Patent Publication Number: US-2023138047-A1

Title: Anti-claudin-1 monoclonal antibodies for the prevention and treatment of fibrotic diseases

Description:
RELATED PATENT APPLICATION 
     The present application claims priority to European Patent Application number EP 19 208 560.3, which was filed on Nov. 12, 2019. The European patent application is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     Fibrotic disease is characterized by excessive deposition of fibrous connective tissue (a process called fibrosis) that can lead to progressive deterioration in the normal structure and function of organs and tissues of the body. Fibrosis is defined by the overgrowth, hardening and/or scarring of a tissue or organ. It is attributed to excessive accumulation of components of the extracellular matrix (ECM), such as collagen and fibronectin (Wynn et al., Nature Medicine, 2012, 18: 1028-1040), in and around inflamed or damaged tissue, which can lead to permanent scarring, organ malfunction and ultimately death. Fibrosis is the final, common pathological outcome of many chronic inflammatory reactions induced by a variety of stimuli including persistent infections, genetic disorders, autoimmune reactions, allergic response, chemical insults, radiations, and tissue injury. Fibrosis can occur in nearly every organ or tissue of the body, more often in the heart, lung, kidney, liver and skin (Rockey et al., N. Engl. J. Med., 2015, 372: 1138-1149) and less frequently in other tissues or organs such as the pancreas, intestine, eye (Wynn, J. Pathol., 2008, 214: 199-210), nerve system (Kawano et al., Cell Tissue Res., 2012, 349: 169-180), mediastinum (Parish and Rosenow, Semin. Respir. Crit. Care Med., 2002, 23: 135-143), retroperitoneum (Caiafa et al., Radiographics, 2013, 33: 535-552), joint and tendon. 
     Human fibrotic diseases have a poor prognosis comparable with end-stage cancer. They represent an increasing cause of morbidity and mortality worldwide. Since fibrosis is a predominant feature of the pathology of a wide range of diseases across multiple organ systems, fibrotic disorders have been estimated to contribute to about 45% of all-cause mortality in the United States (Wynn, Nature Rev. Immunol., 2004, 4: 583-594). The major health problem associated with fibrotic diseases is also due to our incomplete understanding of the underlying pathogenesis, the marked heterogeneity in the etiologies and clinical manifestations of fibrotic disorders, the absence of appropriate and fully validated biomarkers, and most importantly, the current void of effective disease-modifying therapeutic agents. Indeed, at present, there are only two recently approved drugs specifically indicated for the treatment of fibrotic disease. 
     In light of the economic burden of patients with fibrotic disease worldwide, and in view of the limited therapeutic arsenal, novel strategies to prevent and/or treat fibrosis are urgently needed. 
     SUMMARY OF THE INVENTION 
     The present invention relates to systems and strategies for the prevention and/or treatment of fibrotic diseases, in particular renal fibrosis, pulmonary fibrosis and skin fibrosis. In particular, the present invention is directed to the use of anti-Claudin-1 antibodies for preventing and/or treating renal fibrosis, pulmonary fibrosis or skin fibrosis. Indeed, the present Inventors have shown that, in vivo, an anti-Claudin-1 monoclonal antibody specifically binds its target in the lungs, the kidneys and the skin, without any detectable toxicity. Furthermore, using a state-of-the-art mouse model considered as the most important preclinical model of pulmonary fibrosis, they demonstrated that the anti-Claudin-1 monoclonal antibody prevents the formation of lung fibrosis without affecting overall survival or body weight and reduces fibrosis levels in lungs without detectable adverse effects. They have also shown that the anti-Claudin-1 monoclonal antibody binds to Claudin-1 expressed on kidney and lung cancer cells, and reverses fibrosis-related poor-prognosis of a clinical gene-signature in lung cells. In addition, the present Inventors have shown that Claudin-1 expression in lung and kidney fibrosis is associated with disease. Thus, Claudin-1 gene expression is increased in different cohorts of patients with renal fibrosis, pulmonary fibrosis and inflammatory bowel disease. The anti-Claudin-1 monoclonal antibody was found to have a marked and highly significant anti-fibrotic effect on kidney fibrosis in a unilateral ureteral obstruction (UUO) mice model. The anti-Claudin-1 mAb was also found to improve serum creatinine and BUN in an Adriamycin-induced mouse model of renal fibrosis. Moreover, the present Inventors found accumulating evidence indicating different mechanisms involved in the anti-fibrotic effects of the anti-Claudin-1 monoclonal antibody in kidney and lung compared to liver. 
     Consequently, in one aspect, the present invention provides an anti-Claudin-1 antibody, or a biologically active fragment thereof, for use in the prevention or treatment of a fibrotic disease selected from the group consisting of pulmonary fibrosis, renal fibrosis, and skin fibrosis. 
     In certain embodiments, the pulmonary fibrosis represents the end-stage of a chronic lung disease selected from the group consisting of idiopathic pulmonary fibrosis (IPF), idiopathic nonspecific interstitial pneumonitis (NSIP), cryptogenic organizing pneumonia (COP), Hamman-Rich syndrome, lymphocytic interstitial pneumonitis (LIP), respiratory bronchiolitis interstitial lung disease, desquamative interstitial pneumonitis or idiopathic lymphoid interstitial pneumonia, and idiopathic pleuroparenchymal fibroelastosis. 
     In certain embodiments, the pulmonary fibrosis is due to infection such as COVID19-associated infection. 
     In certain embodiments, the pulmonary fibrosis is associated with chronic obstructive pulmonary disease. 
     In certain embodiments, the fibrotic disease is pulmonary fibrosis and the anti-Claudin-1 antibody, or the biologically active fragment thereof, is administered in combination with at least one therapeutic agent selected from the group consisting of corticosteroids, anti-fibrotic agents, pirfenidone, nintedanib, and anti-acid drugs, and/or with a therapeutic procedure selected from the group consisting of lung transplantation, hyperbaric oxygen therapy and pulmonary rehabilitation. 
     In other embodiments, the renal fibrosis is renal interstitial fibrosis or glomerulosclerosis. 
     In certain embodiments, the renal fibrosis is associated with chronic kidney disease. 
     In certain embodiments, the fibrotic disease is renal fibrosis and the anti-Claudin-1 antibody, or the biologically active fragment thereof, is administered in combination with at least one therapeutic agent selected from the group consisting of anti-hypertensive drugs, 1,25-dihydroxyvitamin D3, erythropoietin, angiotensin converting enzyme inhibitors, angiotensin II receptor antagonists AST-120, and calcium polystyrene sulfonate, and/or with one therapeutic procedure selected from the group consisting of dialysis and kidney transplantation. 
     In certain embodiments, the skin fibrosis is associated with a medical condition selected from the group consisting of scleroderma in both localized (morphea, linear scleroderma) and systemic forms, graft-versus-host disease (GVHD), nephrogenic fibrosing dermopathy, mixed connective tissue disease, scleredoma, scleromyxedema, eosinophilic fasciitis, chromoblastomycosis, hypertrophic scars and keloids. In certain embodiments, the skin fibrosis is induced by a medical intervention (e.g., radiotherapy), by environmental or professional exposures to chemicals (e.g., in eosinophilia-myalgia syndrome induced by L-tryptophan); and exposure to certain physical agents (physical trauma, surgical injury, heat or ice skin burns). 
     In certain embodiments, the fibrotic disease is skin fibrosis and the anti-Claudin-1 antibody, or the biologically active fragment thereof, is administered in combination with at least one therapeutic agent selected from the group consisting methotrexate, mycophenolate, mofetil, cyclophosphamide, cyclosporine, tocilizumab, rituximab, and fresolimumab and/or with one therapeutic procedure (e.g., ultraviolet radiation). 
     In certain embodiments, the anti-Claudin-1 antibody used in the prevention or treatment of pulmonary fibrosis, renal fibrosis or skin fibrosis is a monoclonal antibody. 
     In certain embodiments, the anti-Claudin-1 monoclonal antibody has the same epitope as a monoclonal antibody secreted by a hybridoma cell line deposited at the DSMZ on Jul. 29, 2008 under an Accession Number selected from the group consisting of DSM ACC2931, DSM ACC2932, DSM ACC2933, DSM ACC2934, DSM ACC2935, DSM ACC29316, DSM ACC2937, and DSM ACC2938. 
     In certain embodiments, the epitope is strongly dependent on the conservation of the conserved motif W(30)-GLW(51)-C(54)-C(64) in Claudin-1 first extracellular loop. 
     In other embodiments, the anti-Claudin-1 antibody is a monoclonal antibody secreted by a hybridoma cell line deposited at the DSMZ on Jul. 29, 2008 under an Accession Number selected from the group consisting of DSM ACC2931, DSM ACC2932, DSM ACC2933, DSM ACC2934, DSM ACC2935, DSM ACC2936, DSM ACC2937, and DSM ACC2938. 
     In other embodiments, the anti-Claudin-1 antibody is a monoclonal antibody comprising the six complementary determining regions (CDRs) of a monoclonal antibody secreted by a hybridoma cell line deposited at the DSMZ on Jul. 29, 2008 under an Accession Number selected from the group consisting of DSM ACC2931, DSM ACC2932, DSM ACC2933, DSM ACC2934, DSM ACC2935, DSM ACC2936, DSM ACC2937, and DSM ACC2938 In certain embodiments, the anti-Claudin-1 antibody used in the prevention or treatment of pulmonary fibrosis, renal fibrosis or dermal fibrosis is humanized. 
     The humanized anti-Claudin-1 antibody may be a monoclonal antibody comprising all of the six CDRs of monoclonal antibody OM-7D3-B3 secreted by hybridoma cell line deposited under Accession Number DSM ACC2938, wherein the variable heavy chain of OM-7D3-B3 consists of amino acid sequence SEQ ID NO: 1 and the variable light chain of OM-7D3-B3 consists of amino acid sequence SEQ ID NO: 2, said humanized anti-Claudin-1 monoclonal antibody further comprising: 
     a) at least one antibody variable heavy chain (VH) consisting of the amino acid sequence of SEQ ID NO: 3 or SEQ ID NO: 4 or SEQ ID NO: 5, or 
     b) at least one antibody variable light chain (VL) consisting of the amino acid sequence of SEQ ID NO: 6 or SEQ ID NO: 7 or SEQ ID NO: 8. 
     For example, the humanized anti-Claudin-1 monoclonal antibody may comprise: 
     a) two antibody variable heavy chains (VH), both variable heavy chains consisting of the amino acid sequence of SEQ ID NO: 3 or SEQ ID NO: 4 or SEQ ID NO: 5, or 
     b) two antibody variable light chains (VL), both variable light chains consisting of the amino acid sequence of SEQ ID NO: 6 or SEQ ID NO: 7 or SEQ ID NO: 8. 
     For example, the humanized anti-Claudin-1 monoclonal antibody may comprise: 
     1) two antibody variable heavy chains (VH) consisting of the amino acid sequence SEQ ID NO: 3, and two antibody variable light chains (VL) consisting of the amino acid sequence SEQ ID NO: 6 [H3L3]; or 
     2) two antibody variable heavy chains (VH) consisting of the amino acid sequence SEQ ID NO: 3, and two antibody variable light chains (VL) consisting of the amino acid sequence SEQ ID NO: 7 [H3L1]; or 
     3) two antibody variable heavy chains (VH) consisting of the amino acid sequence SEQ ID NO: 3, and two antibody variable light chains (VL) consisting of the amino acid sequence SEQ ID NO: 8 [H3L2]; or 
     4) two antibody variable heavy chains (VH) consisting of the amino acid sequence SEQ ID NO: 4, and two antibody variable light chains (VL) consisting of the amino acid sequence SEQ ID NO: 6 [H1L3]; or 
     5) two antibody variable heavy chains (VH) consisting of the amino acid sequence SEQ ID NO: 4, and two antibody variable light chains (VL) consisting of the amino acid sequence SEQ ID NO: 7 [H1L1]; or 
     6) two antibody variable heavy chains (VH) consisting of the amino acid sequence SEQ ID NO: 4, and two antibody variable light chains (VL) consisting of the amino acid sequence SEQ ID NO: 8 [H1L2]; or 
     7) two antibody variable heavy chains (VH) consisting of the amino acid sequence SEQ ID NO: 5, and two antibody variable light chains (VL) consisting of the amino acid sequence SEQ ID NO: 6 [H2L3]; or 
     8) two antibody variable heavy chains (VH) consisting of the amino acid sequence SEQ ID NO: 5, and two antibody variable light chains (VL) consisting of the amino acid sequence SEQ ID NO: 7 [H2L1]; or 
     9) two antibody variable heavy chains (VH) consisting of the amino acid sequence SEQ ID NO: 5, and two antibody variable light chains (VL) consisting of the amino acid sequence SEQ ID NO: 8 [H2L2]. 
     In certain embodiments, the humanized anti-Claudin-1 monoclonal antibody is a full antibody having an isotype selected from the group consisting of IgG1, IgG2, IgG3, and IgG4. In certain embodiments, these isotypes may be engineered to afford additional properties, for example to attenuate or enhance Fc-receptor mediated interactions, or to attenuate or enhance half-life and distribution properties of the antibody. 
     The present invention also provides a pharmaceutical composition comprising an effective amount of an anti-Claudin-1 antibody, or a biologically active fragment thereof, and at least one pharmaceutically acceptable carrier or excipient, for use in the prevention or treatment of a fibrotic disease selected from pulmonary fibrosis, renal fibrosis, and skin fibrosis in a subject. 
     In such a use of pharmaceutical composition, the pulmonary fibrosis, the renal fibrosis and the skin fibrosis may be as defined above; and the anti-Claudin-1 antibody, or biologically active fragment thereof, may be as defined above. 
     The present invention further provides a method for preventing or treating a pulmonary fibrosis or renal fibrosis or skin fibrosis in a subject, the method comprising administering to the subject a therapeutically efficient amount of an anti-Claudin-1 antibody, or a biologically active fragment thereof. In such a method of prevention and/or treatment, the pulmonary fibrosis, the renal fibrosis, and the dermal fibrosis may be as defined above; and the anti-Claudin-1 antibody, or biologically active fragment thereof, may be as defined above. 
     These and other objects, advantages and features of the present invention will become apparent to those of ordinary skill in the art having read the following detailed description of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG.  1   . Biodistribution of Anti-CLDN1 mAb in Mice. Mice (n=6 per group/time point) were injected with 500 μg of Alexa fluor 750-control mAbs (grey bars) or CLDN1-specific mAbs (blue bars) and sacrificed at (A) 24 hours or (B) 48 hours following injection. The specific fluorescence was detected in each indicated organ using an IVIS Lumina 50 device with specific filter sets and expressed as average efficiency. The horizontal line indicates the mean. The results show the mean±s.e.m. from 6 mice. *p&lt;0.05, ** p&lt;0.01 (Mann-Whitney test). 
         FIG.  2   . Anti-CLDN1 mAb significantly Reduces Lung Fibrosis in a State-of-the-art Mouse Model for Prevention and Early Treatment of Pulmonary Fibrosis. (A) Prevention and early treatment study design. Six-weeks old female C57BL/6J mice underwent intratracheal bleomycin nebulization (3 mg/kg) to induce pulmonary fibrosis and were randomized to receive vehicle, CLDN1-specific mAb and dexamethasone (positive control) for 21 days. Each group included 18 mice. (B) The Ashcroft fibrosis score was significantly reduced in the CLDN1 mAb group compared to the Vehicle group. Data are represented as mean (triangle), median (line), 1 th  and 3 rd  quartile (bottom and top of the box). (C) Trichromic masson staining of one representative mouse lung per treatment group. (D) Kaplan-Meier curves showing that the Dexamethasone treated mice had significant lower survival compared to the Vehicle group. (E) In the Dexamethasone group, a significant reduction of mouse body weight was observed during the experiment. * p&lt;0.05, ** p&lt;0.01, *** p&lt;0.001, N.S.=not significant. 
         FIG.  3   . Anti-CLDN1 mAb Reduces Lung Fibrosis in a State-of-the-art Mouse Model for Late Treatment of Pulmonary Fibrosis. (A) Late treatment study design. Six-weeks old female C57BL/6J mice underwent intratracheal bleomycin nebulization (3 mg/kg) to induce pulmonary fibrosis and were randomized to receive vehicle, anti-human CLDN1-specific mAb or Nintedanib (positive control) from day 7 to day 21. Each group included 18 mice. (B) The lung hydroxyproline levels was significantly reduced in the CLDN1 mAb group. Body weight was not different between the two treatment groups. Data are represented as mean (triangle), median (line), 1 st  and 3 rd  quartile (bottom and top of the box). (C) Trichromic masson staining of one representative mouse lung per treatment group. (D) Kaplan-Meier curves showing no difference between the groups. (E) No significant reduction of mouse body weight was observed during the experiment in all the groups. * p&lt;0.05, N.S.=not significant. 
         FIG.  4   . Binding Properties of Humanized CLDN1-specific MAbs Targeting CLDN1 Expressed on Kidney RPTEC/TERT1 and Lung A549 Cell Lines. Cells were incubated with increasing concentrations of humanized H3L3 CLDN1-specific mAb, as indicated. Representative histograms show binding of humanized H3L3 CLDN1-specific mAb at the saturation point for each specific cells line: (A) RPTEC/TERT1 (50 μg/mL) and (B) A549 (20 μg/mL). Binding was measured by flow cytometry after incubation with PE-labelled anti-human and analyzed with Cytoflex and FlowJo V10. The binding constants K d  of the interaction between the humanized H3L3 CLDN1-specific mAb and CLDN1 expressed by (C) RPTEC/TERT1 (50 μg/mL) and (D) A549 (20 μg/mL) cells were determined by applying the Michaelis-Menten mathematical model in R 3.5.1 using the PE median fluorescence intensity (MFI), respectively. The graphs show binding of humanized H3L3 CLDN1-specific mAb until the saturation point for each specific cell line. 
         FIG.  5   . CLDN1-specific MAbs Reverses PLS and Reduces TGF-β Signaling in A549 Cells. (A) A549 cells were cultured for 24 hours with or without TGF-β (5 ng/mL) and CLDN1 mAb (20 μg/mL) treatment for 24 hours. RNA was extracted and PLS gene expression was measuring using nCounter Nanostring technology and was assessed quantitatively by Gene Set Enrichment Analysis (GSEA). The heatmaps show: PLS status as poor (orange) or good (green) prognosis; (bottom) the significance of induction (red) or suppression (blue) of PLS poor- or good-prognosis genes. (B) Relative gene expression values showing the mean and standard error of mean of two poor-prognosis, differentially expressed genes (SERPINB2 and FMO1) modulated by CLDN1-specific mAb treatment (n=3, fold change −1.7, ****p-value &lt;0.0001). NT: No treatment. (C) 4549 cells were transfected with TGF-β signaling reporter plasmid pGL4.48[luc2P/SBE/Hygro](Promega) and treated with control or CLDN1-specific mAb (50 μg/mL) for 3 hours at 37° C. Cells were stimulated with medium containing TGF-β (10 ng/mL) for 3 hours at 37° C. Fold changes showing the mean and standard error of mean were calculated from luminescence intensities normalized to the mock samples (n=6, CLND1 mAb n=5, **** p-value &lt;0.0001, ** p-value &lt;0.01). 
         FIG.  6   . Bleomycin-induced Skin Fibrosis Model. An area of 1.5×1.5 cm of the mouse skin was shaved and bleomycin (BLM) 1.0 mg/kg was administered at the four corners s.c. alternate days for 4 weeks. The mouse was sacrificed and the skin area was sampled for collagen assay, histological and biochemical analysis. 
         FIG.  7   . Study Design to Test New Treatments for Skin Fibrosis. The study includes normal mice, bleomycin (BLM)+vehicle i.p., BLM+imatinib i.p. (50 mg/kg) as a positive control group and a BLM+anti-CLDN1-specific mAb. Clinical data, biochemistry and histopathological assays are performed and collected. 
         FIG.  8   . Dermal Thickness and Skin Fibrosis Quantification. Hematoxylin and eosin (HE) and Masson Thricromic (MT) are used to quantified dermal thickness and skin fibrosis, respectively. Imatinib showed a significant effect in reducing dermal thickness and a trend in reduction of skin fibrosis. 
         FIG.  9   : CLDN1 is Overexpressed in Fibrotic Kidney and Lung Diseases. (A) CLDN1 gene expression in renal tissues of patients with membranous Glomerulonephritis (MG) (Left panel, GSE11585) and fibrotic kidney tissue (Right panel, GSE60685) compared to healthy kidney is shown as signal intensity values. (B) CLDN1 Expression is Associated with Fibrotic Chronic Kidney Disease. CLDN1 expression in renal tissues of patient cohorts (GSE115857 n=6 healthy tissue and n=11 Membranous Glomerulonephritis (MG)), Focal Segmental Glomerulosclerosis (FSGS) (GSE129973 unaffected sections n=20 and FSGS sections n=20). CLDN1 mRNA expression was analyzed as described in the Materials and Methods of Example 8 and is shown as signal intensity values. (C) Left panel: CLDN1 gene expression in pulmonary tissues of patient with IPF and pulmonary fibrosis of different etiologies compared to healthy lung tissue (GSE2052 and GSE24988, respectively) is shown as signal intensity values. The differences in the scale are due to the different types of arrays and normalization methods and do not reflect absolute expression levels. Students&#39; t-test, **p&lt;0.01, ***p&lt;0.001, ****p&lt;0.0001. 
         FIG.  10   . The anti-CLDN1 mAb Targets TNFα-NFκB-Controlled CLDN1 Expression and Suppresses Lung fibroblast Activation by Interfering with EMT Programing. (A-B) Representative images of CLDN1 expression and binding of the humanized anti-CLDN1 mAb on α-SMA expressing lung fibroblasts (A) and kidney fibroblasts (B) are shown. Specificity of the staining was confirmed by absent binding of control mAb. (C) Kidney fibroblasts (left panel) and lung fibroblasts (right panel) were treated with TNFα (20 ng/ml), IKK-16 (1 μM), TNFα+IKK16 or vehicle control (Mock) and subjected to fluorocytometric analysis of binding of the anti-CLDN1 mAb H3L3, respectively. ΔMFI of the anti-CLDN1 mAb binding to lung or kidney fibroblasts compared to control mAb is shown for each condition (pooled analyses of three experiments performed in triplicate for each condition as described in the Materials and Methods Section of Example 6). (D) Modulation of genes related to lung fibroblast activation (left panel) and EMT programing (HALLMARK_EPITHELIAL_MESENCHYMAL_TRANSITION) (right panel) in lung fibroblasts derived from IPF patients by the anti-CLDN1 mAb compared to the Control mAb is shown. Heatmaps indicate significance (FDR) of reversal. (E) RNA-Seq gene expression data of EMT markers FN1 (left panel), N-Cadherin (Middle panel) and SNAI2 (right panel) in anti-CLDN1 mAb- or Control mAb-treated lung fibroblasts are shown as read counts. Boxplot represents median (▬), 1 st  and 3 rd  quartile (bottom and top of the box) and single data points (0). Student&#39;s t-test. * p-value &lt;0.05, *** p-value &lt;0.001, **** p-value &lt;0.0001. 
         FIG.  11   : Location of PECs in the Bowman&#39;s capsule. The Bowman&#39;s capsule is lined by Parietal Epithelial Cells (PECs) (in green). At the vascular pole, the PECs are in direct continuity with podocytes in blue (visceral podocytes). PECs showing a different phenotype or marker expression profile and increased migration or proliferation in different disease states are aPECs (in red). Proximal tubule epithelial cells are shown in yellow. Abbreviations: PEC, parietal epithelial cell; aPEC, activated PEC. Figure adapted from Shankland et al., Curr. Opin. Nephrol. Hypertens., 2013, 22: 302-309). 
         FIG.  12   : Increase of CLDN1 Expression Upon Inflammatory Stress is Associated with PECs Differentiation. (A-B) Inflammatory stress induces PECs differentiation and CLDN1 overexpression. Human Renal Epithelial Cells (HREpic) were treated with TNFα for a total of 6 days. Gene expression was analyzed by qRT-PCR. Graphs show mean+sd from two independent experiments performed in triplicate (* p&lt;0.05; ** p&lt;0.01; *** p&lt;0.001, T test). (C) Western blot analysis of CLDN1 protein expression after TNFα treatment. One representative experiment out of two is shown. (D) Representative histogram showing the binding of humanized H3L3 CLDN1-specific mAb on HREPic. The binding was assessed by flow cytometry 24 hours after TNFα treatment. (E) CLDN1 knock-down decreases TNFα and collagen 4A (COL4A) expression. CLDN1 knock-down. HREpic cells were reverse transduced by specific siRNA targeting CLDN1 expression (siCLDN1) or non-targeting siRNA (siCTRL) and treated with TNFα 48 h post-transfection. Gene expression was analyzed by qRT-PCR. Graphs show mean+sd from one experiment performed in triplicate (* p&lt;0.05; ** p&lt;0.01; *** p&lt;0.001, T test). 
         FIG.  13   : Treatment with CLDN1-specific mAb Decreases PECs Activation and Proliferation. (A) Experimental procedure (see Example 7). Human Renal Epithelial Cells (HREpic) were grown in 3D and treated with TNFα and Motavizumab (CTRL) or H3L3 (anti-CL DN1 mAb) for a total of 6 days. (B) Cell proliferation/viability was assessed by ATP quantification. Experiment was performed in quadruplicates. One experiment is shown. (C) CLDN1-specific mAb decreases TNFα expression and PECs activation. HREpic cells were treated with CLDN1-specific mAb (H3L3) or control antibody (Motavizumab) for a total of 6 days. Gene expression was analyzed by qRT-PCR. Graphs show mean+sd from one experiment performed in triplicate (* p&lt;0.05; ** p&lt;0.01; *** p&lt;0.001, T test). 
         FIG.  14   : (A) CLDN1 Expression is Associated with Pulmonary Fibrosis. CLDN1 expression in pulmonary tissues of patient cohorts (GSE2052 n=11 healthy tissue and n=13 IPF tissue), pulmonary fibrosis (GSE24988 healthy tissue n=11 and fibrotic tissue n=129). CLDN1 mRNA expression was analyzed as described in the Materials and Methods of Example 8 and is shown as signal intensity values. (B) CLDN1 Expression is Associated with COVID-19 Lung Disease. CLDN1 expression in pulmonary tissues of control healthy patients (GSE2052 healthy tissue n=11) and COVID-19 patient cohorts (GSE150316 n=15). CLDN1 mRNA expression was analyzed as described in the Materials and Methods of Example 8 and is shown as signal intensity values. 
         FIG.  15   : CLDN1 Expression is Associated with Ulcerative Colitis. CLDN1 expression in IBD tissues of patient cohorts. GSE9452 (Non-inflamed mucosa n=18, inflamed mucosa n=8); GSE38713 (Control n=13, Remission UC n=8, Non-mucosal UC n=7, mucosal n=15) and GSE38713 (Control n=8, CD n=11, UC n=5). CLDN1 mRNA expression was analyzed as described in the Materials and Methods of Example 8 and is shown as signal intensity values. UC: ulcerative colitis, CD: Crohn&#39;s disease. 
         FIG.  16   : CLDN1 Expression is Associated with Fibrotic Chronic Kidney Disease in the Unilateral Ureteral Obstruction (UUO) Model. CLDN1 expression in renal fibrosis mouse model (UUO) (GSE60685 healthy tissue n=12 and fibrotic tissue n=13). CLDN1 mRNA expression was analyzed as described in the Materials and Methods of Example 8 and is shown as signal intensity values. 
         FIG.  17   : Effects of anti-CLDN1 mAb on Fibrogenesis in UUO Mouse Model of Kidney Fibrosis. Study protocol: Seven-week-old female C57BL/6J mice were subjected to UUO surgery under anesthesia on Day 0. Humanized anti-CLDN1 mAb (500 μg/mouse i.p. twice weekly, n=8), Telmisartan (30 mg/kg p.o once daily, n=8) or vehicle Control (n=8) were administered from Day 0 to Day 13. 
         FIG.  18   : Body weight changes of Unilateral Ureteral Obstruction (UUO) mice (a model for unilateral ureteral obstruction-induced renal interstitial fibrosis) submitted to a 13 day-treatment with a vehicle, the anti-CLDN1 mAb, or Temisartan (used as control). See Example 9. 
         FIG.  19   : (A) Body weight at the time of sacrifice, (B) right kidney weight and (C) left kidney weight of UUO mice having received a vehicle, the anti-CLDN1 mAb, or Temisartan (used as control). See Example 9. 
         FIG.  20   : Biochemistry. (A) Plasma urea nitrogen and (B) kidney hydroxyproline of UUO mice having received a vehicle, the anti-CLDN1 mAb, or Temisartan (used as control). See Example 9. 
         FIG.  21   : Histological Analyses. Representative photomicrographs of PAS-stained kidney sections from UUO mice having received a vehicle, the anti-CLDN1 mAb, or Temisartan (used as control). See Example 9. 
         FIG.  22   : Sirius Red-Stained Kidney. Representative photomicrographs of Sirius red-stained kidney sections and graph showing the fibrosis areas for kidney sections from UUO mice having received a vehicle, the anti-CLDN1 mAb, or Temisartan (used as control). See Example 9. 
         FIG.  23   : F4/80-Immunostained Kidney. Representative photomicrographs of F4/80-immunostained-stained kidney sections from UUO mice having received a vehicle, the anti-CLDN1 mAb, or Temisartan (used as control). See Example 9. 
         FIG.  24   : Human Tissue Staining Reveals Target Engagement in Human Kidneys: Frozen sections of healthy human kidneys were stained with (A) an anti-CLDN1 mAb or (B) an isotype control to demonstrate target engagement. Distinct staining was observed at the Bowman&#39;s membrane and podocytes (arrows). 
         FIG.  25   : Histological Assessment of Different Forms of Human Kidney Fibrosis Pathologies. Formaline-fixed tissue sections were stained with anti-CLDN 1 poly antibody and compared with normal, healthy kidney. Abbreviations: ANCA (anti-neutrophil cytoplasmic antibody-associated vasculitis), FSGS (focal segmented glomerulosclerosis), CS (corticosteroid) and CyA (cyclosporin A). 
         FIG.  26   : Serum Creatinine and BUN Data (unit mg/dl) from an Adriamycin-Induced Kidney Fibrosis Model (performed at SMC lab). Eight adriamycin-induced nephropathic male BALB/c mice per group were intraperitoneally administered vehicle [saline], anti CLDNA 1 mAb (250 μg/mouse, twice weekly) or with VPA (=valproic acid, 0.4% in drinking water) as a control for 27 days. 
     
    
    
     DEFINITIONS 
     Throughout the specification, several terms are employed that are defined in the following paragraphs. 
     As used herein, the term “subject” refers to a human or another mammal (e.g., primate, dog, cat, goat, horse, pig, mouse, rat, rabbit, and the like), that can develop a fibrotic disease, but may or may not be suffering from the disease. Non-human subjects may be transgenic or otherwise modified animals. In many embodiments of the present invention, the subject is a human being. In such embodiments, the subject is often referred to as an “individual” or a “patient”. The term “individual” does not denote a particular age, and thus encompasses newborns, children, teenagers, and adults. The term “patient” more specifically refers to an individual suffering from a disease. In the practice of the present invention, a patient will generally be diagnosed with a fibrotic disease. 
     The term “treatment” is used herein to characterize a method or process that is aimed at (1) delaying or preventing the onset of a disease or condition (here a fibrotic disease); (2) slowing down or stopping the progression, aggravation, or deterioration of the symptoms of the disease or condition; (3) bringing about amelioration of the symptoms of the disease or condition; or (4) curing the disease or condition. A treatment may be administered prior to the onset of the disease or condition, for a prophylactic or preventive action. Alternatively or additionally, a treatment may be administered after initiation of the disease or condition, for a therapeutic action. 
     The terms “fibrotic disease” and “fibrotic disorder” are used herein interchangeably and have their art understood meaning. They refer to a clinical condition that is characterized by dysregulated tissue growth and scarring destroying healthy tissue, which can lead to disruption of normal function of virtually any organ of the body, including the heart, lung, kidney, liver and skin. 
     A “pharmaceutical composition” is defined herein as comprising an effective amount of at least one anti-Claudin-1 antibody (or a biologically active fragment thereof), and at least one pharmaceutically acceptable carrier or excipient. 
     As used herein, the term “effective amount” refers to any amount of a compound, agent, antibody, or composition that is sufficient to fulfil its intended purpose(s), e.g., a desired biological or medicinal response in a cell, tissue, system or subject. For example, in certain embodiments of the present invention, the purpose(s) may be: to prevent the onset of a fibrotic disease, to slow down, alleviate or stop the progression, aggravation or deterioration of the symptoms of the fibrotic disease; to bring about amelioration of the symptoms of the disease, or to cure the disease. 
     The term “pharmaceutically acceptable carrier or excipient” refers to a carrier medium which does not interfere with the effectiveness of the biological activity of the active ingredient(s) and which is not excessively toxic to the host at the concentration at which it is administered. The term includes solvents, dispersion media, coatings, antibacterial and antifungal agents, isotonic agents, adsorption delaying agents, and the like. The use of such media and agents for pharmaceutically active substances is well known in the art (see for example “ Remington&#39;s Pharmaceutical Sciences ”, E. W. Martin, 18 th  Ed., 1990, Mack Publishing Co.: Easton, Pa., which is incorporated herein by reference in its entirety). 
     The term “human Claudin-1 (or CLDN1)” refers to a protein having the sequence shown in NCBI Accession Number NP_066924, or any naturally occurring variants commonly found in HCV permissive human populations. The term “extracellular domain” or “ectodomain” of Claudin-1 refers to the region of the Claudin-1 sequence that extends into the extracellular space (i.e., the space outside a cell). 
     The term “antibody”, as used herein, refers to any immunoglobulin that contains an antigen binding site that immunospecifically binds an antigen. As such, the term antibody encompasses not only whole antibody molecules, but also antibody fragments as well as variants (including derivatives) of antibodies and of antibody fragments as long as the derivatives and fragments maintain specific binding ability. The term encompasses monoclonal antibodies and polyclonal antibodies. The term also covers any protein having a binding domain, which is homologous or largely homologous to an immunoglobulin-binding domain. These proteins may be derived from natural sources, or partly or wholly synthetically produced. 
     The term “specific binding”, when used in reference to an antibody, refers to an antibody binding to a predetermined antigen. Typically, the antibody binds with an affinity of at least 1×10 7  M −1 , and binds to the predetermined antigen with an affinity that is at least two-fold greater than the affinity for binding to a non-specific antigen (e.g., BSA, casein). 
     As used herein, the term “humanized antibody” refers to a chimeric antibody comprising amino acid residues from non-human hypervariable regions and amino acid residues from human framework regions (FRs). In particular, a humanized antibody comprises all or substantially all of at least one, typically two, variable domains, in which all or substantially all of the complementarity determining regions (CDRs) are those of a human antibody. A humanized antibody optionally may comprise at least a portion of an antibody constant region derived from a human antibody. A “humanized form” of an antibody, e.g., a non-human antibody, refers to an antibody that has undergone humanization. 
     The term “isolated”, as used herein in reference to a protein or polypeptide, means a protein or polypeptide, which by virtue of its origin or manipulation is separated from at least some of the components with which it is naturally associated or with which it is associated when initially obtained. By “isolated”, it is alternatively or additionally meant that the protein or polypeptide of interest is produced or synthesized by the hand of man. 
     The terms “protein”, “polypeptide”, and “peptide” are used herein interchangeably, and refer to amino acid sequences of a variety of lengths, either in their neutral (uncharged) forms or as salts, and either unmodified or modified by glycosylation, side-chain oxidation, or phosphorylation. In certain embodiments, the amino acid sequence is a full-length native protein. In other embodiments, the amino acid sequence is a smaller fragment of the full-length protein. In still other embodiments, the amino acid sequence is modified by additional substituents attached to the amino acid side chains, such as glycosyl units, lipids, or inorganic ions such as phosphates, as well as modifications relating to chemical conversions of the chains such as oxidation of sulfydryl groups. Thus, the term “protein” (or its equivalent terms) is intended to include the amino acid sequence of the full-length native protein, or a fragment thereof, subject to those modifications that do not significantly change its specific properties. In particular, the term “protein” encompasses protein isoforms, i.e., variants that are encoded by the same gene, but that differ in their pI or MW, or both. Such isoforms can differ in their amino acid sequence (e.g., as a result of allelic variation, alternative splicing or limited proteolysis), or in the alternative, may arise from differential post-translational modification (e.g., glycosylation, acylation, phosphorylation). 
     The term “analog”, as used herein in reference to a protein, refers to a polypeptide that possesses a similar or identical function as the protein but need not necessarily comprise an amino acid sequence that is similar or identical to the amino acid sequence of the protein or a structure that is similar or identical to that of the protein. Preferably, in the context of the present invention, a protein analog has an amino acid sequence that is at least 30%, more preferably, at least 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 99% identical to the amino acid sequence of the protein. 
     The term “fragment” and the term “portion”, as used herein in reference to a protein, refers to a polypeptide comprising an amino acid sequence of at least 5 consecutive amino acid residues (preferably, at least about: 10, 15, 20, 25, 30, 35, 40, 50, 60, 70, 80, 90, 100, 125, 150, 175, 200, 250 or more consecutive amino acid residues) of the amino acid sequence of a protein. The fragment of a protein may or may not possess a functional activity of the protein. 
     The term “biologically active”, as used herein to characterize a protein variant, analog or fragment, refers to a molecule that shares sufficient amino acid sequence identity or homology with the protein to exhibit similar or identical properties to the protein. For, example, in many embodiments of the present invention, a biologically active fragment of an anti-Claudin-1 antibody is a fragment that retains the ability of the whole antibody to bind to an antigen. 
     The term “homologous” (or “homology”), as used herein, is synonymous with the term “identity” and refers to the sequence similarity between two polypeptide molecules or between two nucleic acid molecules. When a position in both compared sequences is occupied by the same base or same amino acid residue, the respective molecules are then homologous at that position. The percentage of homology between two sequences corresponds to the number of matching or homologous positions shared by the two sequences divided by the number of positions compared and multiplied by 100. Generally, a comparison is made when two sequences are aligned to give maximum homology. Homologous amino acid sequences share identical or similar amino acid sequences. Similar residues are conservative substitutions for, or “allowed point mutations” of, corresponding amino acid residues in a reference sequence. “Conservative substitutions” of a residue in a reference sequence are substitutions that are physically or functionally similar to the corresponding reference residue, e.g. that have a similar size, shape, electric charge, chemical properties, including the ability to form covalent or hydrogen bonds, or the like. Particularly preferred conservative substitutions are those fulfilling the criteria defined for an “accepted point mutation” as described by Dayhoff et al. (“Atlas of Protein Sequence and Structure”, 1978, Nat. Biomed. Res. Foundation, Washington, D.C., Suppl. 3, 22: 354-352). 
     The terms “labeled”, “labeled with a detectable agent” and “labeled with a detectable moiety” are used herein interchangeably. These terms are used to specify that an entity (e.g., an antibody) can be visualized, for example, following binding to another entity (e.g., an antigen). Preferably, a detectable agent or moiety is selected such that it generates a signal which can be measured and whose intensity is related (e.g., proportional) to the amount of bound entity. Methods for labeling proteins and polypeptides, including antibodies, are well-known in the art. Labeled polypeptides can be prepared by incorporation of, or conjugation to, a label, that is directly or indirectly detectable by spectroscopic, photochemical, biochemical, immunochemical, electrical, optical or chemical means, or any other suitable means. Suitable detectable agents include, but are not limited to, various ligands, radionuclides, fluorescent dyes, chemiluminescent agents, microparticles, enzymes, colorimetric labels, magnetic labels, and haptens. 
     The terms “approximately” and “about” as used herein in reference to a number, generally include numbers that fall within a range of 10% in either direction of the number (greater than or less than the number) unless otherwise stated or otherwise evident from the context (except where such number would exceed 100% of a possible value). 
     Detailed Description of Certain Preferred Embodiments 
     As mentioned above, the present invention concerns the use of anti-Claudin-1 antibodies for the prevention and/or treatment of fibrotic diseases. In particular, the present invention relates to the use of anti-Claudin-1 antibodies for the prevention and/or treatment of pulmonary fibrosis, kidney fibrosis and skin fibrosis. 
     I—Anti-Claudin-1 Antibodies 
     The present Inventors have previously developed monoclonal antibodies directed against human Claudin-1 and demonstrated that these monoclonal antibodies cure HCV infection in vivo without detectable adverse effects (see EP 08 305 597 and WO 2010/034812). They then showed that the anti-Claudin-1 monoclonal antibodies interfere with liver cell signalling and reverse a patient-derived hepatocellular carcinoma (HCC) risk signature in a liver cell-based model system, making them useful in the prevention and/or treatment of hepatocellular carcinoma (HCC) irrespective of the etiology (see EP 15 159 872 and WO 2016/146809). They have now demonstrated that anti-Claudin-1 antibodies can be used in the prevention or treatment of fibrotic diseases, in particular lung fibrosis, such as idiopathic pulmonary fibrosis (IPF). 
     Anti-Claudin-1 antibodies that can be used in the practice of the present invention include any antibody raised against Claudin 1. Examples of anti-Claudin-1 antibodies that can be used in the practice of the present invention include, in particular, the polyclonal and monoclonal anti-CLDN1 antibodies that were developed by the present Inventors (see EP 08 305 597 and WO 2010/034812, Fofana et al., Gastroenterology, 2010, 139(3): 953-64, 964.e1-4). As described in these documents, eight monoclonal antibodies were produced by genetic immunization and shown to efficiently inhibit HCV infection by targeting the extracellular domain of Claudin 1. The monoclonal anti-Claudin-1 antibodies are called OM-4A4-D4, OM-7C8-A8, OM-6D9-A6, OM-7D4-C1, OM-6E1-B5, OM-3E5-B6, OM-8A9-A3, and OM-7D3-B3. Thus, anti-Claudin-1 antibodies suitable for use in the practice of the present invention include monoclonal antibodies secreted by any one of the hybridoma cell lines deposited by INSERM (one of the present Applicants) and GENOVAC at the DSMZ (Deutsche Sammlung von Mikro-organismen und Zelkuturen GmbH, Inhoffenstraße 7 B, 38124 Braunschweig, Germany) on Jul. 29, 2008 under Accession Numbers DSM ACC2931, DSM ACC2932, DSM ACC2933, DSM ACC2934, DSM ACC2935, DSM ACC2936, DSM ACC2937, and DSM ACC2938 (described in EP 08 302 597 and WO 2010/034812). 
     Other anti-Claudin-1 antibodies suitable for use in the practice of the present invention include monoclonal antibodies that have the same epitope as anti-Claudin-1 monoclonal antibodies secreted by any one of the hybridoma cell lines listed above. In certain embodiments, the epitope is strongly dependent on the conservation of the conserved motif W(30)-GLW(51)-C(54)-C(64) in Claudin-1 first extracellular loop (see EP 08 305 597 and WO 2010/034812). 
     Other examples of suitable anti-Claudin-1 antibodies include those disclosed in European Patent No. EP 1 167 389, in U.S. Pat. No. 6,627,439, in international patent application published under No. WO 2014/132307, in international patent applications published under No. WO 2015/014659 and No. WO 2015/014357, and in Yamashita et al., J. Pharmacol. Exp. Ther., 2015, 353(1): 112-118. 
     Anti-Claudin-1 antibodies suitable for use in the present invention may be polyclonal antibodies or monoclonal antibodies. 
     Instead of using the hybridomas described above as a source of the antibodies, the anti-Claudin-1 antibodies may be prepared using any other suitable method known in the art. For example, an anti-Claudin-1 monoclonal antibody may be prepared by recombinant DNA methods. These methods generally involve isolation of the genes encoding the desired antibody, transfer of the genes into a suitable vector, and bulk expression in a cell culture system. The genes or DNA encoding the desired monoclonal antibody may be readily isolated and sequenced using conventional procedures (e.g., using oligonucleotide probes that are capable of binding specifically to genes encoding the heavy and light chains of murine antibodies). Hybridoma cell lines may serve as a preferred source of such DNA. Suitable host cells for recombinant production of antibodies include, but are not limited to, appropriate mammalian host cells, such as CHO, HeLa, or CV1. Suitable expression plasmids include, without limitation, pcDNA3.1 Zeo, pIND(SP1), pREP8 (all commercially available from Invitrogen, Carlsbad, Calif., USA), and the like. The antibody genes may be expressed via viral or retroviral vectors, including MLV-based vectors, vaccinia virus-based vectors, and the like. Cells may be grown using standard methods, in suitable culture media such as, for example, DMEM and RPMI-1640 medium. The anti-Claudin-1 antibodies may be expressed as single chain antibodies. Isolation and purification of recombinantly produced antibodies may be performed by standard methods. For example, an anti-Claudin-1 monoclonal antibody may be recovered and purified from cell cultures by protein A purification, ammonium sulphate or ethanol precipitation, acid extraction, anion or cation exchange chromatography, phosphocellulose chromatography, hydrophobic interaction chromatography, affinity chromatography, such as Protein A column, hydroxylapatite chromatography, lectin chromatography, or any suitable combination of these methods. High performance liquid chromatography (HPLC) can also be employed for purification. 
     Alternatively, an anti-Claudin-1 antibody for use according to the present invention may be obtained from commercial sources. 
     In certain embodiments, an anti-Claudin-1 antibody is used in its native form. In other embodiments, it is truncated (e.g., via enzymatic cleavage or other suitable method) to provide immunoglobulin fragments or portions, in particular, fragments or portions that are biologically active. Biologically active fragments or portions of an anti-Claudin-1 antibody include fragments or portions that retain the ability of the antibody to bind to the antigen of the whole antibody, in particular to the extracellular domain of Claudin-1. 
     A biologically active fragment or portion of an anti-Claudin-1 antibody may be a Fab fragment or portion, a F(ab′) 2  fragment or portion, a variable domain, or one or more CDRs (complementary determining regions) of the antibody (for example an antibody that comprises all 6 CDRs of an anti-Claudin-1 monoclonal antibody). Alternatively, a biologically active fragment or portion of an anti-Claudin-1 antibody may be derived from the carboxyl portion or terminus of the antibody protein and may comprise an Fc fragment, an Fd fragment or an Fv fragment. 
     Anti-Claudin-1 antibody fragments for use according to the present invention may be produced using any suitable method known in the art including, but not limited to, enzymatic cleavage (e.g., proteolytic digestion of intact antibodies) or synthetic or recombinant techniques. For example, F(ab′) 2 , Fab, Fv and ScFv (single chain Fv) antibody fragments can be expressed in and secreted from mammalian host cells or from  E. coli . Antibodies can also be produced in a variety of truncated forms using antibody genes in which one or more stop codons have been introduced upstream of the natural stop site. The various portions of antibodies can be joined together chemically by conventional techniques, or can be prepared as a contiguous protein using genetic engineering techniques. 
     Anti-Claudin-1 antibodies (or biologically active fragments thereof) suitable for use according to the present invention may be produced in a modified form, such as a fusion protein (i.e., an immunoglobulin molecule or portion thereof linked to a polypeptide entity). Preferably, the fusion protein retains the biological activity of the antibody. A polypeptide entity to be fused to an anti-Claudin-1 antibody, or a biologically active fragment thereof, may be selected to confer any of a number of advantageous properties to the resulting fusion protein. For example, the polypeptide entity may be selected to provide increased expression of the recombinant fusion protein. Alternatively or additionally, the polypeptide entity may facilitate purification of the fusion protein, for example, by acting as a ligand in affinity purification. A proteolytic cleavage site may be added to the recombinant protein so that the desired sequence can ultimately be separated from the polypeptide entity after purification. The polypeptide entity may also be selected to confer an improved stability to the fusion protein, when stability is a goal. Examples of suitable polypeptide entities include, for example, polyhistidine tags, that allow for the easy purification of the resulting fusion protein on a nickel chelating column. Glutathione-S-transferase (GST), maltose B binding protein, or protein A are other examples of suitable polypeptide entities. 
     An anti-Claudin-1 antibody for use according to the present invention may be re-engineered so as to optimize stability, solubility, in vivo half-life, or ability to bind additional targets. Genetic engineering approaches as well as chemical modifications to accomplish any or all of these changes in properties are well known in the art. For example, the addition, removal, and/or modification of the constant regions of an antibody are known to play a particularly important role in the bioavailability, distribution, and half-life of therapeutically administered antibodies. The antibody class and subclass, determined by the Fc or constant region of the antibody (which mediates effector functions), when present, imparts important additional properties. 
     Additional fusion proteins of the invention may be generated through the techniques of DNA shuffling well known in the art (see, for example, U.S. Pat. Nos. 5,605,793; 5,811,238; 5,830,721; 5,834,252; and 5,837,458). 
     Anti-Claudin-1 antibodies suitable for use according to the present invention may also be “humanized”: sequence differences between rodent antibodies and human sequences can be minimized by replacing residues which differ from those in the human sequences by site-directed mutagenesis of individual residues or by grafting of entire regions or by chemical synthesis. Humanized antibodies can also be produced using recombinant methods. In the humanized form of the antibody, some, most or all of the amino acids outside the CDR regions are replaced with amino acids from human immunoglobulin molecules, while some, most or all amino acids within one or more CDR regions are unchanged. Small additions, deletions, insertions, substitutions or modifications of amino acids are permissible as long as they do not significantly modify the biological activity of the resulting antibody. Suitable human “replacement” immunoglobulin molecules include IgG1, IgG2, IgG2a, IgG2b, IgG3, IgG4, IgA, IgM, IgD or IgE molecules, and fragments thereof. Alternatively, the T-cell epitopes present in rodent antibodies can be modified by mutation (de-immunization) to generate non-immunogenic rodent antibodies that can be applied for therapeutic purposes in humans (see webpage: accurobio.com). 
     In some embodiments, a humanized anti-Claudin-1 antibody for use according to the present invention is one previously described by the present Inventors in EP 16 305 317 and WO 2017/162678. Such a humanized anti-Claudin-1 monoclonal antibody comprises all of the CDRs of rat monoclonal antibody OM-7D3-B3 (secreted by hybridoma cell line deposited under Accession Number DSM ACC2938—see above), wherein the variable heavy chain of OM-7D3-B3 consists of amino acid sequence SEQ ID NO: 1 and the variable light chain of OM-7D3-B3 consists of amino acid sequence SEQ ID NO: 2, said humanized antibody further comprising: 
     a) at least one antibody variable heavy chain (VH) consisting of the amino acid sequence of SEQ ID NO: 3 or SEQ ID NO: 4 or SEQ ID NO: 5, or 
     b) at least one antibody variable light chain (VL) consisting of the amino acid sequence of SEQ ID NO: 6 or SEQ ID NO: 7 or SEQ ID NO: 8, 
     wherein SEQ ID NO: 1, the variable heavy chain of OM-7D3-B3 is the following amino acid sequence, wherein the CDRs are shown in bold and underlined:
         EVQLVESGGGLVQPGRSLKLSCLGSGFSFSSYGMNWIRQAPGKGLEWVA SISPSGSYFYYADSVKGRFTISRENAKNTLYLQMTSLRAEDTALYYCARL PGFNPPFDHWGQGVVVTVSS
 
and wherein SEQ ID NO: 2, the variable light chain of OM-7D3-B3 is the following amino acid sequence, wherein the CDRs are shown in bold and underlined:
   NTVMTQSPTSMFMSVGDRVTMNCKASONVGGNVDWYQWKPGQSPKL LMYGASNRYTGVPDRFRGSGSGTDFTLTISNMQTEDLAVYYCLOYKNN PWTFGGGTKVELK,
 
wherein SEQ ID NO: 3 is the sequence of the humanized variable heavy chain H3:
   QVQLVESGGGVVQPGRSLRLSCLGSGFSFSSYGMNWVRQAPGKGLEWV ASISPSGSYFYYADSVKGRFTISRDNSKNTLYLQMTSLRAEDTAIYYCARL PGFNPPFDHWGQGTLVTVSS,
 
wherein SEQ ID NO: 4 is the sequence of the humanized variable heavy chain H2:
   QVQLVESGGGVVQPGRSLRLSCAASGFSFSSYGMNWVRQAPGKGLEWV TSISPSGSYFYYADSVKGRFTISRDNSKNTLYLQMNSLRAEDTAIYYCARL PGFNPPFDHWGQGTLVTVSS,
 
wherein SEQ ID NO: 5 is the sequence of the humanized variable heavy chain H1:
   EVQLVESGGGLVKPGGSLRLSCAASGFSFSSYGMNWVRQAPGKGLEWV SSISPSGSYFYYADSVKGRFTISRDNAKNSLYLQMNSLRAEDTAVYYCAR LPGFNPPFDHWGQGTLVTVSS,
 
wherein SEQ ID NO: 6 is the sequence of the humanized variable light chain L3:
   DIQMTQSPSSLSASVGDRVTITCKASQNVGGNVDWYQWKPGKAPKLLIY GASNRYTGVPDRFRGSGSGTDFTLTISSLQPEDVATYYCLQYKNNPWTFG GGTKVEIK,
 
wherein SEQ ID NO: 7 is the sequence of the humanized variable light chain L2:
   DIQMTQSPSSLSASVGDRVTITCKASQNVGGNVDWYQWKPGKAPKLLIY GASNRYTGVPSRFRGSGSGTDFTLTISSLQPEDVATYYCLQYKNNPWTFG QGTKVEIK, and
 
wherein SEQ ID NO: 8 is the sequence of the humanized variable light chain L1:
   DIQMTQSPATLSVSPGERATLSCKASQNVGGNVDWYQWKPGQAPRLLIY GASNRYTGIPARFRGSGSGTEFTLTISSLQSEDFAVYYCLQYKNNPWTFG QGTKVEIK.       

     For example, such a humanized anti-Claudin-1 monoclonal antibody may comprise: 
     a) two antibody variable heavy chains (VH), both variable heavy chains consisting of the amino acid sequence of SEQ ID NO: 3 or SEQ ID NO: 4 or SEQ ID NO: 5, or 
     b) two antibody variable light chains (VL), both variable light chains consisting of the amino acid sequence of SEQ ID NO: 6 or SEQ ID NO: 7 or SEQ ID NO: 8. 
     For example, such a humanized anti-Claudin-1 monoclonal antibody may comprise; 
     1) two antibody variable heavy chains (VH) consisting of the amino acid sequence SEQ ID NO: 3, and two antibody variable light chains (VL) consisting of the amino acid sequence SEQ ID NO: 6 [H3L3]; or 
     2) two antibody variable heavy chains (VH) consisting of the amino acid sequence SEQ ID NO: 3, and two antibody variable light chains (VL) consisting of the amino acid sequence SEQ ID NO: 7 [H3L1]; or 
     3) two antibody variable heavy chains (VH) consisting of the amino acid sequence SEQ ID NO: 3, and two antibody variable light chains (VL) consisting of the amino acid sequence SEQ ID NO: 8 [H3L2]; or 
     4) two antibody variable heavy chains (VH) consisting of the amino acid sequence SEQ ID NO: 4, and two antibody variable light chains (VL) consisting of the amino acid sequence SEQ ID NO: 6 [H1L3]; or 
     5) two antibody variable heavy chains (VH) consisting of the amino acid sequence SEQ ID NO: 4, and two antibody variable light chains (VL) consisting of the amino acid sequence SEQ ID NO: 7 [H1L1]; or 
     6) two antibody variable heavy chains (VH) consisting of the amino acid sequence SEQ ID NO: 4, and two antibody variable light chains (VL) consisting of the amino acid sequence SEQ ID NO: 8 [H1L2]; or 
     7) two antibody variable heavy chains (VH) consisting of the amino acid sequence SEQ ID NO: 5, and two antibody variable light chains (VL) consisting of the amino acid sequence SEQ ID NO: 6 [H2L3]; or 
     8) two antibody variable heavy chains (VH) consisting of the amino acid sequence SEQ ID NO: 5, and two antibody variable light chains (VL) consisting of the amino acid sequence SEQ ID NO: 7 [H2L1]; or 
     9) two antibody variable heavy chains (VH) consisting of the amino acid sequence SEQ ID NO: 5, and two antibody variable light chains (VL) consisting of the amino acid sequence SEQ ID NO: 8 [H2L2]. 
     The humanized anti-Claudin-1 antibody may be a full monoclonal antibody having an isotope selected from the group consisting of IgG1, IgG2, IgG3 and IgG4. Alternatively, the humanized anti-Claudin-1 antibody may be a fragment of a monoclonal antibody selected from the group consisting of Fv, Fab, F(ab′)2, Fab′, dsFv, scFv, sc(Fv)2 and diabodies. 
     Anti-Claudin-1 antibodies (or biologically active variants or fragments thereof) suitable for use according to the present invention may be functionally linked (e.g., by chemical coupling, genetic fusion, non-covalent association or otherwise) to one or more other molecular entities. Methods for the preparation of such modified antibodies (or conjugated antibodies) are known in the art (see, for example, “ Affinity Techniques. Enzyme Purification: Part B ”, Methods in Enzymol., 1974, Vol. 34, Jakoby and Wilneck (Eds.), Academic Press: New York, N.Y.; and Wilchek and Bayer, Anal. Biochem., 1988, 171: 1-32). Preferably, molecular entities are attached at positions on the antibody molecule that do not interfere with the binding properties of the resulting conjugate, e.g., positions that do not participate in the specific binding of the antibody to its target. 
     The antibody molecule and molecular entity may be covalently, directly linked to each other. Or, alternatively, the antibody molecule and molecular entity may be covalently linked to each other through a linker group. This can be accomplished by using any of a wide variety of stable bifunctional agents well known in the art, including homofunctional and heterofunctional linkers. 
     In certain embodiments, an anti-Claudin-1 antibody (or a biologically active fragment thereof) for use according to the present invention is conjugated to a detectable agent. Any of a wide variety of detectable agents can be used, including, without limitation, various ligands, radionuclides (e.g.,  3 H,  125 I,  131 I, and the like), fluorescent dyes (e.g., fluorescein isothiocyanate, rhodamine, phycoerytherin, phycocyanin, allophycocyanin, o-phthalaldehyde and fluorescamine), chemiluminescent agents (e.g., luciferin, luciferase and aequorin), microparticles (such as, for example, quantum dots, nanocrystals, phosphors and the like), enzymes (such as, for example, those used in an ELISA, i.e., horseradish peroxidase, beta-galactosidase, luciferase, alkaline phosphatase), colorimetric labels, magnetic labels, and biotin, digoxigenin or other haptens and proteins for which antisera or monoclonal antibodies are available. 
     Other molecular entities that can be conjugated to an anti-Claudin-1 antibody of the present invention (or a biologically active fragment thereof) include, but are not limited to, linear or branched hydrophilic polymeric groups, fatty acid groups, or fatty ester groups. 
     Thus, in the practice of the present invention, anti-Claudin-1 antibodies can be used under the form of full length antibodies, biologically active variants or fragments thereof, chimeric antibodies, humanized antibodies, and antibody-derived molecules comprising at least one complementary determining region (CDR) from either a heavy chain or light chain variable region of an anti-Claudin-1 antibody, including molecules such as Fab fragments, F(ab′) 2  fragments, Fd fragments, Fabc fragments, Sc antibodies (single chain antibodies), diabodies, individual antibody light single chains, individual antibody heavy chains, chimeric fusions between antibody chains and other molecules, and antibody conjugates, such as antibodies conjugated to a therapeutic agent or a detectable agent. Preferably, anti-Claudin-1 antibody-related molecules according to the present invention retain the antibody&#39;s ability to bind its antigen, in particular the extracellular domain of Claudin-1. 
     One skilled in the art will understand that other compounds targeting Claudin-1, can be used in the practice of the present invention, including, but not limited to, small molecules and siRNAs. 
     II—Treatment and/or Prevention of a Fibrotic Disease 
     A. Indications 
     The present Inventors have shown that anti-Claudin-1 antibodies specifically target the lungs, the kidneys, and the skin, and are able to prevent and treat lung fibrosis in a state-of-the-art model of idiopathic pulmonary fibrosis (IPF) without any significant adverse effects. Therefore, anti-Claudin-1 antibodies, or biologically active fragments thereof, as defined above, may be used in methods to prevent and/or treat pulmonary fibrosis, kidney fibrosis, and skin fibrosis. 
     Methods of treatment of the present invention may be accomplished using an anti-Claudin-1 antibody, or a biologically active fragment thereof, or a pharmaceutical composition comprising such an antibody or fragment (see below). These methods generally comprise administration of an effective amount of an anti-Claudin-1 antibody, or biologically active fragment thereof, or of a pharmaceutical composition thereof, to a subject in need thereof (i.e., a patient diagnosed with lung fibrosis or with kidney fibrosis or with skin fibrosis). Administration may be performed using any of the administration methods known to one skilled in the art (see below). 
     Pulmonary Fibrosis. The terms “lung fibrosis” and “pulmonary fibrosis” are used herein interchangeably. They refer to a number of conditions, of known or unknown etiologies, that cause interstitial lung damage, followed by fibrosis and eventually loss of lung elasticity. These conditions lead to symptoms such as persistent cough, chest pain, difficulty breathing and fatigue. 
     Pulmonary fibrosis that can be treated according to a method of the present invention may be caused by any of a variety of factors including, but not limited to, long-term exposure to certain toxins (e.g., silica dust, asbestos fibers, hard metal dusts, coal dusts, grain dusts, bird and animal droppings); certain medical conditions (e.g., dermatomyositis, polymyositis, mixed connective tissue disease, systemic lupus erythematosus, rheumatoid arthritis, sarcoidosis, scleroderma and pneumonia); radiation therapy (e.g., for lung or breast cancer); and some medications (e.g., chemotherapy drugs such as methotrexate and cyclophosphamide, heart medication such as amiodarone; some antibiotics such as nitrofurantoin and ethambutol; and anti-inflammatory drugs such as rituximab and sulfasalazine). 
     In some embodiments, pulmonary fibrosis that can be treated according to a method of the present invention may have no clear underlying cause. The term idiopathic pulmonary fibrosis is then used. 
     In some embodiments, the pulmonary fibrosis to be treated using a method of treatment of the present invention is selected from the group consisting of idiopathic pulmonary fibrosis (IPF), idiopathic nonspecific interstitial pneumonitis (NSIP), cryptogenic organizing pneumonia (COP), Hamman-Rich syndrome (also known as acute interstitial pneumonia), lymphocytic interstitial pneumonitis (LIP), respiratory bronchiolitis interstitial lung disease, desquamative interstitial pneumonitis or idiopathic lymphoid interstitial pneumonia, and idiopathic pleuroparenchymal fibroelastosis. 
     In certain preferred embodiments, the pulmonary fibrosis is idiopathic pulmonary fibrosis. 
     In some embodiments, the pulmonary fibrosis is associated with chronic obstructive pulmonary disease. Chronic obstructive pulmonary disease (COPD) is a type of progressive respiratory disease characterized by airway obstruction, long-term breathing problems and poor airflow. 
     In certain embodiments, the pulmonary fibrosis is due to infection, such as COVID19-associated fibrosis. 
     Administration of an anti-Claudin-1 antibody, or of a pharmaceutical composition thereof, to patients suffering from pulmonary fibrosis may slow, reduce, stop or alleviate the progression of the disease, in particular the development of complications such as pulmonary hypertension, right-sided heart failure, respiratory failure, lung cancer, or other lung complications such as blood clots in the lung, a collapsed lung or lung infections. 
     Alternatively or additionally, administration of an anti-Claudin-1 antibody, or of a pharmaceutical composition thereof, to a patient suffering from pulmonary fibrosis may result in amelioration of at least one of the symptoms experienced by the individual including, but not limited to, dry cough, shortness of breath, fatigue, muscle pain, join pain, and weight loss. 
     Alternatively or additionally, administration of an anti-Claudin-1 antibody, or of a pharmaceutical composition thereof, to a patient suffering from pulmonary fibrosis may help avoiding or, at least delaying, lung transplantation. 
     In some embodiments, a method of the invention is administered to a subject with a risk of developing pulmonary fibrosis, for example someone who has been exposed to certain toxins known to be associated with lung fibrosis or someone who has received radiation therapy, or yet someone who has been treated with certain medications. Administration of an anti-Claudin-1 antibody, or of a pharmaceutical composition thereof, may result in the prevention of the development of the disease or in the prevention of the progression of the disease beyond the very early stages. 
     The effects of a treatment according to the invention may be monitored using any of the assays and tests known in the art for the diagnosis of pulmonary fibrosis affecting the patient. Such assays and tests include, but are not limited to, imaging tests (such as chest X-ray, computerized tomography (CT) scan, and echocardiogram); lung function tests (such as pulmonary functions testing (e.g., spirometry), pulse oximetry, exercise stress test, and arterial blood gas test); or biopsy by bronchoscopy or surgical biopsy. 
     In certain embodiments of a method of prevention or treatment of pulmonary fibrosis according to the present invention, an anti-Claudin-1 antibody (or a biologically active fragment thereof), or a pharmaceutical composition thereof, is administered alone. In other embodiments, an anti-Claudin-1 antibody (or a biologically active fragment thereof), or a pharmaceutical composition thereof, is administered in combination with at least one additional therapeutic agent and/or therapeutic procedure. The anti-Claudin-1 antibody (or biologically active fragment thereof), or pharmaceutical composition thereof, may be administered prior to administration of the therapeutic agent or therapeutic procedure, concurrently with the therapeutic agent or therapeutic procedure, and/or following administration of the therapeutic agent or therapeutic procedure. 
     Therapeutic agents that may be administered in combination with an anti-Claudin-1 antibody (or biologically active fragment thereof), or a pharmaceutical composition thereof, may be selected among a large variety of biologically active compounds that are known in the art to have a beneficial effect in the treatment or management of pulmonary fibrosis. Examples of such therapeutic agents include, but are not limited to, immunosuppressive agents such as corticosteroids, anti-fibrotic agents such as ciclosporin or colchicine, new medications such as pirfenidone (ESBRIET®) and nintedanib (OFEV®), which have been approved by the Food and Drug Administration (FDA); and anti-acid medications to treat gastroesophageal reflux disease (GERD), a digestive condition that commonly occurs in people with idiopathic pulmonary fibrosis. Examples of therapeutic procedures include, but are not limited to oxygen therapy, which makes breathing and exercise easier, prevents or lessens complications from low blood oxygen levels, reduces blood pressure in the right side of the heart and improves sleep and sense of well-being; pulmonary rehabilitation, which helps manage the symptoms and improves daily functioning by improving physical endurance and lung efficiency; and lung transplant, which improves the quality of life and allows patients to live a longer life. 
     Thus, in certain embodiments, the method of treatment of pulmonary fibrosis according to the invention is administered in combination with a therapeutic agent selected from the group consisting of corticosteroids, ciclosporin, colchicine, pirfenidone, nintedanib and anti-acid drugs to treat gastroesophageal reflux disease (GERD). Alternatively or additionally, the method of treatment of pulmonary fibrosis according to the invention is administered in combination with a therapeutic procedure selected from the group consisting of lung transplantation, hyperbaric oxygen therapy and pulmonary rehabilitation. 
     It is also contemplated that anti-Claudin-1 antibodies, or biologically active fragments thereof, as defined above, be used in methods to prevent and/or treat mediastinal fibrosis. Mediastinal fibrosis (of fibrosing mediastinitis) is a condition characterized by calcified fibrosis that affects the area between the lungs (mediastinum), which contains the heart, large blood vessels, trachea, esophagus, and lymph nodes. 
     Kidney Fibrosis. The terms “kidney fibrosis” and “renal fibrosis” are used herein interchangeably. Renal fibrosis is the hallmark of chronic kidney disease, regardless of underlying etiology. The pathological finding of renal fibrosis is characterized by progressive tissue scarring including glomerulosclerosis, tubulointerstitial fibrosis and loss of renal parenchyma (including tubular atrophy, loss of capillaries and podocytes). All the renal diseases are accompanied by kidney fibrosis, which is a progressive process that ultimately leads to end-stage renal failure (ESRD), a devastating disorder that requires dialysis or kidney transplant. Since chronic deterioration of renal function depends heavily on the extent of fibrosis of the kidney, it is thought that inhibiting the progress of fibrosis can result in suppression of the development of chronic renal failure. The term “chronic renal failure” refers to a state in which the renal functions gradually deteriorate irreversibly and homeostasis of a living body cannot be maintained. 
     Renal fibrosis that can be treated according to a method of the present invention may be caused by any of a variety of factors including, but not limited to, certain medical conditions (nephropathies such as glomerular diseases (e.g., glomerulosclerosis, glomerulonephritis), chronic renal insufficiency, acute kidney injury, high blood pressure, polycystic kidney disease, vesicoureteral reflux, pyelonephritis (recurrent kidney infection), and autoimmune diseases such as diabetes mellitus); certain medical interventions (such as nephrectomy or kidney removal, a procedure which is sometimes performed on patients with kidney cancer and which may negatively impact kidney function of the remaining kidney; dialysis following kidney failure; and catheter placement); and some medications (chemotherapy and immunosuppressive therapy, that are a source of harmful effects to the kidney which result in most of the cases in renal fibrosis; long-time use of lithium and of non-steroidal anti-inflammatory drugs). 
     In some embodiments, renal fibrosis to be treated using a method of treatment of the present invention is selected from the group consisting of renal interstitial fibrosis and glomerulosclerosis. 
     Administration of an anti-Claudin-1 antibody, or of a pharmaceutical composition thereof, to patients suffering from kidney fibrosis may slow, reduce, stop or alleviate the progression of the disease, in particular the development of complications such as fluid retention including pulmonary edema; hyperkalemia (sudden rise of potassium levels in the blood); cardiovascular disease; decreased immune response; pericarditis; and end-stage kidney disease. 
     Alternatively or additionally, administration of an anti-Claudin-1 antibody, or of a pharmaceutical composition thereof, to a patient suffering from renal fibrosis may result in amelioration of at least one of the symptoms experienced by the individual including, but not limited to, nausea, vomiting, loss of appetite, fatigue and weakness, muscle cramps, fluid retention (puffiness or swelling), chest pain, shortness of breath, and hypertension. 
     Alternatively or additionally, administration of an anti-Claudin-1 antibody, or of a pharmaceutical composition thereof, to a patient suffering from renal fibrosis may help avoiding, or at least delaying, dialysis or kidney transplant. 
     The effects of a treatment according to the invention may be monitored using any of the assays and tests known in the art for the diagnosis of renal fibrosis affecting the patient. Such assays and tests include, but are not limited to, imaging tests (such as ultrasound); blood tests (determination of creatinine and urea levels); urine tests, and biopsy. 
     In certain embodiments, an anti-Claudin-1 antibody (or a biologically active fragment thereof), or a pharmaceutical composition thereof, is administered alone. In other embodiments, an anti-Claudin-1 antibody (or a biologically active fragment thereof), or a pharmaceutical composition thereof, is administered in combination with at least one additional therapeutic agent and/or therapeutic procedure. The anti-Claudin-1 antibody (or biologically active fragment thereof), or pharmaceutical composition thereof, may be administered prior to administration of the therapeutic agent or therapeutic procedure, concurrently with the therapeutic agent or therapeutic procedure, and/or following administration of the therapeutic agent or therapeutic procedure. 
     Therapeutic agents that may be administered in combination with an anti-Claudin-1 antibody (or biologically active fragment thereof), or a pharmaceutical composition thereof, may be selected among a large variety of biologically active compounds that are known in the art to have a beneficial effect in the treatment or management of renal fibrosis. Examples of such therapeutic agents include, but are not limited to, anti-hypertensive drugs (in order to alleviate the burden on the glomerulus); supplementation in 1,25-dihydroxyvitamin D3 or erythropoietin, which are secreted by the kidney; angiotensin converting enzyme inhibitors (such as captopril, enalapril, delapril, imidapril, quinapril, temocapril, perindopril erbumine, and lisinopril) and angiotensin II receptor antagonists (such as losartan, valsartan, candesartan cilexetil, telmisartan, olmesartan medoxomil, and irbesartan), which are known to have a renal protective effect per se in addition to suppressing the progress of renal failure by decreasing glomerular blood pressure; diuretics, which relieve swelling; AST-120 (KREMEZIN®), an adsorptive carbon that adsorbs harmful substance in the intestine; and calcium polystyrene sulfonate, an ion-exchange resin that adorbs potassium in the intestine. Examples of therapeutic procedures include dialysis and kidney transplantation. The dialysis may be a hemodialysis or a peritoneal dialysis. In hemodialysis, a machine filters waste and excess fluids from the blood. In peritoneal dialysis, a catheter inserted in the abdomen fills the abdominal cavity with a dialysis solution that absorbs waste and excess fluids. After a period of time, the dialysis solution drains from the body, carrying the waste with it. 
     Thus, in certain embodiments, the method of treatment of kidney fibrosis according to the invention is administered in combination with a therapeutic agent selected from the group consisting of anti-hypertensive drugs 1,25-dihydroxyvitamin D3, erythropoietin, angiotensin converting enzyme inhibitors, angiotensin II receptor antagonists AST-120 (KREMEZIN®), and calcium polystyrene sulfonate. Alternatively or additionally, the method of treatment of kidney fibrosis according to the invention is administered in combination with a therapeutic procedure selected from the group consisting of dialysis and kidney transplantation. 
     It is also contemplated that anti-Claudin-1 antibodies, or biologically active fragments thereof, as defined above, be used in methods to prevent and/or treat retroperitoneal fibrosis. Retroperitoneal fibrosis is a rare inflammatory disorder in which abnormal formation of fibrous tissue in the retroperitoneum, the compartment of the body containing the kidneys, aorta, renal tract, and various other structures. 
     Skin Fibrosis. The terms “skin fibrosis”, “dermal fibrosis” and “cutaneous fibrosis” are used herein interchangeably. They refer to an excessive scarring of the skin which results from a pathologic wound healing response. Skin fibrosis is characterized by fibroblast proliferation and excessive synthesis as well as deposition of extracellular matrix (ECM) proteins, such as collagen, elastin, and fibrillin. Clinically, skin fibrosis manifests as thickened, tightened and hardened areas of skin. Ultimately, skin fibrosis may lead to dermal contractures that affect the ability to flex and extend the joints. Despite the morbidity and socioeconomic burdens associated with skin fibrosis, there are limited effective therapeutic options. Current therapies are associated with significant side effects and even with combination therapy, progression, and recurrence often occurs. 
     Skin fibrosis that can be treated according to a method of the present invention may be caused by any of a variety of factors including, but not limited to, certain medical conditions (scleroderma in both localized (morphea, linear scleroderma) and systemic forms, graft-versus-host disease (GVHD), nephrogenic fibrosing dermopathy, mixed connective tissue disease, scleredoma, scleromyxedema, eosinophilic fasciitis, chromoblastomycosis, hypertrophic scars and keloids); certain medical interventions (radiotherapy-induced skin fibroses); environmental or professional exposures to various chemicals (e.g., in eosinophilia-myalgia syndrome induced by L-tryptophan); and exposure to certain physical agents (e.g., skin fibroses induced by physical trauma, surgical injury, heat or ice skin burns). 
     Administration of an anti-Claudin-1 antibody, or of a pharmaceutical composition thereof, to patients suffering from skin fibrosis may slow, reduce, stop or alleviate the progression of the skin disease, for example the propagation of fibrosis to a non-affected skin area, and/or may slow, reduce, stop or alleviate the development of complications such as disfigurement, dermal contractures, diminished function of an affected limb and propagation to internal organs. 
     Alternatively or additionally, administration of an anti-Claudin-1 antibody, or of a pharmaceutical composition thereof, to a patient suffering from skin fibrosis may result in amelioration of at least one of the symptoms experienced by the individual including, but not limited to, thickened, tightened and hardened areas of skin. 
     The effects of a treatment according to the invention may be monitored using any of the assays and tests known in the art for the diagnosis of dermal fibrosis affecting the patient. Such assays and tests make use of, for example, durometers for measuring skin hardness and/or tautness, cutometers for quantifying skin elasticity, ultrasonographic devices for assessing local dermal and subcutaneous blood flow, and digital infrared thermal imaging of skin. Other non-invasive methods of skin fibrosis diagnosis include ultrasound scan, elastography, confocal microscopy, and optical coherence tomography. 
     In certain embodiments of a method of prevention or treatment of dermal fibrosis according to the present invention, an anti-Claudin-1 antibody (or a biologically active fragment thereof), or a pharmaceutical composition thereof, is administered alone. In other embodiments, an anti-Claudin-1 antibody (or a biologically active fragment thereof), or a pharmaceutical composition thereof, is administered in combination with at least one additional therapeutic agent and/or therapeutic procedure. The anti-Claudin-1 antibody (or biologically active fragment thereof), or pharmaceutical composition thereof, may be administered prior to administration of the therapeutic agent and/or the therapeutic procedure, concurrently with the therapeutic agent and/or the therapeutic procedure, and/or following administration of the therapeutic agent and/or the therapeutic procedure. 
     Therapeutic agents that may be administered in combination with an anti-Claudin-1 antibody (or biologically active fragment thereof), or a pharmaceutical composition thereof, may be selected among immunosuppressive drugs (such as methotrexate, mycophenolyate, mofetil, cyclophosphamide and cyclosporine), tocilizumab (an anti-IL-6 receptor antibody), rituximab (an anti-CD20 antibody), and fresolimumab (an anti-TGF-β antibody, which show promising clinical outcomes. 
     Alternatively or additionally, the anti-Claudin-1 antibody (or biologically active fragment thereof), or a pharmaceutical composition thereof, may be administered in combination with a therapeutic procedure used in the treatment of skin fibrosis, such as ultraviolet phototherapy. 
     B. Administration 
     An anti-Claudin-1 antibody, or a biologically active fragment thereof, (optionally after formulation with one or more appropriate pharmaceutically acceptable carriers or excipients), in a desired dosage, can be administered to a subject in need thereof by any suitable route. Various delivery systems are known and can be used to administer antibodies, including tablets, capsules, injectable solutions, encapsulation in liposomes, microparticles, microcapsules, etc. Methods of administration include, but are not limited to, dermal, intradermal, intramuscular, intraperitoneal, intralesional, intravenous, subcutaneous, intranasal, pulmonary, epidural, and oral routes. An anti-Claudin-1 antibody, or a biologically active fragment thereof, or a pharmaceutical composition thereof, may be administered by any convenient or other appropriate route, for example, by infusion or bolus injection, by absorption through epithelial or mucosa linings (e.g., oral mucosa, bronchial mucosa, rectal and intestinal mucosa, etc). Administration can be systemic or local. As will be appreciated by those of ordinary skill in the art, in embodiments where an inventive antibody is administered in combination with an additional therapeutic agent, the antibody and therapeutic agent may be administered by the same route (e.g., intravenously) or by different routes (e.g., intravenously and orally). 
     C. Dosage 
     An anti-Claudin-1 antibody, or a biologically active fragment thereof, (optionally after formulation with one or more appropriate pharmaceutically acceptable carriers or excipients), will be administered in a dosage such that the amount delivered is effective for the intended purpose. The route of administration, formulation and dosage administered will depend on the therapeutic effect desired, the severity of the condition to be treated if already present, the presence of any infection, the age, sex, weight, and general health condition of the patient as well as upon the potency, bioavailability, and in vivo half-life of the antibody or composition used, the use (or not) of concomitant therapies, and other clinical factors. These factors are readily determinable by the attending physician in the course of the therapy. Alternatively or additionally, the dosage to be administered can be determined from studies using animal models (e.g., chimpanzee or mice). Adjusting the dose to achieve maximal efficacy based on these or other methods are well known in the art and are within the capabilities of trained physicians. As studies are conducted using anti-Claudin-1 antibodies, further information will emerge regarding the appropriate dosage levels and duration of treatment. 
     A treatment according to the present invention may consist of a single dose or multiple doses. Thus, administration of an anti-Claudin-1 antibody, or a biologically active fragment thereof, (or a pharmaceutical composition thereof) may be constant for a certain period of time or periodic and at specific intervals, e.g., hourly, daily, weekly (or at some other multiple day interval), monthly, yearly (e.g., in a time release form). Alternatively, the delivery may occur at multiple times during a given time period, e.g., two or more times per week; two or more times per month, and the like. The delivery may be continuous delivery for a period of time, e.g., intravenous delivery. 
     In general, the amount of anti-Claudin-1 antibody, or a biologically active fragment thereof, (or a pharmaceutical composition thereof) administered will preferably be in the range of about 1 ng/kg to about 100 mg/kg body weight of the subject, for example, between about 100 ng/kg and about 50 mg/kg body weight of the subject; or between about 1 μg/kg and about 10 mg/kg body weight of the subject, or between about 100 μg/kg and about 1 mg/kg body weight of the subject. 
     III—Pharmaceutical Compositions 
     As mentioned above, anti-Claudin-1 antibodies (and related molecules) may be administered per se or as a pharmaceutical composition. Accordingly, the present invention provides pharmaceutical compositions comprising an effective amount of an anti-Claudin-1 antibody, or a biologically active fragment thereof, described herein and at least one pharmaceutically acceptable carrier or excipient for use in the prevention and/or treatment of fibrotic diseases, in particular pulmonary fibrosis, kidney fibrosis and skin fibrosis. In some embodiments, the composition further comprises one or more additional biologically active agents. 
     The antibodies or pharmaceutical compositions may be administered in any amount and using any route of administration effective for achieving the desired prophylactic and/or therapeutic effect. The optimal pharmaceutical formulation can be varied depending upon the route of administration and desired dosage. Such formulations may influence the physical state, stability, rate of in vivo release, and rate of in vivo clearance of the administered active ingredient. 
     The pharmaceutical compositions of the present invention may be formulated in dosage unit form for ease of administration and uniformity of dosage. The expression “unit dosage form”, as used herein, refers to a physically discrete unit of an anti-Claudin-1 antibody, or a biologically active fragment thereof, for the patient to be treated. It will be understood, however, that the total daily dosage of the compositions will be decided by the attending physician within the scope of sound medical judgement. 
     A. Formulation 
     Injectable preparations, for example, sterile injectable aqueous or oleaginous suspensions may be formulated according to the known art using suitable dispersing or wetting agents, and suspending agents. The sterile injectable preparation may also be a sterile injectable solution, suspension or emulsion in a non-toxic parenterally acceptable diluent or solvent, for example, as a solution in 2,3-butanediol. Among the acceptable vehicles and solvents that may be employed are water, Ringer&#39;s solution, U.S.P. and isotonic sodium chloride solution. In addition, sterile, fixed oils are conventionally employed as a solution or suspending medium. For this purpose, any bland fixed oil can be employed including synthetic mono- or di-glycerides. Fatty acids such as oleic acid may also be used in the preparation of injectable formulations. Sterile liquid carriers are useful in sterile liquid form compositions for parenteral administration. 
     Injectable formulations can be sterilized, for example, by filtration through a bacterial-retaining filter, or by incorporating sterilizing agents in the form of sterile solid compositions which can be dissolved or dispersed in sterile water or other sterile injectable medium prior to use. Liquid pharmaceutical compositions which are sterile solutions or suspensions can be administered by, for example, intravenous, intramuscular, intraperitoneal or subcutaneous injection. Injection may be via single push or by gradual infusion. Where necessary or desired, the composition may include a local anesthetic to ease pain at the site of injection. 
     In order to prolong the effect of an active ingredient (here an anti-Claudin-1 antibody, or a biologically active fragment thereof), it is often desirable to slow the absorption of the ingredient from subcutaneous or intramuscular injection. Delaying absorption of a parenterally administered active ingredient may be accomplished by dissolving or suspending the ingredient in an oil vehicle. Injectable depot forms are made by forming micro-encapsulated matrices of the active ingredient in biodegradable polymers such as polylactide-polyglycolide. Depending upon the ratio of active ingredient to polymer and the nature of the particular polymer employed, the rate of ingredient release can be controlled. Examples of other biodegradable polymers include poly(orthoesters) and poly(anhydrides). Depot injectable formulations can also be prepared by entrapping the active ingredient in liposomes or microemulsions which are compatible with body tissues. 
     Liquid dosage forms for oral administration include, but are not limited to, pharmaceutically acceptable emulsions, microemulsions, solutions, suspensions, syrups, elixirs, and pressurized compositions. In addition to the anti-Claudin-1 antibody, or biologically active fragment thereof, the liquid dosage form may contain inert diluents commonly used in the art such as, for example, water or other solvents, solubilising agents and emulsifiers such as ethyl alcohol, isopropyl alcohol, ethyl carbonate, ethyl acetate, benzyl alcohol, benzyl benzoate, propylene glycol, 1,3-butylene glycol, dimethylformamide, oils (in particular, cotton seed, ground nut, corn, germ, olive, castor, and sesame oils), glycerol, tetrahydrofurfuryl alcohol, polyethylene glycols, and fatty acid esters of sorbitan and mixtures thereof. Besides inert diluents, the oral compositions can also include adjuvants such as wetting agents, suspending agents, preservatives, sweetening, flavouring, and perfuming agents, thickening agents, colors, viscosity regulators, stabilizes or osmo-regulators. Examples of suitable liquid carriers for oral administration include water (potentially containing additives as above, e.g., cellulose derivatives, such as sodium carboxymethyl cellulose solution), alcohols (including monohydric alcohols and polyhydric alcohols such as glycols) and their derivatives, and oils (e.g., fractionated coconut oil and  arachis  oil). For pressurized compositions, the liquid carrier can be halogenated hydrocarbon or other pharmaceutically acceptable propellant. 
     Solid dosage forms for oral administration include, for example, capsules, tablets, pills, powders, and granules. In such solid dosage forms, an anti-Claudin-1 antibody, or a biologically active fragment thereof, may be mixed with at least one inert, physiologically acceptable excipient or carrier such as sodium citrate or dicalcium phosphate and one or more of (a) fillers or extenders such as starches, lactose, sucrose, glucose, mannitol, and silicic acid; (b) binders such as, for example, carboxymethylcellulose, alginates, gelatine, polyvinylpyrrolidone, sucrose, and acacia; (c) humectants such as glycerol; (d) disintegrating agents such as agar-agar, calcium carbonate, potato or tapioca starch, alginic acid, certain silicates, and sodium carbonate; (e) solution retarding agents such as paraffin; absorption accelerators such as quaternary ammonium compounds; (g) wetting agents such as, for example, cetyl alcohol and glycerol monostearate; (h) absorbents such as kaolin and bentonite clay; and (i) lubricants such as talc, calcium stearate, magnesium stearate, solid polyethylene glycols, sodium lauryl sulphate, and mixtures thereof. Other excipients suitable for solid formulations include surface modifying agents such as non-ionic and anionic surface modifying agents. Representative examples of surface modifying agents include, but are not limited to, poloxamer 188, benzalkonium chloride, calcium stearate, cetostearyl alcohol, cetomacrogol emulsifying wax, sorbitan esters, colloidal silicon dioxide, phosphates, sodium dodecylsulfate, magnesium aluminum silicate, and triethanolamine. In the case of capsules, tablets and pills, the dosage form may also comprise buffering agents. 
     Solid compositions of a similar type may also be employed as fillers in soft and hard-filled gelatine capsules using such excipients as lactose or milk sugar as well as high molecular weight polyethylene glycols and the like. The solid dosage forms of tablets, dragees, capsules, pills, and granules can be prepared with coatings and shells such as enteric coatings, release controlling coatings and other coatings well known in the pharmaceutical formulating art. They may optionally contain opacifying agents and can also be of a composition such that they release the active ingredient(s) only, or preferably, in a certain part of the intestinal tract, optionally, in a delaying manner. Examples of embedding compositions which can be used include polymeric substances and waxes. 
     In certain embodiments, it may be desirable to administer an inventive composition locally to an area in need of treatment (e.g., the lung, the kidney or the skin). This may be achieved, for example, and not by way of limitation, by local infusion during surgery (e.g., transplantation), topical application, by injection, by means of a catheter, by means of a stent or other implant or yet by means of an inhaler. 
     For topical administration, the composition may preferably be formulated as a gel, an ointment, a lotion, or a cream which can include carriers such as water, glycerol, alcohol, propylene glycol, fatty alcohols, triglycerides, fatty acid esters, or mineral oil. Other topical carriers include liquid petroleum, isopropyl palmitate, polyethylene glycol, ethanol (95%), polyoxyethylenemonolaurat (5%) in water, or sodium lauryl sulphate (5%) in water. Other materials such as antioxidants, humectants, viscosity stabilizers, and similar agents may be added as necessary. 
     In addition, in certain instances, it is expected that the pharmaceutical compositions may be disposed within transdermal devices placed upon, in, or under the skin. Such devices include patches, implants, and injections which release the active ingredient by either passive or active release mechanisms. Transdermal administrations include all administration across the surface of the body and the inner linings of bodily passage including epithelial and mucosal tissues. Such administrations may be carried out using the present compositions in lotions, creams, foams, patches, suspensions, solutions, and suppositories (rectal and vaginal). 
     Transdermal administration may be accomplished through the use of a transdermal patch containing an active ingredient (i.e., an anti-Claudin-1 antibody, or a biologically active fragment thereof) and a carrier that is non-toxic to the skin, and allows the delivery of the ingredient for systemic absorption into the bloodstream via the skin. The carrier may take any number of forms such as creams and ointments, pastes, gels, and occlusive devices. The creams and ointments may be viscous liquid or semisolid emulsions of either the oil-in-water or water-in-oil type. Pastes comprised of absorptive powders dispersed in petroleum or hydrophilic petroleum containing the active ingredient may be suitable. A variety of occlusive devices may be used to release the active ingredient into the bloodstream such as a semi-permeable membrane covering a reservoir containing the active ingredient with or without a carrier, or a matrix containing the active ingredient. 
     Suppository formulations may be made from traditional materials, including cocoa butter, with or without the addition of waxes to alter the suppository&#39;s melting point, and glycerine. Water soluble suppository bases, such as polyethylene glycols of various molecular weights, may also be used. 
     Materials and methods for producing various formulations are known in the art and may be adapted for practicing the subject invention. Suitable formulations for the delivery of antibodies can be found, for example, in “ Remington&#39;s Pharmaceutical Sciences ”, E. W. Martin, 18 th  Ed., 1990, Mack Publishing Co.: Easton, Pa. 
     B. Additional Biologically Active Agents 
     In certain embodiments, an anti-Claudin-1 antibody, or a biologically active fragment thereof, is the only active ingredient in a pharmaceutical composition of the present invention. In other embodiments, the pharmaceutical composition further comprises one or more biologically active agents. Examples of suitable biologically active agents include, but are not limited to, therapeutic agents such as anti-viral agents, anti-inflammatory agents, immunomodulatory agents, analgesics, antimicrobial agents, kinase inhibitors, signalling inhibitors, antibacterial agents, antibiotics, antioxidants, antiseptic agents, and combinations thereof. Examples of other suitable biologically active agents include the therapeutic agents suitable for the treatment of pulmonary fibrosis and for the treatment of kidney fibrosis, pulmonary fibrosis or skin fibrosis, such as those listed above. 
     In such pharmaceutical compositions, the anti-Claudin-1 antibody and additional therapeutic agent(s) may be combined in one or more preparations for simultaneous, separate or sequential administration of the anti-Claudin-1 antibody and therapeutic agent(s). More specifically, an inventive composition may be formulated in such a way that the antibody and therapeutic agent(s) can be administered together or independently from each other. For example, an anti-Claudin-1 antibody and a therapeutic agent can be formulated together in a single composition. Alternatively, they may be maintained (e.g., in different compositions and/or containers) and administered separately. 
     C. Pharmaceutical Packs of Kits 
     In another aspect, the present invention provides a pharmaceutical pack or kit comprising one or more containers (e.g., vials, ampoules, test tubes, flasks or bottles) containing one or more ingredients of an inventive pharmaceutical composition, allowing administration of an anti-Claudin-1 antibody, or a biologically active fragment thereof. 
     Different ingredients of a pharmaceutical pack or kit may be supplied in a solid (e.g., lyophilized) or liquid form. Each ingredient will generally be suitable as aliquoted in its respective container or provided in a concentrated form. Pharmaceutical packs or kits may include media for the reconstitution of lyophilized ingredients. Individual containers of the kits will preferably be maintained in close confinement for commercial sale. 
     In certain embodiments, a pharmaceutical pack or kit includes one or more additional therapeutic agent(s) as described above. Optionally associated with the container(s) can be a notice or package insert in the form prescribed by a governmental agency regulating the manufacture, use or sale of pharmaceutical or biological products, which notice reflects approval by the agency of manufacture, use or sale for human administration. The notice of package insert may contain instructions for use of a pharmaceutical composition according to methods of treatment disclosed herein. 
     An identifier, e.g., a bar code, radio frequency, ID tags, etc., may be present in or on the kit. The identifier can be used, for example, to uniquely identify the kit for purposes of quality control, inventory control, tracking movement between workstations, etc. 
     EXAMPLES 
     The following examples describe some of the preferred modes of making and practicing the present invention. However, it should be understood that the examples are for illustrative purposes only and are not meant to limit the scope of the invention. Furthermore, unless the description in an Example is presented in the past tense, the text, like the rest of the specification, is not intended to suggest that experiments were actually performed or data are actually obtained. 
     Example 1: Anti-Claudin-1 Monoclonal Antibody Biodistribution In Vivo 
     Materials and Methods 
     Reagents and Antibodies. The anti-Claudin-1 monoclonal antibody (anti-CLDN1 mAb-OM-7D3-B3) was produced as previously described (Fofana et al., Gastroenterology, 2010, 139: 953-964, e1-4). Control mAb (rat IgG2b clone LTF-25, Bio X Cell) was also used. 
     Research Experiment on Live Vertebrates. In vivo experiments were performed in the INSERM Unit 1110 animal facility according to local laws following ethical committee approval (CREMEAS, project numbers AL/02/19/08/12 and AL/01/18/08/12). 
     Antibody biodistribution. The antibodies were labeled with Alexa-fluor 750 (RD-Biotech, Besangon, France). Eight week-old Balb/c mice were injected intraperitoneally with 500 μg of Alexa-fluor 750-labeled CLDN1-specific or control mAb. Organs were harvested 24 hours and 48 hours as previously described (Krieger et al., Hepatology, 2010, 51: 1144-1157) and ex vivo organ-specific fluorescence was detected with an IVIS Lumina 50 (Xenogen-Caliper-Perkin-Elmer) and expressed as average efficiency. 
     Statistical Analyses. The Mann-Whitney test was used. A p-value &lt;0.05 was considered significant. Statistical analyzes were performed with GraphPad Prism 6 software. 
     Results 
     Anti-Claudin-1 Antibody Biodistribution. The present Inventors have measured the in vivo biodistribution of the anti-CLDN1 monoclonal antibody in Balb/c mice and compared it to a control monoclonal antibody. The results presented in  FIG.  1    show that an enrichment in the anti-CLDN1 monoclonal antibody was observed in skin, kidneys, lungs, intestines and liver (see  FIG.  1 (A)  measured at 24 hours and  FIG.  1 (B)  measured at 48 hours) (Mailly et al., Nature Biotechnol. 2015, 33(5): 549-554). 
     Example 2: In Vivo Efficacy of an Anti-Claudin-1 Monoclonal Antibody in Preventing Fibrosis in a Bleomycin-Induced Pulmonary Fibrosis Model 
     Materials and Methods Protocol to Examine the Effects of an anti-human CLDN1 Monoclonal Antibody in Preventing Fibrosis in a Bleomycin-Induced Pulmonary Fibrosis Model. Pathogen-free 6 weeks old female C57BL/6Jmice were obtained from Japan SLC, Inc. (Japan). At Day 0, 54 mice were induced to develop pulmonary fibrosis by a single intratracheal administration of bleomycin hydrochloride (BLM, Nippon Kayaku, Japan) in saline at a dose of 3.0 mg/kg, in a volume of 50 μL per animal using Microsprayer® (Penn-Century, USA). In each slot, the mice were randomized into 3 groups of 18 mice based on their body weight on the day before the start of treatment at Day 0. Individual body weights were measured daily during the experimental period. Survival, clinical signs and behaviour of mice were monitored daily. 
     Mice groups. Group 1 (Vehicle): Eighteen bleomycin-induced pulmonary fibrosis model mice were intraperitoneally administered vehicle [Saline] in a volume of 5 mg/kg once weekly from Day 0 to 20. Group 2 (Anti CLDN1 Ab): Eighteen bleomycin-induced pulmonary fibrosis model mice were intraperitoneally administered vehicle supplemented with Anti CLDN1 Ab at a dose of 500 μg/mouse once weekly from Day 0 to 20. Group 3 (Dexamethasone): Eighteen bleomycin-induced pulmonary fibrosis model mice were orally administered pure water supplemented with Dexamethasone at a dose of 0.25 mg/kg (in a volume of 10 mL/kg) once daily from Day 0 to 20. Mice in all groups were sacrificed at Day 21. 
     Survival, biochemical and histological analysis. Mice in all groups were sacrificed at Day 21 for the Survival and histological essays. Survival curves were established using the Kaplan-Meier survival method and compared using the Log Rank Test. Histological analysis for lung sections was performed according to a routine method: Masson&#39;s Trichrome staining and estimation of Ashcroft score. 
     Statistical tests. Statistical tests were performed using Kruskal-Wallis test. P values &lt;0.05 were considered statistically significant. 
     The study design is summarized in  FIG.  2 (A) . 
     Results 
     The anti-CLDN1 mAb group showed a significant decrease in the Ashcroft score compared with the Vehicle group (respective mean±SD were 3.9±1.5 and 2.8±0.9, p&lt;0.05). The Ashcroft score in the Dexamethasone group tended to decrease compared with the Vehicle group ( FIG.  2 (B) ). Representative photomicrographs of Masson&#39;s Trichrome-stained lung sections are shown in  FIG.  2 (C) . 
     During the treatment period, mice found dead before reaching Day 21 were as follows; four out of 18 mice were found dead in the Vehicle group. Five out of 18 mice were found dead in the Anti-CLDN1 mAb group. Ten out of 18 mice were found dead in the Dexamethasone group. The Dexamethasone group showed a significant decrease in survival rate compared with the Vehicle group. There was no significant difference in survival rate between the Vehicle group and the Anti CLDN1 Ab group ( FIG.  2 (D) ). 
     Body weight was expressed as percentage of body weight change from baseline (Day 0). Mean body weight changes of the Dexamethasone group were significantly lower than that of the Vehicle group at Day 4-16, 18, 19 and 21. There were no significant differences in mean body weight changes at any day during the study period between the Vehicle group and the Anti CLDN1 Ab group ( FIG.  2 (E) ). 
     Example 3: In Vivo Efficacy of an Anti-Claudin-1 Monoclonal Antibody in Treating Fibrosis in a Bleomycin-Induced Pulmonary Fibrosis Model 
     Materials and Methods 
     Protocol to Examine the Effects of anti-human CLDN1 Monoclonal Antibody in Treating Fibrosis in a Bleomycin-Induced Pulmonary Fibrosis Model. Pathogen-free 6 weeks old female C57BL/6Jmice will be obtained from Japan SLC, Inc. (Japan). On Day 0, 54 mice were anesthetized with pentobarbital sodium (Kyoritsu Seiyaku, Japan) and intratracheally administered bleomycin (Lot #771840, Nippon Kayaku, Japan) in saline at a dose of 3 mg/kg, in a volume of 50 μL per animal using a Microsprayer® (Penn-Century, USA). The mice were transferred to a clean cage (resting cage) and kept until recovery from anesthesia. The bleomycin administration took place on two separate days, with equal numbers of mice assigned to each day. In each slot, bleomycin-induced pulmonary fibrosis model mice were randomized into 3 groups of 18 mice based on their body weight changes on the day before the start of treatment at Day 7. Survival, clinical signs and behaviour of mice were monitored daily. 
     Mice groups. Group 1 (Vehicle): Eighteen bleomycin-induced pulmonary fibrosis model mice were intraperitoneally administered vehicle [Saline] in a volume of 5 mg/kg once weekly from Day 7 to 20. Group 2 (Anti CLDN1 Ab): Eighteen bleomycin-induced pulmonary fibrosis model mice were intraperitoneally administered vehicle supplemented with Anti CLDN1 Ab at a dose of 500 μg/mouse once weekly from Day 7 to 20. Group 3 (Nintedanib): Eighteen bleomycin-induced pulmonary fibrosis model mice were orally administered pure water supplemented with Nintedanib at a dose of 100 mg/kg (in a volume of 10 mL/kg) once daily from Day 7 to 20. Mice in all groups were sacrificed at Day 21 for the following assays. 
     Survival, biochemical and histological analysis. Mice in all groups were sacrificed at Day 21 for the Survival and histological essays. Survival curves were established using the Kaplan-Meier survival method and compared using the Log Rank Test. Lung hydroxyproline content was assessed according to a routine method. 
     Statistical tests. Statistical tests were performed using Kruskal-Wallis test. P values &lt;0.05 will be considered statistically significant. 
     The study design is summarized in  FIG.  3 (A) . 
     Results 
     The anti-CLDN1 mAb group showed a significant decrease in the lung hydroxyproline levels compared with the Vehicle group (respective mean±SD were 52±8.3 and 45.3±8.4, p&lt;0.05). The lung hydroxyproline levels in the Nintedanib group tended to decrease compared with the Vehicle group (mean±SD 51.3±9.0, see  FIG.  3 (B) ). 
     Representative photomicrographs of Masson&#39;s Trichrome-stained lung sections are shown in  FIG.  3 (C) . 
     There were no significant differences in survival rate and body weight between the Vehicle group and the treatment groups (see  FIG.  3   (D-E)). 
     Example 4: Assessment of an Anti-Claudin-1 Monoclonal Antibody for Therapeutic Applications in Lung and Kidney Fibrosis 
     To study the therapeutic potential applications of CLDN1-specific mAb for lung and kidney fibrosis, the present inventors have assessed the binding of CLDN1-specific mAb to cells from a kidney cell line (RPTEC/TERT1) and a lung cell line (A549). Furthermore, they have assessed the induction and reversal of the progressive liver signature and TGF-β signalling in A549 lung cells. 
     Materials and Methods 
     Cell Lines. The kidney cancer cell line RPTEC/TERT1 and lung cancer cell line A549, both originally from ATCC, were obtained from IGBMC in a collaboration with Dr. Irwin Davidson and Dr. Izabella Sumara, respectively. Both cell lines were cultured according to provider&#39;s instructions: the RPTEC/TERT1 kidney cancer cells were grown in ATCC-formulated DMEM:F12 Medium supplemented with hTERT RPTEC Growth Kit and 0.1 mg/mL G418. The A549 lung cancer cells were grown in ATCC-formulated F-12K Medium supplemented with 10% fetal bovine serum. 
     Binding Studies. Cells were de-attached using a solution of EDTA (4 mM) and re-suspended in PBS containing 1% FBS at 4° C. Then, 150,000 cells were incubated with increasing concentrations of the humanized H3L3 CLDN1-specific mAb (see WO/2017/162678) and the binding signals were read by flow cytometry after incubation with PE-labelled anti-human using a dilution of 1:100 and analyzed with Cytoflex and FlowJo V10. Two washes with PBS containing 1% FBS were performed after every antibody incubation. A binding curve for each cell line was built using the PE median fluorescence intensity (MFI) and the K d  of the interaction was calculated by applying the Michaelis-Menten mathematical model in R 3.5.1. 
     PLS Studies. A549 cells were seeded on a 12 well plate (30,000 cell/well) and incubated with or without TGF-β (5 ng/mL) (Peprotech) and CLDN1-specific mAb (20 μg/mL) for 24 hours. Subsequently, RNA was extracted using the Promega Reliaprep kit and 125 nm were used to determine the induction of the PLS using nCounter Nanostring. 
     TGF-β Signaling Reporter Assay. A549 cells were transfected with TGF-β signalling reporter plasmid pGLA4.48[luc2P/SBE/Hygro] (Promega) using Fugene according to the manufacturer&#39;s instructions. Following transfection, the cells were supplemented with fresh medium containing control or CLDN1-specific mAb (50 μg/mL) for 3 hours at 37° C. Fresh medium was supplemented to the cells containing TGF-β (10 ng/mL) (Sigma) for 3 hours at 37° C. The plate was incubated for 15 minutes at room temperature followed by addition of ONE-Glo substrate (Promega) for 3 minutes at room temperature. Luminescence of the supernatants was read using a Berthold microplate reader. 
     Results 
     CLDN1 mAb binds to CLDNA expressed on RPTEC/TERT1 kidney and A549 lung cell lines. CLDN1 mAb was found to saturate the epitope of both cell lines: 50 μg/mL for the kidney cancer cell line RPTEC/TERT1 ( FIG.  4 (A) ) and 20 mg/mL for the lung cancer cell lineA549 ( FIG.  4 (B) ), hence resulting in a K d  of 53 ( FIG.  4 (C) ) and 16.3 nM ( FIG.  4 (D) ), respectively. These results confirm that CLDN1-specific mAb is able to bind to CLDN1 expressed by kidney and lung cells. 
     CLDN1 nAb reverses fibrosis-related poor-prognosis status of the PLS in A549 lung cell line. To further investigate the functional role of CLDN1 as a driver for fibrosis and carcinogenesis, the present inventors have assessed whether CLDN1 mAb modulates the expression of the clinical PLS, a 32-gene signature predictive of fibrosis and liver disease progression, cancer risk and mortality in patients (Hoshida et al., N. Engl. J. Med., 2008, 359: 1995-2004; Hoshida et al., Gastroenterology, 2013, 144: 1024-1030; King et al., Gut, 2015, 64: 1296-1302; Nakagawa et al., Cancer Cell, 2016, 30: 879-890; Goossens et al., Clin. Gastroenterol. Hepatol., 2016, 14: 1619-1628). The A549 cell line is known to induce the clinical PLS without the presence of a stress inducer (FDR=0.018 for poor prognosis genes and 0.012 for good prognosis genes). Treatment with CLDN1 mAb for 24 hours resulted in the reversal of the clinical PLS (FDR=0.094 for poor prognosis genes and 0.095 for good prognosis genes) ( FIG.  5 (A) ). Two PLS poor prognosis genes (SERPINB2 and FMO1) were significantly down-regulated following CLDN1-specific mAb with fold changes less than 1.5 ( FIG.  5 (B) ). These data suggest that CLDN1 acts as a driver for the poor prognosis of the clinical PLS in a lung fibrosis cell line model and support the potential role of CLDN1 mAb as a candidate therapeutic target. 
     CLDN1 nAb reduces TGF-b signalling in A549 lung cells. TGF-β is essential for the differentiation of lung fibroblasts into myofibroblasts which is a key step in the development of tissue fibrosis. Moreover, increased expression of TGF-β has been reported in fibrotic lungs. TGF-β contributes to the ECM production including collagen, laminin, and fibronectin (Saito et al., Int. J. Mol. Sci., 2018, 19(8): 2460). To further investigate the effect of CLDN1-specific mAb on TGF-β signalling in lung cells, transfected SBE (TGF-β signalling reporter plasmid) A549 cells were treated with TGF-β (10 ng/mL) and CLDN1-specific mAb resulted in significant reduction in TGF-β reporter activity ( FIG.  5 (B) ). 
     Conclusion 
     CLDN1-specific mAb binds to CLDN1-expressing cells from kidney (RPTEC/TERT1) and lung (A549) cell lines. Furthermore, it modulates the reversal of PLS, predictive of fibrosis, in A549 cells. This suggests a role of CLDN1-specific mAb in alleviating fibrosis progression. Lastly, it was shown that CLDN1 mAb reduces TGF-β signalling, a crucial pathway for lung fibrosis. Altogether, these data suggest the potential therapeutic effect of CLDN1-specific mAb for lung and kidney fibrosis. 
     Example 5: Assessment of an Anti-Claudin-1 Monoclonal Antibody for Therapeutic Applications in Skin Fibrosis—BLM-Induced Skin Fibrosis Model 
     Systemic sclerosis (SSc) is a chronic connective tissue disease of unknown cause. It is characterized by fibrosis of the skin and internal organs. Most patients develop tissue fibrosis and organ dysfunction in the late stages of SSc, which results in increased mortality. Symptomatic treatments of SSc are currently limited, and causal therapies have been long awaited. 
     Bleomycin (BLM)-induced skin fibrosis model is a well characterized disease model for skin fibrosis and commonly used for studying biological pathways of SSc. The BLM model encompasses key pathophysiological features of SSc: epidermal hypertrophy and dermal fibrosis, which makes this model attractive for a simple proof-of-concept study for SSc, or in vivo screening for anti-fibrosis molecules (Yamamoto et al., J. Invest. Dermatol, 1999, 112: 456). 
     Materials and Methods 
     BLM Model and Sampling. As indicated on the scheme presented on  FIG.  6   , the BLM is subcutaneously injected every other day into the pre-shaved back of mice for 4 weeks. The injection sites are located at the corners of a 1.5 cm 2 -square shaved area and used in rotation (corner 1, corner 2, corner 3, corner 4, corner 1, etc). A 5-mm circle is clipped using a dermal punch and used for collagen quantification. The remaining intact area is cut out into 3 rectangles, one for histology and two for biochemical analyses. HE staining of skin samples from BLM-induced skin fibrosis model shows an increased thickness 28 days after the BLM injections. In parallel, the subcutaneous adipose layer shows atrophy and shrinkage. 
     Effects of Imatinib on Skin Fibrosis. Imatinib mesylate is a tyrosine kinase inhibitor against c-Abl, PDGFR, and several other tyrosine kinases (Alfiya et al., Arthritis Rheum., 2009, 60: 219). c-Abl is crucial for induction of ECM proteins through the TGF-β pathway. Its inhibition may reduce the synthesis of EMC components. Imatinib interferes with PDGF signalling by blocking the tyrosine kinase activity of PDGFR (Alfiya et al., Arthritis Rheum., 2009, 60: 219). The study design is presented on  FIG.  7   . 
     Results 
     The results obtained are presented on  FIG.  8   . Imatinib was found to induce a significant decrease in dermal thickness and in the skin fibrosis area. 
     A similar experiment will be carried out using the CLDN1-specific mAb instead of Imatinib. 
     Example 6: Divergent Mechanisms Involved in Anti-CLDN1 mAb-Mediated Antifibrotic Effects in Kidney and Lung Compared to Liver 
     Considering the well-established role of CLDN1 in epithelial-mesenchymal transition (EMT) (Stebbing et al., Oncogene, 2013, 32: 4671-4872; Shiozaki et al., PLoS One, 2012, 7: e38049; Suh et al., Oncogene, 2013, 32: 4873-4882; Zhang et al., Oncotarget, 2016, 7: 87449-87461) as well as its association with fibrotic diseases in the liver, the present Inventors aimed at investigating the role of CLDN1 as a driver and therapeutic target for kidney and lung fibrosis by CLDN1 expression analysis in clinical cohorts of patients with chronic kidney and lung disease, assessment of the effects of an anti-CLDN1 mAb in animal models as well as by perturbation studies on patient-derived fibroblasts. 
     Materials and Methods 
     Immunofluorescence. For immunofluorescence characterization of lung and kidney fibroblasts, cells were seeded onto 8-chamber cover glasses (Lab-Tek II #1.5, Sigma-Aldrich). The next day, the cells were washed twice with PBS and fixed with 4% PFA for 15 minutes at room temperature, followed by permeabilization with 0.1×Triton-X for 10 minutes. After two washing steps, the cells were blocked for 30 minutes with 10% FBS. Primary antibody staining with anti-α-SMA Ab (1:100, ab5694, Abcam, France) and anti-CLDN1 mAb H3L3 or control mAb Motavizumab (10 μg/mL, respectively) was performed overnight at 4° C. The cells were washed with PBS and incubated with goat anti-human Alexa Fluor 488 and goat anti-rabbit Alexa Fluor 647 secondary antibodies (Jackson, United Kingdom) at a dilution of 1:200. Nuclear staining was carried out using DAPI (1 μg/mL) and the cells were visualized using epi-fluorescence microscopy. 
     Perturbation Studies on Lung and Kidney Fibroblasts. Primary human diseased lung parenchymal fibroblasts, derived from an IPF patient (#HPCPFIPF-05, BioIVT) and kidney fibroblasts (#P10666, Innoprot) were seeded at 5×10 4  cells/cm 2  in 12 well plates and either treated with TNFα (10 ng/ml), TNFα (10 ng/ml)+IKK16 (1 μM) or vehicle control for 24 hours followed by flow-cytometric analysis of the anti-CLDN1 mAb binding or incubated with the anti-CLDN1 mAb or the isotype control (50 μg/mL, respectively) for 3 days for subsequent genome-wide RNAseq analysis. 
     Flow Cytometry. Membranous expression of human CLDN1 on lung and kidney fibroblasts was analyzed by flow cytometry. Briefly, 100,000 cells per condition were stained in triplicate using humanized CLDN1-specific antibody H3L3 (10 μg/mL). A control isotype mAb was used as negative control. Primary antibodies were detected using a PE-conjugated human-specific secondary antibody. Data were acquired using Cytoflex B2R2V0 (Beckman Coulter) and analyzed using CytExpert 2.1 and FlowJo v10 (Beckman Coulter). CLDN1 expression was calculated as the difference of the mean fluorescence intensities of cells stained with the CLDN1-specific antibody and cells stained with the control IgG 
     Genome-wide RNA-Seq Analyses. RNA-Seq libraries were generated from 300 ng of total RNA using TruSeq Stranded mRNA Sample Preparation Kit (Illumina, Part Number RS-122-2101). Briefly, following purification with poly-T oligo attached magnetic beads, the mRNA was fragmented using divalent cations at 94° C. for 2 minutes. The cleaved RNA fragments were copied into first strand cDNA using reverse transcriptase and random primers. Strand specificity was achieved by replacing dTTP with dUTP during second strand cDNA synthesis using DNA Polymerase I and RNase H. Following addition of a single ‘A’ base and subsequent ligation of the adapter on double stranded cDNA fragments, the products were purified and enriched with PCR (30 seconds at 98° C.; [10 seconds at 98° C., 30 seconds at 60° C., 30 seconds at 72° C.]×12 cycles; 5 minutes at 72° C.) to create the cDNA library. Surplus PCR primers were further removed by purification using AMPure XP beads (Beckman Coulter) and the final cDNA libraries were checked for quality and quantified using 2100 Bioanalyzer (Agilent). Libraries were sequenced on the Illumina HiSeq 4000 as Single-Read 50 base reads following Illumina&#39;s instructions. Image analysis and base calling were performed using RTA v2.7.3 and bcl2fastq v2.17.1.14. Reads were mapped using HISAT2 (Kim et al., Nature Methods, 2015, 12: 357-360) to the human genome hg19. 
     Bioinformatic and Statistical Analysis. CLDN1 gene expression in cohorts of lung and kidney disease (kidney disease: GSE115857 and GSE129973; lung fibrosis: GSE2052 (Pardo et al., PLoS Med, 2005, 2; e251) were compared using the Students&#39; t-test. Expression of EMT markers in anti-CLDN1 mAb or Control mAb treated lung fibroblasts was derived from RNA-seq data and read counts were compared using Students&#39; t-test. Results with a p-value &lt;0.05 were considered statistically significant. For statistical analysis of RNA-seq pathway analysis, lung myofibroblast activation (Peyser et al., Am. J. Respir. Cell. Mol. Biol., 2019, 61: 74-85) and EMT (HALLMARK_EPITHELIAL_MESENCHYMAL_TRANSITION and BUDHU_LIVER_CANCER_METASTASIS_UP (Budhu et al., Cancer Cell, 2006, 10: 99-111) were assessed by Gene Set Enrichment Analysis (GSEA) or GSEA-Preranked with FDR&lt;0.25 (Subramanian et al., Proc. Natl. Acad. Sci., USA, 2005, 102: 15545-15550. 
     Results 
     To investigate the relevance of CLDN1 as a therapeutic target in renal and lung fibrosis patients, the present Inventors analyzed its expression in patients with chronic kidney diseases as well as patients with chronic lung disease associated with fibrosis. 
     CLDN1 Gene Expression is Associated with Chronic Kidney Disease. CLDN1 is overexpressed in focal segmental glomerulosclerosis due to diabetic nephropathy—the leading cause of end-stage renal failure and kidney fibrosis (Calle et al., Int. J. Mol. Sci., 2020, 21: 2806; Hasegawa et al., Nature Med., 2013: 19: 1496-1504). CLDN1 was found to be upregulated in patients with glomerulonephritis, suggesting an involvement of CLDN1 in the pathogenesis of chronic kidney disease ( FIG.  9 (A) ). 
     CLDN1 Gene Expression is Associated with Lung Fibrosis. Supporting implication of CLDN1 in fibrogenesis across organs CLDN1 was further overexpressed in patients with idiopathic pulmonary fibrosis (IPF) ( FIG.  9 (B) ). Collectively, these data indicate implication of CLDN1 in chronic fibrogenic disease across organs. 
     To address the mechanism of action, the present Inventors have characterized kidney and lung myofibroblasts in terms of CLDN1 expression. As shown in  FIGS.  10 (A)  and (B), the anti-CLDN1 mAb specifically binds to CLDN1 expressed on lung fibroblasts as well as on kidney fibroblasts. Moreover, membranous CLDN1 expression accessible to the anti-CLDN1 mAb was found to be regulated via TNFα-NFκB in both kidney ( FIG.  10 (C) , left panel) and lung fibroblasts ( FIG.  10 (D) , right panel), similar to the liver. 
     Functional assessment of a recently characterized gene set of lung fibroblast activation markers (Peyser et al., Am. J. Respir. Cell Mol. Biol., 2019, 61: 74-85) in anti-CLDN1 mAb- or Control mAb-treated lung fibroblasts by RNAseq and GSEA, revealed marked antifibrotic effects of the anti-CLDN1 mAb ( FIG.  10 (D) ). Moreover, the anti-CLDN1 mAb was found to significantly inhibit EMT programming in lung fibroblasts, suggesting potential divergent mechanisms involved in anti-CLDN1 mAb-mediated antifibrotic effects in kidney and lung compared to the liver ( FIG.  10 (D) , right panel). In fact, EMT markers, such as Fibronectin and N-Cadherin, and the transcriptional regulatory factor SNAI2 (SLUG) were found to be markedly and significantly downregulated in anti-CLDN1 mAb-treated lung fibroblasts ( FIG.  10 (E) ). 
     Example 7: Glomerular Parietal Epithelial Cells as Novel Therapeutic Target for Chronic Kidney and Renal Fibrosis, and Effects of CLDN1-Specific 
     Monoclonal Antibody (H3L3) on Glomerular Parietal Epithelial Cells Phenotype for Treatment of Chronic Kidney Disease Chronic kidney disease (CKD) represents a heterogenous group of disorders characterized by irreversible alterations in the structure and function of the kidney over months or years (Webster et al., The Lancet, 2017, 389: 1238-1252). Diabetes and hypertension are the main causes of CKD in all high-income and middle-income countries, and many low-income countries. Irrespective of its underlying etiology, chronic kidney disease is characterized by progressive and irreversible nephron loss, chronic inflammation and fibrosis with reduced regenerative capacity of the kidney, leading to end-stage renal disease and/or death (Bábíčková et al., Kidney Int., 2017, 91: 70-85). People with CKD have diminished quality of life, and poorer socioeconomic circumstances as disease progresses. Current therapies have limited effectiveness, only delaying disease progression, and helping control the signs and symptoms. Moreover, despite significant progress, there is no effective treatment for preventing renal fibrosis (Ruiz-Ortega et al., Nature Rev. Nephrol., 2020, 16: 269-288). Novel targets and therapies are therefore urgently needed. 
     Glomerular diseases are the leading causes of end-stage kidney disease. The glomerulus is a network of specialized capillaries located at the beginning of a nephron. The urinary space of the glomerulus is surrounded by a basement membrane known as the Bowman&#39;s capsule onto which a monolayer of glomerular parietal epithelial cells (PECs) adheres ( FIG.  11   ). The basement membrane, the PECs and another specialized cell type named podocytes constitute the glomerular filtration barrier, which filter the water and solutes from the blood (Kitching et al., Clin. J. Am. Soc. Nephrol., 2016, 11: 1664-1674). Glomerular cells are critical to normal physiology but are targets of a range of injurious processes. During the last decade, the role of PECs in glomerular disease progression has gained increasing attention (Shankland et al., Curr. Opin. Nephrol. Hypertens., 2013, 22: 302-309). Several studies demonstrated that PECs activation, migration and proliferation are involved in glomerulosclerosis by either producing excessive extracellular matrix proteins or by accumulating and leading to crescent formation (Smeets et al., J. Am. Soc. Nephrol., 2011, 22: 1262-1274; Kuppe et al., Kidney Int., 2019, 96: 80-93; Le Hir et al., Kidney Int., 2003, 63: 591-599). In addition, activated PECs produce pro-inflammatory molecules leading to infiltration of inflammatory cells (i.e., subsets of macrophages) which participate in glomerulosclerosis progression (Kanemoto et al., Lab. Invest., 2003, 83: 1615-1625; Djudjaj et al., J. Am. Soc. Nephrol., 2016, 27: 1650-1664; Garcia et al., Am. J. Pathol., 2003, 162: 1061-1073). PECs therefore appear as an attractive therapeutic target. However, the signaling pathways mediating activation and proliferation of PECs is still only partially understood. 
     Characterization of PECs have identified different markers distinguishing PECs from other glomerular cell types. These markers include CD44, a unique activated PECs marker, and Claudin 1 (CLDN1), a tight junction protein having an important role in blood filtration (Ohse et al., Am. J. Physiol.-Ren. Physiol., 2009, 297: F1566-F1574; Yu, J. Am. Soc. Nephrol., 2015, 26: 11-19). It was shown that glomerular cells expressing CD44 and CLDN1 participate in glomerulosclerosis (Smeets et al.,  J. Am. Soc. Nephrol.,  2011, 22: 1262-1274). Moreover, Hasegawa et al. demonstrated that CLDN1 overexpression in glomerulus is associated with severity of diabetic nephropathy and increased albuminuria, an early marker of renal damage (Hasegawa et al., Nature Med., 2013, 19: 1496-1504). CLDN1 overexpression may therefore have a pathogenic role in CKD development. Recently, the present Inventors&#39; lab developed a highly specific humanized monoclonal antibodies targeting CLDN1 for clinical prevention and cure of hepatitis C infection and for liver fibrosis treatment (Mailly et al., Nature Biotechnol., 2015, 33: 549-554; Fofana et al., Gastroenterology, 2010, 139: 953-964, 064.e1-4; Colpitts et al., Gut, 2017, 67(4): 736-745). Exploiting the potential pathogenic role of CLDN1-expressing PECs in CKD, the aim of the present study was to assess the effect of CLDN1-specific monoclonal antibody (H3L3) on PECs phenotype for treatment of CKD. 
     Materials and Methods 
     Reagents and Antibodies. Humanized anti-CLDN1 mAbs (H3L3) and Motavizumab (Mota) have been described (Colpitts et al., Gut, 2017, 67(4): 736-745) and were produced by Evitria, Schlieren. TNFα was purchased from Sigma. 
     Cells. Human Renal Epithelial Cells (HREpic) were purchased from ScienCell Research Laboratories and grown in Epithelial Cell Medium according to manufacturer&#39;s instructions. 
     H3L3 Treatment. For 2D-culture, cells were seeded in 24-well plates coated with Poly-L-Lysine at a cell density of 5.10 4  cells/well. After 24 hours, the cells were treated with TNFα 10 ng/mL and Mota (10 μg/mL) or H3L3 (10 μg/mL). After 3 days, the cells were again treated with TNFα and antibody for 3 more days. After 6 days of treatment in total, the cells were lysed to measure gene expression by qRT-PCR. For 3D-culture, cells were seeded in 96-well ultra-low attachment plates (Corning, Sigma Aldrich, France) at a cell density of 5×10 3  cells/well. The same treatment as described above was applied for 6 days. Cell viability was assessed by ATP quantification using CellTitreGlo (Promega) according to manufacturer&#39;s instructions. 
     Flow cytometry. H3L3 binding and expression of human CLDN1 in HREpic was analyzed by flow cytometry 24 hours after TNFα treatment (10 ng/mL). Briefly, 200,000 cells per conditions were stained using H3L3 (10 μg/mL) or Mota (10 μg/mL) used as negative control. Primary antibodies were detected using an Alexa fluor 647-conjugated human-specific secondary antibody. Data were acquired using Cytoflex B2R2V0 (Beckman Coulter) and analyzed using CytExpert 2.1 and FlowJo v10. CLDN1 expression is shown as the difference of the mean fluorescence intensities of cells stained with H3L3 and cells stained with Mota. 
     Gene Expression Analyses in Cell Culture Experiments. Total RNA extraction from 2D-cell cultures was performed using RNAeasy Mini Kit (Quiagen, France) according to the manufacturer&#39;s instructions. Subsequently, 250 ng of total RNA were reverse-transcribed (H Minus First Strand cDNA synthesis Mix, ThermoScientific, France) on a Thermocycler (Bio-Rad T100, Bio-Rad, Hercules, Calif., USA). Quantitative PCR was performed on the CFX96 Touch Real-Time PCR Detection system TaqMan gene expression Assays (ThermoFisher) according to the manufacturer&#39;s instructions. 
     Statistics. Data are presented as the mean±s.d. and were analyzed by the unpaired Student&#39;s t-test or the two-tailed Mann-Whitney test as indicated after determination of distribution by the Shapiro-Wilk normality test. All experiments were performed at least in triplicates for 2D-culture and quadruplicates for 3D-culture. Data are considered as significant at p&lt;0.05. Statistical analyzes for in vitro experiments were performed with GraphPad Prism 6 software. 
     Results 
     As in vitro model for parietal epithelial cells (PECs), the present Inventors used the Human Renal Epithelial Cells (HREpic), which are primary cell isolated from human kidney. They display a polarized morphology and recapitulate PECs function in cell culture, such as glucose absorption and cytokine production (ScienCell Research Laboratories). To investigate the role of CLDN1 as a therapeutic target in PECs for glomerular diseases and Chronic kidney disease (CKD), the present Inventors first subjected the cells to inflammatory stress using Tumor Necrosis Factor alpha (TNFα). Indeed, TNFα is a pleiotropic cytokine which plays important inflammatory roles in renal diseases such glomerulonephritis (Ernandez et al., Kidney Int., 2009, 76: 262-276). As shown in  FIG.  12 (A) , TNFα results in a marked increase of CLDN1 expression, which correlates with an increase in CD44 expression, a marker of activated PECs (Shankland et al., Curr. Opin. Nephrol. Hypertens., 2013, 22: 302-309). Moreover, PECs activation is shown by an increase in pro-inflammatory gene expression (IL6, TNFα and CCL2) ( FIG.  12 (B) ). Increase in CLDN1 expression upon inflammatory stress was also confirmed at the protein level ( FIG.  12 (C) ). The role of CLDN1 in PECs activation and pro-inflammatory/fibrotic gene expression was further demonstrated by a reduced TNFα and collagen 4A expression after CLDN1 knock-down ( FIG.  12 (D) ). Interestingly, the anti-CLDN1 mAb H3L3 binds to PECs CLDN1 as demonstrated by flow cytometry analysis ( FIG.  12 (E) ). Increase in CLDN1 expression upon inflammatory stress was also confirmed at the protein level ( FIG.  12 (C) ). As the present Inventors previously demonstrated that anti-CLDN1 mAb binds exclusively the non-junctional CLDN1 ((Mailly et al., Nature Biotechnol., 2015, 33: 549-554; Fofana et al., Gastroenterology, 2010, 139: 953-964, 064.e1-4; Colpitts et al., Gut, 2017, 67(4): 736-745), H3L3 most likely binds the extracellular loop of free CLDN1 at the PECs membrane. 
     As CLDN1 is overexpressed in activated PECs, the Inventors assessed the effect of H3L3 on PECs proliferation/viability in a 3D-culture model, which recapitulates cell-cell junction in a 3D system. As expected, they observed an increase in cell proliferation/viability upon TNFα treatment. Moreover, preliminary data showed a slight decrease in cell proliferation/viability after H3L3 treatment indicating that anti-CLDN1 mAb may act on PECs phenotype (see  FIG.  13 (A) ). This finding was further supported by a decrease in TNFα and CD44 expression after treatment with anti-CLDN1 mAb ( FIG.  13 (B) ). 
     Together these data demonstrate that CLDN1 overexpression in PECs is linked to inflammatory stress, cell proliferation and may play a role in the pathogenesis of CKD. CLDN1 present on PECs can be targeted by an anti-CLDN1 mAb for therapeutic purposes. Furthermore, from the data obtained, it can be concluded that, in kidney fibrosis, PECs are the target of the anti-CLDN1 mAb—a situation that is different from what happens in liver fibrosis. 
     Example 8: Expression of CLDN1 in Fibrosis Cohorts 
     To investigate the role of CLDN1 as a therapeutic target in different fibrotic diseases, the present Inventors analyzed its expression in patients with renal fibrosis, pulmonary fibrosis and inflammatory bowel disease (IBD). Analysis of CLDN1 gene expression levels in fibrotic diseases were retrieved from Gene Expression Omnibus database. 
     Materials and Methods 
     The gene expression data were downloaded from Gene Expression Omnibus GEO (website: www.ncbi.nlm.nih.gov/geo/). The data set of Unilateral Ureteral Obstruction (UUO) model was GSE60685 (Lovisa et al., Nature Med, 2105, 21: 998-1009); the data set of pulmonary fibrosis was GSE2052 (Pardo et al., PLoS Med., 2005, 2: e251), and of COVID219 was GSE15316. The data sets of inflammatory bowel diseases used in the present study were GSE9452 (Olsen et al., Inflamm. Bowel Dis., 2009, 15: 1032-1038), GSE38713 (Planell et al., Gut, 2013, 62: 967-976), and GSE38713 (Carey et al., Inflamm. Bowel Dis., 2008, 14: 446-457). These cohorts were selected following comprehensive database analysis, where the present Inventors identified CLDN1 gene as part of the microarray data. 
     Results 
     CLDN1 Gene Expression is Associated with Pulmonary Fibrosis. CLDN1 was shown to be overexpressed in pathological lung conditions associated with fibrosis and EMT changes (Kaarteenaho-Wilk et al., J. Histochem. Cytochem., 2009, 57: 187-195). To investigate the role of CLDN1 as a therapeutic target in pulmonary fibrosis patients, the present Inventors analyzed its expression in patients with lung fibrosis. CLDN1 was found to be overexpressed in patients with lung fibrosis, irrespective of the etiology ( FIG.  14 (A) ), indicating the implication of CLDN1 in fibrogenesis across organs. Of note, CLDN1 was also upregulated in lungs of patients with COVID19 disease ( FIG.  14 (B) ), the current global pandemic associated with high morbidity and mortality due to pulmonary complications, especially fibrosis (George et al., Lancet Respir. Med., 2020, 8: 807-815. 
     CLDN1 Gene Expression is Associated with Ulcerative Colitis. CLDN1 plays important role in intestinal signaling through modulating cell proliferation and inflammation (Garcia-Hernandez et al., Ann. N.Y. Acad. Sci., 2017, 1397: 66-79). Furthermore, CLDN1 has been shown to aggravate colitis and impairs recovery, increases dysplasia and inflammation (Gowrikumar et al., Oncogene, 2019, 38: 6566; Pope et al., Gut, 2014, 63: 622-634). In inflammatory bowel disease (IBD) patients, CLDN1 protein expression is increased in an inflammation-dependent manner (Weber et al. Lab Invest., 2008, 88: 1110-1120). To investigate the role of CLDN1 as a therapeutic target in IBD patients, the present Inventors analyzed CLDN1 expression in patients&#39; cohorts ( FIG.  15   ). CLDN1 was found to be upregulated in patients with ulcerative colitis. 
     CLDN1 Gene Expression is Upregulated in Induced Renal Fibrosis in Unilateral Ureteral Obstruction (UUO) Model. The Unilateral Ureteral Obstruction (UUO) model is used to cause renal fibrosis, where the primary feature of UUO is tubular injury as a result of obstructed urine flow, causing oxidative stress, inflammation and renal fibrosis (Martinez-Klimova et al., Biomolecules, 2019, 9(4): 141). To investigate the role of CLDN1 in the UUO, the present Inventors analyzed its expression in mice renal tissue. CLDN1 was found to be overexpressed in UUO samples indicating its adequacy to study the role of CLDN1 in renal fibrosis ( FIG.  16   ). 
     Example 9: In Vivo Efficacy Study of Anti-CLDN1 mAb in Unilateral Ureteral Obstruction (UUO)-Induced Renal Interstitial Fibrosis 
     The goal of the present study was to examine the effects of an anti-CLDN1 mAb on renal interstitial fibrosis in unilateral ureteral obstruction-induced renal interstitial fibrosis. 
     Materials and Methods 
     Test Substances. A murinized version of an anti CLDN1 mAb was synthetized at the Inventors&#39; laboratory and used in the present study. Affinity studies using mouse and human CLDN1 expressed in 293T cells have shown that the murinized mAb binds to mouse CLDN1 albeit with markedly lower efficacy. To prepare dosing solution, the anti-CLDN1 mAb was diluted with a saline solution used as vehicle. Telmisartan (Micardis®) was purchased from Boehringer Ingelheim GmbH (Germany) and dissolved in pure water. 
     Unilateral Ureteral Obstruction (UUO) Surgery. On Day 0, UUO surgery was performed under three types of mixed anesthetic agents (medetomidine, midazolam, butorphanol). After shaving the hair, the abdomen was cut open and the left ureter was exteriorized. The ureter was ligated by 4-0 silk sutures at two points. The peritoneum and the skin were closed with sutures, and the mice were transferred to a clean cage and kept until recovery from anesthesia. 
     Route of Drug Administration. The anti-CLDN1 mAb was administered intraperitoneally at a volume of 100 μL/mouse. Telmisartan was administered orally at a volume of 10 μL/mouse. 
     Treatment Doses. The anti-CLDN1 mAb was administered at a dose of 500 μg/100 μL/mouse. Telmisartan was administered at a dose of 30 mg/kg once daily. 
     Animals. Seven-week-old female C57BL/6J mice were obtained from Japan SLC, Inc. (Japan). Animals were housed and fed with a normal diet (CE-2; CLEA Japan, Japan) under controlled conditions. All animals used in the study were housed and cared for in accordance with the Japanese Pharmacological Society Guidelines for Animal Use. The animals were maintained in a SPF facility under controlled conditions of temperature (23±3° C.), humidity (50±20%), lighting (12-hour artificial light and dark cycles; light from 8:00 to 20:00) and air exchange. A high pressure was maintained in the experimental room to prevent contamination of the facility. The animals were housed in TPX cages (CLEA Japan) with a maximum of 4 mice per cage. Sterilized Paper-Clean (Japan SLC) was used for bedding and replaced once a week. 
     Sterilized normal diet was provided ad libitum, being placed in a metal lid on the top of the cage. Distilled water was also provided ad libitum from a water bottle equipped with a rubber stopper and a sipper tube. Water bottles were replaced once weekly, cleaned, sterilized in an autoclave and reused. 
     Mice were identified by ear punch. Each cage was labeled with a specific identification code. 
     Measurement of Plasma Biochemistry. For plasma biochemistry, non-fasting blood was collected in polypropylene tubes with anticoagulant (Novo-Heparin, Mochida Pharmaceutical Co. Ltd., Japan) and centrifuged at 1,000×g for 15 minutes at 4° C. The supernatant was collected and stored at −80° C. until use. Plasma urea nitrogen was measured by FUJI DRI-CHEM 7000 (Fujifilm, Japan). 
     Measurement of Kidney Biochemistry. To quantify kidney hydroxyproline content, frozen left kidney samples were processed by an alkaline-acid hydrolysis method as follows. Kidney samples were dissolved in 2N NaOH at 65° C., and autoclaved at 121° C. for 20 minutes. The lysed samples (150 μL) were acid-hydrolyzed with 150 μL of 6N HCl at 121° C. for 20 minutes, and neutralized with 150 μL of 4N NaOH containing 10 mg/mL activated carbon. AC buffer (2.2M acetic acid/0.48M citric acid, 150 μL) was added to the samples, followed by centrifugation to collect the supernatant. A standard curve of hydroxyproline was constructed with serial dilutions of trans-4-hydroxy-L-proline (Sigma-Aldrich, USA) starting at 16 μg/mL. The prepared samples and standards (each 400 μL) were mixed with 400 μL chloramine T solution (Nacalai Tesque Inc., Japan) and incubated for 25 minutes at room temperature. The samples were then mixed with Ehrlich&#39;s solution (400 μL) and heated at 65° C. for 20 minutes for color development. After samples were cooled on ice and centrifuged to remove precipitates, the optical density of each supernatant was measured at 560 nm. The concentrations of hydroxyproline were calculated from the hydroxyproline standard curve. Protein concentrations of kidney samples were determined using a BCA protein assay kit (Thermo Fisher Scientific, USA) and used to normalize the calculated hydroxyproline values. Kidney hydroxyproline contents were expressed as μg per mg protein. 
     Histopathological Analyses. For PAS staining, sections were cut from paraffin blocks and stained with Schiff&#39;s reagent (Wako Pure Chemical Industries) according to the manufacturer&#39;s instructions. To observe the tubular damages, bright field images in the corticomedullary region were captured using a digital camera (DFC295; Leica Microsystems, Germany) at 100- and 400-fold magnifications. 
     To visualize collagen deposition, kidney sections were stained using picro-Sirius red solution (Waldeck, Germany). For quantification of interstitial fibrosis area, bright field images in the corticomedullary region were captured using a digital camera (DFC295) at 200-fold magnification, and the positive areas in 5 fields/section were measured using ImageJ software (National Institute of Health, USA). 
     For immunohistochemistry, sections were cut from paraffin blocks and deparaffinized and rehydrated. Endogenous peroxidase activity was blocked using 0.3% H 2 O 2  for 5 minutes, followed by incubation with Block Ace (Dainippon Sumitomo Pharma Co. Ltd., Japan) for 10 minutes. The sections were incubated with a 100-fold dilution of anti-F4/80 antibody (BMA Biomedicals, Switzerland) at room temperature for 1 hour. After incubation with secondary antibody (HRP-Goat anti-rat antibody, Invitrogen, USA), enzyme-substrate reactions were performed using 3,3′-diaminobenzidine/H 2 O 2  solution (Nichirei Bioscience Inc., Japan). For quantitative analysis of inflammation areas, bright field images of F4/80-immunostained sections were captured using a digital camera (DFC295) at 200- and 400-fold magnifications. 
     Sample Collection. For plasma samples, non-fasting blood was collected in polypropylene tubes with anticoagulant (Novo-Heparin) and centrifuged at 1,000×g for 15 minutes at 4° C. 20 μL of supernatant were collected and stored at −80° C. for biochemistry. The remaining plasma was stored at −80° C. for shipping. 
     For frozen kidney samples, the left kidney was collected and cut into 2 pieces horizontally. The superior part of left kidney was fixed in 10% neutral buffered formalin and then embedded in paraffin. The paraffin blocks were stored at room temperature for histological analyses. The inferior part of the left kidney was cut into 2 pieces coronally. The anterior part of the left kidney was snap frozen in liquid nitrogen and stored at −80° C. for shipping. The posterior part of the left kidney was snap frozen in liquid nitrogen and stored at −80° C. for kidney biochemistry. 
     Statistical Tests. Statistical analyses were performed using Bonferroni Multiple Comparison Test on GraphPad Prism 6 (GraphPad Software Inc., USA). P values &lt;0.05 were considered statistically significant. A trend or tendency was assumed when a one-tailed t-test returned P values &lt;0.1. Results were expressed as mean SD. 
     Experimental Design and Treatment 
     Study Groups.
         Group 1: Vehicle. Eight UUO mice were intraperitoneally administered vehicle [Saline] in a volume of 100 mL/mouse twice weekly from Day 0 to Day 13.   Group 2: Anti-CLDN1 mAb. Eight UUO mice were intraperitoneally administered vehicle supplemented with the anti-CLDN1 mAb at a dose of 500 μg/100 μL/mouse twice weekly from Day 0 to 13.   Group 3: Telmisartan. Eight UUO mice were orally administered pure water supplemented with Telmisartan in a volume of 10 mL/kg at a dose of 30 mg/kg once daily from Day 0 to Day 13.       

     Animal Monitoring and Sacrifice. The viability, clinical signs and behavior were monitored daily. Individual body weight was measured daily before the treatment. Mice were observed for significant clinical signs of toxicity, moribundity and mortality after each administration. The animals were sacrificed by exsanguination through direct cardiac puncture under isoflurane anesthesia (Pfizer Inc.) at Day 14. 
     Results 
     Current therapeutic approaches for chronic kidney diseases, such as diabetic nephropathy, include Telmisartan, a renin-angiotensin receptor antagonist, that exerts protective effects in kidney fibrogenesis by affecting EMT (Balakumar et al., Pharmacol. Res., 2019, 146: 104314). However, due to limited efficacy, the current role of Telmisartan in treatment of chronic kidney disease and fibrosis is only supportive (Ruiz-Ortego et al., Nature Rev. Nephrol., 2020, 16, 269-288; Balakumar et al., Pharmacol. Res., 2019, 146: 104314). In order to investigate CLDN1 as a potential target in renal fibrogenesis, the effects of the humanized anti-CLDN1 mAb H3L3 were studied in comparison to Telmisartan in an unilateral, ureteral obstruction (UUO) mouse model of kidney fibrosis (Chevalier et al., Kidney Int., 2009, 75: 1145-1152) (see the study protocol presented in  FIG.  17 (A) ). 
     Body Weight Changes and General Condition. As shown by  FIG.  18   , no significant differences were found in mean body weight at any day during the treatment period between the Vehicle group and the treatment groups. No death occurred in all three study groups during the treatment period; and none of the animals showed deterioration in general condition. 
     Body Weight on the Day of Sacrifice and Kidney Weight. As shown by  FIG.  19 (A)  and Table 1, no significant differences in mean body weight were observed on the day of sacrifice between the vehicle group and the treatment groups. As shown in  FIG.  19 (B) , the mean right kidney weight in the anti-CLDN1 mAb group was found to tend to increase compared with the vehicle group. There was no significant difference in mean right kidney weight between the vehicle group and the Telmisartan group. As shown in  FIG.  19 (C) , the mean left right kidney weight in the anti-CLDN1 mAb group was found to increase compared with the vehicle group. There was no significant difference in mean left kidney weight between the vehicle group and the Telmisartan group. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Body weight and kidney weight. 
               
            
           
           
               
               
               
               
            
               
                 Parameter 
                 Vehicle 
                 Anti-CLDN1 mAb 
                 Telmisartan 
               
               
                 (mean ± S.D.) 
                 (n = 8) 
                 (n = 8) 
                 (n = 8) 
               
               
                   
               
               
                 Body weight (g) 
                 18.7 ± 0.5 
                 19.2 ± 0.9 
                 18.7 ± 1.1 
               
               
                 Right kidney 
                 140 ± 8  
                 150 ± 14 
                 139 ± 9  
               
               
                 weight (mg) 
               
               
                 Left kidney 
                 552 ± 93 
                  670 ± 156 
                  630 ± 160 
               
               
                 weight (mg) 
               
               
                   
               
            
           
         
       
     
     Biochemistry. Plasma Urea Nitrogen. As shown in  FIG.  20 (A)  and in Table 2, the plasma urea nitrogen level in the Telmisartan group was found to tend to increase compared with the Vehicle group. There was no significant difference in plasma urea nitrogen level compared with the Vehicle group and the anti-CLDN1 mAb group. 
     Kidney Hydroxyproline. As shown in  FIG.  20 (B)  and in Table 2, the kidney hydroxyproline content in the Telmisartan group tended to decrease compared with the Vehicle group. There was no significant difference in kidney hydroxyproline content compared with the Vehicle group and the anti-CLDN1 Ab group. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Biochemistry. 
               
            
           
           
               
               
               
               
            
               
                 Parameter 
                 Vehicle 
                 Anti-CLDN1 mAb 
                 Telmisartan 
               
               
                 (mean ± S.D.) 
                 (n = 8) 
                 (n = 8) 
                 (n = 8) 
               
               
                   
               
               
                 Plasma urea 
                 19.6 ± 2.6  
                 30.7 ± 5.2  
                 33.9 ± 5.2  
               
               
                 nitrogen (mg/dL) 
               
               
                 Kidney hydroxyproline 
                 7.97 ± 2.18 
                 6.78 ± 1.60 
                 6.19 ± 2.31 
               
               
                 (μg/mg total protein) 
               
               
                   
               
            
           
         
       
     
     Histological Analyses. PAS Staining. Representative photomicrographs of PAS-stained kidney sections are shown in  FIG.  21   . Kidney sections from the Vehicle group exhibited inflammatory cell infiltration, severe tubular dilation, atrophy and PAS-positive cast formation in the cortical region. PAS staining demonstrated that the inflammatory cell infiltration in the anti-CLDN1 Ab and Telmisartan groups was lower than in the Vehicle group. 
     Sirius Red Staining and the Fibrosis Area. Representative photomicrographs of Sirius red-stained kidney sections are shown in  FIG.  22   . The anti-CLDN1 mAb and Telmisartan groups showed significant decreases in the collagen proportional (Sirius-red positive area) compared with the Vehicle group (see Table 3). 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Fibrosis Area. 
               
            
           
           
               
               
               
               
            
               
                 Parameter 
                 Vehicle 
                 Anti-CLDN1 mAb 
                 Telmisartan 
               
               
                 (mean ± S.D.) 
                 (n = 8) 
                 (n = 8) 
                 (n = 8) 
               
               
                   
               
               
                 Sirius red-positive 
                 7.49 ± 2.78 
                 2.89 ± 2.02 
                 2.44 ± 1.19 
               
               
                 area (%) 
               
               
                   
               
            
           
         
       
     
     F4/80 Immunostaining. Representative photomicrographs of F4/80-immunostained kidney sections are shown in  FIG.  23   . Kidney sections from the Vehicle group exhibited inflammatory cell infiltration in both the cortical and glomerular regions. F4/80 immunostaining demonstrated that inflammatory cell infiltration in the anti-CLDN1 mAb and Telmisartan groups was lower than that in the Vehicle group. 
     As shown by Sirius-red staining and kidney hydroxyproline content, renal fibrosis was established in the Vehicle group. Treatment with the anti-CLDN1 mAb showed a marked and highly significant decrease in the fibrosis area compared with the Vehicle group without sign of toxicity or increment in plasma urea nitrogen test compared to the Vehicle group. Thus, histological analysis of UUO mouse kidney tissues showed decrease in the fibrosis areas (Sirius-red positive areas) in anti-CLDN1 mAb kidney sections with median values of 2.89% (Q1-Q3 1.52-4.25%) compared with the control group with median values 7.49% (Q1-Q3 5.6-9.36%). While also showing significant antifibrotic effects in vivo, treatment with telmisartan was associated with increase in plasma urea nitrogen, a marker of poor outcome in chronic kidney disease (Seki et al., BMC Nephrol., 2019, 20: 115). In contrast, the anti-CLDN1 mAb did not show any effects on plasma urea nitrogen. Finally, histological assessment of mice kidneys by F4/80 staining revealed suppression of macrophage infiltration by the anti-CLDN1 mAb. 
     Conclusion 
     In conclusion, the results obtained in the present study show that the murinized anti-human anti-CLDN1 mAb has a marked and highly significant anti-fibrotic effect on kidney fibrosis in the UUO model used. 
     Example 10: Expression of CLDN1 in Human Healthy Renal Tissue 
     Materials and Methods 
     Test Substances. A humanized version of an anti CLDN1 mAb and an isotype control were biotinylated (Squarix, Germany) and used in the present study. Healthy human tissues (freshly frozen) were available at Charles River Laboratories (Evreux France) and stained with the biotinylated humanized anti-CLDN1 mAb using a specific procedure. Tissues were fixed with formol zinc for 2 minutes, washed with PBS Tween (Sigma P3563) and endogenous peroxidase activity was quenched with PBS containing 0.3% H 2 O 2  for 20 minutes. Tissue slides were incubated for 1 hour with 10 μg of antibody in a buffer with 1% Tween 20 and 10% human serum, washed 2 times for 30 minutes with PBS and detection was carried out with Streptavidin HRP kit (Kir Elite from Vector) according the manufacturer&#39;s specifications. 
     Results 
       FIG.  24    shows that a distinct Claudin 1-specific staining was observed at the Bowman&#39;s membrane of the glomeruli and podocytes (arrows). A weak staining of tubuli was considered non-specific as it was also observed with the isotype control antibody (study performed at Charles River Laboratories, Evreux, France). 
     Example 11: Expression of CLDN1 in Human Fibrotic Renal Tissues 
     Materials and Methods 
     Test Substances. A rabbit polyclonal anti-CLDN1 antibody Ab (Elabscience, E-AB-30939) was used to stain a series of formalin-fixed tissue sections using standard methodology. The tissues were provided by Prof Solange Moll (University of Geneva, Switzerland). 
     Results 
       FIG.  25    shows differential staining between healthy and diseased tissues with a stronger signal been observed in renal fibrotic tissues: Staining was demonstrated in (1) the crescents of ANCA (anti-neutrophil cytoplasmic antibody-associated vasculitis) glomerulonephritis and (2) in FSGS (focal segmented glomerulosclerosis) type I and II treated with either corticosteroids (CS) and/or cyclosporin A (CyA). This indicates that Claudin-1 as a target is overexpressed in different forms of human kidney fibrosis. Furthermore, this overexpression of Claudin-1 is independent of the treatment status of the patients with state-of-the art therapies such as corticosteroids and cyclosporin A. 
     Example 12: Improvement of Kidney Function and Prevention of Renal Fibrosis Using an Anti-Claudin-1 Monoclonal Antibody 
     This study was carried out using the Adriamycin-induced nephropathy model. 
     Materials and Methods 
     The Adriamycin-induced nephropathy (ADR) model is a well-characterized disease model for chronic kidney disease and mirrors human kidney disease caused by primary focal segmental glomerulosclerosis (FSGS). The Adriamycin-induced nephropathy is a mouse model the mimics human FSGS (Focal Segmental Glomerulosclerosis). An efficacy study was performed at SMC lab (Tokyo, Japan) in accordance with local standards of ethics and animal care. Induction of Adriamycin-induced nephropathy model started on Day 0, when mice were intravenously administered adriamycin (doxorubicin hydrochloride, Wako Pure Chemical Industries, Ltd., Japan) in 0.9% saline at a dose of 13 mg/kg, in a volume of 10 mL/kg. 
     Groups of eight Adriamycin-induced nephropathic male BALB/c mice were administered either vehicle [saline], anti-CLDNA 1 mAb H3L3 (250 μg/mouse, twice weekly) intraperitoneally, or VPA (=valproic acid, provided at 0.4% in the drinking water) as a positive control for 27 days. Serum creatinine and BUN (blood urea nitrogen) was measured by FUJI DRI-CHEM 7000 (Fujifilm Corporation, Japan). 
     Results 
       FIG.  26    shows non-significant but pronounced reduction of both the serum creatinine and serum BUN in the anti-Claudin 1 mAb treated group compared to the control group and the valproic acid treated group. This indicates that treatment with anti-Claudin 1 antibodies improves kidney functions and health status as evidenced by a reduction of these markers, and that the achieved therapeutic benefits are superior to a well-established standard treatment. 
     Other Embodiments 
     Other embodiments of the invention will be apparent to those skilled in the art from a consideration of the specification or practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with the true scope of the invention being indicated by the following claims.