Partial MHC class II constructs as novel immunomodulatory therapy for stroke

Abstract

The worldwide prevalence of stroke continues to rise despite recent successes in treating acute ischemic stroke. With limited patient eligibility and associated risk of tPA and mechanical thrombectomy, new preventive and therapeutic modalities are needed to stave the rising wave of stroke. Inflammation plays a key role in brain damage after cerebral ischemia, and novel therapies that target pro-inflammatory cells have demonstrated promise for treatment for stroke. Partial MHC class II constructs have been shown to prevent and/or reverse clinical signs of various inflammatory diseases such as experimental autoimmune encephalomyelitis, collagen-induced arthritis and experimental autoimmune uveitis, by reducing the number and frequency of activated cells in the damaged CNS. Herein, we review the use of partial MHC class II constructs as a novel treatment for ischemic stroke. These constructs have been shown to reduce infarct volume and neurological deficit in various cerebral ischemia models in young adult and aging male and female mice. In addition, partial MHC class II constructs were shown to reverse stroke-associated splenic atrophy and promote a protective M2 macrophage/microglia phenotype in the CNS which contributes to tissue repair and recovery after stroke. By addressing remaining STAIR criteria, such as efficacy in large animal models of stroke, these constructs will be prime candidates for clinical trials of acute ischemic stroke.

Keywords: Immunotherapy; Inflammation; Partial MHC class II construct; Recombinant T-cell receptor ligand; Stroke.

Figure 1. Rationale for the use of partial MHC class II constructs for treating stroke

A) The reduction of infarct volumes in SCID mice compared to WT C57BL/6 mice implicates the involvement of the immune system in the outcome of stroke. Reprinted from J Cereb Blood Flow Metab. DOI: 10.1038/sj.jcbfm.9600482 http://jcb.sagepub.com/content/27/11/1798.full. With permission from SAGE Journals. B) Myelin specific cells exacerbate stroke severity in SCID mice after 60min MCAO, 96 hrs reperfusion. Reprinted from Metabolic Brain Disease. Myelin specific cells infiltrate MCAO lesions and exacerbate stroke severity. 27(1):7–15, 2011, Ren X, Akiyoshi K, Grafe MR, Vandenbark AA, Hurn PD, Herson PS, Offner H. © Springer Science+Business Media, LLC 2011. With permission of Springer. C) The expression of the partial MHC class II receptor, CD74, is up regulated on microglia and infiltrating macrophages in the ischemic hemisphere 96 hrs after reperfusion (* p<0.05).

Figure 2. Therapeutic time window of RTL1000 for protection from stroke in DR2-Tg mice

Male DR2-Tg mice were subjected to 60-min transient MCAO and treated with 100 μg RTL1000 or 100 μl vehicle given subcutaneously (S.C.) starting at 4hr (A, B), 6hr (C) or 8hr (D) after MCAO, followed by additional injections at 24, 48 and 72 hr after MCAO. Brains were harvested 96 hrs after MCAO, brain slices were stained with TTC and infarct volumes measured and expressed as a percentage of the contralateral region. Panel A shows the four 2-mm TTC-stained coronal brain sections that cover the entire MCAO lesion in RTL1000- and vehicle-treated animals. * p<0.05 compared to vehicle group. Data are represented as mean ± SEM. Differences in infarct size were determined by 2-way ANOVA, followed by Holm-Sidak post hoc test, with the two factors being brain region and treatment group. CTX: cortex; CP: striatum; HMSPHR: hemisphere. Reprinted in part from Translational Stroke Research. Preclinical evaluation of recombinant T cell receptor ligand RTL1000 as a therapeutic agent in ischemic stroke. 6(1):60–8. 2015. Zhu W, Casper A, Libal NL, Murphy SJ, Bodhankar S, Offner H, Alkayed NJ. © Springer Science+Business Media New York 2014. With permission of Springer.

Figure 3. DRα 1-MOG-35-55 treatment reduces number of activated cells and their CD74 surface expression in the ischemic brain 96 hr after MCAO and reverses MCAO-induced splenic atrophy

A) Absolute lymphocytes numbers in the non-ischemic left and ischemic right brain from DRα1-MOG-35-55-treated versus Vehicle-treated mice. B) CD74 cell surface expression on CD11b⁺CD45^high cells in the right brain. C). Absolute cell numbers in the spleen from DRα1-MOG-35-55-treated versus Vehicle-treated mice; * p<0.05, **p<0.01, ***p<0.001. Reprinted from Metabolic Brain Disease. A novel HLA-DRα1-MOG-35-55 construct treats experimental stroke. 29(1):37-45. 2014. Benedek G, Zhu W, Libal N, Casper A, Yu X, Meza-Romero R, Vandenbark AA, Alkayed NJ, Offner H. © Springer Science+Business Media New York 2013. With permission of Springer.

Figure 4. DRα1-MOG-35-55 treatment of MCAO

DRα1-MOG-35-55 (a partial MHC class II construct that lacks the polymorphic β1 domain) can reduce infarct size in female and male mice after MCAO. In males, where peripheral immune cells cause greater MCAO damage than in females and possibly some MIF dependent inflammation, low concentrations of DRα1-MOG-35-55 are sufficient to reduce the infarct size. In females, which appear to have little if any MIF-dependent MCAO damage, a tenfold higher concentration of DRα1-MOG-35-55 is needed to achieve a similar effect. This differential treatment effect between males and females could be based on gender-associated effects of MIF on infarct size, recruitment of peripheral immune cells into the ischemic brain and axonal death. Reprinted from Translational Stroke Research, Novel humanized recombinant T cell receptor ligands protect the female brain after experimental stroke, 5(5), 2014, 577–585, Pan et al. Copyright ©The Author(s) 2014.

Figure 5

DRα1 Partial MHC class II molecules have a dual MOA, acting primarily on monocytes, secondarily on T-cells.