Impact of Chemical-Induced Mutational Load Increase on Immune Checkpoint Therapy in Poorly Responsive Murine Tumors

Area of Science:

• Oncology
• Immunology
• Cancer Research

Background:

• Mouse models often fail to predict clinical responses to cancer therapies, including immune checkpoint inhibitors.
• Low tumor mutational burden in mice may explain the limited efficacy of PD-L1 blockade compared to human patients.
• Enhancing tumor immunogenicity is a strategy to improve immunotherapy outcomes.

Purpose of the Study:

• To investigate if increasing the mutational load of mouse tumors sensitizes them to PD-L1 blockade.
• To evaluate the impact of chemical mutagenesis and chronic chemotherapy exposure on tumor immunogenicity and immunotherapy response.

Main Methods:

• Transplantable mouse tumor cell lines (EMT-6/P, B16F1, RENCA, CT26, MC38) were mutagenized in vitro using MNNG or EMS.
• In vivo chemotherapy (cisplatin, cyclophosphamide) exposure was used to generate variants.
• Exome sequencing confirmed increased somatic mutations; tumor immunogenicity and immune cell infiltration (CD8+ T cells) were assessed.
• Responsiveness to anti-PD-L1 therapy was evaluated in mutagenized and chemotherapy-exposed variants.

Main Results:

• Mutagenesis increased somatic mutations and immunogenicity in B16F1, EMT-6/P, CT26, and MC38 variants.
• Only some mutagenized EMT-6/P and B16F1 variants showed sensitization to anti-PD-L1 therapy.
• Chronic cisplatin exposure increased sensitivity to anti-PD-L1 therapy in EMT-6 variants, associated with increased CD8+ T cell infiltration.
• Tumor PD-L1 expression levels did not consistently correlate with anti-PD-L1 treatment response.

Conclusions:

• Increasing tumor mutational load and immunogenicity does not universally sensitize mouse tumors to PD-L1 blockade.
• Chemically mutagenized mouse tumor models can serve as tools to study immunotherapy in tumors with high mutational burden.
• Chemotherapy may contribute to generating immunologically 'hot' tumors that are more responsive to immunotherapy.