Phase 2a Dose-Defining Safety and Immunogenicity Study of MTBVAC in South African Neonates Living in a High-Burden Tuberculosis-Endemic Region

new effective tuberculosis (TB) vaccine is essential to achieve World Health Organization (WHO) End TB goals and eliminate TB by 2050. The optimal long-term strategy would be a combination of serial mass campaigns in adults, coupled with universal newborn vaccination. Newborns are the only human population without prior mycobacterial exposure in TB endemic countries and as such, live attenuated mycobacterial vaccines may offer better protection to this naïve population compared to adults.

MTBVAC is a novel TB vaccine candidate generated by genetically attenuating an M. tuberculosis clinical isolate of the EuroAmerican lineage. MTBVAC is based on two independent, stable genetic deletions of the genes coding for two major virulence factors, phoP coding for the transcription factor PhoP and fadD26 coding for the synthesis of PDIM. Since MTBVAC contains most of the genes deleted from BCG, it presents a wider collection of mycobacterial antigens to the host immune system. Safety and immunogenicity of MTBVAC has been demonstrated in BCG naive adults; and MTBVAC appears safe in a small ongoing Phase 1b study in South African newborns. Definitive demonstration of safety and immunogenicity at the optimal MTBVAC dose is key to progression into multi-centre efficacy trials in newborns.

A Phase 2a dose-defining study of MTBVAC to evaluate the safety, reactogenicity, immunogenicity, and potential for IGRA conversion and reversion, of MTBVAC in South African newborns. Ninety-nine HIV unexposed, BCG naïve newborns will be randomized to receive either BCG 2.5 x 105 CFU (n=24) or MTBVAC at one of three dose levels (n=75). Allocation will be double blind. Enrolment will be sequential into 3 cohorts of increasing MTBVAC dose (Cohort 1: n=25 MTBVAC 2.5 x 10E+04 and n=8 BCG; Cohort 2: n=25 MTBVAC 2.5 x 10E+05 and n=8 BCG; Cohort 3: n=25 MTBVAC 2.5 x 10E+06 and n=8 BCG). Dose escalation will be staggered to allow gradual evaluation of safety; final selection of the dose for Cohort 3 will be based on all available safety and immunogenicity data.