Interferon induction increased through chemical modification of a synthetic polyribonucleotide.

The alternating copolymer riboadenylic-ribouridylic acid gained asignificant increase in ability to stimulate interferon production (2-to 20-fold) and cellular resistance (100-to 10,000-fold) both in vitro and in vivo upon substitution of phosphate by thiophosphate groups. The resulting nucleotide analog was also 10 to 100 times less sensitive to degradation by pancreatic ribonuclease, as determined byresidual antiviral activity.