The cytoprotective effect of PAR1 non-canonical signaling after cleavage of PAR1 by wild-type APC or mutant APC (3A-APC or 5A-APC) reduces the number of TFH cells relative to TFR cells, the size of GCs, and antibody and collagen deposition in lungs, which improves bronchiolitis obliterans in a murine model of cGVHD. Ig, immunoglobulin.