Deconstructing the germinal center, one cell at a time.

Successful vaccination relies on driving the immune response towards high specificity, affinity and longevity. Germinal centers facilitate the evolution of antigen-specific B cells by iterative rounds of diversification, selection, and differentiation to memory and plasma cells. Experimental evidence points to B cell receptor affinity and amount of antigen presented to follicular helper T cells as main drivers of clonal evolution. Concurrent studies suggest that modifiers of cognate contact, temporal mechanisms, and stochastic factors can also shape diversity and influence differentiation to memory and plasma cells, but molecular pathways driving these selection decisions are unresolved. Due to rapid cycles of transcriptional change in the germinal center, single-cell resolution is imperative to dissect mechanisms dictating the mature antigen-specific repertoire. Future studies linking high-resolution analysis of this diverse evolving population with cellular outcome are needed to fully understand the complex mechanisms of selection driving antigen-specific humoral immunity.