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Reliable in vitro expansion protocols of regulatory T cells (Tregs) are needed for clinical use. We studied the biology of Mauritian Cynomolgus macaque (MCM) Tregs and developed four in vitro Treg expansion protocols for translational studies. Tregs expanded 3000-fold when artificial antigen presenting cells (aAPCs) expressing human CD80, CD58 and CD32 were used throughout the culture. When donor peripheral blood mononuclear cells (PBMCs) were used as the single source of APCs followed by aAPCs, Tregs expanded 2000-fold. Tregs from all protocols suppressed the proliferation of anti-CD2CD3CD28 bead-stimulated autologous PBMCs albeit with different potencies, varying from 1:2-1:4 Treg:PBMC ratios, up to >1:32. Reculture of cryopreserved Tregs permitted reexpansion with improved suppressive activity. Occasionally, CD8 contamination was observed and resolved by resorting. Specificity studies showed greater suppression of stimulation by anti-CD2CD3CD28 beads of PBMCs from the same donor used for stimulation during the Treg cultures and of autologous cells than of third-party PBMC responders. Similar to humans, the Treg-specific demethylated region (TSDR) within the Foxp3 locus correlated with suppressive activity and expression of Foxp3. Contrary to humans, FoxP3 expression did not correlate with CD45RA or CD127 expression. In summary, we have characterized MCM Tregs and developed four Treg expansion protocols that can be used for preclinical applications.

Summary The therapeutic applications of regulatory T cells (Tregs) include treating autoimmune diseases, graft-versus-host disease and induction of transplantation tolerance. For ex-vivo expanded Tregs to be used in deceased donor transplantation, they must be able to suppress T cell responses to a broad range of human leukocyte antigen (HLA). Here, we present a novel approach for the expansion of polyspecific Tregs in cynomolgus macaques that was adapted from a good manufacturing practice-compliant protocol. Tregs were isolated by fluorescence-activated cell sorting (FACS) and expanded in the presence of a panel of CD40L-stimulated B cells (CD40L-sBc). Prior to Treg culture, CD40L-sBc were expanded in vitro from multiple major histocompatibility complex (MHC)-disparate macaques. Expanded Tregs expressed high levels of forkhead box protein 3 (FoxP3) and Helios, a high percentage of Treg-specific demethylated region (TSDR) demethylation and strong suppression of naïve T cell responses in vitro. In addition, these Tregs produced low levels of inflammatory cytokines and were able to expand post-cryopreservation. Specificity assays confirmed that these Tregs were suppressive upon activation by any antigen-presenting cells (APCs) whose MHC was shared by CD40L-sBc used during expansion, proving that they are polyspecific. We developed an approach for the expansion of highly suppressive cynomolgus macaque polyspecific Tregs through the use of a combination of CD40L-engineered B cells with the potential to be translated to clinical studies. To our knowledge, this is the first report that uses a pool of MHC-mismatched CD40L-sBc to create polyspecific Tregs suitable for use in deceased-donor transplants.

Disruption of the blood-brain barrier (BBB) is a defining and early feature of multiple sclerosis (MS) that directly damages the central nervous system (CNS), promotes immune cell infiltration, and influences clinical outcomes. There is an urgent need for new therapies to protect and restore BBB function, either by strengthening endothelial tight junctions or suppressing endothelial vesicular transcytosis. Although wingless integrated MMTV (Wnt)/β-catenin signaling plays an essential role in BBB formation and maintenance in healthy CNS, its role in BBB repair in neurologic diseases such as MS remains unclear. Using a Wnt/β-catenin reporter mouse and several downstream targets, we demonstrate that the Wnt/β-catenin pathway is up-regulated in CNS endothelial cells in both human MS and the mouse model experimental autoimmune encephalomyelitis (EAE). Increased Wnt/β-catenin activity in CNS blood vessels during EAE progression correlates with up-regulation of neuronal Wnt3 expression, as well as breakdown of endothelial cell junctions. Genetic inhibition of the Wnt/β-catenin pathway in CNS endothelium before disease onset exacerbates the clinical presentation of EAE, CD4+ T-cell infiltration into the CNS, and demyelination by increasing expression of vascular cell adhesion molecule-1 and the transcytosis protein Caveolin-1 and promoting endothelial transcytosis. However, Wnt signaling attenuation does not affect the progressive degradation of tight junction proteins or paracellular BBB leakage. These results suggest that reactivation of Wnt/β-catenin signaling in CNS vessels during EAE/MS partially restores functional BBB integrity and limits immune cell infiltration into the CNS.