Stem cell therapy also has serious risks and practical problems that must be solved before most treatments become routine.Rejection
Stem cells from a donor, including most embryonic stem cells, have different antigens, so the patient's immune system may reject them. Immunosuppressant drugs reduce rejection but weaken the immune system, increasing the risk of infection.Tumours
Stem cells divide readily. If they keep dividing out of control after transplantation they may form a tumour. Undifferentiated embryonic stem cells can form a teratoma, a tumour containing a mixture of tissues such as hair, muscle and bone. Every transplanted cell must therefore be fully differentiated.Contamination
Stem cells are grown in culture for long periods, sometimes using animal-derived products, so they may become contaminated with viruses or other pathogens that could infect the patient.Controlling the cells
It is difficult to make stem cells differentiate into exactly the right cell type, and transplanted cells may not survive, integrate or work properly in the tissue. Long-term effects are unknown because most treatments are new.Limits of adult stem cells
A patient's own adult stem cells avoid rejection, but they are rare, hard to isolate and only multipotent, so they can form few cell types.Cost
Growing patient-specific cells is slow and very expensive, so treatments may not be available to everyone.
Stem cells from a donor, including most embryonic stem cells, have different antigens, so the patient's immune system may reject them. Immunosuppressant drugs reduce rejection but weaken the immune system, increasing the risk of infection.Tumours
Stem cells divide readily. If they keep dividing out of control after transplantation they may form a tumour. Undifferentiated embryonic stem cells can form a teratoma, a tumour containing a mixture of tissues such as hair, muscle and bone. Every transplanted cell must therefore be fully differentiated.Contamination
Stem cells are grown in culture for long periods, sometimes using animal-derived products, so they may become contaminated with viruses or other pathogens that could infect the patient.Controlling the cells
It is difficult to make stem cells differentiate into exactly the right cell type, and transplanted cells may not survive, integrate or work properly in the tissue. Long-term effects are unknown because most treatments are new.Limits of adult stem cells
A patient's own adult stem cells avoid rejection, but they are rare, hard to isolate and only multipotent, so they can form few cell types.Cost
Growing patient-specific cells is slow and very expensive, so treatments may not be available to everyone.