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124 | Chapter 5 of EGFR + RAS mut SW480 and EGFR + BRAF mut HT-29 via ADCC 24 . CD16 was expressed by 88 ± 8% (n=5) of A-PBNK after overnight stimulation with cytokines and by 7 ± 2% (n=5) of UCB-NK cells at the end of the 35 day culture period. No added effect of cetuximab was observed when using UCB-NK cells, which is possibly related to their lower in vitro CD16 levels 29 . Of note, tumor cell lysis induced by UCB-NK cells was comparable to that observed with the combination of A-PBNK and cetuximab (Figure 2A) . Measurements of NK cell degranulation reflected equivalent trends observed for tumor cell lysis (Figure 2B). These results show that UCB-NK cells have superior cytotoxic efficacy over A-PBNK cells against cetuximab resistant colon cancer cells in vitro. UCB-NK cells inhibit in vivo tumor growth and increase survival To address whether UCB-NK cells exhibit similar anti-tumor efficacy in vivo, we transferred Gluc transduced SW480 cells to immunodeficient mice (BRGS; see methods). SW480 cells Figure 2: Ex vivo cytotoxic efficacy of A-PBNK and UCB-NK cells against CRC cells (A) CRC cell lines COLO320 (EGFR - , RAS wt ), SW480 (EGFR + , RAS mut ) and HT-29 (EGFR + , RAS wt , BRAF mut ) were subjected to NK killing using two allogeneic NK cell products, i.e. A-PBNK and UCB-NK cells. 7AAD (A) and CD107a (B) were measured after a 4 hr. co-culture of A-PBNK and UCB-NK cells with CRC targets in the presence or absence of cetuximab at an E:T ratio of 1:1. Experiments were carried out in triplicate. Bars represent mean ± SEM, n=5. *P < 0.05 and **P < 0.01, calculated with two-way ANOVA, multiple comparison between column means.