Adjuvant-Associated Peripheral Blood mRNA Profiles and Kinetics Induced by the Adjuvanted Recombinant Protein Candidate Tuberculosis Vaccine M72/AS01 in Bacillus Calmette–Guérin-Vaccinated Adults

Systems biology has the potential to identify gene signatures associated with vaccine immunogenicity and protective efficacy. The main objective of this study was to identify optimal post-vaccination time points for evaluating peripheral-blood RNA-expression profiles in relation to vaccine immunogenicity and potential efficacy in recipients of the candidate tuberculosis vaccine M72/AS01. In this phase II open-label study (NCT01669096; https://clinicaltrials.gov/), healthy Bacillus Calmette-Guerin (BCG) primed, HIV-negative adults were administered two doses (30-days apart) of M72/AS01. Twenty subjects completed the study and 18 subjects received two doses. Blood samples were collected pre-dose 1, pre-dose 2 and 1, 7, 10, 14, 17 and 30 days post-dose 2. RNA expression in whole blood and peripheral-blood mononuclear cells (PBMCs) was quantified using microarray technology. Serum IFNG responses and M72-specific CD4+ T cell responses to vaccination, and the observed safety profile were similar to previous trials. Two different approaches were utilized to analyse the RNA expression data. First, a kinetic analysis of RNA expression changes using Blood Transcriptional Modules revealed early (1 day post dose-2) activation of several pathways related to innate immune activation, both in whole blood and PBMC. Second, using a previously identified gene signature as a classifier, optimal post-vaccination time points were identified. Since M72/AS01 efficacy remains to be established, a PBMC-derived gene signature associated with the protective efficacy of a similarly adjuvanted candidate malaria vaccine was used as a proxy for this purpose. This approach was based on the assumption that the AS01 adjuvant used in both studies could induce shared innate immune pathways. Subjects were classified as gene-signature positive or gene-signature negative. Assignments of subjects to gene-signature positive or gene-signature negative groups were confirmed by significant differences in RNA expression of the gene-signature genes in PBMCs at 14 days post-dose 2 relative to pre-vaccination and in whole-blood samples at 7, 10, 14 and 17 days post-dose 2 relative to pre-vaccination. Hence, in comparison with a pre-vaccination, 7, 10, 14, and 17 days post-vaccination appeared to be suitable time points for identifying potentially clinically relevant transcriptome responses to M72/AS01 in whole blood samples.