Viruses 2:203C209 [PMC free article] [PubMed] [Google Scholar] 27. peak levels of trogocytosis+ T cells were detected earlier, on the 21st day after the second vaccination. The inverse correlation of baseline levels compared to postvaccine fold changes in GMTs of influenza-specific CD4 and CD8 T cells demonstrated that baseline levels of these specific cells could be considered a predictive factor of vaccine immunogenicity. INTRODUCTION Highly pathogenic avian influenza A viruses are considered to be of significant pandemic potentiality in the human population. To 2011, during influenza A (H5N1) outbreaks among poultry and wild birds, more than 500 cases of confirmed human infections were reported in 15 countries in Asia, Europe, and Africa (35). Most human cases with confirmed infection by influenza A (H5N1) manifested severe clinical respiratory disease that progressed rapidly to bilateral pneumonia and cardiac and renal complications with nearly 70% of cases proving fatal (32). Since limited but unsustained human-to-human transmission has been documented (31, 33), WHO has recommended that improvements to vaccines against influenza A (H5N1) vaccine should be pursued to aid in pandemic preparedness. Clinical trials of inactivated influenza A (H5N1) vaccines have shown prominent induction of antibody responses after the second immunization with antigen (13). Live attenuated influenza A (H5N1) vaccines [A LAIV (H5N1)] have been shown to induce both serum and local antibody responses: studied vaccines have included those generated by reverse genetics and BLR1 comprised of internal genes from cold-adapted A/Ann Arbor/6/60 (H2N2) virus along with hemagglutinin (HA) and neuraminidase (NA) genes derived from highly pathogenic H5N1 influenza viruses (10, 12, 27), and a vaccine constructed from replication-deficient A (H5N1) virus that lacks the NS1 gene (13, 23). The live attenuated A (H5N2) influenza vaccine has been developed by a Piromidic Acid traditional reassortant method combining nonpathogenic avian A/Duck/Potsdam/1402-6/68 (H5N2) and well-characterized cold-adapted, attenuated A/Leningrad/134/17/57 (H2N2) viruses (9, 26). The vaccine strain comprises the HA gene of the avian H5N2 virus and all other genes from the cold-adapted, attenuated strain and has been shown to be safe and protective in mice against live H5N1 virus challenge (9). This same vaccine candidate was also shown to be safe and tolerable in human clinical trials and induced significant antibody titers in both serum and nasal secretion (26). Antibodies elicited in humans by this vaccine were also shown to be cross-reactive to H5N1 virus in standard immunological assays for influenza (26). However, as vaccinated subjects have not been exposed to highly pathogenic H5N1 influenza virus, it remains unknown whether antibody levels from seasonal vaccination of live attenuated influenza vaccines (LAIV) that have been shown to be protective against seasonal influenza viruses will be sufficient to protect against H5N1 viruses. Furthermore, it has been shown that inactivated vaccines are poor inducers of cellular immunity, which has been shown to play a significant role in protection against H5N1 infection (11). These findings together make the development of vaccines that induce cellular immunity specific to influenza a high priority for pandemic preparedness. In Piromidic Acid the present study, CD4 and CD8 memory/effector T-cell immunity Piromidic Acid was evaluated in healthy young adults who received two doses of live attenuated A (H5N2) vaccine. T-cell responses were measured by standard methods, namely, intracellular cytokine staining (ICCS) of gamma interferon (IFN-)-producing cells (19) and a novel T-cell recognition of antigen-presenting cells (APCs) by protein capture (TRAP) assay (3, 8) based on the trogocytosis phenomenon, i.e., plasma membrane exchange between interacting immune cells (17). TRAP enables the detection of activated trogocytosis-positive T cells at initial phases of an immune response during the synaptic complex formation between antigen-presenting cells and T lymphocytes. Recently, TRAP was developed for trogocytosis evaluation in Piromidic Acid different cell lines (4, 20, 21) and for the measurement of antigen-specific T-cell responses in mice exposed to ovalbumin (20), lymphocytic choriomeningitis virus (3), or herpesvirus (1). In our study, a modified TRAP assay was used for the evaluation of influenza-specific T-cell responses in humans immunized with live attenuated influenza A (H5N2) vaccine. MATERIALS AND METHODS Clinical subjects. Nineteen healthy adults 18 to 22 years of age met eligibility requirements.