HVEM and CD160: Regulators of Immunopathology During Malaria Blood-Stage

Neuropilin-1 identifies a subset of highly activated CD8+ T cells during parasitic and viral infections

Neuropilin-1 (Nrp-1) expression on CD8+ T cells has been identified in tumor-infiltrating lymphocytes and in persistent murine gamma-herpes virus infections, where it interferes with the development of long-lived memory T cell responses. In parasitic and acute viral infections, the role of Nrp-1 expression on CD8+ T cells remains unclear. Here, we demonstrate a strong induction of Nrp-1 expression on CD8+ T cells in Plasmodium berghei ANKA (PbA)-infected mice that correlated with neurological deficits of experimental cerebral malaria (ECM). Likewise, the frequency of Nrp-1+CD8+ T cells was significantly elevated and correlated with liver damage in the acute phase of lymphocytic choriomeningitis virus (LCMV) infection. Transcriptomic and flow cytometric analyses revealed a highly activated phenotype of Nrp-1+CD8+ T cells from infected mice. Correspondingly, in vitro experiments showed rapid induction of Nrp-1 expression on CD8+ T cells after stimulation in conjunction with increased expression of activation-associated molecules. Strikingly, T cell-specific Nrp-1 ablation resulted in reduced numbers of activated T cells in the brain of PbA-infected mice as well as in spleen and liver of LCMV-infected mice and alleviated the severity of ECM and LCMV-induced liver pathology. Mechanistically, we identified reduced blood-brain barrier leakage associated with reduced parasite sequestration in the brain of PbA-infected mice with T cell-specific Nrp-1 deficiency. In conclusion, Nrp-1 expression on CD8+ T cells represents a very early activation marker that exacerbates deleterious CD8+ T cell responses during both, parasitic PbA and acute LCMV infections.

OMIP-93: A 41-color high parameter panel to characterize various co-inhibitory molecules and their ligands in the lymphoid and myeloid compartment in mice

This 41-color panel has been designed to characterize both the lymphoid and the myeloid compartments in mice. The number of immune cells isolated from organs is often low, whilst an increasing number of factors need to be analyzed to gain a deeper understanding of the complexity of an immune response. With a focus on T cells, their activation and differentiation status, as well as their expression of several co-inhibitory and effector molecules, this panel also allows the analysis of ligands to these co-inhibitory molecules on antigen-presenting cells. This panel enables deep phenotypic characterization of CD4+ and CD8+ T cells, regulatory T cells, γδ T cells, NK T cells, B cells, NK cells, monocytes, macrophages, dendritic cells, and neutrophils. Whilst previous panels have focused on these topics individually, this is the first panel to enable simultaneous analysis of these compartments, thus enabling a comprehensive analysis with a limited number of immune cells/sample size. This panel is designed to analyze and compare the immune response in different mouse models of infectious diseases, but can also be extended to other disease models, for example tumors or autoimmune diseases. Here, we apply this panel to C57BL/6 mice infected with Plasmodium berghei ANKA, a mouse model of cerebral malaria.

The impact of CD160 deficiency on alloreactive CD8 T cell responses and allograft rejection

CD160 is a member of the immunoglobulin superfamily with a pattern of expression mainly restricted to cytotoxic cells. To assess the functional relevance of the HVEM/CD160 signaling pathway in allogeneic cytotoxic responses, exon 2 of the CD160 gene was targeted by CRISPR/Cas9 to generate CD160 deficient mice. Next, we evaluated the impact of CD160 deficiency in the course of an alloreactive response. To that aim, parental donor WT (wild-type) or CD160 KO (knock-out) T cells were adoptively transferred into non-irradiated semiallogeneic F1 recipients, in which donor alloreactive CD160 KO CD4 T cells and CD8 T cells clonally expanded less vigorously than in WT T cell counterparts. This differential proliferative response rate at the early phase of T cell expansion influenced the course of CD8 T cell differentiation and the composition of the effector T cell pool that led to a significant decreased of the memory precursor effector cells (MPECs) / short-lived effector cells (SLECs) ratio in CD160 KO CD8 T cells compared to WT CD8 T cells. Despite these differences in T cell proliferation and differentiation, allogeneic MHC class I mismatched (bm1) skin allograft survival in CD160 KO recipients was comparable to that of WT recipients. However, the administration of CTLA-4.Ig showed an enhanced survival trend of bm1 skin allografts in CD160 KO with respect to WT recipients. Finally, CD160 deficient NK cells were as proficient as CD160 WT NK cells in rejecting allogeneic cellular allografts or MHC class I deficient tumor cells. CD160 may represent a CD28 alternative costimulatory molecule for the modulation of allogeneic CD8 T cell responses either in combination with costimulation blockade or by direct targeting of alloreactive CD8 T cells that upregulate CD160 expression in response to alloantigen stimulation.

Subclone-specific microenvironmental impact and drug response in refractory multiple myeloma revealed by single-cell transcriptomics

Virtually all patients with multiple myeloma become unresponsive to treatment over time. Relapsed/refractory multiple myeloma (RRMM) is accompanied by the clonal evolution of myeloma cells with heterogeneous genomic aberrations and profound changes of the bone marrow microenvironment (BME). However, the molecular mechanisms that drive drug resistance remain elusive. Here, we analyze the heterogeneous tumor cell population and its complex interaction network with the BME of 20 RRMM patients by single cell RNA-sequencing before/after treatment. Subclones with chromosome 1q-gain express a specific transcriptomic signature and frequently expand during treatment. Furthermore, RRMM cells shape an immune suppressive BME by upregulation of inflammatory cytokines and close interaction with the myeloid compartment. It is characterized by the accumulation of PD1⁺ γδ T-cells and tumor-associated macrophages as well as the depletion of hematopoietic progenitors. Thus, our study resolves transcriptional features of subclones in RRMM and mechanisms of microenvironmental reprogramming with implications for clinical decision-making.

CD160 protein as a new therapeutic target in a battle against autoimmune, infectious and lifestyle diseases. Analysis of the structure, interactions and functions

The glycosylphosphatidylinositol-anchored transmembrane glycoprotein CD160 (cluster of differentiation 160) is a member of the immunoglobulin superfamily. Four isoforms, which differ by the presence or absence of an immunoglobulin-like domain and the mode of anchoring in the cell membrane, have been identified. CD160 has a significant impact on the proper functioning of the immune system by activating natural killer cells and inhibiting T cells. CD160 is a natural ligand for herpes virus entry mediator (HVEM), a member of the tumor necrosis factor superfamily. The CD160-HVEM complex is a rare example of direct interaction between the two different superfamilies. The interaction of these two proteins leads to the inhibition of CD4⁺ T cells which, in consequence, leads to the inhibition of the correct response of the immune system. Available research articles indicate that CD160 plays a role in various types of cancer, chronic viral diseases, malaria, paroxysmal nocturnal hemoglobinuria, atherosclerosis, autoimmune diseases, skin inflammation, acute liver damage and retinal vascular disease. We present here an overview of the CD160 protein, the general characteristics of the receptor and its isoforms, details of structural studies of CD160 and the CD160-HVEM complex, as well as a description of the role of this protein in selected human diseases.

Accelerator or Brake: Immune Regulators in Malaria

Malaria is a life-threatening infectious disease, affecting over 250 million individuals worldwide each year, eradicating malaria has been one of the greatest challenges to public health for a century. Growing resistance to anti-parasitic therapies and lack of effective vaccines are major contributing factors in controlling this disease. However, the incomplete understanding of parasite interactions with host anti-malaria immunity hinders vaccine development efforts to date. Recent studies have been unveiling the complexity of immune responses and regulators against Plasmodium infection. Here, we summarize our current understanding of host immune responses against Plasmodium-derived components infection and mainly focus on the various regulatory mechanisms mediated by recent identified immune regulators orchestrating anti-malaria immunity.

BCG Provides Short-Term Protection from Experimental Cerebral Malaria in Mice

Clinical and experimental evidence suggests that the tuberculosis vaccine BCG offers protection against unrelated pathogens including the malaria parasite. Cerebral malaria (CM) is the most severe complication associated with Plasmodium falciparum infection in humans and is responsible for most of the fatalities attributed to malaria. We investigated whether BCG protected C57BL/6 mice from P. berghei ANKA (PbA)-induced experimental CM (ECM). The majority of PbA-infected mice that were immunized with BCG showed prolonged survival without developing clinical symptoms of ECM. However, this protective effect waned over time and was associated with the recovery of viable BCG from liver and spleen. Intriguingly, BCG-mediated protection from ECM was not associated with a reduction in parasite burden, indicating that BCG immunization did not improve anti-parasite effector mechanisms. Instead, we found a significant reduction in pro-inflammatory mediators and CD8⁺ T cells in brains of BCG-vaccinated mice. Together these data suggest that brain recruitment of immune cells involved in the pathogenesis of ECM decreased after BCG vaccination. Understanding the mechanisms underlying the protective effects of BCG on PbA-induced ECM can provide a rationale for developing effective adjunctive therapies to reduce the risk of death and brain damage in CM.

CD160 Plays a Protective Role During Chronic Infection by Enhancing Both Functionalities and Proliferative Capacity of CD8+ T Cells

The understanding of protective immunity during HIV infection remains elusive. Here we showed that CD160 defines a polyfunctional and proliferative CD8+ T cell subset with a protective role during chronic HIV-1 infection. CD160+ CD8+ T cells derived from HIV+ patients correlated with slow progressions both in a cross-sectional study and in a 60-month longitudinal cohort, displaying enhanced cytotoxicity and proliferative capacity in response to HIV Gag stimulation; triggering CD160 promoted their functionalities through MEK–ERK and PI3K–AKT pathways. These observations were corroborated by studying chronic lymphocytic choriomeningitis virus (LCMV) infection in mice. The genetic ablation of CD160 severely impaired LCMV-specific CD8+ T cell functionalities and thereby resulted in loss of virus control. Interestingly, transcriptional profiling showed multiple costimulatory and survival pathways likely to be involved in CD160+ T cell development. Our data demonstrated that CD160 acts as a costimulatory molecule positively regulating CD8+ T cells during chronic viral infections, thus representing a potential target for immune intervention.

CD160 expression on CD8+ T cells is associated with active effector responses but limited activation potential in pancreatic cancer

CD160 is an Ig-like glycoprotein expressed by the majority of circulating natural killer cells and γδ T cells. Whether CD160 could regulate CD8⁺ T-cell functions remains unknown. In this study, we investigated the effects of CD160 on CD8⁺ T cells in pancreatic cancer. First, we found that the frequency of PD-1⁺ cells was comparable between CD160⁺ and CD160^-CD8⁺ T cells, with the former presenting significantly higher PD-1 expression level. In contrast, the frequency of TIM-3⁺ cells was higher among CD160⁺ cells but the expression level was comparable between CD160⁺ and CD160^-CD8⁺ T cells. The IFN-γ and IL-2-expressing CD8⁺ T cells, directly ex vivo, were highly enriched in the CD160⁺ subset. However, when CD160⁺ and CD160^-CD8⁺ T cells were stimulated, the proliferation levels of CD160⁺ and CD160^- cells were initially comparable, but were significantly lower in CD160⁺CD8⁺ T cells than in CD160^-CD8⁺ T cells later on. The IFN-γ and IL-2 transcription levels were initially higher in CD160⁺CD8⁺ T cells, but eventually reduced in CD160⁺CD8⁺ T cells compared to CD160^-CD8⁺ T cells. Also, CD160⁺CD8⁺ T cells presented lower cytotoxic capacity than CD160^-CD8⁺ T cells. Interestingly, we observed that tumor-infiltrating CD8⁺ T cells were significantly enriched with the CD160⁺ subset in pancreatic cancer patients. In addition, patients with higher frequencies of tumor CD160⁺CD8⁺ T cells presented lower survival. Overall, these data demonstrated that tumor-infiltrating CD8⁺ T cells were enriched with the CD160⁺ subset in pancreatic cancer, with active effector responses directly ex vivo but limited potential for further activation.

Title: IL-10-producing T cells and their dual functions

Interleukin (IL)-10 is considered a prototypical anti-inflammatory cytokine, which significantly contributes to the maintenance and reestablishment of immune homeostasis. However, this classical view fails to fully describe the pleiotropic roles of IL-10. Indeed, IL-10 can also promote immune responses, e.g. by supporting B-cell and CD8⁺ T-cell activation. The reasons for these seemingly opposing functions are unclear to a large extent. Recent and previous studies suggest that the cellular source and the microenvironment impact the function of IL-10. However, studies addressing the mechanisms which determine whether IL-10 promotes inflammation or controls it have just begun. This review first summarizes the recent findings on the heterogeneity of IL-10 producing T cells and their impact on the target cells. Finally, we will propose two possible explanations for the dual functions of IL-10.

An Animal Model of Acute and Chronic Chagas Disease With the Reticulotropic Y Strain of Trypanosoma cruzi That Depicts the Multifunctionality and Dysfunctionality of T Cells

Chagas disease (ChD), a complex and persistent parasitosis caused by Trypanosoma cruzi, represents a natural model of chronic infection, in which some people exhibit cardiac or digestive complications that can result in death 20–40 years after the initial infection. Nonetheless, due to unknown mechanisms, some T. cruzi-infected individuals remain asymptomatic throughout their lives. Actually, no vaccine is available to prevent ChD, and treatments for chronic ChD patients are controversial. Chronically T. cruzi-infected individuals exhibit a deterioration of T cell function, an exhaustion state characterized by poor cytokine production and increased inhibitory receptor co-expression, suggesting that these changes are potentially related to ChD progression. Moreover, an effective anti-parasitic treatment appears to reverse this state and improve the T cell response. Taking into account these findings, the functionality state of T cells might provide a potential correlate of protection to detect individuals who will or will not develop the severe forms of ChD. Consequently, we investigated the T cell response, analyzed by flow cytometry with two multicolor immunofluorescence panels, to assess cytokines/cytotoxic molecules and the expression of inhibitory receptors, in a murine model of acute (10 and 30 days) and chronic (100 and 260 days) ChD, characterized by parasite persistence for up to 260 days post-infection and moderate inflammation of the colon and liver of T. cruzi-infected mice. Acute ChD induced a high antigen-specific multifunctional T cell response by producing IFN-γ, TNF-α, IL-2, granzyme B, and perforin; and a high frequency of T cells co-expressed 2B4, CD160, CTLA-4, and PD-1. In contrast, chronically infected mice with moderate inflammatory infiltrate in liver tissue exhibited monofunctional antigen-specific cells, high cytotoxic activity (granzyme B and perforin), and elevated levels of inhibitory receptors (predominantly CTLA-4 and PD-1) co-expressed on T cells. Taken together, these data support our previous results showing that similar to humans, the T. cruzi persistence in mice promotes the dysfunctionality of T cells, and these changes might correlate with ChD progression. Thus, these results constitute a model that will facilitate an in-depth search for immune markers and correlates of protection, as well as long-term studies of new immunotherapy strategies for ChD.

CSF1R antagonism limits local restimulation of antiviral CD8+ T cells during viral encephalitis

BACKGROUND

Microglia are resident macrophages of the central nervous system (CNS) locally maintained through colony-stimulating factor 1 receptor (CSF1R) signaling. Microglial depletion via CSF1R inactivation improves cognition in mouse models of neuroinflammation, but limits virologic control in the CNS of mouse models of neurotropic infections by unknown mechanisms. We hypothesize that CSF1R plays a critical role in myeloid cell responses that restrict viral replication and locally restimulate recruited antiviral T cells within the CNS.

METHODS

The impact of CSF1R signaling during West Nile virus infection was assessed in vivo using a mouse model of neurotropic infection. Pharmacological inactivation of CSF1R was achieved using PLX5622 prior to infection with virulent or attenuated strains of West Nile virus (WNV), an emerging neuropathogen. The subsequent effect of CSF1R antagonism on virologic control was assessed by measuring mortality and viral titers in the CNS and peripheral organs. Immune responses were assessed by flow cytometric-based phenotypic analyses of both peripheral and CNS immune cells.

RESULTS

Mice treated with CSF1R antagonist prior to infection exhibited higher susceptibility to lethal WNV infection and lack of virologic control in both the CNS and periphery. CSFR1 antagonism reduced B7 co-stimulatory signals on peripheral and CNS antigen-presenting cells (APCs) by depleting CNS cellular sources, which limited local reactivation of CNS-infiltrating virus-specific T cells and reduced viral clearance.

CONCLUSIONS

Our results demonstrate the impact of CSF1R antagonism on APC activation in the CNS and periphery and the importance of microglia in orchestrating the CNS immune response following neurotropic viral infection. These data will be an important consideration when assessing the benefit of CSF1R antagonism, which has been investigated as a therapeutic for neurodegenerative conditions, in which neuroinflammation is a contributing factor.