What is the likely cause of a skin rash developing 10 days after a bone marrow transplant?

The development of a skin rash 10 days after a bone marrow transplant is most likely due to the donor T cells attacking the patient's skin cells. This condition is known as graft-versus-host disease (GVHD), which can occur when the donor's immune cells (in this case, T cells) recognize the recipient's body cells as foreign. This immune response can lead to various symptoms, including skin rashes, as the activated T cells target the recipient's tissues.

GVHD is a common complication of bone marrow transplants, particularly when there is a mismatch between donor and recipient tissue types. The timing is significant; a rash typically appears around one to three weeks post-transplant, corresponding with the activation of the donor T cells in response to recognized antigens on the patient's skin cells.

Other options, such as antibody-mediated rejection or hyperacute rejection, are less relevant in this context. The patient's antibodies are not likely to be the primary driver of acute symptoms like a rash since this scenario is primarily about the donor's immune response. Furthermore, hyperacute rejection occurs almost immediately and is due to pre-existing antibodies from the recipient against the donor tissue, which contrasts the timeframe and presentation here. Thus, graft-versus-host disease is the most plausible