Dose-Specific Intratumoral GM-CSF Modulates Breast Tumor Oxygenation and Antitumor Immunity

Area of Science:

• Immunology
• Oncology
• Cancer Biology

Background:

• Granulocyte-macrophage colony-stimulating factor (GM-CSF) is an immunotherapy adjuvant with variable efficacy.
• Previous studies indicated high-dose GM-CSF can worsen tumor hypoxia and angiogenesis in triple-negative breast cancer (TNBC).

Purpose of the Study:

• To compare the immunoregulatory and oxygen-regulatory effects of low-dose versus high-dose GM-CSF.
• To assess GM-CSF's impact on tumor oxygenation, vasculature, and antitumor immunity in TNBC models.
• To determine if GM-CSF dosage influences sensitivity to anti-PD1 immunotherapy.

Main Methods:

• Intratumoral injections of low-dose GM-CSF or saline in FVB/N PyMT TNBC models.
• Assessment of tumor hypoxia, vasculature (CD31+ endothelial cells, NG2+ pericytes), and immune cell phenotypes (TAMs, TILs) via flow cytometry and transcriptional profiling.
• Evaluation of anti-PD1 response in GM-CSF-primed PyMT (cold) and BALB/c 4T1 (hot) TNBC models.

Main Results:

• Low-dose GM-CSF reduced tumor hypoxia and normalized vasculature by increasing pericyte coverage.
• Low-dose GM-CSF sensitized anti-PD1-resistant PyMT tumors to anti-PD1 therapy.
• High-dose GM-CSF exacerbated hypoxia and promoted an immunosuppressive TAM phenotype in PyMT tumors.
• High-dose GM-CSF had disparate effects in 4T1 tumors, increasing MHC class IIhi TAMs and immunostimulatory molecules.

Conclusions:

• Low-dose GM-CSF demonstrates a novel role in reducing tumor hypoxia, enhancing vascular normalization, and improving immunotherapy response.
• High-dose GM-CSF can promote an immunosuppressive tumor microenvironment, particularly under hypoxic conditions.
• GM-CSF dosage is a critical factor influencing tumor oxygenation, immune response, and therapeutic efficacy in cancer immunotherapy.