In Vitro Expanded NK Cells Have Increased Natural Cytotoxity Receptors, TRAIL and NKG2D Expression, and Superior Tumor Cytotoxicity Compared to Short-Term IL-2 –Activated NK Cells.

Abstract 463 IL-2 activates NK cell enhancing their capacity to lyse tumor cells. To date, most clinical studies of adoptive NK cell transfer have utilized short-term (12-16 hours) IL-2-activated NK cells. Because IL-2 alone is ineffective in expanding NK cells in vitro, the relatively low numbers of NK cells obtained for infusion following short term IL-2 activation may limit the full therapeutic impact of this approach. To obtain larger numbers of NK cells, novel ex vivo expansion protocols that utilize irradiated EBV-LCL or K562 feeder cells have recently been developed. However, concerns exist that extensive ex vivo expansion might significantly reduce the in vivo proliferative potential and long-term viability of adoptively transferred NK cells. Here we investigated for differences in phenotype, tumor cytotoxicity and in vivo persistence between short-term IL-2 activated and long-term expanded NK cells. CD56+/CD3- NK cells were isolated from normal donors by immuno-magnetic bead selection and were either activated with IL-2 (500U/ml) for 12-16 hours or were expanded in vitro over 14 days using irradiated EBV-LCL feeder cells in IL-2 containing media (500U/ml). Short-term IL-2 activated NK cells did not expand in number in contrast to EBV-LCL stimulated NK cells which expanded 400-1000 fold by culture day 14. Flow cytometry analysis revealed no differences in expression of DNAM-1, 2B4, LFA-1 or granzyme B between short-term activated and expanded NK cells. However, expanded NK cells had significantly higher expression of TRAIL, NKG2D, and the natural cytotoxicity receptors NKp30, NKp44 and NKp46 and a slight increase in KIR3DL1 and KIR2DL2/3. A 4-hour 51 Cr-release assay showed expanded NK cells were significantly more cytotoxic against K562 cell compared to short-term IL-2 activated NK cells; at a 1:1 effector to target ratio, 67±6%, 26±1%, and 9±1% of K562 cells were killed by expanded, short term IL-2 activated and fresh NK cells respectively (p In conclusion, these results demonstrate that ex vivo expanded NK cells are phenotypically and functionally different than short-term IL-2 activated NK cells. Expanded NK cells have increased expression of natural cytotoxicity receptors, NKG2D and TRAIL and have greater TRAIL-mediated tumor cytotoxicity compared to IL-2 activated NK cells. Importantly, despite extensive ex vivo proliferation, expanded NK cells appear maintain similar longevity in vivo as non-expanded short term IL-2 activated NK cells. Disclosures: No relevant conflicts of interest to declare.