Sustained Macrophage Reprogramming Is Required for CD8+ T cell-Dependent Long-Term Tumor Eradication

Area of Science:

• Immunology
• Oncology
• Cancer Research

Background:

• Tumor-associated macrophages (TAMs) have a complex role in cancer, influencing both tumor progression and immune responses.
• Understanding the specific functional states and molecular drivers of antitumor TAMs is crucial but challenging.

Purpose of the Study:

• To investigate the potential of a combined TLR3 and CD40 agonist treatment (myeloid cell treatment, MCT) to reprogram TAMs into an antitumor phenotype.
• To elucidate the temporal dynamics and molecular mechanisms underlying TAM reprogramming and its impact on tumor regression.

Main Methods:

• Intratumoral administration of TLR3 and CD40 agonists in an orthotopic mouse breast cancer model.
• Single-cell RNA sequencing of TAMs at various time points post-treatment.
• Analysis of immune cell activation, particularly CD8+ T cells, and tumor eradication.

Main Results:

• MCT induced a transient antitumor TAM phenotype characterized by specific markers (e.g., iNOS, CD38) peaking at 12 hours.
• This phenotype shifted by 72 hours to TAMs with mixed tumor-promoting and limiting features.
• Repeated MCT administration was necessary to maintain the antitumor TAM state, leading to CD8+ T cell activation and tumor eradication.
• Reactive oxygen species and TNF-α were identified as key mediators of TAM-driven tumor control.

Conclusions:

• The antitumor reprogramming of TAMs by MCT is transient, highlighting a vulnerability in this therapeutic approach.
• Sustained antitumor immunity and tumor eradication can be achieved through repeated administrations of MCT, overcoming the transient nature of TAM reprogramming.
• This study provides insights into manipulating TAMs for effective cancer immunotherapy.