T cell isolation and in‐vitro activation

T cells were isolated from the spleens of wild‐type (WT) or transferred mice using the EasySep™ mouse T cell isolation kit (Stemcell Technologies Inc., Vancouver, BC, Canada), according to the manufacturer's instructions. Purified T cells were then stimulated in vitro using MACSiBead™ particles (Miltenyi Biotec GmbH, Bergisch Gladbach, Germany) loaded with CD3 and CD28 antibodies for 48 h (bead/cell ratio 2 : 1). Proliferation capacity of the stimulated T cells (20 000 cells/well in a 96‐well plate) was assessed using Promega CellTiter 96^® non‐radioactive cell proliferation assay (Promega, Madison, WI, USA), according to the manufacturer's instructions.