A subset of CD8αβ+ iNKT cells in a humanized mouse model

Invariant NKT (iNKT) cells are unconventional innate-like T cells demonstrating potent anti-tumor function in conventional mouse models. However, the iNKT cell ligands have had limited efficacy in human anti-tumor clinical trials, mostly due to the profound differences in the properties and compositions of iNKT cells between the two species, including the presence of a CD8+ subset of iNKT cells only in humans. To build reliable in vivo models for studying human iNKT cells, we recently developed the first humanized mouse model (hCD1d-KI) with human CD1d knocked in. To further humanize the mouse model, we now introduced the human invariant NKT TCRα chain (Vα24Jα18) into the hCD1d-KI mice. Similar to humans, this humanized mouse model developed a subset of CD8αβ+ iNKT cells among other human-like iNKT subsets. The presence of the CD8αβ+ iNKT cells in the thymus suggests that these cells developed in the thymus. In the periphery, these NKT cells showed a strong Th1-biased cytokine response and potent cytotoxicity for syngeneic tumor cells upon activation, as do human CD8αβ+ iNKT cells. The low binding of iNKT TCRs to the human CD1d/lipid complex and high prevalence of Vβ7 TCRβ among the CD8+ iNKT cells strongly point to a low avidity-based developmental program for these iNKT cells, which included the suppression of Th-POK and up-regulation of Eomes transcriptional factors. Our establishment of this extensively humanized mouse model phenotypically and functionally reflecting the human CD1d/iNKT TCR system will greatly facilitate the future design and optimization of iNKT cell-based immunotherapies.