Immune responses to vaccines: from classical to systems approaches

Vaccines represent one of the most cost-effective tools to control infectious diseases. They work by promoting a long-lasting immunological memory that decreases pathogen circulation and leads to protective immunity. Vaccination induces both innate and adaptive immune responses. Such responses can be monitored by several approaches. To identify the immune correlates of protection and elucidate the mechanisms underlying the vaccination, several approaches can be done in order to evaluate the immune responses. Through the use of classical methods of immunological assessment, such as flow cytometry and enzyme-linked immunosorbent assay (ELISA), associated with “omics” tools, it is possible to better understand the mechanisms by which vaccines stimulate protective immune responses. Omics methods, which are able to provide broad and systemic views of molecules such as mRNAs (transcriptomics), proteins (proteomics), and metabolites (metabolomics), allow faster and more effective validation of new vaccine candidates. The integration of the generated data from the classical methods associated with omics results can give a wider view of vaccination and may help to identify novel correlates of protection after vaccination. In this review, we will focus on describing the innate and specific immune responses, the different approaches to evaluating the immune response induced by the vaccines (classic and high-throughput methods), and the importance of data integration. Focused on data integration, network analysis is applied with aim of categorization of data from various sources in a plan that allows the identification of logical patterns. Through the observation of patterns generated by different routes, it is possible to better understand how vaccines work.