HLA-E-restricted KIR+ CD8+ regulatory T cells are enriched during allograft rejection and suppress activated CD4+ T cells in vitro and ex vivo 2308005

Introduction CD8+T cells expressing NK cell receptors have regulatory function. We have shown that alloreactive CD4+T cells upregulate Qa-1 (human HLA-E) stress-peptide complex in mice, enabling elimination by Qa-1—restricted Ly49+CD8+Tregs and promoting graft survival. We hypothesized that analogous human CD8+Tregs exist, express killer immunoglobulin-like receptor (KIR), are enriched in graft rejection, can be expanded, and suppress HLA-E—upregulated alloimmune CD4+ T cells. Methods Cryopreserved PBMCs from kidney transplant recipients (KTRs) with no rejection (NR), antibody-mediated rejection (AMR), acute cell-mediated rejection (ACR), lupus nephritis, and healthy controls (HC) were phenotyped by flow cytometry. KIR+CD8+T cells from healthy apheresis leukoreduction samples were used to study in vitro expansion and CD4+T-cell suppression. In human kidney organoid (HKO) humanized murine (NSG-BLT) model, KIR+CD8+T cells were isolated to assess ex vivo expansion and suppression of alloreactive CD4+T cells. Results Inhibitory KIR (iKIR) are homologous to murine Ly49 in CD8+ Tregs. In KTRs, frequency of iKIR+ CD8+Tregs were significantly higher in AMR than HC. KIR2DL2/3 and KIR3DL1 subsets of iKIR+CD8+Tregs were most enriched. KIR2DL2/3+KIR3DL1+CD8+Tregs(CD8+Tregs) were enriched in alloimmunity compared to HC and demonstrated effector memory phenotype. IL-15-dependent in vitro expansion of FACS-sorted CD8+Tregs >50-fold in 3weeks while maintaining perforin and granzyme-B expression. In vitro expanded CD8+Tregs suppressed activated HLA-E—upregulated CD4+T cells significantly more in the presence of peptide. In a humanized murine transplant model (HKO-NSG-BLT), we showed that ex vivo—expanded CD8+Tregs eliminated alloreactive CD4+T cells in an antigen-dependent manner. Conclusion In alloimmunity, KIR+CD8+Tregs form a distinct subset of T cells enriched during rejection and suppress activated CD4+T cells in vivo and ex vivo, supporting their development as cell therapy against allograft rejection.