1132 - Functional Radiosensitivity and Immune Profiling in Late Rectal Bleeding after Prostate Radiotherapy: The TransPROUST Study
Presenter(s)
K. Debbi1, N. H. To1, J. Tosello Boari2, A. Bennassi1, M. Brengues3, G. Coraggio1, M. A. Cherif1, E. M. Ozsahin Jr4, A. Ingels5, A. de la Taille6, J. L. Cohen2, D. Azria3, A. Thiolat2, and Y. Belkacemi1; 1Department of Radiation Oncology and Henri Mondor Breast Center. Henri Mondor University Hospital, APHP, UPEC, Creteil, France, 2Institut Mondor, INSERM U955, i-Biot, UPEC, Creteil, France, 3University Federation of Radiation Oncology of Mediterranean Occitanie, Montpelier Cancer Institute (ICM), Montpellier Cancer Research Institute (IRCM), INSERM U1194, University of Montpellier, Montpellier, France, 4Radio-Oncology Service, Riviera-Chablais Hospital, Rennaz, Switzerland, 5Department of Urology, Henri Mondor Hospital, University of Paris Est Créteil (UPEC), Creteil, France, 6Department of Urology, Henri Mondor Hospital, University of Paris Est Créteil (UPEC, Creteil, France
Purpose/Objective(s): Radiotherapy (RT) eliminates tumor cells but inevitably affects surrounding healthy tissues. The Radiation-Induced Lymphocyte Apoptosis (RILA) assay, originally based on CD4? and CD8? T-cell apoptosis, has been clinically validated in its standardized CD8? version as a predictor of late radiation-induced fibrosis, but has not been specifically assessed for hemorrhagic toxicities. No functional immune signature has been reported for clinically adjudicated late rectal bleeding (LRB). Unlike fibrosis, hemorrhagic complications arise from progressive radiation-induced vasculopathy and endothelial damage, where B cells may contribute through vascular homeostasis and immune-mediated vascular injury. We hypothesized that B-cell radiosensitivity may better capture susceptibility to LRB following prostate RT.
Materials/Methods: In a nested case-control study, we compared patients with centrally adjudicated grade =2 LRB at multidisciplinary morbidity and mortality review (MMR) (Tox?, n=9) to matched controls free of toxicity (Tox?, n=15). We performed the CD8? RILA assay on fresh blood and, in parallel, subjected cryopreserved peripheral blood mononuclear cells (PBMCs) to a 0Gy/8Gy ex vivo irradiation challenge. Multiparameter flow cytometry at 24h quantified apoptosis, activation markers (CD38, CD70), and B-cell subsets. Irradiation-induced changes were analyzed as within-sample ?(8Gy-0Gy). Analyses were blinded and interleaved.
Results: The ex vivo PBMC challenge identified a multi-lineage immune response signature: reduced apoptosis induction (within-subject change, 8 Gy–0 Gy) in B cells (6.6% ± 2.4 vs 18.7% ± 1.9; p<0.01), NK cells (10.8% ± 3.1 vs 20.1% ± 2.5; p<0.05), and CD4? T cells (6.0% ± 1.7 vs 13.0% ± 1.5; p<0.01), while CD8? T-cell apoptosis was preserved. Post-irradiation activation/stress-marker profiles differed between groups, with lower CD38? proportions across NK, CD4?, and CD8? T cells at 8 Gy, and reduced CD70? proportions in NK cells; no between-group differences were observed at 0 Gy for these markers. In evaluable B-cell samples, the most discriminant feature was a marked failure of CD70 induction, both in total B cells (57.5% ± 7.6 vs 91.2% ± 1.5; p<0.001) and particularly in naïve B cells (54.4% ± 10.3 vs 92.8% ± 1.2; p<0.001). By contrast, in fresh blood, CD8? RILA was higher in Tox+ (31.6% ± 4.5) than Tox- (19.3% ± 2.6) and increased with time since RT in Tox+ (r=0.56; p<0.05), suggesting time-dependence and limited discrimination for hemorrhagic endpoints.
Conclusion: To our knowledge, this is the first human study to report an irradiation-induced functional immune signature associated with adjudicated LRB after prostate RT, characterized by impaired radiation-induced CD70 upregulation on B cells and reduced apoptosis in NK and CD4? T cells. These findings are hypothesis-generating and warrant prospective validation, including assessment in pre-RT sampling and integration with dosimetry-based risk models.