Correction

IMMUNOLOGY. For the article “Comparative assessment of virulence of recombinant vaccinia viruses expressing IL-2 and IL-15 in immunodeficient mice” by Liyanage P. Perera, Carolyn K. Goldman, and Thomas A. Waldmann, which appeared in number 9, April 24, 2001, of Proc. Natl. Acad. Sci. USA (98, 5146–5151; First Published April 10, 2001; 10.1073/pnas.081080298), the authors note the following printer's error. On page 5147, right column, second paragraph, line 8, the word “secretary” should read “secretory.”