Reversal Of Neurodegeneration By Engineered Monocytes In Alzheimer’S Disease

Author

Chao-Hsien Chen, The University of Texas MD Anderson Cancer Center UTHealth Graduate School of Biomedical SciencesFollow

Author ORCID Identifier

0000-0002-9798-9825

Date of Graduation

12-2020

Document Type

Dissertation (PhD)

Program Affiliation

Immunology

Degree Name

Doctor of Philosophy (PhD)

Advisor/Committee Chair

Michael A. Curran, Ph.D.

Committee Member

Ines Moreno-Gonzalez, Ph.D.

Committee Member

Jeffrey J. Molldrem, M.D.

Committee Member

William J. Ray, Ph.D.

Committee Member

Stephanie S. Watowich, Ph.D.

Abstract

The health challenges posed by Alzheimer’s disease (AD) continue to grow as societies age worldwide. Accumulation of Tau-associated pathology correlates with clinical cognitive deterioration in AD. Resident myeloid cells within the central nervous system (CNS) have a limited capacity to uptake and degrade Tau; however, the resulting secretion of proinflammatory cytokines only acts to accelerate neurodegeneration. Therapeutic antibodies can reduce the neurotoxic oligomeric form of Tau (o-Tau), but in doing so they also aggravate inflammation. Attenuating mutation of the antibody Fc region can silence inflammation but also eliminates its capacity to mediate o-Tau clearance by CNS myeloid cells. Thus, there is an unmet need for a novel therapeutic that catalyzes o-Tau degradation without triggering neurotoxic inflammation. In tumor immunity, scavenger receptors such as CD163, CD204 and FcRIIb act to limit the proinflammatory responses of the myeloid stroma. We sought to repurpose this system to facilitate o-Tau internalization in AD while limiting inflammation. Unlike microglia in late stage AD, monocytes retain the ability to clear Tau assemblies, but also secrete inflammatory cytokines. We propose the novel concept of chimeric scavenger receptors (CSR) that facilitate clearance of o-Tau while limiting proinflammatory responses in monocytes. We successfully engineered a peripheral macrophage/monocyte cell line to stably express our CSR consisting of a scavenger receptor scaffold and an anti-o-Tau single-chain variable fragment. Our engineered CSR-monocytes not only mediate enhanced removal of extracellular o-Tau, but also uncouple phagocytosis from neurotoxic proinflammatory cytokine production. The majority of the monocyte-associated o-Tau is internalized where it co-localizes with lysosomes, likely as a prelude to proteolytic degradation. CSR monocytes demonstrate an elevated lysosome consumption activity relative to parental monocytes, indicative of a similarly higher degradative capacity. In primary culture, CSR-monocytes can protect primary neurons from o-Tau-induced cytopathology. To validate the therapeutic efficacy of these CSR monocytes in relevant in vivo preclinical models, we established a minimally invasive procedure enabling repeated intracerebroventricular adoptive transfer of these cellular therapeutics. In our early in vivo study, we observed a trend of improved motor functions in P301S Tau overexpressing transgenic mice receiving the engineered monocytes. This is the first proof of concept that myeloid cell-based immunotherapies engineered to safely target and reduce Tau pathology through CSR expression can be harnessed to treat neurodegenerative diseases such as AD.

Keywords

Alzheimer’s disease, Tau, inflammation, engineered monocytes, scavenger receptor, chimeric receptor