Quantitative response assessment of combined immunotherapy in a murine melanoma model using multiparametric MRI

Heimer, Maurice M.; Cimic, Amra; Kloiber-Langhorst, Sandra; Antons, Melissa J.; Stueckl, Jennifer; Hirner-Eppeneder, Heidrun; Kunz, Wolfgang G.; Dietrich, Olaf; Ricke, Jens; Herr, Felix L.; Cyran, Clemens C. (2025): Quantitative response assessment of combined immunotherapy in a murine melanoma model using multiparametric MRI. European Radiology Experimental, 9: 59. ISSN 2509-9280

Abstract

Background

We assessed immunotherapy response in a murine melanoma model using multiparametric magnetic resonance imaging (mpMRI) features with ex vivo immunohistochemical validation.

Methods

Murine melanoma cells (B16-F10) were inoculated into the subcutaneous flank of n = 28 C57BL/6 mice (n = 14 therapy; n = 14 control). Baseline mpMRI was acquired on day 7 at 3 T. The immunotherapy group received three intraperitoneal injections of anti-PD-L1 and anti-CTLA-4 antibodies on days 7, 9, and 11 after inoculation. Controls received a volume equivalent placebo. Follow-up mpMRI was performed on day 12. We assessed tumor volume, diffusion-weighted imaging parameters, including the apparent diffusion coefficient (ADC), and dynamic-contrast-enhanced metrics, including plasma volume and plasma flow. Tumor-infiltrating lymphocytes (TIL; CD8+), cell proliferation (Ki-67), apoptosis (terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick-end labeling, TUNEL), and microvascular density (CD31+) were assessed in a validation cohort of n = 24 animals for time-matched ex vivo validation.

Results

An increase in tumor volume was observed in both groups (p ≤ 0.004) without difference at follow-up (p = 0.630). A lower ADC value was observed in the immunotherapy group at follow-up (p = 0.001). Immunohistochemistry revealed higher TUNEL values (p < 0.001) and CD8+ TILs (p = 0.048) following immunotherapy, as well as lower tumor cell Ki-67 values (p < 0.001) and microvascular density/CD31+ (p < 0.001).

Conclusion

Lower tumor ADC, paired with higher intratumoral expression of CD8+ TIL, was observed five days after immunotherapy, suggestive of early immunological response. Ex vivo immunohistochemistry confirmed the antitumoral efficacy of immunotherapy.

Relevance statement

Compared to tumor size, diffusion-weighted MRI demonstrated potential for early response assessment to immunotherapy in a murine melanoma model, which could reflect changes in the tumor microenvironment and immune cell infiltration.

Key Points

No difference in tumor volume was observed between groups before and after therapy.

Lower ADC values paired with increased CD8+ TILs were observed following immunotherapy.

Ex vivo immunohistochemistry confirmed antitumoral efficacy of anti-PD-L1 and anti-CTLA-4 immunotherapy.

• Dokumententyp: Artikel (Klinikum der LMU)
• Organisationseinheit (Fakultäten): 07 Medizin > Klinikum der LMU München > Klinik und Poliklinik für Radiologie
• DFG-Fachsystematik der Wissenschaftsbereiche: Lebenswissenschaften
• DFG: Gefördert durch die Deutsche Forschungsgemeinschaft (DFG) - 491502892