Novel therapeutics to prevent and treat acute GVHD. APC, antigen-presenting cell; CTLA4, cytotoxic T-lymphocyte antigen 4; FMT, fecal microbiome transplant; IL-22, interleukin-22; hCG/EGF, human chorionic gonadotropin/epidermal growth factor; ISC, intestinal stem cell; ITAM, immunoreceptor tyrosine-based activation motif; JAK, Janus kinase; LGI, lower gastrointestinal; MHC II, major histocompatibility complex II; mTOR, mammalian target of rapamycin; NFAT, nuclear factor of activated T cells; PSGL-1, P-selectin glycoprotein ligand 1; PTCy, posttransplant cyclophosphamide; STAT, signal transducer and activator of transcription protein; TCR, T-cell receptor.