## **Core Concept**
Graft-versus-host disease (GVHD) is a major complication of allogeneic hematopoietic stem cell transplantation. It occurs when the immune cells from the donor's graft recognize the recipient's body as foreign and attack it. Prevention of GVHD is crucial for the success of bone marrow transplantation.

## **Why the Correct Answer is Right**
The correct answer, T-cell depletion, is a method used to prevent GVHD. T-cells are the primary effector cells responsible for GVHD. By depleting T-cells from the donor graft, the risk of GVHD decreases. This can be achieved through various techniques, including the use of monoclonal antibodies that target T-cells, such as alemtuzumab. T-cell depletion reduces the graft's ability to recognize and attack the host's tissues, thereby reducing the incidence of GVHD.

## **Why Each Wrong Option is Incorrect**
* **Option A:** Not specified, but generally, other methods might include immunosuppressive drugs which are used to treat GVHD rather than prevent it at the source (graft preparation).
* **Option B:** Not specified, but could involve other GVHD prevention strategies that are not as direct or effective as T-cell depletion in certain contexts.
* **Option C:** Not specified, but might relate to post-transplant treatments rather than preventive measures taken at the time of graft infusion.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that T-cell depletion significantly reduces the risk of GVHD but also increases the risk of graft failure and delayed immune reconstitution. Therefore, the decision to use T-cell depletion involves balancing these risks. Another important point is that GVHD can be acute or chronic, and prevention strategies may target one or both forms.

## **Correct Answer:** D. T-cell depletion.