Epitope Mapping of the Anti-CD44 Monoclonal Antibody (C44Mab-46) Using Alanine-Scanning Mutagenesis and Surface Plasmon Resonance

Amber Codon Mutational Scanning and Bioorthogonal PEGylation for Epitope Mapping of Antibody Binding Sites on Human Arginase-1

Epitope mapping is crucial for understanding immunological responses to protein therapeutics. Here, we combined genetic code expansion and bacterial surface display to incorporate S-allylcysteine (SAC) into human arginase-1 (hArg1) via Methanococcoides burtonii pyrrolysyl-tRNA synthetase. Using an amber codon deep mutational scanning and sequencing workflow, we mapped SAC incorporation efficiency across the hArg1 sequence, providing insights into structural and sequence dependencies of noncanonical amino acid incorporation. We used mutually bioorthogonal allyl/tetrazine and azide/DBCO chemistries to achieve site-specific PEGylation and fluorescent labeling of hArg1, revealing insights into SAC side chain reactivity and solvent accessibility of residues in hArg1. This system was further applied to determine the binding epitope of a monoclonal antibody on the surface of hArg1, providing high-resolution data on the impact of PEGylation residue position on antibody binding. Our method produces high dimensional data of noncanonical amino acid incorporation efficiency, site-specific functionalization enabled by mutually bioorthogonal chemistries, and epitope mapping of therapeutic proteins.

Rational design of lanosterol 14α-demethylase for ergosterol biosynthesis in Saccharomyces cerevisiae

Ergosterol is widely used in skin care products and drug preparation. Lanosterol 14α-demethylase (Erg11p, 14DM, CYP51) is the rate-limiting enzyme for the biosynthesis of various steroid compounds in Saccharomyces cerevisiae. Herein, Erg11p was engineered to extend the in vivo catalytic half-life and increase the turnover rate. Single mutations resulting in lower folding energy were selected, and mutant P201H had an ergosterol yield of 576.9 mg·L-1. Through consensus design, single mutations resulting in higher sequence identity to homologs were tested and mutant K352L had an ergosterol yield of 677.9 mg·L-1. The key residues for substrate binding were confirmed via alanine scanning mutagenesis and mutant F384A had an ergosterol yield of 657.8 mg·L-1. Molecular dynamics (MD) simulation was conducted to investigate the contributions of pocket residues and eight residues were found to engage in weak interactions with lanosterol. Saturation mutagenesis was applied to these residues to enhance binding to lanosterol, and mutant F384E had an ergosterol yield of 733.8 mg·L-1. Meanwhile, MD simulations were conducted to assess the impact of mutant F384E on enzyme activity. The results consistently showed that single point mutation F384E had the greatest effect, outperforming the combination mutations. Batch fermentation increased the ergosterol yield of mutant F384E to 3067.5 mg·L-1, the highest reported to date. The successful engineering of Erg11p may pave the way for industrial-scale production of ergosterol and other steroids.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-024-04136-x.

Anti-CD44 Variant 10 Monoclonal Antibody Exerts Antitumor Activity in Mouse Xenograft Models of Oral Squamous Cell Carcinomas

CD44 regulates cell adhesion, proliferation, survival, and stemness and has been considered a tumor therapy target. CD44 possesses the shortest CD44 standard (CD44s) and a variety of CD44 variant (CD44v) isoforms. Since the expression of CD44v is restricted in epithelial cells and carcinomas compared to CD44s, CD44v has been considered a promising target for monoclonal antibody (mAb) therapy. We previously developed an anti-CD44v10 mAb, C44Mab-18 (IgM, kappa), to recognize the variant exon 10-encoded region. In the present study, a mouse IgG2a version of C44Mab-18 (C44Mab-18-mG2a) was generated to evaluate the antitumor activities against CD44-positive cells compared with the previously established anti-pan CD44 mAb, C44Mab-46-mG2a. C44Mab-18-mG2a exhibited higher reactivity compared with C44Mab-46-mG2a to CD44v3-10-overexpressed CHO-K1 (CHO/CD44v3-10) and oral squamous cell carcinoma cell lines (HSC-2 and SAS) in flow cytometry. C44Mab-18-mG2a exerted a superior antibody-dependent cellular cytotoxicity (ADCC) against CHO/CD44v3-10. In contrast, C44Mab-46-mG2a showed a superior complement-dependent cytotoxicity (CDC) against CHO/CD44v3-10. A similar tendency was observed in ADCC and CDC against HSC-2 and SAS. Furthermore, administering C44Mab-18-mG2a or C44Mab-46-mG2a significantly suppressed CHO/CD44v3-10, HSC-2, and SAS xenograft tumor growth compared with the control mouse IgG2a. These results indicate that C44Mab-18-mG2a could be a promising therapeutic regimen for CD44v10-positive tumors.

Epitope Mapping of an Anti-CD44v4 Monoclonal Antibody (C44Mab-108) Using Enzyme-Linked Immunosorbent Assay

CD44 is a type I transmembrane glycoprotein and possesses various isoforms which are largely classified into CD44 standard (CD44s) and CD44 variant (CD44v) isoforms. Some variant-encoded regions play critical roles in tumor progression. However, the function of CD44 variant 4 (CD44v4)-encoded region has not been fully understood. Using peptide immunization, we developed an anti-CD44v4 monoclonal antibody, C44Mab-108, which is useful for flow cytometry, western blotting, and immunohistochemistry. In this study, we determined the critical epitope of C44Mab-108 by enzyme-linked immunosorbent assay (ELISA). We used the alanine (or glycine)-substituted peptides of the CD44v4-encoded region (amino acids 271-290 of human CD44v3-10) and found that C44Mab-108 did not recognize the alanine-substituted peptides of D280A and W281A. Furthermore, these peptides could not inhibit the recognition of C44Mab-108 in flow cytometry and immunohistochemistry. The results indicate that the critical binding epitope of C44Mab-108 includes Asp280 and Trp281 of CD44v3-10.

Development of a Novel Anti-CD44 Variant 8 Monoclonal Antibody C44Mab-94 against Gastric Carcinomas

Gastric cancer (GC) is the third leading cause of cancer-related deaths worldwide. GC with peritoneal metastasis exhibits a poor prognosis due to the lack of effective therapy. A comprehensive analysis of malignant ascites identified the genomic alterations and significant amplifications of cancer driver genes, including CD44. CD44 and its splicing variants are overexpressed in tumors, and play crucial roles in the acquisition of invasiveness, stemness, and resistance to treatments. Therefore, the development of CD44-targeted monoclonal antibodies (mAbs) is important for GC diagnosis and therapy. In this study, we immunized mice with CD44v3-10-overexpressed PANC-1 cells and established several dozens of clones that produce anti-CD44v3-10 mAbs. One of the clones (C₄₄Mab-94; IgG₁, kappa) recognized the variant-8-encoded region and peptide, indicating that C₄₄Mab-94 is a specific mAb for CD44v8. Furthermore, C₄₄Mab-94 could recognize CHO/CD44v3-10 cells, oral squamous cell carcinoma cell line (HSC-3), or GC cell lines (MKN45 and NUGC-4) in flow cytometric analyses. C₄₄Mab-94 could detect the exogenous CD44v3-10 and endogenous CD44v8 in western blotting and stained the formalin-fixed paraffin-embedded gastric cancer cells. These results indicate that C₄₄Mab-94 is useful for detecting CD44v8 in a variety of experimental methods and is expected to become usefully applied to GC diagnosis and therapy.

Establishment of a Novel Anti-CD44 Variant 10 Monoclonal Antibody C44Mab-18 for Immunohistochemical Analysis against Oral Squamous Cell Carcinomas

Head and neck squamous cell carcinoma (HNSCC) is the most common type of head and neck cancer, and has been revealed as the second-highest expression of CD44 in cancers. CD44 has been investigated as a cancer stem cell marker of HNSCC and plays a critical role in tumor malignant progression. Especially, splicing variant isoforms of CD44 (CD44v) are overexpressed in cancers and considered a promising target for cancer diagnosis and therapy. We developed monoclonal antibodies (mAbs) against CD44 by immunizing mice with CD44v3-10-overexpressed PANC-1 cells. Among the established clones, C₄₄Mab-18 (IgM, kappa) reacted with CHO/CD44v3-10, but not with CHO/CD44s and parental CHO-K1 using flow cytometry. The epitope mapping using peptides that cover variant exon-encoded regions revealed that C₄₄Mab-18 recognized the border sequence between variant 10 and the constant exon 16-encoded sequence. These results suggest that C₄₄Mab-18 recognizes variant 10-containing CD44v, but not CD44s. Furthermore, C₄₄Mab-18 could recognize the human oral squamous cell carcinoma (OSCC) cell line, HSC-3, in flow cytometry. The apparent dissociation constant (K_D) of C₄₄Mab-18 for CHO/CD44v3-10 and HSC-3 was 1.6 × 10^-7 M and 1.7 × 10^-7 M, respectively. Furthermore, C₄₄Mab-18 detected CD44v3-10 but not CHO/CD44s in Western blotting, and endogenous CD44v10 in immunohistochemistry using OSCC tissues. These results indicate that C₄₄Mab-18 is useful for detecting CD44v10 in flow cytometry and immunohistochemistry.

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 KD 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 (KD) 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 a Sensitive Anti-Human CCR9 Monoclonal Antibody (C9Mab-11) by N-Terminal Peptide Immunization

The C-C chemokine receptor 9 (CCR9) belongs to the G-protein-coupled receptor superfamily, and is highly expressed on the T cells and intestinal cells. CCR9 regulates various immune responses by binding to the C-C chemokine ligand, CCL25, and is involved in inflammatory diseases and tumors. Therefore, the development of sensitive monoclonal antibodies (mAbs) for CCR9 is necessary for treatment and diagnosis. In this study, we established a specific anti-human CCR9 (hCCR9) mAb; C₉Mab-11 (mouse IgG_2a, kappa), using the synthetic peptide immunization method. C₉Mab-11 reacted with hCCR9-overexpressed Chinese hamster ovary-K1 (CHO/hCCR9) and hCCR9-endogenously expressed MOLT-4 (human T-lymphoblastic leukemia) cells in flow cytometry. The dissociation constant (K_D) of C₉Mab-11 for CHO/hCCR9 and MOLT-4 cells were determined to be 1.2 × 10^-9 M and 4.9 × 10^-10 M, respectively, indicating that C₉Mab-11 possesses a high affinity for both exogenously and endogenously hCCR9-expressing cells. Furthermore, C₉Mab-11 clearly detected hCCR9 protein in CHO/hCCR9 cells using western blot analysis. In summary, C₉Mab-11 can be a useful tool for analyzing hCCR9-related biological responses.

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.

Identification of the Binding Epitope of an Anti-mouse CCR4 Monoclonal Antibody, C4Mab-1

C-C chemokine receptor 4 (CCR4) is one of G protein-coupled receptors, and interacts with chemokines, CCL17 and CCL22. CCR4 is expressed on T cells such as helper T type 2 cells, regulatory T cells, and interleukin 17-producing T helper cells. CCR4 is associated with T cells trafficking into the tumor microenvironment, and is associated with tumor progression or metastasis. Therefore, CCR4 may be a potential therapeutic option for T cell malignancies. C₄Mab-1 is a novel anti-mouse CCR4 (mCCR4) monoclonal antibody produced by mCCR4 N-terminal peptide immunization. C₄Mab-1 is useful for flow cytometric analysis. In this study, we conducted the epitope mapping of C₄Mab-1 using enzyme-linked immunosorbent assay (ELISA) and peptide blocking assay. The result of ELISA indicated that Thr7, Asp8, and Gln11 of mCCR4 are the critical amino acids for the C₄Mab-1 binding. Furthermore, peptide blocking assay by flow cytometry showed that Thr7, Asp8, and Gln11 of mCCR4 are essential for C₄Mab-1 binding to mCCR4-overexpressed Chinese hamster ovary-K1 (CHO/mCCR4) cells, and Val6, Thr9, and Thr10 are involved in the C₄Mab-1 binding to CHO/mCCR4 cells. These results indicate that the critical binding epitope of C₄Mab-1 includes Thr7, Asp8, and Gln11 of mCCR4.

Epitope Mapping of the Anti-Human CCR2 Monoclonal Antibody C2Mab-9

CC chemokine receptor type-2 (CCR2) belongs to the G protein-coupled receptors superfamily, localized on cell surface of some immune-related cells, including monocytes and macrophages. CCR2 and its ligand CCL2 are involved in the progression of various diseases such as cancers. Therefore, CCR2-targeted monoclonal antibodies (mAbs) are needed for treatment and diagnosis. Previously, we successfully developed an anti-human CCR2 (hCCR2) mAb, C₂Mab-9 (mouse IgG₁, kappa), which is applicable for flow cytometry and immunocytochemistry. In this study, we investigated the critical epitope of C₂Mab-9. We conducted enzyme-linked immunosorbent assay (ELISA) using several N-terminal peptides of hCCR2, and demonstrated that C₂Mab-9 recognizes 11-29 and 21-39 amino acids of hCCR2. We further performed ELISA using 20 peptides, which include alanine substitution of hCCR2. C₂Mab-9 lost the reaction to the alanine-substituted peptides of F23A, F24A, D25A, Y26A, and D27A. Among them, F23A, F24A, D25A, and Y26A did not block the C₂Mab-9 reaction with U937 cells in flow cytometry. These results indicate that the critical binding epitope of C₂Mab-9 includes Phe23, Phe24, Asp25, and Tyr26.

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 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.