Abstract
T cellular responses play a significant role in mediating protective immune responses against influenza in humans. In the current study, we evaluated the ability of a candidate virosomal H5N1 vaccine adjuvanted with Matrix M(TM) to induce CD4(+) and CD8(+) T cell responses in a phase 1 clinical trial. We vaccinated 60 healthy adult volunteers (at days 0 and 21) with 30 μg haemagglutinin (HA) alone or 1.5, 7.5, or 30 μg HA formulated with Matrix M(TM). To evaluate the T cellular responses, lymphocytes were stimulated in vitro with homologous (A/Vietnam/1194/2004 [H5N1]) and heterologous H5N1 (A/Anhui/1/05 or A/Bar-headed Goose/Qinghai/1A/05) antigens. The antigen-specific cytokine responses were measured by intracellular cytokine staining and by multiplex (Luminex) assays. An increase in CD4(+) Th1 and Th2 cytokines was detected 21 days after the first vaccine dose. No increase in Th cytokine responses was observed after the second dose, although it is possible that the cytokine levels peaked earlier than sampling point at day 42. Formulation with the Matrix M(TM) adjuvant augmented both the homologous and cross-reactive cytokine response. Antigen-specific CD8(+) T cell responses were detected only in a few vaccinated individuals. The concentrations of Th1 and to a lesser extent, Th2 cytokines at 21 days post-vaccination correlated moderately with subsequent days 35 and 180 serological responses as measured by the microneutralisation, haemagglutination inhibition, and single radial hemolysis assays. Results presented here show that the virosomal H5N1 vaccine induced balanced Th1/Th2 cytokine responses and that Matrix M(TM) is a promising adjuvant for future development of candidate pandemic influenza vaccines.