G-Protein Coupled Receptor 18 Contributes to Establishment of the CD8 Effector T Cell Compartment

Single-cell transcriptomic and T cell antigen receptor analysis of human cytomegalovirus (hCMV)-specific memory T cells reveals effectors and pre-effectors of CD8+- and CD4+-cytotoxic T cells

Latent human cytomegalovirus (hCMV) infection can pose a serious threat of reactivation and disease occurrence in immune-compromised individuals. Although T cells are at the core of the protective immune response to hCMV infection, a detailed characterization of different T cell subsets involved in hCMV immunity is lacking. Here, in an unbiased manner, we characterized over 8000 hCMV-reactive peripheral memory T cells isolated from seropositive human donors, at a single-cell resolution by analysing their single-cell transcriptomes paired with the T cell antigen receptor (TCR) repertoires. The hCMV-reactive T cells were highly heterogeneous and consisted of different developmental and functional memory T cell subsets such as, long-term memory precursors and effectors, T helper-17, T regulatory cells (TREGs) and cytotoxic T lymphocytes (CTLs) of both CD4 and CD8 origin. The hCMV-specific TREGs, in addition to being enriched for molecules known for their suppressive functions, showed enrichment for the interferon response signature gene sets. The hCMV-specific CTLs were of two types, the pre-effector- and effector-like. The co-clustering of hCMV-specific CD4-CTLs and CD8-CTLs in both pre-effector as well as effector clusters suggest shared transcriptomic signatures between them. The huge TCR clonal expansion of cytotoxic clusters suggests a dominant role in the protective immune response to CMV. The study uncovers the heterogeneity in the hCMV-specific memory T cells revealing many functional subsets with potential implications in better understanding of hCMV-specific T cell immunity. The data presented can serve as a knowledge base for designing vaccines and therapeutics.

Potent, Selective Agonists for the Cannabinoid-like Orphan G Protein-Coupled Receptor GPR18: A Promising Drug Target for Cancer and Immunity

The human orphan G protein-coupled receptor GPR18, activated by Δ9-tetrahydrocannabinol (THC), constitutes a promising drug target in immunology and cancer. However, studies on GPR18 are hampered by the lack of suitable tool compounds. In the present study, potent and selective GPR18 agonists were developed showing low nanomolar potency at human and mouse GPR18, determined in β-arrestin recruitment assays. Structure-activity relationships were analyzed, and selectivity versus cannabinoid (CB) and CB-like receptors was assessed. Compound 51 (PSB-KK1415, EC50 19.1 nM) was the most potent GPR18 agonist showing at least 25-fold selectivity versus CB receptors. The most selective GPR18 agonist 50 (PSB-KK1445, EC50 45.4 nM) displayed >200-fold selectivity versus both CB receptor subtypes, GPR55, and GPR183. The new GPR18 agonists showed minimal species differences, while THC acted as a weak partial agonist at the mouse receptor. The newly discovered compounds represent the most potent and selective GPR18 agonists reported to date.

Keratinocyte proline-rich protein modulates immune and epidermal response in imiquimod-induced psoriatic skin inflammation

Psoriasis is a persistent inflammatory skin disease thought to arise as a result of the infiltration of inflammatory cells and activation of keratinocytes. Recent advances in basic research and clinical experience revealed that the interleukin (IL)-23/IL-17 axis has been identified as a major immune pathway in psoriasis. However, it remains unclear how keratinocyte factors contribute to the pathology of psoriasis. Keratinocyte proline-rich protein (KPRP) is a proline-rich insoluble protein, which is present in the epidermis and is likely to be involved in the skin barrier function. Here, to investigate the potential roles of KPRP in psoriatic skin inflammation, Kprp-modified mice were applied in the imiquimod (IMQ)-induced skin inflammation model, which develops psoriasis-like epidermal hyperplasia and cutaneous inflammation features. Then, heterozygous knockout (Kprp+/- ) but not homozygous knockout (Kprp-/- ) mice displayed attenuated skin erythema compared to control wild-type mice. In addition, RNA sequencing, quantitative PCR and/or histological analysis detected changes in the expression of several molecules related to psoriatic inflammation or keratinocyte differentiation in Kprp+/- mice, but not Kprp-/- mice. Further analysis exhibited reduced IL-17-producing γδlow T cells and amplified epidermal hyperplasia in Kprp+/- mice, which were implied to be related to decreased expression of β-defensins and increased expression of LPAR1 (Lysophosphatidic acid receptor 1), respectively. Thus, our results imply that KPRP has the potential as a therapeutic target in psoriatic skin inflammation.

Resolvin D2 and its receptor GPR18 in cardiovascular and metabolic diseases: A promising biomarker and therapeutic target

Accumulating evidence suggests that inflammation plays an important role in the pathophysiology of the initiation and progression of cardiovascular and metabolic diseases (CVMDs). Anti-inflammation strategies and those that promote inflammation resolution have gradually become potential therapeutic approaches for CVMDs. Resolvin D2 (RvD2), a specialized pro-resolving mediator, exerts anti-inflammatory and pro-resolution effects through its receptor GPR18, a G protein-coupled receptor. Recently, the RvD2/GPR18 axis has received more attention due to its protective role in CVMDs, including atherosclerosis, hypertension, ischaemiareperfusion, and diabetes. Here, we introduce basic information about RvD2 and GPR18, summarize their roles in different immune cells, and review the therapeutic potential of the RvD2/GPR18 axis in CVMDs. In summary, RvD2 and its receptor GPR18 play an important role in the occurrence and development of CVMDs and are potential biomarkers and therapeutic targets.

Gpr18 agonist dampens inflammation, enhances myogenesis, and restores muscle function in models of Duchenne muscular dystrophy

Introduction: Muscle wasting in Duchenne Muscular Dystrophy is caused by myofiber fragility and poor regeneration that lead to chronic inflammation and muscle replacement by fibrofatty tissue. Our recent findings demonstrated that Resolvin-D2, a bioactive lipid derived from omega-3 fatty acids, has the capacity to dampen inflammation and stimulate muscle regeneration to alleviate disease progression. This therapeutic avenue has many advantages compared to glucocorticoids, the current gold-standard treatment for Duchenne Muscular Dystrophy. However, the use of bioactive lipids as therapeutic drugs also faces many technical challenges such as their instability and poor oral bioavailability. Methods: Here, we explored the potential of PSB-KD107, a synthetic agonist of the resolvin-D2 receptor Gpr18, as a therapeutic alternative for Duchenne Muscular Dystrophy. Results and discussion: We showed that PSB-KD107 can stimulate the myogenic capacity of patient iPSC-derived myoblasts in vitro. RNAseq analysis revealed an enrichment in biological processes related to fatty acid metabolism, lipid biosynthesis, small molecule biosynthesis, and steroid-related processes in PSB-KD107-treated mdx myoblasts, as well as signaling pathways such as Peroxisome proliferator-activated receptors, AMP-activated protein kinase, mammalian target of rapamycin, and sphingolipid signaling pathways. In vivo, the treatment of dystrophic mdx mice with PSB-KD107 resulted in reduced inflammation, enhanced myogenesis, and improved muscle function. The positive impact of PSB-KD107 on muscle function is similar to the one of Resolvin-D2. Overall, our findings provide a proof-of concept that synthetic analogs of bioactive lipid receptors hold therapeutic potential for the treatment of Duchenne Muscular Dystrophy.

N-arachidonylglycine is a caloric state-dependent circulating metabolite which regulates human CD4+T cell responsiveness

Caloric deprivation interventions such as intermittent fasting and caloric restriction ameliorate metabolic and inflammatory disease. As a human model of caloric deprivation, a 24-h fast blunts innate and adaptive immune cell responsiveness relative to the refed state. Isolated serum at these time points confers these same immunomodulatory effects on transformed cell lines. To identify serum mediators orchestrating this, metabolomic and lipidomic analysis was performed on serum extracted after a 24-h fast and re-feeding. Bioinformatic integration with concurrent peripheral blood mononuclear cells RNA-seq analysis implicated key metabolite-sensing GPCRs in fasting-mediated immunomodulation. The putative GPR18 ligand N-arachidonylglycine (NAGly) was elevated during fasting and attenuated CD4⁺T cell responsiveness via GPR18 MTORC1 signaling. In parallel, NAGly reduced inflammatory Th1 and Th17 cytokines levels in CD4⁺T cells isolated from obese subjects, identifying a fasting-responsive metabolic intermediate that may contribute to the regulation of nutrient-level dependent inflammation associated with metabolic disease.

Inflammatory Cytokines That Enhance Antigen Responsiveness of Naïve CD8+ T Lymphocytes Modulate Chromatin Accessibility of Genes Impacted by Antigen Stimulation

Naïve CD8⁺ T lymphocytes exposed to certain inflammatory cytokines undergo proliferation and display increased sensitivity to antigens. Such 'cytokine priming' can promote the activation of potentially autoreactive and antitumor CD8⁺ T cells by weak tissue antigens and tumor antigens. To elucidate the molecular mechanisms of cytokine priming, naïve PMEL-1 TCR transgenic CD8⁺ T lymphocytes were stimulated with IL-15 and IL-21, and chromatin accessibility was assessed using the assay for transposase-accessible chromatin (ATAC) sequencing. PMEL-1 cells stimulated by the cognate antigenic peptide mgp100_25-33 served as controls. Cytokine-primed cells showed a limited number of opening and closing chromatin accessibility peaks compared to antigen-stimulated cells. However, the ATACseq peaks in cytokine-primed cells substantially overlapped with those of antigen-stimulated cells and mapped to several genes implicated in T cell signaling, activation, effector differentiation, negative regulation and exhaustion. Nonetheless, the expression of most of these genes was remarkably different between cytokine-primed and antigen-stimulated cells. In addition, cytokine priming impacted the expression of several genes following antigen stimulation in a synergistic or antagonistic manner. Our findings indicate that chromatin accessibility changes in cytokine-primed naïve CD8⁺ T cells not only underlie their increased antigen responsiveness but may also enhance their functional fitness by reducing exhaustion without compromising regulatory controls.

The druggable transcription factor Fli-1 regulates T cell immunity and tolerance in graft-versus-host disease

Graft-versus-host disease (GVHD), manifesting as either acute (aGVHD) or chronic (cGVHD), presents significant life-threatening complications following allogeneic hematopoietic cell transplantation. Here, we investigated Friend virus leukemia integration 1 (Fli-1) in GVHD pathogenesis and validated Fli-1 as a therapeutic target. Using genetic approaches, we found that Fli-1 dynamically regulated different T cell subsets in allogeneic responses and pathogenicity in the development of aGVHD and cGVHD. Compared with homozygous Fli1-deficient or WT T cells, heterozygous Fli1-deficient T cells induced the mildest GVHD, as evidenced by the lowest Th1 and Th17 cell differentiation. Single-cell RNA-Seq analysis revealed that Fli-1 differentially regulated CD4+ and CD8+ T cell responses. Fli-1 promoted the transcription of Th1/Th17 pathways and T cell receptor-inducible (TCR-inducible) transcription factors in CD4+ T cells, while suppressing activation- and function-related gene pathways in CD8+ T cells. Importantly, a low dose of camptothecin, topotecan, or etoposide acted as a potent Fli-1 inhibitor and significantly attenuated GVHD severity, while preserving the graft-versus-leukemia (GVL) effect. This observation was extended to a xenograft model, in which GVHD was induced by human T cells. In conclusion, we provide evidence that Fli-1 plays a crucial role in alloreactive CD4+ T cell activation and differentiation and that targeting Fli-1 may be an attractive strategy for treating GVHD without compromising the GVL effect.

Intravital Microscopy to Visualize Murine Small Intestinal Intraepithelial Lymphocyte Migration

Intraepithelial lymphocytes (IELs) are critical sentinels involved in host defense and maintenance of the intestinal mucosal barrier. IELs expressing the γδ T-cell receptor provide continuous surveillance of the villous epithelium by migrating along the basement membrane and into the lateral intercellular space between adjacent enterocytes. Intravital imaging has furthered our understanding of the molecular mechanisms by which IELs navigate the epithelial compartment and interact with neighboring enterocytes at steady state and in response to infectious or inflammatory stimuli. Further, evaluating IEL migratory behavior can provide additional insight into the nature and extent of cellular interactions within the intestinal mucosa. Three protocols describe methodology to visualize small intestinal IEL motility in real time using fluorescent reporter-transgenic mice and/or fluorophore-conjugated primary antibodies and spinning-disk confocal microscopy. Using Imaris image analysis software, a fourth protocol provides a framework to analyze IEL migration and quantify lymphocyte/epithelial interactions. Together, these protocols for intravital imaging and subsequent analyses provide the basis for elucidating the spatiotemporal dynamics of mucosal immune cells and interactions with neighboring enterocytes under physiological or pathophysiological conditions. © 2022 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Mouse preparation and laparotomy Support Protocol: Antibody labeling of cell surface markers Basic Protocol 2: Image acquisition by spinning-disk confocal microscopy Basic Protocol 3: 4D analysis of images.

Bitter taste receptor T2R38 is expressed on skin-infiltrating lymphocytes and regulates lymphocyte migration

Bitter taste receptors (T2Rs) are G protein-coupled receptors involved in the perception of bitter taste on the tongue. In humans, T2Rs have been found in several sites outside the oral cavity. Although T2R38 has been reported to be expressed on peripheral lymphocytes, it is poorly understood whether T2R38 plays immunological roles in inflammatory skin diseases such as atopic dermatitis (AD). Then, we first confirmed that T2R38 gene expression was higher in lesional skin of AD subjects than healthy controls. Furthermore, skin T2R38 expression levels were correlated with serum thymus and activation-regulated chemokine and IgE levels in AD patients. In lesional skin of AD, section staining revealed that CD3⁺ T cells in the dermis were T2R38 positive. In addition, flow cytometry analysis showed T2R38 expression in skin T cells. Migration assays using T2R38-transduced Jurkat T cell leukemia cells revealed that T2R38 agonists exerted a dose-dependent migration inhibitory effect. Moreover, skin tissue extracts, as well as supernatants of cultured HaCaT keratinocytes, caused T2R38-dependent migration inhibition, indicating that there should be an endogenous ligand for T2R38 in the skin epidermis. These findings implicate T2R38 as a migratory inhibitory receptor on the skin-infiltrating lymphocytes and as a therapeutic target for allergic/inflammatory skin diseases.

Fabrication of a Silk Sericin Hydrogel System Delivering Human Lactoferrin Using Genetically Engineered Silk with Improved Bioavailability to Alleviate Chemotherapy-Induced Immunosuppression

Chemotherapy is one of the main treatments for cancer; however, it usually causes severe atrophy of immune organs and self-immunity damage to patients. Human lactoferrin (hLF) is a multiple biofunctional protein in regulating the immune response and thus holds great promise to alleviate chemotherapy-caused immunosuppression. However, a sufficient hLF resource and efficient delivery of hLF remain a challenge. Here, we provide a useful strategy to simultaneously solve these two problems. A silk sericin hydrogel system delivering recombinant hLF (SSH-rhLF) was fabricated to alleviate the chemotherapeutic drug-caused side effects by rhLF-carrying silk cocoons, which were cost-effectively produced by a transgenic silkworm strain as the resource. SSH-rhLF with a uniform porous microstructural morphology, a dominant β-sheet internal structure, adjustable concentration and sustainable release of the rhLF, and non-cytotoxicity properties was demonstrated. Interestingly, the sericin hydrogel showed effective protection of the rhLF from degradation in the stomach and small intestine, thus prolonging the bioactivity and bioavailability of rhLF. As a result, the oral administration of SSH-rhLF with a low rhLF dose showed significant therapeutic effects on enhancing the immune organs of cyclophosphamide (CTX)-treated mice by protecting the splenic follicles, promoting the expression of immunoregulatory factors, and recovering the intestinal flora family from CTX-induced imbalance, which were similar to those achieved by oral administration of a high dose of free hLF in the solution form. The results suggest that the strategy of producing rhLF silk cocoons via feeding transgenic silkworms overcomes well the shortage of rhLF resources, improves the bioavailability of oral rhLF, and alleviates the side effects of chemotherapeutic drugs on immune organs. The oral SSH-rhLF will be promising for applications in cancer chemotherapy and immunity enhancement of patients.

Endocannabinoid signaling pathways: beyond CB1R and CB2R

The search for cannabinoid receptors other than CB1R and CB2R has been ongoing for over a decade. A number of orphan receptors have been proposed as potential cannabinoid receptors primarily based on phylogenic arguments and reactivity towards known endocannabinoids and phytocannabinoids. Seven putative cannabinoid receptors are described and discussed, and evidence for and against their inclusion in this category are presented.

Motility Matters: How CD8+ T-Cell Trafficking Influences Effector and Memory Cell Differentiation

Immunological memory is a hallmark of adaptive immunity that confers long-lasting protection from reinfections. Memory CD8⁺ T cells provide protection by actively scanning for their cognate antigen and migrating into inflamed tissues. Trafficking patterns of CD8⁺ T cells are also a major determinant of cell fate outcomes during differentiation into effector and memory cell states. CD8⁺ T-cell trafficking must therefore be dynamically and tightly regulated to ensure that CD8⁺ T cells arrive at the correct locations and differentiate to acquire appropriate effector functions. This review aims to discuss the importance of CD8⁺ T-cell trafficking patterns in regulating effector and memory differentiation, maintenance, and reactivation.

Transcriptomic Changes in Mouse Bone Marrow-Derived Macrophages Exposed to Neuropeptide FF

Neuropeptide FF (NPFF) is a neuropeptide that regulates various biological activities. Currently, the regulation of NPFF on the immune system is an emerging field. However, the influence of NPFF on the transcriptome of primary macrophages has not been fully elucidated. In this study, the effect of NPFF on the transcriptome of mouse bone marrow-derived macrophages (BMDMs) was explored by RNA sequencing, bioinformatics, and molecular simulation. BMDMs were treated with 1 nM NPFF for 18 h, followed by RNA sequencing. Differentially expressed genes (DEGs) were obtained, followed by GO, KEGG, and PPI analysis. A total of eight qPCR-validated DEGs were selected as hub genes. Subsequently, the three-dimensional (3-D) structures of the eight hub proteins were constructed by Modeller and Rosetta. Next, the molecular dynamics (MD)-optimized 3-D structure of hub protein was acquired with Gromacs. Finally, the binding modes between NPFF and hub proteins were studied by Rosetta. A total of 2655 DEGs were obtained (up-regulated 1442 vs. down-regulated 1213), and enrichment analysis showed that NPFF extensively regulates multiple functional pathways mediated by BMDMs. Moreover, the 3-D structure of the hub protein was obtained after MD-optimization. Finally, the docking modes of NPFF-hub proteins were predicted. Besides, NPFFR2 was expressed on the cell membrane of BMDMs, and NPFF 1 nM significantly activated NPFFR2 protein expression. In summary, instead of significantly inhibiting the expression of the immune-related gene transcriptome of RAW 264.7 cells, NPFF simultaneously up-regulated and down-regulated the gene expression profile of a large number of BMDMs, hinting that NPFF may profoundly affect a variety of cellular processes dominated by BMDMs. Our work provides transcriptomics clues for exploring the influence of NPFF on the physiological functions of BMDMs.

Recent advances in roles of G-protein coupled receptors in intestinal intraepithelial lymphocytes

Intestinal intraepithelial lymphocytes (IELs) potentially provide the first line of immune defense against enteric pathogens. In addition, there is growing evidence supporting the involvement of IELs in the pathogenesis of gut disorders such as inflammatory bowel diseases. Various kinds of molecules are involved in the dynamics of IELs, such as homing to the intestinal epithelium and retention in the intestinal mucosa. G protein-coupled receptors (GPCRs) comprise the largest family of cell surface receptors and regulate many biological responses. Although some GPCRs, like CCR9, have been implicated to have roles in IEL homing, little is still known regarding the functional roles of GPCRs in IEL biology. In this review, we provide a concise overview of recent advances in the roles of novel GPCRs like GPR55 and GPR18 in the dynamics of IELs.

Intratumoral CD4+ T Cells Mediate Anti-tumor Cytotoxicity in Human Bladder Cancer

Responses to anti-PD-1 immunotherapy occur but are infrequent in bladder cancer. The specific T cells that mediate tumor rejection are unknown. T cells from human bladder tumors and non-malignant tissue were assessed with single-cell RNA and paired T cell receptor (TCR) sequencing of 30,604 T cells from 7 patients. We find that the states and repertoires of CD8⁺ T cells are not distinct in tumors compared with non-malignant tissues. In contrast, single-cell analysis of CD4⁺ T cells demonstrates several tumor-specific states, including multiple distinct states of regulatory T cells. Surprisingly, we also find multiple cytotoxic CD4⁺ T cell states that are clonally expanded. These CD4⁺ T cells can kill autologous tumors in an MHC class II-dependent fashion and are suppressed by regulatory T cells. Further, a gene signature of cytotoxic CD4⁺ T cells in tumors predicts a clinical response in 244 metastatic bladder cancer patients treated with anti-PD-L1.

Omics-wide quantitative B-cell infiltration analyses identify GPR18 for human cancer prognosis with superiority over CD20

Tumor-infiltrating B lymphocyte (TIL-B), and TIL-B-related biomarkers have clinical prognostic values for human cancers. CD20 (encoded by MS4A1) is a widely used TIL-B biomarker. Using TCGA-quantitative multiomics datasets, we first cross-compare prognostic powers of intratumoral CD20 protein, mRNA and TIL-B levels in pan-cancers. Here, we show that MS4A1 and TIL-B are consistently prognostic in 5 cancers (head and neck, lung, cervical, kidney and low-grade glioma), while unexpectedly, CD20 protein levels lack quantitative correlations with MS4A1/TIL-B levels and demonstrate limited prognosticity. Subsequent bioinformatics discovery for TIL-B prognostic gene identifies a single gene, GPR18 with stand-alone prognosticity across 9 cancers (superior over CD20), with further validations in multiple non-TCGA cohorts. GPR18's immune signature denotes major B-cell-T-cell interactions, with its intratumoral expression strongly tied to a "T-cell active", likely cytolytic, status across human cancers, suggesting its functional link to cytolytic T-cell activity in cancer. GPR18 merits biological and clinical utility assessments over CD20.

Computational Investigations on the Binding Mode of Ligands for the Cannabinoid-Activated G Protein-Coupled Receptor GPR18

GPR18 is an orphan G protein-coupled receptor (GPCR) expressed in cells of the immune system. It is activated by the cannabinoid receptor (CB) agonist ∆⁹-tetrahydrocannabinol (THC). Several further lipids have been proposed to act as GPR18 agonists, but these results still require unambiguous confirmation. In the present study, we constructed a homology model of the human GPR18 based on an ensemble of three GPCR crystal structures to investigate the binding modes of the agonist THC and the recently reported antagonists which feature an imidazothiazinone core to which a (substituted) phenyl ring is connected via a lipophilic linker. Docking and molecular dynamics simulation studies were performed. As a result, a hydrophobic binding pocket is predicted to accommodate the imidazothiazinone core, while the terminal phenyl ring projects towards an aromatic pocket. Hydrophobic interaction of Cys251 with substituents on the phenyl ring could explain the high potency of the most potent derivatives. Molecular dynamics simulation studies suggest that the binding of imidazothiazinone antagonists stabilizes transmembrane regions TM1, TM6 and TM7 of the receptor through a salt bridge between Asp118 and Lys133. The agonist THC is presumed to bind differently to GPR18 than to the distantly related CB receptors. This study provides insights into the binding mode of GPR18 agonists and antagonists which will facilitate future drug design for this promising potential drug target.

Dynamics and clinical significance of intestinal intraepithelial lymphocytes

Intestinal intraepithelial lymphocytes (IELs) are one of the largest populations of lymphocytes and comprised of heterogeneous populations with varying phenotypes and physiological/pathological functions. IELs located between the basolateral surfaces of the epithelial cells and then potentially provide a first line of immune defense against enteric pathogens, although, the precise roles of each IEL populations are not well defined. A variety of molecules are involved in the IEL-homing to the intestinal epithelium. Conventional IELs originate from circulating T cells activated in lymphoid organs and imprinted for gut homing. On the other hand, unconventional IELs derive from thymocytes and migrate to the intestinal epithelium, although, some of them may arise extrathymically. Regarding the interaction between IELs and epithelial cells, IELs are known to be highly motile and actively migrate along the basement membrane, suggesting their roles in immune surveillance. In addition, there has been growing evidence to support that IELs are involved in the pathogenesis of gut disorders such as celiac disease and inflammatory bowel diseases. In this review, we provide a comprehensive overview of IEL dynamics and their clinical significance.

PD-1/PD-L1 Pathway Modulates Macrophage Susceptibility to Mycobacterium tuberculosis Specific CD8+ T cell Induced Death

CD8⁺T cells contribute to tuberculosis (TB) infection control by inducing death of infected macrophages. Mycobacterium tuberculosis (Mtb) infection is associated with increased PD-1/PD-L1 expression and alternative activation of macrophages. We aimed to study the role of PD-1 pathway and macrophage polarization on Mtb-specific CD8⁺T cell-induced macrophage death. We observed that both PD-L1 on CD14⁺ cells and PD-1 on CD8⁺T cells were highly expressed at the site of infection in pleurisy TB patients’ effusion samples (PEMC). Moreover, a significant increase in CD8⁺T cells’ Mtb-specific degranulation from TB-PEMC vs. TB-PBMC was observed, which correlated with PD-1 and PDL-1 expression. In an in vitro model, M1 macrophages were more susceptible to Mtb-specific CD8⁺T cells’ cytotoxicity compared to M2a macrophages and involved the transfer of cytolytic effector molecules from CD8⁺T lymphocytes to target cells. Additionally, PD-L1 blocking significantly increased the in vitro Ag-specific CD8⁺T cell cytotoxicity against IFN-γ-activated macrophages but had no effect over cytotoxicity on IL-4 or IL-10-activated macrophages. Interestingly, PD-L1 blocking enhanced Mtb-specific CD8⁺ T cell killing of CD14⁺ cells from human tuberculous pleural effusion samples. Our data indicate that PD-1/PD-L1 pathway modulates antigen-specific cytotoxicity against M1 targets in-vitro and encourage the exploration of checkpoint blockade as new adjuvant for TB therapies.