HLA-DRB1 and influenza: The HLA class I/II composition of our transgenic mouse model appears to be well warranted for studying the immunogenicity of double restricted influenza epitopes, first, because 50% and 20% of the European population carry the HLA-A*02:01 and the HLA-DRB1*01:01 allele, respectively [www.allelefrequencies.net], and secondly, because many CD8 T cell responses in influenza A virus infections appear to be restricted by the HLA-A*02:01 allele [9].