Combined immune checkpoint blockade as a therapeutic strategy for BRCA1-mutated breast cancer

Area of Science:

• Oncology
• Immunology
• Genetics

Background:

• Immune checkpoint inhibitors (ICIs) are effective against hypermutated tumors.
• Breast cancer, particularly BRCA1-mutated types, has shown limited response to ICIs.
• BRCA1-associated tumors often display a triple-negative phenotype and significant lymphocyte infiltration.

Purpose of the Study:

• To investigate the mutational load, immune profile, and response to checkpoint inhibition in BRCA1-deficient breast cancer.
• To evaluate the efficacy of combining cisplatin with dual anti-PD-1 and anti-CTLA-4 therapy in a BRCA1-deficient tumor model.

Main Methods:

• Comparison of mutational load and immune profiles between BRCA1-mutated and wild-type triple-negative breast cancers (TNBCs).
• Assessment of combined cisplatin and dual ICI therapy in a Brca1-deficient mouse model.
• Analysis of immune responses including dendritic cell activation, regulatory T cell populations, and cytotoxic T cell function.

Main Results:

• BRCA1-mutated TNBCs exhibited increased somatic mutational load and tumor-infiltrating lymphocytes, with higher expression of PD-1 and CTLA-4.
• Combined cisplatin and dual ICI therapy induced robust systemic and intratumoral immune responses in Brca1-deficient mice.
• This included enhanced dendritic cell activation, reduced FOXP3+ regulatory T cells, and increased polyfunctional CD8+ and CD4+ T cell responses.
• Dual ICI therapy plus cisplatin significantly inhibited tumor growth and improved survival in vivo.

Conclusions:

• BRCA1-associated breast cancers possess an immunogenic profile that can be exploited by combination therapy.
• Dual immune checkpoint blockade combined with cisplatin demonstrates significant anti-tumor activity in preclinical models of BRCA1-deficient TNBC.
• These findings support the clinical investigation of this combination strategy for patients with BRCA1-associated TNBC.