TESTING OF INNATE IMMUNITY STIMULATION VIA TLR9 ON CEREBRAL AMYLOID ANGIOPATHY USING NON-HUMAN PRIMATES

Considerable effort has been directed toward the development of immunotherapeutic approaches for AD. A potential complication of immunomodulation is the occurrence of cerebral microhemorrhages associated with increased cerebral amyloid angiopathy (CAA). Our initial findings indicate that stimulation of innate immunity with TLR9 agonist CpG ODN is an effective means of reducing CAA without inducing toxicity in AD mouse models. Transgenic models are ideal for initial screening of a potential therapy; however prior to clinical trials it is imperative to also perform studies in models more similar to humans that naturally develop AD related pathology. We advanced our study using the well characterized non-human primate model of sporadic CAA, squirrel monkey (Saimiri Boliviensis). Safety and efficacy assessment studies were first performed in young monkeys. Varying doses of the class B CpG ODN preparations containing the primate specific immunostimulatory sequence were administered subcutaneously. The most effective and non-toxic dosage determined was selected for our long term studies in elderly monkeys (with expected CAA deposits). Both age groups were subjected to behavioral testing. The peripheral cytokine responses were analyzed in plasma and PBMC supernatants. Expression of TLR9 in squirrel monkey PBMCs was confirmed by flow cytometry and immunofluorescence microscopy. CpG ODN elevated the levels of various Th1/Th2 cytokines in plasma from young monkeys. The cytokine responses were dose related and with inter-subject variability in kinetics. No signs of toxicity were observed. Elderly monkeys underwent behavioral testing before immunization. Old animals demonstrated cognitive deficits on the Inhibitory Control of Behavior and Delayed Response tests. Learning and memory will also be assessed in the final month of treatment. Plasma samples are being analyzed to further define immune responses and potential AD biomarkers. Administration of CpG ODN 2006 in young monkeys was effective in inducing immunostimulatory response in the absence of any toxicity. We believe that this type of immunomodulation will lead to reductions in CAA burden correlating with behavioral improvements, without associated microhemorrhages or encephalitis. Our studies represent the first trial of treatment specifically targeting CAA in non-human primates and will provide essential information prior to any clinical use of CpG ODN.