Methods: 100 adults 65 years of age or older were randomized to receive either the high dose or the standard dose vaccine. We evaluated activation of pTfh cells and plasmablast frequency at baseline (day 0) and day 7 after vaccination in a subset of 50 participants (high dose influenza vaccine (n=26) and the standard dose influenza vaccine (n=24)). Hemagglutinin inhibition titers were measured at day 0 and day 28 in these same individuals.
Results: There was a significantly higher increase from baseline in the frequency of ICOS+pTfh cells in the high dose group compared to the standard dose group (p=0.02). The increase in ICOS+pTfh cells positively correlated with the humoral immune response as measured by the increase in plasmablasts (r=0.45, p=0.0009). The increase in frequency of ICOS+pTfh cells significantly greater for individuals who seroconverted at week 4 to to H1N1 (p=0.0045), H3N2 (p=0.0037), and influenza B (p=0.019).
Conclusion: We conclude that the high dose influenza vaccine increases the frequency of activated pTfh cells at day 7 greater than the standard dose, and that a more robust increase in ICOS+Tfh cells can predict seroconversion at 4 weeks post-vaccination.
K. Nicholas, None
S. Yoder, None
H. K. Talbot, MedImmune: Investigator , Research support
Sanofi Pasteur: Investigator , Research support
Gilead: Investigator , Research support
Teva: Scientific Advisor , Consulting fee
VaxInnate: Scientific Advisor , Consulting fee
S. Kalams, None