Interactions Between Circulating Tumor Cells and the Immune System in Colorectal Cancer: Friends or Foes?

Area of Science:

• Oncology
• Immunology
• Cancer Metastasis

Background:

• Colorectal cancer (CRC) is a major global health concern, with metastasis being the primary cause of mortality.
• Circulating tumor cells (CTCs) are crucial for cancer dissemination but face significant immune pressure in the bloodstream.
• The interaction between CTCs and immune cells is complex, involving both immune evasion and potential exploitation by cancer cells.

Purpose of the Study:

• To review the bidirectional interactions between colorectal cancer (CRC) circulating tumor cells (CTCs) and immune cells.
• To explore how CTCs evade immune surveillance and potentially utilize the immune system for survival and metastasis.
• To discuss the role of CTCs as biomarkers for immunotherapy in CRC.

Main Methods:

• Literature review of studies examining CTC-immune cell interactions in CRC.
• Analysis of intrinsic and extrinsic immune evasion mechanisms employed by CTCs.
• Examination of CTC clustering with immune cells and their impact on systemic immunity.

Main Results:

• CTCs employ various strategies to evade immune detection, including MHC-I modulation, immune checkpoint expression (PD-L1, CD47, FasL), platelet cloaking, and NET formation.
• CTCs form heterotypic clusters with immune cells (monocytes, neutrophils, lymphocytes), creating pro-metastatic niches.
• CTCs influence systemic immunity by reprogramming immune cells like NK cells, T lymphocytes, and MDSCs.

Conclusions:

• CTCs are not just passive targets but actively interact with and can manipulate the immune system for metastatic progression.
• CTCs show promise as dynamic biomarkers for predicting immunotherapy response, particularly PD-L1+ CTCs.
• Further research is needed to standardize CTC detection and clinical validation for improved CRC treatment strategies.