What can be a reason for a high rate of graft failure post-transplant?

A high rate of graft failure post-transplant can indeed be associated with a low CD34+ cell count. CD34+ cells are hematopoietic stem cells that play a crucial role in the engraftment process after transplantation. In cases where the CD34+ cell count is low, there may be insufficient stem cells present to promote effective hematopoiesis and immune reconstitution in the recipient. This can lead to delayed or inadequate engraftment, increasing the risk of graft failure as the immune system may not properly recognize or support the new cells.

The other options relate to factors that generally support successful transplantation. For instance, high leukocyte counts in the graft might indicate an abundance of immune cells that could help in fighting infections but is not typically a direct cause of graft failure. ABO blood type compatibility is generally essential for reducing the risk of acute rejection and promoting successful engraftment but does not inherently lead to graft failure by itself. Having an HLA-identical donor is one of the best scenarios for transplant success, drastically lowering the chances of rejection due to immune incompatibility.