Immunogenic compositions comprising an M72 related antigen, wherein the conductivity of the composition is 13 mS/cm or lower, or the concentration of salts of the composition is 130 mM or lower, and their use in medicine, are provided.本發明提供包含M72相關抗原之免疫原組合物,其中該組合物之導電率係13 mS/cm或更低,或該組合物之鹽濃度係130 mM或更低;及該組合物在醫學中之用途。