Survival and expansion of NK cells expressing IL-15 in vitro. (A) Percentage of NK cell recovery compared with input cells after 7-day parallel cultures without IL-2 for mock- and mbIL15-transduced cells from 15 donors (left) and mbIL15- or wtIL15-transduced NK cells from 9 donors (right). Horizontal bars indicate median value. Results of paired t tests are shown. Data of cultures with IL-2 (10 and 100 IU/mL) are shown in supplemental Figure 1. (B) Survival and expansion of mock- and mbIL15-transduced NK cells from 6 donors with low-dose IL-2 (10 IU/mL). (C) Expansion and long-term survival of mbIL15-, wtIL15-, or mock-transduced NK cells from 1 donor cultured with no IL-2 or low-dose IL-2 (results with 100 IU/mL IL2 are shown in supplemental Figure 1). Percentage of NK cell recovery at the indicated days of culture is shown.