TB Vaccines: The (Human) Challenge Ahead

Tuberculosis (TB) remains a global health threat, with 8.6 million new cases and 1.3 million deaths (including 0.3 million in HIV-positive people) in 2012 [1]. An estimated one-third of the world's population is infected with Mycobacterium tuberculosis (Mtb) [2]. TB is one of the leading causes of death by an infectious disease worldwide, second only to HIV (1.6 million deaths in 2012), and the increase in drug resistant strains of Mtb is alarming [1,3]. An effective vaccine to prevent infection and/or pulmonary TB disease is desperately needed. However, there are several hurdles that have made TB vaccine research and development painfully slow, including the slow growth rate of Mtb, the lack of a predictive animal model, and the lack of an immune correlate [3]. In addition, animal challenge models are very expensive due to the requirement of an ABSL-3 facility, and clinical efficacy studies are long and require large numbers of patients. Funding continues to be an issue in the TB vaccine field (Figure 1) [1,4-6], particularly given the difficulties and the expense of preclinical and clinical studies. New tools are needed to evaluate candidate vaccines that produce a more rapid and accurate assessment of the potential for vaccine efficacy and, therefore, help to increase the speed, and reduce the cost, of vaccine candidate selection.