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Characterization, biology, and expansion of regulatory T cells in the Cynomolgus macaque for preclinical studies

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.