Innate Immunity Stimulation via CpG ODN in a Non-Human Primate Model of Sporadic Cerebral Amyloid Angiopathy

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ABSTRACT Several reports have outlined the potential benefit of therapeutically targeting mononuclear cells to reduce Alzheimer's disease (AD) related pathology. Innate immune cells can exhibit dysfunctional/senescent profiles characterized by impaired migration and phagocytosis as AD progresses. Therefore, modulating macrophage/microglia profiles represents a potential therapeutic avenue to reduce AD pathology. We have focused on reconciling the age related defects in immune cell function and tackling AD via Toll-like receptor 9 (TLR9). Our findings from multiple AD mouse models demonstrate that stimulation of innate immunity via TLR9 with CpG ODN can safely ameliorate all the pathological lesions that characterize AD without any toxicity. A drawback of present immunotherapeutic approaches is a limited effectiveness against cerebral amyloid angiopathy (CAA) and excessive neuroinflamation. Current evidence points to a key role for CAA in the pathophysiology leading to development of amyloid-related imaging abnormalities (ARIA). Solving the problem of CAA is becoming the priority for ensuring the success of immunotherapy. Our recent data from a biologically advantageous non-human primate model of sporadic CAA, squirrel monkey (Saimiri Boliviensis), indicate that treatment with CpG ODN results in cognitive improvements and a reduction of CAA in the absence of adverse events. Here we propose using a TLR9 ligand, class B CpG ODN 1018 ISS, which has shown good safety profiles in humans and is currently being tested in clinical trials for a variety of indications. The present study will be the first to evaluate the 1018 ISS treatment effects and long term safety in aged squirrel monkeys with established pathology, and will provide essential preclinical evidence for an IND application and subsequent phase Ib testing of 1018 ISS in AD patients. 1018 ISS efficacy on CAA levels, as well as the low levels of parenchymal amyloid deposits present in this model, will be correlated with behavioral assessments, biomarker evaluation and MRI. Our novel MRI methodology, using bi-functional ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles coupled to polyethylene glycol (PEG) and A40, will allow 1018 ISS treatment effects on amyloid burden to be followed longitudinally. Hence, our planned studies will also demonstrate the suitability of USPIO-PEG-Aβ for future clinical trials. Furthermore, monitoring for ARIA will add further complexity to evaluation of 1018 ISS efficacy and safety. The project described here is designed to characterize gene expression and protein expression profiles involved in CpG ODN-mediated signaling and phagocytic pathways. We plan to assess 1018 ISS immunostimulatory effects responsible for activating macrophages/microglia towards beneficial phenotypes, which may contribute to clearance of CAA pathology. We believe the proposed comprehensive assessments will help establish a panel of novel biomarkers and determine appropriate outcome measures for future 1018 ISS clinical trials. Overall, we believe that the proposed studies are essential to make use of CpG ODN 1018 ISS more feasible for human application.