Association Between Natural Killer Cell Subsets (CD56bright and CD56dim) and Infectious Complications in Newly Diagnosed Multiple Myeloma (NDMM) Patients

Background and objective: Natural killer (NK) cells are a subset of CD3-CD56+ lymphocytes that can recognize and destroy virus-infected and cancerous cells. Infection is the main factor contributing to morbidity and mortality in individuals with multiple myeloma (MM). Therefore, this study was conducted to develop a framework for assessing the association between NK cell subsets (CD56bright and CD56dim) and infections in patients with newly diagnosed multiple myeloma (NDMM). Methods: Peripheral blood samples were obtained from 47 NDMM patients, and NK cell immunophenotype analysis was performed using flow cytometry. Screening for infection was based on the pathogens and combined clinical symptoms. Results: NDMM patients exhibited a significant increase in the overall frequency of circulating NK cells (p = 0.001) when compared to healthy controls. Clinically, infectious complications were observed in 31% of the NDMM patients, with viral infections accounting for 19.1% and bacterial infections for 12.7%. Interestingly, phenotypic analysis revealed a marked shift among NK cell subsets, characterized by an expansion of the CD56bright subset (p = 0.01) and a concurrent reduction in the CD56dim subset (p = 0.01). Additionally, NDMM patients who developed infections had significantly lower NK cell percentages, whereas those without infections showed higher levels, clustering at the upper end. Conclusions: These findings suggest a skewing of the NK cell population toward the CD56bright phenotype. According to the results, NDMM patients should be closely monitored for infection.