ICOS and influenza: While influenza infection and administration of non-adjuvanted influenza vaccines induced robust Tfh responses in adults, addition of MF59 as an adjuvant significantly enhanced the response (95) with expansion of HA-specific Tfh (CD4+ICOS+, CD4±ICOS+CXCR5+IL-21+) by day 7 postimmunization that highly correlated with HAI titers 1 and 6 months later (95).