Influenza A virus matrix protein 1-specific human CD8+ T-cell response induced in trivalent inactivated vaccine recipients.

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.

Vaccinia virus-specific CD8(+) T-cell responses target a group of epitopes without a strong immunodominance hierarchy in humans.

Immunization with vaccinia virus (VACV) resulted in long-lasting protection against smallpox and successful global eradication of the disease. VACV elicits strong cellular and humoral immune responses. Although neutralizing antibody is essential for protection, cellular immunity seems to be more important for recovery from infection in humans. We analyzed the immunodominance hierarchy of 73 previously identified VACV human CD8(+) T-cell epitopes restricted by HLA-A1, -A2, -A3, -A24, -B7, or -B44 alleles or the alleles belonging to one of these supertypes in 56 donors after primary VACV immunization. With the exception of the responses to HLA-A24 supertype-restricted epitopes, there were no consistent patterns of epitope immunodominance among donors sharing the same HLA alleles or supertypes, which is in sharp contrast with the mouse studies. However, we identified 12 epitopes that were recognized by >or=20% of donors sharing the same HLA allele; 6 of these epitopes contributed >or=20% of the total VACV-specific T-cell response in at least one individual. VACV-specific CD8(+) T-cell responses targeted a group of epitopes, "relatively dominant" epitopes, without a strong immunodominance hierarchy in humans, which may be advantageous to humans to prevent the emergence of T-cell escape mutants.

Genome-wide screening of human T-cell epitopes in influenza A virus reveals a broad spectrum of CD4(+) T-cell responses to internal proteins, hemagglutinins, and neuraminidases.

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 identified a total of 83 peptides, 54 of them novel, to which specific T cells were detectable in interferon-gamma (IFN-gamma) enzyme-linked immunosorbent spot assays using peripheral blood mononuclear cells from four healthy adult donors. The surface glycoproteins, HA and NA, major components of vaccines, expressed many T-cell epitopes. HA and matrix protein 1 expressed 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. Fifty-three percent of donors gave a positive response to H3 HA peptides, whereas 17% gave a positive response to H1 HA peptides. Our genome-wide screening is useful in identifying T-cell epitopes and is complementary to the approach based on the predicted binding peptides to well-studied HLA-A, -B, and -DR alleles.

In vitro evidence that commercial influenza vaccines are not similar in their ability to activate human T cell 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 IFNgamma producing cells activated. These data suggest that TIV vaccines are not similar in their ability to activate human T cell responses.

Discordance between antibody and T cell responses in recipients of trivalent inactivated influenza vaccine.

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 IFNgamma-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 IFNgamma-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 trivalent inactivated influenza vaccine.

Induction of human T cell-mediated immune responses after primary and secondary smallpox vaccination.

BACKGROUND: Postexposure vaccination strategies rely on a rapid induction of poxvirus-specific immune responses. Postvaccination cell-mediated immune (CMI) responses have not been compared by use of controlled trials in previously vaccinated (vaccinia-nonnaive) and nonvaccinated (vaccinia-naive) individuals. METHODS: To assess the time course of vaccinia-specific CMI responses, 20 previously vaccinated and 10 vaccinia-naive individuals were vaccinated with Dryvax, and serial blood samples were drawn. RESULTS: Both groups developed peak levels of vaccinia-specific interferon (IFN)- gamma -producing T cells by day 14 after vaccination. In vaccinia-nonnaive individuals, vaccinia-specific CMI responses were detected by day 7 after vaccination and preceded the increase in antibody titers. IFN- gamma enzyme-linked immunospot responses were significantly different between the 2 groups on days 7 (greater in vaccinia-nonnaive than in vaccinia-naive individuals) and 14 (greater in vaccinia-naive than in vaccinia-nonnaive individuals). Lymphoproliferation responses in vaccinia-nonnaive individuals were significantly higher on days 3 and 7, but cytotoxic T cell lysis activity was not statistically different at any time point. Antibody responses conformed to expected primary and secondary patterns of induction. CONCLUSIONS: 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.