Use of Tocilizumab (TCZ) to prevent acute graft versus host disease (GVHD)

This study is testing whether a drug called Tocilizumab can help prevent a serious complication called graft versus host disease (GVHD) in people receiving a stem cell transplant. GVHD happens when donor immune cells attack the recipient's body. Participants will receive a single dose of Tocilizumab one day before their transplant, and researchers will follow them for up to 2 years. You may be eligible if: - You are between 18 and 65 years old - You are having an HLA-mismatched stem cell (bone marrow) transplant - Your organ function is adequate for transplant - Your ECOG performance status is less than 2 (you are able to carry out basic activities) - You have a life expectancy of more than 3 months - You are able to give written informed consent You may NOT be eligible if: - You are pregnant or breastfeeding - You have HIV, hepatitis C, or active hepatitis B infection - You have had a solid tumour diagnosis within the past 2 years (other than certain treated skin cancers) - You have had complicated diverticulitis, bowel perforation, or fistula - You have an uncontrolled infection or serious heart condition - You are allergic to Tocilizumab or similar biological medicines - Your donor is an identical twin Talk to your doctor about whether this trial might be right for you.