A study of high dose immune reconstitution in MS patients after autologous hematopoietic stem cell transplant revealed that an early expansion of PD-1-expressing CD8-positive T cells and PD-1-expressing CD19-positive B cells was associated with favorable neurological outcomes, restoring immune tolerance in MS patients caused by PD-1-inhibitory signaling [45]. Here, CD19 is linked to myeloid sarcoma.