Antileprosy protective vaccination of rhesus monkeys with BCG or BCG plus heat-killed Mycobacterium leprae: immunologic observations.

Groups of rhesus monkeys were vaccinated and boosted with Mycobacterium bovis bacillus Calmette Guerin (BCG) or BCG plus low-dose (LD) or high-dose (HD) heat-killed M. leprae (HKML), or were unvaccinated. Prior to and following vaccination-boosting and subsequent M. leprae (ML) challenge, these and unvaccinated, unchallenged control monkeys were observed longitudinally for approximately 3 years. Vaccination with BCG plus HKML initially stimulated significant in vitro blood mononuclear cell blastogenic responses to lepromin, which returned to baseline post-boosting and post-live-ML-challenge, minimally reappearing significantly 2 years post-ML-challenge. Vaccination with BCG failed to stimulated positive blastogenic responses to lepromin before ML-challenge but small, marginally positive, intermittent responses were seen post-ML-challenge. Compared to the unvaccinated ML-challenged group, significant increases in the numbers of blood CD4+ and CD8+ T-cell subsets and an increased CD4+:CD8+ ratio were observed in both BCG plus HKML-vaccinated, ML-challenged groups, but not in the BCG-only-vaccinated, ML-challenged group. CD4+CD29+ and CD4+CD45RA+ subset numbers increased significantly over time in only the BCG plus LD HKML-vaccinated, ML-challenged group. Compared to unvaccinated, ML-challenged groups, vaccination with BCG or BCG plus HKML followed by ML-challenge produced lower IgM:IgG antiphenolic glycolipid-I (PGL-I) serum antibody ratios and protected rhesus monkeys from clinical leprosy, consistent with prior observations that low IgM:IgG anti-PGL-I responses correlated with resistance to and protection from leprosy.