Approach to discover T- and B-cell antigens of intracellular pathogens applied to the design of Chlamydia trachomatis vaccines

Abstract

Natural immunity against obligate and/or facultative intracellular pathogens is usually mediated by both humoral and cellular immunity. The identification of those antigens stimulating both arms of the immune system is instrumental for vaccine discovery. Although high-throughput technologies have been applied for the discovery of antibody-inducing antigens, few examples of their application for T-cell antigens have been reported. We describe how the compilation of the immunome, here defined as the pool of immunogenic antigens inducing T- and B-cell responses in vivo, can lead to vaccine candidates against Chlamydia trachomatis . We selected 120 C. trachomatis proteins and assessed their immunogenicity using two parallel high-throughput approaches. Protein arrays were generated and screened with sera from C. trachomatis -infected patients to identify antibody-inducing antigens. Splenocytes from C. trachomatis -infected mice were stimulated with 79 proteins, and the frequency of antigen-specific CD4 + /IFN-γ + T cells was analyzed by flow cytometry. We identified 21 antibody-inducing antigens, 16 CD4 + /IFN-γ + –inducing antigens, and five antigens eliciting both types of responses. Assessment of their protective activity in a mouse model of Chlamydia muridarum lung infection led to the identification of seven antigens conferring partial protection when administered with LTK63/CpG adjuvant. Protection was largely the result of cellular immunity as assessed by CD4 + T-cell depletion. The seven antigens provided robust additive protection when combined in four-antigen combinations. This study paves the way for the development of an effective anti- Chlamydia vaccine and provides a general approach for the discovery of vaccines against other intracellular pathogens.

Directional Evolution of Chlamydia trachomatis towards Niche-Specific Adaptation

“…5) and involve genes whose functions may underlie distinct phenotypes. In fact, among the 25 genes identified as positively selected along specific lineages (Table 1), we found genes encoding proteins implicated in immune response elicitation (such as CT147, CT442/crpA, CT529, CT694, and pmp's) (21,30,31,69,72,78), proteolytic activity (such as CT867 and CT868) (57), and subversion of hostcell functions (such as CT223 and CT456/tarp) (25,44). Some of these genes were also identified in a previous study (49), but no genotype-phenotype associations could be established because only six serovars were evaluated, in contrast to the present study, which constitutes a considerable scale-up in terms of genetic variability (enrolling all major 15 serovars represented by 59 strains).…”

Genital Chlamydia trachomatis: Understanding the Roles of Innate and Adaptive Immunity in Vaccine Research

“…While there is ample evidence that CD4 ϩ T cells play an integral part in C. muridarum and C. trachomatis infection resolution (90)(91)(92)(93), the role for CD8 ϩ T cells has been controversial. Indeed, CD8…”

“…Previous studies demonstrated that in humans, Chlamydia-specific antibodies play a role in C. trachomatis protective immunity (98,99), and numerous C. trachomatis proteins have been shown to induce antigen-specific antibodies (91). However, even though anti-Chlamydia antibodies are able to neutralize infection in vitro (100,101), growing evidence shows that B cells may not be important for initial chlamydial infection but, instead, play an important role in the secondary memory response (102,103).…”

Predicting protective bacterial antigens using random forest classifiers

“…For comparison with existing methods for predicting antigenic proteins, we constructed two test sets from a set of 895 proteins corresponding to the complete Chlamydia trachomatis DUW-3CX proteome. The first data set, called Chlamydia trachomatis data set, consists of a set of 83 Chlamydia trachomatis antigens compiled by Finco et al [14] from several recent high-throughput studies [15,16,17,18,19] and served as positive data and the remaining 812 proteins were considered as negative data. The second data set, called balanced Chlamydia trachomatis data set, is a balanced version of the first data set in which the negative instances were reduced to only 83 proteins selected at random from the set of 812 non-antigens.…”