NK Cell Therapy In Combination With Low-Dose Chemoradiotherapy

Introduction

Natural killer (NK) cells hold great potential for their application in tumor immunotherapy, mainly due to their MHC-unrestricted and pan-specific recognition capabilities.

5-fluorouracil (5FU) is the most effective and commonly used chemotherapeutic drug in the treatment of colorectal cancer (CRC) and chemoradiotherapy (CRT) is one of the most effective combined modalities for improving overall survival in preoperative settings for patients with locally advanced rectal cancer.

In this study, the authors explore the potential of combining CRT with NK cell-related immune responses, as a therapeutic modality against CRC, especially in intractable cold human CRC.

Main Points

• For the experiments performed in this paper, NK cells were expanded for 14 days, and only activated NK cells with over 90% purity (CD56+, CD3-) were used.
• Human colorectal cancer cell lines (HT29 and HCT116) irradiated with 4-20Gy followed by low-dose 5FU for 24 hours showed an increased expression of NK cell receptor-related target ligands.
• Co-culture experiments in vitro, showed that HT29 cells treated with low-dose 5FU in combination with irradiation significantly increased NK cell degranulation (increased CD107a expression). Furthermore, the expression of IFN-ϒ released from the NK cells was significantly increased.
• Real-time NK cell cytotoxicity demonstrated a synergistic killing effect of a combination of low-dose CRT, mainly through NKp30 and NKG2D (NK cell activating receptors). This was further confirmed by decreased NK cell degranulation after blocking of NKp30 and NKG2D.
• To investigate the synergistic effects of CRT and NK cells, HT29-bearing NSG mice were subjected to low-dose (2Gy) tumor irradiation when tumors had reached a volume of 50mm3 (early stage) together with 5FU treatment followed by NK cell injections. The proportion of mice with gross secondary tumors and/or lung metastases was significantly lower in groups treated with NK cells, indicating suppressed distant metastasis to lung and axillary regions. However, there was no difference in primary tumour growth.
• To evaluate the synergistic role of adoptive NK cell therapy in the establish HT-29 subcutaneous tumor model, increasing doses of NK cells were administered intravenously every 4 days, starting 3 days after mice had been treated with low-dose (2Gy) local RT (when tumors had reached a volume of 100mm3) and 5FU (25mg/kg). All mice treated with NK cells showed an increased survival compared to controls and the effect was dose dependent. This suggests the potential for NK cell intensification under low-dose CRT as an alternative therapeutic immunotherapy in a human CRC model.

Conclusion

The intensified NK cell administration showed significantly better primary tumor control and survival outcomes than the non-intensified NK cell administration in the human colorectal HT-29 model treated with low-dose chemoradiotherapy.

Optimized NK cell therapy combined with low-dose chemoradiotherapy can provide effective therapeutic potential for intractable cold human colorectal cancer.

Services

Epistem offers several pre-clinical human cancer models (including colorectal cancer) to assess the efficacy of cancer immunotherapies as single agents or in combination with chemo- and/or local radio-therapy. To aid in the assessment we have a Cytation 5 live-cell imaging system and a 15 colour Novocyte flow cytometer, which gives the opportunity to evaluate treatment effects and elucidate the function of specific immune cell types in vitro and ex vivo.