Invariant NKT cells demonstrate antitumor activity through their intrinsic cytotoxicity and adjuvant properties. To evaluate the safety and tolerability of clinical-grade iNKT cells generated from induced pluripotent stem cells (iPSC-iNKT cells), we conducted the phase I clinical trial of allogeneic iPSC-iNKT cells in patients with recurrent head and neck cancer. In three out of ten enrolled patients for whom samples were available before administration and 8 and 21 days after administration, peripheral blood T cells and NK cells were submitted for single-cell RNA sequencing and TCR sequencing. In all three patients' NK cells and T cells, the IFN-γ pathway was activated after iPSC-iNKT cell administration. In the two patients, clonal expansion of CD8 T cells was identified. Although this trial's antitumor effect was weak because of iNKT cell monotherapy, we found that iPSC-iNKT cells can induce T-cell clonal expansion. In the future, we intend to enhance this adjuvant effect by combining therapy with αGalCer-pulsed antigen-presenting cells.