Thymosin alpha1 enhanced cytotoxicity of iNKT cells against colon cancer via upregulating CD1d expression.

Increasing evidence showed invariant NKT cells (iNKT cell) are an attractive candidate for cancer immunotherapy, but its role in colorectal cancer treatment was still unclear. Here we reported iNKT cells exerted moderate cytotoxic effect against colorectal cancer cells (CRC cells) with the stimulation of α-Galcer, and the mutual recognition between CRC and iNKT cells could be greatly enhanced by Thymosinα1 (TA), which resulted in stronger killing efficiency both in vitro and in vivo. TA is widely used as an immune adjuvant for cancer therapy, but how it works on cancer cells still remains unclear. We found TA could upregulate CD80, B7H2 and CD1d expression on CRC cells. However, neutralization assay revealed iNKT cells' activation depended on CD1d expression rather than CD80 or B7H2. Moreover, colon cancer stem cells expressed higher CD1d level, which accounted for their greater sensitization to iNKT cells. Mechanistically, inhibition of Erk/MAPK pathway greatly attenuated the upregulation of CD1d by TA. Taken together, depending on Erk/MAPK pathway, TA promoted the activation and cytotoxicity of iNKT cells via upregulating CD1d expression on CRC cells, which indicated a novel immunotherapeutic strategy of iNKT cells against CRC.