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Updated: Jun 16, 2025
Experimental Melanoma Immunotherapy Model Using Tumor Vaccination with a Hematopoietic Cytokine
Published on: February 24, 2023
Quantitative response assessment of combined immunotherapy in a murine melanoma model using multiparametric MRI
Maurice M Heimer1, Amra Cimic2, Sandra Kloiber-Langhorst2
1Department of Radiology, LMU University Hospital, LMU Munich, Munich, Germany. maurice.heimer@med.uni-muenchen.de.
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.
