Activated Human Neonatal CD8+ T Cells Are Subject to Immunomodulation by Direct TLR2 or TLR5 Stimulation

In conditions of optimal priming, the neonate possess competency to mount quantitatively adult-like responses. Vaccine formulations containing sufficiently potent adjuvants may overcome the neonates’ natural tendency for immunosuppression and provoke a similarly robust immune response. TLR expression on T cells represents the possibility of directly enhancing T cell immunity. We examined the ex vivo responsiveness of highly purified human cord blood-derived CD8+ T cells to direct TLR ligation by a repertoire of TLR agonists. In concert with TCR stimulation, only Pam3Cys (palmitoyl-3-Cys-Ser-(Lys)4) and flagellin monomers significantly enhanced proliferation, CD25+ expression, IL-2, IFN-γ, TNF-α, and intracellular granzyme B expression. TLR2 and TLR5 mRNA was detected in the CD8+ T cells. Blocking studies confirmed that the increase in IFN-γ production was by the direct triggering of surface TLR2 or TLR5. The simultaneous exposure of CD8+ T cells to both TLR agonists had an additive effect on IFN-γ production. These data suggest that a combination of the two TLR ligands would be a potent T cell adjuvant. This may represent a new approach to TLR agonist-based adjuvant design for future human neonatal vaccination strategies requiring a CD8+ component.