21.   Right now, the main approaches in gene therapy research are to infuse naked DNA into cells or to use viruses to add DNA to the genome.

22.   Roth plans to use a virus to take antisense genes into the tumor cells.

23.   The cat vaccine was developed using virus collected from animals that had been infected for years without showing symptoms.

24.   The initial test used a virus that targets rod-shaped bacteria such as anthrax, and it turned up positive.

25.   The monkey virus is used because it can stimulate immunity in a human being without causing illness.

26.   The scientists were trying to use mousepox virus to create an artificial strain of the microbe that would render mice infertile.

27.   The vaccine may be needed only if there is a terrorist attack using the virus, an unlikely event.

28.   They hope this form of vaccination can give immunity that lasts longer and covers more strains than normal flu shots, which use inactivated viruses.

29.   Thus far, efforts to use viruses as carriers to introduce healthy genes to replace the defective ones that cause cystic fibrosis have not worked very well.

30.   Using a virus to treat a disease seems counterproductive.