Characterization of human PA2.26 antigen (T1alpha-2, podoplanin), a small membrane mucin induced in oral squamous cell carcinomas

What is new in cancer-associated fibroblast biomarkers?

The tumor microenvironment is one of the important drivers of tumor development. Cancer-associated fibroblasts (CAFs) are a major component of the tumor stroma and actively participate in tumor development, invasion, metastasis, drug resistance, and other biological behaviors. CAFs are a highly heterogeneous group of cells, a reflection of the diversity of their origin, biomarkers, and functions. The diversity of CAF origin determines the complexity of CAF biomarkers, and CAF subpopulations expressing different biomarkers may play contrasting roles in tumor progression. In this review, we provide an overview of these emerging CAF biomarkers and the biological functions that they suggest, which may give a better understanding of the relationship between CAFs and tumor cells and be of great significance for breakthroughs in precision targeted therapy for tumors. Video Abstract.

Podoplanin: A potential therapeutic target for thrombotic diseases

As a specific lymphatic marker and a key ligand of C-type lectin-like receptor 2 (CLEC-2), podoplanin (Pdpn) is involved in various physiological and pathological processes such as growth and development, respiration, blood coagulation, lymphangiogenesis, angiogenesis, and inflammation. Thrombotic diseases constitute a major cause of disability and mortality in adults, in which thrombosis and inflammation play a crucial role. Recently, increasing evidence demonstrates the distribution and function of this glycoprotein in thrombotic diseases such as atherosclerosis, ischemic stroke, venous thrombosis, ischemic-reperfusion injury (IRI) of kidney and liver, and myocardial infarction. Evidence showed that after ischemia, Pdpn can be acquired over time by a heterogeneous cell population, which may not express Pdpn in normal conditions. In this review, the research progresses in understanding the roles and mechanisms of podoplanin in thromobotic diseases are summarized. The challenges of podoplanin-targeted approaches for disease prognosis and preventions are also discussed.

Modulation of cardiac ventricular conduction: Impact on QRS duration, amplitude and dispersion

Alterations in cardiac impulse conduction may exert both beneficial and detrimental effects. The assessment of ventricular conduction properties is of paramount importance both in clinical and in experimental settings. Currently the duration of the QRS complex is regarded as hallmark of in-vivo assessment of global ventricular conduction time. In addition, the amplitude of the QRS complex has been suggested to reflect ventricular conduction time in man and in rats. Here, for the first time, we systematically investigated the relationship between QRS duration ("QRS") and QRS amplitude ("RS-height"; RSh) in the murine ECG obtained during anesthesia. In mice harbouring a homozygous knockout of the transmembrane protein podoplanin (PDPN-/-; n = 10) we found both a shorter QRS and a greater RSh than in wild-type animals (n = 13). In both genotypes cumulative i.p. administration of 5 mg/kg and 10 mg/kg of the Na channel blocker flecainide resulted in dose-dependent QRS increase and RSh decrease, whereby the drug-induced changes in RSh were greater than in QRS. In both genotypes the flecainide-induced changes in QRS and in RSh were significantly correlated with each other (R = -0.56, P = 0.004). Whereas dispersion of QRS and RSh was similar between genotypes, dispersion of the ratio QRS/RSh was significantly smaller in PDPN-/- than in wild-types. We conclude that in the murine ECG QRS is inversely related to RSh. We suggest that both parameters should be considered in the analysis of ventricular conduction time in the murine ECG.

Lymphatic Vascular Density, the Expression of Podoplanin and Tumor Budding in Oral Squamous Cell Carcinoma

BACKGROUND

Notwithstanding recent advances in oral squamous cell carcinoma (OSCC) management, its mortality rate is still high. It is imperative to investigate new parameters that are complementary to clinical staging for OSCC to provide better prognostic insight. The presence of isolated neoplastic cells or small clusters of up to four cells at the tumor's invasive front, called tumor budding, is a morphological marker of OSCC with prognostic value. Increased lymphatic vascular density (LVD) and a high expression of podoplanin in neoplastic cells have also been associated with worse prognosis in OSCC. To investigate these markers in OSCC, we evaluated differences in LVD and the expression of podoplanin in neoplastic cells between tumors with high-intensity tumor budding versus low-intensity or no tumor budding. In the samples of high-intensity budding, differences in those parameters between the​​ budding area and the area outside the budding were also evaluated. Furthermore, the study assessed differences in LVD and in the expression of podoplanin in neoplastic cells concerning OSCC clinicopathological characteristics.

METHODS

To those ends, we subjected 150 samples of OSCC to immunohistochemistry to evaluate the intensity of tumor budding (via multi-cytokeratin immunostaining). Moreover, the 150 samples of OSCC and 15 specimens of normal oral mucosa (used as a control) were employed to assess LVD and the expression of podoplanin (in neoplastic cells of OSCC and in the lining epithelium of normal oral mucosa), both via podoplanin immunostaining. Data were processed into descriptive and analytical statistics.

RESULTS

No differences were observed neither in the LVD nor in the expression of podoplanin in neoplastic cells concerning sex, age, tobacco smoking, tumor location and tumor size. The LVD was greater in OSCC and in tumors with high-intensity budding than in normal mucosa but did not differ between normal mucosa and tumors with low-intensity or no tumor budding. The data analyses also revealed that LVD was greater in tumors with high-intensity tumor budding than in tumors with low-intensity or no budding and showed no difference in LVD between the budding area and the area outside the budding. When compared to the lining epithelium of the normal mucosa, the expression of podoplanin was greater in neoplastic cells of OSCC, tumors with high-intensity budding and tumors with low-intensity or no tumor budding. The expression of podoplanin in neoplastic cells was also greater in tumors with high-intensity budding and, within those tumors, greater in the budding area than in the area outside de budding.

CONCLUSION

Those findings support the hypothesis that tumor budding is a biological phenomenon associated with the progression and biological behavior of OSCC.

Synovial gene signatures associated with the development of rheumatoid arthritis in at risk individuals: A prospective study

OBJECTIVE

To identify molecular changes in synovium before arthritis development in individuals at risk of developing rheumatoid arthritis (RA).

MATERIALS AND METHODS

We included 67 IgM rheumatoid factor and/or anti-citrullinated protein antibody positive individuals with arthralgia but without arthritis. Synovial biopsies were collected after which individuals were prospectively followed for at least 2 years during which 17 developed arthritis. An exploratory genome-wide transcriptional profiling study was performed in 13 preselected individuals to identify transcripts associated with arthritis development (n = 6). Findings were validated using quantitative real-time PCR and immunohistochemistry in the total cohort.

RESULTS

Microarray-based survival analyses identified 5588 transcripts whose expression levels in synovium were significantly associated with arthritis development. Pathway analysis revealed that synovial tissue of at risk individuals who later developed arthritis display higher expression of genes involved in adaptive immune response-related pathways compared to at risk individuals who did not develop arthritis. Lower expression was observed for genes involved in extracellular matrix receptor interaction, Wnt-mediated signal transduction and lipid metabolism. Two-way hierarchical clustering analyses of a 27-gene signature separated the total at risk cohort into two groups, where pre-RA individuals preferred to cluster together. Immunohistochemistry studies revealed more podoplanin positive cells and lower lipid droplet staining in synovial tissue from pre-RA individuals.

CONCLUSION

Synovial alterations in adaptive immune response and lipid metabolism are associated with future development of arthritis. Since this data show synovial changes without overt cellular infiltration, these may be attributed to preclinical changes in resident synovial tissue cells such as fibroblasts, macrophages and tissue resident T cells.

Podoplanin: Its roles and functions in neurological diseases and brain cancers

Podoplanin is a small mucin-like glycoprotein involved in several physiological and pathological processes in the brain including development, angiogenesis, tumors, ischemic stroke and other neurological disorders. Podoplanin expression is upregulated in different cell types including choroid plexus epithelial cells, glial cells, as well as periphery infiltrated immune cells during brain development and neurological disorders. As a transmembrane protein, podoplanin interacts with other molecules in the same or neighboring cells. In the past, a lot of studies reported a pleiotropic role of podoplanin in the modulation of thrombosis, inflammation, lymphangiogenesis, angiogenesis, immune surveillance, epithelial mesenchymal transition, as well as extracellular matrix remodeling in periphery, which have been well summarized and discussed. Recently, mounting evidence demonstrates the distribution and function of this molecule in brain development and neurological disorders. In this review, we summarize the research progresses in understanding the roles and mechanisms of podoplanin in the development and disorders of the nervous system. The challenges of podoplanin-targeted approaches for disease prognosis and preventions are also discussed.

PDPN marks a subset of aggressive and radiation-resistant glioblastoma cells

Treatment-resistant glioma stem cells are thought to propagate and drive growth of malignant gliomas, but their markers and our ability to target them specifically are not well understood. We demonstrate that podoplanin (PDPN) expression is an independent prognostic marker in gliomas across multiple independent patient cohorts comprising both high- and low-grade gliomas. Knockdown of PDPN radiosensitized glioma cell lines and glioma-stem-like cells (GSCs). Clonogenic assays and xenograft experiments revealed that PDPN expression was associated with radiotherapy resistance and tumor aggressiveness. We further demonstrate that knockdown of PDPN in GSCs in vivo is sufficient to improve overall survival in an intracranial xenograft mouse model. PDPN therefore identifies a subset of aggressive, treatment-resistant glioma cells responsible for radiation resistance and may serve as a novel therapeutic target.

Podoplanin expression in lymph node metastases of head and neck cancer and cancer of unknown primary patients

INTRODUCTION

Head and neck squamous cell carcinomas (HNSCCs) are cancers with generally poor prognosis. Outcomes have not improved in decades, with more than half of the patients presenting with lymph node metastases at the time of diagnosis. A unique subtype of HNSCC, cancer of unknown primary of the head and neck (HNCUP) is associated with a poor outcome. Increased expression of the D2-40 gene (podoplanin) has been described for several human malignancies and has been associated with increased metastatic potential of cancer cells.

METHODS

In order to examine the role of podoplanin in lymph node metastasis of HNSCC generally and HNCUP specifically, we evaluated the prognostic impact of podoplanin expression in HNSCC- (n = 68) and HNCUP-associated lymph node metastases (n = 30). The expression of podoplanin was analyzed by immunohistochemical staining of lymph node tissue samples and correlated with clinical and histopathological data.

RESULTS

We found a non-significant tendency towards a higher podoplanin expression in HNCUP compared to HNSCC lymph node metastases and a significant correlation between a high podoplanin expression and advanced node-stage classification. Podoplanin expression had no significant impact on overall survival for both groups and did not correlate with human papillomavirus tumor status.

CONCLUSION

Taken together, our results suggest that upregulation of podoplanin may be associated with a stimulation of lymphatic metastasis in head and neck cancer.

The Role of Podoplanin in the Immune System and Inflammation

Podoplanin is a small cell-surface mucin-like glycoprotein that participates in multiple physiological and pathological processes. Podoplanin exerts an important function in the immune response and is upregulated in fibroblasts, macrophages, T helper cells, and epithelial cells during inflammation. Herein, we summarize the latest knowledge on the functional expression of podoplanin in the immune system and review the contribution of podoplanin to several inflammatory diseases. Furthermore, we discuss podoplanin as a novel therapeutic target for various inflammatory diseases.

Targeting Podoplanin for the Treatment of Osteosarcoma

PURPOSE

Osteosarcoma, the most common bone malignancy in children, has a poor prognosis, especially when the tumor metastasizes to the lungs. Therefore, novel therapeutic strategies targeting both proliferation and metastasis of osteosarcoma are required. Podoplanin (PDPN) is expressed by various tumors and is associated with tumor-induced platelet activation via its interaction with C-type lectin-like receptor 2 (CLEC-2) on platelets. We previously found that PDPN contributed to osteosarcoma growth and metastasis through platelet activation; thus, in this study, we developed an anti-PDPN humanized antibody and evaluated its effect on osteosarcoma growth and metastasis.

EXPERIMENTAL DESIGN

Nine osteosarcoma cell lines and two osteosarcoma patient-derived cells were collected, and we evaluated the efficacy of the anti-DPN-neutralizing antibody PG4D2 and the humanized anti-PDPN antibody AP201, which had IgG4 framework region. The antitumor and antimetastasis effect of PG4D2 and AP201 were examined in vitro and in vivo. In addition, growth signaling by the interaction between PDPN and CLEC-2 was analyzed using phospho-RTK (receptor tyrosine kinase) array, growth assay, or immunoblot analysis under the supression of RTKs by knockout and inhibitor treatment.

RESULTS

We observed that PG4D2 treatment significantly suppressed tumor growth and pulmonary metastasis in osteosarcoma xenograft models highly expressing PDPN. The contribution of PDGFR activation by activated platelet releasates to osteosarcoma cell proliferation was confirmed, and the humanized antibody, AP201, suppressed in vivo osteosarcoma growth and metastasis without significant adverse events.

CONCLUSIONS

Targeting PDPN with a neutralizing antibody against PDPN-CLEC-2 without antibody-dependent cell-mediated cytotoxicity and complement-dependent cytotoxicity is a novel therapeutic strategy for PDPN-positive osteosarcoma.

The Role of Podoplanin in Skin Diseases

Podoplanin is a sialomucin-like type I transmembrane receptor glycoprotein that is expressed specifically in lymphatic vessels, sebaceous glands, and hair follicles in normal skin. However, under pathological conditions podoplanin expression is upregulated in various cells, such as keratinocytes, fibroblasts, tumor cells, and inflammatory cells, and plays pivotal roles in different diseases. In psoriasis, podoplanin expression is induced in basal keratinocytes via the JAK-STAT pathway and contributes toward epidermal hyperproliferation. Podoplanin expression on keratinocytes can also promote IL-17 secretion from lymphocytes, promoting chronic inflammation. During wound healing, the podoplanin/CLEC-2 interaction between keratinocytes and platelets regulates re-epithelialization at the wound edge. In skin cancers, podoplanin expresses on tumor cells and promotes their migration and epithelial-mesenchymal transition, thereby accelerating invasion and metastasis. Podoplanin is also expressed in normal peritumoral cells, such as cancer-associated fibroblasts in melanoma and keratinocytes in extramammary Paget's disease, which promote tumor progression and predict aggressive behavior and poor prognosis. This review provides an overview of our current understanding of the mechanisms via which podoplanin mediates these pathological skin conditions.

Exosomes produced by melanoma cells significantly influence the biological properties of normal and cancer-associated fibroblasts

The incidence of cutaneous malignant melanoma is increasing worldwide. While the treatment of initial stages of the disease is simple, the advanced disease frequently remains fatal despite novel therapeutic options . This requires identification of novel therapeutic targets in melanoma. Similarly to other types of tumours, the cancer microenvironment plays a prominent role and determines the biological properties of melanoma. Importantly, melanoma cell-produced exosomes represent an important tool of intercellular communication within this cancer ecosystem. We have focused on potential differences in the activity of exosomes produced by melanoma cells towards melanoma-associated fibroblasts and normal dermal fibroblasts. Cancer-associated fibroblasts were activated by the melanoma cell-produced exosomes significantly more than their normal counterparts, as assessed by increased transcription of genes for inflammation-supporting cytokines and chemokines, namely IL-6 or IL-8. We have observed that the response is dependent on the duration of the stimulus via exosomes and also on the quantity of exosomes. Our study demonstrates that melanoma-produced exosomes significantly stimulate the tumour-promoting proinflammatory activity of cancer-associated fibroblasts. This may represent a potential new target of oncologic therapy .

Expression of podoplanin in various types of feline tumor tissues

Podoplanin is expressed in various human tumors where it promotes tumor progression, epithelial-mesenchymal transition, and distant metastasis. Podoplanin is also expressed in cancer-associated fibroblasts and induces tumor malignancy. The objective of this study was to evaluate podoplanin expression in various types of feline tumor tissues. Immunohistochemical analysis revealed that podoplanin was expressed in cells of 13/15 (87%) squamous cell carcinomas and 5/19 (26%) fibrosarcomas. Moreover, cancer-associated fibroblasts expressed podoplanin in most tumor types, including 18/21 (86%) mammary adenocarcinoma tissues. Our findings demonstrate that various types of feline tumor tissues expressed podoplanin, indicating the importance of the comparative aspects of podoplanin expression, which may be used as a novel research model for podoplanin biology.

Immunohistochemical and immunofluorescence expression profile of lymphatic endothelial cell markers in oral cancer

Lymphangiogenesis makes an important contribution to the tumour microenvironment (TME), but little is known about this in oral squamous cell carcinoma (OSCC). Archival formalin-fixed paraffin-embedded specimens (28 OSCC, 10 inflamed and 6 normal oral mucosa controls) were processed using immunohistochemistry (IHC) with antibodies against lymphatic markers D2-40 (podoplanin), LYVE-1, VEGFR3 and Prox1. After the endothelial cells had been highlighted by the various markers for lymphatic endothelium, the positive stained cells and vessels were identified and counted in a systematic manner to determine microvessel density. Double-labelling immunofluorescence (DLIF) was used to investigate the specificity of D2-40 and LYVE-1 to lymphatic endothelial cells (LECs) as opposed to blood ECs. There was higher D2-40 and Prox1 lymphatic vessel density (P = .001) in the OSCC group when compared with both control groups. Some malignant keratinocytes expressed lymphatic markers, as did a much smaller number of epithelial cells in the control groups. DLIF showed that no vessels co-expressed D2-40/CD34 or LYVE/CD34. Some D2/40⁺ LVs were LYVE^- . D2-40 was the most specific LEC marker in OSCC tissues. These results establish that the OSCC TME contains significantly more lymphatic vessels expressing D2-40 and Prox1 than the control groups, which may play a role in facilitating lymphatic invasion and metastases.

Fibroblastic reticular cell response to dendritic cells requires coordinated activity of podoplanin, CD44 and CD9

In adaptive immunity, CLEC-2+ dendritic cells (DCs) contact fibroblastic reticular cells (FRCs) inhibiting podoplanin-dependent actomyosin contractility, permitting FRC spreading and lymph node expansion. The molecular mechanisms controlling lymph node remodelling are incompletely understood. We asked how podoplanin is regulated on FRCs in the early phase of lymph node expansion, and which other proteins are required for the FRC response to DCs. We find that podoplanin and its partner proteins CD44 and CD9 are differentially expressed by specific lymph node stromal populations in vivo, and their expression in FRCs is coregulated by CLEC-2 (encoded by CLEC1B). Both CD44 and CD9 suppress podoplanin-dependent contractility. We find that beyond contractility, podoplanin is required for FRC polarity and alignment. Independently of podoplanin, CD44 and CD9 affect FRC-FRC interactions. Furthermore, our data show that remodelling of the FRC cytoskeleton in response to DCs is a two-step process requiring podoplanin partner proteins CD44 and CD9. Firstly, CLEC-2 and podoplanin binding inhibits FRC contractility, and, secondly, FRCs form protrusions and spread, which requires both CD44 and CD9. Together, we show a multi-faceted FRC response to DCs, which requires CD44 and CD9 in addition to podoplanin.

Development of Monoclonal Antibody PMab-269 Against California Sea Lion Podoplanin

The development of protein-specific antibodies is essential for understanding a wide variety of biological phenomena. Parasitic and viral infections and cancers are known to occur within California sea lion (Zalophus californianus) populations. However, sensitive and specific monoclonal antibodies (mAbs) for the pathophysiological analysis of California sea lion tissues have not yet been developed. A type I transmembrane glycoprotein, podoplanin (PDPN), is a known diagnostic marker of lymphatic endothelial cells. We have previously developed several anti-PDPN mAbs in various mammalian species, with applications in flow cytometry, Western blotting, and immunohistochemistry. In this study, we established a novel mAb against California sea lion PDPN (seaPDPN), clone PMab-269 (mouse IgG₁, kappa), using a Cell-Based Immunization and Screening method. PMab-269 is specifically detected in seaPDPN-overexpressed Chinese hamster ovary (CHO)-K1 cells using flow cytometry and Western blotting. Moreover, PMab-269 clearly identified pulmonary type I alveolar cells, renal podocytes, and colon lymphatic endothelial cells in California sea lion tissues using immunohistochemistry. These findings demonstrate the usefulness of PMab-269 for the pathophysiological analysis of lung, kidney, and lymphatic tissues of the California sea lion.

Novel knock-in mouse model for the evaluation of the therapeutic efficacy and toxicity of human podoplanin-targeting agents

Podoplanin is a key molecule for enhancing tumor‐induced platelet aggregation. Podoplanin interacts with CLEC‐2 on platelets via PLatelet Aggregation–inducing domains (PLAGs). Among our generated antibodies, those targeting the fourth PLAG domain (PLAG4) strongly suppress podoplanin–CLEC‐2 binding and podoplanin‐expressing tumor growth and metastasis. We previously performed a single‐dose toxicity study of PLAG4‐targeting anti‐podoplanin–neutralizing antibodies and found no acute toxicity in cynomolgus monkeys. To confirm the therapeutic efficacy and toxicity of podoplanin‐targeting antibodies, a syngeneic mouse model that enables repeated dose toxicity tests is needed. Replacement of mouse PLAG1‐PLAG4 domains with human homologous domains drastically decreased the platelet‐aggregating activity. Therefore, we searched the critical domain of the platelet‐aggregating activity in mouse podoplanin and found that the mouse PLAG4 domain played a critical role in platelet aggregation, similar to the human PLAG4 domain. Human/mouse chimeric podoplanin, in which a limited region containing mouse PLAG4 was replaced with human homologous region, exhibited a similar platelet‐aggregating activity to wild‐type mouse podoplanin. Thus, we generated knock‐in mice with human/mouse chimeric podoplanin expression (Pdpn^KI/KI mice). Our previously established PLAG4‐targeting antibodies could suppress human/mouse chimeric podoplanin–mediated platelet aggregation and tumor growth in Pdpn^KI/KI mice. Repeated treatment of Pdpn^KI/KI mice with antibody‐dependent cell‐mediated cytotoxicity activity–possessing PG4D2 antibody did not result in toxicity or changes in hematological and biochemical parameters. Our results suggest that anti‐podoplanin–neutralizing antibodies could be used safely as novel anti‐tumor agents. Our generated Pdpn^KI/KI mice are useful for investigating the efficacy and toxicity of human podoplanin–targeting drugs.

Podoplanin is required for tumor cell invasion in cutaneous squamous cell carcinoma

The invasiveness of late-stage cutaneous squamous cell carcinoma (cSCC) is associated with poor patients' prognosis and linked to strong upregulation of the glycoprotein Podoplanin (PDPN) in cancer cells. However, the function of PDPN in these processes in cSCC carcinogenesis has not been characterized in detail yet. Employing a CRISPR/Cas9-based loss-of-function approach on murine cSCC cells, we show that the loss of Pdpn results in decreased migration and invasion in vitro. Complementing these in vitro studies, labelled murine control and Pdpn knockout cells were injected orthotopically into the dermis of nude mice to recapitulate the formation of human cSCC displaying a well-differentiated morphology with a PDPN-positive reaction in fibroblasts in the tumor stroma. Smaller tumors were observed upon Pdpn loss, which is associated with reduced tumor cell infiltration into the stroma. Utilizing Pdpn mutants in functional experiments in vitro, we provide evidence that both the intra- and extracellular domains are essential for cancer cell invasion. These findings underline the critical role of PDPN in cSCC progression and highlight potential therapeutic strategies targeting PDPN-dependent cancer cell invasion, especially in late-stage cSCC patients.

Crystal structure of an anti-podoplanin antibody bound to a disialylated O-linked glycopeptide

Podoplanin (PDPN) is a highly O-glycosylated glycoprotein that is utilized as a specific lymphatic endothelial marker under pathophysiological conditions. We previously developed an anti-human PDPN (hPDPN) monoclonal antibody (mAb), clone LpMab-3, which recognizes the epitope, including both the peptides and the attached disialy-core-l (NeuAcα2-3Galβl-3 [NeuAcα2-6]GalNAcαl-O-Thr) structure at the Thr76 residue in hPDPN. However, it is unclear if the mAb binds directly to both the peptides and glycans. In this study, we synthesized the binding epitope region of LpMab-3 that includes the peptide (-₆₇LVATSVNSV-T-GIRIEDLP₈₄-) possessing a disialyl-core-1 O-glycan at Thr76, and we determined the crystal structure of the LpMab-3 Fab fragment that was bound to the synthesized glycopeptide at a 2.8 Å resolution. The six amino acid residues and two sialic acid residues are directly associated with four complementarity-determining regions (CDRs; H1, H2, H3, and L3) and four CDRs (H2, H3, L1, and L3), respectively. These results suggest that IgG is advantageous for generating binders against spacious epitopes such as glycoconjugates.

Phase I/II Clinical Trial of the Anti-Podoplanin Monoclonal Antibody Therapy in Dogs with Malignant Melanoma

Podoplanin (PDPN), a small transmembrane mucin-like glycoprotein, is ectopically expressed on tumor cells. PDPN is known to be linked with several aspects of tumor malignancies in certain types of human and canine tumors. Therefore, it is considered to be a novel therapeutic target. Monoclonal antibodies targeting PDPN expressed in human tumor cells showed obvious anti-tumor effects in preclinical studies using mouse models. Previously, we generated a cancer-specific mouse-dog chimeric anti-PDPN antibody, P38Bf, which specifically recognizes PDPN expressed in canine tumor cells. In this study, we investigated the safety and anti-tumor effects of P38Bf in preclinical and clinical trials. P38Bf showed dose-dependent antibody-dependent cellular cytotoxicity against canine malignant melanoma cells. In a preclinical trial with one healthy dog, P38Bf administration did not induce adverse effects over approximately 2 months. In phase I/II clinical trials of three dogs with malignant melanoma, one dog vomited, and all dogs had increased serum levels of C-reactive protein, although all adverse effects were grade 1 or 2. Severe adverse effects leading to withdrawal of the clinical trial were not observed. Furthermore, one dog had stable disease with P38Bf injections. This is the first reported clinical trial of anti-PDPN antibody therapy using spontaneously occurring canine tumor models.

Interplay between Podoplanin, CD44s and CD44v in Squamous Carcinoma Cells

Podoplanin and CD44 are transmembrane glycoproteins involved in inflammation and cancer. In this paper, we report that podoplanin is coordinately expressed with the CD44 standard (CD44s) and variant (CD44v) isoforms in vivo—in hyperplastic skin after a pro-inflammatory stimulus with 12-O-tetradecanoylphorbol-13-acetate (TPA)—and in vitro—in cell lines representative of different stages of mouse-skin chemical carcinogenesis, as well as in human squamous carcinoma cell (SCC) lines. Moreover, we identify CD44v10 in the mouse-skin carcinogenesis model as the only CD44 variant isoform expressed in highly aggressive spindle carcinoma cell lines together with CD44s and podoplanin. We also characterized CD44v3-10, CD44v6-10 and CD44v8-10 as the major variant isoforms co-expressed with CD44s and podoplanin in human SCC cell lines. Immunofluorescence confocal microscopy experiments show that these CD44v isoforms colocalize with podoplanin at plasma membrane protrusions and cell–cell contacts of SCC cells, as previously reported for CD44s. Furthermore, CD44v isoforms colocalize with podoplanin in chemically induced mouse-skin SCCs in vivo. Co-immunoprecipitation experiments indicate that podoplanin physically binds to CD44v3-10, CD44v6-10 and CD44v8-10 isoforms, as well as to CD44s. Podoplanin–CD44 interaction is mediated by the transmembrane and cytosolic regions and is negatively modulated by glycosylation of the extracellular domain. These results point to a functional interplay of podoplanin with both CD44v and CD44s isoforms in SCCs and give insight into the regulation of the podoplanin–CD44 association.

Podoplanin as an Attractive Target of CAR T Cell Therapy

To date, various kinds of cancer immunotherapy methods have been developed, but T cell immunotherapy is one of the most promising strategies. In general, T cell receptor (TCR) or chimeric antigen receptor (CAR) is used to modify the antigen specificity of T cells. CARs possess an underlying potential with treatment efficacy to treat a broad range of cancer patients compared with TCRs. Although a variety of CAR molecules have been developed so far, the clinical application for solid tumors is limited partly due to its adverse effect known as “on-target off-tumor toxicity”. Therefore, it is very important for CAR T cell therapy to target specific antigens exclusively expressed by malignant cells. Here, we review the application of T cell immunotherapy using specific antigen receptor molecules and discuss the possibility of the clinical application of podoplanin-targeted CAR derived from a cancer-specific monoclonal antibody (CasMab).

Keratinocyte-Expressed Podoplanin is Dispensable for Multi-Step Skin Carcinogenesis

Podoplanin is a small transmembrane mucin-like glycoprotein that plays a crucial role in the development of the lung, heart and lymphatic vascular system. Its expression is upregulated in several types of human carcinomas and podoplanin levels in squamous cell carcinomas (SCCs) of the oral cavity and the lung correlate with cancer invasiveness, lymph node metastasis and shorter survival time of patients, indicating that podoplanin promotes tumor progression. However, its role during the early stages of carcinogenesis remain unclear. We generated mice with a specific deletion of podoplanin in epidermal keratinocytes (K5-Cre;Pdpn^flox/flox mice) and subjected them to a multistep chemical skin carcinogenesis regimen. The rate of tumor initiation; the number, size and differentiation of tumors; and the malignant transformation rate were comparable in K5-Cre;Pdpn^flox/flox mice and Pdpn^flox/flox control mice. However, tumor cell invasion was reduced in K5-Cre;Pdpn^flox/flox mice, in particular single cell invasion. Quantitative immunofluorescence analyses revealed that peritumoral lymphangiogenesis was reduced in K5-Cre;Pdpn^flox/flox mice, whereas there were no major changes of tumor-associated immune cell subpopulations. Thus, keratinocyte-expressed podoplanin is dispensable for the early steps of skin carcinogenesis but contributes to the progression of established tumors.

Expression of Podoplanin in Sinonasal Squamous Cell Carcinoma and Its Clinical Significance

BACKGROUND

It was recently suggested that the upregulation of podoplanin (PDPN) in cancer cells plays a significant role in tumor invasion and metastasis and that it is significantly associated with poor prognosis in oral, cutaneous, and esophageal squamous cell carcinoma. The aim of this study was to investigate the expression pattern of PDPN in sinonasal squamous cell carcinoma (SNSCC) and to evaluate its role as a prognostic factor for survival outcome.

PATIENTS AND METHODS

This study included 59 subjects with SNSCC. We retrospectively collected the clinical features of these patients from medical records and retrieved the associated formalin-fixed, paraffin-embedded tissues for PDPN immunohistochemical staining. Furthermore, PDPN expression was analyzed in relation to the patients' clinicopathological features and prognosis.

RESULTS

We observed positive staining for PDPN in both cancer cells and stromal cancer-associated fibroblasts (CAFs). Positive expression of PDPN in cancer cells of patients with SNSCC was significantly correlated with the primary tumor site (p = 0.009) and local recurrence (p = 0.024). In addition, patients with PDPN-positive cancer cells had significantly lower overall survival (OS) and disease-free survival (DFS) rates than did patients with PDPN-negative cancer cells (both p < 0.05). Multivariate analysis revealed that PDPN expression in cancer cells was an independent prognostic factor for both OS (p = 0.038) and DFS (p = 0.039).

CONCLUSIONS

Our findings demonstrated that PDPN overexpression may be both an independent prognostic biomarker and a therapeutic target in SNSCC.

Restoring synovial homeostasis in rheumatoid arthritis by targeting fibroblast-like synoviocytes

Rheumatoid arthritis (RA) is a chronic immune-mediated disease that primarily affects the synovium of diarthrodial joints. During the course of RA, the synovium transforms into a hyperplastic invasive tissue that causes destruction of cartilage and bone. Fibroblast-like synoviocytes (FLS), which form the lining of the joint, are epigenetically imprinted with an aggressive phenotype in RA and have an important role in these pathological processes. In addition to producing the extracellular matrix and joint lubricants, FLS in RA produce pathogenic mediators such as cytokines and proteases that contribute to disease pathogenesis and perpetuation. The development of multi-omics integrative analyses have enabled new ways to dissect the mechanisms that imprint FLS, have helped to identify potential FLS subsets with distinct functions and have identified differences in FLS phenotypes between joints in individual patients. This Review provides an overview of advances in understanding of FLS biology and highlights omics approaches and studies that hold promise for identifying future therapeutic targets.

Epitope Analysis of an Anti-Whale Podoplanin Monoclonal Antibody, PMab-237, Using Flow Cytometry

Podoplanin (PDPN) is a small mucin-type transmembrane glycoprotein, which was first discovered in podocytes of the kidney. PDPN is a specific lymphatic endothelial marker and is also known as T1alpha, a marker of lung type I alveolar cells, or Aggrus, a platelet aggregation-inducing factor. PDPN possesses three platelet aggregation-stimulating (PLAG) domains and PLAG-like domains (PLDs), which bind to C-type lectin-like receptor-2. Previously, we developed a novel anti-whale PDPN (wPDPN) monoclonal antibody (mAb) PMab-237 using the Cell-Based Immunization and Screening (CBIS) method and the RIEDL tag of Arg-Ile-Glu-Asp-Leu sequence. PMab-237 detected wPDPN by flow cytometry, western blot, and immunohistochemical analyses. However, the specific binding epitope of PMab-237 for wPDPN remains unknown. In this study, deletion mutants and point mutants of wPDPN with N-terminal RIEDL tag were produced to analyze the PMab-237 epitope using flow cytometry. The analysis of deletion mutants showed that the N-terminus of the PMab-237 epitope exists between the 80th amino acid (AA) and the 85th AA of wPDPN. In addition, the analysis of point mutants demonstrated that the critical epitope of PMab-237 includes Leu82 and Thr84 of wPDPN, indicating that the PMab-237 epitope is located in the PLD of wPDPN.

The Epitope of PMab-210 Is Located in Platelet Aggregation-Stimulating Domain-3 of Pig Podoplanin

Podoplanin (PDPN)/T1alpha/Aggrus, a small mucin-type transmembrane glycoprotein, has been shown to be expressed on lymphatic endothelial cells and epithelial cells of many organs. PDPN is also upregulated in many cancers, and is involved in cancer metastasis and malignant progression. Human PDPN possesses three platelet aggregation-stimulating (PLAG) domains and the PLAG-like domain, which bind to C-type lectin-like receptor-2 (CLEC-2). Previously, we reported a novel antipig PDPN (pPDPN) monoclonal antibody (PMab-210) using Cell-Based Immunization and Screening (CBIS) method. PMab-210 specifically detected pPDPN-overexpressed Chinese hamster ovary (CHO)-K1 cells by flow cytometry and Western blot analysis. Immunohistochemical analyses demonstrated that PMab-210 stained pulmonary type I alveolar cells strongly and renal corpuscles weakly in pig or microminipig. However, the specific binding epitope of PMab-210 for pPDPN could not be determined by enzyme-linked immunosorbent assay using a series of pPDPN peptides. In this study, deletion mutants or point mutants of pPDPN were produced for analyzing the PMab-210 epitope using flow cytometry. The analysis of deletion mutants showed that N-terminus of PMab-210 epitope exists between 45th amino acid (aa) and 50th aa of pPDPN. In addition, the analysis of point mutants demonstrated that the critical epitope of PMab-210 could include Glu47, Asp48, Tyr49, Thr50, and Val51 of pPDPN, indicating that PMab-210 epitope is located in PLAG3 domain of pPDPN.

Markers of Cancer Cell Invasion: Are They Good Enough?

Invasion, or directed migration of tumor cells into adjacent tissues, is one of the hallmarks of cancer and the first step towards metastasis. Penetrating to adjacent tissues, tumor cells form the so-called invasive front/edge. The cellular plasticity afforded by different kinds of phenotypic transitions (epithelial-mesenchymal, collective-amoeboid, mesenchymal-amoeboid, and vice versa) significantly contributes to the diversity of cancer cell invasion patterns and mechanisms. Nevertheless, despite the advances in the understanding of invasion, it is problematic to identify tumor cells with the motile phenotype in cancer tissue specimens due to the absence of reliable and acceptable molecular markers. In this review, we summarize the current information about molecules such as extracellular matrix components, factors of epithelial-mesenchymal transition, proteases, cell adhesion, and actin cytoskeleton proteins involved in cell migration and invasion that could be used as invasive markers and discuss their advantages and limitations. Based on the reviewed data, we conclude that future studies focused on the identification of specific invasive markers should use new models one of which may be the intratumor morphological heterogeneity in breast cancer reflecting different patterns of cancer cell invasion.

An important role of podoplanin in hair follicle growth

Podoplanin (PDPN) is a glycoprotein that is expressed by various cell types, including keratinocytes, fibroblasts, and lymphatic endothelial cells. We found that PDPN is expressed in the hair follicle (HF) keratinocyte region and HF stem cell area during the late anagen phase but not during the telogen phase in mice. Importantly, keratinocyte-specific PDPN deletion in mice (K5-Cre;PDPN^flox/flox) promoted anagen HF growth after depilation-induced HF regeneration as compared to control mice. RNA sequencing, followed by gene ontology analysis, showed down-regulation of focal adhesion and extracellular matrix interaction pathways in HF stem cells isolated from K5-Cre;PDPN^flox/flox mice as compared to control mice. Furthermore, HF keratinocytes isolated from K5-Cre;PDPN^flox/flox mice exhibited a decreased ability to interact with collagen type I in cell adhesion assays. Taken together, these results show that PDPN deletion promotes HF cycling, possibly via reduced focal adhesion and concomitantly enhanced migration of HF stem cells towards the bulb region. They also indicate potential new therapeutic strategies for the treatment of conditions associated with hair loss.

PMab-213: A Monoclonal Antibody for Immunohistochemical Analysis Against Pig Podoplanin

Podoplanin (PDPN) is known to be expressed in normal tissues, including lymphatic endothelial cells, renal podocytes, and type I lung alveolar cells. Monoclonal antibodies (mAbs) against human, mouse, rat, rabbit, dog, cat, and bovine PDPN have already been established; however, mAbs against pig PDPN (pPDPN) are lacking. In the present study, mice were immunized with pPDPN-overexpressing Chinese hamster ovary (CHO)-K1 cells (CHO/pPDPN), and hybridomas producing mAbs against pPDPN were identified by flow cytometric screening. One of the mAbs, PMab-213 (IgG_2b, kappa), could specifically detect CHO/pPDPN cells through flow cytometry and detect pPDPN through western blot analysis. K_D of PMab-213 for CHO/pPDPN was determined to be 2.1 × 10^-9 M, indicating a high affinity for CHO/pPDPN. Furthermore, PMab-213 strongly stained lymphatic endothelial cells, renal podocytes, and type I lung alveolar cells through immunohistochemistry. PMab-213 is expected to be useful in investigating the function of pPDPN.

Thrombosis Risk Associated with Head and Neck Cancer: A Review

Venous thromboembolism (VTE) is a common complication for cancer patients. VTE-associated risk varies according to the type of tumor disease. Head and neck cancer is a common cancer worldwide, and most tumors are squamous cell carcinomas due to tobacco and alcohol abuse. The risk of VTE associated with head and neck (H&N) cancer is considered empirically low, but despite the high incidence of H&N cancer, few data are available on this cancer; thus, it is difficult to state the risk of VTE. Our review aims to clarify this situation and tries to assess the real VTE risk associated with H&N cancer. We report that most clinical studies have concluded that there is a very low thrombosis risk associated with H&N cancer. Even with the biases that often exist, this clinical review seems to confirm that the risk of VTE was empirically hypothesized. Furthermore, we highlight that H&N cancer has all the biological features of a cancer associated with a high thrombosis risk, including a strong expression of procoagulant proteins, modified thrombosis/fibrinolysis mechanisms, and secretions of procoagulant microparticles and procoagulant cytokines. Thus, this is a paradoxical situation, and some undiscovered mechanisms that could explain this clinical biological ambivalence might exist.

Anti-Horse Podoplanin Monoclonal Antibody PMab-219 is Useful for Detecting Lymphatic Endothelial Cells by Immunohistochemical Analysis

Podoplanin (PDPN) is expressed in lymphatic endothelial cells, where it induces platelet aggregation through C-type lectin-like receptor-2 (CLEC-2). This protein has been characterized for a number of animal species using specific anti-PDPN monoclonal antibodies (mAbs). We recently established the mAb against horse PDPN (horPDPN) named PMab-219. Therefore, in this study, we investigated whether PMab-219 can detect lymphatic endothelial cells in horse tissues. Immunohistochemical analysis demonstrated that PMab-219 strongly stained lymphatic endothelial cells in horse colon tissues, indicating that it will be useful for investigating the function of horPDPN in these cells.

Establishment of a monoclonal antibody PMab-225 against alpaca podoplanin for immunohistochemical analyses

Podoplanin (PDPN) is known as a lymphatic endothelial cell marker. Monoclonal antibodies (mAbs) against human, mouse, rat, rabbit, dog, cat, bovine, pig, and horse PDPN have been established in our previous studies. However, mAbs against alpaca PDPN (aPDPN), required for immunohistochemical analysis, remain to be developed. In the present study, we employed the Cell-Based Immunization and Screening (CBIS) method for producing anti-aPDPN mAbs. We immunized mice with aPDPN-overexpressing Chinese hamster ovary (CHO)-K1 cells (CHO/aPDPN), and hybridomas producing mAbs against aPDPN were screened using flow cytometry. One of the mAbs, PMab-225 (IgG_2b, kappa), specifically detected CHO/aPDPN cells via flow cytometry and recognized the aPDPN protein on Western blotting. Further, PMab-225 strongly stained lung type I alveolar cells, colon lymphatic endothelial cells, and kidney podocytes via immunohistochemistry. These findings demonstrate that PMab-225 antibody is useful to investigate the function of aPDPN via different techniques.

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PDPN is known as a specific lymphatic endothelial cell (LEC) marker.

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Sensitive and specific PMab-225 mAb against alpaca PDPN was produced.

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PMab-225 strongly reacted with alpaca PDPN in flow cytometry.

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PMab-225 is useful for IHC using paraffin-embedded cell sections.

Podoplanin Positive Myeloid Cells Promote Glioma Development by Immune Suppression

The dynamic and interactive tumor microenvironment is conceived as a considerable parameter in tumor development and therapy response. Implementing this knowledge in the development of future cancer treatments could provide novel options in the combat of highly aggressive and difficult-to-treat tumors such as gliomas. One compartment of the tumor microenvironment that has gained growing interest is the immune system. As endogenous defense machinery the immune system has the capacity to fight against cancer cells. This, however, is frequently circumvented by tumor cells engaging immune-regulatory mechanisms that disable tumor-directed immune responses. Thus, in order to unlock the immune system against cancer cells, it is crucial to characterize in great detail individual tumor-associated immune cell subpopulations and dissect whether and how they influence immune evasion. In this study we investigated the function of a tumor-associated myeloid cell subpopulation characterized by podoplanin expression on the development of high-grade glioma tumors. Here, we show that the deletion of podoplanin in myeloid cells results in increased (CD8⁺) T-cell infiltrates and significantly prolonged survival in an orthotopic transplantation model. In vitro co-cultivation experiments indicate a podoplanin-dependent transcriptional regulation of arginase-1, a well-known player in myeloid cell-mediated immune suppression. These findings identify podoplanin positive myeloid cells as one novel mediator of the glioma-induced immune suppression. Thus, the targeted ablation of podoplanin positive myeloid cells could be included in combinatorial cancer therapies to enhance immune-mediated tumor elimination.

Therapeutic efficacy evaluation of radioimmunotherapy with 90 Y-labeled anti-podoplanin antibody NZ-12 for mesothelioma

Podoplanin is a type I transmembrane sialomucin‐like glycoprotein that is highly expressed in malignant mesothelioma. The rat‐human chimeric antibody NZ‐12 has high affinity for human podoplanin and antibody‐dependent cellular cytotoxicity and is applicable for radioimmunotherapy (RIT) to enhance the antitumor effect. In the present study, we evaluated the in vivo and in vitro properties of radiolabeled NZ‐12 and the antitumor effect of RIT with ⁹⁰Y‐labeled NZ‐12 in an NCI‐H226 (H226) malignant mesothelioma xenograft mouse model. ¹¹¹In‐labeled NZ‐12 bound specifically to H226 cells with high affinity, and accumulation was high in H226 tumors but low in major organs. RIT with ⁹⁰Y‐labeled NZ‐12 significantly suppressed tumor growth and prolonged survival without body weight loss and obvious adverse effects. Higher podoplanin expression levels were observed in human mesothelioma specimens, suggesting higher tumor accumulation of ⁹⁰Y‐labeled NZ‐12 in patients compared with the H226 tumor xenografts. Our findings suggest that ⁹⁰Y‐labeled NZ‐12 is a promising RIT agent as a new therapeutic option for malignant mesothelioma that warrants further clinical studies to evaluate the dosimetry and efficacy in patients.

Podoplanin regulates the migration of mesenchymal stromal cells and their interaction with platelets

Mesenchymal stromal cells (MSCs) upregulate podoplanin at sites of infection, chronic inflammation and cancer. Here, we investigated the functional consequences of podoplanin expression on the migratory potential of MSCs and their interactions with circulating platelets. Expression of podoplanin significantly enhanced the migration of MSCs compared to MSCs lacking podoplanin. Rac-1 inhibition altered the membrane localisation of podoplanin and in turn significantly reduced MSC migration. Blocking Rac-1 activity had no effect on the migration of MSCs lacking podoplanin, indicating that it was responsible for regulation of migration through podoplanin. When podoplanin-expressing MSCs were seeded on the basal surface of a porous filter, they were able to capture platelets perfused over the uncoated apical surface and induce platelet aggregation. Similar microthrombi were observed when endothelial cells (ECs) were co-cultured on the apical surface. Confocal imaging shows podoplanin-expressing MSCs extending processes into the EC layer, and these processes could interact with circulating platelets. In both models, platelet aggregation induced by podoplanin-expressing MSCs was inhibited by treatment with recombinant soluble C-type lectin-like receptor 2 (CLEC-2; encoded by the gene Clec1b). Thus, podoplanin may enhance the migratory capacity of tissue-resident MSCs and enable novel interactions with cells expressing CLEC-2.

Summary: Podoplanin enhances the migration of mesenchymal stromal cells in a Rac-1-dependent manner, enabling direct interactions of subendothelial stroma with circulating platelets.

The stem cell markers expression CD44v6 and podoplanin in lip cancer: clinical significance

This study aimed to analyze the immunoexpression of cancer stem cell markers, CD44v6, and podoplanin in 91 patients with lip squamous cell carcinomas (LSCC). The immunostaining of podoplanin and CD44v6 was evaluated in ten high-power fields (× 400 magnification) at the invasive front of LSCC, using a semi-quantitative score method. Chi-square test or Fisher's exact test was used to verify the association of podoplanin and CD44v6 expressions with clinicopathologic variables. Spearman's correlation test was used to analyze the correlation between the two antibodies in lip cancer. Disease-free survival probabilities in 5 and 10 years were estimated according to the Kaplan-Meier method and compared using the log-rank test. The independent effects of the significant variables were analyzed by Cox proportional hazards regression model. A strong podoplanin expression was observed in the membrane and cytoplasm of most lip tumor cells, and this was inversely associated with locoregional recurrence (p = 0.028) and with histopathological grade of malignancy (p = 0.026). Additionally, CD44v6 immunostaining was strongly expressed in the membrane of tumor cells in 95.4% of the LSCC. Patients with strong membranous (p = 0.016) or strong cytoplasmic (p = 0.030) podoplanin-positive tumors resulted in significantly better disease-free survival than those who had podoplanin weak/negative tumors, confirming podoplanin expression as a favorable independent prognostic factor. Podoplanin and CD44v6 were strongly expressed by tumor cells and podoplanin immunoexpression can help to determine lip cancer patients with lower risk for disease recurrence.

Podoplanin in Inflammation and Cancer

Podoplanin is a small cell-surface mucin-like glycoprotein that plays a crucial role in the development of the alveoli, heart, and lymphatic vascular system. Emerging evidence indicates that it is also involved in the control of mammary stem-cell activity and biogenesis of platelets in the bone marrow, and exerts an important function in the immune response. Podoplanin expression is upregulated in different cell types, including fibroblasts, macrophages, T helper cells, and epithelial cells, during inflammation and cancer, where it plays important roles. Podoplanin is implicated in chronic inflammatory diseases, such as psoriasis, multiple sclerosis, and rheumatoid arthritis, promotes inflammation-driven and cancer-associated thrombosis, and stimulates cancer cell invasion and metastasis through a variety of strategies. To accomplish its biological functions, podoplanin must interact with other proteins located in the same cell or in neighbor cells. The binding of podoplanin to its ligands leads to modulation of signaling pathways that regulate proliferation, contractility, migration, epithelial⁻mesenchymal transition, and remodeling of the extracellular matrix. In this review, we describe the diverse roles of podoplanin in inflammation and cancer, depict the protein ligands of podoplanin identified so far, and discuss the mechanistic basis for the involvement of podoplanin in all these processes.

PMab-219: A monoclonal antibody for the immunohistochemical analysis of horse podoplanin

Monoclonal antibodies (mAbs) against human, mouse, rat, rabbit, dog, cat, and bovine podoplanin (PDPN), a lymphatic endothelial cell marker, have been established in our previous studies. However, mAbs against horse PDPN (horPDPN), which are useful for immunohistochemical analysis, remain to be developed. In the present study, mice were immunized with horPDPN-overexpressing Chinese hamster ovary (CHO)-K1 cells (CHO/horPDPN), and hybridomas producing mAbs against horPDPN were screened using flow cytometry. One of the mAbs, PMab-219 (IgG_2a, kappa), specifically detected CHO/horPDPN cells via flow cytometry and recognized horPDPN protein using Western blotting. Furthermore, PMab-219 strongly stained CHO/horPDPN via immunohistochemistry. These findings suggest that PMab-219 is useful for investigating the function of horPDPN.

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PDPN is known as a specific lymphatic endothelial cell (LEC) marker.

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Sensitive and specific PMab-219 mAb against horse PDPN was produced.

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PMab-219 reacted with a horse renal cell line sensitively in flow cytometry.

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PMab-219 is useful for IHC using paraffin-embedded cell sections.