Gene therapy focuses on replacing defective genes with modified working genes. Many diseases are caused by a faulty gene, meaning the body is unable to produce essential proteins or enzymes. In its simplest form, gene therapy aims to identify the defective gene and repair it by replacing a normal gene (Senn). 2.2 Types of Gene Therapy There are two types of gene therapy, somatic gene therapy and germline gene therapy. Somatic gene therapy involves repairing the defective gene. With this form of therapy, only somatic cells are targeted and not germline cells, otherwise known as gametes or sex cells. If the DNA modification is limited to only the body's cells, then the altered gene affects only the treated patient and not his or her offspring. Germline gene therapy changes the gene pool of the treated person and involves the incorporation of an engineered gene into the gametes that permanently alters the patient's genes and these genes would be inherited by future generations. This type of therapy is banned in many countries such as Australia, Canada and Germany due to ethical and technical concerns, including insufficient knowledge about possible risks for future generations (Strachnan). The United States has no federal legislation specific to germline or somatic gene therapy other than the general U.S. Food and Drug Administration (FDA) testing regulations that apply to all therapies (Is Gene Therapy Safe?). The types of diseases that can be treated with Gene therapies are those in which the replacement of a single gene can cure the disease. Some of the major diseases currently being researched in gene therapy trials include cancer, hemophilia, sickle cell disease, muscular dystrophy… the focus of the article… the removal of millions of white blood cells called T cells , which are then genetically modified and restructured to target tumor cells. These cells are then returned to the patient's body where they multiply to fight cancer (Marchione). This and other recent clinical successes are very encouraging and have led to a renewal of interest in gene therapy with scientists, doctors and commentators all calling for continued investment in the area. Additionally, we are now seeing gene therapy treatments inch closer to commercialization. The approval of the first gene therapy treatment in the United States or Europe occurred in November 2012, when the European Commission approved the European Medicines Agency's recommendation to approve Glybera, a gene therapy that addresses lipoprotein lipase deficiency , cause of severe pancreatitis (Richards).