How closely related is graft-vs-leukemia to donor/recipient disparity?

Graft-vs-host disease (GVHD) is an unwanted complication of stem cell transplant, but the graft-vs-leukemia (GVL) effect has been shown to positively affect outcomes. GVHD and GVL have similar but not identical alloreactivity, and GVL may be affected by the source of grafts, the preparative conditioning regimen, and donor genetic elements. Human leukocyte antigen (HLA) mismatch does not appear to augment the GVL effect, and increased GVHD does not necessarily lead to decreased relapse.