NKG2D is required for NK cell activation and function in response to E1-deleted adenovirus

Deletion of the RGD motif from the penton base in oncolytic adenoviruses enhances antitumor efficacy of combined CAR T cell therapy

Oncolytic viruses often face challenges in achieving optimal antitumor immunity as standalone therapies. The penton base RGD-integrin interactions play a significant role in wild-type adenovirus-induced innate immune responses. To modify these responses, we present ISC301, a novel oncolytic adenovirus engineered by deleting the natural RGD motifs in the penton base while incorporating artificial RGD motifs in the fiber knobs. ISC301 demonstrated comparable in vitro infectivity, cytotoxic effects, and signaling profiles across various cell types to its parental ICOVIR-5, which retains the penton base RGD motif. In immunodeficient and immunocompetent mouse models, ISC301 exhibited similar in vivo antitumor efficacy to ICOVIR-5. However, ISC301 induced higher intratumoral inflammation through NF-κB activation, leading to increased levels of tumor-infiltrating leukocytes and higher proportion of cytotoxic CD8+ T cells. In addition, ISC301 elicits a heightened pro-inflammatory response in peripheral blood. Importantly, when combined with CAR T cell therapy, ISC301 exhibited superior antitumor efficacy, surpassing monotherapy outcomes. These findings emphasize the impact of adenoviral modifications on antitumor immune responses. The deletion of penton base RGD motifs enhances ISC301's pro-inflammatory profile and boosts CAR T cell therapy efficacy. This study enhances understanding of oncolytic virus engineering strategies, positioning ISC301 as a promising candidate for combined immunotherapeutic approaches in cancer treatment.

IL27 Signaling Serves as an Immunologic Checkpoint for Innate Cytotoxic Cells to Promote Hepatocellular Carcinoma

Although inflammatory mechanisms driving hepatocellular carcinoma (HCC) have been proposed, the regulators of anticancer immunity in HCC remain poorly understood. We found that IL27 receptor (IL27R) signaling promotes HCC development in vivo. High IL27EBI3 cytokine or IL27RA expression correlated with poor prognosis for patients with HCC. Loss of IL27R suppressed HCC in vivo in two different models of hepatocarcinogenesis. Mechanistically, IL27R sig-naling within the tumor microenvironment restrains the cytotoxicity of innate cytotoxic lymphocytes. IL27R ablation enhanced their accumulation and activation, whereas depletion or functional impairment of innate cytotoxic cells abrogated the effect of IL27R disruption. Pharmacologic neutralization of IL27 signaling increased infiltration of innate cytotoxic lymphocytes with upregulated cytotoxic molecules and reduced HCC development. Our data reveal an unexpected role of IL27R signaling as an immunologic checkpoint regulating innate cytotoxic lymphocytes and promoting HCC of different etiologies, thus indicating a therapeutic potential for IL27 pathway blockade in HCC.

SIGNIFICANCE

HCC, the most common form of liver cancer, is characterized by a poor survival rate and limited treatment options. The discovery of a novel IL27-dependent mechanism controlling anticancer cytotoxic immune response will pave the road for new treatment options for this devastating disease. This article is highlighted in the In This Issue feature, p. 1825.

Human Adenovirus Associated Hepatic Injury

Human adenovirus (HAdV) is a common virus, but the infections it causes are relatively uncommon. At the same time, the methods for the detection of HAdV are varied, among which viral culture is still the gold standard. HAdV infection is usually self-limited but can also cause clinically symptomatic in lots of organs and tissues, of which human adenovirus pneumonia is the most common. In contrast, human adenovirus hepatitis is rarely reported. However, HAdV hepatitis has a high fatality rate once it occurs, especially in immunocompromised patients. Although human adenovirus hepatitis has some pathological and imaging features, its clinical symptoms are not typical. Therefore, HAdV hepatitis is not easy to be found in the clinic. There are kinds of treatments to treat this disease, but few are absolutely effective. In view of the above reasons, HAdV hepatitis is a disease that is difficult to be found in time. We reviewed and summarized the previously reported cases, hoping to bring some relatively common characteristics to clinicians, so as to facilitate early detection, early diagnosis, and early treatment of patients.

Heparanase is a regulator of natural killer cell activation and cytotoxicity

Heparanase is the only mammalian enzyme capable of cleaving heparan sulfate, a glycosaminoglycan of the extracellular matrix and cell surfaces. Most immune cells express heparanase that contributes to a range of functions including cell migration and cytokine expression. Heparanase also promotes natural killer (NK) cell migration; however, its role in other NK cell functions remains to be defined. In this study, heparanase-deficient (Hpse^-/- ) mice were used to assess the role of heparanase in NK cell cytotoxicity, activation, and cytokine production. Upon challenge with the immunostimulant polyinosinic:polycytidylic acid (poly(I:C)), NK cells isolated from Hpse^-/- mice displayed impaired cytotoxicity against EO771.LMB cells and reduced levels of activation markers CD69 and NKG2D. However, in vitro cytokine stimulation of wild-type and Hpse^-/- NK cells resulted in similar CD69 and NKG2D expression, suggesting the impaired NK cell activation in Hpse^-/- mice results from elements within the in vivo niche. NK cells are activated in vivo by dendritic cells (DCs) in response to poly(I:C). Poly(I:C)-stimulated Hpse^-/- bone marrow DCs (BMDCs) expressed less IL-12, and when cultured with Hpse^-/- NK cells, less MCP-1 mRNA and protein was detected. Although cell-cell contact is important for DC-mediated NK cell activation, co-cultures of Hpse^-/- BMDCs and NK cells showed similar levels of contact to wild-type cells, suggesting heparanase contributes to NK cell activation independently of cell-cell contact with DCs. These observations define a role for heparanase in NK cell cytotoxicity and activation and have important implications for how heparanase inhibitors currently in clinical trials for metastatic cancer may impact NK cell immunosurveillance.

Brain transforms natural killer cells that exacerbate brain edema after intracerebral hemorrhage

Perihematomal edema (PHE) occurs within hours after intracerebral hemorrhage (ICH), leading to secondary injury manifested by impaired blood–brain barrier (BBB) integrity and destruction of adjacent tissue. To dissect the mechanisms underlying PHE formation, we profiled human and mouse perihematomal tissues and identified natural killer (NK) cells as the predominant immune cell subset that outnumbers other infiltrating immune cell types during early stages of ICH. Unbiased clustering of single-cell transcriptional profiles revealed two major NK cell subsets that respectively possess high cytotoxicity or robust chemokine production features in the brain after ICH, distinguishing them from NK cells of the periphery. NK cells exacerbate BBB disruption and brain edema after ICH via cytotoxicity toward cerebral endothelial cells and recruitment of neutrophils that augment focal inflammation. Thus, brain-bound NK cells acquire new features that contribute to PHE formation and neurological deterioration following ICH.

NK Cells Augment Oncolytic Adenovirus Cytotoxicity in Ovarian Cancer

Oncolytic viruses (OVs) can trigger profound innate and adaptive immune responses, which have the potential both to potentiate and reduce the activity of OVs. Natural killer (NK) cells can mediate potent anti-viral and anti-tumoral responses, but there are no data on the role of NK cells in oncolytic adenovirus activity. Here, we have used two different oncolytic adenoviruses-the Ad5 E1A CR2-deletion mutant dl922-947 (group C) and the chimeric Ad3/Ad11p mutant enadenotucirev (group B)-to investigate the effect of NK cells on overall anti-cancer efficacy in ovarian cancer. Because human adenoviruses do not replicate in murine cells, we utilized primary human NK cells from peripheral blood and ovarian cancer ascites. Our results show that dl922-947 and enadenotucirev do not infect NK cells, but induce contact-dependent activation and anti-cancer cytotoxicity against adenovirus-infected ovarian cancer cells. Moreover, manipulation of NK receptors DNAM-1 (DNAX accessory molecule-1) and TIGIT (T cell immunoreceptor with Ig and ITIM domains) significantly influences NK cytotoxicity against adenovirus-infected cells. Together, these results indicate that NK cells act to increase the activity of oncolytic adenovirus in ovarian cancer and suggest that strategies to augment NK activity further via the blockade of inhibitory NK receptor TIGIT could enhance therapeutic potential of OVs.

Innate immunity to adenovirus: lessons from mice

Adenovirus is a highly evolutionary successful pathogen, as it is widely prevalent across the animal kingdom, infecting hosts ranging from lizards and frogs to dolphins, birds, and humans. Although natural adenovirus infections in humans rarely cause severe pathology, intravenous injection of high doses of adenovirus-based vectors triggers rapid activation of the innate immune system, leading to cytokine storm syndrome, disseminated intravascular coagulation, thrombocytopenia, and hepatotoxicity, which individually or in combination may cause morbidity and mortality. Much of the information on exactly how adenovirus activates the innate immune system has been gathered from mouse experimental systems. Intravenous administration of adenovirus to mice revealed mechanistic insights into cellular and molecular components of the innate immunity that detect adenovirus particles, activate pro-inflammatory signaling pathways and cytokine production, sequester adenovirus particles from the bloodstream, and eliminate adenovirus-infected cells. Collectively, this information greatly improved our understanding of mechanisms of activation of innate immunity to adenovirus and may pave the way for designing safer adenovirus-based vectors for therapy of genetic and acquired human diseases.

Skin immunisation activates an innate lymphoid cell-monocyte axis regulating CD8+ effector recruitment to mucosal tissues

CD8⁺ T cells provide a critical defence from pathogens at mucosal epithelia including the female reproductive tract (FRT). Mucosal immunisation is considered essential to initiate this response, however this is difficult to reconcile with evidence that antigen delivered to skin can recruit protective CD8⁺ T cells to mucosal tissues. Here we dissect the underlying mechanism. We show that adenovirus serotype 5 (Ad5) bio-distributes at very low level to non-lymphoid tissues after skin immunisation. This drives the expansion and activation of CD3^- NK1.1⁺ group 1 innate lymphoid cells (ILC1) within the FRT, essential for recruitment of CD8⁺ T-cell effectors. Interferon gamma produced by activated ILC1 is critical to licence CD11b⁺Ly6C⁺ monocyte production of CXCL9, a chemokine required to recruit skin primed CXCR3⁺ CD8⁺T-cells to the FRT. Our findings reveal a novel role for ILC1 to recruit effector CD8⁺ T-cells to prevent virus spread and establish immune surveillance at barrier tissues.

Upregulation of Natural Killer Cells Proliferation by Cytokine Stimulation

Natural killer (NK) cells can discriminate between normal and cancer cells and are known to directly recognize and kill malignant cells or induce apoptosis. Thus, activation of NK cells is considered as a promising strategy for cancer treatment. However, clinical application has been somewhat limited because of difficulties in the preparation of sufficient number of highly cytotoxic/activated NK cells in vitro. We used cytokine stimulation to provide a suitable environment (activating receptor-ligand interactions) for the expansion of NK cells. This method potently expanded NK cells, and the final product was composed of highly proliferating NK cells. The expanded NK cells showed significant upregulation of various activation receptors such as CD69 and NKG2D. The latter is a particularly important receptor for triggering NK cell responses toward tumor cells.

Adenovirus Vector Vaccination Impacts NK Cell Rheostat Function following Lymphocytic Choriomeningitis Virus Infection

Natural killer (NK) cells respond rapidly as a first line of defense against infectious pathogens. In addition, NK cells may provide a "rheostat" function and have been shown to reduce the magnitude of antigen-specific T cell responses following infection to avoid immunopathology. However, it remains unknown whether NK cells similarly modulate vaccine-elicited T cell responses following virus challenge. We used the lymphocytic choriomeningitis virus (LCMV) clone 13 infection model to address whether NK cells regulate T cell responses in adenovirus vector-vaccinated mice following challenge. As expected, NK cell depletion in unvaccinated mice resulted in increased virus-specific CD4⁺ and CD8⁺ T cell responses and immunopathology following LCMV challenge. In contrast, NK cell depletion had minimal to no impact on antigen-specific T cell responses in mice that were vaccinated with an adenovirus serotype 5 (Ad5)-GP vector prior to LCMV challenge. Moreover, NK cell depletion in vaccinated mice prior to challenge did not result in immunopathology and did not compromise protective efficacy. These data suggest that adenovirus vaccine-elicited T cells may be less sensitive to NK cell rheostat regulation than T cells primed by LCMV infection.IMPORTANCE Recent data have shown that NK cell depletion leads to enhanced virus-elicited T cell responses that can result in severe immunopathology following LCMV infection in mice. In this study, we observed that NK cells exerted minimal to no impact on vaccine-elicited T cells following LCMV challenge, suggesting that adenovirus vaccine-elicited T cells may be less subject to NK cell regulation. These data contribute to our understanding of NK cell regulatory functions and T cell-based vaccines.

IL-18-dependent NKG2D ligand upregulation on accessory cells is mediated by the PI3K/GSK-3 pathway

NK cells are critical for the control of viral infections. Studies have shown that efficient NK cell activation in response to infection with VV in vivo requires multiple pathways, including the NKG2D pathway. We have recently shown that IL-18 is necessary for the activation of NK cells through upregulation of the NKG2D ligand Rae-1 on DCs upon VV infection. However, how IL-18R signaling on the accessory cells contributes to Rae-1 up-regulation remains to be defined. In this study, we found IL-18-mediated Rae-1 up-regulation in accessory cells, including macrophages and DCs, to be dependent on the MyD88-PI3K pathway. We further found that IL-18 signaling through PI3K led to inhibition of GSK-3, which we found to be a negative regulator of Rae-1. Finally, we demonstrated that in vivo inhibition of GSK-3 could restore Rae-1 up-regulation on IL18R-/- DCs and partially rescue NK-cell activation against VV, leading to improved viral control in IL-18R-/- mice. Our results showed that IL18-dependent Rae-1 up-regulation on accessory cells is mediated by the MyD88-PI3K-GSK3 pathway. These observations may provide important insights into the design of effective NK cell-based immunotherapies.

Aged Garlic Extract Modifies Human Immunity

Garlic contains numerous compounds that have the potential to influence immunity. Immune cells, especially innate immune cells, are responsible for the inflammation necessary to kill pathogens. Two innate lymphocytes, γδ-T and natural killer (NK) cells, appear to be susceptible to diet modification. The purpose of this review was to summarize the influence of aged garlic extract (AGE) on the immune system. The author's laboratory is interested in AGE's effects on cell proliferation and activation and inflammation and to learn whether those changes might affect the occurrence and severity of colds and flu. Healthy human participants (n = 120), between 21 and 50 y of age, were recruited for a randomized, double-blind, placebo-controlled parallel-intervention study to consume 2.56 g AGE/d or placebo supplements for 90 d during the cold and flu season. Peripheral blood mononuclear cells were isolated before and after consumption, and γδ-T and NK cell function was assessed by flow cytometry. The effect on cold and flu symptoms was determined by using daily diary records of self-reported illnesses. After 45 d of AGE consumption, γδ-T and NK cells proliferated better and were more activated than cells from the placebo group. After 90 d, although the number of illnesses was not significantly different, the AGE group showed reduced cold and flu severity, with a reduction in the number of symptoms, the number of days participants functioned suboptimally, and the number of work/school days missed. These results suggest that AGE supplementation may enhance immune cell function and may be partly responsible for the reduced severity of colds and flu reported. The results also suggest that the immune system functions well with AGE supplementation, perhaps with less accompanying inflammation. This trial was registered at clinicaltrials.gov as NCT01390116.

Transient blocking of NK cell function with small molecule inhibitors for helper dependant adenoviral vector-mediated gene delivery

One major challenge in gene therapy is the host immune responses against viral vectors. Previous studies indicate the involvement of NK cells in stunted gene expression in viral vector mediated gene therapy. To understand the problem of the immune responses, we have developed an in-vitro co-culture system with human NK cell line, macrophages and airway epithelial cells. We showed that small molecule blockers, CAPE and ruxolitinib, for NF-κB and JAK-STAT pathways, respectively, significantly inhibited cytokine secretion by macrophages. When NK cells are co-cultured with helper-dependent adenoviral (HD-Ad) vector activated macrophages, IFN-γ cytokine expression by NK cells increased significantly, which was inhibited effectively by ruxolitinib and CAPE, and there was an additive effect when both inhibitors were used. We demonstrated that NK cells activated by cytokines produced by HD-Ad-activated macrophages kill HD-Ad vector transduced bronchial epithelial cells. This cell killing activity was significantly reduced by CAPE and ruxolitinib. Combination of these two inhibitors had an additive effect on inhibiting NK cell mediate killing of gene transduced cells. Transient inhibition of NK cell response at its peak may enhance sustained gene expression. Our data suggest that combination of CAPE and ruxolitinib may help in protecting gene transduced airway epithelial cells to prolong transgene expression.

T-cell Ig and ITIM domain regulates natural killer cell activation in murine acute viral hepatitis

Uncontrolled natural killer (NK) cell activation during the early response to acute viral infection can lead to severe immunopathology, and the mechanisms NK cells use to achieve self-tolerance in such contexts are currently unclear. Here, NK cells up-regulated a coinhibitory receptor, T-cell Ig and ITIM domain (TIGIT), during challenge with the viral double-stranded RNA (dsRNA) analog poly I:C. Blocking TIGIT by antibody treatment in vivo or a genetic deficiency in Tigit enhanced NK cell activation and aggravated liver injury in a poly I:C/D-GalN-induced model of acute fulminant hepatitis, suggesting that TIGIT is normally required for protecting against NK cell-mediated liver injury. Furthermore, adoptively transferring Tigit(-/-) NK cells into NK cell-deficient Nfil3(-/-) mice also resulted in elevated liver injury. Reconstituting Kupffer cell-depleted mice with poliovirus receptor (PVR/CD155, a TIGIT ligand)-silenced Kupffer cells led to aggravated liver injury in a TIGIT-dependent manner. Blocking TIGIT in an NK-Kupffer cell coculture in vitro enhanced NK cell activation and interferon-gamma (IFN-γ) production in a PVR-dependent manner. We also found that TIGIT was up-regulated selectively on NK cells and protected against liver injury in an acute adenovirus infection model in both an NK cell- and Kupffer cell-dependent manner. Knocking down PVR in Kupffer cells resulted in aggravated liver injury in response to adenovirus infection in a TIGIT-dependent manner.

CONCLUSION

TIGIT negatively regulates NK-Kupffer cell crosstalk and alleviates liver injury in response to poly I:C/D-GalN challenge or acute adenovirus infection, suggesting a novel mechanism of NK cell self-tolerance in liver homeostasis during acute viral infection.

Natural killer cell intrinsic toll-like receptor MyD88 signaling contributes to IL-12-dependent IFN-γ production by mice during infection with Toxoplasma gondii

Myeloid differentiation factor 88 (MyD88)-dependent IL-12 secretion by dendritic cells is critical for natural killer cell-mediated IFN-γ production and innate resistance to Toxoplasma gondii. Although MyD88(-/-) mice challenged with T. gondii have defective IL-12 responses and succumb to infection, administration of IL-12 to MyD88(-/-) mice fails to prevent acute mortality, suggesting that MyD88 may mediate signals within natural killer cells important for IL-12-dependent IFN-γ production and innate resistance to this parasite. In this study, we found that T. gondii antigens and IL-12 could synergistically trigger IFN-γ secretion by natural killer cells, which was dependent on toll-like receptor-MyD88 signaling. Further analysis showed that p38 mitogen-activated protein kinase, extracellular signal-regulated kinase, c-Jun N-terminal kinase and NF-κB multiple pathways downstream of MyD88 contributed to IFN-γ production by natural killer cells. Moreover, the well-established toll-like receptor agonists, T. gondii profilin (Tgprofilin) and T. gondii heat shock protein 70 (TgHSP70) could evoke a similar IFN-γ secretory response in natural killer cells to that evoked by T. gondii antigens. In vivo adoptive transfer experiments showed that, upon challenge with T. gondii, NOD/SCID-β2 microglobulin null (NOD/SCID-β2m(-/-)) mice injected i.v. with MyD88(-/-) natural killer cells had reduced serum IFN-γ levels and increased splenic tachyzoite burdens compared with those injected i.v. with wild-type natural killer cells. Taken together, these findings demonstrate a critical role for natural killer cell intrinsic toll-like receptor-MyD88 signaling in IL-12-dependent early IFN-γ production and innate resistance to T. gondii.

NK cells in hepatitis B virus infection: a potent target for immunotherapy

Viruses, including hepatitis B virus (HBV), are the most prevalent and infectious agents that lead to liver disease in humans. Hepatocellular carcinoma (HCC) and cirrhosis of the liver are the most serious complications arising from prolonged forms of hepatitis B. Previous studies demonstrated that patients suffering from long-term HBV infections are unable to eradicate HBV from hepatocytes completely. The mechanisms responsible for progression of these forms of infection have not yet been clarified. However, it seems that there are differences in genetic and immunological parameters when comparing patients to subjects who successfully clear HBV infections, and these may represent the causes of long-term infection. Natural killer (NK) cells, the main innate immune cells that target viral infections, play important roles in the eradication of HBV from hepatocytes. NK cells carry several stimulatory and inhibitor receptors, and binding of receptors with their ligands results in activation and suppression of NK cells, respectively. The aim of this review is to address the recent information regarding NK cell phenotype, functions and modifications in hepatitis B. This review addresses the recent data regarding the roles of NK cells as novel targets for immunotherapies that target hepatitis B infection. It also discusses the potential to reduce the risk of HCC or cirrhosis of the liver by targeting NK cells.

Mechanism of autoimmune hepatic fibrogenesis induced by an adenovirus encoding the human liver autoantigen cytochrome P450 2D6

Autoimmune hepatitis type 2 (AIH-2) is a severe autoimmune liver disease with unknown etiology. We recently developed the CYP2D6 mouse model for AIH-2, in which mice are challenged with an adenovirus (Ad-2D6) expressing human cytochrome P450 2D6 (hCYP2D6), the major autoantigen in AIH-2. Such mice develop chronic hepatitis with cellular infiltrations and generation of hCYP2D6-specific antibodies and T cells. Importantly, the CYP2D6 model represents the only model displaying chronic fibrosis allowing for a detailed investigation of the mechanisms of chronic autoimmune-mediated liver fibrogenesis. We found that hCYP2D6-dependent chronic activation of hepatic stellate cells (HSC) resulted in an increased extracellular matrix deposition and elevated expression of α-smooth muscle actin predominantly in and underneath the liver capsule. The route of Ad-2D6 infection dramatically influenced the activation and trafficking of inflammatory monocytes, NK cells and hCYP2D6-specific T cells. Intraperitoneal Ad-2D6 infection caused subcapsular fibrosis and persistent clustering of inflammatory monocytes. In contrast, intravenous infection caused an accumulation of hCYP2D6-specific CD4 T cells throughout the liver parenchyma and induced a strong NK cell response preventing chronic HSC activation and fibrosis. In summary, we found that the location of the initial site of inflammation and autoantigen expression caused a differential cellular trafficking and activation and thereby determined the outcome of AIH-2-like hepatic damage and fibrosis.

Proposed mechanisms of action for prostate cancer vaccines

Prostate cancer is responsible for the deaths of more than 33,000 American men every year. Once this disease has become metastatic, there is no curative treatment. Alternative therapies to chemotherapy and radical prostatectomy are being increasingly explored. Prostate cancer vaccines--which trigger a tumour-specific cytotoxic-T-lymphocyte-mediated immune attack by the patient's immune system--have been investigated in clinical trials with modest, yet encouraging, results. When developing and administering prostate cancer vaccines, it is critical to consider how vital parameters, such as the stage of disease progression and the nature of adjuvant therapies, could influence treatment outcome. Of particular interest are current and future strategies for diminishing the activity of regulatory T lymphocytes.

Myeloid-derived suppressor cells regulate natural killer cell response to adenovirus-mediated gene transfer

The attendant innate and adaptive immune responses to viral vectors have posed a significant hurdle for clinical application of viral vector-mediated gene therapy. Previous studies have shown that natural killer (NK) cells play a critical role in innate immune elimination of adenoviral vectors in the liver. However, it is not clear how the NK cell response to adenoviral vectors is regulated. In this study, we identified a role for granulocytic myeloid-derived suppressor cells (G-MDSCs) in this process. We show that in vivo administration of adenoviral vectors results in rapid accumulation of G-MDSCs early during adenoviral infection. In vivo depletion of both MDSC populations, but not monocytic MDSCs (M-MDSCs) alone, resulted in accelerated clearance of adenoviral vectors in the liver. This was accompanied by enhanced NK cell proliferation and activation, suggesting a role for MDSCs, probably G-MDSCs, in suppressing NK cell activation and function in vivo. We further demonstrate in vitro that G-MDSCs, but not M-MDSCs, are responsible for the suppression of NK cell activation. In addition, we show that adenoviral infection activated G-MDSCs to produce higher levels of reactive oxygen species (ROS) and that G-MDSC-mediated suppression of NK cells is mediated by ROS, specifically, H(2)O(2). This study demonstrates for the first time that the NK cell response to adenoviral vectors is negatively regulated by G-MDSCs and suggests that G-MDSC-based strategies could potentially improve the outcome of viral vector-mediated gene therapy.

Adenovirus type 35, but not type 5, stimulates NK cell activation via plasmacytoid dendritic cells and TLR9 signaling

In hematopoietic stem cell transplant (HSCT) recipients, disseminated adenoviral infections during the first two months after HSCT can lead to severe complications and fatal outcome. Since NK cells are usually the first lymphocytes to reconstitute after HSCT and have been implicated in the clearance of adenovirus-infected cells, it was investigated whether NK cells are activated by adenovirus in vitro. Exposure of PBMC to human adenovirus type 5 (HAdV5) or HAdV35 resulted in the up-regulation of the activation marker CD69 on NK cells and enhanced the cytolytic activity of NK cells. HAdV5-induced NK cell activation relied on the contribution of T cells as the depletion of T cells from PBMC abolished NK cell activation. In contrast, NK cell activation in response to HAdV35 occurred in the absence of T cells. Plasmacytoid dendritic cells (pDC) were necessary and sufficient to mediate NK cell activation. HAdV35 induced significantly more interferon-α (IFN-α) production by pDC than HAdV5. The increased IFN-α production and NK cell activation correlated with a higher infection efficiency of viruses with the type 35 fiber. The IFN-α response of pDC was enhanced by the presence of NK cells, suggesting a reciprocal interaction between pDC and NK cells. Incubation with a TLR9 antagonist impaired the IFN-α production by pDC as well as NK cell activation, implying that TLR9 signaling is critically involved in the IFN-α response of pDC and NK cell activation after HAdV35 exposure. In conclusion, two human adenovirus serotypes from two different species differ considerably in their capacity to stimulate pDC and NK cells.

Tumorigenic adenovirus 12 cells evade NK cell lysis by reducing the expression of NKG2D ligands

Activation of natural killer (NK) cells depends on a balance between signals received from activation and inhibitory ligands expressed on the surface of target cells. Tumorigenic human adenovirus 12 (Ad12) transformed cells express low levels of the NK cell inhibitory ligand MHC I, but do not exhibit increased sensitivity to NK cell lysis compared to their non-tumorigenic counterparts. Analysis of the expression of activation ligands that bind to the NKG2D receptor revealed that RAE1β and H60 were reduced on the surface of Ad12 mouse cells as well as at the level of transcription. In accord with these results, RAE1 localization to the synapse and sensitivity to NK cell cytotoxicity were also diminished. The reduced transcription of the rat NKG2D ligands, RAEt1L and RRTL, in tumorigenic rat cells compared to non-tumorigenic counterparts implies that both mouse and rat cell lines share a common mechanism of NKG2D ligand activation subverted by Ad12.

Chapter six--Adenovirus-based immunotherapy of cancer: promises to keep

Progress in vector design and an increased knowledge of mechanisms underlying tumor-induced immune suppression have led to a new and promising generation of Adenovirus (Ad)-based immunotherapies, which are discussed in this review. As vaccine vehicles Ad vectors (AdVs) have been clinically evaluated and proven safe, but a major limitation of the commonly used Ad5 serotype is neutralization by preexistent or rapidly induced immune responses. Genetic modifications in the Ad capsid can reduce intrinsic immunogenicity and facilitate escape from antibody-mediated neutralization. Further modification of the Ad hexon and fiber allows for liver and scavenger detargeting and selective targeting of, for example, dendritic cells. These next-generation Ad vaccines with enhanced efficacy are now becoming available for testing as tumor vaccines. In addition, AdVs encoding immune-modulating products may be used to convert the tumor microenvironment from immune-suppressive and proinvasive to proinflammatory, thus facilitating cell-mediated effector functions that can keep tumor growth and invasion in check. Oncolytic AdVs, that selectively replicate in tumor cells and induce an immunogenic form of cell death, can also be armed with immune-activating transgenes to amplify primed antitumor immune responses. These novel immunotherapy strategies, employing highly efficacious AdVs in optimized configurations, show great promise and warrant clinical exploration.

Immune recognition of gene transfer vectors: focus on adenovirus as a paradigm

Recombinant Adenovirus (Ad) based vectors have been utilized extensively as a gene transfer platform in multiple pre-clinical and clinical applications. These applications are numerous, and inclusive of both gene therapy and vaccine based approaches to human or animal diseases. The widespread utilization of these vectors in both animal models, as well as numerous human clinical trials (Ad-based vectors surpass all other gene transfer vectors relative to numbers of patients treated, as well as number of clinical trials overall), has shed light on how this virus vector interacts with both the innate and adaptive immune systems. The ability to generate and administer large amounts of this vector likely contributes not only to their ability to allow for highly efficient gene transfer, but also their elicitation of host immune responses to the vector and/or the transgene the vector expresses in vivo. These facts, coupled with utilization of several models that allow for full detection of these responses has predicted several observations made in human trials, an important point as lack of similar capabilities by other vector systems may prevent detection of such responses until only after human trials are initiated. Finally, induction of innate or adaptive immune responses by Ad vectors may be detrimental in one setting (i.e., gene therapy) and be entirely beneficial in another (i.e., prophylactic or therapeutic vaccine based applications). Herein, we review the current understanding of innate and adaptive immune responses to Ad vectors, as well some recent advances that attempt to capitalize on this understanding so as to further broaden the safe and efficient use of Ad-based gene transfer therapies in general.

Natural killer cell responses to viral infection

Natural killer (NK) cells, as part of the innate immune system, play a key role in host defense against viral infections. Recent advances have indicated that NK cell activation and function are regulated by the interplay between inhibitory and activating signals. Thus, a better understanding of mechanisms responsible for NK cell activation and function in the control of viral infections will help develop NK cell-based therapies. In this review, we will first discuss how NK cells are activated in response to viral infections. We will then focus on the recruitment of activated NK cells to the site of infection as well as on NK cell effector mechanisms against virally infected cells.