Vitamin A plays a key role in the maintenance of gastrointestinal homeostasis and promotes a tolerogenic phenotype in tissue resident macrophages. We conducted a prospective randomized double-blinded placebo-controlled clinical trial in which 80 hematopoietic stem cell transplant recipients were randomized 1:1 to receive pre-transplant high-dose vitamin A or placebo. A single oral dose of vitamin A of 4000 I.U/kg, maximum 250,000 I.U was given prior to conditioning. Primary endpoint …