These are now candidate T cell clones as all of the T cells expanded in response to a single 15mer peptide. have remained elusive3. Containment of Mtb infection requires the induction and maintenance of a robust Th1 immune response2,4,5,6 and evidence from pre-clinical animal7 and human8 vaccination studies suggest the breadth of the vaccine-induced cytokine response (IFN- and TNF-, IL-2) is associated with efficacy9. Collectively, these T cells have been termed polyfunctional10. Recent results from the first Phase IIb vaccine study using MVA-Ag85A in human infants has highlighted the possibility that the induction of polyfunctional CD4+ T cell immunity, while important, may not be sufficient11 to confer protection. While human Cefiderocol Mtb specific CD4+ and CD8+ T cells are similar in the cytolytic and pro-inflammatory capacity12,13, CD8+ T cells are capable of discerning Mtb-infected cells, particularly those that are HLA-II negative. Human Mtb-specific CD8+ T cells are further Cefiderocol distinguished by both their preferential recognition of heavily infected cells and restriction by HLA-B14,15. Additionally, it is increasingly evident that CD8+ T cells have an important and complex role in Mtb containment and immunity14,16,17,18,19,20. Specifically, we note that CD8+ T cells are uniquely capable of discerning the Mtb-infected cell, and that a role for these cells in the long-term progression of mycobacterial growth has been demonstrated in the mouse and non-human primate models. For most vaccination studies, the assessment of vaccine-induced CD8+ T cells has relied upon the measurement of antigen-specific polyfunctional cells, typically using peptide pools. However, as these measurements have been considered as a surrogate of protective immunity, it leaves open the question as Cefiderocol to whether or not polyfunctional CD8+ T cells are capable of recognizing epitopes displayed in the context of Mtb infection and hence leaves open the possibility that a key parameter of vaccine immunogenicity may be overlooked. AERAS-402 is a replication-deficient serotype 35 adenovirus containing DNA that expresses KR2_VZVD antibody a fusion protein that includes three Mtb antigens, 85A (Ag85A), 85B (Ag85B) and TB10.421,22. Prior work has established that AERAS-402 boosting of BCG vaccination elicits high-frequency, polyfunctional CD4+ and CD8+ T cells in adults and infants21,23,24,25. To further study human cellular immune responses to AERAS-402 and define the capacity of vaccine-induced CD8+ T cells to recognize Mtb-infected cells, we performed a phase I double-blind, randomized, placebo-controlled trial. Results Study enrollment, vaccine administration, and immunologic studies Eleven adults between the ages of 18 and 45, without exposure to Mtb were enrolled (Tables 1 and ?and2).2). All received BCG vaccine 84 days prior to adenoviral vaccination. After randomization, 9 participants received AERAS-402 at day 0, 8 received AERAS-402 at day 28, and 2 received placebo at day 0 and 28 respectively (Supplementary Fig. S1; Consort Diagram26). To perform Cefiderocol immunologic characterization of vaccine-induced epitopes, study participants underwent leukapheresis prior to (day -14) and after AERAS-402 vaccination (between day 56 and 98). Peripheral blood mononuclear cells (PBMC) for intracellular cytokine staining (ICS) and IFN- ELISPOT was collected on days ?84, ?14, 28, and 56 respectively (Table 3 and Supplementary Table S1). ICS was also performed on day 98. ICS and IFN- ELISPOT assays were performed as described previously24,27 using synthetic peptide pools with 15-mers overlapping by 11 amino acids (aa) from each antigen contained within AERAS-402. For the CD8 ELISPOT assay (CD8/others), CD8+ T cells were negatively selected from peripheral blood mononuclear cells (PBMC) using a combination of CD4 and CD56 magnetic beads. For the PBMC ELISPOT, unfractionated PBMC were used as the source of responding T cells and largely consist of CD4+ T cells. Table 1 Summary of patient baseline characteristics ((%)?PBMC ELISPOT response from day -84 to day 56, reported as the Cefiderocol mean, standard error of the mean (SEM), median and IQR (25 to 75 percentile) respectively are [ (Ag85A): 597.1; 378.4; 50.0; 16 to 1315 ], [ (Ag85B): 540.7; 286.6; 60.0; 16 to 1312 ], [ (TB10.4): 243.1; 87.2; 164.0; 13 to 391], compared with the two participants receiving BCG/placebo [ (Ag85A: 55.0; 53.0; 55.0; 2.0 to.