An APS–hydrogel composite provides dual molecular–physical protection to NK-92 cells by preserving membrane stability and surface microstructures

The surface microstructures of Natural Killer (NK) cells, such as microvilli, are essential for target cell recognition and the subsequent formation of immunological synapses. However, traditional cryopreservation protocols (e.g., 10% DMSO and serum) severely damage the cell surface structure, which further impairs cytotoxicity. Although a variety of novel cryoprotectants or ice inhibitors have emerged to improve the post-thaw viability of cells, there are currently few reports on strategies for the preservation of surface microstructures essential for immune synapse formation in natural killer (NK) cells. Here, we introduce a dual-protection strategy that combines the membrane-stabilizing capacity of Astragalus Polysaccharide (APS), a bioactive compound from traditional Chinese medicine, with a hydrogel encapsulation system to mitigate cryo-injury from ice crystal formation. The results demonstrated that, in the absence of DMSO, the experimental group achieved an 85% viability rate for NK-92 cells. Furthermore, the surface microstructure was significantly better preserved compared to conventional protocols, and the corresponding cytokine secretion and cytotoxicity showed no significant difference from the fresh group. This study demonstrates that the synergistic cryoprotective effect of APS and hydrogel, thereby laying a solid foundation for immune cell preservation and cell-based therapies.