Cell therapy works by introducing new cells into a target tissue in order to treat a disease. These may be either cells from the patient (autologous) or cells from other patient, often a close relative (allogeneic). Occasionally, non-human cells may be used to produce a desired response in the patient (xenotransplantation) although this involves a new set of ethical considerations.
Cells used for cell therapy may be mature cells, cells that have been functionalised in some way, e.g. by the insertion of a gene (see the section below) or stem cells, which have the ability to differentiate into a wide variety of mature cells.
A large part of the current research focus is on the use of stem cell therapies to treat, amongst others, cardiovascular disease, type 1 diabetes, and brain and spinal injuries. Human embryonic stem cells are pluripotent, meaning they have the capacity to differentiate into all cell and tissue types derived from the three primary germ layers, the endoderm, mesoderm and ectoderm. Because of ethical constraints concerning the use of embryonic stem cells in some countries, much research is focused on the use of adult stem cells or those derived from umbilical cord blood. These are multipotent, meaning they can differentiate only into a limited number of cell types, although some research indicates the ability to generate pluripotent, non-embryonic stem cells. Some recent research suggests a breakthrough in establishing embryonic stem cell lines without destruction of the parent embryos.
Gene therapy involves the insertion of genes into a patients's cells and tissues with the intention of treating a disease or condition. One current focus of intense research is in using gene therapy to treat hereditary diseases such as muscular dystrophy, cystic fibtrosis or haemophilia, where a defective gene or, more correctly, mutant allele is replaced with a functional one.
The first approved gene therapy procedure was carried out in 1990 on a very young patient with a disease known as severe combined immunodeficiency. In the procedure, the missing gene was inserted into white blood cells which were then infused into the patient's bloodstream. A carrier, known as a vector, must be used to transport the therapeutic gene to the desired target cells and sites and a commonly used vector is a genetically modified virus in which any harmful genetic material has been removed and the desired gene incorporated. Various biomolecules also lend themselves to use as vectors.
The vast majority of gene therapy research is focused on somatic cells (which comprise most of the cells in the body). While it is possible to modify germline cells, this remains an ethically contentious area.
Nanotechnology may play an important role in future development of gene therapy, for example in designing new types of vector like dendrimers that can be constructed to carry DNA or RNA and targeted to cells with a high level of specificity and low toxicity.