Effects of bacterial pathogens on efficacy of radiotherapy in interaction of NSCLC with T-Cells
Background: To this day, lung cancer still is the leading cause of cancer-related deaths. Pulmonary infections are a common complication for patients suffering from non-small cell lung cancer (NSCLC). Toxins of gram-positive and gram-negative bacteria play an important role in this, possibly by inducing radioresistance and immune escape of NSCLC cells via upregulation of PD-L1 and its interaction with its receptor PD-1.
Methods: For our in-vitro model, the human adenocarcinoma cell lines A549 and H1975 were treated with lipopolysaccharide and lipoteichoic acid prior to exposure to varying doses of ionizing radiation and direct co-culture with either Jurkat cells or human lymphocytes, both of which possess PD-1. Clonogenic survival of the NSCLC lines in co-culture with Jurkat was quantified by colony formation assay. Flow cytometry was used to measure PD-L1-expression of NSCLC cells. In addition, we quantified changes in the Jurkat cell’s metabolic activity after co-culture by MTS-assay as well as the production of TNF-α and IFN-γ by lymphocytes by ELISA. Furthermore, we investigated possible reversal of the effects we discovered by immunotherapeutic targeting of PD-L1.
Results: Both stimulation with LPS and LTA significantly increased the expression of PD-L1 in A549 cells, as did ionizing radiation. In colony formation assays, performed on both A549 and H1975, LPS- and LTA-treated cells were less sensitive to radiation. The metabolic activity of Jurkat cells was significantly decreased when co-cultured with NSCLC. Similarly, TNF-α and IFN-γ levels were significantly lower when lymphocytes were co-cultured with A549.
Using a PD-L1 antibody, we were able to reverse both radioresistance of A549 and suppressed metabolic activity of Jurkat in co-culture with A549. Blocking the interaction between PD-L-1 and PD 1, however, did not have an effect on the production of TNF-α and IFN-γ by lymphocytes in co culture.
Conclusions: Our findings suggest that bacterial infections can contribute to induction of radioresistance in NSCLC by upregulating PD-L1. This could also possibly have an immunosuppressory effect on T-cells. The use of PD-L1-targeting immunotherapy in combination with radiotherapy may offer therapeutic benefits.
Autoren: F. Fliegl1, U. Grandel1,2, F.S.B. Subtil3,4, N. Lachmann1, G. Dahlem1, F. Grimminger1,2, U. Sibelius1, K. Hattar1
1 Department of Internal Medicine IV/V, Universities of Giessen and Marburg Lung Center, Giessen, Germany
2 Asklepios Klinik Lich, Lich, Germany
3 Department of Radiotherapy and Radiooncology, Philipps-University, Marburg, Germany
4 Department of Radiotherapy, Universities of Giessen and Marburg Lung Center, Member of the German Center for Lung Research, Giessen, Germany