“…In general, in experimental settings without adjuvants, heterotypic immunity is efficiently induced by infections of the lung with live influenza A virus (28,38). Likewise, recombinant vectors capable of expressing the conserved viral proteins in host cells, particularly in the lung, tend to be efficient inducers of heterotypic protection (42,49). The specificity of the protective effect correlates with the conserved viral core antigens recognized by T cells (reviewed in references 12, 14, 20, 29, and 68), and protection can be transferred with core protein-specific T cells, particularly class I restricted cytotoxic T lymphocytes (32,59,70).…”