Although a substantive CD4+ T cell response to a given neo-epitope is rather rare (~0.5% of neo-epitopes) [51], it is contended that neo-epitope-specific CD4+ T cells aid cancer regression in various ways, among others through direct killing of cancer cells and by supporting the priming, function and tumor infiltration of cancer-specific CD8+ T cells [52]. Here, CD4 is linked to cancer.