Memory-like NK (NKm) cells, present in individuals seropositive for cytomegalovirus (HCMV+), exhibit characteristics to be exploited in monoclonal antibody (MAb)-therapy directed against tumor antigens, mainly their amplified production of cytokines and proliferation in response to stimulation through CD16 receptors. We aimed to evaluate in vitro the functionality of NKm cells against Triple-Negative Breast Cancer (TNBC) cells opsonized with IgG1 isotype MAbs. Peripheral blood samples were obtained from healthy donors (HD; n=16) and BC patients (n=25) without prior treatment, at the time of primary tumor surgery. The proportion of individuals seropositive for HCMV+ was similar in BC patients and HD (84% vs. 81%, respectively). We determined two NK cell subpopulations based on their expression of FcεRIγ by FACS: FcεRIγ negative -NKγ¯-  (memory) and NKγ+ (conventional). BC patients presented a NKγ¯ subpopulation in about half of the HCMV+ individuals with phenotypic characteristics similar to those previously described in these cells in HD: lower expression of NKp30 and CD161, and higher of NKG2C and CD85j, with respect to NKγ+ cells. Then, we performed functional assays. In HD, NKγ¯ cells showed a higher production of IFN-γ (p<0.05; paired t-test) and TNF-α against TNBC cells opsonized with Cetuximab (anti EGFR) or Avelumab (anti PD-L1) than NKγ+ cells. Given that in some patients, NKγ¯ cells were less functional than those in HD, this point will be further investigated after recruiting more patients.