Inhibition of Human Coronaviruses by Antimalarial Peroxides.

As the toll of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic continues, efforts are ongoing to identify new agents and repurpose safe drugs for its treatment. Antimalarial peroxides have reported antiviral and anticancer activities. Here, we evaluated the in vitro activities of artesunate (AS) and two ozonides (OZ418 and OZ277) against human α-coronavirus NL63 and ß-coronaviruses OC43 and SARS-CoV-2 in several cell lines. OZ418 had the best selectivity index (SI) in NL63-infected Vero cells and MK2 cells. The overall SI of the tested compounds was cell-type dependent. In OC43-infected human foreskin fibroblasts, AS had the best cell-associated SI, ≥17 µM, while the SI of OZ418 and OZ277 was ≥12 µM and ≥7 µM, respectively. AS did not inhibit SARS-CoV-2 in either Vero or Calu-3 cells. A comparison of OZ418 and OZ277 activity in SARS-CoV2-infected Calu-3 cells revealed similar EC50 (5.3 µM and 11.6 µM, respectively), higher than the EC50 of remdesivir (1.0 ± 0.1 µM), but the SI of OZ418 was higher than OZ277. A third ozonide, OZ439, inhibited SARS-CoV-2 efficiently in Vero cells, but compared to OZ418 in Calu-3 cells, it showed higher toxicity. Improved inhibition of SARS-CoV-2 was observed when OZ418 was used together with remdesivir. Although the EC50 of ozonides might be clinically achieved in plasma after intravenous administration, sustained virus suppression in tissues will require further considerations, including drug combination. Our work supports the potential repurposing of ozonides and calls for future in vivo models.

Immune-Checkpoint Protein VISTA Regulates Antitumor Immunity by Controlling Myeloid Cell-Mediated Inflammation and Immunosuppression.

Immune-checkpoint protein V-domain immunoglobulin suppressor of T-cell activation (VISTA) controls antitumor immunity and is a valuable target for cancer immunotherapy. This study identified a role of VISTA in regulating Toll-like receptor (TLR) signaling in myeloid cells and controlling myeloid cell-mediated inflammation and immunosuppression. VISTA modulated the polyubiquitination and protein expression of TRAF6. Consequently, VISTA dampened TLR-mediated activation of MAPK/AP-1 and IKK/NF-κB signaling cascades. At cellular levels, VISTA regulated the effector functions of myeloid-derived suppressor cells and tolerogenic dendritic cell (DC) subsets. Blocking VISTA augmented their ability to produce proinflammatory mediators and diminished their T cell-suppressive functions. These myeloid cell-dependent effects resulted in a stimulatory tumor microenvironment that promoted T-cell infiltration and activation. We conclude that VISTA is a critical myeloid cell-intrinsic immune-checkpoint protein and that the reprogramming of tolerogenic myeloid cells following VISTA blockade promotes the development of T cell-mediated antitumor immunity.

γ-herpesvirus latency attenuates Mycobacterium tuberculosis infection in mice.

Tuberculosis is caused by Mycobacterium tuberculosis (Mtb), a bacterial pathogen which is transmitted via aerosol and establishes a chronic lung infection. In naïve hosts, Mtb grows for several weeks without being restricted by IFNγ-producing T cells, which eventually accumulate and limit Mtb dissemination. In this study, we used a mouse model of Mtb/γ-herpesvirus (γHV) coinfection to test the hypothesis that latent γHV infection alters host resistance to Mtb. γHVs are DNA viruses which elicit a polyclonal T cell response and attenuate some acute bacterial pathogens in mice; whether γHVs modulate infection with Mtb is unknown. Here, mice harboring latent mouse gammaherpesvirus 68 (MHV68)-a γHV genetically and biologically related to human Epstein Barr virus (EBV)-were infected via aerosol with a low dose of virulent Mtb. Mtb burdens and IFNγ+ T cell frequencies in mice with latent MHV68 (MHV68POS mice) were subsequently measured and compared to control mice that did not harbor latent MHV68 (MHV68NEG mice). Relative to MHV68NEG controls, MHV68POS mice more effectively limited Mtb growth and dissemination, and had higher frequencies of CD4+IFNγ+ cells in lung-draining lymph nodes. Collectively, our results support a model wherein latent γHV confers moderate protection against subsequent Mtb infection.

Author Correction: Immune-checkpoint protein VISTA critically regulates the IL-23/IL-17 inflammatory axis.

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Immune-checkpoint protein VISTA critically regulates the IL-23/IL-17 inflammatory axis.

V-domain Immunoglobulin Suppressor of T cell Activation (VISTA) is an inhibitory immune-checkpoint molecule that suppresses CD4+ and CD8+ T cell activation when expressed on antigen-presenting cells. Vsir -/- mice developed loss of peripheral tolerance and multi-organ chronic inflammatory phenotypes. Vsir -/- CD4+ and CD8+ T cells were hyper-responsive towards self- and foreign antigens. Whether or not VISTA regulates innate immunity is unknown. Using a murine model of psoriasis induced by TLR7 agonist imiquimod (IMQ), we show that VISTA deficiency exacerbated psoriasiform inflammation. Enhanced TLR7 signaling in Vsir -/- dendritic cells (DCs) led to the hyper-activation of Erk1/2 and Jnk1/2, and augmented the production of IL-23. IL-23, in turn, promoted the expression of IL-17A in both TCRγδ+ T cells and CD4+ Th17 cells. Furthermore, VISTA regulates the peripheral homeostasis of CD27- γδ T cells and their activation upon TCR-mediated or cytokine-mediated stimulation. IL-17A-producing CD27- γδ T cells were expanded in the Vsir -/- mice and amplified the inflammatory cascade. In conclusion, this study has demonstrated that VISTA critically regulates the inflammatory responses mediated by DCs and IL-17-producing TCRγδ+ and CD4+ Th17 T cells following TLR7 stimulation. Our finding provides a rationale for therapeutically enhancing VISTA-mediated pathways to benefit the treatment of autoimmune and inflammatory disorders.

The introduction of RNA-DNA differences underlies interindividual variation in the human IL12RB1 mRNA repertoire.

Human interleukin 12 and interleukin 23 (IL12/23) influence susceptibility or resistance to multiple diseases. However, the reasons underlying individual differences in IL12/23 sensitivity remain poorly understood. Here we report that in human peripheral blood mononuclear cells (PBMCs) and inflamed lungs, the majority of interleukin-12 receptor ß1 (IL12RB1) mRNAs contain a number of RNA-DNA differences (RDDs) that concentrate in sequences essential to IL12Rß1's binding of IL12p40, the protein subunit common to both IL-12 and IL-23. IL12RB1 RDDs comprise multiple RDD types and are detectable by next-generation sequencing and classic Sanger sequencing. As a consequence of these RDDs, the resulting IL12Rß1 proteins have an altered amino acid sequence that could not be predicted on the basis of genomic DNA sequencing alone. Importantly, the introduction of RDDs into IL12RB1 mRNAs negatively regulates IL12Rß1's binding of IL12p40 and is sensitive to activation. Collectively, these results suggest that the introduction of RDDs into an individual's IL12RB1 mRNA repertoire is a novel determinant of IL12/23 sensitivity.

Immune-checkpoint proteins VISTA and PD-1 nonredundantly regulate murine T-cell responses.

V-domain immunoglobulin suppressor of T-cell activation (VISTA) is a negative immune-checkpoint protein that suppresses T-cell responses. To determine whether VISTA synergizes with another immune-checkpoint, programmed death 1 (PD-1), this study characterizes the immune responses in VISTA-deficient, PD-1-deficient (KO) mice and VISTA/PD-1 double KO mice. Chronic inflammation and spontaneous activation of T cells were observed in both single KO mice, demonstrating their nonredundancy. However, the VISTA/PD-1 double KO mice exhibited significantly higher levels of these phenotypes than the single KO mice. When bred onto the 2D2 T-cell receptor transgenic mice, which are predisposed to development of inflammatory autoimmune disease in the CNS, the level of disease penetrance was significantly enhanced in the double KO mice compared with in the single KO mice. Consistently, the magnitude of T-cell response toward foreign antigens was synergistically higher in the VISTA/PD-1 double KO mice. A combinatorial blockade using monoclonal antibodies specific for VISTA and PD-L1 achieved optimal tumor-clearing therapeutic efficacy. In conclusion, our study demonstrates the nonredundant role of VISTA that is distinct from the PD-1/PD-L1 pathway in controlling T-cell activation. These findings provide the rationale to concurrently target VISTA and PD-1 pathways for treating T-cell-regulated diseases such as cancer.

IL12Rß1ΔTM is a secreted product of il12rb1 that promotes control of extrapulmonary tuberculosis.

IL12RB1 is a human gene that is important for resistance to Mycobacterium tuberculosis infection. IL12RB1 is expressed by multiple leukocyte lineages, and encodes a type I transmembrane protein (IL12Rß1) that associates with IL12p40 and promotes the development of host-protective T(H)1 cells. Recently, we observed that il12rb1­the mouse homolog of IL12RB1­is alternatively spliced by leukocytes to produce a second isoform (IL12Rß1ΔTM) that has biological properties distinct from IL12Rß1. Although the expression of IL12Rß1ΔTM is elicited by M. tuberculosis in vivo, and its overexpression enhances IL12p40 responsiveness in vitro, the contribution of IL12Rß1ΔTM to controlling M. tuberculosis infection has not been tested. Here, we demonstrate that IL12Rß1ΔTM represents a secreted product of il12rb1 that, when absent from mice, compromises their ability to control M. tuberculosis infection in extrapulmonary organs. Furthermore, elevated M. tuberculosis burdens in IL12Rß1ΔTM-deficient animals are associated with decreased lymph node cellularity and a decline in TH1 development. Collectively, these data support a model wherein IL12Rß1ΔTM is a secreted product of il12rb1 that promotes resistance to M. tuberculosis infection by potentiating T(H) cells response to IL-12.

IL12B expression is sustained by a heterogenous population of myeloid lineages during tuberculosis.

IL12B is required for resistance to Mycobacterium tuberculosis (Mtb) infection, promoting the initiation and maintenance of Mtb-specific effector responses. While this makes the IL12-pathway an attractive target for experimental tuberculosis (TB) therapies, data regarding what lineages express IL12B after infection is established are limited. This is not obvious in the lung, an organ in which both hematopoietic and non-hematopoietic lineages produce IL12p40 upon pathogen encounter. Here, we use radiation bone marrow chimeras and Yet40 reporter mice to determine what lineages produce IL12p40 during experimental TB. We observed that hematopoietic IL12p40-production was sufficient to control Mtb, with no contribution by non-hematopoietic lineages. Furthermore, rather than being produced by a single subset, IL12p40 was produced by cells that were heterogenous in their size, granularity, autofluorescence and expression of CD11c, CD11b and CD8α. While depending on the timepoint and tissue examined, the surface phenotype of IL12p40-producers most closely resembled macrophages based on previous surveys of lung myeloid lineages. Importantly, depletion of CD11c(hi) cells during infection had no affect on lung IL12p40-concentrations. Collectively, our data demonstrate that IL12p40 production is sustained by a heterogenous population of myeloid lineages during experimental TB, and that redundant mechanisms of IL12p40-production exist when CD11c(hi) lineages are absent.

Inflammatory signals direct expression of human IL12RB1 into multiple distinct isoforms.

IL12RB1 is essential for human resistance to multiple intracellular pathogens, including Mycobacterium tuberculosis. In its absence, the proinflammatory effects of the extracellular cytokines IL-12 and IL-23 fail to occur, and intracellular bacterial growth goes unchecked. Given the recent observation that mouse leukocytes express more than one isoform from il12rb1, we examined whether primary human leukocytes similarly express more than one isoform from IL12RB1. We observed that human leukocytes express as many as 13 distinct isoforms, the relative levels of each being driven by inflammatory stimuli both in vitro and in vivo. Surprisingly, the most abundant isoform present before stimulation is a heretofore uncharacterized intracellular form of the IL-12R (termed "isoform 2") that presumably has limited contact with extracellular cytokine. After stimulation, primary PBMCs, including the CD4(+), CD8(+), and CD56(+) lineages contained therein, alter the splicing of IL12RB1 RNA to increase the relative abundance of isoform 1, which confers IL-12/IL-23 responsiveness. These data demonstrate both a posttranscriptional mechanism by which cells regulate their IL-12/IL-23 responsiveness, and that leukocytes primarily express IL12RB1 in an intracellular form located away from extracellular cytokine.

Early control of Mycobacterium tuberculosis infection requires il12rb1 expression by rag1-dependent lineages.

IL12RB1 is essential for human resistance to Mycobacterium tuberculosis infection. In the absence of a functional IL12RB1 allele, individuals exhibit susceptibility to disseminated, recurrent mycobacterial infections that are associated with defects in both RAG1-dependent and RAG1-independent hematopoietic lineages. Despite this well-established association, a causal relationship between M. tuberculosis susceptibility and IL12RB1 deficiency in either RAG1-dependent or RAG1-independent lineages has never been formally tested. Here, we use the low-dose aerosol model of experimental tuberculosis (TB) to both establish that infected il12rb1(-/-) mice recapitulate important aspects of TB in IL12RB1 null individuals and, more importantly, use radiation bone marrow chimeras to demonstrate that restriction of il12rb1 deficiency solely to rag1-dependent lineages (i.e., T and B cells) allows for the full transfer of the il12rb1(-/-) phenotype. We further demonstrate that the protection afforded by adaptive lymphocyte il12rb1 expression is mediated partially through ifng and that, within the same infection, il12rb1-sufficient T cells exhibit dominance over il12rb1-deficient T cells by enhancing ifng expression in the latter population. Collectively, our data establish a basic framework in which to understand how IL12RB1 promotes control of this significant human disease.

The ß3-integrin ligand of Borrelia burgdorferi is critical for infection of mice but not ticks.

P66 is a Borrelia burgdorferi surface protein with ß3 integrin binding and channel forming activities. In this study, the role of P66 in mammalian and tick infection was examined. B. burgdorferiΔp66 strains were not infectious in wild-type, TLR2⁻/⁻- or MyD88⁻/⁻-deficient mice. Strains with p66 restored to the chromosome restored near wild-type infectivity, while complementation with p66 on a shuttle vector did not restore infectivity. Δp66 mutants are cleared quickly from the site of inoculation, but analyses of cytokine expression and cellular infiltrates at the site of inoculation did not reveal a specific mechanism of clearance. The defect in these mutants cannot be attributed to nutrient limitation or an inability to adapt to the host environment in vivo as Δp66 bacteria were able to survive as well as wild type in dialysis membrane chambers in the rat peritoneum. Δp66 bacteria were able to survive in ticks through the larva to nymph moult, but were non-infectious in mice when delivered by tick bite. Independent lines of evidence do not support any increased susceptibility of the Δp66 strains to factors in mammalian blood. This study is the first to define a B. burgdorferi adhesin as essential for mammalian, but not tick infection.