Introduction: Cord blood (CB) derived natural killer (NK) cells are a promising alternative to autologous T cell immunotherapy, which provide strong anti-tumour activity with a low risk for the development of GvHD. This study aimed to characterise the phenotype, cytotoxicity, and proliferative profile of CB NK cells and detect donor characteristics that marked optimal NK cells for downstream use in immunotherapy. Pinpointing such characteristics will enable the selection of highly proliferative and cytotoxic CB NKs for use in adoptive cell therapies, reducing processing costs.

Methods: T cell-depleted CB mononuclear cells (CBMCs; n=21) were cultured in NKMACS medium with 1000 IU/ml IL-2 and 10ng/ml IL-15 for 21 days. Percentage of CD3⁻CD56⁺ cells was >95% post-expansion. Cells were phenotyped post-isolation and every 7-days subsequently. NK cell cytotoxicity against K562 leukaemia cell line was measured via bioluminescent cytolysis assay.

Results: NK cell quantification throughout expansion revealed intrinsic variability between donors that became more apparent over time (13 – 144-fold expansion at day 21). K562 cell specific lysis on days 7, 14 and 21 showed similar inter-cord variability in cytotoxicity (14 – 93%). Phenotypic profiling similarly reflected such variability in the expression of activation receptors CD16 and NKp44 throughout expansion, which were found to correlate cell specific lysis, in addition to other donor characteristics (p<0.05).

Conclusion: Characterisation of CB derived NK cells pre- and post- expansion has demonstrated considerable variability between donors in terms of expansion potential and cytotoxicity. Results indicate that differential marker expression correlates with the observed variation in NK cell cytotoxicity.