Epitope mapping and key amino acid identification of anti-CD22 immunotoxin CAT-8015 using hybrid β-lactamase display

Mechanisms of Action and Limitations of Monoclonal Antibodies and Single Chain Fragment Variable (scFv) in the Treatment of Cancer

Monoclonal antibodies are among the most effective tools for detecting tumor-associated antigens. The U.S. Food and Drug Administration (FDA) has approved more than 36 therapeutic antibodies for developing novel alternative therapies that have significant success rates in fighting cancer. However, some functional limitations have been described, such as their access to solid tumors and low interaction with the immune system. Single-chain variable fragments (scFv) are versatile and easy to produce, and being an attractive tool for use in immunotherapy models. The small size of scFv can be advantageous for treatment due to its short half-life and other characteristics related to the structural and functional aspects of the antibodies. Therefore, the main objective of this review was to describe the current situation regarding the mechanisms of action, applications, and limitations of monoclonal antibodies and scFv in the treatment of cancer.

Epitope Fine Mapping by Mass Spectrometry: Investigations of Immune Complexes Consisting of Monoclonal Anti-HpTGEKP Antibody and Zinc Finger Protein Linker Phospho-Hexapeptides

Accurate formation of antibody-antigen complexes has been relied on in both, multitudes of scientific projects and ample therapeutic and diagnostic applications. Mass spectrometrically determined dissociation behavior of immune complexes with the anti-HpTGEKP antibody revealed that the ten most frequently occurring phospho-hexapeptide linker sequences from C2H2 zinc finger proteins could be divided into two classes: orthodox binders, where strong noncovalent interactions developed as anticipated, and unorthodox binders with deviating structures and weaker binding. Phosphorylation of threonine was compulsory for antibody binding in an orthodox manner. Gas phase dissociation energy determinations of seven C2H2 zinc finger protein linker phospho-hexapeptides with orthodox binding properties revealed a bipolar binding motif of the antibody paratope. Epitope peptides, which in addition to the negatively charged phospho-threonine residue were C-terminally flanked by positively charged residues provided stronger binding, i. e. dissociation was endothermic, than peptides with acidic amino acid residues at these positions, for which dissociation was exothermic.

Ectopic expression of a novel CD22 splice-variant regulates survival and proliferation in malignant T cells from cutaneous T cell lymphoma (CTCL) patients

CD22 is a member of the Sialic acid-binding Ig-like lectin (Siglec) family of lectins described to be exclusively present in B lymphocytes and B cell-derived neoplasms. Here, we describe a novel splice form of CD22 (designated CD22∆N), which lacks the N-terminal domain as demonstrated by exon-specific RT-PCR and differential recognition by anti-CD22 antibodies. Importantly, CD22∆N mRNA is expressed in skin lesions from 39 out of 60 patients with cutaneous T cell lymphoma (CTCL), whereas few patients (6 out of 60) expresses full-length, wild type CD22 (CD22wt). In addition, IHC staining of tumor biopsies confirmed the expression of CD22 in CD4+ T cells. Moreover, four out of four malignant T cell lines express CD22: Two cell lines express CD22∆N (MyLa2059 and PB2B) and two express CD22wt (MAC-1 and MAC-2A). siRNA-mediated silencing of CD22 impairs proliferation and survival of malignant T cells, demonstrating a functional role for both CD22∆N and CD22wt in these cells.In conclusion, we provide the first evidence for an ectopic expression of CD22 and a novel splice variant regulating malignant proliferation and survival in CTCL. Analysis of expression and function of CD22 in cutaneous lymphomas may form the basis for development of novel targeted therapies for our patients.

Development and scale-up of a commercial fed batch refolding process for an anti-CD22 two chain immunotoxin

We describe the development and scale-up of a novel two chain immunotoxin refolding process. This work provides a case study comparing a clinical manufacturing process and the commercial process developed to replace it. While the clinical process produced high quality material, it suffered from low yield and high yield variability. A systematic approach to process development and understanding led to a number of improvements that were implemented in the commercial process. These include a shorter inclusion body recovery process, limiting the formation of an undesired deamidated species and the implementation of fed batch dilution refolding for increased refold titers. The use of a combination of urea, arginine and DTT for capture column cleaning restored the binding capacity of the capture step column and resulted in consistent capture step yields compared to the clinical process. Scalability is shown with data from 250 L and 950 L scale refolding processes. Compared to the clinical process it replaces, the commercial process demonstrated a greater than fivefold improvement in volumetric productivity at the 950 L refolding scale. © 2014 American Institute of Chemical Engineers Biotechnol. Prog., 30:1380–1389, 2014

Class A β-lactamases as versatile scaffolds to create hybrid enzymes: applications from basic research to medicine

Designing hybrid proteins is a major aspect of protein engineering and covers a very wide range of applications from basic research to medical applications. This review focuses on the use of class A β-lactamases as versatile scaffolds to design hybrid enzymes (referred to as β-lactamase hybrid proteins, BHPs) in which an exogenous peptide, protein or fragment thereof is inserted at various permissive positions. We discuss how BHPs can be specifically designed to create bifunctional proteins, to produce and to characterize proteins that are otherwise difficult to express, to determine the epitope of specific antibodies, to generate antibodies against nonimmunogenic epitopes, and to better understand the structure/function relationship of proteins.

Process scale separation of an anti-CD22 immunotoxin charge variant

We describe the analytical characterization and process scale separation of a deamidated variant of an immunotoxin. The different charge variants of the immunotoxin were separated using analytical ion-exchange HPLC. These charge variants were analyzed by peptide mapping and LC-MS/MS to identify the site of modification, which was determined to reside in the toxin portion of the molecule. Using a cell-based bioassay it was also determined that deamidation led to reduced biological activity, requiring it be controlled during manufacturing. This was accomplished using process scale anion-exchange chromatography. The process was capable of reducing the deamidated form to a level low enough for the resulting product to maintain acceptable biological activity. Keys to the successful control of this impurity at process scale were a good understanding of structure-function relationship and the availability of an analytical HPLC assay to provide a surrogate for the cell-based bioassay.

In vitro and in vivo properties of a fully human IgG1 monoclonal antibody that combats multidrug resistant Pseudomonas aeruginosa

The development of an anti-bacterial drug in the form of a monoclonal antibody (mAb) targeting an exposed virulence factor, represents an innovative therapeutic strategy. Consequently, a fully human IgG1 mAb (LST-007) targeting Pseudomonas aeruginosa (PA) flagellin type b was recombinantly expressed and characterized in vitro and in an infection model driven by a multidrug resistant (MDR) PA strain. LST-007 demonstrated a highly specific binding towards whole PA bacteria harboring flagellin type b and its recombinant counterpart, with a K(D) of 7.4x10(-10) M. In bioactivity assays, LST-007 or titers of Cmax sera derived from pharmacokinetic studies, markedly attenuated PA motility in an equipotent manner. In vivo, parenteral LST-007 (20 mg/kg) given as a single or double-dosing paradigm post-infection, afforded survival (up to 75% at Day 7) in a lethal model of pneumonia driven by the intratracheal (i.t.) instillation of an LD(80) of the MDR PA isolate. This protective effect was markedly superior to that of imipenem (30% survival at Day 7) and totally devoid with an irrelevant, human isotype mAb. These data lay credence that LST-007 may be a valuable adjunct to the limited list of anti-bacterials that can tackle MDR PA strains, thereby warranting its continued development for eventual clinical evaluation.

7th annual European Antibody Congress 2011: November 29-December 1, 2011, Geneva, Switzerland

The 7th European Antibody Congress (EAC), organized by Terrapin Ltd., was again held in Geneva, Switzerland, following on the tradition established with the 4th EAC. The 2011 version of the EAC was attended by nearly 250 delegates who learned of the latest advances and trends in the global development of antibody-based therapeutics. The first day focused on advances in understanding structure-function relationships, choosing the best format, glycoengineering biobetter antibodies, improving the efficacy and drugability of mAbs and epitope mapping. On the second day, the discovery of novel targets for mAb therapy, clinical pipeline updates, use of antibody combinations to address resistance, generation and identification of mAbs against new targets and biosimilar mAb development were discussed. Antibody-drug conjugates, domain antibodies and new scaffolds and bispecific antibodies were the topics of the third day. In total, nearly 50 speakers provided updates of programs related to antibody research and development on-going in the academic, government and commercial sectors.

The improvement of an anti-CD22 immunotoxin: conversion to single-chain and disulfide stabilized form and affinity maturation by alanine scan

HA22-LR is a recombinant immunotoxin for the treatment of B-cell malignancies that contains the Fv portion of an anti-CD22 antibody fused to a functional portion of Pseudomonas exotoxin A. In the present study, we attempted to improve this molecule. First, we produced a single-chain version of HA22-LR (scdsFv-HA22-LR) in which a peptide linker was introduced between the disulfide-linked light and heavy chains to enable production via single fermentation. No difference in cytotoxic activity was observed between scdsFv-HA22-LR and prototype HA22-LR. Next, we attempted to increase the affinity of scdsFv-HA22-LR by using alanine scanning mutagenesis of complementarity determining regions (CDRs) to assess the specific contribution of each CDR residue to the antigen binding. We found that mutation of asparagine 34 in VLCDR1, which is located at the VL/VH interface, to alanine (N34A) caused a substantial increase in affinity and activity. Estimated KD values measured by fluorescence-activated cell sorting were lowered by 10-fold: 0.056 nM in the N34A mutant compared to 0.58 nM in wild type (WT). Cell viability assays of CD22-positive B-cell lymphoma and leukemia cell lines showed that the N34A mutant had increased cytotoxicity ranging from ~2 (HAL-1, IC 50(WT): 2.37 ± 0.62 ng/ml, IC 50(N34A): 1.32 ± 0.41 ng/ml) to 10 (SUDHL-6, IC 50(WT): 0.47 ± 0.090 ng/ml, IC 50(N34A): 0.048 ± 0.018 ng/ml)-fold compared to WT immunotoxin. The present study suggests that the N34A mutant of scdsFv-HA22-LR could have important consequences in a clinical setting.