Ex vivo T cell treatment Immunomagnetic negative isolation was used to obtain untouched human T cells from previously frozen PBMC samples of treatment-naïve (n=6) and MTX-IR (n=3) RA patients (Table S1). The isolated T cells were then cultured and stimulated in a 96-well round-bottom plates for suspension cells in a concentration of 1.5×105 cells per well in full HPLM and CD3/CD28 Dynabeads as described above in the presence of TH9619 (1uM) or MTX (1uM) or DMSO (vehicle control) for 24 hours. After incubation, cells were washed twice with DPBS, pelleted, snap-frozen, and stored for subsequent lysis and processing.