Neuroprotective B Cell Immunotherapy for Contusion Traumatic Brain Injury

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ABSTRACT: In addition to antibody production, B lymphocytes are efficient regulators of the immune system both through direct cell-cell interactions and through secretion of soluble molecules. Recent investigations have underscored the beneficial role of anti-inflammatory (regulatory) B cells in the central nervous system (CNS), and shown that B cell depletion can worsen the symptoms of neurodegenerative diseases. We have demonstrated for the first time that exogenous B cells can be applied therapeutically to restore function in diverse injury models, including myocardial infarction, healing of acute and chronic wounds, and controlled cortical impact (CCI) traumatic brain injury (TBI). In our mouse CCI model a single injection of B cells to the brain parenchyma at the time of injury significantly reduced learning and memory deficits, reduced lesion volume by 40-60%, as well as gliosis and microglial activation at 35 days post-injury. Preliminary studies show that B cells administered as late as 6h after CCI remain equally effective in reducing motor learning deficits. Little is known about the mechanisms underlying the neuroprotective effects of B cells in TBI. Here, we propose to investigate the cellular and molecular mechanisms of B cell-mediated neuroprotection after CCI, ultimately positioning this novel cell-based therapy for clinical use in the context of contusion TBI. In Aim 1 we will assess at multiple time points the effect of intraparenchymal B cell administration on neuronal survival and axonal degeneration (1a), regulation of infiltrating immune cells (1b) and resident microglia (1c), and cell proliferation and differentiation at the injury site (1d). Based on preliminary mechanistic investigations of B cells in both wound healing and CCI, we hypothesize that naïve B cells placed at the site of CCI sense local inflammatory signals and damage- associated molecular patterns (DAMPs) via Toll-like receptor (TLR)- and B cell receptor (BCR)-dependent pathways, and adopt a regulatory phenotype. This cell state is associated with production of anti-inflammatory cytokines (including IL-10, but also IL-4, IL-35, and TGFβ), that act on adjacent infiltrating and resident (microglia) immune cells and bias their phenotype towards an anti-inflammatory, neuroprotective state. In Aim 2 we will interrogate the sensor and effector pathways that mediate the neuroprotective effects of B cells in a CCI model. Targeted gene knockout mouse models will be used to determine the involvement of key molecular pathways (TLR-dependent vs. CD19/BCR-dependent) in B cell environmental sensing at the injury site (2a) and to define key effector molecules required for mediating the B cell response to injury (2b). To investigate the role of microglia as down-stream mediators of inflammatory regulation via IL-10, we will modulate IL-10R expression on local microglia and test the efficacy of B cell treatment in the absence of responsive microglial partners (2c). Findings from the proposed studies will establish a foundation for clinical development of a novel, safe and cost- effective immune cell therapy to address TBI, a major unmet medical need.