The Toll-Like Receptor 4 (TLR4)–Myeloid Differentiation primary response gene 88 (MyD88) pathway is also contributing to insufficient expansion of donor MDSCs and initiation of aGVHD [56,72,73], whereas pharmacological induction of TLR4 aggravates GVHD lethality [74]. The gene discussed is MYD88; the disease is graft versus host disease.