Unique B7-H1 expression on masticatory mucosae in the oral cavity and trans-coinhibition by B7-H1-expressing keratinocytes regulating CD4+ T cell-mediated mucosal tissue inflammation

Oral mucosa: anti-inflammatory function, mechanisms, and applications

Large soft tissue injuries require several weeks to heal and frequently leave fibrotic scars that can negatively impact tissue function. However, the applicability of traditional skin and mucous membrane transplantation for the treatment of lesions in the ocular surface and urethra is limited owing to the unique locations and functions of these tissues. Oral mucosa has been widely used in the repair of such injuries owing to its reduced propensity for inducing an inflammatory response, angiogenesis, and scarring. Enhancing chronic wound healing while avoiding scar formation requires a broader understanding of the cellular and molecular pathways that drive wound repair in the oral mucosa. This review integrates current knowledge on the mechanisms underlying the resistance of the oral mucosa to inflammation and its application as a graft material, highlighting its challenges and potential advancements. The aim of this review is to offer insights into future therapeutic strategies for wound healing and related conditions.

The role of programmed death receptor (PD-)1/PD-ligand (L)1 in periodontitis and cancer

The programmed-death-ligand-1 (PD-L1) is an immune-modulating molecule that is constitutively expressed on various immune cells, different epithelial cells and a multitude of cancer cells. It is a costimulatory molecule that may impair T-cell mediated immune response. Ligation to the programmed-death-receptor (PD)-1, on activated T-cells and further triggering of the related signaling pathways can induce T-cells apoptosis or anergy. The upregulation of PD-L1 in various cancer types, including oral squamous cell carcinomas, was demonstrated and has been linked to immune escape of tumors and poor prognosis. A bidirectional relationship exists between the increased PD-L1 expression and periodontitis as well as the epithelial-mesenchymal transition (EMT), a process of interconversion of epithelial cells to mesenchymal cells that may induce immune escape of tumors. Interaction between exosomal PD-L1 and PD-1 on T-cells may cause immunosuppression by blocking the activation and proliferation of T-cells. The efficacy and importance of treatment with PD-1/PD-L1 checkpoint inhibitors and their prognostic influence on human cancers was demonstrated. Regarding PD-1/PD-L1 checkpoint inhibitors, resistances exist or may develop, basing on various factors. Further investigations of the underlying mechanisms will help to overcome the therapeutic limitations that result from resistances and to develop new strategies for the treatment of cancer.

PD-L1, a Potential Immunomodulator Linking Immunology and Orthodontically Induced Inflammatory Root Resorption (OIIRR): Friend or Foe?

Orthodontically induced inflammatory root resorption (OIIRR) is considered an undesired and inevitable complication induced by orthodontic forces. This inflammatory mechanism is regulated by immune cells that precede orthodontic tooth movement (OTM) and can influence the severity of OIIRR. The process of OIIRR is based on an immune response. On some occasions, the immune system attacks the dentition by inflammatory processes during orthodontic treatment. Studies on the involvement of the PD-1/PD-L1 immune checkpoint have demonstrated its role in evading immune responses, aiming to identify possible novel therapeutic approaches for periodontitis. In the field of orthodontics, the important question arises of whether PD-L1 has a role in the development of OIIRR to amplify the amount of resorption. We hypothesize that blocking of the PD-L1 immune checkpoint could be a suitable procedure to reduce the process of OIIRR during orthodontic tooth movement. This review attempts to shed light on the regulation of immune mechanisms and inflammatory responses that could influence the pathogenesis of OIIRR and to acquire knowledge about the role of PD-L1 in the immunomodulation involved in OIIRR. Possible clinical outcomes will be discussed in relation to PD-L1 expression and immunologic changes throughout the resorption process.

Tolerogenic properties of CD206+ macrophages appeared in the sublingual mucosa after repeated antigen-painting

The sublingual mucosa (SLM) in the oral cavity is utilized as the site for sublingual immunotherapy to induce tolerance against allergens. We previously reported that CD206+ round-type macrophage-like cells were induced in the SLM after repeated antigen (e.g. cedar pollen or fluorescein isothiocyanate (FITC))-painting. In this study, we examined the phenotypic and functional properties of CD206+ cells induced by repeated FITC-painting on the SLM. CD206+ cells after the repeated FITC-painting possessed a macrophage-like CD11b+Ly6C+ F4/80+CD64+ phenotype and expressed TIM-4, which was expressed in tolerogenic tissue-resident macrophages, at a high level. SLM CD206+ cells preferentially expressed molecules related to endocytosis and homeostatic processes, including the novel B7 family of immune checkpoint molecules, as assessed by microarray analyses. SLM CD206+ cells showed preferential expression of M2-related genes such as Fizz1, Aldh1a1 and Aldh1a2 but not Ym-1 and Arginase-1. A CD206+ cell-rich status inhibited OVA-specific CD4+ T-cell responses but reciprocally enhanced the proportion of both IL-10+CD4+ cells and Foxp3+ regulatory T-cells in regional lymph nodes. Co-culture of CD206+ cells with dendritic cells (DCs) showed that IL-12 production was suppressed in DCs concurrent with the decline of the MHC class IIhiCD86+ population, which was restored by neutralization of IL-10. These results demonstrate SLM CD206+ cells show the feature of tolerogenic macrophages and down-regulate the antigen-presenting cell function of mature DCs resulting in the inhibition of CD4+ T-cell responses.

High PD-L1 Expression on Tumor Cells Indicates Worse Overall Survival in Advanced Oral Squamous Cell Carcinomas of the Tongue and the Floor of the Mouth but Not in Other Oral Compartments

The markers of the tumor microenvironment (TME) are promising prognostic and predictive factors in oral squamous cell carcinoma (OSCC). The current study aims to analyze the immunohistochemical expression of programmed cell death-ligand 1 (PD-L1) and interleukin-33 (IL-33) in a cohort of 95 chemonaïve OSCCs. PD-L1 and IL-33 were assessed separately in tumor cells (TCs) and tumor-infiltrating lymphocytes (TILs). High PD-L1 expression in TILs was associated with better overall survival (OS) in univariate analysis. Tumors localized in the floor of the oral cavity and tongue tended to have a lower percentage of PD-L1-positive TCs when compared to other locations. PD-L1 expression on TCs had no prognostic significance when the whole cohort was analyzed. However, along with the T descriptor (TNM 8th), it was included in the multivariable model predicting death in carcinomas of the floor of the oral cavity and tongue (HR = 2.51, 95% CI = 1.97-5.28). In other locations, only nodal status was identified as an independent prognostic factor in multivariate analysis (HR = 0.24, 95% CI = 0.08-0.70). Expression of IL-33 had no impact on survival, but it was differently expressed in various locations. In conclusion, the prognostic significance of PD-L1 in oral cancer depends on the tumor site and type of cell expressing immune checkpoint receptor (TCs vs. TILs).

Overexpression of PD-L1 in gingival basal keratinocytes reduces periodontal inflammation in a ligature-induced periodontitis model

Background

The immune checkpoint programmed cell death 1 (PD‐1): PD‐1 ligand 1 (PD‐L1) pathway plays a crucial role in maintaining immune tolerance and preventing tissue damages by excessive immune responses. PD‐L1 is physiologically expressed and upregulated in keratinocytes (KCs) in the oral cavity. We here investigated the contribution of PD‐L1 that was overexpressed in gingival basal KCs in a ligature‐induced periodontitis model.

Methods

Wild‐type (WT) BALB/c and K14/PD‐L1 transgenic (tg) mice, in which PD‐L1 was overexpressed in basal KCs under control of the keratin 14 promoter, were used. To induce periodontitis, a 9‐0 silk ligature was placed around the upper right second molar, and lipopolysaccharide from Porphyromonas gingivalis was applied on the suture. Gingival tissues were collected on day 7, after which histological analyses were performed, including by hematoxylin and eosin and tartrate‐resistant acid phosphate staining (TRAP) and quantitative PCR for proinflammatory cytokines and bone metabolism‐related genes. Alveolar bone loss at 7 weeks after ligature placement was assessed by micro‐computed tomography analysis.

Results

PD‐L1 was overexpressed in the basal KCs of all gingival epithelia in K14/PD‐L1tg mice. Early ligature‐induced periodontal inflammation, as assessed based on histological changes, elevation of proinflammatory cytokine (IL‐1β, IL‐6, TNF‐α) expression, periodontal ligament degeneration, and osteoclastogenesis as assessed by Rankl and Opg expression and TRAP+ cells, was markedly impaired in K14/PD‐L1tg mice. Alveolar bone resorption at a late time point was also clearly minimized in K14/PD‐L1tg mice.

Conclusion

Overexpression of PD‐L1 in gingival basal keratinocytes in K14/PD‐L1tg mice reduces periodontal inflammation and alveolar bone resorption in a ligature‐induced periodontitis model.

Polymorphonuclear Myeloid-Derived Cells That Contribute to the Immune Paralysis Are Generated in the Early Phase of Sepsis via PD-1/PD-L1 Pathway

Immune paralysis is a protracted state of immune suppression following the early/acute inflammatory phase of sepsis. CD11b⁺ Gr-1⁺ cells induced during sepsis are heterogeneous myeloid-derived cells (MDCs). This study investigated the contribution of MDCs to immune paralysis. Treatment of mice with zymosan (ZM) induced a marked increase in the total number of splenocytes with an increase in the proportion of Gr-1^hi cells and a decrease in the proportion of T cells on day 7; levels of these cells eventually return to levels similar to those of control mice on day 21. T-cell activation and gamma interferon (IFN-γ) expression by CD8⁺ T cells were clearly impaired in ZM-treated mice on day 21 (d21-ZM mice). Gr-1^hi cells showed a CD11b⁺ Ly6G^hi polymorphonuclear phenotype. Injection of lipopolysaccharide (LPS) into d21-ZM mice impaired interleukin 6 (IL-6) production in serum, accompanied by accumulation of CD11b⁺ Gr-1^hi cells in the peripheral blood. Transfer of Gr-1^hi cells from d21-ZM mice into intact mice impaired IL-6 production, but similar transfer of Gr-1^hi cells from PD-1/PD-L1-deficient d21-ZM mice showed no such suppressive effect. Conversely, either depletion of Gr-1^hi cells by treatment with anti-Gr-1 monoclonal antibody (MAb) or neutralization of the PD-1/PD-L1 pathway by anti-PD-1 and anti-PD-L1 MAbs during the induction phase of sepsis ameliorated ZM-induced immune suppression. Our results suggest that the PD-1/PD-L1-mediated generation of Gr-1^hi cells in the early phase of sepsis is required for the late phase of immune paralysis.

The implication of the PD-1/PD-L1 checkpoint in chronic periodontitis suggests novel therapeutic opportunities with natural products

An analysis of the implication of the PD-1/PD-L1 immune checkpoint in periodontitis is provided with the objective to propose a novel therapeutic approach. An exhaustive survey of the literature has been performed to answer two questions: (1) Is there a role for PD-1 and/or PD-L1 in the development of periodontitis? (2) Which natural products interfere with the checkpoint activity and show activity against periodontitis? All online published information was collected and analyzed. The pathogenic bacteria Porphyromonas gingivalis, through its membrane-attached peptidoglycans, exploits the PD-1/PD-L1 checkpoint to evade immune response and to amplify the infection. Three anti-inflammatory natural products (and derivatives or plant extracts) active against periodontitis and able to interfere with the checkpoint were identified. Both curcumin and baicalin attenuate periodontitis and induce a down-regulation of PD-L1 in cells. The terpenoid saponin platycodin D inhibits the growth of P. gingivalis responsible for periodontitis and shows a rare capacity to induce the extracellular release of a soluble form of PD-L1, thereby restoring T cell activation. A potential PD-L1 shedding mechanism is discussed. The targeting of the PD-1/PD-L1 immune checkpoint could be considered a suitable approach to improve the treatment of chronic periodontitis. The plant natural products curcumin, baicalin and platycodin D should be further evaluated as PD-1/PD-L1 checkpoint modulators active against periodontitis.

A Severe, Refractory Case of Mucous Membrane Pemphigoid After Treatment With Pembrolizumab: Brief Communication

Pembrolizumab is a humanized antibody that targets the programmed death-1 receptor expressed in T cells with high selectivity. This therapeutic is of great importance in cancer immunotherapy yet managing the potential immune-related adverse events remains a concern. Here, we report a rare case of mucous membrane pemphigoid in the oral mucosa, upper respiratory tract, and conjunctiva of a patient with ovarian adenocarcinoma without cutaneous manifestation, which persisted even after pembrolizumab discontinuation. A brief review of pembrolizumab-related bullous pemphigoid cases is presented and possible mechanisms underlying these lesions are discussed.

Silencing of PD-L2/B7-DC by Topical Application of Small Interfering RNA Inhibits Elicitation of Contact Hypersensitivity

PD-L2 is a ligand for the immune checkpoint receptor PD-1; however, its regulatory function is unclear. We previously reported that silencing of CD86 in cutaneous dendritic cells by topical application of small interfering RNA (siRNA) inhibits the elicitation of contact hypersensitivity (CHS). Here, we investigated the effects of topical application of PD-L2 siRNA on allergic skin disease. PD-L2 was induced in dendritic cells concurrently with the elevation of major histocompatibility complex class II and CD86 expression. Topical application of PD-L2 siRNA inhibited the elicitation of CHS by suppressing early proinflammatory cytokine expression and migration of hapten-carrying dendritic cells into lymph nodes. Local injection of neutralizing anti-PD-L2 mAb inhibited CHS to the same extent. PD-L2 siRNA treatment inhibited CHS in PD-1/PD-L1 double knockout mice and in the sensitized T-cell-transferred skin. These results suggest that the effects of PD-L2 silencing are independent of PD-1 but dependent on local memory T cells. Most of the inhibitory effects of PD-L2 and CD86 silencing on CHS were comparable, but PD-L2 siRNA treatment did not inhibit atopic disease-like manifestations and T helper type 2 responses in NC/Nga mice. Our results suggest that PD-L2 in cutaneous dendritic cells acts as a costimulator rather than a regulator. Local PD-L2 silencing by topical application of siRNA represents a therapeutic approach for contact allergy.

Differences of tumor-recruiting myeloid cells in murine squamous cell carcinoma influence the efficacy of immunotherapy combined with a TLR7 agonist and PD-L1 blockade

OBJECTIVES

The immune status of the tumor microenvironment has a marked impact on clinical outcomes. Here we examined the immune environments of tumor-infiltrating leukocytes (TILes) in two murine models of squamous cell carcinoma and compared the effects of immunotherapeutic agents, including a TLR7 agonist and an immune checkpoint inhibitor, and a chemotherapeutic agent, gemcitabine, in these models.

MATERIALS AND METHODS

TILes from NR-S1- and SCCVII-grafted mice were analyzed by flow cytometry. NR-S1-inoculated mice received resiquimod (a synthetic TLR7 agonist), an anti-PD-L1 antibody, or both, and tumor growth and TILs were examined. Gemcitabine was administered to deplete CD11b⁺ cells.

RESULTS

More than 50% of TILes from NR-S1- and SCCVII-inoculated mice were CD11b⁺Gr-1⁺ cells. A major fraction of NR-S1 CD11b⁺ cells was Ly6G^highLy6C^low-negaF4/80^- tumor-associated neutrophils (TANs) and the majority of SCCVII CD11b⁺ cells were Ly6G^lowLy6C^-F4/80⁺ tumor-associated macrophages. NR-S1 TANs did not express MHC class II and CD86, but did express reactive oxygen species and PD-L1. Resiquimod, alone and in combination with an anti-PD-L1 antibody, did not regress NR-S1 tumors, but the combination increased the CD8/regulatory T cell-ratio, and IFN-γ and PD-1 expression in CD8⁺ TILes. Pre-administration of low-dose gemcitabine prior to the combination treatment suppressed the progression of NR-S1 tumors.

CONCLUSIONS

NR-S1 tumors with abundant recruitment of TANs were resistant to treatments with a TLR7 agonist, alone and in combination with PD-1 blockade, and required an additional gemcitabine treatment. The phenotype and status of tumor-infiltrating CD11b⁺ myeloid cells may influence the efficacy of immunotherapeutic agents.

The CD28-B7 Family of Co-signaling Molecules

Immune responses are controlled by the optimal balance between protective immunity and immune tolerance. T-cell receptor (TCR) signals are modulated by co-signaling molecules, which are divided into co-stimulatory and co-inhibitory molecules. By expression at the appropriate time and location, co-signaling molecules positively and negatively control T-cell differentiation and function. For example, ligation of the CD28 on T cells provides a critical secondary signal along with TCR ligation for naive T-cell activation. In contrast, co-inhibitory signaling by the CD28-B7 family is important to regulate immune homeostasis and host defense, as these signals limit the strength and duration of immune responses to prevent autoimmunity. At the same time, microorganisms or tumor cells can use these pathways to establish an immunosuppressive environment to inhibit the immune responses against themselves. Understanding these co-inhibitory pathways will support the development of new immunotherapy for the treatment of tumors and autoimmune and infectious diseases. Here, we introduce diverse molecules belonging to the members of the CD28-B7 family.