Preclinical development of a dengue tetravalent recombinant subunit vaccine: Immunogenicity and protective efficacy in nonhuman primates.

We describe here the preclinical development of a dengue vaccine composed of recombinant subunit carboxy-truncated envelope (E) proteins (DEN-80E) for each of the four dengue serotypes. Immunogenicity and protective efficacy studies in Rhesus monkeys were conducted to evaluate monovalent and tetravalent DEN-80E vaccines formulated with ISCOMATRIX™ adjuvant. Three different doses and two dosing regimens (0, 1, 2 months and 0, 1, 2, and 6 months) were evaluated in these studies. We first evaluated monomeric (DEN4-80E) and dimeric (DEN4-80EZip) versions of DEN4-80E, the latter generated in an attempt to improve immunogenicity. The two antigens, evaluated at 6, 20 and 100 µg/dose formulated with ISCOMATRIX™ adjuvant, were equally immunogenic. A group immunized with 20 µg DEN4-80E and Alhydrogel™ induced much weaker responses. When challenged with wild-type dengue type 4 virus, all animals in the 6 and 20 µg groups and all but one in the DEN4-80EZip 100 µg group were protected from viremia. Two out of three monkeys in the Alhydrogel™ group had breakthrough viremia. A similar study was conducted to evaluate tetravalent formulations at low (3, 3, 3, 6 µg of DEN1-80E, DEN2-80E, DEN3-80E and DEN4-80E respectively), medium (10, 10, 10, 20 µg) and high (50, 50, 50, 100 µg) doses. All doses were comparably immunogenic and induced high titer, balanced neutralizing antibodies against all four DENV. Upon challenge with the four wild-type DENV, all animals in the low and medium dose groups were protected against viremia while two animals in the high-dose group exhibited breakthrough viremia. Our studies also indicated that a 0, 1, 2 and 6 month vaccination schedule is superior to the 0, 1, and 2 month schedule in terms of durability. Overall, the subunit vaccine was demonstrated to induce strong neutralization titers resulting in protection against viremia following challenge even 8-12 months after the last vaccine dose.