Abstract W P92: Preclinical Evaluation of Recombinant T-cell Receptor Ligand RTL1000 as a Therapeutic Agent in Stroke

Abstract

Objective: RTL1000, a partial human MHC molecule coupled to a human myelin peptide, reduces infarct size after experimental stroke in HLA-DR2 transgenic mice expressing the human MHC class II allele. In this study, we characterized the therapeutic window of RTL1000. We then determined if RTL1000 efficacy is altered when combined with t-PA, a standard therapy for stroke, and if it affords long-term neurobehavioral functional improvement after stroke in mice. Methods: Male DR2 mice underwent 60 min of intraluminal MCA occlusion (MCAO). RTL1000 (100 μg) or vehicle (100 μl) was given S.C. at 4, 6 or 8 h after MCAO, followed by 3 daily S.C. injections. t-PA (10 mg/kg) or vehicle was infused I.V. over 30 min starting at 15 min into ischemia. Brains were collected at either 24 or 96 h of reperfusion. Cortical, striatal and hemispheric infarcts were measured after staining with 2, 3, 5-triphenyltetrazolium chloride. Behavioral testing neuroscore, open field, paw preference and novel object recognition was performed up to 28 days after MCAO. Results: RTL1000 significantly reduced infarct size when administered at 4 and 6, but not 8 h after MCAO. Protection was more robust when RTL1000 was given at 4 h, and was limited to cortex when first administration was delayed for 6 h. When administered alone, t-PA reduced infarct size when measured at 24 but not 96 h after MCAO. Importantly, RTL1000 alone reduced infarct size at 96 h after MCAO, and the addition of t-PA did not reduce its ability to protect against ischemic injury. Behavioral testing showed RTL1000 had no effect on acute cognitive impairment on day 7, but improved long term cognitive outcome 28 days after MCAO. Conclusions: RTL1000 is protective against ischemic stroke with a therapeutic window of up to 6 h. Protection by RTL1000 is preserved in the presence of t-PA, is long-lasting and improves neurobehavioral functional outcomes after experimental cerebral ischemia.