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-K1 (CHO) 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 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 KD 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.

CD44 has been known as a marker of tumor initiating cells, and plays pro-tumorigenic functions in many cancers. The splicing variants play critical roles in malignant progression of cancers by promoting the stemness, cancer cell invasion or metastasis, and resistance to chemo- and radiotherapy. To understand each CD44 variant (CD44v) function is essential to know the property of cancers and establishment of the therapy. However, the function of the variant 4-encoded region has not to be elucidated. Therefore, specific monoclonal antibodies (mAbs) against the variant 4 are indispensable for basic research, tumor diagnosis, and therapy. In this study, we established anti-CD44 variant 4 (CD44v4) monoclonal antibodies (mAbs) by immunizing mice with a peptide containing the variant 4-encoded region. We next performed flow cytometry, western blotting, and immunohistochemistry to characterized them. One of the established clones (C₄₄Mab-108; IgG₁, kappa) reacted with CD44v3-10-overexpressed Chinese hamster ovary-K1 cells (CHO/CD44v3-10). The K_D of C₄₄Mab-108 for CHO/CD44 v3-10 was 3.4 × 10⁻⁷ M. In western blot analysis, C₄₄Mab-108 detected CD44v3-10 in the lysate of CHO/CD44v3-10 cells. Furthermore, C₄₄Mab-108 stained formalin-fixed paraffin-embedded oral squamous carcinoma tissues in immunohistochemistry. These results indicated that C₄₄Mab-108 is useful to detect CD44v4 in various applications.

C-C chemokine receptor 9 (CCR9) is a receptor for C-C-chemokine ligand 25 (CCL25). CCR9 is crucial in the chemotaxis of immune cells and inflammatory responses. Moreover, CCR9 is highly expressed in tumors including several solid tumors and T-cell acute lymphoblastic leukemia. Several preclinical studies have shown that anti-CCR9 monoclonal antibodies (mAbs) exert antitumor activity. Therefore, CCR9 is an attractive target for tumor therapy. In this study, we conducted the epitope mapping of an anti-mouse CCR9 (mCCR9) mAb, C9Mab-24 (rat IgG2a, kappa), using a 1 × alanine (1 × Ala) and 2 × alanine (2 × Ala)-substitution method via enzyme-linked immunosorbent assay. We first performed the 1 × Ala-substitution method using one alanine-substituted peptides of the mCCR9 N-terminus (amino acids 1-19). C9Mab-24 did not recognize two peptides (F14A and F17A), indicating that Phe14 and Phe17 are critical for C9Mab-24-binding to mCCR9. Furthermore, we conducted the 2 × Ala-substitution method using two consecutive alanine-substituted peptides of the mCCR9 N-terminus, and showed that C9Mab-24 did not react with four peptides (M13A–F14A, F14A–D15A, D16A–F17A, and F17A–S18A), indicating that 13-MFDDFS-18 is involved in C9Mab-24-binding to mCCR9. Overall, combining, the 1 × Ala or 2 × Ala scanning methods could be useful for understanding for target-antibody interaction.

CD44 is a cell surface glycoprotein, which is widely expressed on normal and 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 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 CD44s-overexpressed Chinese hamster ovary-K1 cells (CHO/CD44s) or esophageal squamous cell carcinoma (ESCC) cell lines (KYSE70 and KYSE770). The KD 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 CD44v of KYSE770 in western blot analysis. Furthermore, C44Mab-46 strongly stained esophageal squamous carcinoma cells in immunohistochemistry using formalin-fixed paraffin-embedded ESCC tissues. Taken together, C44Mab-46 is very useful for detecting CD44 in various applications.

The epithelial cell adhesion molecule (EpCAM) is a cell surface glycoprotein, which is widely expressed on normal and cancer cells. EpCAM is involved in cell adhesion, proliferation, survival, stemness, and tumorigenesis. Therefore, EpCAM is thought to be a promising target for cancer diagnosis and therapy. In this study, we established anti-EpCAM monoclonal antibodies (mAbs) using the Cell-Based Immunization and Screening (CBIS) method. We characterized them using flow cytometry, western blotting, and immunohistochemistry. One of the established recombinant anti-EpCAM mAbs, recEpMab-37 (mouse IgG1, kappa), reacted with EpCAM-overexpressed Chinese hamster ovary-K1 cells (CHO/EpCAM) or a colorectal carcinoma cell line (Caco-2). In contrast, recEpMab-37 did not react with EpCAM-knocked out Caco-2 cells. The KD of recEpMab-37 for CHO/EpCAM and Caco-2 was 2.0 × 10-8 M and 3.2 × 10-8 M, respectively. In western blot analysis, recEpMab-37 detected EpCAM of CHO/EpCAM and Caco-2 cells. Furthermore, recEpMab-37 could stain formalin-fixed paraffin-embedded colorectal carcinoma tissues by immunohistochemistry. Taken together, recEpMab-37, established by CBIS method, is useful for detecting EpCAM in various applications.

The CC chemokine receptor 3 (CCR3) is a receptor for CC chemokines, including CCL5/RANTES, CCL7/MCP-3, and CCL11/eotaxin. CCR3 is expressed on the surface of eosinophils, basophils, a subset of Th2 lymphocytes, mast cells, and airway epithelial cells. CCR3 and its ligands are involved in airway hyperresponsiveness in allergic asthma, ocular allergy, and cancers. Therefore, CCR3 is an attractive target for those therapies. Previously, anti-mouse CCR3 (mCCR3) monoclonal antibodies (mAbs), C3Mab-3 (rat IgG2a, kappa), and C3Mab-4 (rat IgG2a, kappa) were developed using the Cell-Based Immunization and Screening (CBIS) method. In this study, the binding epitope of these mAbs was investigated using flow cytometry. The CCR3 extracellular domain-substituted mutant analysis showed that C3Mab-3, C3Mab-4, and a commercially available mAb (J073E5) recognized the N-terminal region (amino acids 1–38) of mCCR3. Next, the alanine scanning was conducted in the N-terminal region. The results revealed that Ala2, Phe3, Asn4, and Thr5 of mCCR3 are involved in C3Mab-3 binding, whereas Ala2, Phe3, and Thr5 are essential to C3Mab-4 binding, and Ala2 and Phe3 are crucial to J073E5 binding. These results reveal the involvement of the N-terminus of mCCR3 in the recognition of C3Mab-3, C3Mab-4, and J073E5.

The epithelial cell adhesion molecule (EpCAM) is a stem cell and carcinoma antigen, which mediates cellular adhesion and proliferative signaling by the proteolytic cleavage. In contrast to low expression in normal epithelium, EpCAM is frequently overexpressed in various carcinomas, which correlates with poor prognosis. Therefore, EpCAM has been considered as a promising target for tumor diagnosis and therapy. Using the Cell-Based Immunization and Screening (CBIS) method, we previously established an anti‐EpCAM monoclonal antibody (EpMab-37; mouse IgG1, kappa). In this study, we investigated the antibody‐dependent cellular cytotoxicity (ADCC), complement‐dependent cytotoxicity (CDC), and an antitumor activity by a defucosylated mouse IgG2a-type of EpMab-37 (EpMab-37-mG2a-f) against an EpCAM‐expressing breast cancer cell line (BT-474). EpMab-37-mG2a-f recognized BT-474 cells with a moderate binding-affinity [a dissociation constant (KD): 2.9x10-8 M] by flow cytometry. EpMab-37-mG2a-f exhibited ADCC and CDC for BT-474 cells by murine splenocytes and complements, respectively. Furthermore, administration of EpMab-37-mG2a-f significantly suppressed the BT-474 xenograft tumor development compared with the control mouse IgG. These results indicated that EpMab-37-mG2a-f exerts antitumor activities against the BT-474 xenograft, and could provide valuable therapeutic regimen for the breast cancers.

The overexpression of epidermal growth factor receptors (EGFRs) has been reported in various human tumors, including breast, gastric, lung, colorectal, and pancreatic cancers. Humanized anti‐EGFR and human epidermal growth factor receptor 2 (HER2) monoclonal antibodies (mAbs) have been shown to improve patients’ survival. Canine tumors resemble human tumors in the initiation and progression. We previously established a defucosylated mouse-dog chimeric anti‐EGFR mAb (E134Bf) and a mouse-dog chimeric anti‐HER2 mAb (H77Bf), which exerted antitumor activities in canine tumor xenograft models. Here, we produced E134Bf antibody fused to H77Bf single chain Fv at the light chains (E134Bf-H77scFv). The bispecific E134Bf-H77scFv recognized dog EGFR (dEGFR) and dog HER2 (dHER2)-overexpressed Chinese hamster ovary-K1 cells by flow cytometry. E134Bf-H77scFv also reacted with dEGFR and dHER2‐positive canine osteosarcoma D-17 cells, and possesses a high binding-affinity (KD: 1.3x10-9 M). Furthermore, E134Bf-H77scFv exerted antibody‐dependent cellular cytotoxicity and complement‐dependent cytotoxicity against D-17 cells in the presence of canine mononuclear cells and complement, respectively. Moreover, administration of E134Bf-H77scFv suppressed the development of D-17 xenograft tumor in mice early compared with the control dog IgG, E134Bf and H77Bf alone. These results indicate that E134Bf-H77scFv exerts antitumor activities against dEGFR/dHER2-positive canine tumors, and could be a valuable treatment regimen for canine tumors.

CD39 is involved in adenosine metabolism through conversion of extracellular ATP to adenosine. Because extracellular adenosine plays a critical role in the immune suppression of tumor microenvironment, the inhibition of CD39 activity by monoclonal antibodies (mAbs) is one of the important strategies for tumor therapy. In this study, we developed specific and sensitive mAbs for mouse CD39 (mCD39) using the Cell-Based Immunization and Screening (CBIS) method. The established anti-mCD39 mAbs, which were established by the CBIS method including C₃₉Mab-1 (rat IgG_2a, kappa) and C₃₉Mab-2 (rat IgG_2a, lambda), reacted with not only mCD39-overexpressed Chinese hamster ovary-K1 (CHO/mCD39) but also endogenously mCD39-expressed cell lines, such as L1210 (mouse lymphocytic leukemia) and J774-1 (mouse macrophage-like) cell lines through flow cytometry. Kinetic analyses using flow cytometry indicated that the dissociation constant (K_D) of C₃₉Mab-1 and C₃₉Mab-2 for CHO/mCD39 was 7.3 × 10⁻⁹ M and 5.5 × 10⁻⁹ M, respectively. K_D of C₃₉Mab-1 and C₃₉Mab-2 for L1210 was 3.3 × 10⁻⁹ M and 3.6 × 10⁻¹⁰ M, respectively. Furthermore, C₃₉Mab-1 could detect the lysate of CHO/mCD39 by western blot analysis. These results indicate that C₃₉Mab-1 and C₃₉Mab-2 are useful for the detection of mCD39 in many functional studies.