We are doing this study to find out if an experimental drug called abatacept (the study drug) is a safe and effective option to help prevent graft-versus-host (GVHD) disease for people who get an omidubicel hematopoietic stem cell transplant to treat blood cancer. Omidubicel is a recently approved (2023) stem cell transplantation that uses modified umbilical cord blood. This new method of stem cell transplantation helps patients' immune systems recover more quickly after intensive chemotherapy.

Graft-Versus-Host Disease (GVHD) Prevention

Adults ages 18+ who:

• Are candidates to receive allogeneic hematopoietic stem cell transplantation
• Do not have a matched donor for their transplant

For more information, contact the study team at jennifer.tichon@duke.edu.

If you choose to join this study, you will start the study regimen shortly before you get your omidubicel transplant.

You will get your first dose of the study drug the day before your transplant. You will get 3 more doses of the study drug at the following times:

• 5 days after your transplant
• 2 weeks after your transplant
• 4 weeks after your transplant

The study drug is given as an injection (shot) into a vein. In addition to the study drug, you will also take the drugs mycophenolate mofetil and tacrolimus as preventatives against GVHD.