anti-A33 Antibody Research Articles

Establishment of a novel cell-based assay using HLA-transfected cells to detect HLA antibodies

The detection of HLA antibodies is important in clinical practice, such as platelet transfusion refractoriness and transfusion-related lung injury. However, difficulties are associated with the preparation of panel cells for conventional HLA detection systems using intact cells, such as the immunocomplex capture fluorescence analysis (ICFA).Based on an ICFA analysis, HEK293 cells stably transfected with the HLA-A locus were used instead of peripheral blood mononuclear cells (PBMC). The reactivity, sensitivity, and stability of transfectants were examined.All 20 antisera to HLA-A identified by LABScreen® Single Antigen class I (LS-SA1) were reactive to our modified-ICFA (m-ICFA) and showed the same specificities as those in LS-SA1, indicating the cell surface expression and correct antigenicity of the HLA-A locus in transfectants. The expression of HLA class I antigens was similar between transfectants frozen for 6 years and those prior to freezing. In the reaction of the anti-A24 or anti-A33 antibody vs each transfectant, the index of m-ICFA was higher than that of WAKFlow® ICFA. Our m-ICFA also showed that false negative reactions sometimes observed in capture assays may be avoided.By using HLA-A transfectants as ICFA targets, we herein developed m-ICFA. Our m-ICFA may avoid false negative reactions of capture assay like enzyme-linked immunosorbent assay and can also be carried out in almost any laboratory without cell culture facilities.

Particle-specific neutralizing activity of a monoclonal antibody targeting the poxvirus A33 protein reveals differences between cell associated and extracellular enveloped virions

Only a small subset of the hundreds of proteins encoded by the poxvirus genome have been shown to be effective as vaccine and/or therapeutic targets. One of these proteins is A33. Here we assess and dissect the ability of an anti-A33 humanized monoclonal antibody, c6C, to affect vaccinia virus infection in vitro. Enveloped virions (EV) released from infected cells can be sensitive or resistant to neutralization by c6C indicating there are different types of EV particles, extracellular enveloped virions (EEV) and released cellular-associated virions (rCEV), that are biologically distinct. Through a combination of plaque phenotype, confocal imaging, and neutralization assays, we found that c6C differentially affects EV from two different virus strains, IHD-J and WR. Evidence for an anti-A33 resistant EV particle, and strain differences in this phenotype, provides a logical answer as to why certain functional assays in the literature have been unable to detect anti-viral effects of anti-A33 antibodies.

Immunotherapy for the treatment of colorectal tumors: focus on approved and in-clinical-trial monoclonal antibodies.

Colorectal cancer is considered a disease of the elderly population. Since the number of geriatric patients continues to rise, monoclonal antibody therapy is the most promising therapy in the recent research. Presently, the monoclonal antibodies most frequently used in the treatment of colorectal tumors are bevacizumab, cetuximab, panitumumab, and ramucirumab. Bevacizumab is a monoclonal antibody that acts on VEGF. Cetuximab and panitumumab act on EGFR. Ramucirumab binds directly to the ligand-binding pocket of VEGFR-2 to block the binding of VEGF-A, VEGF-C, and VEGF-D. These monoclonal antibodies, alone or in association with radiotherapy or chemotherapy, are presenting good results and are increasing patient survival, despite the side effects. Due to the limited number of molecules available, several studies are trying to develop new monoclonal antibodies for the treatment of colorectal tumors. Among those being studied, some recent molecules are in phase I and/or II trials and are yielding advantageous results, such as anti-DR5, anti-Fn14, anti-IGF-1R, anti-EGFR, anti-NRP1, and anti-A33 antibodies. This has been successful in reducing side effects and in treating nonresponsive patients.

Heterogeneous expression of A33 in colorectal cancer: possible explanation for A33 antibody treatment failure.

The A33 protein, expressed in colorectal tumors, is a target for improving treatment of patients with colorectal cancer. Over the last decade, studies have tested anti-A33 antibody as a therapeutic agent for these patients. Preclinical results were promising, but clinical trials did not confirm positive results. Here, immunohistochemistry in colorectal cancer tissue showed that samples from well-differentiated tumors presented a strong A33 membrane staining, whereas poorly differentiated tumors and mucinous adenocarcinomas showed weak cytoplasmic and nuclear staining. Moderately differentiated tumors presented variable staining. We suggest that in future clinical trials, patients should be selected on the basis of membrane expression of A33.

Structural and Functional Characterization of Anti-A33 Antibodies Reveal a Potent Cross-Species Orthopoxviruses Neutralizer

Vaccinia virus A33 is an extracellular enveloped virus (EEV)-specific type II membrane glycoprotein that is essential for efficient EEV formation and long-range viral spread within the host. A33 is a target for neutralizing antibody responses against EEV. In this study, we produced seven murine anti-A33 monoclonal antibodies (MAbs) by immunizing mice with live VACV, followed by boosting with the soluble A33 homodimeric ectodomain. Five A33 specific MAbs were capable of neutralizing EEV in the presence of complement. All MAbs bind to conformational epitopes on A33 but not to linear peptides. To identify the epitopes, we have adetermined the crystal structures of three representative neutralizing MAbs in complex with A33. We have further determined the binding kinetics for each of the three antibodies to wild-type A33, as well as to engineered A33 that contained single alanine substitutions within the epitopes of the three crystallized antibodies. While the Fab of both MAbs A2C7 and A20G2 binds to a single A33 subunit, the Fab from MAb A27D7 binds to both A33 subunits simultaneously. A27D7 binding is resistant to single alanine substitutions within the A33 epitope. A27D7 also demonstrated high-affinity binding with recombinant A33 protein that mimics other orthopoxvirus strains in the A27D7 epitope, such as ectromelia, monkeypox, and cowpox virus, suggesting that A27D7 is a potent cross-neutralizer. Finally, we confirmed that A27D7 protects mice against a lethal challenge with ectromelia virus.

124I-huA33 Antibody Uptake Is Driven by A33 Antigen Concentration in Tissues from Colorectal Cancer Patients Imaged by Immuno-PET

The primary aim of this analysis was to examine the quantitative features of antibody-antigen interactions in tumors and normal tissue after parenteral administration of antitumor antibodies to human patients. Humanized anti-A33 antibody (10 mg) labeled with the positron-emitting radionuclide (124)I ((124)I-huA33) was injected intravenously in 15 patients with colorectal cancer. Clinical PET/CT was performed approximately 1 wk later, followed by a detailed assay of surgically removed tissue specimens including radioactivity counting, autoradiography, immunohistochemistry, and antigen density determination. PET/CT showed high levels of antibody targeting in tumors and normal bowel. In tissue specimens, the spatial distribution of (124)I-huA33 conformed to that of A33 antigen, and there was a linear relationship between the amount of bound antibody and antigen concentration. Antibody uptake was high in 1- to 2-mm regions of antigen-positive tumor cells (mean, ~0.05 percentage injected dose per gram) and in antigen-positive normal colonic mucosa (mean, ~0.03 percentage injected dose per gram). The estimated binding site occupancy for tumor and normal colon was 20%-50%. The in vivo biodistribution of (124)I-huA33 in human patients 1 wk after antibody administration was determined by A33 antigen expression. Our data imply that the optimal strategy for A33-based radioimmunotherapy of colon cancer will consist of a multistep treatment using a radionuclide with short-range (α- or β-particle) emissions.

Antibody against extracellular vaccinia virus (EV) protects mice through complement and Fc receptors.

Protein-based subunit smallpox vaccines have shown their potential as effective alternatives to live virus vaccines in animal model challenge studies. We vaccinated mice with combinations of three different vaccinia virus (VACV) proteins (A33, B5, L1) and examined how the combined antibody responses to these proteins cooperate to effectively neutralize the extracellular virus (EV) infectious form of VACV. Antibodies against these targets were generated in the presence or absence of CpG adjuvant so that Th1-biased antibody responses could be compared to Th2-biased responses to the proteins with aluminum hydroxide alone, specifically with interest in looking at the ability of anti-B5 and anti-A33 polyclonal antibodies (pAb) to utilize complement-mediated neutralization in vitro. We found that neutralization of EV by anti-A33 or anti-B5 pAb can be enhanced in the presence of complement if Th1-biased antibody (IgG2a) is generated. Mechanistic differences found for complement-mediated neutralization showed that anti-A33 antibodies likely result in virolysis, while anti-B5 antibodies with complement can neutralize by opsonization (coating). In vivo studies found that mice lacking the C3 protein of complement were less protected than wild-type mice after passive transfer of anti-B5 pAb or vaccination with B5. Passive transfer of anti-B5 pAb or monoclonal antibody into mice lacking Fc receptors (FcRs) found that FcRs were also important in mediating protection. These results demonstrate that both complement and FcRs are important effector mechanisms for antibody-mediated protection from VACV challenge in mice.

Abstract 2431: In vivo antibody binding to tumor in xenograft rodent models and colorectal cancer patients treated with anti-A33 antibody KRN330

Abstract Purpose: Many antibody therapies have been introduced into clinical practice in the past decade. Although pharmacokinetic data provide information regarding serum concentration, there are few reports that show the interaction of antibodies with the tumor in vivo. KRN330 is a novel recombinant human IgG1 monoclonal antibody (mAb) targeting the A33 surface differentiation antigen that is uniformly expressed on the surface of 95% of colorectal cancer (CRC) cells. We investigated whether KRN330 binds and stays bound to tumors established in a xenograft rodent model as well as biopsied tumors from CRC patients treated with KRN330 on a phase I trial. Methods: Time-course of KRN330 binding was analyzed using a rodent xenograft tumor model bearing human LS174 colon cancer cells. Tumors were collected at specified time points, ranging from the end of infusion on Day 1 to Day 36 after a single dose of KRN330 (1 mg/kg). KRN330 on the tumor was detected with either flow cytometry or an immunohistochemical method (IHC) for each time point. Clinical KRN330 binding data were analyzed using A33-positive tumor biopsies from 4 patients with advanced CRC who consented to be enrolled into the Phase 1 monotherapy study of KRN330. The biopsy was conducted on Day 8-9, or Day 14, after an initial 3 mg/kg dose of KRN330. KRN330 binding on human CRC tissues was assessed using IHC with the anti KRN330 idiotype antibody. Serum concentrations of KRN330 were obtained at several time points in both studies. Results: Xenograft KRN330 binding analyses indicate that KRN330 rapidly bound to the tumor after dosing and remained bound throughout the study period. Although the serum concentration decreased to 15% of that originally observed at 10 minutes post administration by Day 8, based on flow cytometry data, the KRN330 bound on tumors on Days 8 and 15 was 100% and 70%, respectively, of the maximum level bound (Day 2). Xenograft tumors in animals that were infused with a non-specific human immunoglobulin G control showed there was very minimal binding on Day 2. IHC results demonstrated that staining intensity supported the flow cytometry analysis and remained at a similar level for up to Day 15. Clinical binding data confirmed KRN330 bound and remained bound to the CRC tumor cells even at Day 14 as well as Days 8 and 9. On the other hand, serum concentrations of KRN330 decreased to 12% and 4% of the value at the end of infusion on Day 8-9 and Day 15, respectively. Conclusion: These data are the first to show that KRN330 binds rapidly and stays bound to CRC tumors for an extended period in rodent xenograft models as well as CRC patients. This suggests that KRN330 might be able to remain active on tumor even after the serum concentration drops to very low levels. Further investigation of this mAb in clinical studies is currently underway. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2431.

Autoantibody to heterogeneous nuclear ribonucleoprotein‐A2 (RA33) in juvenile idiopathic arthritis: Clinical significance

Objective biomarkers are needed for early diagnosis of juvenile idiopathic arthritis (JIA). Anti-A33 antibodies are considered good markers for adult rheumatoid arthritis (RA), but little information is available on their occurrence in JIA. The aim of the present study was therefore to investigate the value of anti-RA33 for diagnosis of JIA (both early and established disease), and its relation to markers of disease activity, and bone resorption. This case-control study was conducted on 34 children with JIA. Ten patients with arthritis of short duration (<6 weeks) were included, as undifferentiated arthritis. Forty-four age- and sex- matched healthy children served as controls. Beside evaluation and assessment of disease activity, urinary calcium, serum parathyroid hormone and serum anti-RA33 were measured in included subjects. Joints were examined radiologically and modified Larsen index (LI) was estimated. During follow up, eight of the patients with undifferentiated arthritis were diagnosed as having early JIA. Patients with JIA (early and established cases) had higher anti-RA33 levels than the control group (z = 6.04, 3.95, respectively). A total of 66.7% of the patients were positive for anti-RA33, results were comparable in early and established cases. Anti-RA33 values were correlated to disease activity (clinical and laboratory), to laboratory markers (urinary calcium, parathyroid hormone levels) and radiological evidence (LI) of bone resorption (r = 0.95, 0.63, 0.94, respectively). Anti-RA33 is detected in two-thirds of JIA patients and occurs with comparable frequency early in the disease. Its levels are correlated to disease activity and markers of bone resorption and it seems to convey diagnostic and prognostic insights for appropriate management.

Combinations of Polyclonal or Monoclonal Antibodies to Proteins of the Outer Membranes of the Two Infectious Forms of Vaccinia Virus Protect Mice against a Lethal Respiratory Challenge

Previous studies demonstrated that antibodies to live vaccinia virus infection are needed for optimal protection against orthopoxvirus infection. The present report is the first to compare the protective abilities of individual and combinations of specific polyclonal and monoclonal antibodies that target proteins of the intracellular (IMV) and extracellular (EV) forms of vaccinia virus. The antibodies were directed to one IMV membrane protein, L1, and to two outer EV membrane proteins, A33 and B5. In vitro studies showed that the antibodies to L1 neutralized IMV and that the antibodies to A33 and B5 prevented the spread of EV in liquid medium. Prophylactic administration of individual antibodies to BALB/c mice partially protected them against disease following intranasal challenge with lethal doses of vaccinia virus. Combinations of antibodies, particularly anti-L1 and -A33 or -L1 and -B5, provided enhanced protection when administered 1 day before or 2 days after challenge. Furthermore, the protection was superior to that achieved with pooled immune gamma globulin from human volunteers inoculated with live vaccinia virus. In addition, single injections of anti-L1 plus anti-A33 antibodies greatly delayed the deaths of severe combined immunodeficiency mice challenged with vaccinia virus. These studies suggest that antibodies to two or three viral membrane proteins optimally derived from the outer membranes of IMV and EV, may be beneficial for prophylaxis or therapy of orthopoxvirus infections.