Genetic variation of hemolysin co-regulated protein 1 affects the immunogenicity and pathogenicity of Burkholderia pseudomallei

by Sarunporn Tandhavanant, Thatcha Yimthin, Sineenart Sengyee, Ratana Charoenwattanasatien, Andrey A. Lebedev, Eric R. Lafontaine, Robert J. Hogan, Claire Chewapreecha, T. Eoin West, Paul J. Brett, Mary N. Burtnick, Narisara Chantratita

Hemolysin co-regulated protein 1 (Hcp1) is a component of the cluster 1 Type VI secretion system (T6SS1) that plays a key role during the intracellular lifecycle of Burkholderia pseudomallei. Hcp1 is recognized as a promising target antigen for developing melioidosis diagnostics and vaccines. While the gene encoding Hcp1 is retained across B. pseudomallei strains, variants of hcp1 have recently been identified. This study aimed to examine the prevalence of hcp1 variants in clinical isolates of B. pseudomallei, assess the antigenicity of the Hcp1 variants, and the ability of strains expressing these variants to stimulate multinucleated giant cell (MNGC) formation in comparison to strains expressing wild-type Hcp1 (Hcp1^wt). Sequence analysis of 1,283 primary clinical isolates of B. pseudomallei demonstrated the presence of 8 hcp1 alleles encoding three types of Hcp1 proteins, including Hcp1^wt (98.05%), Hcp1^{variant A} (1.87%) and Hcp1^{variant B} (0.08%). Compared to strains expressing Hcp1^wt, those expressing the dominant variant, Hcp1^{variant A}, stimulated lower levels of Hcp1^{variant A}-specific antibody responses in melioidosis patients. Interestingly, when Hcp1^{variant A} was expressed in B. pseudomallei K96243, this strain retained the ability to stimulate MNGC formation in A549 cells. In contrast, however, similar experiments with the Hcp1^{variant B} demonstrated a decreased ability of B. pseudomallei to stimulate MNGC formation. Collectively, these results show that B. pseudomallei strains expressing variants of Hcp1 elicit variable antibody responses in melioidosis patients and differ in their ability to promote MNGC formation in cell culture.