Development of an Anti-EphB4 Monoclonal Antibody for Multiple Applications Against Breast Cancers

The erythropoietin-producing hepatocellular carcinoma (Eph) receptors are the largest receptor tyrosine kinase family. EphB4 is essential for cell adhesion and motility during embryogenesis. Pathologically, EphB4 is overexpressed and contributes to poor prognosis in various tumors. Therefore, specific monoclonal antibodies (mAbs) should be developed to predict the prognosis for multiple tumors with high EphB4 expression, including breast and gastric cancers. This study aimed to develop specific anti-EphB4 mAbs for multiple applications using the Cell-Based Immunization and Screening method. EphB4-overexpressed Chinese hamster ovary (CHO)-K1 (CHO/EphB4) cells were immunized into mice, and we established an anti-EphB4 mAb (clone B4Mab-7), which is applicable for flow cytometry, Western blot, and immunohistochemistry (IHC). B4Mab-7 reacted with endogenous EphB4-positive breast cancer cell line, MCF-7, but did not react with EphB4-knockout MCF-7 (BINDS-52) in flow cytometry. Dissociation constant (KD) values were determined to be 2.9 × 10-9 M and 1.3 × 10-9 M by flow cytometric analysis for CHO/EphB4 and MCF-7 cells, respectively. B4Mab-7 detected the EphB4 protein bands from breast cancer cells in Western blot, and stained breast cancer tissues in IHC. Altogether, B4Mab-7 is very useful for detecting EphB4 in various applications.

Defucosylated Monoclonal Antibody (H2Mab-139-mG2a-f) Exerted Antitumor Activities in Mouse Xenograft Models of Breast Cancers against Human Epidermal Growth Factor Receptor 2

The clinically approved human epidermal growth factor receptor 2 (HER2)-targeting monoclonal antibodies (mAbs), trastuzumab, and pertuzumab, target domains IV and II, respectively. Trastuzumab is now the standard treatment for HER2-overexpressed breast and gastric cancers, and trastuzumab in combination with pertuzumab showed clinical benefit. However, there still exist patients who do not respond to the therapy. Furthermore, HER2 mutants that cannot be recognized by pertuzumab were found in tumors. Therefore, novel anti-HER2 mAbs and modalities have been desired. In our previous study, we developed a novel anti-HER2 domain I mAb, H2Mab-139 (mouse IgG1, kappa). We herein produced a defucosylated mouse IgG2a type of mAb against HER2 (H2Mab-139-mG2a-f) to enhance antibody-dependent cellular cytotoxicity (ADCC)-mediated antitumor activity. H2Mab-139-mG2a-f exhibits a high binding affinity in flow cytometry with the dissociation constant (KD) determined to be 3.9 × 10-9 M and 7.7 × 10-9 M against HER2-overexpressed Chinese hamster ovary (CHO)-K1 (CHO/HER2) and HER2-positive BT-474 cells, respectively. Moreover, we showed that H2Mab-139-mG2a-f exerted ADCC and complement-dependent cytotoxicity against CHO/HER2 and BT-474 in vitro and exhibited potent antitumor activities in mouse xenograft models. These results indicated that H2Mab-139-mG2a-f exerts antitumor effects against HER2-positive human breast cancers and is useful as an antibody treatment for HER2-positive human cancers.

Epitope Mapping of Anti-Mouse CCR3 Monoclonal Antibodies (C3Mab-6 and C3Mab-7)

One of G protein-coupled receptors, CC chemokine receptor 3 (CCR3), is expressed in eosinophils, basophils, a subset of Th2 lymphocytes, mast cells, and airway epithelial cells. CCR3 levels in the serum of colorectal cancer patients are significantly higher than in control groups. Moreover, CCR3 is essential for recruiting eosinophils into the lung. Therefore, CCR3 is considered both a therapeutic target for colorectal cancer and allergic diseases. Previously, we established anti-mouse CCR3 (mCCR3) monoclonal antibodies (mAbs), C₃Mab-6 (rat IgG₁, kappa) and C₃Mab-7 (rat IgG₁, kappa), by immunizing a rat with an N-terminal peptide of mCCR3. These mAbs can be used in flow cytometry and enzyme-linked immunosorbent assays. In this study, we performed the epitope mapping of C₃Mab-6 and C₃Mab-7 using alanine scanning. The reactivity between these mAbs and point mutants of mCCR3 were analyzed using flow cytometry. The results indicated that Phe3, Asn4, Thr5, Asp6, Glu7, Lys9, Thr10, and Glu13 of mCCR3 are essential for C₃Mab-6 binding, whereas Phe15 and Glu16 are essential for C₃Mab-7 binding.

Defucosylated Mouse-Dog Chimeric Anti-Human Epidermal Growth Factor Receptor 2 Monoclonal Antibody (H77Bf) Exerts Antitumor Activities in Mouse Xenograft Models of Canine Osteosarcoma

Human epidermal growth factor receptor 2 (HER2) has been studied in many human cancer types, and its overexpression and/or gene mutation contribute to the poor prognosis. Therefore, HER2 is an important therapeutic target in various cancer types, including breast and gastric cancers. We previously developed an anti-HER2 monoclonal antibody (mAb), H₂Mab-77 (mouse IgG₁, kappa), which detects HER2 and dog HER2 (dHER2) with high sensitivity and specificity. In this study, we produced a defucosylated mouse-dog chimeric anti-HER2 mAb (H77Bf), and investigated the reactivity against canine osteosarcoma D-17 cells by flow cytometry. Furthermore, we showed that H77Bf exerted antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity against D-17 cells in vitro and exhibited the potent antitumor activity in vivo. These results suggest that H77Bf exerts antitumor effects against dHER2-expressing canine tumors and could be valuable as part of an antibody treatment regimen for them.

Development of a Novel Anti-Mouse CCR6 Monoclonal Antibody (C6Mab-13) by N-Terminal Peptide Immunization

The CC chemokine receptor 6 (CCR6) is a G protein-coupled receptor family member that is highly expressed in B lymphocytes, certain subsets of effector and memory T cells, and immature dendritic cells. CCR6 has only one chemokine ligand, CCL20. The CCL20-CCR6 axis has been recognized as a therapeutic target for autoimmune diseases and tumor. This study developed specific monoclonal antibodies (mAbs) against mouse CCR6 (mCCR6) using the peptide immunization method. The established anti-mCCR6 mAb, C₆Mab-13 (rat IgG₁, kappa), reacted with mCCR6-overexpressed Chinese hamster ovary-K1 (CHO/mCCR6), and mCCR6-endogenously expressed P388 (mouse lymphoid neoplasma) and J774-1 (mouse macrophage-like) cells in flow cytometry. The dissociation constant (K_D) of C₆Mab-13 for CHO/mCCR6 cells was determined to be 2.8 × 10^-9 M, indicating that C₆Mab-13 binds to mCCR6 with high affinity. In summary, C₆Mab-13 is useful for detecting mCCR6-expressing cells through flow cytometry.

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.

Epitope Mapping of an Anti-Mouse CCR2 Monoclonal Antibody (C2Mab-6) Using Enzyme-Linked Immunosorbent Assay

CC chemokine receptor type-2 (CCR2) is a member of the G protein-coupled receptors, and is mainly expressed on cell surface of immune cells. CCR2 binds to its ligand, C-C motif chemokine 2 (also named as monocyte chemoattractant protein-1), which involves in the tumor progression by modulating the tumor microenvironment. Therefore, the monoclonal antibody (mAb) targeting CCR2 could be one of the strategies for cancer treatment. In this study, we investigated the critical epitope of C₂Mab-6, an anti-mouse CCR2 (mCCR2) mAb developed by N-terminal peptides immunization. We first performed enzyme-linked immunosorbent assay (ELISA) using N-terminal peptides of mCCR2 and demonstrated that C₂Mab-6 recognizes 1-19 amino acids of mCCR2. We further performed ELISA using 20 alanine-substituted peptides of mCCR2. C₂Mab-6 lost the reaction to the alanine-substituted peptides of D3A, N4A, M6A, P8A, Q9A, and F10A. These results indicate that the binding epitope of C₂Mab-6 includes Asp3, Asn4, Met6, Pro8, Gln9, and Phe10 of mCCR2.

C3Mab-3: A Monoclonal Antibody for Mouse CC Chemokine Receptor 3 for Flow Cytometry

CC chemokine receptor 3 (CCR3) belongs to the G protein-coupled receptor family and is highly expressed in eosinophils and basophils. CCR3 is essential for recruiting eosinophils into the lung. Moreover, CCR3 was found in the serum of colorectal cancer patients higher than in the control group. Therefore, CCR3 will be a useful target for asthma and colorectal cancer diagnosis. This study developed a specific and sensitive monoclonal antibody (mAb) for mouse CCR3 (mCCR3), which is useful for flow cytometry using the Cell-Based Immunization and Screening method. The established anti-mCCR3 mAb, C₃Mab-3 (rat IgG_2a, kappa), reacted with mCCR3-overexpressed Chinese hamster ovary-K1 (CHO/mCCR3) cells through flow cytometry. C₃Mab-3 also reacted with P388 (mouse lymphoid neoplasma) and J774-1 (mouse macrophage-like) cells, which express mCCR3 endogenously. Kinetic analyses using flow cytometry indicated that K_Ds of C₃Mab-3 for CHO/mCCR3, P388, and J774-1 cells were 4.3 × 10^-8 M, 2.6 × 10^-7 M, and 2.4 × 10^-7 M, respectively. C₃Mab-3 could be a valuable tool for elucidating mCCR3-related biological response using flow cytometry.

C8Mab-2: An Anti-Mouse C-C Motif Chemokine Receptor 8 Monoclonal Antibody for Immunocytochemistry

C-C motif chemokine receptor 8 (CCR8) is a G protein-coupled receptor predominantly expressed in regulatory T (Treg) and T helper 2 cells. The evidence that CCR8 expression in Treg is increased in cancers, CCR8 increases migration activity of Treg, and CCR8 induces the anti-apoptotic activity in T cell leukemia and lymphoma suggests that CCR8 is associated with cancer development. Thus, developing a specific monoclonal antibody (mAb) for CCR8 is useful for diagnostic and therapeutic purposes and the anti-CCR8 mAb becomes a remarkable experimental tool for basic research. We previously developed an anti-mouse CCR8 (mCCR8) mAb called C₈Mab-2 (rat IgG_2b, kappa) that was applicable to flow cytometric analysis for both endogenous and exogenous mCCR8. This study showed that C₈Mab-2 and recombinant C₈Mab-2 (recC₈Mab-2) were specifically bound to exogenously expressed mCCR8 in mCCR8-overexpressed Chinese hamster ovary-K1 cells. In addition, we found that C₈Mab-2 and recC₈Mab-2 recognized endogenous mCCR8 in P388 (a mouse lymphocyte-like cell line) and J774-1 cells (a mouse macrophage-like cell line). These data demonstrate that C₈Mab-2 and recC₈Mab-2 are useful for immunocytochemical analysis.

Defucosylated Anti-Epidermal Growth Factor Receptor Monoclonal Antibody (134-mG2a-f) Exerts Antitumor Activities in Mouse Xenograft Models of Canine Osteosarcoma

The epidermal growth factor receptor (EGFR) is a transmembrane glycoprotein. Although EGFR is physiologically essential in normal cells, it contributes to tumor malignancy through gene amplification and/or protein overexpression, which augment signaling cascades in tumor cells. We previously developed an anti-human EGFR (hEGFR) monoclonal antibody (mAb), EMab-134 (mouse IgG₁, kappa), which detects hEGFR and dog EGFR (dEGFR) with high sensitivity and specificity. The mouse IgG_2a version of EMab-134 (134-mG_2a) has antitumor effects toward mouse xenografts of hEGFR-expressing oral squamous cell carcinomas. Furthermore, 134-mG_2a-f, the defucosylated version of 134-mG_2a, exhibits antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) in dEGFR-overexpressed CHO-K1 (CHO/dEGFR) cells and antitumor activities in mouse xenografts of CHO/dEGFR cells. Herein, the reactivity of 134-mG_2a-f against canine cancer cells with endogenous dEGFR was first examined by flow cytometry and immunocytochemistry. In vitro analysis demonstrated that 134-mG_2a-f highly exerted ADCC and CDC for a canine osteosarcoma cell line, D-17, which expresses endogenous dEGFR. Moreover, in vivo administration of 134-mG_2a-f significantly suppressed the development of D-17 compared with the results in response to control mouse IgG. These results suggest that 134-mG_2a-f exerts antitumor effects against dEGFR-expressing canine cancers, and could be valuable as part of an antibody treatment regimen for them.

Epitope Mapping of an Anti-Human Epidermal Growth Factor Receptor Monoclonal Antibody (EMab-51) Using the RIEDL Insertion for Epitope Mapping Method

The classic method for identifying the epitope that monoclonal antibodies (mAbs) bind uses deletion mutants and point mutants of the target protein. However, determining the epitope of mAbs-reactive membrane proteins is often challenging. We recently developed the RIEDL insertion for epitope mapping (REMAP) method to identify mAb-binding epitopes. Herein, we first checked the reactivity of an anti-epidermal growth factor receptor (EGFR) mAb (EMab-51) to several EGFR deletion mutants such as EGFR/dN152, EGFR/dN313, EGFR/dN370, EGFR/dN375, EGFR/dN380, and EGFR/dN482. We found the N-terminus of the EMab-51-binding epitope between residues 375 and 380 of EGFR. We next produced EGFR/dN313 mutants with the RIEDL peptide tag inserted at each possible position of ₃₇₅-AFRGDSFTHTPPLDP-₃₈₉. EMab-51 lost its reactivity with the mutants having a RIEDL tag inserted at each position of ₃₇₇-RGDSFTHTPP-₃₈₆, whereas LpMab-7 (an anti-RIEDL mAb) detected every mutant. Thus, using the REMAP method, we identified the EMab-51-binding epitope of EGFR as ₃₇₇-RGDSFTHTPP-₃₈₆.

Defucosylated Anti-Epidermal Growth Factor Receptor Monoclonal Antibody 134-mG2a-f Exerts Antitumor Activities in Mouse Xenograft Models of Dog Epidermal Growth Factor Receptor-Overexpressed Cells

The epidermal growth factor receptor (EGFR) is a type I transmembrane protein, which is a member of the human epidermal growth factor receptor (HER) family of receptor tyrosine kinases. EGFR is a crucial mediator of cell growth and differentiation and forms homodimers or heterodimers with other HER family members to activate downstream signaling cascades. We previously established an anti-human EGFR (hEGFR) monoclonal antibody (mAb), clone EMab-134 (mouse IgG₁), by immunizing mice with the ectodomain of hEGFR. In this study, the subclass of EMab-134 was converted from IgG₁ to IgG_2a (134-mG_2a) and further defucosylated (134-mG_2a-f) to facilitate antibody-dependent cellular cytotoxicity (ADCC). Although 134-mG_2a-f was developed against hEGFR, it was shown to cross-react with dog EGFR (dEGFR) using flow cytometry. The dissociation constant (K_D) of 134-mG_2a-f against dEGFR-overexpressed CHO-K1 (CHO/dEGFR) cells was determined by flow cytometry to be 3.3 × 10^-9 M, indicating that 134-mG_2a-f possesses a high binding affinity to dEGFR. Analysis in vitro revealed that 134-mG_2a-f contributed to high levels of ADCC and complement-dependent cytotoxicity (CDC) in experiments targeting CHO/dEGFR cells. Furthermore, the in vivo administration of 134-mG_2a-f significantly inhibited the development of CHO/dEGFR in comparison with the results observed in response to control mouse IgG. Taken together, the findings of this study demonstrate that 134-mG_2a-f could be useful as part of a therapeutic regimen for dEGFR-expressing canine cancers.

An Anti-HER2 Monoclonal Antibody H2Mab-41 Exerts Antitumor Activities in Mouse Xenograft Model Using Dog HER2-Overexpressed Cells

Overexpression of human epidermal growth factor receptor 2 (HER2) has been reported in a variety of cancer types, including breast, lung, gastric, pancreatic, and colorectal cancers. Trastuzumab, a humanized anti-HER2 monoclonal antibody (mAb), has been shown to provide significant survival benefits in HER2-overexpressing breast cancer and gastric cancer patients. Previously, an anti-HER2 mAb, H₂Mab-41 (IgG_2b, kappa), was developed in our laboratory and its antitumor activity was demonstrated in mouse xenograft models of human colon cancer. The present study aimed to investigate the ability of H₂Mab-41 to induce antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) in dog HER2 (dHER2)-overexpressed cell lines, and thus exert its antitumor activity against dHER2-overexpressed tumors in vivo. Flow cytometry results demonstrated the cross-reactivity of H₂Mab-41 with dHER2. Further evaluation of interaction between H₂Mab-41 and dHER2-overexpressed CHO-K1 (CHO/dHER2) cells indicated moderate binding affinity of H₂Mab-41 toward dHER2, with a dissociation constant (K_D) of 2.6 × 10^-8 M. In vitro analysis revealed that the administration of H₂Mab-41 induced high levels of ADCC and CDC in CHO/dHER2 cells. Furthermore, intraperitoneal administration of H₂Mab-41 in mouse xenograft models of CHO/dHER2 resulted in significant inhibition of tumor development compared to the control mouse IgG. Thus, the findings of the present study demonstrated the in vivo safety and efficacy of H₂Mab-41, highlighting its suitability to be included as a part of a therapeutic regimen for dHER2-expressing canine cancers.

Development of a Novel Anti-HER2 Monoclonal Antibody H2Mab-181 for Gastric Cancer

Human epidermal growth factor receptor 2 (HER2) is a type I transmembrane 185 kDa protein. HER2 is expressed in a variety of normal tissue types and cancer cells. HER2 is associated with cell proliferation, differentiation, and migration. The overexpression of HER2 has been observed in a number of cancers, including breast and gastric cancers. Gastric cancer is one of the most common cancers worldwide, with an annual case rate of ∼1 million people diagnosed with the disease. Trastuzumab is a humanized anti-HER2 monoclonal antibody (mAb) that has been utilized in gastric cancer therapy. In this study, we have developed a novel anti-HER2 mAb, H₂Mab-181 (IgG₁, kappa), through the immunization of mice with a purified recombinant extracellular domain of HER2. H₂Mab-181 can specifically and sensitively detect HER2 in both flow cytometry and Western blot applications in gastric cancer cell lines and can also be utilized in immunohistochemical analyses of gastric cancer tissues. Together, H₂Mab-181 could be useful for the diagnosis and therapy in gastric cancers.

Epitope Mapping of the Anti-California Sea Lion Podoplanin Monoclonal Antibody PMab-269 Using Alanine-Scanning Mutagenesis and ELISA

Podoplanin (PDPN) plays a pivotal role in platelet aggregation, embryo development, and tumor progression. PDPN is universally expressed in many mammalian species, and is considered a typical lymphatic endothelial cell marker. We have previously developed the mouse anti-California sea lion (Zalophus californianus) PDPN (seaPDPN) monoclonal antibody (mAb), clone PMab-269, which is suitable for different experimental applications, including flow cytometry, Western blotting, and immunohistochemistry. In this study, we identified the PMab-269 epitope of the seaPDPN by enzyme-linked immunosorbent assay using deletion mutants and point mutants generated for seaPDPN. Our results demonstrated that PMab-269 recognized the peptide, corresponding to the amino acids 63-82 of seaPDPN. Furthermore, the reactions of PMab-269 to seven alanine-substituted peptides, such as P68A, D76A, F77A, H78A, L79A, E80A, and D81A, were abolished among 20 alanine-substituted peptides. We identified the seven amino acids (Pro68, Asp76, Phe77, His78, Leu79, Glu80, and Asp81) as the critical epitope targeted by PMab-269. The successful identification of the PMab-269 epitope might contribute to the pathophysiological investigations of seaPDPN.

Anti‑HER3 monoclonal antibody exerts antitumor activity in a mouse model of colorectal adenocarcinoma

HER3 belongs to the epidermal growth factor receptor (EGFR) family and is known to form an active heterodimer with other three family members EGFR, HER2, and HER4. HER3 is overexpressed in lung, breast, colon, prostate, and gastric cancers. In the present study, we developed and validated an anti-HER3 monoclonal antibody (mAb), H₃Mab-17 (IgG_2a, kappa), by immunizing mice with HER3-overexpressed CHO-K1 cells (CHO/HER3). H₃Mab-17 was found to react specifically with endogenous HER3 in colorectal carcinoma cell lines, using flow cytometry. The K_D for H₃Mab-17 in CHO/HER3 and Caco-2 (a colon cancer cell line) were determined to be 3.0×10⁻⁹ M and 1.5×10⁻⁹ M via flow cytometry, respectively, suggesting high binding affinity of H₃Mab-17 to HER3. Then, we assessed the H₃Mab-17 antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) against Caco-2, and evaluated its antitumor capacity in a Caco-2 ×enograft model. In vitro experiments revealed H₃Mab-17 had strongly induced both ADCC and CDC against Caco-2 cells. In vivo experiments on Caco-2 ×enografts revealed that H₃Mab-17 treatment significantly reduced tumor growth compared with the control mouse IgG. These data indicated that H₃Mab-17 could be a promising treatment option for HER3-expressing colon cancers.

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 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.

An anti‑TROP2 monoclonal antibody TrMab‑6 exerts antitumor activity in breast cancer mouse xenograft models

Trophoblast cell surface antigen 2 (TROP2), reported to be overexpressed in several types of cancer, is involved in cell proliferation, invasion, metastasis, and poor prognosis of many types of cancer. Previously, a highly sensitive anti-TROP2 monoclonal antibody (clone TrMab-6; mouse IgG_2b, κ) was developed using a Cell-Based Immunization and Screening (CBIS) method. TrMab-6 was useful for investigations using flow cytometry, western blot, and immunohistochemistry. The aim of the present study was to investigate whether TrMab-6 possesses in vitro antibody-dependent cellular cytotoxicity (ADCC) or complement-dependent cytotoxicity (CDC) activities or in vivo antitumor activities using mouse xenograft models of TROP2-overexpressed CHO-K1 (CHO/TROP2) and breast cancer cell lines, including MCF7, MDA-MB-231, and MDA-MB-468. In vitro experiments revealed that TrMab-6 strongly induced ADCC and CDC activities against CHO/TROP2 and the three breast cancer cell lines, whereas it did not show those activities against parental CHO-K1 and MCF7/TROP2-knockout cells. Furthermore, in vivo experiments on CHO/TROP2 and MCF7 ×enografts revealed that TrMab-6 significantly reduced tumor growth, whereas it did not show antitumor activities against parental CHO-K1 and MCF7/TROP2-knockout xenografts. The findings suggest that TrMab-6 is a promising treatment option for TROP2-expressing breast cancers.

Development of Anti-Mouse CC Chemokine Receptor 3 Monoclonal Antibodies for Flow Cytometry

CC chemokine receptor 3 (CCR3), also known as CD193, belongs to class A of G protein-coupled receptors and is present in high levels in eosinophils, basophils, and airway epithelial cells. CCR3 is considered the therapeutic target for human immunodeficiency virus (HIV) infections and allergic diseases; therefore, the development of sensitive monoclonal antibodies (mAbs) for CCR3 has been desired. This study aimed to establish a specific and sensitive mAb against mouse CCR3 (mCCR3) useful for flow cytometry analysis by employing the Cell-Based Immunization and Screening (CBIS) method. The generated anti-mCCR3 mAb, C₃Mab-2 (rat IgG_2b, kappa), was found to react with mCCR3-overexpressed Chinese hamster ovary-K1 (CHO/mCCR3) cells, according to flow cytometric analysis. Also, it reacted with P388 (mouse lymphoid neoplasm) or J774-1 (mouse macrophage-like) cells, which express endogenous mCCR3. Taken together, C₃Mab-2, generated by the CBIS method, can be a valuable tool for detecting mCCR3 on the surface of mouse cells.

Development of Antihuman Killer Cell Lectin-Like Receptor Subfamily G Member 1 Monoclonal Antibodies for Flow Cytometry

Killer cell lectin-like receptor subfamily G member 1 (KLRG1), a type II transmembrane protein, was identified as an inhibitory receptor expressed on natural killer (NK) cells and certain T cells. The protein regulates effector functions and developmental processes in these cells. In this study, we established a specific and sensitive monoclonal antibody (mAb) for human KLRG1 (hKLRG1), which is useful for flow cytometry, using a Cell-Based Immunization and Screening (CBIS) method. The established anti-hKLRG1 mAb, KLMab-1 (mouse IgG₁, kappa), reacted with overexpressed hKLRG1 in Chinese hamster ovary-K1 (CHO/hKLRG1) and human NK cells, which also expressed endogenous hKLRG1 as confirmed by flow cytometry. KLMab-1, which was established by the CBIS method, could be useful for elucidating the hKLRG1-related biological response by flow cytometry.

Development of Anti-human T Cell Immunoreceptor with Ig and ITIM Domains (TIGIT) Monoclonal Antibodies for Flow Cytometry

Immune checkpoint inhibitors targeting programmed cell death-ligand 1 (PD-L1), programmed cell death-1 (PD-1), and cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) recently made a significant survival rate improvement in cancer treatment. T cell immunoreceptor with Ig and ITIM domains (TIGIT) is expressed in T and NK cells related to their activities. It has a single extracellular immunoglobulin domain, a type 1 transmembrane domain, and a single intracellular ITIM. TIGIT binds with poliovirus receptor (PVR) or PVR2, resulting in suppressing T and NK cell activities. Some studies showed that the combined use of a TIGIT inhibitor with another immune checkpoint inhibitor enhanced antitumor activities more strongly than their single use. Therefore, TIGIT should be a new target for immunotherapy. In this study, we developed new anti-human TIGIT (hTIGIT) monoclonal antibodies (mAbs) using the Cell-Based Immunization and Screening (CBIS) method. Mice were immunized with hTIGIT-overexpressed Chinese hamster ovary (CHO)-K1 cells (CHO/hTIGIT), and hybridomas were screened by flow cytometry. One of the mAbs, TgMab-2 (IgG₁, kappa), specifically and sensitively detects hTIGIT in CHO/hTIGIT and NK cells. The dissociation constants (K_D) of TgMab-2 for CHO/hTIGIT cells were determined to be 3.5 × 10^-9 M. These results suggest that TgMab-2, which was developed by CBIS method, is useful for analyzing the function of hTIGIT by flow cytometry.

Development of Anti-Mouse CC Chemokine Receptor 8 Monoclonal Antibodies for Flow Cytometry

CC chemokine receptor 8 (CCR8) belongs to the class A of G protein-coupled receptor. It is highly expressed on Treg and T helper 2 (T_H2) cells recruited to the inflammation site and is implicated in allergy and asthma. Recently, CCR8+Treg cells have been suggested to be a master regulator in the immunosuppressive tumor microenvironment; therefore, developing sensitive monoclonal antibodies (mAbs) for CCR8 has been desired. This study established a specific and sensitive mAb for mouse CCR8 (mCCR8), which is useful for flow cytometry by using the Cell-Based Immunization and Screening (CBIS) method. The established anti-mCCR8 mAb, C₈Mab-2 (rat IgG_2b, kappa), reacted with mCCR8-overexpressed Chinese hamster ovary-K1 (CHO/mCCR8) cells and P388 (mouse lymphoid neoplasma) or J774-1 (mouse macrophage-like) cells, which express endogenous mCCR8 by flow cytometry. C₈Mab-2, which was established by the CBIS method, could be useful for elucidating the mCCR8-related biological response by flow cytometry.

11β hydroxysteroid dehydrogenase 1: a new marker for predicting response to immune-checkpoint blockade therapy in non-small-cell lung carcinoma

Background

Understanding the status of intratumoural immune microenvironment is necessary to ensure the efficacy of immune-checkpoint (IC) blockade therapy. Cortisol plays pivotal roles in glucocorticoid interactions in the immune system. We examined the correlation between intratumourally synthesised cortisol through 11β hydroxysteroid dehydrogenase (HSD) 1 and the immune microenvironment in non-small-cell lung carcinoma (NSCLC).

Methods

We correlated 11βHSD1 immunoreactivity in 125 cases of NSCLC with the amount of intratumoural immune cells present, and 11βHSD1 immunoreactivity with the efficacy of IC blockade therapy in 18 specimens of NSCLC patients. In vitro studies were performed to validate the immunohistochemical examination.

Results

11βHSD1 immunoreactivity showed a significant inverse correlation with the number of tumour-infiltrating lymphocytes and CD3- or CD8-positive T cells. 11βHSD1 immunoreactivity tended to be inversely correlated with the clinical efficacy of the IC blockade therapy. In vitro studies revealed that 11βHSD1 promoted the intratumoural synthesis of cortisol. This resulted in a decrease in cytokines and in the inhibition of monocyte migration.

Conclusions

Our study is the first report clarifying the inhibitory effects of intratumourally synthesised cortisol through 11βHSD1 on immune cell migration. We propose that the response to IC blockade therapy in NSCLC may be predicted by 11βHSD1.

The correlation of p22phox and chemosensitivity in EGFR-TKI resistant lung adenocarcinoma

Background

Enhancing the chemosensitivity in the patients with epidermal growth factor receptor-tyrosine kinase inhibitor (EGFR-TKI) resistant lung adenocarcinoma (LUAD) is pivotal in achieving their successful therapeutic outcome. We aimed to explore the mechanisms regarding the development of therapeutic resistance to chemotherapy in EGFR-TKI resistant LUAD. Methods: Microarray analysis lead to potential involvement of p22^phox, which was abundantly expressed in the cell lines harboring EGFR-TKI resistance and chemoresistance, and was known to regulate several important chemoresistance-associated factors such as hypoxia inducible factor-1α (HIF-1α) and epithelial-mesenchymal transition (EMT). We compared the status of p22^phox with that of chemoresistance, HIF-1α expression and EMT in LUAD cell lines. We immunolocalized p22^phox in the specimens of lung cancer patients.

Results

p22^phox and HIF-1α mRNAs were significantly elevated in the cells harboring EMT and chemoresistance. p22^phox knockdown enhanced chemosensitivity and reduced the expression of HIF-1α and EMT-associated factors. HIF-1α knockdown enhanced the chemosensitivity, while HIF-1α transfection induced EMT and chemoresistance in these cell lines. All LUAD patients with T790M mutation were associated with abundant p22^phox immunoreactivity in carcinoma cells.

Conclusions

The analysis of p22^phox in lung carcinoma tissues could provide new insights into the selection of chemotherapy for the patients with EGFR-TKI resistant LUAD.