Abstract
Immune rejection is one of the most serious challenges in allogeneic transplantation, including allogeneic induced pluripotent stem cell (allo-iPSC)-derived cell therapy. Beta-2-Microglobulin gene-knockout, human leukocyte antigen (HLA) class I-deficient iPSCs can evade immune rejection by host T cells, which occurs due to HLA mismatches. However, natural killer (NK) cells recognize HLA class Ⅰ-deficient cells and reject them, which is known as the missing-self response. Introducing chimeric HLA-E protein to HLA class Ⅰ-deficient iPSCs suppresses the missing-self response of NK cells expressing the inhibitory receptor NKG2A; however, technology to suppress NKG2A-negative NK cells is still required. Here, we developed novel agonists for the other inhibitory receptor, killer immunoglobulin receptor (KIR), on NK cells. We found that antibodies that bind to activating KIR enhance NK cell activation and developed selective agonists for inhibitory KIRs (KIR2DL1, KIR2DL2/3, and KIR3DL1). Introducing these selective inhibitory KIR agonists on T cells and HLA class Ⅰ-deficient iPSCs allowed them to evade immune rejection by NK cells. Additionally, we identified an NKG2A-selective agonist as an alternative to chimeric HLA-E, which stimulates the activating receptor NKG2C. This technology enhances immune tolerance in allo-iPSCs and facilitates the development of various iPSC-derived regenerative medicines.