A New Tuberculin for the Diagnosis of Tuberculosis

DESCRIPTION (provided by applicant):Accurate diagnosis of tuberculosis (TB) infection is one of the pillars of effective TB control programs. The current tool to diagnose infection with Mycobacterium tuberculosis is the tuberculin skin test (TST). Because of the cross-reactive nature of purified protein derivative (PPD) of tuberculin, TST currently does not discriminate between infection with M. tuberculosis, vaccination with M. bovis BCG and sensitization with non-tuberculous mycobacteria found in the environment. The recent achievements in the field of bacterial genomics enable us to undertake a new approach to formulate a M. tuberculosis-specific tuberculin and to overcome poor TST specificity. Comparative genomic analyses show that the M. tuberculosis genome includes regions that do not exist in M. bovis BCG (RD regions). Thus, we can tailor a new, M. tuberculosis-specific tuberculin by selecting from the pool encoded by the RD regions those antigens that elicit TB-specific, cell-mediated immune responses. Our specific aims are 1) Identification of candidate antigens. Gene selection will be based on published results of comparative genomic analyses, BLAST protein homology searches, and Southern blot analyses. 2) Antigen screening in guinea pigs. Antigens will be selected that induce skin test reactions in tuberculous guinea pigs but not in control animals sensitized with M. bovis BCG and with non-tuberculous mycobacteria. 3) Antigen evaluation in human TB. Antigens selected in guinea pig studies will be evaluated for the ability to induce in vitro lymphoproliferation and cytokine secretion by peripheral blood mononuclear cells (PBMC) of M. tuberculosis-infected persons but not by PBMC of negative control individuals (BCG vaccinees, patients having non-tuberculous mycobacterioses, and healthy, PPD-negative individuals). Antigens selected in the proposed Phase I studies will be used to formulate a multi-antigen tuberculin to be taken to human clinical trials during Phase II work. PROPOSED COMMERCIAL APPLICATION: 2.1 Billion people harbor a TB infection. UNICEF reports that tuberculosis poses a serious risk to Asia's sustained socioeconomic development. In a recent National Intelligence Estimate, the Central Intelligence Agency singled out drug-resistant TB-and especially its incidence among immigrants-as a potential threat to national security. Salomon and Murray report that world expenditure on TB therapy and diagnosis was $4.1 Billion (USD) in 1998. Diagnosis of TB worldwide is by sputum smear, with 50% accuracy. This new diagnostic is desperately needed. Short term markets will be in developing countries where the test will replace the current skin test as an adjunct diagnostic.