Abstract. Transepithelial migration of neutrophils (PMN) is a defining characteristic of active inflammatory states of mucosal surfaces. The process of PMN transepithelial migration, while dependent on the neutrophi1132 integrin CDllb/CD18, remains poorly understood. In these studies, we define a monoclonal antibody, C5/D5, raised against epithelial membrane preparations, which markedly inhibits PMN migration across polarized monolayers of the human intestinal epithelial cell line T84 in a bidirectional fashion. In T84 cells, the antigen defined by C5/D5 is upregulated by epithelial exposure to IFN-% and represents a membrane glycoprotein of ~60 kD that is expressed on the basolateral membrane. While transepithelial migration of PMN was markedly inhibited by either C5/D5 IgG or C5/D5 Fab fragments, the antibody failed to inhibit both adhesion of PMN to T84 monolayers and adhesion of isolated T84 cells to the purified PMN integrin, CDllb/CD18. Thus, epithelial-PMN interactions blocked by C5/D5 appear to be downstream from initial CDllb/CD18-mediated adhesion of PMN to epithelial cells. Purification, microsequence analysis, and cross-blotting experiments indicate that the C5/D5 antigen represents CD47, a previously cloned integral membrane glycoprotein with homology to the immunoglobulin supeffamily. Expression of the CD47 epitope was confirmed on PMN and was also localized to the basolateral membrane of normal human colonic epithelial cells. While C5/D5 IgG inhibited PMN migration even in the absence of epithelia, preincubation of T84 monolayers with C5/D5 IgG followed by antibody washout also resulted in inhibition of transmigration. These results suggest the presence of both neutrophil and epithelial components to CD47-mediated transepithelial migration. Thus, CD47 represents a potential new therapeutic target for downregulating active inflammatory disease of mucosal surfaces. TIVE inflammation of surfaces lined by columnar epithelia is histologically defined by transmigration of neutrophils (PMN) 1 across such epithelial monolayers and subsequent collection of PMN in the lumen (26,53). Recently, neutrophils have been recognized not only to influence epithelial function during transmigration, but also to interact with biochemically distinct apical domains after translocation to the lumenal compartment, thus further modifying key epithelial processes (33, 51). For example, in intestinal epithelia it appears that PMN transepithelial migration may reversibly influence epithelial barrier function (19,37,44), while arrival in the lumenal space may result in interactions promoting electrogenic C1-secretion (32, 33), the known basis for secretory diarrhea

Target-mediated toxicity constitutes a major limitation for the development of therapeutic antibodies. To redirect the activity of antibodies recognizing widely distributed targets to the site of disease, we have applied a prodrug strategy to create an epidermal growth factor receptor (EGFR)-directed Probody therapeutic-an antibody that remains masked against antigen binding until activated locally by proteases commonly active in the tumor microenvironment. In vitro, the masked Probody showed diminished antigen binding and cell-based activities, but when activated by appropriate proteases, it regained full activity compared to the parental anti-EGFR antibody cetuximab. In vivo, the Probody was largely inert in the systemic circulation of mice, but was activated within tumor tissue and showed antitumor efficacy that was similar to that of cetuximab. The Probody demonstrated markedly improved safety and increased half-life in nonhuman primates, enabling it to be dosed safely at much higher levels than cetuximab. In addition, we found that both Probody-responsive xenograft tumors and primary tumor samples from patients were capable of activating the Probody ex vivo. Probodies may therefore improve the safety profile of therapeutic antibodies without compromising efficacy of the parental antibody and may enable the wider use of empowered antibody formats such as antibody-drug conjugates and bispecifics.

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Purpose: The goal of this research was to harness a monoclonal antibody (mAb) discovery platform to identify cell-surface antigens highly expressed on cancer and develop, through Fc optimization, potent mAb therapies toward these tumor-specific antigens.Experimental Design: Fifty independent mAbs targeting the cell-surface immunoregulatory B7-H3 protein were obtained through independent intact cell-based immunizations using human tissue progenitor cells, cancer cell lines, or cell lines displaying cancer stem cell properties. Binding studies revealed this natively reactive B7-H3 mAb panel to bind a range of independent B7-H3 epitopes. Immunohistochemical analyses showed that a subset displayed strong reactivity to a broad range of human cancers while exhibiting limited binding to normal human tissues. A B7-H3 mAb displaying exquisite tumor/normal differential binding was selected for humanization and incorporation of an Fc domain modified to enhance effectormediated antitumor function via increased affinity for the activating receptor CD16A and decreased binding to the inhibitory receptor CD32B.Results: MGA271, the resulting engineered anti-B7-H3 mAb, mediates potent antibody-dependent cellular cytotoxicity against a broad range of tumor cell types. Furthermore, in human CD16A-bearing transgenic mice, MGA271 exhibited potent antitumor activity in B7-H3-expressing xenograft models of renal cell and bladder carcinoma. Toxicology studies carried out in cynomolgus monkeys revealed no significant test article-related safety findings.Conclusions: This data supports evaluation of MGA271 clinical utility in B7-H3-expressing cancer, while validating a combination of a nontarget biased approach of intact cell immunizations and immunohistochemistry to identify novel cancer antigens with Fc-based mAb engineering to enable potent antitumor activity.

Background: Epithelial dysfunction and patient symptoms in inflammatory intestinal diseases such as ulcerative colitis and Crohn's disease correlate with migration of neutrophils (PMN) across the intestinal epithelium. In vitro modeling of PMN transepithelial migration has revealed distinct differences from transendothelial migration. By using polarized monolayers of human intestinal epithelia (T84), PMN transepithelial migration has been shown to be dependent on the leukocyte integrin CDllb/CD18 (Mac-i), but not on CD11a/CD18 (LFA-1). Since intercellular adhesion molecule-i (ICAM-1) is an important endothelial counterreceptor for these integrins, its expression in intestinal epithelia and role in PMN-intestinal epithelial interactions was investigated. Materials and Methods: A panel of antibodies against different domains of ICAM-1, polarized monolayers of human intestinal epithelia (T84), and natural human colonic epithelia were used to examine the polarity of epithelial ICAM-1 surface expression and the functional role of ICAM-1 in neutrophil-intestinal epithelial adhesive interactions. Results: While no surface expression of ICAM-1 was detected on unstimulated T84 cells, interferon-y (IFNy) elicited a marked expression of ICAM-1 that selectively polarized to the apical epithelial membrane. Similarly, apically restricted surface expression of ICAM-1 was detected in natural human colonic epithelium only in association with active inflammation. With or without IFN,y pre-exposure, physiologically directed (basolateralto-apical) transepithelial migration of PMN was unaffected by blocking monoclonal antibodies (mAbs) to ICAM-1. In contrast, PMN migration across IFNy-stimulated monolayers in the reverse (apical-to-basolateral) direction was inhibited by anti-ICAM-1 antibodies. Adhesion studies revealed that T84 cells adhered selectively to purified CDllb/CD18 and such adherence, with or without IFNy pre-exposure, was unaffected by ICAM-1 mAb. Similarly, freshly isolated epithelial cells from inflamed human intestine bound to CD llb/CD18 in an ICAM-i-independent fashion. Conclusions: These data indicate that ICAM-1 is strictly polarized in intestinal epithelia and does not represent a counterreceptor for neutrophil CD1 lb/CD 18 during physiologically directed transmigration, but may facilitate apical membrane-PMN interactions after the arrival of PMN in the intestinal lumen.

Occludin is an integral membrane protein that has been suggested to play a role in the organization and dynamic function of the epithelial tight junction (TJ). A number of other proteins have also been described to localize to the TJ. We have used a novel bait peptide method to investigate potential protein-protein interactions of the putative coiled-coil domain of occludin with some of these other TJ proteins. A 27-amino acid peptide of the human occludin sequence was synthesized, biotinylated at the N terminus, and modified to contain a photoactive moiety at either its hydrophobic or hydrophilic surface. These bait peptides were ␣-helical in solution, characteristic of coiled-coil structures. Photoactivation studies in the presence and absence of control peptides were used to assess the potential interactions in polarized sheets of a human intestinal cell line T84. Although a large number of proteins associated with the TJ or that are known to be involved in regulatory events of epithelial cells failed to be specifically labeled, occludin itself, ZO-1, protein kinase C-, c-Yes, the regulatory subunit of phosphatidylinositol 3-kinase, and the gap junction component connexin 26 were specifically labeled. Our data demonstrate the potential of one specific domain of occludin, contained within 27 amino acids, to coordinate the binding of proteins that have been previously suggested to modulate TJ structure and function.Over the last decade a number of proteins have been identified that localize to the tight junction (TJ) 1 structures of epithelial cells. Possible functional interactions between these proteins have been described (reviewed in Ref. 1). Critical extracellular interactions in TJs have been attributed to two transmembrane proteins, claudin(s) and occludin (2). Although it has been suggested that claudins recruit occludin to TJ sites (3), several recent studies have suggested instead that occludin dynamically regulates claudin-based TJ strands. Transfection of occludin mutants lacking either the intracellular (4) or extracellular (5) domains induces disruption of epithelial barrier properties. In addition, TJ barrier function is also influenced by incubation with peptides containing the two extracellular loop amino acid sequences (6 -8). As yet, analogous studies have not been described for claudin(s). Finally, disruption of TJ function mediated by the constitutive activation of Raf-1 is associated with down-regulation of occludin and claudin-1 expression, an effect that can be reversed by the reintroduction of occludin expression that in turn restores claudin-1 protein levels (9).Human occludin is approximately 65 kDa with what appears to be a 65-amino acid cytosolic N terminus, two extracellular loops of 46 and 48 amino acids separated by a 10-amino acid cytosolic loop, and a C-terminal tail of approximately 255 amino acids (10). Both the N-and C-terminal domains have a large number of serine and threonine residues, and the functionally active form of the protein localizing to the TJ appears to be hype...

Screening expressed sequence tag databases for endothelial-specific homologs to human junctional adhesion molecule (JAM) and A33-Ag, we identified a protein of 298 aa that represents the recently described vascular endothelial-JAM (VE-JAM)/JAM 2. We confirmed VE-JAM/JAM 2 expression to be restricted to the high endothelial venule of tonsil and lymph nodes, and we further expanded the localization to the endothelium of arterioles in and around inflammatory and tumor foci. In our functional characterizations of VE-JAM/JAM 2, we discovered that it can function as an adhesive ligand for the T cell line J45 and can interact with GM-CSF/IL-4-derived peripheral blood dendritic cells, circulating CD56+ NK cells, circulating CD56+CD3+ NK/T cells, and circulating CD56+CD3+CD8+ cytolytic T cells. In the course of our studies, we also isolated and characterized the functional VE-JAM/JAM 2 receptor, which, upon cloning, turned out to be a submitted sequence representing JAM 3 (accession number NP 113658). With these understandings, we have characterized a protein-interacting pair that can be important in the role of T, NK, and dendritic cell trafficking and inflammation.

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