Evidence of NK cell cytotoxicity by IPH2101. (A) In n = 6 of 8 subjects evaluated, IPH2101 appeared to increase NK cell cytotoxicity against MM. Shown are ex vivo NK cell cytotoxicity results measuring NK cell production of GrB by ELISPOT in coculture with RPMI 8226 MM cell line targets. The light gray condition shows GrB production against MM cell line targets before first dose of IPH2101. The black bar represents GrB production 24 hours after first dose of IPH2101. As a control for the possibility of spontaneous activation; and dark gray bar, effector cell GrB production after IPH2101 dosing in the absence of targets. All pair-wise comparisons between predose and postdose and effectors alone versus postdose are statistically significant: *P < .05. (B) NK cell cytotoxicity for n = 5 patients who received repeated doses of IPH2101 on the extension cohort. *GrB production significantly greater than baseline.