PROJECT SUMMARY / ABSTRACT Traumatic brain injury (TBI) is a major health problem; 2.5 million Americans sustain TBI each year at a cost of 80 billion dollars annually. Few therapies reduce long-term cognitive sequelae of TBI, and there are only limited options for rehabilitation. Brain injury causes a primary structural injury followed by a secondary phase, which involves the activation of the innate and adaptive immune systems. Neuroinflammation with microglia’s involvement has been identified as a major contributor to the pathogenesis of TBI. However, there is still no effective immune therapy to modulate the microglial response post-injury. Nasal administration of anti-CD3 monoclonal antibody induces an anti-inflammatory immune response that down-regulates microglial activation in animal models of multiple sclerosis. The mechanism involves localization of nasal anti-CD3 to cervical lymph nodes where it induces IL-10-secreting (CD4+LAP+ and CD4+FoxP3+) regulatory T cells (Tregs) that migrate to the brain and inhibit microglial activation. Nasal anti-CD3 therapy is an unexplored area in TBI, and the mechanisms by which Tregs modulate microglia in TBI are largely unknown. Dr. Saef Izzy, a trained neurointensivist with a background in acute brain injury research, hypothesized that nasal anti-CD3 represents a unique, clinically applicable immunomodulatory approach for the treatment of TBI. Dr. Izzy worked closely with his primary mentor, Dr. Howard Weiner, to investigate the effects of nasal anti-CD3 on TBI outcomes in mice. His preliminary data showed that nasal anti-CD3 increases CD4+Tregs and IL 10 expression and reduces microglial activation in the brain 7 days after controlled cortical impact injury (CCI). It also improves behavioral outcomes at 1-month post-injury. In this K08 proposal, Dr. Izzy will determine the effects of nasal anti-CD3 on long-term histopathological and behavioral outcomes after CCI (Aim 1). He will survey the microglial, effector, and regulatory T cell responses after injury and study the effects of Tregs on microglial inflammatory response in vitro after CCI (Aim 2). He will investigate the effect of nasal anti-CD3 on IL-10/IL- 10R signaling in microglia using a C57BL6/J mouse harboring IL-10Rflox/floxTMEM119CreETR2, which does not express the IL-10 receptor on microglia after tamoxifen administration. He will also delineate the role(s) of other anti-inflammatory cytokines produced by Tregs by neutralizing TGF-β and IL-4 in vitro and in vivo and study their effects on behavior and microglial inflammatory response post-CCI (Aim 3). Dr. Izzy's career goal is to better understand how the adaptive immune response interfaces with the innate immune system after TBI. Successful completion of this proposal will provide insight into the mechanisms by which Tregs modulate the microglial response after TBI and the identification of novel immune-based therapeutics to improve patients’ outcomes. The proposed K08 application leverag...