Major histocompatibility complex class I polypeptide-related sequence A (MICA) is a prototypical NKG2D ligand. Because immune cells, such as natural killer (NK) cells, recognize virally infected or transformed cells and eliminate them through the interaction between NKG2D receptors on NK cells and NKG2D ligands on pathogenic cells, MICA expression levels are associated with NK cell-mediated immunity. Here, we report that an engineered clustered regularly interspaced short palindromic repeats-Cas9-related complex targeting MICA gene promoter sequences activates transcription of the MICA gene from its endogenous locus. Inhibiting microRNA function, which targets the 3' untranslated region of the MICA gene, enhances this activation. These results demonstrate that the combination of Cas9-based transcriptional activators and simultaneous modulation of microRNA function may be a powerful tool for enhancing MICA protein expression and efficient anti-pathogenic cell immunity. (C) 2017 Elsevier Inc. All rights reserved.