ILT3.Fc-CD166 Interaction Induces Inactivation of p70 S6 Kinase and Inhibits Tumor Cell Growth

Area of Science:

• Immunology
• Cancer Biology
• Molecular Biology

Background:

• Immune checkpoint blockade using monoclonal antibodies (mAbs) is a key cancer immunotherapy strategy.
• The interaction between Ig-like transcript 3 (ILT3) and its ligand on T cells is a potential target for immune modulation.
• ILT3 is a marker of tolerogenic dendritic cells and is also known as LILRB4/LIR5/CD85k.

Purpose of the Study:

• To identify the unknown ligand for ILT3 on activated human T cells.
• To investigate the role of the ILT3-ligand interaction in T cell regulation and cancer immunotherapy.
• To evaluate the therapeutic potential of blocking the ILT3-ligand interaction.

Main Methods:

• Generation of anti-ILT3 mAbs using Jurkat cells.
• Flow cytometry, mass spectrometry, and Biacore analysis to identify the ILT3 ligand.
• Nucleofection for CD166 knockdown in primary human T cells.
• CRISPR-Cas9 for CD166 knockout in tumor cell lines.
• In vitro and in vivo experiments using tumor cell lines and mouse models.

Main Results:

• CD166 (activated leukocyte cell adhesion molecule) was identified as the ILT3 ligand.
• CD166 knockdown abolished ILT3.Fc's ability to inhibit T helper cell proliferation and induce T suppressor cells.
• ILT3.Fc inhibited the growth of CD166+ tumor cell lines in vitro and in vivo.
• CD166 knockout abrogated ILT3.Fc binding and its anti-tumor effect.
• ILT3.Fc mechanism involves p70S6K signaling pathway inhibition.
• ILT3.Fc blockade inhibited human lymphoid malignancy tumor progression in mice.

Conclusions:

• CD166 is the functional ligand for ILT3 on activated human T cells.
• The ILT3-CD166 interaction plays a critical role in T cell regulation.
• Targeting the ILT3-CD166 axis holds significant promise for cancer immunotherapy, particularly for lymphoid malignancies.