2134 - Comparative Analysis of the Impact of Proton vs. Photon-Based Chemoradiation In Esophageal Cancer Patients on Peripheral Blood Lymphocyte Profile and Clonal Diversity Using Single Cell Combinational Sequencing
Presenter(s)
S. H. Lin1, C. Braun2, Y. L. Son2, M. Wang2, C. Grassberger3, J. J. Smith4, P. M. Reeves5, A. I. Argueta2, R. J. H. Park6, H. Paganetti7, M. C. Poznansky4, T. S. Hong8, and R. Mohan9; 1Department of Thoracic Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, 2Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, 3Department of Radiation Oncology, University of Washington/Fred Hutchinson Cancer Center, Seattle, WA, 4Vaccine & Immunotherapy Center, Massachusetts General Hospital and Harvard Medical School, Boston, MA, 5Vaccine & Immunotherapy Center, Massachusetts General Hospital and Harvard Medical School, Boston, MA, Boston, MA, 6Department of Genitourinary Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, 7Department of Radiation Oncology, Massachusetts General Hospital/Mass General Brigham and Harvard Medical School, Boston, MA, 8Dana Farber Cancer Institute and Beth Israel Deaconess Medical Center, Boston, MA, 9Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX
Purpose/Objective(s): Severe radiation-induced lymphopenia (RIL) is a common toxicity seen during and after chemoradiation (CRT) that is mitigated with proton therapy (PT) in multiple cancer types, especially esophageal cancers. The objective of this study is to determine if the quantitative sparing of lymphocytes seen with PT could result in qualitative improvements in lymphocytes after CRT compared to photons.
Materials/Methods: Patients were prospectively enrolled for longitudinal blood collection before, during and after radiation treatment. Peripheral blood mononuclear cells (PBMCs) were isolated by Ficoll-gradient centrifugation and cryopreserved. PT were mainly delivered with passive scattering technique. Photons were delivered with intensity modulated radiation therapy (IMRT). For this analysis, 30 patients (15 patients in each group) were propensity-score matched according to planning treatment volume, baseline ALC, histology, age and body mass index. Up to 3-4 timepoints were analyzed per patient. PBMC lymphocytes were isolated using STEMCELL magnetic affinity assay, fixed, and single-cell RNA (scRNA) and single-cell T cell receptor (scTCR) libraries were generated using PARSE TCR Mega Kit. Downstream analyses of sequencing data were performed using RStudio Seurat.
Results: For scRNAseq, ~1.5 million cells and for scTCRseq, >1.1 million cells were analyzed. Both scRNA and scTCRseq shared cell-barcodes which allowed for overlaying clonality to the transcriptome for each cell. TCR clonality analysis showed no significant differences between the PT and IMRT groups at baseline, mid or end of treatment time points. However, during follow up after CRT, IMRT was associated with a significant depletion of unique TCR clones, whereas no significant clonal depletion was observed in the PT group. Clonal depletion was significantly more pronounced beyond 6 months after CRT compared to within the first 6 months following CRT. Transcriptomic and TCR clonality analyses revealed that IMRT (compared to PT) markedly depleted T-cell diversity within the rare clonotypes of naïve T cells and expanded large clonotypes of activated effector and regulatory T cell populations, particularly in the post-CRT period, possibly due to enhanced inflammatory changes.
Conclusion: In this propensity-matched cohort study, quantitative lymphocyte sparing by PT appears to also improve qualitative sparing of lymphocyte diversity, particularly in naïve T-lymphocytes. This study supports the view that PT may be the optimal radiation modality when combined with therapies that may rely on an intact immune system.