This IP centers on a natural killer (NK) cell function, specifically the identification of interleukin 1 receptor antagonist (IL-1ra) as a potential biomarker. The research highlights the secretion ability of IL-1ra in response to NK cell stimulation by phytohemaglutinin, indicating optimal NK cell function. It offers significant advantages over existing methods, providing a quick, simple, and inexpensive assay to select potentially optimally functional NK cells for cancer therapy augmentation. The stage of development is conceptual and proof of principle with further work planned to characterize IL-1ra secreting donors and explore associated mechanisms. Notably, this finding has not been reported elsewhere, positioning it as a potential replacement for complex cytotoxicity assays in assessing NK cell function. Commercial applications include selecting allogeneic hematopoietic stem cell donors and off-the-shelf cellular therapy for cancer patients.