Human gene therapy is a technique of treating various diseases and disorders through replacement of defective genes with healthy ones. Gene therapy is performed on a cellular level, and much of it was still in experimental stages as of 2011. Normal genes function by using proteins to carry out certain coding sequences; when a gene is defective, the proteins can not carry out these instructions correctly. Using human gene therapy, scientists have attempted to introduce healthy genes to specific cells through a few different methods.
One of the types of gene therapy uses a modified virus as a carrier for a new, healthy gene. Scientists have developed techniques to alter the natural way that viruses deliver their pathogenic matter to cells. Instead of infection-causing matter, carrier viruses can insert normal human genes into targeted cells. This method has been attempted with lung and liver cells to help cure infections of these organs.
Human gene therapy treatments can also involve methods that do not use viruses. Some scientists have tried repairing the original genes through a process called reverse mutation, with mixed results. Different genes can be changed in varying degrees, and researchers have attempted to manipulate these rates of change as well.
Some experiments in human gene therapy have been more successful when the faulty gene is removed altogether and replaced with a healthy gene. This technique is known as gene swapping. Other gene therapy trials have had better results when the defective gene is left in place and a normal one is inserted along with it. Factors influencing these results can include the type of target cell as well as the nature of the disorder being treated.
Disease gene therapy has had some success in treating inherited conditions such as hemophilia and severe combined immune deficiency. The biggest challenge with using gene therapy for these conditions is the possibility of cell rejection. If a patient's body recognizes cells with modified genes as foreign objects, the results can be life-threatening if that patient has a non-functioning immune system.
Medical researchers have continued to explore the possibilities of using human gene therapy for a wider range of conditions. Trials in animal gene therapy have been effective in improving health problems such as degenerative blindness and even depression. Retinal genes introduced into the cells of nearly blind rats have successfully restored more of their sight. Similar gene therapy in the brains of mice has restored the function of a key protein needed to relieve severe clinical depression.