Galectin-9 binding to Tim-3 renders activated human CD4+ T cells less susceptible to HIV-1 infection

The Role of Coinhibitory Receptors in B Cell Dysregulation in SARS-CoV-2-Infected Individuals with Severe Disease

Severe SARS-CoV-2 infection is associated with significant immune dysregulation involving different immune cell subsets. In this study, when analyzing critically ill COVID-19 patients versus those with mild disease, we observed a significant reduction in total and memory B cell subsets but an increase in naive B cells. Moreover, B cells from COVID-19 patients displayed impaired effector functions, evidenced by diminished proliferative capacity, reduced cytokine, and Ab production. This functional impairment was accompanied by an increased apoptotic potential upon stimulation in B cells from severely ill COVID-19 patients. Our further studies revealed the expansion of B cells expressing coinhibitory molecules (PD-1, PD-L1, TIM-1, VISTA, CTLA-4, and Gal-9) in intensive care unit (ICU)-admitted patients but not in those with mild disease. The coinhibitory receptor expression was linked to altered IgA and IgG expression and increased the apoptotic capacity of B cells. Also, we found a reduced frequency of CD24hiCD38hi regulatory B cells with impaired IL-10 production. Our mechanistic studies revealed that the upregulation of PD-L1 was linked to elevated plasma IL-6 levels in COVID-19 patients. This implies a connection between the cytokine storm and altered B cell phenotype and function. Finally, our metabolomic analysis showed a significant reduction in tryptophan but elevation of kynurenine in ICU-admitted COVID-19 patients. We found that kynurenine promotes PD-L1 expression in B cells, correlating with increased IL-6R expression and STAT1/STAT3 activation. Our observations provide novel insights into the complex interplay of B cell dysregulation, implicating coinhibitory receptors, IL-6, and kynurenine in impaired B cell effector functions, potentially contributing to the pathogenesis of COVID-19.

Membrane organization by tetraspanins and galectins shapes lymphocyte function

Immune receptors are not randomly distributed at the plasma membrane of lymphocytes but are segregated into specialized domains that function as platforms to initiate signalling, as exemplified by the B cell or T cell receptor complex and the immunological synapse. 'Membrane-organizing proteins' and, in particular, tetraspanins and galectins, are crucial for controlling the spatiotemporal organization of immune receptors and other signalling proteins. Deficiencies in specific tetraspanins and galectins result in impaired immune synapse formation, lymphocyte proliferation, antibody production and migration, which can lead to impaired immunity, tumour development and autoimmunity. In contrast to conventional ligand-receptor interactions, membrane organizers interact in cis (on the same cell) and modulate receptor clustering, receptor dynamics and intracellular signalling. New findings have uncovered their complex and dynamic nature, revealing shared binding partners and collaborative activity in determining the composition of membrane domains. Therefore, immune receptors should not be envisaged as independent entities and instead should be studied in the context of their spatial organization in the lymphocyte membrane. We advocate for a novel approach to study lymphocyte function by globally analysing the role of membrane organizers in the assembly of different membrane complexes and discuss opportunities to develop therapeutic approaches that act via the modulation of membrane organization.

Immunological responses in SARS-CoV-2 and HIV co-infection versus SARS-CoV-2 mono-infection: case report of the interplay between SARS-CoV-2 and HIV

BACKGROUND

There is an urgent need to understand the interplay between SARS-CoV-2 and HIV to inform risk-mitigation approaches for HIV-infected individuals.

OBJECTIVES

We conclude that people living with HIV (PLWH) who are antiretroviral therapy (ART) naïve could be at a greater risk of morbidity or mortality once co-infected with SARS-CoV-2.

METHODS

Here, we performed extensive immune phenotyping using flow cytometry. Moreover, to compare the range of values observed in the co-infected case, we have included a larger number of mono-infected cases with SARS-CoV-2. We also quantified soluble co-inhibitory/co-stimulatory molecules in the plasma of our patients.

RESULTS

We noted a robust immune activation characterized by the expansion of CD8+ T cells expressing co-inhibitory/stimulatory molecules (e.g. PD-1, TIM-3, 2B4, TIGIT, CD39, and ICOS) and activation markers (CD38, CD71, and HLA-DR) in the co-infected case. We further found that neutrophilia was more pronounced at the expense of lymphopenia in the co-infected case. In particular, naïve and central memory CD8+ T cells were scarce as a result of switching to effector and effector memory in the co-infected case. CD8+ T cell effector functions such as cytokine production (e.g. TNF-α and IFN-γ) and cytolytic molecules expression (granzyme B and perforin) following anti-CD3/CD28 or the Spike peptide pool stimulation were more prominent in the co-infected case versus the mono-infected case. We also observed that SARS-CoV-2 alters T cell exhaustion commonly observed in PLWH.

CONCLUSION

These findings imply that inadequate immune reconstitution and/or lack of access to ART could dysregulate immune response against SARS-CoV-2 infection, which can result in poor clinical outcomes in PLWH. Our study has implications for prioritizing PLWH in the vaccination program/access to ART in resource-constrained settings.

Analysis of SARS-CoV-2 isolates, namely the Wuhan strain, Delta variant, and Omicron variant, identifies differential immune profiles

There is an urgent need to better understand the impact of different severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants on immune response and disease dynamics to facilitate better intervention strategies. Here, we show that SARS-CoV-2 variants differentially affect host immune responses. The magnitude and quantity of cytokines and chemokines were comparable in those infected with the Wuhan strain and the Delta variant. However, individuals infected with the Omicron variant had significantly lower levels of these mediators. We also found an elevation of plasma galectins (Gal-3, Gal-8, and Gal-9) in infected individuals, in particular, in those with the original strain. Soluble galectins exert a proinflammatory role in COVID-19 pathogenesis. This was illustrated by their correlation with the plasma levels of sCD14, sCD163, enhanced TNF-α/IL-6 secretion, and increased SARS-CoV-2 infectivity in vitro. Moreover, we observed enhanced CD4+ and CD8+ T cell activation in Wuhan strain-infected individuals. Surprisingly, there was a more pronounced T cell activation in those infected with the Omicron in comparison to the Delta variant. In line with T cell activation status, we observed a more pronounced expansion of T cells expressing different co-inhibitory receptors in patients infected with the Wuhan strain, followed by the Omicron and Delta variants. Individuals infected with the Wuhan strain or the Omicron variant had a similar pattern of plasma soluble immune checkpoints. Our results imply that a milder innate immune response might be beneficial and protective in those infected with the Omicron variant. Our results provide a novel insight into the differential impact of SARS-CoV-2 variants on host immunity. IMPORTANCE There is a need to better understand how different SARS-CoV-2 variants influence the immune system and disease dynamics to facilitate the development of better vaccines and therapies. We compared immune responses in 140 SARS-CoV-2-infected individuals with the Wuhan strain, the Delta variant, or the Omicron variant. All these patients were admitted to the intensive care unit and were SARS-CoV-2 vaccination naïve. We found that SARS-CoV-2 variants differentially affect the host immune response. This was done by measuring soluble biomarkers in their plasma and examining different immune cells. Overall, we found that the magnitude of cytokine storm in individuals infected with the Wuhan strain or the Delta variant was greater than in those infected with the Omicron variant. In light of enhanced cytokine release syndrome in individuals infected with the Wuhan strain or the Delta variant, we believe that a milder innate immune response might be beneficial and protective in those infected with the Omicron variant.

Antiretroviral Treatment-Induced Galectin-9 Might Impact HIV Viremia in Addition to Contributing to Inflammaging

BACKGROUND

Galectin-9 induces HIV reactivation and also contributes to non-AIDS events through inflammaging. Hence, it is important to assess its levels in HIV-infected individuals to determine their association with HIV viremia and other comorbidities.

METHODS

Plasma galectin-9 levels were estimated in viremic (n = 152) and aviremic (n = 395) individuals on first-line antiretroviral therapy (ART). They were assessed for correlation with HIV-1 viral load (VL), CD4 count, and ART duration, as well as for receiver operating characteristic curve analysis.

RESULT

Plasma galectin-9 levels correlated positively with VL (r = 0.507, p < 0.0001) and ART duration (r = 0.308, p = 0.002) and negatively with CD4 count (r = -0.186, p < 0.0001). Area under the curve for galectin-9/CD4 count ratio for identifying viremic individuals was 0.906. Sensitivity and specificity of the ratio at a cutoff of 14.47 were 90.13% and 70.05%, respectively, for detecting viremic individuals. Further, galectin-9 levels correlated with cystatin C (r = 0.239, p = 0.0183), IL-18 (r = 0.311, p = 0.006), and systolic blood pressure (r = 0.220, p = 0.0355). Galectin-9-induced HIV reactivation was significantly lower in individuals on long-term ART than those on short-term ART.

CONCLUSION

The galectin-9-to-CD4 count ratio indicated the potential of galectin-9 as a cheaper monitoring tool to detect HIV viremia. Strategies for countering the effects of galectin-9 for controlling HIV viremia and non-AIDS events are urgently warranted.

Galectin-9 promotes natural killer cells activity via interaction with CD44

Natural killer (NK) cells are a potent innate source of cytokines and cytoplasmic granules. Their effector functions are tightly synchronized by the balance between the stimulatory and inhibitory receptors. Here, we quantified the proportion of NK cells and the surface presence of Galectin-9 (Gal-9) from the bone marrow, blood, liver, spleen, and lungs of adult and neonatal mice. We also examined the effector functions of Gal-9+NK cells compared with their Gal-9- counterparts. Our results revealed that Gal-9+NK cells are more abundant in tissues, in particular, in the liver than in the blood and bone marrow. We found Gal-9 presence was associated with enhanced cytotoxic effector molecules granzyme B (GzmB) and perforin expression. Likewise, Gal-9 expressing NK cells displayed greater IFN-γ and TNF-α expression than their negative counterparts under hemostatic circumstances. Notably, the expansion of Gal-9+NK cells in the spleen of mice infected with E. coli implies that Gal-9+NK cells may provide a protective role against infection. Similarly, we found the expansion of Gal-9+NK cells in the spleen and tumor tissues of melanoma B16-F10 mice. Mechanistically, our results revealed the interaction of Gal-9 with CD44 as noted by their co-expression/co-localization. Subsequently, this interaction resulted in enhanced expression of Phospho-LCK, ERK, Akt, MAPK, and mTOR in NK cells. Moreover, we found Gal-9+NK cells exhibited an activated phenotype as evidenced by increased CD69, CD25, and Sca-1 but reduced KLRG1 expression. Likewise, we found Gal-9 preferentially interacts with CD44high in human NK cells. Despite this interaction, we noted a dichotomy in terms of effector functions in NK cells from COVID-19 patients. We observed that the presence of Gal-9 on NK cells resulted in a greater IFN-γ expression without any changes in cytolytic molecule expression in these patients. These observations suggest differences in Gal-9+NK cell effector functions between mice and humans that should be considered in different physiological and pathological conditions. Therefore, our results highlight the important role of Gal-9 via CD44 in NK cell activation, which suggests Gal-9 is a potential new avenue for the development of therapeutic approaches to modulate NK cell effector functions.

Human galectin-9 promotes the expansion of HIV reservoirs in vivo in humanized mice

OBJECTIVE

The human endogenous protein galectin-9 (Gal-9) reactivates latently HIV-infected cells in vitro and ex vivo , which may allow for immune-mediated clearance of these cells. However, Gal-9 also activates several immune cells, which could negatively affect HIV persistence by promoting chronic activation/exhaustion. This potential 'double-edged sword' effect of Gal-9 raises the question of the overall impact of Gal-9 on HIV persistence in vivo .

DESIGN

We used the BLT (bone marrow, liver, thymus) humanized mouse model to evaluate the impact of Gal-9 on HIV persistence in vivo during antiretroviral therapy (ART).

METHODS

Two independent cohorts of ART-suppressed HIV-infected BLT mice were treated with either recombinant Gal-9 or phosphate-buffered saline control. Plasma viral loads and levels of tissue-associated HIV DNA and RNA were measured by qPCR. Immunohistochemistry and HIV RNAscope were used to quantify CD4 + T, myeloid, and HIV RNA+ cells in tissues. T cell activation and exhaustion were measured by flow cytometry, and plasma markers of inflammation were measured by multiplex cytokine arrays.

RESULTS

Gal-9 did not induce plasma markers of inflammation or T cell markers of activation/exhaustion in vivo . However, the treatment significantly increased levels of tissue-associated HIV DNA and RNA compared to controls ( P  = 0.0007 and P  = 0.011, respectively, for cohort I and P  = 0.002 and P  = 0.005, respectively, for cohort II). RNAscope validated the Gal-9 mediated induction of HIV RNA in tissue-associated myeloid cells, but not T cells.

CONCLUSIONS

Our study highlights the overall adverse effects of Gal-9 on HIV persistence and the potential need to block Gal-9 interactions during ART-suppressed HIV infection.

Both N- and C-terminal domains of galectin-9 are capable of inducing HIV reactivation despite mediating differential immunomodulatory functionalities

Background

The shock-and-kill strategy for HIV cure requires the reactivation of latent HIV followed by the killing of the reactivated cellular reservoir. Galectin-9, an immunomodulatory protein, is shown to induce HIV reactivation as well as contribute to non-AIDS- and AIDS-defining events. The protein is prone to cleavage by inflammatory proteases at its linker region separating the N- and C-terminal carbohydrate-binding domains (N- and C-CRDs) which differ in their binding specificities. It is important to study the activity of its cleaved as well as uncleaved forms in mediating HIV reactivation and immunomodulation in order to understand their role in HIV pathogenesis and their further utilization for the shock-and-kill strategy.

Methodology

The PBMCs of HIV patients on virally suppressive ART (n = 11) were stimulated using 350 nM of the full-length protein and N- and C-CRDs of Gal-9. HIV reactivation was determined by analyzing gag RNA copies using qPCR using isolated CD4 cells and intracellular P24 staining of PBMCs by flow cytometry. Cytokine responses induced by the full-length protein and N- and C-CRDs of Gal-9 were also assessed by flow cytometry, Luminex, and gene expression assays. Changes in T helper cell gene expression pattern after the stimulation were also determined by real-time PCR array.

Results

Both N- and C-CRDs of galectin-9 induced HIV reactivation in addition to the full-length galectin-9 protein. The two domains elicited higher cytokine responses than the full-length protein, possibly capable of mediating higher perturbations in the immune system if used for HIV reactivation. N-CRD was found to induce the development of Treg cells, whereas C-CRD inhibited the induction of Treg cells. Despite this, both domains elicited IL-10 secretory response although targeting different CD4 cell phenotypes.

Conclusion

N- and C-CRDs were found to induce HIV reactivation similar to that of the full-length protein, indicating their possible usefulness in the shock-and-kill strategy. The study indicated an anti-inflammatory role of N-CRD versus the proinflammatory properties of C-CRD of galectin-9 in HIV infection.

Galectin-9/Tim-3 pathway mediates dopaminergic neurodegeneration in MPTP-induced mouse model of Parkinson’s disease

Galectin-9 (Gal-9) is a crucial immunoregulatory mediator in the central nervous system. Microglial activation and neuroinflammation play a key role in the degeneration of dopaminergic neurons in the substantia nigra (SN) in Parkinson’s disease (PD). However, it remains unknown whether Gal-9 is involved in the pathogenesis of PD. We found that MPP+ treatment promoted the expression of Gal-9 and pro-inflammatory cytokines (IL-6, IL-1β, TNF-α, and MIP-1α) in a concentration-dependent manner in BV2 cells. Gal-9 enhanced neurodegeneration and oxidative stress induced by MPP+ in SH-SY5Y cells and primary neurons. Importantly, deletion of Gal-9 or blockade of Tim-3 ameliorated microglial activation, reduced dopaminergic neuronal loss, and improved motor performance in an MPTP-induced mouse model of PD. These observations demonstrate a pathogenic role of the Gal-9/Tim-3 pathway in exacerbating microglial activation, neuroinflammation, oxidative stress, and dopaminergic neurodegeneration in the pathogenesis of PD.

Elevated ATP via enhanced miRNA-30b, 30c, and 30e downregulates the expression of CD73 in CD8+ T cells of HIV-infected individuals

CD8⁺ T cells play a crucial role against chronic viral infections, however, their effector functions are influenced by the expression of co-stimulatory/inhibitory receptors. For example, CD73 works with CD39 to convert highly inflammatory ATP to adenosine. However, its expression on T cells in the context of viral infections has not been well defined. Here, we analyzed the expression of CD73 on human T cells in a cohort of 102 HIV-infected individuals including those on antiretroviral therapy (ART), ART-naïve, and long-term non-progressors who were not on ART. We found that the frequency of CD73⁺ T cells was markedly lower among T cell subsets (e.g. naïve, effector or memory) in the peripheral blood of all HIV-infected individuals. Notably, CD73 was decreased at the cell surface, intracellular and gene levels. Functionally, CD8⁺CD73⁺ T cells exhibited decreased cytokine expression (TNF-α, IFN-γ and IL-2) upon global or antigen-specific stimulation and impaired expression of cytolytic molecules at the gene and protein levels. In contrast, CD8⁺CD73⁺ T cells expressed elevated levels of homing receptors such as CCR7, α4β7 integrin, which suggests a migratory advantage for these cells as observed in vitro. We also observed significant migration of CD73⁺CD8⁺ T cells into the cerebrospinal fluids of multiple sclerosis (MS) patients at the time of disease relapse. Moreover, we found that elevated levels of ATP in the plasma of HIV-infected individuals upregulates the expression of miRNA30b-e in T cells in vitro. In turn, inhibition of miRNAs (30b, 30c and 30e) resulted in significant upregulation of CD73 mRNA in CD8⁺ T cells. Therefore, we provide a novel mechanism for the downregulation of CD73 via ATP-induced upregulation of miRNA30b, 30c and 30e in HIV infection. Finally, these observations imply that ATP-mediated downregulation of CD73 mainly occurs via its receptor, P2X1/P2RX1. Our results may in part explain why HIV-infected individuals have reduced risk of developing MS considering the role of CD73 for efficient T cell entry into the central nervous system.

CD8⁺ T cells (killer T cells) play an important role against chronic viral infections, however, their functional properties get compromised during the course of HIV infection. CD73, is one of molecules that influences T cell functions, however, its role in the context of viral infections has not been well defined. Here, we analyzed the expression of CD73 on T cells in a cohort of 102 HIV-infected individuals including those on antiretroviral therapy (ART), ART-naïve, and long-term non-progressors who were not on ART. We found that the frequency of T cells expressing this molecule was markedly lower among different T cell subsets obtained from the blood of HIV-infected individuals. Notably, CD73 was decreased at the intracellular protein and gene levels. Furthermore, we found that T cells expressing this molecule (CD73) had impaired functional properties. In contrast, we observed that T cells expressing CD73 had elevated levels of homing receptors, which suggests a migratory advantage for these cells. This was also supported by increased CD73⁺ T cells in the cerebrospinal fluids of multiple sclerosis patients when they experienced disease replace. Moreover, we found that the elevated level of ATP in the plasma of HIV-infected individuals is responsible for the upregulation of miRNA30b, 30c and 30e, resulting in reduced expression of CD73.

An Emerging Role of TIM3 Expression on T Cells in Chronic Kidney Inflammation

T cell immunoglobulin domain and mucin domain 3 (TIM3) was initially identified as an inhibitory molecule on IFNγ-producing T cells. Further research discovered the broad expression of TIM3 on different immune cells binding to multiple ligands. Apart from its suppressive effects on the Th1 cells, recent compelling experiments highlighted the indispensable role of TIM3 in the myeloid cell-mediated inflammatory response, supporting that TIM3 exerts pleiotropic effects on both adaptive and innate immune cells in a context-dependent manner. A large number of studies have been conducted on TIM3 biology in the disease settings of infection, cancer, and autoimmunity. However, there is a lack of clinical evidence to closely evaluate the role of T cell-expressing TIM3 in the pathogenesis of chronic kidney disease (CKD). Here, we reported an intriguing case of Mycobacterium tuberculosis (Mtb) infection that was characterized by persistent overexpression of TIM3 on circulating T cells and ongoing kidney tubulointerstitial inflammation for a period of 12 months. In this case, multiple histopathological biopsies revealed a massive accumulation of recruited T cells and macrophages in the enlarged kidney and liver. After standard anti-Mtb treatment, repeated renal biopsy identified a dramatic remission of the infiltrated immune cells in the tubulointerstitial compartment. This is the first clinical report to reveal a time-course expression of TIM3 on the T cells, which is pathologically associated with the progression of severe kidney inflammation in a non-autoimmunity setting. Based on this case, we summarize the recent findings on TIM3 biology and propose a novel model of CKD progression due to the aberrant crosstalk among immune cells.

Hematopoietic responses to SARS-CoV-2 infection

Under physiological conditions, hematopoietic stem and progenitor cells (HSPCs) in the bone marrow niches are responsible for the highly regulated and interconnected hematopoiesis process. At the same time, they must recognize potential threats and respond promptly to protect the host. A wide spectrum of microbial agents/products and the consequences of infection-induced mediators (e.g. cytokines, chemokines, and growth factors) can have prominent impact on HSPCs. While COVID-19 starts as a respiratory tract infection, it is considered a systemic disease which profoundly alters the hematopoietic system. Lymphopenia, neutrophilia, thrombocytopenia, and stress erythropoiesis are the hallmark of SARS-CoV-2 infection. Moreover, thrombocytopenia and blood hypercoagulability are common among COVID-19 patients with severe disease. Notably, the invasion of erythroid precursors and progenitors by SARS-CoV-2 is a cardinal feature of COVID-19 disease which may in part explain the mechanism underlying hypoxia. These pieces of evidence support the notion of skewed steady-state hematopoiesis to stress hematopoiesis following SARS-CoV-2 infection. The functional consequences of these alterations depend on the magnitude of the effect, which launches a unique hematopoietic response that is associated with increased myeloid at the expense of decreased lymphoid cells. This article reviews some of the key pathways including the infectious and inflammatory processes that control hematopoiesis, followed by a comprehensive review that summarizes the latest evidence and discusses how SARS-CoV-2 infection impacts hematopoiesis.

Examining the Impact of Galectin-9 on Latent HIV Transcription

The β-galactoside-binding protein Galectin-9 (Gal-9) functions as a double-edged sword during HIV infection. On the one hand, Gal-9 can reactivate HIV latently infected cells, the main barrier to achieving HIV eradication, making them visible to immune clearance. On the other hand, Gal-9 induces latent HIV transcription by activating T cell Receptor (TCR) signaling pathways. These signaling pathways induce undesirable pro-inflammatory responses. While these unwanted responses can be mitigated by rapamycin without impacting Gal-9-mediated latent HIV reactivation, this effect raises the concern that Gal-9 may play a role in the chronic immune activation/inflammation that persists in people living with HIV despite antiretroviral therapy. Together, these data highlight the need to understand the positive and negative impacts of galectin interactions on immunological functions during HIV infection. In this chapter, we describe methods that can be used to investigate the effects of galectins, in particular Gal-9, on latent HIV transcription in vitro and ex vivo.

Differential Signature of the Microbiome and Neutrophils in the Oral Cavity of HIV-Infected Individuals

HIV infection is associated with a wide range of changes in microbial communities and immune cell components of the oral cavity. The purpose of this study was to evaluate the oral microbiome in relationship to oral neutrophils in HIV-infected compared to healthy individuals. We evaluated oral washes and saliva samples from HIV-infected individuals (n=52) and healthy controls (n=43). Using 16S-rRNA gene sequencing, we found differential β-diversity using Principal Coordinate Analysis (PCoA) with Bray-Curtis distances. The α-diversity analysis by Faith’s, Shannon, and observed OTUs indexes indicated that the saliva samples from HIV-infected individuals harbored significantly richer bacterial communities compared to the saliva samples from healthy individuals. Notably, we observed that five species of Spirochaeta including Spirochaetaceae, Spirochaeta, Treponema, Treponema amylovorum, and Treponema azotonutricum were significantly abundant. In contrast, Helicobacter species were significantly reduced in the saliva of HIV-infected individuals. Moreover, we found a significant reduction in the frequency of oral neutrophils in the oral cavity of HIV-infected individuals, which was positively related to their CD4⁺ T cell count. In particular, we noted a significant decline in CD44 expressing neutrophils and the intensity of CD44 expression on oral neutrophils of HIV-infected individuals. This observation was supported by the elevation of soluble CD44 in the saliva of HIV-infected individuals. Overall, the core oral microbiome was distinguishable between HIV-infected individuals on antiretroviral therapy compared to the HIV-negative group. The observed reduction in oral neutrophils might likely be related to the low surface expression of CD44, resulting in a higher bacterial diversity and richness in HIV-infected individuals.

Galectin-9 inhibits cell proliferation and induces apoptosis in Jurkat and KE-37 acute lymphoblastic leukemia cell lines via caspase-3 activation

Background and purpose:

Acute lymphoblastic leukemia (ALL) is a type of cancer of blood and bone marrow characterized by abnormal proliferation of lymphoid progenitor cells. Galectin-9 is a tandem-repeat type galectin expressed in various tumor cells. It seems that the connection between galectin-9 and T cell immunoglobulin mucin-3 receptor acts as a negative regulator of cancer cells proliferation.

Experimental approach:

In this research, the effects of galectin-9 were investigated using MTS cell proliferation colorimetric, colony-forming, annexin V-FITC/PI, and caspase-3 assays in the Jurkat and KE-37 cell lines of ALL. Furthermore, the western blotting technique was used to evaluate the levels of apoptotic proteins such as Bax and Bcl-2 in these cell lines.

Findings/Results:

Our results indicated that galectin-9 can considerably reduce the cell growth and colony formation ability of both Jurkat and KE-37 cell lines in a concentration-dependent manner. Besides, galectin-9 induced apoptosis in a concentration-dependent manner in ALL cells by a mechanism associated with Bax/Bcl-2 expression and activation of the caspase-3 activation.

Conclusion and implications:

Galectin-9 inhibited the growth and proliferation of cell lines with increased programmed cell death, therefore it can be considered as a potential factor in the progression of ALL therapeutics that needs more research in this context.

Identification of Differential Responses of Goat PBMCs to PPRV Virulence Using a Multi-Omics Approach

Peste des petits ruminants (PPR) is an acute transboundary infectious viral disease of small ruminants, mainly sheep and goats. Host susceptibility varies considerably depending on the PPR virus (PPRV) strain, the host species and breed. The effect of strains with different levels of virulence on the modulation of the immune system has not been thoroughly compared in an experimental setting so far. In this study, we used a multi-omics approach to investigate the host cellular factors involved in different infection phenotypes. Peripheral blood mononuclear cells (PBMCs) from Saanen goats were activated with a T-cell mitogen and infected with PPRV strains of different virulence: Morocco 2008 (high virulence), Ivory Coast 1989 (low virulence) and Nigeria 75/1 (live attenuated vaccine strain). Our results showed that the highly virulent strain replicated better than the other two in PBMCs and rapidly induced cell death and a stronger inhibition of lymphocyte proliferation. However, all the strains affected lymphocyte proliferation and induced upregulation of key antiviral genes and proteins, meaning a classical antiviral response is orchestrated regardless of the virulence of the PPRV strain. On the other hand, the highly virulent strain induced stronger inflammatory responses and activated more genes related to lymphocyte migration and recruitment, and inflammatory processes. Both transcriptomic and proteomic approaches were successful in detecting viral and antiviral effectors under all conditions. The present work identified key immunological factors related to PPRV virulence in vitro.

Glycan-Lectin Interactions in Cancer and Viral Infections and How to Disrupt Them

Glycan-lectin interactions play an essential role in different cellular processes. One of their main functions is involvement in the immune response to pathogens or inflammation. However, cancer cells and viruses have adapted to avail themselves of these interactions. By displaying specific glycosylation structures, they are able to bind to lectins, thus promoting pathogenesis. While glycan-lectin interactions promote tumor progression, metastasis, and/or chemoresistance in cancer, in viral infections they are important for viral entry, release, and/or immune escape. For several years now, a growing number of investigations have been devoted to clarifying the role of glycan-lectin interactions in cancer and viral infections. Various overviews have already summarized and highlighted their findings. In this review, we consider the interactions of the lectins MGL, DC-SIGN, selectins, and galectins in both cancer and viral infections together. A possible transfer of ways to target and disrupt them might lead to new therapeutic approaches in different pathological backgrounds.

Neutrophils promote T-cell activation through the regulated release of CD44-bound Galectin-9 from the cell surface during HIV infection

The interaction of neutrophils with T cells has been the subject of debate and controversies. Previous studies have suggested that neutrophils may suppress or activate T cells. Despite these studies, the interaction between neutrophils and T cells has remained a largely unexplored field. Here, based on our RNA sequencing (RNA-seq) analysis, we found that neutrophils have differential transcriptional and functional profiling depending on the CD4 T-cell count of the HIV-infected individual. In particular, we identified that neutrophils in healthy individuals express surface Galectin-9 (Gal-9), which is down-regulated upon activation, and is consistently down-regulated in HIV-infected individuals. However, down-regulation of Gal-9 was associated with CD4 T-cell count of patients. Unstimulated neutrophils express high levels of surface Gal-9 that is bound to CD44, and, upon stimulation, neutrophils depalmitoylate CD44 and induce its movement out of the lipid raft. This process causes the release of Gal-9 from the surface of neutrophils. In addition, we found that neutrophil-derived exogenous Gal-9 binds to cell surface CD44 on T cells, which promotes LCK activation and subsequently enhances T-cell activation. Furthermore, this process was regulated by glycolysis and can be inhibited by interleukin (IL)-10. Together, our data reveal a novel mechanism of Gal-9 shedding from the surface of neutrophils. This could explain elevated plasma Gal-9 levels in HIV-infected individuals as an underlying mechanism of the well-characterized chronic immune activation in HIV infection. This study provides a novel role for the Gal-9 shedding from neutrophils. We anticipate that our results will spark renewed investigation into the role of neutrophils in T-cell activation in other acute and chronic conditions, as well as improved strategies for modulating Gal-9 shedding.

This study shows that HIV-infected individuals have different neutrophil profiles depending on their CD4 T cell count. In particular, neutrophils express high levels of surface Gal-9 but this is shed upon stimulation; this exogenous Gal-9 binds to CD44 on T cells, which promotes LCK activation and subsequently enhances T cell activation.

Plasma Extracellular Vesicles Enhance HIV-1 Infection of Activated CD4+ T Cells and Promote the Activation of Latently Infected J-Lat10.6 Cells via miR-139-5p Transfer

HIV latency is a challenge to the success of antiretroviral therapy (ART). Hence patients may benefit from interventions that efficiently reactivate the latent virus to be eliminated by ARTs. Here we show that plasma extracellular vesicles (pEVs) can enhance HIV infection of activated CD4⁺ T cells and reactivate the virus in latently infected J-Lat 10.6 cells. Evaluation of the extravesicular miRNA cargo by a PCR array revealed that pEVs from HIV patients express miR-139-5p. Furthermore, we found that increased levels of miR-139-5p in J-Lat 10.6 cells incubated with pEVs corresponded with reduced expression of the transcription factor, FOXO1. pEV treatment also corresponded with increased miR-139-5p expression in stimulated PD1+ Jurkat cells, but with concomitant upregulation of FOXO1, Fos, Jun, PD-1 and PD-L1. However, J-Lat 10.6 cells incubated with miR-139-5p inhibitor-transfected pEVs from HIV ART-naïve and on-ART patients expressed reduced levels of miR-139-5p than cells treated with pEVs from healthy controls (HC). Collectively, our results indicate that pEV miR-139-5p belongs to a network of miRNAs that can promote cell activation, including latent HIV-infected cells by regulating the expression of FOXO1 and the PD1/PD-L1 promoters, Fos and Jun.

Differential transcriptional and functional properties of regulatory T cells in HIV-infected individuals on antiretroviral therapy and long-term non-progressors

Objectives

Regulatory T cells (Tregs) are widely recognised as a subset of CD4⁺CD25⁺FOXP3⁺ T cells that have a key role in maintaining immune homeostasis. The impact of HIV‐1 infection on immunological properties and effector functions of Tregs has remained the topic of debate and controversy. In the present study, we investigated transcriptional profile and functional properties of Tregs in HIV‐1‐infected individuals either receiving antiretroviral therapy (ART, n = 50) or long‐term non‐progressors (LTNPs, n = 24) compared to healthy controls (HCs, n = 38).

Methods

RNA sequencing (RNAseq), flow cytometry‐based immunophenotyping and functional assays were performed to study Tregs in different HIV cohorts.

Results

Our RNAseq analysis revealed that Tregs exhibit different transcriptional profiles in HIV‐infected individuals. While Tregs from patients on ART upregulate pathways associated with a more suppressive (activated) phenotype, Tregs in LTNPs exhibit upregulation of pathways associated with impaired suppressive properties. These observations may explain a higher propensity for autoimmune diseases in LTNPs. Also, we found substantial upregulation of HLA‐F mRNA and HLA‐F protein in Tregs from HIV‐infected subjects compared to healthy individuals. These observations highlight a potential role for this non‐classical HLA in Tregs in the context of HIV infection, which should be investigated further in other chronic viral infections and cancer.

Conclusion

Our study has provided a novel insight into Tregs at the transcriptional and functional levels in different HIV‐infected groups.

Erythroid precursors and progenitors suppress adaptive immunity and get invaded by SARS-CoV-2

SARS-CoV-2 infection is associated with lower blood oxygen levels, even in patients without hypoxia requiring hospitalization. This discordance illustrates the need for a more unifying explanation as to whether SARS-CoV-2 directly or indirectly affects erythropoiesis. Here, we show significantly enriched CD71⁺ erythroid precursors/progenitors in the blood circulation of COVID-19 patients. We found that these cells have distinctive immunosuppressive properties. In agreement, we observed a strong negative correlation between the frequency of these cells with T and B cell proportions in COVID-19 patients. The expansion of these CD71⁺ erythroid precursors/progenitors was negatively correlated with the hemoglobin levels. A subpopulation of abundant erythroid cells, CD45⁺ CD71⁺ cells, co-express ACE2, TMPRSS2, CD147, and CD26, and these can be infected with SARS-CoV-2. In turn, pre-treatment of erythroid cells with dexamethasone significantly diminished ACE2/TMPRSS2 expression and subsequently reduced their infectivity with SARS-CoV-2. This provides a novel insight into the impact of SARS-CoV-2 on erythropoiesis and hypoxia seen in COVID-19 patients.

Galectin-9, a Player in Cytokine Release Syndrome and a Surrogate Diagnostic Biomarker in SARS-CoV-2 Infection

The outbreak of SARS-CoV-2 infection has enormously impacted our lives. Clinical evidence has implicated the emergence of cytokine release syndrome as the prominent cause of mortality in COVID-19 patients. In this study, we observed massive elevation of plasma Galectin-9 (Gal-9) in COVID-19 patients compared to healthy controls (HCs). By using the receiver operating characteristic (ROC) curve, we found that a baseline of 2,042 pg/ml plasma Gal-9 can differentiate SARS-CoV-2-infected from noninfected individuals with high specificity/sensitivity (95%). Analysis of 30 cytokines and chemokines detected a positive correlation of the plasma Gal-9 with C-reactive protein (CRP) and proinflammatory cytokines/chemokines such as interleukin-6 (IL-6), tumor necrosis factor alpha (TNF-α), IP-10, MIP-1α, and MCP-1 but an inverse correlation with transforming growth factor β (TGF-β) in COVID-19 patients. In agreement, we found enhanced production of IL-6 and TNF-α by monocytes and NK cells of COVID-19 patients once treated with the recombinant human Gal-9 in vitro. Also, we observed that although the cell-membrane expression of Gal-9 on monocytes does not change in COVID-19 patients, those with higher Gal-9 expression exhibit an activated phenotype. Furthermore, we noted significant downregulation of surface Gal-9 in neutrophils from COVID-19 patients compared to HCs. Our further investigations indicated that immune activation following SARS-CoV-2 infection results in Gal-9 shedding from neutrophils. The strong correlation of Gal-9 with proinflammatory mediators suggests that inhibition of Gal-9 may severe as a therapeutic approach in COVID-19 infection. Besides, the plasma Gal-9 measurement may be used as a surrogate diagnostic biomarker in COVID-19 patients.

Blood Levels of Galectin-9, an Immuno-Regulating Molecule, Reflect the Severity for the Acute and Chronic Infectious Diseases

Galectin-9 (Gal-9) is a β-galactoside-binding lectin capable of promoting or suppressing the progression of infectious diseases. This protein is susceptible to cleavage of its linker-peptides by several proteases, and the resulting cleaved forms, N-terminal carbohydrate recognition domain (CRD) and C-terminal CRD, bind to various glycans. It has been suggested that full-length (FL)-Gal-9 and the truncated (Tr)-Gal-9s could exert different functions from one another via their different glycan-binding activities. We propose that FL-Gal-9 regulates the pathogenesis of infectious diseases, including human immunodeficiency virus (HIV) infection, HIV co-infected with opportunistic infection (HIV/OI), dengue, malaria, leptospirosis, and tuberculosis (TB). We also suggest that the blood levels of FL-Gal-9 reflect the severity of dengue, malaria, and HIV/OI, and those of Tr-Gal-9 markedly reflect the severity of HIV/OI. Recently, matrix metallopeptidase-9 (MMP-9) was suggested to be an indicator of respiratory failure from coronavirus disease 2019 (COVID-19) as well as useful for differentiating pulmonary from extrapulmonary TB. The protease cleavage of FL-Gal-9 may lead to uncontrolled hyper-immune activation, including a cytokine storm. In summary, Gal-9 has potential to reflect the disease severity for the acute and chronic infectious diseases.

Galectin-9 as a biomarker of disease severity

Galectin-9 (Gal-9) is a β-galactoside binding lectin known for its immunomodulatory role in various microbial infections. Gal-9 is expressed in all organ systems and localized in the nucleus, cell surface, cytoplasm and the extracellular matrix. It mediates host-pathogen interactions and regulates cell signalling via binding to its receptors. Gal-9 is involved in many physiological functions such as cell growth, differentiation, adhesion, communication and death. However, recent studies have emphasized on the elevated levels of Gal-9 in autoimmune disorders, viral infections, parasitic invasion, cancer, acute liver failure, atopic dermatitis, chronic kidney disease, type-2 diabetes, coronary artery disease, atherosclerosis and benign infertility-related gynecological disorders. In this paper we have reviewed the potential of Gal-9 as a reliable, sensitive and non-invasive biomarker of disease severity. Tracking changes in Gal-9 levels and its implementation as a biomarker in clinical practice will be an important tool to monitor disease activity and facilitate personalized treatment decisions.

The role of galectins in virus infection - A systemic literature review

BACKGROUND

Galectins are β-Galactose binding lectins expressed in numerous cells and play multiple roles in various physiological and cellular functions. However, few information is available regarding the role of galectins in virus infections. Here, we conducted a systemic literature review to analyze the role of galectins in human virus infection.

METHODS

This study uses a systematic method to identify and select eligible articles according to the PRISMA guidelines. References were selected from PubMed, Web of Science and Google Scholar database covering publication dated from August 1995 to December 2018.

RESULTS

Results indicate that galectins play multiple roles in regulation of virus infections. Galectin-1 (Gal-1), galectin-3 (Gal-3), galectin-8 (Gal-8), and galectin-9 (Gal-9) were found as the most predominant galectins reported to participate in virus infection. The regulatory function of galectins occurs by extracellularly binding to viral glycosylated envelope proteins, interacting with ligands or receptors on immune cells, or acting intracellularly with viral or cellular components in the cytoplasm. Several galectins express either positive or negative regulatory role, while some had dual regulatory capabilities on virus propagation based on the conditions and their localization. However, limited information about the endogenous function of galectins were found. Therefore, the endogenous effects of galectins in host-virus regulation remains valuable to investigate.

CONCLUSIONS

This study offers information regarding the various roles galectins shown in viral infection and suggest that galectins can potentially be used as viral therapeutic targets or antagonists.

Galectin-9 expression defines exhausted T cells and impaired cytotoxic NK cells in patients with virus-associated solid tumors

BACKGROUND

We have previously reported that the upregulation of galectin-9 (Gal-9) on CD4+ and CD8+ T cells in HIV patients was associated with impaired T cell effector functions. Gal-9 is a ligand for T cell immunoglobulin and mucin domain-3, and its expression on T cells in cancer has not been investigated. Therefore, we aimed to investigate the expression level and effects of Gal-9 on T cell functions in patients with virus-associated solid tumors (VASTs).

METHODS

40 patients with VASTs through a non-randomized and biomarker-driven phase II LATENT trial were investigated. Peripheral blood mononuclear cells and tumor biopsies were obtained and subjected to immunophenotyping. In this trial, the effects of oral valproate and avelumab (anti-PD-L1) was investigated in regards to the expression of Gal-9 on T cells.

RESULTS

We report the upregulation of Gal-9 expression by peripheral and tumor-infiltrating CD4+ and CD8+ T lymphocytes in patients with VASTs. Our results indicate that Gal-9 expression is associated with dysfunctional T cell effector functions in the periphery and tumor microenvironment (TME). Coexpression of Gal-9 with PD-1 or T cell immunoglobulin and ITIM domain (TIGIT) exhibited a synergistic inhibitory effect and enhanced an exhausted T cell phenotype. Besides, responding patients to treatment had lower Gal-9 mRNA expression in the TME. Translocation of Gal-9 from the cytosol to the cell membrane of T cells following stimulation suggests persistent T cell receptor (TCR) stimulation as a potential contributing factor in Gal-9 upregulation in patients with VASTs. Moreover, partial colocalization of Gal-9 with CD3 on T cells likely impacts the initiation of signal transduction via TCR as shown by the upregulation of ZAP70 in Gal-9+ T cells. Also, we found an expansion of Gal-9+ but not TIGIT+ NK cells in patients with VASTs; however, dichotomous to TIGIT+ NK cells, Gal-9+ NK cells exhibited impaired cytotoxic molecules but higher Interferon gamma (IFN-γ) expression.

CONCLUSION

Our data indicate that higher Gal-9-expressing CD8+ T cells were associated with poor prognosis following immunotherapy with anti-Programmed death-ligand 1 (PD-L1) (avelumab) in our patients' cohort. Therefore, for the very first time to our knowledge, we report Gal-9 as a novel marker of T cell exhaustion and the potential target of immunotherapy in patients with VASTs.

Plasma Levels of a Cleaved Form of Galectin-9 Are the Most Sensitive Biomarkers of Acquired Immune Deficiency Syndrome and Tuberculosis Coinfection

Acquired immunodeficiency syndrome (AIDS) complicated with tuberculosis (TB) is a global public issue. Due to the paucity of bacteria in AIDS/TB, blood-based biomarkers that reflect disease severity are desired. Plasma levels of matricellular proteins, such as osteopontin (OPN) and galectin-9 (Gal-9), are known to be elevated in AIDS and TB. Therefore, full-length (FL)-Gal9 and FL-OPN, and their truncated forms (Tr-Gal9, Ud-OPN), and 38 cytokines/chemokines were measured in the plasma of 24 AIDS (other than TB), 49 TB, and 33 AIDS/TB patients. Receiver-operating characteristic analysis was used to screen molecules that could distinguish either between disease and normal group, among each disease group, or between deceased patients and survivors. Selected molecules were further analyzed for significant differences. Tr-Gal9 had the highest ability to differentiate TB from AIDS or AIDS/TB, while Ud-OPN distinguished multidrug resistance (MDR)-TB from non-MDR TB, and extra-pulmonary TB from pulmonary TB. Molecules significantly elevated in deceased patients included; FL-Gal9, Tr-Gal9, interleukin (IL)-1 receptor antagonist, IL-17A and transforming growth factor-α in AIDS; IL-6, granulocyte colony-stimulating factor and monocyte chemotactic protein-1 in TB; and macrophage inflammatory protein-1β in AIDS/TB. From the sensitivity, specificity, and significant elevation, Tr-Gal9 is the best biomarker of inflammation and severity in AIDS and AIDS/TB.

Exosomal LGALS9 in the cerebrospinal fluid of glioblastoma patients suppressed dendritic cell antigen presentation and cytotoxic T-cell immunity

Glioblastoma multiforme (GBM) is highly invasive, with a high recurrence rate and limited treatment options, and is the deadliest glioma. Exosomes (Exos) have attracted much attention in the diagnosis and treatment of GBM and are expected to address the severe limitations of biopsy conditions. Exos in the cerebrospinal fluid (CSF) have great potential in GBM dynamic monitoring and intervention strategies. Here, we evaluated the difference in the proteome information of Exos from the CSF (CSF-Exos) between GBM patients and low-grade glioma patients, and the correlations between GBM-CSF-Exos and immunosuppressive properties. Our results indicates that GBM-CSF-Exos contained a unique protein, LGALS9 ligand, which bound to the TIM3 receptor of dendritic cells (DCs) in the CSF to inhibit antigen recognition, processing and presentation by DCs, leading to failure of the cytotoxic T-cell-mediated antitumor immune response. Blocking the secretion of exosomal LGALS9 from GBM tumors could cause mice to exhibit sustained DC tumor antigen-presenting activity and long-lasting antitumor immunity. We concluded that GBM cell-derived exosomal LGALS9 acts as a major regulator of tumor progression by inhibiting DC antigen presentation and cytotoxic T-cell activation in the CSF and that loss of this inhibitory effect can lead to durable systemic antitumor immunity.

Immune Checkpoints in Viral Infections

As evidence has mounted that virus-infected cells, such as cancer cells, negatively regulate the function of T-cells via immune checkpoints, it has become increasingly clear that viral infections similarly exploit immune checkpoints as an immune system escape mechanism. Although immune checkpoint therapy has been successfully used in cancer treatment, numerous studies have suggested that such therapy may also be highly relevant for treating viral infection, especially chronic viral infections. However, it has not yet been applied in this manner. Here, we reviewed recent findings regarding immune checkpoints in viral infections, including COVID-19, and discussed the role of immune checkpoints in different viral infections, as well as the potential for applying immune checkpoint blockades as antiviral therapy.

Selective Upregulation of CTLA-4 on CD8+ T Cells Restricted by HLA-B*35Px Renders them to an Exhausted Phenotype in HIV-1 infection

HLA-B*35Px is associated with HIV-1 disease rapid progression to AIDS. However, the mechanism(s) underlying this deleterious effect of this HLA allele on HIV-1 infection outcome has not fully understood. CD8⁺ T cells play a crucial role to control the viral replication but impaired CD8⁺ T cells represent a major hallmark of HIV-1 infection. Here, we examined the effector functions of CD8⁺ T cells restricted by HLA-B*35Px (HLA-B*35:03 and HLA-B*35:02), HLA-B*27/B57 and non-HLA-B*27/B57 (e.g. HLA-A*01, A*02, A*03, A*11, A*24, A*26, B*40, B*08, B*38, B*44). CD8⁺ T cells restricted by HLA-B*35Px exhibited an impaired phenotype compared with those restricted by HLA-B*27/B57 and even non-HLA-B*27/B57. CD8⁺ T cells restricted by non-HLA-B*27/B57 when encountered their cognate epitopes upregulated TIM-3 and thus became suppressed by regulatory T cells (Tregs) via TIM-3: Galectin-9 (Gal-9). Strikingly, CD8⁺ T cells restricted by HLA-B*35Px expressed fewer TIM-3 and therefore did not get suppressed by Tregs, which was similar to CD8⁺ T cells restricted by HLA-B*27/B57. Instead, CD8⁺ T cells restricted by HLA-B*35Px upon recognition of their cognate epitopes upregulated CTLA-4. The transcriptional and impaired phenotype (e.g. poor effector functions) of HIV-specific CD8⁺ T cells restricted by HLA-B*35 was related to persistent CTLA-4, elevated Eomes and blimp-1 but poor T-bet expression. As such, anti-CTLA-4 antibody, Ipilimumab, reversed the impaired proliferative capacity of antigen-specific CD8⁺ T cells restricted by HLA-B*35Px but not others. This study supports the concept that CD8⁺ T resistance to Tregs-mediated suppression is related to allele restriction rather than the epitope specificity. Our results aid to explain a novel mechanism for the inability of HIV-specific CD8⁺ T cells restricted by HLA-B*35Px to control viral replication.

A rare group of HIV-infected individuals with HLA-B*35Px rapidly progress to AIDS but those with HLA-B*27 and HLA-B*57 spare disease progression. Previous studies have suggested that viral mutation may prevent a robust immune response against the virus in these with HLA-B*35Px. However, the functionality of HIV-specific CD8⁺ T cells restricted by HLA-B*35Px remains unclear. In this study, we demonstrate that HIV-specific CD8⁺ T cells restricted by HLA-B*35Px (HLA-B*35:03 and HLA-B*35:02) exhibit an impaired phenotype (e.g. low proliferative capacity, poor cytotoxic molecules expression and, poor cytokine production ability). Interestingly, CD8⁺ T cells restricted by HLA-B*27/B*57 evade regulatory T cells (Tregs) suppression but not those restricted by non-HLA-B*27/B*57. CD8⁺ T cells restricted by non-HLA-B*27/B*57 when encountering their epitopes upregulate TIM-3 but not those restricted by HLA-B*27/B*57 and HLA-B*35Px. As a result, CD8⁺ T cells restricted by non-HLA-B*27/B*57 become suppressed by Tregs via TIM-3: Galectin-9 interactions. Strikingly, CD8⁺ T cells restricted by HLA-B*35Px upregulate CTLA-4 when encountering their epitopes, which render them to an exhausted phenotype. This differential response is linked to the up-regulation of Eomes, Blimp-1 but low T-bet expression in CD8⁺ T cells restricted by HLA-B*35Px. These results implicate that reinvigoration of these cells might be feasible using an anti-CTLA-4 antibody.

Elevated Levels of Galectin-9 but Not Osteopontin in HIV and Tuberculosis Infections Indicate Their Roles in Detecting MTB Infection in HIV Infected Individuals

Galectin-9 (Gal-9) and osteopontin (OPN) play immunomodulatory roles in tuberculosis and HIV infections. Evaluation of their levels as well as their interplay with different pro-inflammatory cytokines is critical to understand their role in immunopathogenesis of HIV/tuberculosis co-infection considering the complexity of the disease. Plasma levels of these proteins were measured by ELISAs in HIV-negative individuals with pulmonary (n = 21), extrapulmonary (n = 33), and latent tuberculosis (n = 22) and in HIV infected patients with pulmonary (n = 14), latent tuberculosis (n = 17), and without tuberculosis (n = 41). Levels of pro-inflammatory cytokines were estimated by Luminex assay. Receiver operated characteristic curve analysis was performed to evaluate discriminatory roles of these proteins. Spearman's correlation analysis was performed with the markers of HIV and tuberculosis disease progression to evaluate their immunopathogenic roles. Gal-9 and OPN levels were higher in HIV uninfected patients with active tuberculosis than with latent tuberculosis. Gal-9 but not OPN levels were higher in HIV infected patients with active tuberculosis than with latent tuberculosis. Area under curve for Galectin-9 was >0.9 in HIV/tuberculosis co-infection and extrapulmonary tuberculosis. OPN and IL-6 levels were higher in patients with severe chest X-ray grade indicating its association with severity of the disease and positively correlated with each other. Stronger positive and negative correlations of Gal-9 levels, respectively, with viral loads and CD4 cell counts in HIV infected patients were observed than OPN levels indicating their association with HIV disease progression. Thus, significantly elevated Gal-9 levels were reported for the first time in HIV/tuberculosis co-infection and extrapulmonary tuberculosis in our study than single infections with HIV and tuberculosis. The study indicated a need for further evaluation of monitoring role of Gal-9 for detection of developing tuberculosis in HIV infected individuals. The findings also indicated differential roles of Gal-9 and OPN in the pathogenesis of tuberculosis and HIV infections.

Increased expression of CDKN1A/p21 in HIV-1 controllers is correlated with upregulation of ZC3H12A/MCPIP1

Background

Some multifunctional cellular proteins, as the monocyte chemotactic protein-induced protein 1 (ZC3H12A/MCPIP1) and the cyclin-dependent kinase inhibitor CDKN1A/p21, are able to modulate the cellular susceptibility to the human immunodeficiency virus type 1 (HIV-1). Several studies showed that CDKN1A/p21 is expressed at high levels ex vivo in cells from individuals who naturally control HIV-1 replication (HIC) and a recent study supports a coordinate regulation of ZC3H12A/MCPIP1 and CDKN1A/p21 transcripts in a model of renal carcinoma cells. Here, we explored the potential associations between mRNA expression of ZC3H12A/MCPIP1 and CDKN1A/p21 in HIC sustaining undetectable (elite controllers–EC) or low (viremic controllers–VC) viral loads.

Results

We found a selective upregulation of ZC3H12A/MCPIP1 and CDKN1A/p21 mRNA levels in PBMC from HIC compared with both ART–suppressed and HIV–negative control groups (P≤ 0.02) and higher MCPIP1 and p21 proteins levels in HIC than in HIV-1 negative subjects. There was a moderate positive correlation (r ≥ 0.57; P ≤ 0.014) between expressions of both transcripts in HIC and in HIC combined with control groups. We found positive correlations between the mRNA level of CDKN1A/p21 with activated CD4⁺ T cells levels in HIC (r ≥ 0.53; P ≤ 0.017) and between the mRNA levels of both CDKN1A/p21 (r = 0.74; P = 0.005) and ZC3H12A/MCPIP1 (r = 0.58; P = 0.040) with plasmatic levels of sCD14 in EC. Reanalysis of published transcriptomic data confirmed the positive association between ZC3H12A/MCPIP1 and CDKN1A/p21 mRNA levels in CD4⁺ T cells and monocytes from disparate cohorts of HIC and other HIV-positive control groups.

Conclusions

These data show for the first time the simultaneous upregulation of ZC3H12A/MCPIP1 and CDKN1A/p21 transcripts in the setting of natural suppression of HIV-1 replication in vivo and the positive correlation of the expression of these cellular factors in disparate cohorts of HIV-positive individuals. The existence of a common regulatory pathway connecting ZC3H12A/MCPIP1 and CDKN1A/p21 could have a synergistic effect on HIV-1 replication control and pharmacological manipulation of these multifunctional host factors may open novel therapeutic perspectives to prevent HIV-1 replication and disease progression.

The Examination of Viral Characteristics of HIV-1 CRF07_BC and Its Potential Interaction with Extracellular Galectin-3

HIV-1 CRF07_BC is a B’ and C subtype recombinant emerging virus and many of its viral characteristics remain unclear. Galectin-3 (Gal3) is a β-galactose binding lectin that has been reported as a pattern recognition receptor (PRR) and is known to mediate adhesion between cells and microbes. This study aims to examine the viral characteristics of HIV-1 CRF07_BC virus and the role of extracellular galectin-3 in HIV-1 CRF07_BC infection. A total of 28 HIV-1+ injecting drug users (IDUs) were recruited and 24 (85.7%) were identified as HIV-1 CRF07_BC. Results indicate that significant higher serum galectin-3 was measured in CRF07_BC infected patients and CRF07_BC infection triggered significant galectin-3 expression (p < 0.01). Viral characteristics demonstrate that CRF07_BC virions display a higher level of envelope gp120 spikes. The virus infectivity assay demonstrated that co-treatment with galectin-3 significantly promoted CRF07_BC attachment and internalization (p < 0.01). A co-immunoprecipitation assay showed that pulldown galectin-3 co-precipitated both CD4 and gp120 proteins. Results from an enzyme-linked immunosorbent assay (ELISA) indicate that the galectin-3 promoting effect occurs through enhancement of the interaction between gp120 and CD4. This study suggests that CRF07_BC was predominant in HIV-1+ IDUs and CRF07_BC utilized extracellular galectin-3 to enhance its infectivity via stabilization of the gp120-CD4 interaction.

Differential expression of interferon-lambda receptor 1 splice variants determines the magnitude of the antiviral response induced by interferon-lambda 3 in human immune cells

Type III interferons (IFN-lambdas(λ)) are important cytokines that inhibit viruses and modulate immune responses by acting through a unique IFN-λR1/IL-10RB heterodimeric receptor. Until now, the primary antiviral function of IFN-λs has been proposed to be at anatomical barrier sites. Here, we examine the regulation of IFN-λR1 expression and measure the downstream effects of IFN-λ3 stimulation in primary human blood immune cells, compared with lung or liver epithelial cells. IFN-λ3 directly bound and upregulated IFN-stimulated gene (ISG) expression in freshly purified human B cells and CD8+ T cells, but not monocytes, neutrophils, natural killer cells, and CD4+ T cells. Despite similar IFNLR1 transcript levels in B cells and lung epithelial cells, lung epithelial cells bound more IFN-λ3, which resulted in a 50-fold greater ISG induction when compared to B cells. The reduced response of B cells could be explained by higher expression of the soluble variant of IFN-λR1 (sIFN-λR1), which significantly reduced ISG induction when added with IFN-λ3 to peripheral blood mononuclear cells or liver epithelial cells. T-cell receptor stimulation potently, and specifically, upregulated membrane-bound IFNLR1 expression in CD4+ T cells, leading to greater antiviral gene induction, and inhibition of human immunodeficiency virus type 1 infection. Collectively, our data demonstrate IFN-λ3 directly interacts with the human adaptive immune system, unlike what has been previously shown in published mouse models, and that type III IFNs could be potentially utilized to suppress both mucosal and blood-borne viral infections.

Advances toward Curing HIV-1 Infection in Tissue Reservoirs

A disease of more than 39.6 million people worldwide, HIV-1 infection has no curative therapy. To date, one man has achieved a sterile cure, with millions more hoping to avoid the potential pitfalls of lifelong antiretroviral therapy and other HIV-related disorders, including neurocognitive decline. Recent developments in immunotherapies and gene therapies provide renewed hope in advancing efforts toward a sterilizing or functional cure. On the horizon is research concentrated in multiple separate but potentially complementary domains: vaccine research, viral transcript editing, T-cell effector response targeting including checkpoint inhibitors, and gene editing. Here, we review the concept of targeting the HIV-1 tissue reservoirs, with an emphasis on the central nervous system, and describe relevant new work in functional cure research and strategies for HIV-1 eradication.

CD71+ Erythroid Cells Exacerbate HIV-1 Susceptibility, Mediate trans-Infection, and Harbor Infective Viral Particles

Immature red blood cells (erythroid precursors or CD71⁺ erythroid cells) have a wide range of immunomodulatory properties. In this study, we found that these erythroid precursors are abundant in the human cord blood/placental tissues, in the blood of HIV-infected and anemic individuals. We observed that these cells exacerbate HIV-1 replication/infection in target cells and even make HIV target cells more permissible to HIV infection. In addition, we found that HIV gets a free ride by binding on the surface of these cells and thus can travel to different parts of the body. In agreement, we noticed a positive correlation between the plasma viral load and the frequency of these cells in HIV patients. More importantly, we observed that infective HIV particles reside inside these erythroid precursors but not mature red blood cells. Therefore, these cells by harboring HIV can play an important role in HIV pathogenesis.

CD71⁺ erythroid cells (CECs) have a wide range of immunomodulatory properties. Here, we show that CECs are expanded in the peripheral blood of HIV patients, with a positive correlation between their frequency and the plasma viral load. CECs from HIV patients and human cord blood/placenta exacerbate HIV-1 infection/replication when cocultured with CD4⁺ T cells, and that preexposure of CD4⁺ T cells to CECs enhances their permissibility to HIV infection. However, mature red blood cells (RBCs) do not enhance HIV replication when cocultured with CD4⁺ T cells. We also found CECs express substantial levels of the NOX2 gene and via a mitochondrial reactive oxygen species (ROS)-dependent mechanism possibly upregulate NF-κB in CD4⁺ T cells once cocultured, which affects the cell cycle machinery to facilitate HIV-1 replication. The complement receptor-1 (CD35) and the Duffy antigen receptor for chemokines (DARC) as potential HIV target molecules are expressed significantly higher on CECs compared to mature red blood cells. Blocking CD35 or DARC substantially abolishes HIV-1 transmission by RBCs to uninfected CD4⁺ T cells but not by CECs. In contrast, we observed CECs bind to HIV-1 via CD235a and subsequently transfer the virus to uninfected CD4⁺ T cells, which can be partially blocked by the anti-CD235a antibody. More importantly, we found that CECs from HIV-infected individuals in the presence of antiretroviral therapy harbor infective viral particles, which mediate HIV-1 trans-infection of CD4⁺ T cells. Therefore, our findings provide a novel insight into the role of CECs in HIV pathogenesis as potential contributing cells in viral persistence and transmission.

TIM3 comes of age as an inhibitory receptor

T cell immunoglobulin and mucin domain-containing protein 3 (TIM3), a member of the TIM family, was originally identified as a receptor expressed on interferon-γ-producing CD4⁺ and CD8⁺ T cells. Initial data indicated that TIM3 functioned as a 'co-inhibitory' or 'checkpoint' receptor, but due to the lack of a definable inhibitory signalling motif, it was also suggested that TIM3 might act as a co-stimulatory receptor. Recent studies have shown that TIM3 is part of a module that contains multiple co-inhibitory receptors (checkpoint receptors), which are co-expressed and co-regulated on dysfunctional or 'exhausted' T cells in chronic viral infections and cancer. Furthermore, co-blockade of TIM3 and programmed cell death 1 (PD1) can result in tumour regression in preclinical models and can improve anticancer T cell responses in patients with advanced cancers. Here, we highlight the developments in understanding TIM3 biology, including novel ligand identification and the discovery of loss-of-function mutations associated with human disease. In addition, we summarize emerging data from human clinical trials showing that TIM3 indeed acts as a 'checkpoint' receptor and that inhibition of TIM3 enhances the antitumour effect of PD1 blockade.

Exploring the key communicator role of exosomes in cancer microenvironment through proteomics

There have been many attempts to fully understand the mechanism of cancer behavior. Yet, how cancers develop and metastasize still remain elusive. Emerging concepts of cancer biology in recent years have focused on the communication of cancer with its microenvironment, since cancer cannot grow and live alone. Cancer needs to communicate with other cells for survival, and thus they secrete various messengers, including exosomes that contain many proteins, miRNAs, mRNAs, etc., for construction of the tumor microenvironment. Moreover, these intercellular communications between cancer and its microenvironment, including stromal cells or distant cells, can promote tumor growth, metastasis, and escape from immune surveillance. In this review, we summarized the role of proteins in the exosome as communicators between cancer and its microenvironment. Consequently, we present cancer specific exosome proteins and their unique roles in the interaction between cancer and its microenvironment. Clinically, these exosomes might provide useful biomarkers for cancer diagnosis and therapeutic tools for cancer treatment.

Breaking the Glyco-Code of HIV Persistence and Immunopathogenesis

PURPOSE OF REVIEW

Glycoimmunology is an emerging field focused on understanding how immune responses are mediated by glycans (carbohydrates) and their interaction with glycan-binding proteins called lectins. How glycans influence immunological functions is increasingly well understood. In a parallel way, in the HIV field, it is increasingly understood how the host immune system controls HIV persistence and immunopathogenesis. However, what has mostly been overlooked, despite its potential for therapeutic applications, is the role that the host glycosylation machinery plays in modulating the persistence and immunopathogenesis of HIV. Here, we will survey four areas in which the links between glycan-lectin interactions and immunology and between immunology and HIV are well described. For each area, we will describe these links and then delineate the opportunities for the HIV field in investigating potential interactions between glycoimmunology and HIV persistence/immunopathogenesis.

RECENT FINDINGS

Recent studies show that the human glycome (the repertoire of human glycan structures) plays critical roles in driving or modulating several cellular processes and immunological functions that are central to maintaining HIV infection. Understanding the links between glycoimmunology and HIV infection may create a new paradigm for discovering novel glycan-based therapies that can lead to eradication, functional cure, or improved tolerance of lifelong infection.

Galectin-9 Mediates HIV Transcription by Inducing TCR-Dependent ERK Signaling

Endogenous plasma levels of the immunomodulatory carbohydrate-binding protein galectin-9 (Gal-9) are elevated during HIV infection and remain elevated after antiretroviral therapy (ART) suppression. We recently reported that Gal-9 regulates HIV transcription and potently reactivates latent HIV. However, the signaling mechanisms underlying Gal-9-mediated viral transcription remain unclear. Given that galectins are known to modulate T cell receptor (TCR)-signaling, we hypothesized that Gal-9 modulates HIV transcriptional activity, at least in part, through inducing TCR signaling pathways. Gal-9 induced T cell receptor ζ chain (CD3ζ) phosphorylation (11.2 to 32.1%; P = 0.008) in the J-Lat HIV latency model. Lck inhibition reduced Gal-9-mediated viral reactivation in the J-Lat HIV latency model (16.8-0.9%; P < 0.0001) and reduced both Gal-9-mediated CD4+ T cell activation (10.3 to 1.65% CD69 and CD25 co-expression; P = 0.0006), and IL-2/TNFα secretion (P < 0.004) in primary CD4+ T cells from HIV-infected individuals on suppressive ART. Using phospho-kinase antibody arrays, we found that Gal-9 increased the phosphorylation of the TCR-downstream signaling molecules ERK1/2 (26.7-fold) and CREB (6.6-fold). ERK and CREB inhibitors significantly reduced Gal-9-mediated viral reactivation (16.8 to 2.6 or 12.6%, respectively; P < 0.0007). Given that the immunosuppressive rapamycin uncouples HIV latency reversal from cytokine-associated toxicity, we also investigated whether rapamycin could uncouple Gal-9-mediated latency reactivation from its concurrent pro-inflammatory cytokine production. Rapamycin reduced Gal-9-mediated secretion of IL-2 (4.4-fold, P = 0.001) and TNF (4-fold, P = 0.02) without impacting viral reactivation (16.8% compared to 16.1%; P = 0.2). In conclusion, Gal-9 modulates HIV transcription by activating the TCR-downstream ERK and CREB signaling pathways in an Lck-dependent manner. Our findings could have implications for understanding the role of endogenous galectin interactions in modulating TCR signaling and maintaining chronic immune activation during ART-suppressed HIV infection. In addition, uncoupling Gal-9-mediated viral reactivation from undesirable pro-inflammatory effects, using rapamycin, may increase the potential utility of recombinant Gal-9 within the reversal of HIV latency eradication framework.

Dysregulation of FTX/miR-545 signaling pathway downregulates Tim-3 and is responsible for the abnormal activation of macrophage in cirrhosis

BACKGROUND

Accumulating evidence has suggested the involvement of miR-545 and long noncoding RNA (lncRNA) FTX in a wide range of diseases. Therefore, this study aimed to investigate the molecular mechanism underlying the function of miR-545 and lncRNA FTX in hepatitis B virus (HBV)-related cirrhosis.

METHOD

The level of Tim-3, TLR-4, and endotoxin was detected in CD14⁺ , CD14 ⁺ CD16 ⁺ , and CD14 ⁺ CD16 ^- monocytes isolated from both patients with cirrhosis and healthy controls. ELISA assays were performed to detect the effect of Lipopolysaccharide (LPS) or FTX on the expression of tumor necrosis factor alpha (TNF-a), interleukin-6 (IL-6), IL-1β, and Nuclear factor kB (NF-kB). In-silico analysis, luciferase assay, real-time polymerase chain reaction (PCR), and Western blot analysis were utilized to determine the regulatory relationship between miR-545 and Tim-3.

RESULTS

The levels of Tim-3, Tim-3 MIF and endotoxin were reduced in the CD14⁺ monocytes isolated from patients with cirrhosis. In addition, the level of Tim-3 was also decreased in the CD14 ⁺ CD16 ^- monocytes isolated from patients with cirrhosis, whereas the level of Tim-3 in CD14 ⁺ CD16 ⁺ monocytes showed no evident difference between healthy controls and patients with cirrhosis. Furthermore, TLR-4 was highly expressed in CD14 ⁺ CD16 ⁺ monocytes isolated from patients with cirrhosis, whereas Tim-3 was negatively regulated by endotoxin and the correlation coefficient was -0.5287. After the LPS stimulation, although the level of TNF-a, IL-6, IL-1β, and NF-kB was higher in both patients with cirrhosis and healthy controls, the effect of LPS in patients with cirrhosis was much more significant. In addition, the cirrhosis group showed a lower level of FTX and Tim-3, but a higher level of miR-545. Moreover, miR-545 directly bound to the 3'untranslated region (3'UTR) of Tim-3 and inhibited the luciferase activity of cells cotransfected with miR-545 mimics and wild-type 3'UTR of Tim-3. Furthermore, FTX downregulated the expression of miR-545, TNF-a, IL-6, IL-1β, and NF-kB, but upregulated the expression of Tim-3.

CONCLUSION

The results of this study confirmed the effect of FTX, miR-545, and Tim-3 on the expression of inflammatory cytokines, the lymphocyte/monocyte ratio, and the severity and prognosis of HBV-related cirrhosis.

Restriction of Human Cytomegalovirus Infection by Galectin-9

Human cytomegalovirus (HCMV) is a ubiquitous human herpesvirus. While HCMV infection is generally asymptomatic in the immunocompetent, it can have devastating consequences in those with compromised or underdeveloped immune systems, including transplant recipients and neonates. Galectins are a widely expressed protein family that have been demonstrated to modulate both antiviral immunity and regulate direct host-virus interactions. The potential for galectins to directly modulate HCMV infection has not previously been studied, and our results reveal that galectin-9 (Gal-9) can potently inhibit HCMV infection. Gal-9-mediated inhibition of HCMV was dependent upon its carbohydrate recognition domains and thus dependent on glycan interactions. Temperature shift studies revealed that Gal-9 specific inhibition was mediated primarily at the level of virus-cell fusion and not binding. Additionally, we found that during reactivation of HCMV in hematopoietic stem cell transplant (HSCT) patients soluble Gal-9 is upregulated. This study provides the first evidence for Gal-9 functioning as a potent antiviral defense effector molecule against HCMV infection and identifies it as a potential clinical candidate to restrict HCMV infections.IMPORTANCE Human cytomegalovirus (HCMV) continues to cause serious and often life-threatening disease in those with impaired or underdeveloped immune systems. This virus is able to infect and replicate in a wide range of human cell types, which enables the virus to spread to other individuals in a number of settings. Current antiviral drugs are associated with a significant toxicity profile, and there is no vaccine; these factors highlight a need to identify additional targets for the development of anti-HCMV therapies. We demonstrate for the first time that secretion of a member of the galectin family of proteins, galectin-9 (Gal-9), is upregulated during natural HCMV-reactivated infection and that this soluble cellular protein possesses a potent capacity to block HCMV infection by inhibiting virus entry into the host cell. Our findings support the possibility of harnessing the antiviral properties of Gal-9 to prevent HCMV infection and disease.

Gal power: the diverse roles of galectins in regulating viral infections

Viruses, as a class of pathogenic microbe, remain a significant health burden globally. Viral infections result in significant morbidity and mortality annually and many remain in need of novel vaccine and anti-viral strategies. The development of effective novel anti-viral therapeutics, in particular, requires detailed understanding of the mechanism of viral infection, and the host response, including the innate and adaptive arms of the immune system. In recent years, the role of glycans and lectins in pathogen-host interactions has become an increasingly relevant issue. This review focuses on the interactions between a specific lectin family, galectins, and the broad range of viral infections in which they play a role. Discussed are the diverse activities that galectins play in interacting directly with virions or the cells they infect, to promote or inhibit viral infection. In addition we describe how galectin expression is regulated both transcriptionally and post-transcriptionally by viral infections. We also compare the contribution of known galectin-mediated immune modulation, across a range of innate and adaptive immune anti-viral responses, to the outcome of viral infections.

α4β7 integrin inhibitors: a patent review

INTRODUCTION

The α₄β₇ integrin is heterodimeric cell surface receptors expressed on most leukocytes. Mucosal addressing cell adhesion molecule 1(MAdCAM-1) is an exclusive ligand for α₄β₇ integrin. Areas covered: This article will highlight the progress that has been made in the discovery and development of α₄β₇ integrin inhibitors, and their use in the treatment of inflammatory bowel diseases, multiple sclerosis, asthma, hepatic disorders, human immunodeficiency virus, allergic conjunctivitis and type 1 diabetes. Expert opinion: α₄β₇ integrin inhibitors have attracted much interest for their clinical implication. Natalizumab and Vedolizumab are monoclonal antibodies (mAbs) successfully utilized clinically. Natalizumab is a mAbs of α₄-subunit blocking both α₄β₁ and α₄β₇ integrin. Vedolizumab selectively targets the α₄β₇ integrin. Several mAbs are still in the process of research and development. Among these mAbs, etrolizumab selectively against the β₇-subunit and AMG-181 specifically against the α₄β₇ integrin are the most promising anti-α₄β₇ integrin antibodies. Despite the unclear development stage of TR-14035 and R411, several low molecular compounds show bright future of further development, such as AJM300 and CDP323. In addition, results from laboratory data show that peptide inhibitors, such as peptide X, are effective α₄β₇ integrin inhibitors.

CD71+ Erythroid Suppressor Cells Promote Fetomaternal Tolerance through Arginase-2 and PDL-1

Survival of the allogeneic pregnancy depends on the maintenance of immune tolerance to paternal alloantigens at the fetomaternal interface. Multiple localized mechanisms contribute to the fetal evasion from the mother's immune rejection as the fetus is exposed to a wide range of stimulatory substances such as maternal alloantigens, microbes and amniotic fluids. In this article, we demonstrate that CD71⁺ erythroid cells are expanded at the fetomaternal interface and in the periphery during pregnancy in both humans and mice. These cells exhibit immunosuppressive properties, and their abundance is associated with a Th2 skewed immune response, as their depletion results in a proinflammatory immune response at the fetomaternal interface. In addition to their function in suppressing proinflammatory responses in vitro, maternal CD71⁺ erythroid cells inhibit an aggressive allogeneic response directed against the fetus such as reduction in TNF-α and IFN-γ production through arginase-2 activity and PD-1/programmed death ligand-1 (PDL-1) interactions. Their depletion leads to the failure of gestation due to the immunological rejection of the fetus. Similarly, fetal liver CD71⁺ erythroid cells exhibit immunosuppressive activity. Therefore, immunosuppression mediated by CD71⁺ erythroid cells on both sides (mother/fetus) is crucial for fetomaternal tolerance. Thus, our results reveal a previously unappreciated role for CD71⁺ erythroid cells in pregnancy and indicate that these cells mediate homeostatic immunosuppressive/immunoregulatory responses during pregnancy.

Galectin-9 binds to O-glycans on protein disulfide isomerase

Changes in the T cell surface redox environment regulate critical cell functions, such as cell migration, viral entry and cytokine production. Cell surface protein disulfide isomerase (PDI) contributes to the regulation of T cell surface redox status. Cell surface PDI can be released into the extracellular milieu or can be internalized by T cells. We have found that galectin-9, a soluble lectin expressed by T cells, endothelial cells and dendritic cells, binds to and retains PDI on the cell surface. While endogenous galectin-9 is not required for basal cell surface PDI expression, exogenous galectin-9 mediated retention of cell surface PDI shifted the disulfide/thiol equilibrium on the T cell surface. O-glycans on PDI are required for galectin-9 binding, and PDI recognition appears to be specific for galectin-9, as galectin-1 and galectin-3 do not bind PDI. Galectin-9 is widely expressed by immune and endothelial cells in inflamed tissues, suggesting that T cells would be exposed to abundant galectin-9, in cis and in trans, in infectious or autoimmune conditions.

LAG-3 Represents a Marker of CD4+ T Cells with Regulatory Activity in Patients with Bone Fracture

The lymphocyte activation gene 3 (LAG-3) is a CD4 homolog with binding affinity to MHC class II molecules. It is thought that LAG-3 exerts a bimodal function, such that co-ligation of LAG-3 and CD3 could deliver an inhibitory signal in conventional T cells, whereas, on regulatory T cells, LAG-3 expression could promote their inhibitory function. In this study, we investigated the role of LAG-3 expression on CD4⁺ T cells in patients with long bone fracture. We found that LAG-3⁺ cells represented approximately 13% of peripheral blood CD4⁺ T cells on average. Compared to LAG-3^- CD4⁺ T cells, LAG-3⁺ CD4⁺ T cells presented significantly higher Foxp3 and CTLA-4 expression. Directly ex vivo or with TCR stimulation, LAG-3⁺ CD4⁺ T cells expressed significantly higher levels of IL-10 and TGF-β than LAG-3^- CD4⁺ T cells. Interestingly, blocking the LAG-3-MHC class II interaction actually increased the IL-10 expression by LAG-3⁺ CD4⁺ T cells. The frequency of LAG-3⁺ CD4⁺ T cell was positively correlated with restoration of healthy bone function in long bone fracture patients. These results together suggested that LAG-3 is a marker of CD4⁺ T cells with regulatory function; at the same time, LAG-3 might have limited the full suppressive potential of Treg cells.

Adaptive NKG2C+CD57+ Natural Killer Cell and Tim-3 Expression During Viral Infections

Repetitive stimulation by persistent pathogens such as human cytomegalovirus (HCMV) or human immunodeficiency virus (HIV) induces the differentiation of natural killer (NK) cells. This maturation pathway is characterized by the acquisition of phenotypic markers, CD2, CD57, and NKG2C, and effector functions—a process regulated by Tim-3 and orchestrated by a complex network of transcriptional factors, involving T-bet, Eomes, Zeb2, promyelocytic leukemia zinc finger protein, and Foxo3. Here, we show that persistent immune activation during chronic viral co-infections (HCMV, hepatitis C virus, and HIV) interferes with the functional phenotype of NK cells by modulating the Tim-3 pathway; a decrease in Tim-3 expression combined with the acquisition of inhibitory receptors skewed NK cells toward an exhausted and cytotoxic phenotype in an inflammatory environment during chronic HIV infection. A better understanding of the mechanisms underlying NK cell differentiation could aid the identification of new immunological targets for checkpoint blockade therapies in a manner that is relevant to chronic infection and cancer.