Immune Control of Burkholderia pseudomallei––Common, High-Frequency T-Cell Responses to a Broad Repertoire of Immunoprevalent Epitopes

Abstract

Burkholderia pseudomallei (Bp) is an environmental bacterial pathogen that causes potentially lethal sepsis in susceptible individuals and is considered a Category B, Tier-1 biothreat agent. As such, it is crucial to gain an improved understanding of protective immunity and potential vaccine candidates. The nature of immune correlates dictating why most exposed individuals in endemic regions undergo asymptomatic seroconversion while others succumb to life-threatening sepsis is largely uncharted. Bp seroreactive, immunogenic proteins have previously been identified by antigen microarray. We here set out to conduct an analysis of T-cell recognition of the Bp immunome using serodominant antigens represented in the original antigen microarray, examining immune correlates of disease in healthy seropositive individuals and those with acute disease or in convalescence. By screening a library of 739 overlapping peptides representing the sequences of 20 different Bp antigens, we aimed to define immune correlates of protection at the level of immunoprevalent T-cell epitopes. Responses to a large number of epitopes were common in healthy seropositive individuals: we found remarkably broad responsiveness to Bp epitopes, with 235 of 739 peptides recognized by ≥80% of all tested donors. The cumulative response to Bp epitopes in healthy, seropositive, donors from this endemic region were of the order of thousands of spot forming cells per million cells, making Bp recognition a significant component of the T-cell repertoire. Noteworthy among our findings, analysis revealed 10 highly immunoprevalent T-cell epitopes, able to induce Bp-specific IFNγ responses that were high in responding T-cell frequency within the repertoire, and also common across individuals with different human leukocyte antigen types. Acute melioidosis patients showed poor T-cell responses to the immunoprevalent epitopes, but acquired responsiveness following recovery from infection. Our findings suggest that a large repertoire of CD4 T cells, high in frequency and with broad coverage of antigens and epitopes, is important in controlling Bp infection. This offers an attractive potential strategy for subunit or epitope-based vaccines.

Human Immune Responses to Melioidosis and Cross-Reactivity to Low-Virulence Burkholderia Species, Thailand1

“…Cell-mediated immune responses by IFN-γ and type I immune responses (e.g., interleukin [IL] 12, IL-18, tumor necrosis factor α) are essential for the host immune system in fighting against intracellular infections (29)(30)(31). Nithichanon et al showed that most of an exposed healthy population has acquired cellular immunity against broad immunogenic B. pseudomallei epitopes (32). Our IFN-γ ELISpot experiments suggest that both melioidosis patients and HH contacts engage strong cross-immune IFN-γ responses between B. pseudomallei, B. thailandensis, and BTCV, despite low humoral responses in the HH cohort.…”

A DUF4148 family protein produced inside RAW264.7 cells is a critical Burkholderia pseudomallei virulence factor

“…NanoRPLC-MS/MS was utilized in this study to identify proteins produced by B. pseudomallei while inside murine macrophages. The intracellular protein profile closely resembled the gene expression of B. pseudomallei in vivo, especially as described for human immune responses characterized using sera from patients infected with B. pseudomallei [25,26,[28][29][30][31][32][45][46][47][48]. We predicted that previously characterized Burkholderia proteins would be identified and serve as a positive control for our technical approach.…”

“…B. pseudomallei AhpC was found to be highly expressed in plasma from melioidosis survivors, but not in healthy controls [31]. In addition, T cell mediated immunity to AhpC was associated with protection against disease and shown to be a correlate of survival [46,48] and it represents a melioidosis vaccine candidate [30,46,48]. BPSL2748 is a putative AhpC-type peroxiredoxin, but it has not been as extensively studied as B. pseudomallei AhpC.…”

“…The bacterial heat shock proteins (HSPs) detected inside macrophages included the chaperones GroES, GroEL, HtpG, DnaK and GrpE (Table 1). These proteins are highly conserved proteins but have been shown to have important roles in infection, and in the immune response to and diagnosis of infection [25][26][27][28][29][30][31][32][33]. Additional intracellularly produced bacterial proteins associated with host-mediated nutritional and oxidative stress included the universal stress protein A (UspA), peroxiredoxin BPSL2748 and superoxide dismutase BPSL0880 (SodB).…”

Postgenomic Approaches and Bioinformatics Tools to Advance the Development of Vaccines against Bacteria of the Burkholderia cepacia Complex

“…Epitope identification is expensive and laborious, requiring experimental screening of large arrays of potential epitope candidates. However, recent works of epitope mapping of Burkholderia strains have been performed using the peptide microarray approach [ 59 , 60 , 61 ]. This technique relies on the use of libraries of synthesized linear peptides spotted on a single chip and screening for antigenicity using patients’ antisera.…”