Cell therapy can be defined as therapy in which cellular material is injected into a patient. There are two branches of cell therapy: one is legitimate and established, whereby human cells are transplanted from a donor to a patient; the other is dangerous alternative medicine, whereby injected animal cells are used to attempt to treat illness.The origins of cell therapy can perhaps be traced to the nineteenth century, when Charles-Édouard Brown-Séquard (1817–1894) injected animal testicle extracts in an attempt to stop the effects of aging.In 1931 Paul Niehans (1882–1971) – who has been called the inventor of cell therapy – attempted to cure a patient by injecting material from calf embryos.Niehans claimed to have treated many people for cancer using this technique, though his claims have never been validated by research. In 1953 researchers found that laboratory animals could be helped not to reject organ transplants by pre-inoculating them with cells from donor animals; in 1968, in Minnesota, the first successful human bone marrow transplantation took place. Bone marrow transplants have been found to be effective, along with some other kinds of human cell therapy – for example in treating damaged knee cartilage. In recent times, cell therapy using human material has been recognized as an important field in the treatment of human disease.The experimental field of Stem cell therapy has shown promise for new types of treatment. In mainstream medicine, cell therapy is supported by a distinct healthcare industry which sees strong prospects for future growth.