti-mycobacterial immunity

Vaccination strategies against mycobacteria, focusing mostly on classical T‐ and B‐cells, have shown limited success, encouraging the addition of alternative targets. Classically restricted T‐cells recognize antigens presented via highly polymorphic HLA class Ia and class II molecules, while donor‐unrestricted T‐cells (DURTs), with few exceptions, recognize ligands via genetically conserved antigen presentation molecules. Consequently, DURTs can respond to the same ligands across diverse human populations. DURTs can be activated either through cognate TCR ligation or via bystander cytokine signaling. TCR‐driven antigen‐specific activation of DURTs occurs upon antigen presentation via non‐polymorphic molecules such as HLA‐E, CD1, MR1, and butyrophilin, leading to the activation of HLA‐E–restricted T‐cells, CD1‐restricted T‐cells, mucosal‐associated invariant T‐cells (MAITs), and TCRγδ T‐cells, respectively. NK cells and innate lymphoid cells (ILCs), which lack rearranged TCRs, are activated through other receptor‐triggering pathways, or can be engaged through bystander cytokines, produced, for example, by activated antigen‐specific T‐cells or phagocytes. NK cells can also develop trained immune memory and thus could represent cells of interest to mobilize by novel vaccines. In this review, we summarize the latest findings regarding the contributions of DURTs, NK cells, and ILCs in anti–M tuberculosis, M leprae, and non‐tuberculous mycobacterial immunity and explore possible ways in which they could be harnessed through vaccines and immunotherapies to improve protection against Mtb.

Innate immunology in COVID-19-a living review. Part II: dysregulated inflammation drives immunopathology

The current pandemic of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) poses a global health crisis and will likely continue to impact public health for years. As the effectiveness of the innate immune response is crucial to patient outcome, huge efforts have been made to understand how dysregulated immune responses may contribute to disease progression. Here we have reviewed current knowledge of cellular innate immune responses to SARS-CoV-2 infection, highlighting areas for further investigation and suggesting potential strategies for intervention. We conclude that in severe COVID-19 initial innate responses, primarily type I interferon, are suppressed or sabotaged which results in an early interleukin (IL)-6, IL-10 and IL-1β-enhanced hyperinflammation. This inflammatory environment is driven by aberrant function of innate immune cells: monocytes, macrophages and natural killer cells dispersing viral pathogen-associated molecular patterns and damage-associated molecular patterns into tissues. This results in primarily neutrophil-driven pathology including fibrosis that causes acute respiratory distress syndrome. Activated leukocytes and neutrophil extracellular traps also promote immunothrombotic clots that embed into the lungs and kidneys of severe COVID-19 patients, are worsened by immobility in the intensive care unit and are perhaps responsible for the high mortality. Therefore, treatments that target inflammation and coagulation are promising strategies for reducing mortality in COVID-19.