Antigen-Specific CD4⁺T Cells Recognize Epitopes of Protective Antigen following Vaccination with an Anthrax Vaccine

Abstract

Detection of antigen-specific CD4؉ T cells is facilitated by the use of fluorescently labeled soluble peptidemajor histocompatibility complex (MHC) multimers which mirror the antigen specificity of T-cell receptor recognition. We have used soluble peptide-MHC class II tetramers containing peptides from the protective antigen (PA) of Bacillus anthracis to detect circulating T cells in peripheral blood of subjects vaccinated with an anthrax vaccine. PA-specific HLA class II-restricted T lymphocytes were isolated which displayed both TH1-and TH2-like characteristics, indicating heterogeneity of the lymphocyte lineage within the CD4 ؉ response. Presentation of antigen to these T-cell clones by HLA-matched antigen-presenting cells exposed to the intact PA protein confirmed that the identified epitopes are indeed naturally processed by the human immune system. Specific tetramer-derived T-cell profiling may be useful for monitoring helper CD4؉ T-cell responses to anthrax vaccination.

A Three-Dose Intramuscular Injection Schedule of Anthrax Vaccine Adsorbed Generates Sustained Humoral and Cellular Immune Responses to Protective Antigen and Provides Long-Term Protection against Inhalation Anthrax in Rhesus Macaques

“…The reasons for the delay between completion of the priming series and attainment of maximum responses are unknown. The sustained presence of PAspecific IFN-␥ (Th1)-and IL-4 (Th2)-secreting cells, together with the sustained SI, indicated that the 3-IM series provided effective immunological priming and stimulated a mixed Th1/Th2 response in NHPs, in agreement with the observations of Laughlin and coworkers for AVA in humans (19). CD4 ϩ T cells contribute to activation of naïve B cells to produce clones of germinal center-located, activated B cells and to produce memory B cells and long-lived plasma cells.…”

“…Previous studies in humans showed that AVA stimulated the production of CD4 ϩ T cells that recognized multiple epitopes within PA and that these responses were detected in vaccinated and, surprisingly, also in nonvaccinated subjects (18,19). The frequencies of PA-specific T cells were higher in vaccinees than in nonvaccinees.…”

“…ϩ T cells to a Th2 lineage and the generation of PAspecific pre-Th2 central memory T cells carrying the CD45RA Ϫ phenotypic marker (19). In this NHP study, development of antigen-specific effector T cell types was examined by measuring the ELISpot frequencies of IFN-␥-and IL-4-secreting cells from PAstimulated PBMC.…”

Analysis of epitope information related toBacillus anthracisandClostridium botulinum

“…Indeed, antibody responses to PA after vaccination are T-helper (Th) dependent [40] and PA peptides are presented by infected macrophages [43], suggesting that the epitope-specific T cells may be required for mounting a protective immune response.…”

“…Domains 3 and 4 contain murine T-cell epitopes [41][42][43], while single human T-cell epitopes have been described in domains 1 and 2 [40]. Interestingly, the domain-1 epitopes described for PA-immunized mice and a vaccinated human are located within the PA20 region that is cleaved before heptamerization [19], suggesting that this region is still processed for presentation on MHC class II molecules after vaccination, allowing the immune system to respond to the entire PA83 molecule and not just the active PA63.…”