2611 - Regulatory T Cell-Enriched Immune Trajectories during Radiotherapy Associate with Reduced PFS and Diverge during Photon vs. Proton Therapy
Presenter(s)
J. J. Smith1,2, K. Zvonícková3, U. Pala1, A. I. Argueta4, C. Braun4, Y. L. Son5, Y. Chen6, R. J. H. Park4, T. S. Hong7, H. Paganetti8, R. Mohan9, M. C. Poznansky1, S. H. Lin10, P. M. Reeves11, and C. Grassberger12; 1Vaccine & Immunotherapy Center, Massachusetts General Hospital and Harvard Medical School, Boston, MA, 2Department of Infectious Disease, Imperial College London, London, United Kingdom, 3Imperial College London, London, United Kingdom, 4Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, 5University of Texas Health Science Center at Houston, Houston, TX, 6Department of Epidemiology and Biostatistics, Texas A&M University, College Station, TX, 7Department of Radiation Oncology, Dana Farber Cancer Institute, Harvard Medical School, Boston, MA, 8Department of Radiation Oncology, Massachusetts General Hospital/Mass General Brigham and Harvard Medical School, Boston, MA, 9Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, 10Department of Thoracic Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, 11Department of Surgery, Massachusetts General Hospital and Harvard Medical School, Boston, MA, 12Department of Radiation Oncology, University of Washington/Fred Hutchinson Cancer Center, Seattle, WA
Purpose/Objective(s):
Radiation therapy (RT) can promote antitumor immunity, yet responses are heterogeneous and are not fully explained by variable lymphocyte depletion. We hypothesized that baseline immune composition and longitudinal trajectories, as revealed by deep immune profiling, predict progression-free survival (PFS) and differ between proton (PT) and photon (IMRT) therapy.Materials/Methods:
Peripheral blood mononuclear cells were collected retrospectively from propensity-matched patients with esophageal adenocarcinoma or squamous cell carcinoma treated with PT (n = 17) or IMRT (n = 17) chemoradiation. Samples were obtained at baseline, during RT, immediately post-RT, and ~45 and 180 days post-RT. Immune subsets were quantified using a 39-marker mass cytometry panel, and proportions were normalized to absolute lymphocyte/myeloid counts (ALC/AMC). Manual gating and FlowSOM clustering followed by generalized linear mixed models (GLMM), Cox hazards regression and Mann–Whitney U tests assessed associations with PFS and RT modality.Results:
RT induced transient lymphopenia (mean ALC decrease 0.96 K/µL) that did not differ between PT and IMRT (p = 0.67). Survival was not associated with nadir ALC (p = 0.67) nor modality (p = 0.89). In contrast, higher baseline frequencies of activated memory T-cell phenotypes, including CTLA-4? (HR 4.01, p = 0.018) and CD71? (HR 3.71, p = 0.026) subsets, independently predicted inferior PFS. Unsupervised FlowSOM clustering in patients with complete longitudinal sampling (n = 20) identified a regulatory-skewed CD4? T-cell population enriched for CTLA-4?FOXP3? cells co-expressing CD39, CD95, and CD7 that was associated with reduced PFS (p = 0.02). In the full cohort, longitudinal persistence of CD127?FOXP3? regulatory CD4? T cells during, immediately following, and ~45 days after RT remained strongly associated with inferior PFS (HR 12.87, 3.07, and 2.7, respectively; all p < 0.05), indicating persistence of regulatory phenotypes through RT, differentiates PFS outcome. Consistent with this trajectory, sustained CTLA-4? (HR 18.56, p = 0.005) and CD39? (HR 4.35, p = 0.029) memory T-cell phenotypes were similarly correlated with poor outcomes. Compared with PT, IMRT was associated with relative expansion of FOXP3? regulatory T cells at ~45 days post-RT (p = 0.030), suggesting photon therapy may promote persistence of regulatory T cells following RT.Conclusion:
A regulatory-skewed systemic immune phenotype at baseline and its persistence during RT strongly associates to inferior PFS, independent of lymphocyte depletion. Photon therapy appears to favor persistence of suppressive regulatory T-cell phenotypes relative to proton therapy. These findings highlight that deep immune profiling can identify patients at high risk of progression and provide a rationale for immune-informed RT modality selection or integration of immunomodulatory strategies targeting regulatory pathways, including CTLA-4.