Cryopreserved Sporozoites with and without the Glycolipid Adjuvant 7DW8-5 Protect in Prime-and-Trap Malaria Vaccination.

Repeated intravenous (IV) administration of radiation-attenuated sporozoite (RAS) vaccines induces Plasmodium-specific CD8+ liver-resident memory T (Trm) cells in mice and achieves sterile protection against challenge. Our heterologous "prime-and-trap" vaccine strategy was previously shown to simplify and improve upon RAS vaccination. Prime-and-trap vaccination combines epidermal priming by DNA-encoded circumsporozoite protein (CSP) antigen followed by a single IV dose of freshly dissected RAS (fresh-RAS) to direct and trap activated and expanding CD8+ T cells in the liver. Prime-and-trap vaccination protects mice against wild-type sporozoite (spz) challenge. Assessment of prime-and-trap vaccines in nonhuman primate (NHP) models and/or humans would be greatly enabled if fresh-RAS could be replaced by cryopreserved RAS (cryo-RAS). Here, we investigated if fresh-RAS could be replaced with cryo-RAS for prime-and-trap vaccination in BALB/cj mice. Despite a reduction in spz vaccine liver burden following cryo-RAS administration compared with fresh-RAS, cryo-RAS induced a similar level of Plasmodium yoelii (Py) CSP-specific CD8+ liver Trm cells and completely protected mice against Py spz challenge 112 days after vaccination. Additionally, when the glycolipid adjuvant 7DW8-5 was co-administered with cryo-RAS, 7DW8-5 permitted the dose of cryo-RAS to be reduced four-fold while still achieving high rates of sterile protection. In summary, cryo-RAS with and without 7DW8-5 were compatible with prime-and-trap malaria vaccination in a mouse model, which may accelerate the pathway for this vaccine strategy to move to NHPs and humans.