Double-edged sword.

chemotherapy or HIV. Therefore, flight attendants and others say that airplane cabin air should be held to higher standards than workplaces. Pressure from passengers may be a major contributing factor in encouraging airlines to increase fresh air. In the August issue of Consumer Reports, airlines were ranked according to levels of carbon dioxide in airplane cabins and criticized for the low amounts of fresh air. Consumer Reports recommended that passengers choose airlines according to the amounts of fresh air they circulate. They also recommended that the FAA set a comfort standard of 1,000 ppm. Although individuals with genetic disorders and diseases such as cancer, AIDS, diabetes, or Alzheimer's may view the potential of gene therapy as just the weapon they're looking for, other people perceive the "slicing and dicing" of genetic material as a potential double-edged sword. Scientists are attempting to estimate the real risks associated with gene therapy. Most current gene therapies use retro-viral vectors to transfer a therapeutic gene into the cells of a patient who lacks a normally functioning copy of the gene. Retroviral vectors are made by deleting portions of a retroviral genome and replacing the deleted viral genes with the therapeutic gene. The resulting vector integrates a DNA copy of its genome, containing the therapeutic gene, into the genome of a host cell, but because of the missing viral genes the vector cannot be replicated like a normal retrovirus. Typically, bone marrow cells are removed and exposed to the vector in culture. The cells containing the therapeutic gene are then infused back into the patient. The fear is that the vector may integrate its DNA copy near a gene involved in regulation of growth or development of the cell and interfere with the normal regulatory processes, causing the cell to become cancerous. Although, says toxicologist Richard Irwin of NIEHS, "there is absolutely a finite probability that it will occur," the risk of insertional mutagenesis is believed to be very low. The difficulty comes in trying to determine exactly what "very low" means in terms of absolute risk to humans from gene therapy. Scientists are concerned about other potential side effects of the process of gene therapy. First, it is not currently possible to target a vector carrying a therapeutic gene to a specific cell population. Expression of the gene in nontargeted cells may interfere ~~~~~ 6N Viral genes Desired gene removed Packaging r dsired gene …