Platelets - help blood to clot in order to stop bleeding. White blood cells - fight infections. Lymphocytes - fight bacterial, viral and fungal infections. T cells from the donor can also attack the recipient resulting in a reaction called graft versus host disease. T cells from the recipient can reject the donor bone marrow cell resulting in graft failure.
B lymphocytes make antibodies which help destroy germs in our body.
Patients who are recovering from chemotherapy and normal individuals who are treated with certain drugs that stimulate the growth of the bone marrow have relatively large numbers of PBSC in their blood. The PBSC can be collected and used in certain situations as a source of stem cells for transplantation. Another source of stem cells is the blood that is found in the placenta of a newborn baby once the umbilical cord is cut. Umbilical cord blood, or UCB, has been successfully used as a source of bone marrow stem cells for transplantation in both related and unrelated transplants. These three situations are covered in more detail below.