Short overview of the program:

IgG4-TREAT consortium is looking for highly motivated and talented PhD students to contribute to groundbreaking research in the field of IgG4-autoimmune diseases (IgG4-AID). The PhD researchers will have the opportunity to participate in a comprehensive training programme in academic and industry setup. Next to their transferable skills training, the IgG4-TREAT PhD students will pursue 10 individual, multidisciplinary research projects (organised into four scientific work packages) aimed to advance our understanding of IgG4-AID. 

PhD candidates will become part of a network of 9 host laboratories and 7 associated partners from 7 different European countries. Funding for these projects has been provided by the EU under the competitive MSCA Doctoral Networks 2022 program (Grant Agreement No. 101119457). For more information on IgG4-TREAT visit our website: https://www.igg4-treat.eu/.

Project R8: In vivo study of pathogenic mechanisms of IgG4-AID

Hosting lab + location: The Research group of Neuroinflammation and autoimmunity led by Prof. Martinez-Martinez at Maastricht University, Maastricht, The Netherlands

Research project description:

IgG4 autoimmune diseases (IgG4-AID) are a group of severe autoimmunopathies that are characterized by pathogenic IgG4 autoantibodies (Abs) against defined target antigens. While affecting different organs, they share important mechanistic and therapeutic commonalities. IgG4-AID are individually rare, but together affect up to 11 patients per 10,000 (cumulative prevalence) thus >490,000 patients in the EU. IgG4-AID are clinically severe, difficult to diagnose and challenging to treat. They affect different organs and were therefore previously not recognized to be related.

IgG4 Abs exert their effects by blocking protein-protein interaction thus disrupting signal transduction pathways and tissue architecture, instead of complement-mediated injury of target-organs. For example, MuSK Abs interrupt signal transduction pathways required for the maintenance of neuromuscular junctions resulting in impaired neuromuscular transmission and causing severe skeletal muscle weakness. Current treatment of IgG4-AID utilizes non-specific immunosuppression and plasma separation, but the response is often incomplete and patients tend to relapse. Chronic, therapeutic B-cell depletion only benefits a subgroup of patients and has relevant side effects. Importantly, there are no biomarkers that would predict treatment response and many IgG4-AID are not well characterized, and lack strategies and guidelines for successful clinical management. This may lead to reduced quality of life or even death for the patients.

IgG4 antibodies have unusual features distinguishing them from other immunoglobulins: They do not activate the classical complement pathway, do not recruit immune cells via Fcγ receptor binding, and undergo a process named "Fab-arm exchange" (FAE): IgG4 may split up into two half-molecules and recombine to form bi-specific Abs. We and others have started to unravel the mechanisms and consequences underlying IgG4 class switch and IgG4 predominance in IgG4-AID, yet many factors are still unknown. We lack an understanding of which cells and how the IgG4 subclass itself, including Ab structure, sequence and posttranslational modifications (PTM) such as glycosylation and FAE may contribute to its pathogenicity. FAE leads to bi-specific, functionally monovalent antibodies, changing Ab valency and avidity, and glycosylation may affect Ab interaction with Fcγ receptors and immune cells. The main objective of WP3 is to characterize the structural, molecular and functional characteristics of IgG4 Abs.

In collaboration with other members of the consortium, the PhD candidate in this project will:

• analyze the lipidomic profile and spectral imagining of IgG4+ B cells from IgG4-AID patients' PBMCs using (liquid and imagining) LC-MS. By comparing the IgG4+ B cells from IgG4-AID patients to IgG4+ B cells from healthy donors, IgG1-3+ B cells from AID patients and IgG1+ B cells from IgG4-AID patients.
• characterize the pathogenic mechanisms of different IgG4-AID patients' derived IgG4 autoantibodies against LGI1 and Caspr2 using different in vitro assays
• study the in vivo effect of the pathogenic of LGI1 and Caspr2 autoantibodies using a passive transfer model to describe the relevance of IgG4 valency and FAE on pathogenicity. Abs effects on neuronal firing and in vivo electrophysiology will help to characterize the model and develop more suitable animal models to test therapeutic strategies
• develop and characterize a chronic model for LGI1/Caspr2. Using a battery of biochemical and behavioural tests, we will study the functional effects of the valency in IgG4 Abs and characterize their effector mechanisms in an IgG4 humanized model

Methods used in the project: LC-MS, Animal work (surgery, behavior), Passive transfer mouse model,  Biochemical assays, In vitro assays, Electrophysiology, ELISA, MSI, Primary cell cultures, Immunohistochemistry, Flow cytometry

Project duration: 48 months* (36-40h/week)

*In The Netherlands a PhD project takes at least 4 years, therefore the project will continue one year beyond the duration of the consortium.

Hosting lab description:

The Research group of Neuroinflammation and autoimmunity led by Prof. Martinez is working on understanding the pathophysiological mechanisms of neuroinflammatory and neurodegenerative disorders and nervous system autoimmunity as well as discovering biomarkers and developing new diagnostic assays and studying the potential of novel treatment strategies. The group has 2 main research lines; 1) Role of lipids and their transporters in Neuropsychiatric disorders and 2) Autoimmune factors in Neurological, Psychiatric and Neuropsychiatric disorders.

Foreseen mobility: Secondments are planned in:

• Sanquin (supervised by T. Rispens, the Netherlands): Isolation of antigen-specific IgG4+ B-cells for lipidomics analysis.
• LUMC (supervised by M. Huijbers, the Netherlands): Development of new IgG4-AID models.
• TND (Tzartos NeuroDiagnostics, supervised by S. Tzartos, Greece): Role of FAE in passive transfer models.