DOMINANT HLA-MEDIATED PROTECTION FROM THE RISK OF AUTOIMMUNE RENAL DISEASE IS CONFERRED BY ANTIGEN-SPECIFIC REGULATORY CELLS

OOI JD¹, PETERSEN J², TAN YH², HUYNH M¹, WILLETT ZJ¹, RAMARATHINAM SH², EGGENHUIZEN PJ¹, LOH KL², WATSON KA³, GAN PY¹, ALIKHAN MA¹, DUDEK NL², HANDEL A⁴, HUDSON BG⁵, FUGGER L⁶, POWER DA⁷, HOLT SG⁸, COATES PT⁹, GREGERSEN JW¹⁰, PURCELL AW², HOLDSWORTH SR^1,11, LA GRUTA NL^2,3, REID HH², ROSSJOHN J², KITCHING AR^1,11

¹Monash University Centre for Inflammatory Diseases, Clayton, VIC, ² Monash University Biomedicine Discovery Institute, Clayton, VIC, ³ Dept. of Microbiology and Immunology, Melbourne University, Melbourne, VIC, ⁴ University of Georgia, GA, USA, ⁵ Vanderbilt University, TN, USA, ⁶ University of Oxford, Oxford, UK, ⁷ Dept. of Nephrology, Austin Health, Heidelberg, VIC, ⁸ Dept. of Nephrology, Melbourne Health, Parkville, VIC, ⁹ Royal Adelaide Hospital, Adelaide, SA, ¹⁰ Dept. of Medicine, Viborg Regional Hospital, Viborg, Denmark, ¹¹ Dept. of Nephrology, Monash Health, Clayton, VIC.

Aim: To use Goodpasture’s disease (GPD), a classical form of HLA-linked autoimmunity, to define the mechanism of HLA-mediated risk, and dominant protection from risk of disease.

Background: The mechanisms underpinning HLA-mediated susceptibility to, and protection from autoimmune diseases are unknown. GPD is HLA-linked and characterised by an immunodominant CD4+ self-epitope derived from the a3 chain of Type IV collagen (a3_135-145).

Methods: HLA-DR transgenic mice, cells from HLA-typed healthy humans and from patients with GPD were used, with HLA-DR-a3_135-145 tetramers, X-ray crystallography, and in vivo/in vitro models of autoimmunity.

Results: Autoreactive a3_135-145-specific T cells clonally expanded in GPD patients. In a3_135-145-immunised HLA-DR15 transgenic mice with GPD, a3_135-145-specific T cells infiltrated the kidney. Structurally, HLA-DR15 and HLA-DR1 presented a3_135-145 in different binding registers, resulting in differential T cell receptor (TCR) usage. HLA-DR15-a3_135-145 tetramer+ CD4+ T cells in disease susceptible HLA-DR15 transgenic mice exhibited a conventional phenotype (Tconv), secreting pro-inflammatory cytokines. In contrast, HLA-DR1-a3_135-145 tetramer+ cells in disease resistant HLA-DR1 and HLA-DR15/DR1 transgenic mice were largely CD4+Foxp3+ regulatory T cells (Tregs) expressing tolerogenic cytokines. In HLA-DR15/DR1 transgenic mice, HLA-DR1-a3_135-145 specific Tregs conferred protection to a3_135-145-specific autoimmunity and protected from GPD (a3_135-145-immunised, Treg intact vs Treg depleted: segmental necrosis 0±0 vs 50±13% P<0.01, serum urea 9±1 vs 31±10 P<0.001). HLA-DR15+ and HLA-DR1+ healthy human donors displayed altered a3_135-145-specific TCRs, with HLA-DR15-a3_135-145 tetramer+ Foxp3- Tconv and HLA-DR1-a3_135-145 tetramer+ Foxp3+CD25^hiCD127^lo Treg dominant phenotypes (a3_135-145 tetramer+ Treg:Tconv ratios: DR15 0.04±0.00, DR1 9.61±1.79, P<0.001).

Conclusions: These studies define, for the first time in an autoimmune disease, a mechanism for the dominantly protective effect of HLA, where HLA polymorphisms determine the abundance of self-epitope specific Tregs, leading to protection or causation of autoimmunity.