The invention relates to a modified human CYP4B1 protein and a nucleic acid encoding for the modified human CYP4B1 protein. The invention further relates to an expression vector comprising a nucleic acid encoding for a modified human CYP4B1 protein, as well as to a cell comprising a modified CYP4B1 protein. In addition, the invention relates to a modified human CYP4B1 protein for use in treating transplantation induced graft-versus-host-disease (GvHD), and to 4-ipomeanol (4-IPO) for use in killing a cell.