Autoantibody potential of cancer therapeutic monoclonal antibodies

Interaction of clinical-stage antibodies with heme predicts their physiochemical and binding qualities

Immunoglobulin repertoires contain a fraction of antibodies that recognize low molecular weight compounds, including some enzymes' cofactors, such as heme. Here, by using a set of 113 samples with variable region sequences matching clinical-stage antibodies, we demonstrated that a considerable number of these antibodies interact with heme. Antibodies that interact with heme possess specific sequence traits of their antigen-binding regions. Moreover they manifest particular physicochemical and functional qualities i.e. increased hydrophobicity, higher propensity of self-binding, higher intrinsic polyreactivity and reduced expression yields. Thus, interaction with heme is a strong predictor of different molecular and functional qualities of antibodies. Notably, these qualities are of high importance for therapeutic antibodies, as their presence was associated with failure of drug candidates to reach clinic. Our study reveled an important facet of information about relationship sequence-function in antibodies. It also offers a convenient tool for detection of liabilities of therapeutic antibodies.

Neutralization of Japanese Encephalitis Virus by heme-induced broadly reactive human monoclonal antibody

Geographical expansion and re-emerging new genotypes of the Japanese encephalitis virus (JEV) require the development of novel therapeutic approaches. Here, we studied a non-conventional approach for antibody therapy and show that, upon exposure to heme, a fraction of natural human immunoglobulins acquires high-affinity reactivity with the antigenic domain-III of JEV E glycoprotein. These JEV-reactive antibodies exhibited neutralizing activity against recently dominant JEV genotypes. This study opens new therapeutic options for Japanese encephalitis.

Molecularly Targeted Therapy of Human Hepatocellular Carcinoma Xenografts with Radio-iodinated Anti-VEGFR2 Murine-Human Chimeric Fab

Vascular endothelial growth factor receptor 2 (VEGFR2) is traditionally regarded as an important therapeutic target in a wide variety of malignancies, such as hepatocellular carcinoma (HCC). We previously generated a murine-human anti-VEGFR2 chimeric Fab (cFab), named FA8H1, which has the potential to treat VEGFR2-overexpressing solid tumors. Here, we investigated whether FA8H1 can be used as a carrier in molecularly targeted therapy in HCC xenograft models. FA8H1 was labeled with ¹³¹I, and two HCC xenograft models were generated using BEL-7402 (high VEGFR2-expressing) and SMMC-7721 (low VEGFR2-expressing) cells, which were selected from five HCC cell lines. The biodistribution of ¹³¹I-FA8H1 was determined in both models by Single-Photon Emission Computed Tomography and therapeutic effects were monitored in nude mice bearing BEL-7402 xenografts. Finally, we determined the involvement of necrosis and apoptotic pathways in treated mice using immunohistochemistry. ¹³¹I-FA8H1 levels were dramatically reduced in blood and other viscera. The therapeutic effect of ¹³¹I-labeled FA8H1 in the BEL-7402 model was significantly better than that by ¹³¹I and FA8H1 alone. We observed extensive necrosis in the treated tumors, and both FasL and caspase 3 were up-regulated. Thus, ¹³¹I-anti-VEGFR2 cFab has the potential to be used for molecularly targeted treatment of HCC overexpressing VEGFR2.

Prevalence and gene characteristics of antibodies with cofactor-induced HIV-1 specificity

The healthy immune repertoire contains a fraction of antibodies that bind to various biologically relevant cofactors, including heme. Interaction of heme with some antibodies results in induction of new antigen binding specificities and acquisition of binding polyreactivity. In vivo, extracellular heme is released as a result of hemolysis or tissue damage; hence the post-translational acquisition of novel antigen specificities might play an important role in the diversification of the immunoglobulin repertoire and host defense. Here, we demonstrate that seronegative immune repertoires contain antibodies that gain reactivity to HIV-1 gp120 upon exposure to heme. Furthermore, a panel of human recombinant antibodies was cloned from different B cell subpopulations, and the prevalence of antibodies with cofactor-induced specificity for gp120 was determined. Our data reveal that upon exposure to heme, ∼24% of antibodies acquired binding specificity for divergent strains of HIV-1 gp120. Sequence analyses reveal that heme-sensitive antibodies do not differ in their repertoire of variable region genes and in most of the molecular features of their antigen-binding sites from antibodies that do not change their antigen binding specificity. However, antibodies with cofactor-induced gp120 specificity possess significantly lower numbers of somatic mutations in their variable region genes. This study contributes to the understanding of the significance of cofactor-binding antibodies in immunoglobulin repertoires and of the influence that the tissue microenvironment might have in shaping adaptive immune responses.

Autoimmune reactivity of IgM acquired after oxidation

OBJECTIVES

Redox-reactive antibodies, mainly of the IgG class, gained a wide area of interest after their autoimmune reactivity was revealed following the application of chemical and physiological oxidants. In this study, we examined the susceptibility of IgMs to oxidation and evaluated their binding to the autoantigens important in some autoimmune diseases.

METHODS

IgM and IgG fractions, isolated from healthy individuals' sera, were oxidized using direct electric current or physiological oxidant hemin. Specificities towards beta-2-glycoprotein I (β(2)-GPI), cardiolipin (CL), and rheumatoid factor were evaluated with the enzyme-linked immunosorbent assays (ELISAs). Post-translational modification was investigated by 2,4-dinitrophenylhydrazine reaction.

RESULTS

Electrochemically oxidized IgM fractions exhibited altered immunoreactivity - low to medium titers in anti-CL and low positive titers in anti-β(2)-GPI ELISA but exhibited no rheumatoid factor reactivity. Oxidized IgG and IgM fractions exhibited 2.5- and 5-fold increase in the carbonyl content, respectively.

DISCUSSION

An increase in the carbonyl content along with increased immunoreactivity after oxidation suggests modifications of the IgM paratopes. These results point towards possible modifications of native IgMs to their autoimmune state despite the fact that IgMs were less susceptible to oxidation than IgGs. The importance of an individual's redox status in maintenance of autoimmune reactions was emphasized by in vitro diagnostic tests.