<P> Bone marrow transplant can replace the transplant recipient's immune system with the donor's, and the recipient accepts the new organ without rejection . The marrow's hematopoietic stem cells--the reservoir of stem cells replenishing exhausted blood cells including white blood cells forming the immune system--must be of the individual who donated the organ or of an identical twin or a clone . There is a risk of graft - versus - host disease (GVHD), however, whereby mature lymphocytes entering with marrow recognize the new host tissues as foreign and destroy them . </P> <P> Gene therapy is another method that can be used . In this method, the genes that cause the body to reject transplants would be deactivated . Research is still being conducted, and no gene therapies are being used to date to treat patients . Current research tends to focus on Th1 and Th17 which mediate allograft rejection via the CD4 and CD8 T cells </P>

When is organ rejection most typically seen after transplant