Impacts of cryopreservation on phenotype and functionality of mononuclear cells in peripheral blood and ascites.

Background: Mononuclear cells in peripheral blood and ascites are important clinical resources commonly used in translational and basic research. However, the impact of different cryopreservation durations and extra freeze-thaw cycles on the number and function of mononuclear cells is unknown.

Methods: Peripheral blood samples (n = 21) and ascites samples (n = 8) were collected from healthy volunteers and ovarian cancer patients. Mononuclear cells were isolated, frozen, and thawed at 6 and 12 months. The impact of cryopreservation on cell viability, the phenotype, and the activation and proliferation of T cells were analyzed by flow cytometry. Single-cell sequencing was applied to investigate the underlying mechanism.

Results: The cell number and viability of mononuclear cells in peripheral blood and ascites were significantly decreased after cryopreservation. The T lymphocytes, especially CD4⁺ T cells, were affected the most significantly. By contrast, monocytes, natural killer (NK) cells, natural killer T (NKT) cells, and B cells were more tolerant. Meanwhile, T cell proliferation and IL-2 secretion are significantly affected after long-term cryopreservation. Mechanistically, the cell death induced by elevated reactive oxygen species (ROS) was involved in the reduction of CD4⁺ T cells after cryopreservation.

Conclusions: Our data indicates that different subtypes of mononuclear cells exhibit different tolerance capacities upon cryopreservation. Thus, our research can provide evidence and support for individuals who are conducting experiments using frozen clinical patient-derived mononuclear cells, for basic research or clinical trials. In addition, extra caution is worthwhile when researchers compare immune cell functionality from peripheral blood or ascites across datasets obtained in different cryopreservation conditions.