Defective adhesion in tumor infiltrating CD8+ T cells

Area of Science:

• Immunology
• Cancer Biology
• Cellular Signaling

Background:

• CD8(+) tumor-infiltrating lymphocytes (TIL) are crucial for anti-tumor immunity but often exhibit defective cytotoxic activity.
• Tumor-induced inhibition of proximal T-cell receptor (TCR)-mediated signaling impairs TIL function, a defect reversible upon purification and culture.

Purpose of the Study:

• To investigate the underlying causes of defective conjugation between nonlytic TIL and tumor cells.
• To determine if impaired T-cell adhesion molecule function contributes to reduced anti-tumor immune responses.

Main Methods:

• Comparative analysis of conjugation frequency, strength, and duration between lytic and nonlytic TIL and tumor cells.
• Assessment of LFA-1 activation and ICAM-1 binding upon phorbol ester stimulation.
• Quantification of CD2 and CD8 expression and their localization within the immune synapse.

Main Results:

• Nonlytic TIL exhibit significantly lower conjugation frequency, strength, and duration with tumor cells compared to lytic TIL.
• While LFA-1 can be activated in nonlytic TIL bypassing proximal TCR signaling, phorbol ester stimulation does not increase their conjugation frequency.
• Nonlytic TIL show reduced surface expression of CD2 and CD8, which are also excluded from the immune synapse.

Conclusions:

• Adhesion defects in nonlytic TIL stem from a combination of reduced cell surface adhesion molecules, impaired LFA-1 activation, and failure to recruit these molecules to the immune synapse.
• These defects collectively compromise the ability of TIL to effectively conjugate with and eliminate tumor cells, contributing to immune evasion.