Induction of an Immune-Protective T-Cell Repertoire With Diverse Genetic Coverage by a Novel Viral-Vectored Tuberculosis Vaccine in Humans

BACKGROUND:  Whether a candidate tuberculosis vaccine induces clinically relevant protective T-cell repertoires in humans will not be known until the completion of costly efficacy clinical trials. METHODS:  We have developed an integrated immunologic approach to investigate the clinical relevance of T cells induced by a novel tuberculosis vaccine in a phase 1 trial. This approach consists of screening for likely dominant T-cell epitopes, establishing antigen-specific memory T-cell lines for identifying CD8⁺ and CD4⁺ T-cell epitopes, determining the ability of vaccine-induced T cells to inhibit mycobacterial growth in infected cells, and examining the genetic diversity of HLA recognition and the clinical relevance of identified T-cell epitopes. RESULTS:  A single-dose immunization in BCG-primed adults with an adenovirus-based tuberculosis vaccine elicits a repertoire of memory T cells capable of recognizing multiple Ag85A epitopes. These T cells are polyfunctional and cytotoxic and can inhibit mycobacterial growth in infected target cells. Some identified T-cell epitopes are promiscuous and recognizable by the common HLA alleles. These epitopes are clinically relevant to the epitopes identified in people with latent Mycobacterium tuberculosis infection and treated patients with tuberculosis. CONCLUSIONS:  These data support further clinical development of this candidate vaccine. Our approach helps fill the gap in clinical tuberculosis vaccine development.