Cutaneous delayed-type hypersensitivity (DTH) in a multi-formulation comparator trial of the anti-falciparum malaria vaccine candidate RTS,S in rhesus macaques

Abstract

Background: Studies are underway to identify more immunogenic formulations of the existing anti-falciparum malaria vaccine RTS,S/AS02A. To supplement in vitro immunogenicity assays, cutaneous delayed-type hypersensitivity (DTH) may be a useful indicator of functional, cell-mediated immunogenicity.

Methods: Adult rhesus monkeys were immunized with saline or one of four RTS,S/adjuvant formulations: RTS,S/AS01B, RTS,S/AS02A-standard (current formulation), RTS,S/AS05 or RTS,S/AS06 at 0, 4, and 12 weeks. An additional cohort received RTS,S/AS02A-accelerated, at 0, 1, and 4 weeks. Six months after completing immunizations, five vaccine-relevant antigens (high and low doses) and two controls were administered intradermally. DTH reactivity (induration) was measured at 48 and 72h, and selected sites were biopsied for histological confirmation.

Results: In comparison with RTS,S/AS02A-standard, RTS,S/AS01B and RTS,S/AS05 each had larger mean reactions (induration) at 5 of 10 (p<0.01, at each site) and 1 of 10 (p<0.05, at the single site) vaccine relevant test sites, respectively. Histologically, perivascular mononuclear cell infiltrates, a cardinal feature of DTH, were largest in the RTS,S/AS01B monkeys.

Interpretation: In DTH testing, with histological confirmation, RTS,S/AS01B was immunogenically superior to RTS,S/AS02A-standard and two other novel RTS,S formulations. The DTH outcomes paralleled conventional in vitro cellular immunogenicity assessments in distinguishing among similar RTS,S formulations, even at 6 months after final vaccination.