In response to cytomegalovirus (HCMV) infection, a pool of specialized “adaptive” NK cells with immunological memory traits develops in humans. This process is based on the recognition of HCMV peptides presented in the context of the HLA-E molecule by the activating receptor NKG2C. Using retroviral transduction, members of the Laboratory of Cell Interactions of the Immunology Department, IBCH RAS, together with colleagues from the European Medical Center, obtained K562-21E feeder cells expressing HLA-E and identified a subpopulation, whose size is associated with the magnitude of NK cell proliferative response to the presentation of the HCMV peptide. The K562-21E cells can be applied both for the accumulation of HCMV-specific NK cells and for studying the adaptive cells maturation.