Unique T-cell Sub-Population Shifts after SBPT and Nivolumab in Platinum Refractory HNC: Biomarker Correlates from ROR1771.

PURPOSE/OBJECTIVE(S): ROR1771 was a clinical trial investigating the use of stereotactic body proton radiotherapy (SBPT) and nivolumab in recurrent platinum refractory head and neck squamous cell carcinoma (HNSCC). The planned analysis of T-cell subpopulation and biomarker response is herein presented.

MATERIALS/METHODS: Patients with metastatic histologically confirmed HNSCC from any primary site received 2 cycles of nivolumab followed by SBPT to 1-2 selected target lesion(s) (hilar/lung: 8 of 12 patients), followed by maintenance nivolumab. Peripheral blood mononuclear cells were isolated pre-/post-treatment. Flow cytometry identified T-cell subpopulations. Single Cell 5' Gene Expression (GEX) and V(D)J T Cell Receptor libraries were prepared using Single Cell Immune Profiling. Seurat (v4.1.1) was used to identify cell type clusters, and differential expression post-filtration was evaluated using the Wilcoxon Rank Sum test.

RESULTS: A total of 12 patients were eligible for analysis, with one alive at time of analysis, 52 months from start of treatment. Median overall survival here was 12.5 months vs. 7.5-months on CheckMate 141. SBPT ranged from 35-50 Gy. Sequential changes in T-cell populations from baseline were noted with initiation of nivolumab, driving decrease in tumor-reactive (TTR; CD11ahigh PD1+ CD8+ ), central memory (TCM; CCR7+CD45RA-), and effector T-cells (TEF; CCR7-CD45RA-). TTR and TCM increased following SBPT, with greatest increase (3.5x TTR and 5.2x TCM) in the surviving patient. An average of 68 genes with significant differential expression between timepoints (p<0.0001) demonstrated RNA gene expression changes across all cell subtypes, including ribosomal (RPL and RPS) genes, ACTB, FTL, MALAT1, and others. This averaged 113 genes across all timepoints in the surviving patient, with peak following nivolumab induction. On T-cell receptor (TCR) analysis of this patient, the predominant clonotype diversity changed substantially following nivolumab. Following SBPT, clonotype diversity again changed to include a milieu seen neither at baseline nor with nivolumab alone. These TCRs persisted for approximately 2 weeks following SBPT before returning to resemble the nivolumab-induced TCR diversity alone, coinciding with disease recurrence.

CONCLUSION: ROR1771 demonstrated overall survival favorably comparable to CheckMate 141. Biomarker analysis of peripheral blood samples demonstrated significant shifts in T-cell subpopulations and underlying gene expression to nivolumab and then to SBPT administration. SBPT to a target lesion changed TCR clonotypes within the peripheral blood beyond those seen with nivolumab administration, with fading of these TCR clonotypes coinciding with recurrence. SBPT in combination with nivolumab may drive systemic immunologic change above that induced by nivolumab alone and warrants further investigation.