This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
Method of prevention of GVHD in bone marrow transplantation is? 
Select and explain. 
A. T-cell removal, B. Prior immune suppression, C. Post procedure immune suppression, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: Treatments used to prevent GVHD include
1) Prior immunosuppression

Ciclosporin is used most commonly. This drug works by reducing the number of T cells in donated marrow or stem cells. Started a couple of days before transplant and continued for about 6 months after the transplant.
Other drugs used are- MMF, tacrolimus, sirolimus

2) T cell depletion from the marrow or stem cells

Removal of T cells from donor's bone marrow after it has been donated, or during the donation of stem cells. This method is not commonly used.

3) Treatment after transplant

Low doses of the chemotherapy drug methotrexate to suppress your immune system. This helps to keep the t cells down and so stops them attacking body cells. Cyclophosphamide is also used.