This is a clinical trial to see if the addition of etanercept helps in preventing two major complications of hematopoietic stem cell transplantation (HSCT). The main objective will be to see whether the addition of etanercept to standard preventative medicines will decrease the rate of acute graft-vs-host disease (GVHD) and the risk of death by 100 days following allogeneic HSCT from volunteer donors.