Pathologic and Immunologic Response After Ablative Radiation in Lung Cancer

Lung cancer is the leading cause of cancer death in the United States. While stereotactic ablative radiotherapy (SABR) is delivered as standard treatment in patients with medically inoperable stage I non-small cell lung cancer (NSCLC), an alarming 30-40% of these patients still develop disease recurrence just outside of the radiation field and deadly distant metastases in their lifetime. Furthermore, since the abscopal response was reported in advanced NSCLC where a systemic cancer response was induced in areas away from the irradiated site when radiation was combined with immunotherapy, multiple clinical trials are currently investigating the role of combining these two modalities. Significantly, how SABR alone increases immunogenicity of a tumor is unknown. There is a critical need to elucidate the mechanism by which SABR alone incites the immune system to better develop future rational combinations of immunotherapy with SABR. SABR induced cell death will ultimately activate downstream cytotoxic T-cells and cause T-cell influx into the tumor to enhance immunogenic tumor cell kill. This is accomplished with SABR-induced tumor antigen-both mutation-associated neoantigen and tumor-associated antigen- release, priming of downstream cytotoxic T-cells, leading to specific T-cell clonal expansion, and resultant influx of these activated cytotoxic T-cells into the tumor and blood to enhance immune-mediated tumor cell kill. Herein the investigator proposes a pilot study to compare pre- and post-SABR core biopsies of stage I NSCLC tumors to identify SABR-induced immune-mediated tumor recognition based on a significant and specific expansion of T-cell clones using a novel T-cell receptor (TCR) sequencing assay. This will be coupled with (1) novel genomic analysis of candidate tumor antigens that may be released from the pre-SABR tumor and (2) functional validation assays to screen post-treatment peripheral blood T-cells for reactivity to these released candidate tumor antigens. In addition, cell-based analysis will be used to identify changes in key T-cell infiltrates into the post-SABR tumor. The results of this pilot study may have the potential to translate into improved systemic outcomes for patients with NSCLC through future integrated trials of immune checkpoint blockade antibodies that specifically relieve the immunosuppression on the T-cell population found to be activated by SABR. Clarifying SABR-induced immune changes in the tumor and blood will identify pathways that may be exploited to enhance systemic immunity to kill micro-metastatic disease and mitigate relapse in the next generation of clinical trials. Additional corollary imaging studies using dual-energy (DE) computed tomography (CT), a novel imaging modality that improves the material decomposition ability of CTs, may identify new imaging markers for post-SABR treatment response by comparing DE-CT imaging characteristics with SABR fields and pathologic response.