Baseline immune profile by CyTOF can predict response to an investigational adjuvanted vaccine in elderly adults

Background: Mass cytometry, or CyTOF (Cytometry by Time-of-Flight), permits the simultaneous detection of over 40 phenotypic and functional immune markers in individual cells without the issues of spectral overlap seen in traditional flow cytometry. Methods: In this study, we applied CyTOF to comprehensively characterize the circulating immune cell populations in elderly individuals both before and after administration of an investigational adjuvanted protein vaccine against respiratory syncytial virus (RSV) in a Phase 1a trial. Antigen-specific T cell responses to RSV by IFN gamma ELISPOT had been observed in most but not all recipients in the highest dose cohort in this trial. Here, CyTOF was used to characterize the cellular response profile of ELISPOT responders and non-responders in this vaccine dose cohort. Results: Both CD4(+) and CD8(+) T cell antigen-specific IFN. responses were observed. Principal components analysis revealed baseline differences between responders and non-responders, including differences in activated (HLA-DR+) CD4(+) and CD8(+) T cells, which were higher in non-responders versus responders. Using viSNE to analyze RSV-responsive CD4(+) and CD8(+) T cells, we also found increased expression of HLA-DR, CCR7, CD127 and CD69 in non-responders versus responders. Conclusions: High parameter CyTOF can help profile immune components associated with differential vaccine responsiveness.