CD4 and cytomegalovirus infection: Another intriguing possibility is that a relevant fraction of the HLA-II-mediated CD4 + T cell activation might be elicited by cells that are resistant to HCMV infections, such as the recently described HLA-DR +NKG2C+memory NK cells (Costa-García et al., 2019), which have been shown to be mediators of viral control in transplanted patients (Davis et al., 2015).