CD27 and viral infectious disease: Previous study of Tmem cells using acute viral infection models (Gerlach et al., 2016) have described CX3CR1neg cells as TCM (CD62L+, CD27+, CD127+), CX3CR1hi cells as TEM (CD62L−, CD27−, CD127−), and CX3CR1int cells as having phenotypic features more similar to CX3CR1neg cells (CD62L+/−, CD27+, CD127+).