Peripheral blood immune cell profiling in survivors of testicular germ cell tumors

417 Background: Testicular germ cell tumors (GCT) achieve exceptional cure rate with cisplatin-based chemotherapy. Survivors of GCTs represent a unique population to study post-cancer treatment physiology and late toxicities. The impact of cancer treatment on the immune-cell profile in long-term GCT survivors is unknown. In this study, we performed an immune-phenotyping in survivors of GCTs. Methods: Whole peripheral blood was obtained from GCT survivors (N = 202) at National Cancer Institute of Slovakia within the protocol of the ongoing survivorship study on a day of their annual follow-up visit. The median follow-up was 11 years (2-25). GCT survivors were distributed into treatment groups: RT – radiotherapy to the retroperitoneum (N = 18), CT - chemotherapy (N = 143), CTRT - chemotherapy + radiotherapy (N=9); and a control group: AS - active surveillance/orchiectomy only (N=32). Immuno-phenotyping of peripheral blood leukocyte populations was performed with flow-cytometry. Immune cell subpopulations were statistically assessed for associations with received treatment. Results: Survivors treated with RT vs AS had higher no of classical dendritic cells (DCs) (mean ± SEM = 82.0 ± 1.9 vs 76.5 ±1.5, p = 0.03) and non-significantly lower no of plasmacytoid DCs and CD16+ DCs (0.11 ± 0.01 vs 0.15 ± 0.01, p = 0.06 and 54.4 ± 4.1 vs 64.8 ± 3.2, p = 0.07, respectively). Survivors treated with CT vs AS had higher no of CD19+ B cells (11.9 ± 0.3 vs 10.4 ± 0.7, p = 0.04)and lower no of CD8+ T cells (26.0 ± 1.3 vs 23.7 ± 0.6, p = 0.04). Similarly, survivors treated with CTRT vs AS had higher no of CD19+ B cells (13.6 ± 1.4 vs 10.4 ± 0.7, p = 0.04) and lower no of CD8+ T cells (20.7 ± 2.4 vs 26.0 ± 1.3, p = 0.04). Survivors treated with ≥ 400mg/m2 of cisplatin-based chemotherapy vs AS had no of CD19+ B cells (12.2 ± 0.5 vs 10.4 ± 0.7, p = 0.04) and lower no of CD8+ T cells (23.4 ± 0.9 vs 26.3 ±1.3, p = 0.04). The immunoregulatory index CD4/CD8 was higher in CTRT vs AS (2.5 ± 0.3 vs 1.8 ± 0.1, p = 0.04). Conclusions: Certain subpopulations of leukocytes differ according to received treatment in survivors of GCTs. Our results may suggest that chemotherapy and/or radiotherapy may produce long-term immunomodulatory effects. Interplay between B and T cells may be a contributing mechanism of late toxicities. Further research is needed to uncover the causal relationship to the long-term health of GCT survivors.