Human inherited PD-L1 deficiency is clinically and immunologically less severe than PD-1 deficiency.

We previously reported two siblings with inherited PD-1 deficiency who died from autoimmune pneumonitis at 3 and 11 years of age after developing other autoimmune manifestations, including type 1 diabetes (T1D). We report here two siblings, aged 10 and 11 years, with neonatal-onset T1D (diagnosed at the ages of 1 day and 7 wk), who are homozygous for a splice-site variant of CD274 (encoding PD-L1). This variant results in the exclusive expression of an alternative, loss-of-function PD-L1 protein isoform in overexpression experiments and in the patients' primary leukocytes. Surprisingly, cytometric immunophenotyping and single-cell RNA sequencing analysis on blood leukocytes showed largely normal development and transcriptional profiles across lymphoid and myeloid subsets in the PD-L1-deficient siblings, contrasting with the extensive dysregulation of both lymphoid and myeloid leukocyte compartments in PD-1 deficiency. Our findings suggest that PD-1 and PD-L1 are essential for preventing early-onset T1D but that, unlike PD-1 deficiency, PD-L1 deficiency does not lead to fatal autoimmunity with extensive leukocytic dysregulation.

Depletion of PD-1 or PD-L1 did not affect the mortality of mice infected with Mycobacterium avium.

The programmed cell death-1 (PD-1) and programmed cell death-ligand 1 (PD-L1) pathway could affect antimicrobial immune responses by suppressing T cell activity. Several recent studies demonstrated that blocking of the PD-1/PD-L1 pathway exacerbated Mycobacterium tuberculosis infection. However, the effect of blocking this pathway in pulmonary Mycobacterium avium-intracellulare complex (MAC) infection is not fully understood. Wild-type, PD-1-deficient mice, and PD-L1-deficient mice were intranasally infected with Mycobacterium avium bacteria. Depletion of PD-1 or PD-L1 did not affect mortality and bacterial burden in MAC-infected mice. However, marked infiltration of CD8-positive T lymphocytes was observed in the lungs of PD-1 and PD-L1-deficient mice compared to wild-type mice. Comprehensive transcriptome analysis showed that levels of gene expressions related to Th1 immunity did not differ according to the genotypes. However, genes related to the activity of CD8-positive T cells and related chemokine activity were upregulated in the infected lungs of PD-1 and PD-L1-deficient mice. Thus, the lack of change in susceptibility to MAC infection in PD-1 and PD-L1-deficient mice might be explained by the absence of obvious changes in the Th1 immune response. Furthermore, activated CD8-positive cells in response to MAC infection in these mice seemed to not be relevant in the control of MAC infection.

Niche-specific MHC II and PD-L1 regulate CD4+CD8αα+ intraepithelial lymphocyte differentiation.

Conventional CD4+ T cells are differentiated into CD4+CD8αα+ intraepithelial lymphocytes (IELs) in the intestine; however, the roles of intestinal epithelial cells (IECs) are poorly understood. Here, we showed that IECs expressed MHC class II (MHC II) and programmed death-ligand 1 (PD-L1) induced by the microbiota and IFN-γ in the distal part of the small intestine, where CD4+ T cells were transformed into CD4+CD8αα+ IELs. Therefore, IEC-specific deletion of MHC II and PD-L1 hindered the development of CD4+CD8αα+ IELs. Intracellularly, PD-1 signals supported the acquisition of CD8αα by down-regulating the CD4-lineage transcription factor, T helper-inducing POZ/Krüppel-like factor (ThPOK), via the Src homology 2 domain-containing tyrosine phosphatase (SHP) pathway. Our results demonstrate that noncanonical antigen presentation with cosignals from IECs constitutes niche adaptation signals to develop tissue-resident CD4+CD8αα+ IELs.

PD-1/PDL1 Blockade Exacerbates Pancreatic Damage and Immune Response in a Mouse Model of Acute Pancreatitis.

Programmed necrosis factor 1 (PD-1) is significantly overexpressed in lymphocytes, neutrophils, and macrophages and has been studied in depth in tumors. As a member of the negative costimulatory family of immune regulatory molecules, expression of PD-1 and its primary regulatory pathway are related to immune cells. Recently, PD-1 was demonstrated to be clinically important in inflammatory diseases, such as multiple sclerosis, glomerulonephritis, and inflammatory bowel disease. PD-1, a negative regulator molecule, was recently found to protect tissues from the inflammatory response and inflammatory cell infiltration. Conversely, PD-1 deficiency may contribute to the occurrence of a diverse array of inflammatory diseases. However, whether PD-1 regulates the pathogenesis of acute pancreatitis (AP) is unclear. AP is a noninfectious inflammatory disease with primary pathological manifestations that include edema, inflammatory cell infiltration, and acinar cell necrosis. Among these features, costimulatory molecules including PD-1/PDL1 play a critical role in the regulation of immune response and immune activation. Here, we first found that PD-1 is notably upregulated in neutrophils and macrophages in peripheral blood and pancreatic injury tissue in AP mice. PD-1 gene deficiency exacerbated pancreatic injury in an experimental mouse model of AP. We observed more severe pancreatic injury in PD-1-deficient mice than in control mice, including increased pancreatic edema, inflammatory cells, infiltration, and acinar cell necrosis. We also found that PD-1-deficient mice exhibited higher levels of serum enzymology and inflammatory factors in AP. Furthermore, PD-1/PDL1 neutralizing antibodies significantly aggravated pancreatic and lung injury and increased serum inflammatory cytokine levels. These findings were consistent with those in PD-1-deficient mice. In summary, PD-1 may protect against AP in mice and act as a potential target for the prevention of AP in the future.

Loss of tumor intrinsic PD-L1 confers resistance to drug-induced apoptosis in human colon cancer.

Colorectal cancer (CRC) with BRAF (V600E) is associated with microsatellite instability (MSI) that predicts response to immune checkpoint inhibitors. We demonstrated the interrogation of TCGA RNA-seq human datasets revealed that BRAFV600E tumors had significantly higher Programmed Death Ligand 1 (PD-L1) mRNA compared to non-mutated BRAF CRCs. Also, MSI-H tumors were evaluated as higher PD-L1 than MSS CRCs. Inhibition of MEK/ERK by cobimetinib or CDK inhibitor dinaciclib was shown to attenuate mutant BRAF-induced PD-L1 coincident with reduced c-JUN and YAP expression whose combined knockdown reduced PD-L1. Using TCGA datasets, PD-L1 mRNA expression in human colon cancers was significantly associated with YAP expression. The deletion of PD-L1 can reduce tumor cell growth shown by clonogenic assay. Analysis of the role of PD-L1 as a mediator of chemosensitivity was then performed. Knockout of PD-L1 was shown to attenuate the induction of DNA double-strand breaks (pH2AX) and caspase-3 cleavage by 5-fluorouracil (5-FU) and paclitaxel compared to parental CRC cells. Results were confirmed in PD-L1 knockout MC38 murine CRC cells where re-expression of wild-type PD-L1 promoted DNA damage and apoptosis. We also performed the clonogenic assay and flow cytometry to prove that loss of PD-L1 attenuated DNA damage and apoptosis induced by diverse anti-cancer drugs that could be reversed by restoration of wild-type PD-L1. Mechanistically, knockout of PD-L1 reduced chemosensitivity in association with reductions in p-AKT and in BH3-only proteins BIM and BIK, rather than STAT3 in CRC cells. However, STAT3 had a significant role in melanoma, which shows the heterogeneity of cancers. In summary, BRAFV600E can upregulate PD-L1 expression that was induced by c-jun and YAP to enhance chemotherapy-induced apoptosis. Together, we demonstrate a potential role for PD-L1 as a regulator of chemotherapy-induced apoptosis whose deletion or suppression confers chemoresistance. These findings expand the understanding of PD-L1 functions to include nonimmune mechanisms and suggest the potential use of PD-L1 as a biomarker of response to cytotoxic chemotherapy.

PD-L1 Reverse Signaling in Dermal Dendritic Cells Promotes Dendritic Cell Migration Required for Skin Immunity.

Although the function of the extracellular region of programmed death ligand 1 (PD-L1) through its interactions with PD-1 on T cells is well studied, little is understood regarding the intracellular domain of PD-L1. Here, we outline a major role for PD-L1 intracellular signaling in the control of dendritic cell (DC) migration from the skin to the draining lymph node (dLN). Using a mutant mouse model, we identify a TSS signaling motif within the intracellular domain of PD-L1. The TSS motif proves critical for chemokine-mediated DC migration to the dLN during inflammation. This loss of DC migration, in the PD-L1 TSS mutant, leads to a significant decline in T cell priming when DC trafficking is required for antigen delivery to the dLN. Finally, the TSS motif is required for chemokine receptor signaling downstream of the Gα subunit of the heterotrimeric G protein complex, ERK phosphorylation, and actin polymerization in DCs.

Targeting tumor-associated macrophages and granulocytic myeloid-derived suppressor cells augments PD-1 blockade in cholangiocarcinoma.

Immune checkpoint blockade (ICB) has revolutionized cancer therapeutics. Desmoplastic malignancies, such as cholangiocarcinoma (CCA), have an abundant tumor immune microenvironment (TIME). However, to date, ICB monotherapy in such malignancies has been ineffective. Herein, we identify tumor-associated macrophages (TAMs) as the primary source of programmed death-ligand 1 (PD-L1) in human and murine CCA. In a murine model of CCA, recruited PD-L1+ TAMs facilitated CCA progression. However, TAM blockade failed to decrease tumor progression due to a compensatory emergence of granulocytic myeloid-derived suppressor cells (G-MDSCs) that mediated immune escape by impairing T cell response. Single-cell RNA sequencing (scRNA-Seq) of murine tumor G-MDSCs highlighted a unique ApoE G-MDSC subset enriched with TAM blockade; further analysis of a human scRNA-Seq data set demonstrated the presence of a similar G-MDSC subset in human CCA. Finally, dual inhibition of TAMs and G-MDSCs potentiated ICB. In summary, our findings highlight the therapeutic potential of coupling ICB with immunotherapies targeting immunosuppressive myeloid cells in CCA.

Cancer cell membrane cloaking nanoparticles for targeted co-delivery of doxorubicin and PD-L1 siRNA.

Nanoparticles coated with cell membranes have been garnering growing attention due to their homologous binding capability of membrane molecules and consequent self-recognition by their source cells. In the present study, we report on the construction of doxorubicin and PD-L1 siRNA-loaded PLGA nanoparticles and their biological functionalization by cancer cell-derived membrane cloaking. The resulting cancer cell membrane-coated nanoparticles (CCMNPs) presented a core-shell nanostructure with highly specific self-recognition affinity to the homotypic cells, which can be attributed to the transference of cell adhesion molecules with homotypic binding properties. These findings facilitate the application of this bioinspired strategy for effective delivery of siRNA and precise tumour therapy.

Maturation of hematopoietic stem cells from prehematopoietic stem cells is accompanied by up-regulation of PD-L1.

Hematopoietic stem cells (HSCs) mature from pre-HSCs that originate in the major arteries of the embryo. To identify HSCs from in vitro sources, it will be necessary to refine markers of HSCs matured ex vivo. We purified and compared the transcriptomes of pre-HSCs, HSCs matured ex vivo, and fetal liver HSCs. We found that HSC maturation in vivo or ex vivo is accompanied by the down-regulation of genes involved in embryonic development and vasculogenesis, and up-regulation of genes involved in hematopoietic organ development, lymphoid development, and immune responses. Ex vivo matured HSCs more closely resemble fetal liver HSCs than pre-HSCs, but are not their molecular equivalents. We show that ex vivo-matured and fetal liver HSCs express programmed death ligand 1 (PD-L1). PD-L1 does not mark all pre-HSCs, but cell surface PD-L1 was present on HSCs matured ex vivo. PD-L1 signaling is not required for engraftment of embryonic HSCs. Hence, up-regulation of PD-L1 is a correlate of, but not a requirement for, HSC maturation.

Divergent Function of Programmed Death-Ligand 1 in Donor Tissue versus Recipient Immune System in a Murine Model of Bronchiolitis Obliterans.

Costimulatory molecules, such as the programmed death ligand (PD-L1), might exert differential effects on T-cell function, depending on the clinical setting and/or immunological environment. Given the impact of T cells on bronchiolitis obliterans (BO) in lung transplantation, we used an established tracheal transplant model inducing BO-like lesions to investigate the impact of PD-L1 on alloimmune responses and histopathological outcome in BO. In contrast to other transplant models in which PD-L1 generally shows protective functions, we demonstrated that PD-L1 has divergent effects depending on its location in donor versus recipient tissue. Although PD-L1 deficiency in donor tissue worsened histopathological outcome, and increased systemic inflammatory response, recipient PD-L1 deficiency induced opposite effects. Mechanistic studies revealed PD-L1-deficient recipients were hyporesponsive toward alloantigen, despite increased numbers of CD8+ effector T cells. The function of PD-L1 on T cells after unspecific stimulation was dependent on both cell type and strength of stimulation. This novel function of recipient PD-L1 may result from the high degree of T-cell activation within the highly immunogenic milieu of the transplanted tissue. In this model, both decreased T-cell alloimmune responses and the reduction of BO in PD-L1-deficient recipients suggest a potential therapeutic role of selectively blocking PD-L1 in the recipient. Further investigation is warranted to determine the impact of this finding embedded in the complex pathophysiological context of BO.

The PD-1: PD-L1 pathway promotes development of brain-resident memory T cells following acute viral encephalitis.

BACKGROUND: Previous work from our laboratory has demonstrated that during acute viral brain infection, glial cells modulate antiviral T cell effector responses through the PD-1: PD-L1 pathway, thereby limiting the deleterious consequences of unrestrained neuroinflammation. Here, we evaluated the PD-1: PD-L1 pathway in development of brain-resident memory T cells (bTRM) following murine cytomegalovirus (MCMV) infection. METHODS: Flow cytometric analysis of immune cells was performed at 7, 14, and 30 days post-infection (dpi) to assess the shift of brain-infiltrating CD8+ T cell populations from short-lived effector cells (SLEC) to memory precursor effector cells (MPEC), as well as generation of bTRMs. RESULTS: In wild-type (WT) animals, we observed a switch in the phenotype of brain-infiltrating CD8+ T cell populations from KLRG1+ CD127- (SLEC) to KLRG1- CD127+ (MPEC) during transition from acute through chronic phases of infection. At 14 and 30 dpi, the majority of CD8+ T cells expressed CD127, a marker of memory cells. In contrast, fewer CD8+ T cells expressed CD127 within brains of infected, PD-L1 knockout (KO) animals. Notably, in WT mice, a large population of CD8+ T cells was phenotyped as CD103+ CD69+, markers of bTRM, and differences were observed in the numbers of these cells when compared to PD-L1 KOs. Immunohistochemical studies revealed that brain-resident CD103+ bTRM cells were localized to the parenchyma. Higher frequencies of CXCR3 were also observed among WT animals in contrast to PD-L1 KOs. CONCLUSIONS: Taken together, our results indicate that bTRMs are present within the CNS following viral infection and the PD-1: PD-L1 pathway plays a role in the generation of this brain-resident population.

Upregulation of programmed cell death ligand 1 promotes resistance response in non-small-cell lung cancer patients treated with neo-adjuvant chemotherapy.

To assess the association of the programmed cell death ligand 1 (PD-L1) with cisplatin-based neo-adjuvant chemotherapy (NAC) response, we investigated the level of PD-L1 and found increased PD-L1 expression in chemo-resistant tumors compared with chemo-sensitive tumors according to RNA-Seq analysis. In a cohort of 92 patients with NAC, the positive staining of PD-L1 was correlated with TNM stage, lower sensitive-response rates and shorter overall survival rates. In another 30 paired tumor specimens pre- and post-chemotherapy, the patients with high PD-L1 expression post-chemotherapy had a worse outcome and higher stable disease rate. CD8+ tumor-infiltrating lymphocytes were found to be related to chemosensitive response and better prognosis and negative PD-L1 expression. Furthermore, in two patient-derived xenograft models and cell lines A549 and PC-9, cisplatin upregulated PD-L1 expression, and the enhancement of PD-L1 in cancer cell lines was in a drug dose-dependent manner. Moreover, the depletion of PD-L1 significantly reduced cisplatin resistance. When phosphatidylinositol 3-kinase/protein kinase B signaling was inhibited by corresponding inhibitors, PD-L1 expression was downregulated and apoptosis was upregulated in the cisplatin-treated cancer cells. These results suggest that the upregulation of PD-L1 promotes a resistance response in lung cancer cells that might be through activation of the phosphatidylinositol 3-kinase/protein kinase B pathway and suppression of tumor-infiltrating lymphocytes. The high expression of PD-L1 after NAC could be an indication of therapeutic resistance and poor prognosis in patients with non-small-cell lung cancer.

PD-L1 Deficiency within Islets Reduces Allograft Survival in Mice.

BACKGROUND: Islet transplantation may potentially cure type 1 diabetes mellitus (T1DM). However, immune rejection, especially that induced by the alloreactive T-cell response, remains a restraining factor for the long-term survival of grafted islets. Programmed death ligand-1 (PD-L1) is a negative costimulatory molecule. PD-L1 deficiency within the donor heart accelerates allograft rejection. Here, we investigate whether PD-L1 deficiency in donor islets reduces allograft survival time. METHODS: Glucose Stimulation Assays were performed to evaluate whether PD-L1 deficiency has detrimental effects on islet function. Islets isolated from PDL1-deficient mice or wild- type (WT) mice (C57BL/6j) were implanted beneath the renal capsule of streptozotocin (STZ)-induced diabetic BALB/c mice. Blood glucose levels and graft survival time after transplantation were monitored. Moreover, we analyzed the residual islets, infiltrating immune cells and alloreactive cells from the recipients. RESULTS: PD-L1 deficiency within islets does not affect islet function. However, islet PD-L1 deficiency increased allograft rejection and was associated with enhanced inflammatory cell infiltration and recipient T-cell alloreactivity. CONCLUSIONS: This is the first report to demonstrate that PD-L1 deficiency accelerated islet allograft rejection and regulated recipient alloimmune responses.

IL-10 producing B cells partially restore E2-mediated protection against EAE in PD-L1 deficient mice.

Women with multiple sclerosis (MS) often experience clinical improvement during pregnancy, indicating that sex hormones might have therapeutic effects in MS. Our previous studies have demonstrated that B cells and PD-L1 are crucial for E2 (17ß-estradiol)-mediated protection against experimental autoimmune encephalomyelitis (EAE). We here demonstrate that the transfer of IL-10(+) B cells into E2-treated PD-L1(-/-) mice after EAE induction could partially restore E2-mediated protection and decrease the frequency of pro-inflammatory cells in the CNS compared to E2/saline treated PD-L1(-/-) mice. Hence, co-administration of IL-10(+) B cells and E2 might have a powerful therapeutic potential for treatment of EAE.

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

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

Immunological in vivo effects of B7-H1 deficiency.

B7-H1 regulatory protein, a member of the B7-H family, plays a crucial role in the modulation of immune response in healthy steady-state conditions as well as in different pathologies. B7-H1 knockout mice represent an important model to elucidate further molecular and cellular mechanisms involved, among others, in autoimmunity development and cancer progression. However, a deep immunologic characterization of this model is not complete yet. This study examined the role of B7-H1 in vivo further by direct comparison of specifically phenotyped spleen immune-cell subpopulations and their activation and naïve/memory state as well as cytokine profile in wild-type and B7-H1 knockout mice. Our results demonstrated that B7-H1 deficiency in vivo modulates several immunological parameters, including the amount and composition of Gr1(+)CD11b(+) myeloid population, the composition and activation state of the DC compartment, the frequency and status of NK and NKT cells, B-cells, naïve/memory state of CD8 T-cells and production of IL-2 and IL-10 cytokines. Moreover, we observed an increase in the PD-1 expression in the immune cells in B7-H1 knockout mice compared to the wild-type animals. Valuing the importance of B7-H1 knockout mice for their use in disease models, these data underline the role of B7-H1 in vivo also in healthy state and should be taken into account in future studies on this immunosuppressive molecule.

Identification of B7-H1 as a novel mediator of the innate immune/proinflammatory response as well as a possible myeloid cell prognostic biomarker in sepsis.

Identifying relevant mediators responsible for the pathogenesis during sepsis may lead to finding novel diagnostic and therapeutic targets. Recent studies indicate programmed cell death receptor (PD)-1 plays a significant role in the development of immune suppression associated with sepsis. In this study, we determine whether B7-H1, the primary ligand of PD-1, contributes to the pathogenesis of sepsis. We report that B7-H1 is upregulated extensively on various immune cells during sepsis and B7-H1 gene deficiency protects mice from the lethality of sepsis. In terms of the histological development of multiple organ damage and inflammatory cytokine levels in circulation or at infectious site, B7-H1-deficient mice showed a remarkable reduction in these indices when compared with wild-type mice. However, B7-H1 gene-deficient mice did not exhibit a lower bacterial burden when compared with wild-type mice, although they recruited more macrophages and neutrophils into infectious site. In addition, we found that, during sepsis, whereas there were no marked differences affecting ex vivo macrophage cytokine productive capacity between PD-1 and B7-H1 gene-deficient mice, preservation of ex vivo macrophage phagocytic function was only seen in septic PD-1 knockout mouse cells. Finally, higher percentage B7-H1(+) neutrophils in peripheral blood correlated not only with higher levels of pro- and anti-inflammatory cytokines/chemokines (CCL2, IL-6, CXCL2, KC, TNF-α, and IL-10), but with lethal outcome as well. Together, these results indicate B7-H1 contributes to septic morbidity in fashion distinct from PD-1 and suggest B7-H1 expression on neutrophils could be used as a biomarker of septic severity.

PD-L1 limits the mucosal CD8+ T cell response to Chlamydia trachomatis.

Chlamydia trachomatis infection is the most common bacterial sexually transmitted disease in the United States. Repeated infections with C. trachomatis lead to serious sequelae, such as infertility. It is unclear why the adaptive immune system, specifically the CD8(+) T cell response, is unable to protect against subsequent C. trachomatis infections. In this article, we characterize the mucosal CD8(+) T cell response to C. trachomatis in the murine genital tract. We demonstrate that the immunoinhibitory ligand, PD-L1, contributes to the defective CD8(+) T cell response. Deletion or inhibition of PD-L1 restores the CD8(+) T cell response and enhances C. trachomatis clearance.

[Preparation and knockdown efficiency evaluation of shRNA expressing lentiviral vector targeting B7-H1].

OBJECTIVE: To design and package shRNA expressing lentiviral particles targeting B7-H1, and evaluate their inhibitory effect on B7-H1 expression in U251 cells. METHODS: Three shRNAs targeting B7-H1 was designed and the sense and antisense primers were produced by chemical synthesis. After annealing, they were linked into restriction enzyme digested pLKO.1 vector. Confirmed by DNA sequencing, the lentiviral particles were packaged and applied to infect U251 cells. qRT-PCR and Western blotting were used to detect the B7-H1 mRNA and protein levels respectively. RESULTS: qRT-PCR and Western blotting showed that two of the three shRNAs effectively knocked-down B7-H1 expression in U251 cells. CONCLUSION: The packaged lentiviral particles can specifically inhibit B7-H1 expression, which will be helpful for further functional study on B7-H1.