ALT-803 results in expansion of CD56^brightand CD56^dimNK cell subsets, with sustained proliferation of CD56^brightNK cells. (A-B) Absolute numbers of the CD56^bright (A) and CD56^dim (B) NK cell subsets of peripheral blood. The SQ administration route increases CD56^bright NK cell percentages over 4 weeks of therapy. (C-D) Proliferation of CD56^bright (C) and CD56^dim (D) NK cell subsets measured by intracellular Ki67 expression. CD56^bright NK cells exhibit sustained proliferation for weeks during weekly ALT-803 administration via the SQ route (2-way ANOVA). (E) Representative flow bivariate flow cytometry plots showing the NK cell subset flow cytometry gates and expression of Ki67 in CD56^bright and CD56^dim subsets 21 days after 6 µg/kg ALT-803 administered SQ (UMN16, left) or IV (WSU002, right). (F) CD56^bright NK cell expression of GzmB in a subset of patients analyzed by mass cytometry revealed ALT-803 priming of CD56^bright NK cells in vivo (Friedman test).