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

PMab-314: An Anti-Giant Panda Podoplanin Monoclonal Antibody

The giant panda (Ailuropoda melanoleuca) is one of the important species in worldwide animal conservation. Because it is essential to understand the disease of giant panda for conservation, histopathological analyses of tissues are important to understand the pathogenesis. However, monoclonal antibodies (mAbs) against giant panda-derived proteins are limited. Podoplanin (PDPN) is an essential marker of lung type I alveolar epithelial cells, kidney podocytes, and lymphatic endothelial cells. PDPN is also overexpressed in various human tumors, which are associated with poor prognosis. Here, an anti-giant panda PDPN (gpPDPN) mAb, PMab-314 (mouse IgG1, kappa) was established using the Cell-Based Immunization and Screening method. PMab-314 recognized N-terminal PA16-tagged gpPDPN-overexpressed Chinese hamster ovary-K1 cells (CHO/PA16-gpPDPN) in flow cytometry. The KD value of PMab-314 for CHO/PA16-gpPDPN was determined as 1.3 × 10-8 M. Furthermore, PMab-314 is useful for detecting gpPDPN in western blot analysis. These findings indicate that PMab-314 is a useful tool for the analyses of gpPDPN-expressed cells.

Development of a Sensitive Anti-Mouse CD39 Monoclonal Antibody (C39Mab-1) for Flow Cytometry and Western Blot Analyses

CD39 is involved in adenosine metabolism by converting extracellular ATP to adenosine. As extracellular adenosine plays a critical role in the immune suppression of the tumor microenvironment, the inhibition of CD39 activity by monoclonal antibodies (mAbs) is one of the important strategies for tumor therapy. This study developed specific and sensitive mAbs for mouse CD39 (mCD39) using the Cell-Based Immunization and Screening method. The established anti-mCD39 mAb, C39Mab-1 (rat IgG2a, kappa), reacted with mCD39-overexpressed Chinese hamster ovary-K1 (CHO/mCD39) by flow cytometry. The kinetic analysis using flow cytometry indicated that the dissociation constant of C39Mab-1 for CHO/mCD39 was 7.3 × 10-9 M. Furthermore, C39Mab-1 detected the lysate of CHO/mCD39 by western blot analysis. These results indicated that C39Mab-1 is useful for the detection of mCD39 in many functional studies.

PMab-301: An Anti-Giraffe Podoplanin Monoclonal Antibody for Immunohistochemistry

Immunohistochemistry staining is an essential method in pathological diagnoses. Podoplanin (PDPN) is a specific maker of alveolar epithelium, lymphatic vessels, and glomeruli. In this study, we established a novel anti-giraffe PDPN (girPDPN) mAb, PMab-301, using the Cell-Based Immunization and Screening (CBIS) method. PMab-301 (mouse IgG1, kappa) detected girPDPN in various applications, such as flow cytometry, western blot, and immunohistochemistry. PMab-301 specifically stained type-I alveolar cells using formalin-fixed paraffin-embedded giraffe lung tissues. Our findings suggest the potential usefulness of PMab-301 for the pathophysiological analyses of giraffe tissues.

A Rat Anti-Mouse CD39 Monoclonal Antibody for Flow Cytometry

By converting extracellular adenosine triphosphate to adenosine, CD39 is involved in adenosine metabolism. The extracellular adenosine plays a critical role in the immune suppression of the tumor microenvironment. Therefore, the inhibition of CD39 activity by monoclonal antibodies (mAbs) is thought to be one of the important strategies for tumor therapy. In this study, we developed novel mAbs for mouse CD39 (mCD39) using the Cell-Based Immunization and Screening (CBIS) method. One of the established anti-mCD39 mAbs, C39Mab-2 (rat IgG2a, lambda), reacted with mCD39-overexpressed Chinese hamster ovary-K1 (CHO/mCD39) and an endogenously mCD39-expressed cell line (SN36) by flow cytometry. The kinetic analysis using flow cytometry indicated that the dissociation constant (KD) values of C39Mab-2 for CHO/mCD39 and SN36 were 5.5 × 10-9 M and 4.9 × 10-9 M, respectively. These results indicated that C39Mab-2 is useful for the detection of mCD39 in flow cytometry.

EMab-300 Detects Mouse Epidermal Growth Factor Receptor-Expressing Cancer Cell Lines in Flow Cytometry

Epidermal Growth Factor Receptor (EGFR) overexpression or its mutation mediates the sustaining proliferative signaling, which is an important hallmark of cancer. Human EGFR-targeting monoclonal antibody (mAb) therapy such as cetuximab has been approved for clinical use in patients with colorectal cancers and head and neck squamous cell carcinomas. A reliable preclinical mouse model is essential to further develop the mAb therapy against EGFR. Therefore, sensitive mAbs against mouse EGFR (mEGFR) should be established. In this study, we developed a specific and sensitive mAb for mEGFR using the Cell-Based Immunization and Screening (CBIS) method. The established anti-mEGFR mAb, EMab-300 (rat IgG₁, kappa), reacted with mEGFR-overexpressed Chinese hamster ovary-K1 (CHO/mEGFR) and endogenously mEGFR-expressed cell lines, including NMuMG (a mouse mammary gland epithelial cell) and Lewis lung carcinoma cells, using flow cytometry. The kinetic analysis using flow cytometry indicated that the K_D of EMab-300 for CHO/mEGFR and NMuMG was 4.3 × 10^-8 M and 1.9 × 10^-8 M, respectively. These results indicated that EMab-300 applies to the detection of mEGFR using flow cytometry and may be useful to obtain the proof of concept in preclinical studies.

A Novel Anti-CD44 Variant 3 Monoclonal Antibody C44Mab-6 Was Established for Multiple Applications

Cluster of differentiation 44 (CD44) promotes tumor progression through the recruitment of growth factors and the acquisition of stemness, invasiveness, and drug resistance. CD44 has multiple isoforms including CD44 standard (CD44s) and CD44 variants (CD44v), which have common and unique functions in tumor development. Therefore, elucidating the function of each CD44 isoform in a tumor is essential for the establishment of CD44-targeting tumor therapy. We have established various anti-CD44s and anti-CD44v monoclonal antibodies (mAbs) through the immunization of CD44v3-10-overexpressed cells. In this study, we established C₄₄Mab-6 (IgG₁, kappa), which recognized the CD44 variant 3-encoded region (CD44v3), as determined via an enzyme-linked immunosorbent assay. C₄₄Mab-6 reacted with CD44v3-10-overexpressed Chinese hamster ovary (CHO)-K1 cells (CHO/CD44v3-10) or some cancer cell lines (COLO205 and HSC-3) via flow cytometry. The apparent K_D of C₄₄Mab-6 for CHO/CD44v3-10, COLO205, and HSC-3 was 1.5 × 10^-9 M, 6.3 × 10^-9 M, and 1.9 × 10^-9 M, respectively. C₄₄Mab-6 could detect the CD44v3-10 in Western blotting and stained the formalin-fixed paraffin-embedded tumor sections in immunohistochemistry. These results indicate that C₄₄Mab-6 is useful for detecting CD44v3 in various experiments and is expected for the application of tumor diagnosis and therapy.

Development of a Novel Anti-CD44 Variant 5 Monoclonal Antibody C44Mab-3 for Multiple Applications against Pancreatic Carcinomas

Pancreatic cancer exhibits a poor prognosis due to the lack of early diagnostic biomarkers and the resistance to conventional chemotherapy. CD44 has been known as a cancer stem cell marker and plays tumor promotion and drug resistance roles in various cancers. In particular, the splicing variants are overexpressed in many carcinomas and play essential roles in the cancer stemness, invasiveness or metastasis, and resistance to treatments. Therefore, the understanding of each CD44 variant's (CD44v) function and distribution in carcinomas is essential for the establishment of CD44-targeting tumor therapy. In this study, we immunized mice with CD44v3-10-overexpressed Chinese hamster ovary (CHO)-K1 cells and established various anti-CD44 monoclonal antibodies (mAbs). One of the established clones (C₄₄Mab-3; IgG₁, kappa) recognized peptides of the variant-5-encoded region, indicating that C₄₄Mab-3 is a specific mAb for CD44v5. Moreover, C₄₄Mab-3 reacted with CHO/CD44v3-10 cells or pancreatic cancer cell lines (PK-1 and PK-8) by flow cytometry. The apparent K_D of C₄₄Mab-3 for CHO/CD44v3-10 and PK-1 was 1.3 × 10^-9 M and 2.6 × 10^-9 M, respectively. C₄₄Mab-3 could detect the exogenous CD44v3-10 and endogenous CD44v5 in Western blotting and stained the formalin-fixed paraffin-embedded pancreatic cancer cells but not normal pancreatic epithelial cells in immunohistochemistry. These results indicate that C₄₄Mab-3 is useful for detecting CD44v5 in various applications and is expected to be useful for the application of pancreatic cancer diagnosis and therapy.

A Novel Anti-CD44 Variant 9 Monoclonal Antibody C44Mab-1 Was Developed for Immunohistochemical Analyses against Colorectal Cancers

Cluster of differentiation 44 (CD44) is a type I transmembrane glycoprotein and has been shown to be a cell surface marker of cancer stem-like cells in various cancers. In particular, the splicing variants of CD44 (CD44v) are overexpressed in cancers and play critical roles in cancer stemness, invasiveness, and resistance to chemotherapy and radiotherapy. Therefore, the understanding of the function of each CD44v is indispensable for CD44-targeting therapy. CD44v9 contains the variant 9-encoded region, and its expression predicts poor prognosis in patients with various cancers. CD44v9 plays critical roles in the malignant progression of tumors. Therefore, CD44v9 is a promising target for cancer diagnosis and therapy. Here, we developed sensitive and specific monoclonal antibodies (mAbs) against CD44 by immunizing mice with CD44v3-10-overexpressed Chinese hamster ovary-K1 (CHO/CD44v3-10) cells. We first determined their critical epitopes using enzyme-linked immunosorbent assay and characterized their applications as flow cytometry, western blotting, and immunohistochemistry. One of the established clones, C₄₄Mab-1 (IgG₁, kappa), reacted with a peptide of the variant 9-encoded region, indicating that C₄₄Mab-1 recognizes CD44v9. C₄₄Mab-1 could recognize CHO/CD44v3-10 cells or colorectal cancer cell lines (COLO201 and COLO205) in flow cytometric analysis. The apparent dissociation constant (K_D) of C₄₄Mab-1 for CHO/CD44v3-10, COLO201, and COLO205 was 2.5 × 10^-8 M, 3.3 × 10^-8 M, and 6.5 × 10^-8 M, respectively. Furthermore, C₄₄Mab-1 was able to detect the CD44v3-10 in western blotting and the endogenous CD44v9 in immunohistochemistry using colorectal cancer tissues. These results indicated that C₄₄Mab-1 is useful for detecting CD44v9 not only in flow cytometry or western blotting but also in immunohistochemistry against colorectal cancers.

Development of a Novel Anti-CD44 Variant 7/8 Monoclonal Antibody, C44Mab-34, for Multiple Applications against Oral Carcinomas

Cluster of differentiation 44 (CD44) has been investigated as a cancer stem cell (CSC) marker as it plays critical roles in tumor malignant progression. The splicing variants are overexpressed in many carcinomas, especially squamous cell carcinomas, and play critical roles in the promotion of tumor metastasis, the acquisition of CSC properties, and resistance to treatments. Therefore, each CD44 variant (CD44v) function and distribution in carcinomas should be clarified for the establishment of novel tumor diagnosis and therapy. In this study, we immunized mouse with a CD44 variant (CD44v3–10) ectodomain and established various anti-CD44 monoclonal antibodies (mAbs). One of the established clones (C44Mab-34; IgG1, kappa) recognized a peptide that covers both variant 7- and variant 8-encoded regions, indicating that C44Mab-34 is a specific mAb for CD44v7/8. Moreover, C44Mab-34 reacted with CD44v3–10-overexpressed Chinese hamster ovary-K1 (CHO) cells or the oral squamous cell carcinoma (OSCC) cell line (HSC-3) by flow cytometry. The apparent KD of C44Mab-34 for CHO/CD44v3–10 and HSC-3 was 1.4 × 10−9 and 3.2 × 10−9 M, respectively. C44Mab-34 could detect CD44v3–10 in Western blotting and stained the formalin-fixed paraffin-embedded OSCC in immunohistochemistry. These results indicate that C44Mab-34 is useful for detecting CD44v7/8 in various applications and is expected to be useful in the application of OSCC diagnosis and therapy.

Development of a Novel Anti-CD44 Variant 6 Monoclonal Antibody C44Mab-9 for Multiple Applications against Colorectal Carcinomas

CD44 is a cell surface glycoprotein, and its isoforms are produced by the alternative splicing with the standard and variant exons. The CD44 variant exon-containing isoforms (CD44v) are overexpressed in carcinomas. CD44v6 is one of the CD44v, and its overexpression predicts poor prognosis in colorectal cancer (CRC) patients. CD44v6 plays critical roles in CRC adhesion, proliferation, stemness, invasiveness, and chemoresistance. Therefore, CD44v6 is a promising target for cancer diagnosis and therapy for CRC. In this study, we established anti-CD44 monoclonal antibodies (mAbs) by immunizing mice with CD44v3-10-overexpressed Chinese hamster ovary (CHO)-K1 cells. We then characterized them using enzyme-linked immunosorbent assay, flow cytometry, western blotting, and immunohistochemistry. One of the established clones (C₄₄Mab-9; IgG₁, kappa) reacted with a peptide of the variant 6-encoded region, indicating that C₄₄Mab-9 recognizes CD44v6. Furthermore, C₄₄Mab-9 reacted with CHO/CD44v3-10 cells or CRC cell lines (COLO201 and COLO205) by flow cytometry. The apparent dissociation constant (K_D) of C₄₄Mab-9 for CHO/CD44v3-10, COLO201, and COLO205 was 8.1 × 10^-9 M, 1.7 × 10^-8 M, and 2.3 × 10^-8 M, respectively. C₄₄Mab-9 detected the CD44v3-10 in western blotting, and partially stained the formalin-fixed paraffin-embedded CRC tissues in immunohistochemistry. Collectively, C₄₄Mab-9 is useful for detecting CD44v6 in various applications.

Development of Monoclonal Antibody 281-mG2a-f Against Golden Hamster Podoplanin

Golden (Syrian) hamster (Mesocricetus auratus) is a small animal model of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections. Pathological analyses of the tissues are required to understand the pathogenesis of SARS-CoV-2 and the evaluation of therapeutic modalities, including neutralizing monoclonal antibodies (mAbs). However, mAbs that recognize the golden hamster-derived antigens and distinguish specific cell types, such as the pneumocytes, are limited. Podoplanin (PDPN) is an essential marker of lung type I alveolar epithelial cells, kidney podocytes, and lymphatic endothelial cells. In this study, an anti-Chinese hamster (Cricetulus griseus) PDPN mAb PMab-281 (IgG₃, kappa) was established using the Cell-Based Immunization and Screening (CBIS) method. A defucosylated mouse IgG_2a version of PMab-281 (281-mG_2a-f) was also developed. The 281-mG_2a-f strongly recognized both the Chinese hamster and the golden hamster PDPN using flow cytometry and could detect lung type I alveolar epithelial cells, lymphatic endothelial cells, and Bowman's capsules in the kidney from the golden hamster using immunohistochemistry. These results suggest the usefulness of 281-mG_2a-f for analyzing the golden hamster-derived tissues and cells for SARS-CoV-2 research.

KLMab-1: An Anti-human KLRG1 Monoclonal Antibody for Immunocytochemistry

Immune checkpoint molecules have received attention as targets of cancer immunotherapy. Killer cell lectin-like receptor subfamily G member 1 (KLRG1) is one of the immune checkpoint molecules expressed in CD4⁺ T, CD8⁺ T, and natural killer (NK) cells. KLRG1 exhibits antiviral and antitumor immunity, and its expression in T and NK cells is upregulated by viral infectious diseases and some tumors. Thus, monoclonal antibodies (mAbs) for KLRG1 would be useful tools for the diagnosis and immunotherapy against viral infectious diseases and cancers. We have developed anti-human KLRG1 (hKLRG1) mAb (clone KLMab-1, mouse IgG₁, kappa) by the Cell-Based Immunization and Screening method. We have also demonstrated that KLMab-1 recognizes both exogenous and endogenous hKLRG1 in flow cytometry. In this study, we first showed that KLMab-1 and its recombinant mAb (recKLMab-1) bound to exogenous hKLRG1 overexpressed in Chinese hamster ovary (CHO)-K1 cells, but not in parental CHO-K1 cells, in immunocytochemistry. We next showed that both mAbs detected endogenous hKLRG1 expressed in human NK cells. These results demonstrate that KLMab-1 and recKLMab-1 are available for immunocytochemistry.

Epitope Mapping of an Anti-elephant Podoplanin Monoclonal Antibody (PMab-295) Using Enzyme-Linked Immunosorbent Assay

Podoplanin (PDPN) is a marker of lung type I alveolar cells, kidney podocytes, and lymphatic endothelial cells. The overexpression of PDPN contributes to the malignant progression of tumors. Therefore, the development of anti-PDPN monoclonal antibodies (mAbs) to animals is essential to evaluate the pathogenesis and cellular functions. Using peptide immunization, we previously developed an anti-elephant PDPN (elePDPN) mAb, PMab-295, which is useful for flow cytometry, Western blotting, and immunohistochemistry. In this study, we determined the critical epitope of PMab-295 by enzyme-linked immunosorbent assay (ELISA). We performed ELISA with the alanine-substituted peptides of elePDPN extracellular domain (amino acids 38-51), and found that PMab-295 did not recognize the alanine-substituted peptides of M41A, P44A, and E47A. Furthermore, these peptides could not inhibit the recognition of PMab-295 to elePDPN-expressing cells by flow cytometry and immunohistochemistry. The results indicate that the binding epitope of PMab-295 includes Met41, Pro44, and Glu47 of elePDPN.

Development of a Monoclonal Antibody PMab-295 Against Elephant Podoplanin

Podoplanin (PDPN) is an essential marker of lung type I alveolar cells, kidney podocytes, and lymphatic endothelial cells. Monoclonal antibodies (mAbs) that can specifically recognize PDPN in immunohistochemistry are important to analyze the development of tissues and the pathogenesis of diseases, including cancers. We have developed anti-PDPN mAbs against many animal species; however, mAbs that can recognize elephant-derived membrane proteins and distinguish the specific cell types in immunohistochemistry are limited. In this study, a novel anti-elephant PDPN (elePDPN) mAb, PMab-295 (IgG₁, kappa), was established using the peptide immunization method. PMab-295 recognized both elePDPN-overexpressed Chinese hamster ovary (CHO)-K1 cells and endogenous elePDPN-expressed LACF-NaNaI cells by flow cytometry and western blotting. Kinetic analyses using flow cytometry showed that the K_D of PMab-295 for CHO/elePDPN was 1.5 × 10^-8 M. Furthermore, PMab-295 detected elePDPN-expressing cells using immunohistochemistry. These results showed the usefulness of PMab-295 to investigate the molecular function of elePDPN and the pathogenesis of diseases.

Epitope Mapping of an Anti-Chinese/Golden Hamster Podoplanin Monoclonal Antibody

Chinese hamster (Cricetulus griseus) and golden hamster (Mesocricetus auratus) are important animal models of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections, which affect several organs, including respiratory tract, lung, and kidney. Podoplanin (PDPN) is a marker of lung type I alveolar cells, kidney podocytes, and lymphatic endothelial cells. The development of anti-PDPN monoclonal antibodies (mAbs) for these animals is essential to evaluate the pathogenesis by SARS-CoV-2 infections. Using the Cell-Based Immunization and Screening method, we previously developed an anti-Chinese hamster PDPN (ChamPDPN) mAb, PMab-281 (mouse IgG₃, kappa), and further changed its subclass into IgG_2a (281-mG_2a-f), both of which can recognize not only ChamPDPN but also golden hamster PDPN (GhamPDPN) by flow cytometry and immunohistochemistry. In this study, we examined the critical epitope of 281-mG_2a-f, using enzyme-linked immunosorbent assay (ELISA) with synthesized peptides. First, we performed ELISA with peptides derived from ChamPDPN and GhamPDPN extracellular domain, and found that 281-mG_2a-f reacted with the peptides, which commonly possess the KIPFEELxT sequence. Next, we analyzed the reaction with the alanine-substituted mutants, and revealed that 281-mG_2a-f did not recognize the alanine-substituted peptides of I75A, F77A, and E79A of ChamPDPN. Furthermore, these peptides could not inhibit the recognition of 281-mG_2a-f to ChamPDPN-expressing cells by flow cytometry. The results indicate that the binding epitope of 281-mG_2a-f includes Ile75, Phe77, and Glu79 of ChamPDPN, which are shared with GhamPDPN.

TgMab-2: An Anti-human T Cell Immunoglobulin and Immunoreceptor Tyrosine-Based Inhibitory Motif Domain Monoclonal Antibody for Immunocytochemistry

T cell immunoglobulin and immunoreceptor tyrosine-based inhibitory motif domain (TIGIT) is one of the immune checkpoint molecules. TIGIT is expressed in T or natural killer (NK) cells and is upregulated in several cancers. Because TIGIT suppresses the antitumor activity of the T or NK cells by binding to its ligand, such as CD155, CD112, and CD113, TIGIT can be a molecular marker or a therapeutic target for cancer immunotherapy. We previously developed an anti-human TIGIT (hTIGIT) monoclonal antibody (mAb; clone TgMab-2; mouse IgG₁, kappa) by the Cell-Based Immunization and Screening method. TgMab-2 binds to hTIGIT with high binding affinity in flow cytometry. In this study, we investigated the availability of TgMab-2 and its recombinant mAb (recTgMab-2) in immunocytochemistry. We found that TgMab-2 and recTgMab-2 bind to hTIGIT-overexpressed Chinese hamster ovary (CHO)-K1 cells, but not parental CHO-K1 cells, indicating that both mAbs specifically recognize hTIGIT. Furthermore, both mAbs recognized endogenous hTIGIT expressed in human NK cells in immunocytochemistry. These results demonstrate that TgMab-2 and recTgMab-2 are applicable for immunocytochemistry against hTIGIT.

Cx6Mab-1: A Novel Anti-Mouse CXCR6 Monoclonal Antibody Established by N-Terminal Peptide Immunization

The CXC chemokine receptor 6 (CXCR6) is a member of the G protein-coupled receptor family that is highly expressed in helper T type 1 cells, natural killer cells, cytotoxic T lymphocytes, and various type of cells in tumor microenvironment (TME). CXCR6 has been proposed as a therapeutic target against tumors through regulation of the tumor TME. In this study, we developed specific and sensitive monoclonal antibodies (mAbs) for mouse CXCR6 (mCXCR6), which are useful for flow cytometry and Western blotting by N-terminal peptide immunization into rat. The established anti-mCXCR6 mAb, Cx₆Mab-1 (rat IgG₁, kappa), reacted with not only mCXCR6-overexpressed Chinese hamster ovary-K1 (CHO/mCXCR6) but also mCXCR6-endogenously expressed cell lines, such as P388 (mouse lymphoid neoplasm) and J774-1 (mouse macrophage-like) through flow cytometry. Kinetic analyses using flow cytometry indicated that the dissociation constants (K_D) of Cx₆Mab-1 for CHO/mCXCR6, P388, and J774-1 cells were 1.7 × 10^-9 M, 3.4 × 10^-7 M, and 3.8 × 10^-7 M, respectively. Furthermore, Cx₆Mab-1 could detect endogenous mCXCR6 in P388 and J774-1 cells by Western blotting. These results indicated that Cx₆Mab-1 is useful for detecting mCXCR6 by flow cytometry and Western blotting, and provides a possibility for targeting CXCR6-expressing cells in vivo experiments.

Development of a Novel Anti-CD44 Monoclonal Antibody for Multiple Applications against Esophageal Squamous Cell Carcinomas

CD44 is a cell surface glycoprotein, which is expressed on normal cells, and overexpressed on cancer cells. CD44 is involved in cell adhesion, migration, proliferation, survival, stemness, and chemo-resistance. Therefore, CD44 is thought to be a promising target for cancer diagnosis and therapy. In this study, we established anti-CD44 monoclonal antibodies (mAbs) by immunizing mice with a CD44 variant (CD44v3-10) ectodomain and screening using enzyme-linked immunosorbent assay. We then characterized them using flow cytometry, Western blotting, and immunohistochemistry. One of the established clones (C₄₄Mab-46; IgG₁, kappa) reacted with CD44 standard isoform (CD44s)-overexpressed Chinese hamster ovary-K1 cells (CHO/CD44s) or esophageal squamous cell carcinoma (ESCC) cell lines (KYSE70 and KYSE770). The apparent K_D of C₄₄Mab-46 for CHO/CD44s, KYSE70, and KYSE770 was 1.1 × 10^-8 M, 4.9 × 10^-8 M, and 4.1 × 10^-8 M, respectively. C₄₄Mab-46 detected CD44s of CHO/CD44s and KYSE70, and CD44 variants of KYSE770 in Western blot analysis. Furthermore, C₄₄Mab-46 strongly stained the formalin-fixed paraffin-embedded ESCC tissues in immunohistochemistry. Collectively, C₄₄Mab-46 is very useful for detecting CD44 in various applications.

Development of a Novel Anti-Mouse CCR4 Monoclonal Antibody (C4Mab-1) by N-Terminal Peptide Immunization

The CC chemokine receptor type-4 (CCR4) belongs to the G-protein-coupled receptor superfamily, expressed on the cell surface of T cells and its malignancy. Two CCR4 ligands (CCL17 and CCL22) bind to CCR4 that mediate physiological and pathological functions of T cell immune responses. Anti-CCR4 monoclonal antibody (mAb) mogamulizumab is approved for adult T cell leukemia/lymphoma and cutaneous T cell lymphomas. In addition, mogamulizumab can deplete regulatory T cells, implying the application to solid tumors as an immunomodulator. Therefore, the development of sensitive mAbs for CCR4 has been desired for basic research, diagnosis, and therapy. In this study, a specific, and sensitive anti-mouse CCR4 (mCCR4) mAb, C₄Mab-1 (rat IgG₁, kappa), was established using N-terminal peptide immunization. C₄Mab-1 reacted with mCCR4-overexpressed Chinese hamster ovary (CHO)-K1 cells, P388 (mouse lymphoid neoplasm), and J774-1 (mouse macrophage-like) cells in flow cytometry. Kinetic analyses using flow cytometry showed that K_Ds of C₄Mab-1 for CHO/mCCR4, P388, and J774-1 cells were 4.2 × 10^-9 M, 5.4 × 10^-7 M, and 1.1 × 10^-6 M, respectively. C₄Mab-1 could be a valuable tool for elucidating mCCR4-related biological responses.

Development of a Monoclonal Antibody PMab-292 Against Ferret Podoplanin

Ferrets (Mustela putorius furo) have been used as small animal models to investigate severe acute respiratory syndrome coronaviruses (SARS-CoV and SARS-CoV-2) infections. Pathological analyses of these tissue samples, including those of the lung, are, therefore, essential to understand the pathogenesis of SARS-CoVs and evaluate the action of therapeutic monoclonal antibodies (mAbs) against this disease. However, mAbs that recognize ferret-derived proteins and distinguish between specific cell types, such as lung epithelial cells, are limited. Podoplanin (PDPN) has been identified as an essential marker in lung type I alveolar epithelial cells, kidney podocytes, and lymphatic endothelial cells. In this study, an anti-ferret PDPN (ferPDPN) mAb PMab-292 (mouse IgG₁, kappa) was established using the Cell-Based Immunization and Screening (CBIS) method. PMab-292 recognized ferPDPN-overexpressed Chinese hamster ovary-K1 (CHO/ferPDPN) cells by flow cytometry and Western blotting. The kinetic analysis using flow cytometry showed that the K_D of PMab-292 for CHO/ferPDPN was 3.4 × 10^-8 M. Furthermore, PMab-292 detected lung type I alveolar epithelial cells, lymphatic endothelial cells, and glomerular/Bowman's capsule in the kidney using immunohistochemistry. Hence, these results propose the usefulness of PMab-292 in analyzing ferret-derived tissues for SARS-CoV-2 research.

Development of a Novel Anti-Mouse CCR2 Monoclonal Antibody (C2Mab-6) by N-Terminal Peptide Immunization

The CC chemokine receptor type-2 (CCR2) belongs to the G-protein-coupled receptor superfamily, expressed on the cell surface of immune cells and tumors. CCR2 binds to the CC motif chemokine 2/monocyte chemoattractant protein-1, a CC chemokine, which is produced by various cells, including immune-related cells and tumors. Therefore, the development of sensitive monoclonal antibodies (mAbs) for CCR2 has been desired for treatment and diagnosis. This study established a novel, specific, and sensitive anti-mouse CCR2 (mCCR2) mAb; C₂Mab-6 (rat IgG₁, kappa), using the mCCR2 synthetic peptide immunization method. C₂Mab-6 reacted with mCCR2-overexpressed Chinese hamster ovary-K1 cells and L1210 (murine leukemia) cells, which express endogenous mCCR2 in flow cytometry. Furthermore, C₂Mab-6 showed a high binding affinity for both cells. Hence, C₂Mab-6 can be a useful tool for analyzing mCCR2-related biological responses, using flow cytometry.

Immunohistochemical Analysis Using Monoclonal Antibody PMab-269 Against Steller Sea Lion Podoplanin

Monoclonal antibodies (mAbs) that specifically target podoplanin (PDPN), a marker for type I alveolar cells, are required for immunohistochemical analyses. Anti-PDPN mAbs are available for many species, including human, mouse, rat, rabbit, dog, cat, bovine, pig, Tasmanian devil, alpaca, tiger, whale, goat, horse, bear, sheep, and California sea lion PDPNs. However, no anti-Steller sea lion PDPN (stePDPN) antibody has been developed. Immunohistochemical analysis showed that an anti-California sea lion PDPN mAb (PMab-269) reacted with type I alveolar cells from the Steller sea lion lung, renal glomeruli and Bowman's capsules from kidney, and lymphatic endothelial cells from the colon, indicating that PMab-269 is useful for detecting stePDPN.

Roles of Podoplanin in Malignant Progression of Tumor

Podoplanin (PDPN) is a cell-surface mucin-like glycoprotein that plays a critical role in tumor development and normal development of the lung, kidney, and lymphatic vascular systems. PDPN is overexpressed in several tumors and is involved in their malignancy. PDPN induces platelet aggregation through binding to platelet receptor C-type lectin-like receptor 2. Furthermore, PDPN modulates signal transductions that regulate cell proliferation, differentiation, migration, invasion, epithelial-to-mesenchymal transition, and stemness, all of which are crucial for the malignant progression of tumor. In the tumor microenvironment (TME), PDPN expression is upregulated in the tumor stroma, including cancer-associated fibroblasts (CAFs) and immune cells. CAFs play significant roles in the extracellular matrix remodeling and the development of immunosuppressive TME. Additionally, PDPN functions as a co-inhibitory molecule on T cells, indicating its involvement with immune evasion. In this review, we describe the mechanistic basis and diverse roles of PDPN in the malignant progression of tumors and discuss the possibility of the clinical application of PDPN-targeted cancer therapy, including cancer-specific monoclonal antibodies, and chimeric antigen receptor T technologies.

Epitope Mapping of the Anti-CD44 Monoclonal Antibody (C44Mab-46) Using the REMAP Method

CD44 functions as a major hyaluronan receptor on most cell types, with roles in cell adhesion, migration, proliferation, differentiation, and survival. The CD44 gene comprises 20 exons, with alternative splicing producing many different isoforms. CD44 variant isoforms exhibit tissue-specific expression patterns and have been studied as therapeutic targets for several cancers; therefore, anti-CD44 monoclonal antibodies (mAbs) are useful for investigating CD44 expression in various cancers. Previously, we established an anti-CD44 mAb, C₄₄Mab-46 (IgG₁, κ), by immunizing mice with the CD44v3-10 ectodomain. Although C₄₄Mab-46 recognized all CD44 isoforms, the binding epitope of C₄₄Mab-46 has not been determined. In this study, we first checked the reactivity of C₄₄Mab-46 to several CD44v3-10 deletion mutants such as dN79, dN124, dN147, and dN224. We found the N-terminus of the C₄₄Mab-46-binding epitope between residues 147 and 224 of CD44v3-10. We next investigated this epitope using a novel mapping system: RIEDL insertion for epitope mapping (REMAP) method. We constructed 31 CD44 standard (CD44s) mutants where the RIEDL tag was inserted into the expected epitope region in CD44s. We observed that the C₄₄Mab-46 epitope constituted five amino acids: ₁₇₄-TDDDV-₁₇₈ of CD44s. Thus, the REMAP method could be used to determine mAb binding epitopes for membrane proteins.

Ferret Podoplanin Is Detected by PMab-241 in Immunohistochemistry

Podoplanin (PDPN) plays an important role in the development of many normal tissues and is expressed in various cancers. We have previously developed multiple monoclonal antibodies (mAbs) against PDPNs from a variety of animal species and characterized each of these PDPNs using the anti-PDPN mAbs. In this study, we evaluated whether these anti-PDPN mAbs possess cross-reactivity with ferret PDPN (ferPDPN) using flow cytometry. Comprehensive analysis using 17 differing anti-PDPN mAbs available for immunohistochemistry use, demonstrated that the anti-bear PDPN mAb (clone PMab-241) strongly cross-reacts with ferPDPN-overexpressed Chinese hamster ovary-K1 (CHO/ferPDPN) cells. Immunohistochemistry analysis demonstrated intense PMab-241 staining within Bowman's capsules and glomeruli of the ferret kidney, and lymphatic endothelial cells of the ferret lung. These results demonstrate that PMab-241 is suitable for the detection of PDPN in ferret tissues.

Development of Anti-Human CC Chemokine Receptor 9 Monoclonal Antibodies for Flow Cytometry

CC chemokine receptor 9 (CCR9) belongs to the beta chemokine receptor family and is mainly distributed on the surface of immature T lymphocytes and enterocytes. This receptor is highly expressed in rheumatoid arthritis, colitis, type 2 diabetes, and various tumors. Therefore, more sensitive monoclonal antibodies (mAbs) need to be developed to predict the prognosis of many high CCR9 expression diseases. Because CCR9 is a structurally unstable G protein-coupled receptor, it has been difficult to develop anti-CCR9 mAbs using the traditional method. This study developed anti-human CCR9 (hCCR9) mAbs for flow cytometry using a Cell-Based Immunization and Screening (CBIS) method. Two mice were immunized with hCCR9-overexpressed Chinese hamster ovary (CHO)-K1 cells (CHO/hCCR9), and hybridomas showing strong signals from CHO/hCCR9 and no signals from CHO-K1 cells were selected by flow cytometry. We established an anti-hCCR9 mAb, C₉Mab-1 (IgG₁, kappa), which detected hCCR9 in MOLT-4 leukemia T lymphoblast cells and CHO/hCCR9 cells by flow cytometry. Our study showed that an anti-hCCR9 mAb was developed more rapidly by the CBIS method than the previous method.

Development of an Anti-Elephant Podoplanin Monoclonal Antibody PMab-265 for Flow Cytometry

The development of specific antibodies is essential to understand a wide variety of biological phenomena and pathophysiological analyses. Podoplanin (PDPN), a type I transmembrane glycoprotein, is known as a diagnostic marker. Anti-PDPN monoclonal antibodies (mAbs) against many species, such as human, mouse, rat, rabbit, dog, bovine, cat, tiger, horse, pig, goat, alpaca, Tasmanian devil, bear, whale, and sheep, have been established in recent studies. However, sensitive and specific mAbs against elephant PDPN (elePDPN) have not been established. Thus, this study established a novel mAb against African savanna elephant (Loxodonta africana) PDPN using the Cell-Based Immunization and Screening method. elePDPN-overexpressed Chinese hamster ovary-K1 (CHO/elePDPN) cells were immunized, and mAbs were screened against elePDPN using flow cytometry. One of the mAbs, PMab-265 (IgM, κ), specifically detected CHO/elePDPN cells by flow cytometry. These findings suggested the potential usefulness of PMab-265 for the functional analyses of elePDPN.

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.

Establishment of a novel anti-TROP2 monoclonal antibody TrMab-29 for immunohistochemical analysis

TROP2 is a type I transmembrane glycoprotein originally identified in human trophoblast cells that is overexpressed in several types of cancer. To better understand the role of TROP2 in cancer, we herein aimed to develop a sensitive and specific anti-TROP2 monoclonal antibody (mAb) for use in flow cytometry, Western blot, and immunohistochemistry using a Cell-Based Immunization and Screening (CBIS) method. Two mice were immunized with N-terminal PA-tagged and C-terminal RAP/MAP-tagged TROP2-overexpressed Chinese hamster ovary (CHO)-K1 cells (CHO/PA-TROP2-RAP-MAP), and hybridomas showing strong signals from PA-tagged TROP2-overexpressed CHO-K1 cells (CHO/TROP2-PA) and weak-to-no signals from CHO-K1 cells were selected using flow cytometry. We demonstrated using flow cytometry that the established anti-TROP2 mAb, TrMab-29 (mouse IgG₁ kappa), detected TROP2 in MCF7 breast cancer cell line as well as CHO/TROP2-PA cells. Western blot analysis showed a 40 kDa band in lysates prepared from both CHO/TROP2-PA and MCF7 cells. Furthermore, TROP2 was strongly detected by immunohistochemical analysis using TrMab-29, indicating that TrMab-29 may be a valuable tool for the detection of TROP2 in cancer.

A cancer-specific anti-podocalyxin monoclonal antibody (60-mG2a-f) exerts antitumor effects in mouse xenograft models of pancreatic carcinoma

Overexpression of podocalyxin (PODXL) is associated with progression, metastasis, and poor outcomes in several cancers. PODXL also plays an important role in the development of normal tissues. For antibody-based therapy to target PODXL-expressing cancers using monoclonal antibodies (mAbs), cancer-specificity is necessary to reduce the risk of adverse effects to normal tissues. In this study, we developed an anti-PODXL cancer-specific mAb (CasMab), named as PcMab-60 (IgM, kappa) by immunizing mice with soluble PODXL, which is overexpressed in LN229 glioblastoma cells. The PcMab-60 reacted with the PODXL-overexpressing LN229 (LN229/PODXL) cells and MIA PaCa-2 pancreatic cancer cells in flow cytometry but did not react with normal vascular endothelial cells (VECs), whereas one of non-CasMabs, PcMab-47 showed high reactivity for not only LN229/PODXL and MIA PaCa-2 cells but also VECs, indicating that PcMab-60 is a CasMab. Next, we engineered PcMab-60 into a mouse IgG_2a-type mAb, named as 60-mG_2a, to add antibody-dependent cellular cytotoxicity (ADCC). We further developed a core fucose-deficient type of 60-mG_2a, named as 60-mG_2a-f, to augment its ADCC activity. In vivo analysis revealed that 60-mG_2a-f exerted antitumor activity in MIA PaCa-2 xenograft models at a dose of 100 μg/mouse/week administered three times. These results suggested that 60-mG_2a-f could be useful for antibody-based therapy against PODXL-expressing pancreatic cancers.

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PODXL is associated with poor outcomes in several cancers.

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We developed an anti-PODXL cancer-specific mAb (PcMab-60).

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A core fucose-deficient IgG_2a type of PcMab-60 (60-mG_2a-f) exerted antitumor activity in MIA PaCa-2 xenograft models.

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60-mG_2a-f could be useful for antibody-based therapy against PODXL-expressing pancreatic cancers.

Development and Characterization of Anti-Sheep Podoplanin Monoclonal Antibodies PMab-253 and PMab-260

Anti-podoplanin (PDPN) monoclonal antibodies (mAbs) are needed as markers for lymphatic endothelial cells or type I alveolar cells in immunohistochemical analyses. We have developed anti-PDPN mAbs for many species, including humans, mice, rats, rabbits, dogs, cats, bovines, pigs, Tasmanian devils, alpacas, tigers, whales, goats, horses, and bears. This study develops and characterizes anti-sheep PDPN (sPDPN) mAbs using Cell-Based Immunization and Screening (CBIS) method. A RAP14 tag was added to the N-terminus of sPDPN, and an anti-RAP14 tag mAb (PMab-2) was used to measure the expression level of sPDPN in flow cytometry and Western blots. We immunized mice with sPDPN-overexpressing Chinese hamster ovary (CHO)-K1 (CHO/sPDPN) cells and screened mAbs against sPDPN using flow cytometry. Two of the mAbs, PMab-253 (immunoglobulin M [IgM], kappa) and PMab-260 (IgM, kappa), detected CHO/sPDPN cells specifically using flow cytometry and Western blots. Both PMab-253 and PMab-260 stained the renal glomerulus and Bowman's capsule, lymphatic endothelial cells of the lung and colon, and type I alveolar cells of the lung, suggesting PMab-253 and PMab-260, which were developed by CBIS method, can be applied to functional analyses of sPDPN. We also determined the binding epitope of PMab-253 and PMab-260 using flow cytometry. Analysis of sPDPN deletion mutants revealed that the N-terminus of the PMab-253 and PMab-260 epitope exists between amino acids 110 and 115 of sPDPN. Analysis of sPDPN point mutations revealed that the critical epitope of PMab-253 and PMab-260 includes Thr112 and Ser113 of sPDPN, indicating that the PMab-253 and PMab-260 epitope are independent of the platelet aggregation-stimulating (PLAG) domain or the PLAG-like domain of sPDPN.

Functional, structural, and molecular identification of lymphatic outflow from subconjunctival blebs

The purpose of this study is to evaluate outflow pathways from subconjunctival blebs and to identify their identity. Post-mortem porcine (n = 20), human (n = 1), and bovine (n = 1) eyes were acquired, and tracers (fluorescein, indocyanine green, or fixable/fluorescent dextrans) were injected into the subconjunctival space to create raised blebs where outflow pathways were visualized qualitatively and quantitatively. Rodents with fluorescent reporter transgenes were imaged for structural comparison. Concurrent optical coherence tomography (OCT) was obtained to study the structural nature of these pathways. Using fixable/fluorescent dextrans, tracers were trapped to the bleb outflow pathway lumen walls for histological visualization and molecular identification using immunofluorescence against lymphatic and blood vessel markers. Bleb outflow pathways could be observed using all tracers in all species. Quantitative analysis showed that the nasal quadrant had more bleb-related outflow pathways compared to the temporal quadrant (nasal: 1.9±0.3 pathways vs. temporal: 0.7±0.2 pathways; p = 0.003). However, not all blebs resulted in an outflow pathway (0-pathways = 18.2%; 1-pathway = 36.4%; 2-pathways = 38.6%; and 3-pathways = 6.8%). Outflow signal was validated as true luminal pathways using optical coherence tomography and histology. Bicuspid valves were identified in the direction of flow in porcine eyes. Immunofluorescence of labeled pathways demonstrated a lymphatic (Prox-1 and podoplanin) but not a blood vessel (CD31) identity. Therefore, subconjunctival bleb outflow occurs in discrete luminal pathways. They are lymphatic as assessed by structural identification of valves and molecular identification of lymphatic markers. Better understanding of lymphatic outflow may lead to improved eye care for glaucoma surgery and ocular drug delivery.

Establishment of C20Mab-11, a novel anti-CD20 monoclonal antibody, for the detection of B cells

CD20 is one of several B-lymphocyte antigens that has been shown to be an effective target for the detection and treatment of B-cell lymphomas. Sensitive and specific monoclonal antibodies (mAbs) are required for every application used for the diagnosis of B-cell lymphoma. Although many anti-CD20 mAbs have been established, the types of applications, those anti-CD20 can be used in, are limited. In this study, we aimed to establish novel anti-CD20 mAbs to be used for broad applications, such as flow cytometry, western blot, and immunohistochemical analyses, using the Cell-Based Immunization and Screening (CBIS) method. One of the established mAbs, C₂₀Mab-11 (IgM, kappa), detected overexpression of CD20 in CHO-K1 or LN229 cell lines, indicating that C₂₀Mab-11 is specific for CD20. In western blot analyses, C₂₀Mab-11 detected not only overexpression of CD20 in CHO-K1 or LN229 cell lines, but also CD20 of BALL-1 and Raji cells with both sensitivity and specificity. Furthermore, C₂₀Mab-11 strongly stained B cells of the lymph follicle and B cell lymphomas in immunohistochemical analyses. These results indicate that C₂₀Mab-11 develped by CBIS method, is useful for the detection of CD20 in lymphoma tissues by flow cytometry, western blot, and immunohistochemical analyses and potentially could be beneficial for the treatment of B cell lymphomas.

Thr80 of Sheep Podoplanin Is a Critical Epitope of the Antisheep Podoplanin Monoclonal Antibody: PMab-256

An antisheep podoplanin (sPDPN) monoclonal antibody (mAb), PMab-256, has recently been established. PMab-256 shows positive immunostaining for lymphatic endothelial cells, lung type I alveolar cells, and kidney podocytes. PDPN possesses three platelet-aggregation-stimulating (PLAG) domains, PLAG1, PLAG2, and PLAG3, and a PLAG-like domain (PLD). The binding epitope of many anti-PDPN mAbs is located in PLAG domains or PLD. The purpose of this study is to determine the binding epitope of PMab-256. Analysis of sPDPN deletion mutants revealed that the N-terminus of the PMab-256 epitope exists between amino acids 75 and 80 of sPDPN. Furthermore, analysis of sPDPN point mutations demonstrated that the critical epitope includes Thr80 of sPDPN, indicating that the PMab-256 epitope is in the PLD of sPDPN.

Detection of Lion Podoplanin Using the Antitiger Podoplanin Monoclonal Antibody PMab-231

Monoclonal antibodies (mAbs) that specifically target podoplanin (PDPN), a marker for type I alveolar cells, are needed for immunohistochemical analyses. Anti-PDPN mAbs are available for many species, including human, mouse, rat, rabbit, dog, cat, bovine, pig, Tasmanian devil, alpaca, tiger, whale, goat, horse, bear, and sheep PDPNs. However, no antilion PDPN (lioPDPN) antibody has been developed. In this study, possible cross-reaction between available anti-PDPN mAbs and lioPDPN was examined. Immunohistochemical analysis showed that antitiger PDPN mAb PMab-231 (IgG_2a, kappa) reacted with type I alveolar cells from lion lung, indicating that PMab-231 is useful for the detection of lioPDPN.

Epitope Mapping of PMab-241, a Lymphatic Endothelial Cell-Specific Anti-Bear Podoplanin Monoclonal Antibody

Anti-bear podoplanin (bPDPN) monoclonal antibodies (mAbs), including PMab-247 and PMab-241, have been previously established. Although PMab-247 has shown positive immunostaining for lymphatic endothelial cells (LECs), type I alveolar cells of the lung, and podocytes of the kidney, PMab-241 stains LECs but does not react with lung type I alveolar cells. PDPN possesses three platelet aggregation-stimulating (PLAG) domains (PLAG1, PLAG2, and PLAG3) and the PLAG-like domain (PLD). The binding epitope of PMab-247 was previously determined to include bPDPN residues Asp76, Arg78, Glu80, and Arg82. Among these, Glu80 and Arg82 are included in PLD of bPDPN. The purpose of this study is to determine the binding epitope of PMab-241 and to clarify the difference between these two anti-bPDPN mAbs. Analysis of bPDPN deletion mutants revealed that the N-terminus of the PMab-241 epitope exists between amino acids (aa) 75 and 80 of bPDPN. In addition, analysis of bPDPN point mutants demonstrated that the critical epitope of PMab-241 includes Thr75, Asp76, and Arg78 of bPDPN. The binding epitopes of PMab-241 and PMab-247 seem to overlap, but this slight difference may be sufficient to provide the specificity of PMab-241 to discriminate LECs from type I alveolar cells of the lung.

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.

PMab-247 Detects Bear Podoplanin in Immunohistochemical Analysis

Podoplanin (PDPN) is utilized as a specific marker of type I alveolar cells of lung and lymphatic endothelial cells of every tissue. Therefore, sensitive and specific monoclonal antibodies detecting PDPN are necessary for immunohistochemical analyses, especially using formalin-fixed paraffin-embedded tissues. Recently, we developed an anti-bear PDPN (bPDPN) mAb, PMab-247, which is useful for Western blot, flow cytometry, and immunohistochemical analyses. In this study, immunohistochemical analyses showed that PMab-247 strongly detected bPDPN, which is expressed in type I alveolar cells and lymphatic endothelial cells of bear lung and podocytes of bear kidney. These findings suggest that PMab-247 could be useful for pathophysiological analyses using immunohistochemistry.

PMab-235: A monoclonal antibody for immunohistochemical analysis against goat podoplanin

Sensitive and specific monoclonal antibodies (mAbs) against not only human but also mouse, rat, rabbit, dog, cat, bovine, pig, and horse podoplanins (PDPNs) have been established in our previous studies. However, anti-goat PDPN (gPDPN) has not been established yet. PDPN has been utilized as a lymphatic endothelial cell marker especially in pathological diagnoses; therefore, mAbs for immunohistochemical analyses using formalin-fixed paraffin-embedded tissues are needed. Although we recently demonstrated that an anti-bovine PDPN mAb, PMab-44 cross-reacted with gPDPN, PMab-44 did not detect lymphatic endothelial cells in immunohistochemistry. In this study, we immunized mice with gPDPN-overexpressing Chinese hamster ovary (CHO)–K1 (CHO/gPDPN) cells, and screened mAbs against gPDPN using flow cytometry. One of the mAbs, PMab-235 (IgG₁, kappa), specifically detected CHO/gPDPN cells by flow cytometry. Furthermore, PMab-235 strongly detected lung type I alveolar cells, renal podocytes, and lymphatic endothelial cells of colon by immunohistochemistry. These findings suggest that PMab-235 may be useful as a lymphatic endothelial cell marker for goat tissues.

Establishment of an Anticetacean Podoplanin Monoclonal Antibody PMab-237 for Immunohistochemical Analysis

Podoplanin (PDPN) has been utilized as a lymphatic endothelial cell marker especially in pathological diagnoses. Therefore, sensitive and specific monoclonal antibodies (mAbs) targeting PDPN are needed for immunohistochemical analyses using formalin-fixed paraffin-embedded tissues. Recently, anti-PDPN mAbs against many species, such as human, mouse, rat, rabbit, dog, cat, bovine, pig, and horse were established in our studies. However, anticetacean (whale) PDPN (wPDPN) has not been established yet. In this study, we immunized mice with wPDPN-overexpressing Chinese hamster ovary (CHO)-K1 (CHO/wPDPN) cells, and screened mAbs against wPDPN using flow cytometry. One of the mAbs, PMab-237 (IgG₁, kappa), specifically detected CHO/wPDPN cells by flow cytometry and immunohistochemistry. Our findings suggest the potential usefulness of PMab-237 for the functional analyses of wPDPN.

Immunohistochemical Analysis of the Harbor Porpoise Using Antipodoplanin Antibody PMab-237

Podoplanin (PDPN)/T1 alpha is known as a specific marker of lymphatic endothelial cells and type I alveolar cells. Sensitive and specific monoclonal antibodies (mAbs) for PDPN are needed for immunohistochemical analyses. Recently, we developed an anticetacean PDPN mAb, PMab-237. Herein, immunohistochemical analyses showed that PMab-237 strongly detected pulmonary type I alveolar cells, renal podocytes, and lymphatic endothelial cells of the harbor porpoise. These findings suggest that PMab-237 may be useful for immunohistochemical analyses for cetacean tissues.

Development of an anti-bear podoplanin monoclonal antibody PMab-247 for immunohistochemical analysis

Sensitive and specific monoclonal antibodies (mAbs) targeting podoplanin (PDPN) are needed for immunohistochemical analyses using formalin-fixed paraffin-embedded tissues because PDPN is known as a lymphatic endothelial cell maker in pathology. Recently, we established anti-PDPN mAbs against many species, such as human, mouse, rat, rabbit, dog, cat, bovine, pig, horse, goat, tiger, alpaca, and Tasmanian devil. However, anti-bear PDPN (bPDPN) has not been established yet. In this study, we immunized mice with bPDPN-overexpressing Chinese hamster ovary (CHO)-K1 (CHO/bPDPN) cells, and screened mAbs against bPDPN using flow cytometry. One of the mAbs, PMab-247 (IgG₁, kappa), specifically detected CHO/bPDPN cells by flow cytometry and immunohistochemistry. Our findings suggest the potential usefulness of PMab-247 for the functional analyses of bPDPN.

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

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Sensitive and specific PMab-247 mAb against bear PDPN was produced.

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PMab-247 strongly reacted with bear PDPN in flow cytometry.

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PMab-247 is useful for IHC using paraffin-embedded cell sections.