We performed a genome-wide screening for T cell epitopes using synthetic peptides that encompass all of the influenza A viral proteins, including subtype variants for hemagglutinin (HA) (H1, H3 and H5) and neuraminidase (NA) (human and avian N1 and N2) proteins, based on the sequence information of recently circulating strains. We found a total of 83 peptides, 54 of them novel, to which specific T cells were detectable in IFN-γ ELISPOT assays using peripheral blood mononuclear cells from four healthy adult donors. The surface glycoproteins, HA and NA, major components of vaccines, had many T cell epitopes. HA and matrix protein 1 had more T cell epitopes than other viral proteins, most of which were recognized by CD4 + T cells. We established several cytotoxic CD4 + T cell lines from these donors. We also analyzed H1 and H3 HA-specific T cell responses using the peripheral blood mononuclear cells of 30 hospital workers. 53% of donors gave a positive response to H3 HA peptides, while 17% gave a positive response to H1 HA peptides. Our genomewide screening is useful in identifying T cell epitopes and complementary to the approach based on the predicted binding peptides to well-studied HLA-A, B and DR alleles.

This study demonstrates that the kinetics of CMI responses are different after primary vaccination versus after revaccination and indicates that memory can exist in individuals vaccinated >/=30 years ago. These data support the epidemiological observation in smallpox outbreaks that successful revaccination within 4 days of exposure is partially protective. In vaccinia-nonnaive individuals, protection against smallpox during the postexposure revaccination period may require T cell memory as an essential component for the rapid induction of protective cellular and humoral responses.

We evaluated three commercial trivalent inactivated vaccines (TIVs) from the 2007-2008 season in terms of their ability to elicit in vitro T cell responses. T cell-mediated immunity may offer a more cross-reactive vaccine approach for the prevention of pandemic or epidemic influenza. Human cytotoxic T cell lines demonstrated differences in matrix protein 1 and nucleocapsid protein recognition of autologous target cells. Peripheral blood mononuclear cells stimulated with each of the TIVs showed statistically significant differences between the vaccines in the numbers of IFNγ producing cells activated. These data suggest that TIV vaccines are not similar in their ability to activate human T cell responses.

Thirty adults were tested for humoral and cellular immune responses following immunization with the trivalent inactivated influenza vaccine. Modest but significant inverse correlations between the baseline and the fold changes in the number of IFNγ producing cells and the levels of neutralizing antibodies were observed. Specific increases in proliferative responses in the CD8 CD45RA+ population were noted after vaccination. Minimal correlations between neutralizing antibody titers and the number of IFNγ producing cells in terms of prevaccination levels or fold increases were observed. These results show specific increases in a CD8 T cell subset and discordant T and B responses induced by the inactivated influenza vaccine.

Among 17 HLA-A2-positive healthy adults, CD8؉ T-cell responses against an HLA-A2-restricted matrix protein 1 (M1) epitope increased after immunization with trivalent inactivated influenza vaccine (TIV) in two individuals. The presence of M1 in TIV was confirmed by Western blotting. T-cell cytotoxicity assays showed that TIV is processed and the epitope is presented by antigen-presenting cells to an M1 epitope-specific CD8 ؉ T-cell line for specific lysis. These data show that TIV, which is formulated to contain surface glycoproteins to induce serotype-specific antibody responses, also contains M1, capable of inducing subtype cross-reactive CD8 ؉ T-cell responses in some vaccinees.