Monoclonal antibodies to antigens associated with transitional cell carcinoma of the human urinary bladder. II. Identification of the cellular target structures by immunoprecipitation and SDS-PAGE analysis

CD40/CD40L and Related Signaling Pathways in Cardiovascular Health and Disease-The Pros and Cons for Cardioprotection

The CD40–CD40 ligand (CD40L) dyad represents a scientific and clinical field that has raised many controversies in the past and cannot be clearly defined as being an either beneficial or harmful pathway. Being crucially involved in physiological immunological processes as well as pathological inflammatory reactions, the signaling pathway has been recognized as a key player in the development of both autoimmune and cardiovascular disease. Even though the possibilities of a therapeutic approach to the dyad were recognized decades ago, due to unfortunate events, detailed in this review, pharmacological treatment targeting the dyad, especially in patients suffering from atherosclerosis, is not available. Despite the recent advances in the treatment of classical cardiovascular risk factors, such as arterial hypertension and diabetes mellitus, the treatment of the associated low-grade inflammation that accounts for the progression of atherosclerosis is still challenging. Low-grade inflammation can be detected in a significant portion of patients that suffer from cardiovascular disease and it is therefore imperative to develop new therapeutic strategies in order to combat this driver of atherosclerosis. Of note, established cardiovascular drugs such as angiotensin-converting enzyme inhibitors or statins have proven beneficial cardiovascular effects that are also related to their pleiotropic immunomodulatory properties. In this review, we will discuss the setbacks encountered as well as new avenues discovered on the path to a different, inflammation-centered approach for the treatment of cardiovascular disease with the CD40–CD40L axis as a central therapeutic target.

The Contribution of CD40/CD40L Axis in Inflammatory Bowel Disease: An Update

Inflammatory bowel disease (IBD) is a chronic and multifactorial disease of the gastrointestinal tract. The exact etiology of IBD remains complex and unclear involving an inadequately defined relationship between microbial insult, genetic predisposition, altered intestinal barrier permeability, oxidative stress components and abnormal immune responses. The role of the co-stimulatory system made up of cluster of differentiation 40 protein (CD40) and its ligand (CD40L) in the response of the immune system to pathogens is now widely accepted. The implication of CD40/CD40L axis in immune system disorders due to its important role as signal transduction pathway among immune cells is well documented. Several studies have suggested that CD40/CD40L interactions regulate oxidative stress; this can affect various signaling pathways leading to IBD development. Hence, CD40/CD40L signaling pathway may become a new target for IBD treatment. This review will cover the general contribution of the CD40/CD40L dyad in the development of IBD in order to facilitate future approaches aiming to elucidate the immunological mechanisms that control gut inflammation.

Engineered Fc variant antibodies with enhanced ability to recruit complement and mediate effector functions

Engineering the antibody Fc region to enhance the cytotoxic activity of therapeutic antibodies is currently an active area of investigation. The contribution of complement to the mechanism of action of some antibodies that target cancers and pathogens makes a compelling case for its optimization. Here we describe the generation of a series of Fc variants with enhanced ability to recruit complement. Variants enhanced the cytotoxic potency of an anti-CD20 antibody up to 23-fold against tumor cells in CDC assays, and demonstrated a correlated increase in C1q binding affinity. Complement-enhancing substitutions combined additively, and in one case synergistically, with substitutions previously engineered for improved binding to Fc gamma receptors. The engineered combinations provided a range of effector function activities, including simultaneously enhanced CDC, ADCC, and phagocytosis. Variants were also effective at boosting the effector function of antibodies targeting the antigens CD40 and CD19, in the former case enhancing CDC over 600-fold, and in the latter case imparting complement-mediated activity onto an IgG1 antibody that was otherwise incapable of it. This work expands the toolkit of modifications for generating monoclonal antibodies with improved therapeutic potential and enables the exploration of optimized synergy between Fc gamma receptors and complement pathways for the destruction of tumors and infectious pathogens.

Fc-engineered anti-CD40 antibody enhances multiple effector functions and exhibits potent in vitro and in vivo antitumor activity against hematologic malignancies

CD40 is highly expressed on various B-lineage malignancies and represents an attractive immunotherapy target for neoplastic disease. Previous work showed that engineering the Fc domain of an antibody for increased binding to Fcγ receptors (FcγRs) significantly enhanced Fc-mediated immune effector function and antitumor activity in vitro and in vivo. We developed a humanized anti-CD40 antibody similarly Fc-engineered for increased FcγR binding (XmAbCD40) and compared its efficacy with that of an anti-CD40 native IgG1 analog and the anti-CD20 antibody rituximab. XmAbCD40 increased antibody-dependent cell-mediated cytotoxicity (ADCC) up to 150-fold relative to anti-CD40 IgG1 against B-lymphoma, leukemia, and multiple myeloma cell lines, and significantly enhanced ADCC against primary tumors. XmAbCD40 was also superior to rituximab in enhancing ADCC (both in cell lines and primary tumors) and in augmenting antibody-dependent cellular phagocytosis. XmAbCD40 significantly inhibited lymphoma growth in disseminated and established mouse xenografts and was more effective than the IgG1 analog or rituximab. An anti-CD40 antibody constructed to abrogate FcγR binding showed no reduction of tumor growth, indicating that the in vivo antitumor activity of XmAbCD40 is primarily mediated via FcγR-dependent mechanisms. These data demonstrate that XmAbCD40 displays potent antitumor efficacy and merits further evaluation for the treatment of CD40(+) malignancies.

Therapeutic interventions targeting CD40L (CD154) and CD40: the opportunities and challenges

CD40 was originally identified as a receptor on B-cells that delivers contact-dependent T helper signals to B-cells through interaction with CD40 ligand (CD40L, CD154). The pivotal role played by CD40-CD40L interaction is illustrated by the defects in B-lineage cell development and the altered structures of secondary lymphoid tissues in patients and engineered mice deficient in CD40 or CD40L. CD40 signaling also provides critical functions in stimulating antigen presentation, priming of helper and cytotoxic T-cells and a variety of inflammatory reactions. As such, dysregulations in the CD40-CD40L costimulation pathway are prominently featured in human diseases ranging from inflammatory conditions to systemic autoimmunity and tissue-specific autoimmune diseases. Moreover, studies in CD40-expressing cancers have provided convincing evidence that the CD40-CD40L pathway regulates survival of neoplastic cells as well as presentation of tumor-associated antigens to the immune system. Extensive research has been devoted to explore CD40 and CD40L as drug targets. A number of anti-CD40L and anti-CD40 antibodies with diverse biological effects are in clinical development for treatment of cancer and autoimmune diseases. This chapter reviews the role of CD40-CD40L costimulation in disease pathogenesis, the characteristics of therapeutic agents targeting this pathway and status of their clinical development.

Preclinical antilymphoma activity of a humanized anti-CD40 monoclonal antibody, SGN-40

SGN-40 is a humanized IgG1 antihuman CD40 that is currently in a phase I clinical trial for the treatment of multiple myeloma. As surface CD40 expression on B-lineage cells is maintained from pro-B cells to plasma cells, SGN-40 may be applicable to treatment of other B-cell neoplasias, including non-Hodgkin's lymphoma. In this study, we examined potential in vitro and in vivo anti-B-lineage lymphoma activity of SGN-40. Recombinant SGN-40 was expressed and purified from Chinese hamster ovary cells and characterized based on binding affinity, specificity, and normal B-cell stimulation. The ability of SGN-40 to target neoplastic B cells was examined in vitro by proliferation inhibition, cytotoxicity, and antibody-dependent cell cytotoxicity assays and in vivo by human lymphoma xenograft models. Recombinant SGN-40 showed high affinity, Kd of approximately 1 nmol/L, and specific binding to CD40. Whereas SGN-40 was a weak agonist in stimulating normal B-cell proliferation in the absence of IL-4 and CD40L, it delivered potent proliferation inhibitory and apoptotic signals to, and mediated antibody-dependent cytotoxicity against, a panel of high-grade B-lymphoma lines. These in vitro antilymphoma effects were extended to disseminated and s.c. xenograft CD40 tumor models. In these xenograft models, the antitumor activity of SGN-40 was comparable with that of rituximab. The preclinical in vitro and in vivo antilymphoma activity of SGN-40 observed in this study provides a rationale for the clinical testing of SGN-40 in the treatment of CD40+ B-lineage lymphomas.

Short-circuiting long-lived humoral immunity by the heightened engagement of CD40

Agonistic alpha CD40 Ab's have been shown to be potent immune adjuvants for both cell- and humoral-mediated immunity. While enhancing short-lived humoral immunity, the administration of a CD40 agonist during thymus-dependent immune responses ablates germinal center formation, prematurely terminates the humoral immune response, blocks the generation of B cell memory, and prevents the generation of long-lived bone marrow plasma cells. Interestingly, some of these effects of heightened CD40 engagement could be mimicked by enhancing the magnitude of antigen-specific T cell help. Taken together, these studies demonstrate that as the magnitude of CD40 signaling intensifies, the fate of antigen-reactive B cells can be dramatically altered. These are the first studies to describe the multifaceted function of CD40 in determining the fate of antigen-reactive B cells and provide novel insights into how CD40 agonists can short-circuit humoral immunity.

Identification of a human epithelial cell surface protein sharing an epitope with the C3d/Epstein-Barr virus receptor molecule of B lymphocytes

This work examines the basis for our earlier observation that certain monoclonal antibodies (MAbs) specific for the B-cell-associated C3d/Epstein-Barr virus (EBV) receptor molecule CD21 also react with the surface of some epithelial cells. Of 9 proven anti-CD21 MAbs now examined on frozen sections of human nasopharynx, tonsil and ecto-cervix, only 3 (HB5, anti-B2, AB1) showed staining of stratified epithelium; 2 of these (HB5, anti-B2) also reacted with the surface of epithelial cells freshly dispersed from these sites. The proportion of HB5- and anti-B2-reactive cells in primary epithelial cultures fell to a low but stable level within days of explantation, while almost all permanently established epithelial cell lines, whether SV40 virus-transformed or of malignant origin, were not reactive with either MAb. This contrasts with the pattern of expression of another surface marker also found selectively on cells of the lymphoid and epithelioid lineages, the CDw40 antigen. Staining with CDw40 MAbs on epithelial sections was usually restricted to the basal (proliferating) layer, but the proportion of CDw40-positive cells increased to a relatively high level in normal epithelial cultures; furthermore, most epithelial cell lines expressed this antigen. Immunoprecipitation from the surface of metabolically labelled epithelial cells with the anti-CD21 MAb HB5 yielded a protein of approximate MW 200 kDa, clearly different in size from the 145 kDa CD21 molecule on B cells. This 200 kDa protein was identified on fresh ecto-cervical epithelium, on primary cultures of a laryngeal carcinoma and on one unusual SV40-transformed epithelial cell line. We conclude that stratified human epithelial cells express a 200 kDa surface molecule which is antigenically related to, but not identical with, the CD21 antigen on B cells. It remains to be seen whether this epithelial cell protein can function as an EBV receptor.

Polymorphic expression of a human superficial bladder tumor antigen defined by mouse monoclonal antibodies

Three mouse monoclonal antibodies (mAbs), which define a highly restricted antigen, were obtained by simultaneous immunizations with superficial papillary bladder tumor cells and mouse polyclonal serum against normal urothelium. The antigen was detected by the avidin/biotin/peroxidase method in 30/44 superficial bladder tumors (68%) but in only 4/27 infiltrating urothelial cancers (with much less intensity). No normal adult or fetal tissues tested expressed the antigen, including normal urothelium from 40 individuals, 13 of whom had a bladder tumor positive for the antigen. Only 1 of 45 nonbladder tumors showed some reactivity with one of the three mAbs. Serological tests on a large panel of human cancer cell lines and normal cultured cells were negative. The antigen is highly stable and well preserved on paraffin-embedded tissues. Electrophoretic transfer blot experiments with fresh tumor extracts showed that all three mAbs react with a determinant on a component of 300,000 Mr (pI 9.5) and 62,000 Mr (pI 6.5). The antigen shows polymorphic expression at the cellular level on tissue sections and also at a molecular level on immunoblots where the two bands are differentially detected on extracts of a series of tumors but are not visualized on normal urothelium extracts. The characteristics of this antigenic system suggest that it may provide some insights about the biology of bladder cancer. Specific detection of the antigen on 70% of superficial bladder tumors with normal cytology may be useful for their diagnosis and follow-up.

Isolation and characterization of two bladder carcinoma-associated antigens

By the use of mouse monoclonal antibodies we have earlier defined five distinct antigens associated with transitional cell carcinoma of the human urinary bladder (TCC). Two of these antigens have now been purified and partially characterized. For their purification from isolated tumor cell membranes, a rapid and efficient method of affinity chromatography was developed in which the coupling of monoclonal antibodies to protein A-Sepharose was fortified by treatment with glutaraldehyde. From these columns, 60-80% of the antigenic activity present in membrane lysates could be recovered by acid elution, corresponding to approximately 0.25-0.5 micrograms antigen protein per mg membrane protein added. The two isolated antigens are relatively hydrophobic membrane components not found in normal bladder tissue. The antigen defined by the monoclonal antibody S2C6 is confined to bladder carcinoma and B cells. It is a glycosylated, ConA-binding polypeptide with Mr 50 000 as established by SDS-PAGE. It is acidic with an IP of 3.2, heat stable up to 85 degrees C, stable at low pH (2.0) but sensitive to SDS. The antigen defined by the monoclonal antibody 7E9 is confined to bladder carcinoma but is also weakly expressed in some blood vessel endothelium. It consists of two main polypeptides of Mr 29,000 and 23,000 which do not bind to ConA. It has an IP of 7.4 and its antigenic activity is abolished by heating to 50 degrees C for 5 min. As the S2C6 antigen, it is stable at low pH but susceptible to SDS.

Specificities and binding properties of 2 monoclonal antibodies against carcinoma cells of the human urinary bladder

Mice were immunized with cultured cells derived from transitional cell carcinoma of the human urinary bladder (TCC). Spleen cells were fused with mouse myeloma cell line Sp2/0-Ag14 and the hybridomas obtained screened for antibody production against a panel of human cells. Two hybridomas were selected for further studies. The antibodies from one of these hybridomas (P7A5-4) could clearly discriminate between malignant and normal cells from the bladder, both when tested with cultured cells and fresh tissue. The P7A5-4 antibodies, however, also reacted with some non-TCC cultured carcinoma and melanoma cells but to a lesser extent. This difference in reactivity was even more pronounced in the fresh tumours tested, thus indicating a quantitative difference in antigen expression between TCC and other cells. From extracts of TCC cells, P7A5-4 bound three polypeptides of mol. wts 92Kd (ConA+), 23 and 17Kd (ConA-). The antibody derived from hybridoma SK4H-12 bound a ConA reactive glycopeptide of 100Kd mol. wt, the expression of which was almost entirely restricted to urothelial cell lines and tissue of TCC origin, as shown by immunocytochemical studies. The finding in this study of new antigens associated with urinary bladder carcinoma, extend the results obtained previously in our laboratory (Koho et al., 1984; Paulie et al., 1984) and further delineate the heterogeneity of tumour-associated antigens in this human tumour system.

Monoclonal antibodies against human urinary bladder carcinomas: selectivity and utilization for gamma scintigraphy

Mouse monoclonal antibodies to human urinary bladder carcinoma cells have been examined by indirect membrane immunofluorescence using a panel of 27 human cell lines. Two of the monoclonal antibodies, 7E9 (IgG3) and S2C6 (IgGl), were found to distinguish between urinary bladder carcinoma cells and normal urothelium. The third monoclonal antibody, T24.06.5(IgGl), discriminated among cell lines of urothelial and non-urothelial origin but did not distinguish between urinary bladder carcinoma and normal urothelial cells. None of the of the antibodies was found to be strictly selective, and occasional cross-reactions with unrelated cell types were observed. The monoclonal antibody 7E9, showing the highest degree of selectivity, was further examined by an indirect immunoperoxidase technique on frozen tissue sections from 19 patients. The antibody reacted with all (7/7) bladder carcinomas examined and gave negative results with control normal bladder mucosa (0/8) and unrelated tumor tissue (0/4) sections. The 7E9 antibody was purified by protein A affinity chromatography, labeled with 131I and used for gamma-scintigraphy in nude mice xenografted with human urinary bladder carcinoma T24. The 7E9 antibody was capable of locating the T24 xenografts in nude mice; it localized preferentially in the T24 tissue compared to normal mouse tissues. The T24 xenografts could not be detected by gamma-scintigraphy with 131I-labeled monoclonal antibody against human mammary carcinoma cells and two other control antibodies. Likewise the 131I-labeled 7E9 antibody was not capable of locating human mammary carcinoma xenografts in nude mice.

A p50 surface antigen restricted to human urinary bladder carcinomas and B lymphocytes

We have previously described the derivation of a monoclonal antibody, S2C6, to a novel 50 Kdalton antigen associated with human urinary bladder carcinoma. No reactions were obtained with carcinomas of unrelated origin or with normal urothelial cells. However, the antibody also reacted with a similar antigen on some cell lines of B lymphocyte origin. Using large panels of target cells we have now shown that this reactivity was entirely restricted to cells of the B lineage within the haematopoietic system. As opposed to its apparent restriction to malignant cells of the urothelium, the S2C6 antigen was expressed by normal B lymphocytes as well as by many malignant B cells (chronic lymphocytic leukaemia, hairy cell leukaemia and immunocytoma). Pre-B cells derived from acute lymphocytic leukaemia and plasma cells from multiple myeloma lacked the antigen. Expression was significantly enhanced on cultured B cells from Burkitt lymphomas and on Epstein-Barr virus-transformed lymphoblastoid cell lines including those of the pre-B phenotype derived from fetal bone marrow. As judged from the molecular size and the distribution pattern displayed by the S2C6 antigen it appears to be distinct from other B cell antigens previously described. A possible relation of the S2C6 antigen to a receptor for B cell growth factors is discussed.

Monoclonal antibodies to antigens associated with transitional cell carcinoma of the human urinary bladder. I. Determination of the selectivity of six antibodies by cell ELISA and immunofluorescence

Spleen cells from BALB/c mice immunized with cells derived from transitional cell carcinomas (TCC) of the human urinary bladder were fused with mouse myeloma Sp 2/0 Ag14 cells. Monoclonal antibodies from six established hybridomas were investigated for specificity in a cell ELISA and in indirect immunofluorescence against a large panel of fixed intact cells. Three of the antibodies reacted with half or more of the eight bladder tumors and with a few unrelated tumors. They did not react at all with malignant or normal cells of hematopoietic origin. A fourth antibody reacted with seven of eight bladder tumors. It also reacted weakly with a prostatic carcinoma, with five of six malignant or transformed B cell lines, and with a subpopulation of normal lymphocytes, but not with any of the other cells on the test panel. These four antibodies did not react with cells derived from normal urothelium. The results suggest that these antibodies might recognize cell-type-restricted antigens associated with malignancy. Another antibody reacted with almost all urothelium-derived cells. It also reacted with three of three melanomas but not with any other cells on the panel. The sixth antibody reacted with 32 of the 37 cells tested. The spectrum of reactivities displayed by the antibody suggested that it recognizes HLA antigens.