The following tests were included in the evaluation:
- Cy-Tb (Serum Institute of India, India);
- Diaskintest (Generium, Russian Federation); and
- C-TST (formerly known as ESAT6-CFP10 test, Anhui Zhifei Longcom, China)
All these tests use intradermal injection of ESAT-6 and CFP-10 antigens that are specific to Mtb and stimulate T-cell release of IFN-γ. The effects of the products are based on a cellular immune response to Mtb-specific antigens. When administered intracutaneously in people with TB infection, tests included in this class induce a specific skin reaction, which is a manifestation of delayed-type hypersensitivity. The immune response is measured after 48–72 hours as induration in millimetres.
Cy-Tb was manufactured by the Statens Serum Institut (SSI), Denmark, as a solution of two recombinant proteins of ESAT-6 and CFP-10 (in a 1:1 ratio), produced by genetically modified Lactobacillus lactis. One single test dose of 0.1 mL contains 0.05 μg of rd ESAT-6 and 0.05 μg of rCFP-10. In 2019, SSI entered into a partnership with the Serum Institute of India, which is licensed to produce and distribute the test.
Diaskintest is a recombinant protein that is produced by genetically modified Escherichia coli BL21 (DE3)/pCFP-ESAT, diluted with sterile isotonic phosphate buffer solution, with a preservative (phenol). One dose (0.1 mL) of the product contains 0.2 μg of ESAT-6 and CFP10 recombinant protein and auxiliary ingredients: disodium phosphate dihydrate, sodium chloride, potassium dihydrogen phosphate, polysorbate 80, phenol and water for injections. The product is approved by the Russian National Medicines Regulatory Authority.
C-TST uses a recombinant fusion protein of ESAT-6 and CFP-10, and is manufactured by Anhui Zhifei Longcom Biopharmaceutical Co. Ltd. The product is approved by the Chinese National Medicines Regulatory Authority. The active ingredient in this test is an ESAT-6 and CFP-10 fusion recombinant protein expressed in genetically modified E. coli. Each test dose of 0.1 mL contains 5 units (U) of recombinant Mtb fusion protein and auxiliary ingredients: disodium hydrogen phosphate, potassium dihydrogen phosphate, sodium chloride, phenol and polysorbate 80.