Pathways of antigen presentation during alloSCT. Before conditioning, all APCs are recipient and noninflamed (blue). After conditioning, damage-associated molecular pattern (DAMP)/pathogen-associated molecular pattern (PAMP) signals promote antigen presentation by recipient hematopoietic and nonhematopoietic APCs (red). After transplantation, recipient hematopoietic APCs are rapidly eradicated by conditioning and GVHD and donor APC constitute. In contrast, nonhematopoietic APCs continue in the host indefinitely, although their antigen presentation capacity is dependent on environmental cues, particularly the presence of active inflammation.