The problem with this is the bone marrow contains a high concentration of T cells. And these T cells, when they're transferred into the host individual, the T cells contain receptors that might not recognize the cell's antigens and the major histocompatibility complexes found on the host cells. And what that means is, when the grass cell binds onto the host cell, it will begin to release these enzymes that will destroy the host cells of that host individual. So when transplanting tissue that contains a high concentration of white blood cells such as T cells, there is a high probability that the graft T cells will recognize the host cells of that individual as being foreign, as being pathogenic. And this will begin a defense response in which these T cells will begin attacking and destroying our host cells. And this is of particular importance when transplanting things like the bone marrow because bone marrow actually contains a very high concentration of T cells.