A Live Attenuated Listeria Monocytogenes Vaccine Vector Expressing SIV Gag Is Safe and Immunogenic in Macaques and Can Be Administered Repeatedly

Abstract Listeria monocytogenes(Lm) is known to induce strong cellularimmune responses. We constructed a live-attenuated Lm vector, Lmdd-BdopSIVgag , which encodes SIVmac239 gag . Intragastric (i.g.) administration of 3 × 10 12 bacteria to rhesus macaqueswas safe and induced anti-Gag cellularbut no humoral immuneresponses. Boosting of Gag-specific cellularresponses was observed after i.g. administration of Lmdd-BdopSIVgag to previously vaccinated RM despite preexisting anti-Lm immunity shown by lymphoproliferative responses. Surprisingly, anti-Lm cellularresponses were also detected in non-vaccinated controls, which may reflect the fact that Lm is a ubiquitous bacterium. The novel, live-attenuated Lmdd-BdopSIVgag may be an attractive platform for oral vaccine delivery.