Apoptotic Cell–Induced, Antigen-Specific Immunoregulation to Treat Experimental Antimyeloperoxidase GN
Authors: Gan Poh-Yi , Godfrey Andrea S. , Ooi Joshua D. , O’Sullivan Kim-Maree , Oudin Virginie , Kitching A. Richard , Holdsworth Stephen R. 
Published: July 2019

Significance Statement
Current therapies for myeloperoxidase-ANCA–associated vasculitis (MPO-AAV), an autoimmune disease causing rapidly progressive GN, are nonspecific with considerable toxicities. Previous research defined the nephritogenic immunodominant myeloperoxidase (MPO) CD4+ T cell peptide, MPO409–428, in a mouse model. In this study, the authors explored the therapeutic potential of generating endogenous MPO409–428-specific regulatory T cells to achieve tolerance to MPO and regulate the anti-MPO autoimmune response driving GN. They created apoptotic MPO409–428-conjugated splenocytes that were administered to mice before the animals had been immunized to MPO or after anti-MPO autoimmunity had been established. The resultant generation of antigen-specific type 1 regulatory T cells significantly attenuated GN. Defining the immunodominant MPO peptide(s) in patients with MPO-AAV offers the potential to restore tolerance to MPO via treatments focused on enhancing endogenous antigen-specific regulatory T cells.

Background
Myeloperoxidase (MPO)-ANCA–associated GN is a significant cause of renal failure. Manipulating autoimmunity by inducing regulatory T cells is potentially a more specific and safer therapeutic option than conventional immunosuppression.

Methods
To generate MPO-specific regulatory T cells, we used a modified protein-conjugating compound, 1-ethyl-3-(3′dimethylaminopropyl)-carbodiimide (ECDI), to couple the immunodominant MPO peptide (MPO409–428) or a control ovalbumin peptide (OVA323–339) to splenocytes and induced apoptosis in the conjugated cells. We then administered MPO- and OVA-conjugated apoptotic splenocytes (MPO-Sps and OVA-Sps, respectively) to mice and compared their effects on development and severity of anti-MPO GN. We induced autoimmunity to MPO by immunizing mice with MPO in adjuvant; to trigger GN, we used low-dose antiglomerular basement membrane globulin, which transiently recruits neutrophils that deposit MPO in glomeruli. We also compared the effects of transferring CD4+ T cells from mice treated with MPO-Sp or OVA-Sp to recipient mice with established anti-MPO autoimmunity.

Results
MPO-Sp but not OVA-Sp administration increased MPO-specific, peripherally derived CD4+Foxp3− type 1 regulatory T cells and reduced anti-MPO autoimmunity and GN. However, in mice depleted of regulatory T cells, MPO-Sp administration did not protect from anti-MPO autoimmunity or GN. Mice with established anti-MPO autoimmunity that received CD4+ T cells transferred from mice treated with MPO-Sp (but not CD4+ T cells transferred from mice treated with OVA-Sp) were protected from anti-MPO autoimmunity and GN, confirming the induction of therapeutic antigen-specific regulatory T cells.

Conclusions
These findings in a mouse model indicate that administering apoptotic splenocytes conjugated with the immunodominant MPO peptide suppresses anti-MPO GN by inducing antigen-specific tolerance.