Dihydrolipoamide dehydrogenase‐Lpd (Rv0462)‐specific T cell recall responses are higher in healthy household contacts of TB: a novel immunodominant antigen from M. tuberculosis

M. tuberculosis antigen Lpd showed strong cellular immune response in healthy contacts of TB; its use is encouraged for subunit TB vaccine development. The partial effectiveness against pulmonary tuberculosis (PTB), displayed by the existing tuberculosis (TB) vaccine, bacillus Calmette‐Guérin (BCG), highlights the need for novel vaccines to replace or improve BCG. In TB immunology, antigen‐specific cellular immune response is frequently considered indispensable. Latency‐associated antigens are intriguing as targets for TB vaccine development. The mycobacterial protein, dihydrolipoamide dehydrogenase (Lpd; Rv0462), the third enzyme of the pyruvate dehydrogenase (PDH) complex, facilitates Mycobacterium tuberculosis to resist host reactive nitrogen intermediates. Multicolor flow cytometry analysis of whole‐blood cultures showed higher Lpd‐specific Th1 recall response (IFN‐γ, TNF‐α, and IL‐2; P = 0.0006) and memory CD4+ and CD8+ T cells (CCR7+ CD45RA− and CCR7− CD45RA−) in healthy household contacts (HHC) of TB (P < 0.0001), which is comparable with or higher than the standard antigens, ESAT‐6 and CFP‐10. The frequency of Lpd‐specific multifunctional T cells was higher in HHC compared with PTB patients. However, there is no significant statistical correlation. Regulatory T cell (Treg) analysis of HHCs and active TB patients demonstrated very low Lpd‐specific CD4+ Tregs relative to ESAT‐6 and CFP‐10. Our study demonstrates that the Lpd antigen induces a strong cellular immune response in healthy mycobacteria‐infected individuals. In consideration of this population having demonstrated immunologic protection against active TB disease development, our data are encouraging about the possible use of Lpd as a target for further TB subunit vaccine development.