Engineering IgG-specific endoglycosidases to selectively defeat effector functions

Emory University, Atlanta GA

Investigators

Linked publications & trials

Abstract

While IgG antibodies are critical components of the adaptive immune system and constitute an important and growing class of drugs for the treatment of a wide range of diseases, they are also responsible for numerous IgG-mediated pathologies. These include acute conditions, such as the antibody-dependent enhancement (ADE) resulting from sub-neutralizing antibodies in severe dengue disease and severe Covid disease, and chronic illnesses, such as autoantibody-driven autoimmune diseases. All of these IgG-mediated pathologies arise from antibody-mediated effector functions, which themselves rely on the presence of N-glycans linked to the Asn297 residues on IgG Fc regions. Certain human pathogens secrete endoglycosidases that are absolutely specific to Asn297-linked N-glycans on human IgG antibodies. Hydrolysis of these N-glycans results in a loss of Fc γ receptor (FcγR) binding and renders these antibodies incapable of eliciting host effector functions; ultimately, this provides the bacteria that secrete these IgG-specific endoglycosidases with a survival advantage. The best characterized of these enzymes come from Streptococcus pyogenes, one of the most common human pathogens, which secretes the IgG-specific endoglycosidase EndoS. In the previous award period, we elucidated the molecular mechanisms by which this multi-domain enzyme specifically hydrolyzes IgG Fc region Asn297- linked N-glycans to defeat antibody-mediated effector functions. We also discovered a novel family of single- domain IgG-specific endoglycosidases from Corynebacterial species that are human pathogens. Furthermore, we have shown that one of these Corynebacterial endoglycosidases prevents diverse IgG-mediated pathologies in FcγR humanized mouse models, exhibits naturally low immunogenicity, and outperforms drugs currently used in the clinic to treat IgG-mediated pathologies. Despite their therapeutic promise, we currently have an incomplete understanding of how these enzymes function at the atomic level, which prohibits efforts to engineer these enzymes to be selectively specific for subsets of IgG antibodies – a critical property for enzyme-based therapeutics designed to treat IgG-mediated pathologies without fully immunocompromising the patient. Our proposed studies aim to fill this knowledge gap by defining the molecular mechanisms by which this new family of Corynebacterial IgG-specific endoglycosidases recognize both glycan and protein components of their IgG glycoprotein substrates in order to modulate glycosylation, as well as to endow them with new substrate selectivity properties in order to advance their therapeutic potential. To do so, we have assembled a highly collaborative and complementary multi-PI team who have pioneered the understanding of IgG-specific endoglycosidases and antibody-mediated effector functions. This work is significant because it will generate and leverage mechanistic understanding of IgG-specific endoglycosidases to develop a range of therapeutic options for difficult to treat IgG-mediated pathologies. The proposed studies are innovative in that they are the first to advance the development of IgG glycoform-specific and autoantibody-specific enzymes.