Immune regulatory activities of early secreted antigenic target of 6-kD protein of Mycobacterium tuberculosis and implications for tuberculosis vaccine design.

Although ESAT-6 was originally identified as a strong T cell immunogen in short-term culture filtrate of Mtb, and has therefore been a candidate vaccine antigen for many years, recent work has demonstrated that ESAT-6 is also a virulence factor that mediates pathogenicity of Mtb. The studies described in this review suggest that ESAT-6 secreted by Mtb subverts host immunity by manipulating intracellular signaling pathways in macrophages and T cells, which are critical in protection against Mtb. Furthermore, ESAT-6 elicits pro-inflammatory responses that can be detrimental to the host. Understanding the molecular mechanisms through which ESAT-6 inhibits immunity will permit design of ESAT-6-based vaccine constructs that elicit protective immune responses with minimal negative effects.