iPSC-derived cells lack immune tolerance to autologous NK-cells due to imbalance in ligands for activating and inhibitory NK-cell receptors

Abstract:Background: Dozens of transplants generated from pluripotent stem cells are currently in clinical trials. The creation of patient-specific iPSCs makes personalized therapy possible due to their main advantage of immunotolerance. However, some reports have claimed recently that aberrant gene expression followed by proteome alterations and neoantigen formation can result in iPSCs recognition by autologous T-cells. Meanwhile, the possibility of NK-cell activation has not been previously considered. This study focused on the comparison of autologous and allogeneic immune response to iPSC-derived cells and isogeneic parental somatic cells used for reprogramming. Methods: We established an isogeneic cell model consisting of parental dermal fibroblasts, fibroblast-like iPSC-derivatives (iPS-fibro) and iPS-fibro lacking beta-2-microglobulin (B2M). Using the cells obtained from two patients, we analyzed the activation of autologous and allogeneic T-lymphocytes and NK-cells cocultured with target cells. Results: Here we report that cells differentiated from iPSCs can be recognized by NK-cells rather than by autologous T-cells. We observed that iPS-fibro elicited a high level of NK-cell degranulation and cytotoxicity, while isogeneic parental skin fibroblasts used to obtain iPSCs barely triggered an NK-cell response. iPSC-derivatives with B2M knockout did not cause an additional increase in NK-cell activation, although they were devoid of HLA-I, the major inhibitory molecules for NK-cells. Transcriptome analysis revealed a significant imbalance of ligands for activating and inhibitory NK-cell receptors in iPS-fibro. Compared to parental fibroblasts, iPSC-derivatives had a reduced expression of HLA-I simultaneously with an increased gene expression of major activating ligands, such as MICA, NECTIN2, and PVR. The lack of inhibitory signals might be due to insufficient maturity of cells differentiated from iPSCs. In addition, we showed that the ligand imbalance could be reversed to normal. Longer cultivation and passaging of iPS-fibro or pretreatment with proinflammatory cytokines boosted HLA class I expression, which reduced the degranulation and cytotoxicity of NK-cells. Conclusion: In summary, we showed that iPSC-derived cells can be sensitive to the cytotoxic potential of autologous NK-cells regardless of HLA-I status. Thus, the balance of ligands for NK-cell receptors should be considered prior to iPSC-based cell therapies. Trial registration: Not applicable.