ESX1 and infection: Interestingly, a recombinant M. tuberculosis strain H37Rv EsxAΔ84–95 expressing a mutant form of ESAT-6 with a C-terminal deletion of 12 amino acid residues was found to possess a functional ESX-1 system (as it was shown to secrete ESAT-6 and CFP-10 efficiently), but was attenuated in a mouse infection model [13]–[15].