Conjugation of a TLR5 agonist to the Plasmodium falciparum Circumsporozoite (CS) protein enhances murine and human Dendritic cells (DC) interaction in vitro and increases protective immunity following intranasal immunization in mice (37.4)

Abstract A needle-free malaria vaccine has been developed based on intranasal (I.N) immunization with a recombinant P. falciparum circumsporozoite (CS) protein conjugated to the TLR5 agonist flagellin. Mice immunized I.N, but not subcutaneously, with flagellin-modified CS developed sporozoite neutralizing antibodies that protect against challenge with a transgenic rodent parasite expressing P. falciparum CS repeats. To better understand the role of innate immune cells in the induction of protective immunity, we analyzed the interaction of flagellin-modified CS with murine bone marrow-derived dendritic cells (DC) and human monocyte-derived DC in vitro. The fusion protein was rapidly taken up by DC and remained detectable in the cytosol as long as 24 hours post antigen pulse. A murine DC line (D1), and a sub-population of human DC, matured and expressed increased levels of CD40 and CD86 following stimulation with flagellin-modified CS. In I.N. immunized mice, the Nasopharyngeal-associated Lymphoid Tissue (NALT) was enlarged 2-fold over naïve NALT, and increased levels of CD11c+ DC were observed by confocal microscopy and FACS analysis. NALT cell subpopulations exhibited a higher B:T cell ratio than those observed in lymph nodes. A better understanding of innate and adaptive immune responses elicited in NALT by TLR ligand-modified CS protein will help identify critical immune parameters required for the induction of sporozoite specific immunity that protects from malaria infection.