Testudinidosis: A New Mechanism of Resistance to Immune Attack

Antibody dependent cell-mediated cytotoxicity (ADCC) provides a model for uncovering immune resistance mechanisms. We continuously exposed epidermal growth factor receptor (EGFR)+ A431 cells to KIR-deficient NK92-CD16V effector cells and the anti-EGFR mAb cetuximab. Persistent ADCC exposure yielded ADCC-resistant cells (ADCCR1) that, compared with control ADCC-sensitive cells (ADCCS1), exhibited reduced EGFR expression, overexpression of histone- and interferon-related genes and failure to activate NK cells, without evidence of epithelial: mesenchymal transition. These properties gradually reversed following withdrawal of ADCC selection pressure. A second A431-derived ADCC-resistant cell line maintained EGFR expression. Remarkably, ADCCR1 cells possessed lower expression of multiple cell surface molecules that contribute to cell: cell interactions and immune synapse formation. Classic immune checkpoints did not modulate ADCC in this unique model system of immune resistance. Just as giant tortoises (Testudinidae) can hide in their shells to avoid predation, this novel immune evasion mechanism, termed testudinidosis, can protect cells against immune attack. Time course Illumina microarray data for continuously exposed epidermal growth factor receptor (EGFR)+ A431 cells to KIR-deficient NK92-CD16V effector cells and the anti-EGFR mAb cetuximab and control sensitive cells.