Evaluation of the abscopal-like effect of radioimmunotherapy on sentinel lymph nodes in H22 hepatocellular carcinoma via dynamic lymphography

Abstract Background The synergistic suppressive effects of the radioimmunotherapy-induced abscopal effect on distant non-irradiated tumors have recently emerged as a research hotspot. However, studies on its specific regulatory role in adjacent sentinel lymph nodes (SLNs) remain limited. The deep location and small size of SLNs hinder the monitoring of treatment-related changes, underscoring the need for lymphography-based approaches. In this study, we aimed to evaluate the abscopal-like effect of radioimmunotherapy on SLNs in an H22 hepatocellular carcinoma mouse model via dynamic lymphography. Methods H22 murine hepatocarcinoma cells were transplanted into the right hind foot sole of C57BL/6 mice. Fourteen days post-inoculation, mice with SLNs were selected and divided into six groups: control, isotype control Ig, anti-PD-1 alone, irradiation (IR) alone, irradiation + isotype control Ig, and IR + anti-PD-1. The volume and weights of tumors and non-irradiated SLNs were measured. The SLNs were imaged with ¹⁸F-fluorodeoxyglucose ( 18 F-FDG) dynamic lymphography at 14, 21, and 28 days post-inoculation. CD8 immunohistochemistry assays were performed to assess CD8 + T cell infiltration. Results In this mouse model, the IR + anti-PD-1 combination treatment exerted a marked suppressive effect on the growth of both irradiated tumors and non-irradiated SLNs, demonstrating a robust enhancement of the abscopal-like effect compared with the monotherapy groups. Mechanistic investigations demonstrated elevated CD8⁺ T cell infiltration in non-irradiated SLNs, suggesting that enhanced systemic anti-tumor immunity mediated the effect. Dynamic ¹⁸F-FDG PET lymphography enabled clear visualization of SLNs as early as 30 s post-injection, with sustained imaging clarity for over 30 min. This method also demonstrated decreased radioactive accumulation in irradiated tumors and non-irradiated SLNs, confirming an enhanced abscopal-like effect with the IR and anti-PD-1 combination approach. Conclusions Our data demonstrate that the regression of SLNs adjacent to the irradiation field, mediated by the abscopal-like effect of radioimmunotherapy, can be sensitively and effectively tracked via dynamic 18 F-FDG lymphography. Furthermore, our findings provide an effective and straightforward lymphographic approach with substantial translational potential for assessing the efficacy of the radioimmunotherapeutic abscopal-like effect against SLNs.