Another Setback for A Simple Concept

The concept of gene therapy is pretty simple. Sometimes people inherit "broken" genes which prevent the production of functional proteins that play important roles in the body. The idea is to introduce a functional copy of the gene into a population of cells and hope that they will begin to function normally. The gene is delivered to the cells by one of several defective virus strategies. However the implementation of the strategy is more difficult.


Continue Reading

In the case of X-linked SCID (severe combined inmunodeficiency), a protein component of a receptor in immune cells is broken resulting in a non-functional adaptive immune system. Seinfeld jokes aside, this disease made the "bubble boy" famous.

A doctor in France has been treating kids with this disease by introducing the correct gene in to bone marrow stem cells, and the results have been encouraging. His program was halted a couple of years ago, however, because two kids developed cancer as a result of treatment--one has since died. Since the correct copy of the gene integrates into the genome somewhat randomly, there are risks that normal genes can be disturbed. Unexpectedly, the same gene was found to be affected in both of the kids with cancer. I had not heard much since then, but apparently treatments resumed.

Unfortunately, Nature reports that the program has been halted again because of another cancer case.

Fischer is now investigating why the third child, who was treated at a later age than the previous two children, developed cancer. The child's cells did not seem to have the same genetic glitch that caused the first two cancers, he says, but he cautions that the analysis is still under way.

Fischer adds that he still believes in gene therapy as a treatment for X-linked SCID, because 15 children treated in this way are still alive, and 14 are doing well four years later. But his group will not treat any more children using its current gene-therapy system, he says. He adds that he plans to change a key step in the treatment by changing the vector — the modified virus that delivers the therapeutic gene to the patients.

This is one of those difficult ethical scenarios. I don't know what the average lifespan of these kids is, but I'm pretty sure it is less than a decade (with good care.) They have no other real options for long-term survival. Hopefully change in treatment will occur quickly and be at least as successful.