Immunisation with proteins expressed during chronic murine melioidosis provides enhanced protection against disease

There is an urgent need for an effective vaccine against human disease caused by Burkholderia pseudomallei, and although a wide range of candidates have been tested in mice none provide high level protection. We considered this might reflect the inability of these vaccine candidates to protect against chronic disease. Using Q-RT PCR we have identified 6 genes which are expressed in bacteria colonising spleens and lungs of chronically infected mice. Three of the genes (BPSL1897, BPSL3369 and BPSL2287) have been expressed in Escherichia coli and the encoded proteins purified. We have also included BPSL2765, a protein known to induce immune responses associated with a reduced incidence of chronic/recurrent disease in humans. Immunisation of mice with a combination of these antigens resulted in the induction of antibody responses against all of the proteins. Compared with mice immunised with capsular polysaccharide or LolC protein, mice immunised with the combination of chronic stage antigens showed enhanced protection against experimental disease in mice.