The search for correlates of protection in the TB vaccine field has generally focused on mechanistic correlates and in this regard, polyfunctional CD4+ T cells, defined by the simultaneous co-expression of multiple pro-inflammatory cytokines (e.g., IFN-γ, TNF-α, IL-2) on a single cell level, have garnered much attention (4). The gene discussed is TNF; the disease is tuberculosis.