The transgene contains a single base deletion that causes a frameshift and results in expression of a polypeptide containing the N-terminal signal sequence plus amino acids 1-237 of PR8 hemagglutinin (HA) driven by the SV40 early region promoter-enhancer and polyadenylation sequences. Two lineages were established, HA28 and HA37, with two to three transgene copies each. (J:137514)