Umbilical cord blood−derived natural killer cells as a viable and potent source for adoptive cell therapy

BACKGROUND AIMS: Natural killer (NK) cells represent a key component of the innate immune response, capable of targeting a wide range of tumor and virus-infected cells independently of major histocompatibility complex restriction. Umbilical cord blood (UCB) is a promising source of NK cells because of its availability, lower human leukocyte antigen requirements and reduced risk of graft-versus-host disease. METHODS: In this study, UCB-derived NK cells were expanded ex vivo for 14 days using CSTX002 under Good Manufacturing Practice conditions. RESULTS: The expanded NK cells exhibited high viability (94.8 ± 1.3%) cryopreservation, which remained stable after 180 days (87.7 ± 1.1%) and after 365 days (91 ± 8.1%; n = 4). The immunophenotype (CD56⁺CD3⁻) was preserved, with more than 90% of cells maintaining this profile after long-term cryopreservation. Cytotoxic activity, assessed using a calcein-AM assay against K562 and HL-60 leukemia cell lines, remained robust after cryopreservation. At day 14, NK cells killed 54.55 ± 10.92% of K562 cells at a 0.5:1 effector-to-target ratio and 98.60 ± 0.66% at a 40:1 ratio. Cryopreserved NK cells demonstrated comparable activity, killing 44.56 ± 11.98% and 97.64 ± 2.36% of target cells at the same respective ratios. CONCLUSIONS: These findings support the feasibility of producing cryopreserved, UCB-derived NK cells as a stable and effective "off-the-shelf" product for adoptive immunotherapy, particularly in the treatment of acute myeloid leukemia, with advantages in scalability, standardization, and rapid clinical deployment.