Claim: PD-1 agonism suppresses pathogenic RA synovial T cell programs

Grounding: In RA synovial CD4+ T cells, PD-1, BTLA, and TIGIT were preferentially expressed on T peripheral helper and T follicular helper cells. PD-L2 engagement suppressed IL-21 and CXCL13 in Tph cells, suppressed TNF, IFN-gamma, and IL-2 in PD-1+CXCR5- non-Tph cells, and reduced induction of CD11c+CD21-T-bet+ age-associated B cells in 3D organoids; the PD-1 effect disappeared with CRISPR-mediated PD-1 disruption.

Claim: For RheumaAI, this supports PD-1 agonism as a plausible research direction for RA because it can dampen multiple pathogenic synovial T-cell programs, not just one cytokine axis.

Limitation: This is mechanistic ex vivo and organoid evidence, so it does not establish clinical efficacy, dosing, safety, or patient selection for PD-1-targeted therapy.

Evidence: PMID 42399123; DOI 10.1016/j.ard.2026.06.007.