CD4⁺ T-helper Type 1 Cytokines and Trastuzumab Facilitate CD8⁺ T-cell Targeting of HER-2/neu-expressing Cancers

Abstract

Vaccination strategies incorporating the immunodominant HLA-A2-restricted HER2/neu-derived peptide 369-377 (HER2_369-377) are increasingly utilized in HER2/neu-expressing cancer patients. The failure of post-vaccination HER2_369-377-specific CD8⁺ T-cells to recognize HLA-A2^pos HER2/neu-expressing cells in vitro, however, has been attributed to impaired MHC class I/HLA-A2 presentation observed in HER2/neu-overexpressing tumors. We reconcile this controversy by demonstrating that HER2_369-377 is directly recognized by high functional-avidity HER2_369-377-specific CD8⁺ T-cells-either genetically modified to express a novel HER2_369-377-TCR or sensitized using HER2_369-377-pulsed type 1-polarized dendritic cells (DC1)-on class I-abundant HER2^low, but not class I-deficient HER2^high, cancer cells. Importantly, a critical cooperation between CD4⁺ T-helper type-1 (Th1) cytokines IFN-γ/TNF-α and HER2/neu-targeted antibody trastuzumab is necessary to restore class I expression in HER2^high cancers, thereby facilitating recognition and lysis of these cells by HER2_369-377-specific CD8⁺ T-cells. Concomitant induction of PD-L1 on HER2/neu-expressing cells by IFN-γ/TNF and trastuzumab, however, has minimal impact on DC1-sensitized HER2_369-377-CD8+ T-cell-mediated cytotoxicity. Although activation of EGFR and HER3 signaling significantly abrogates IFN-γ/TNF-α and trastuzumab-induced class I restoration, EGFR/HER3 receptor blockade rescues class I expression and ensuing HER2_369-377-CD8⁺ cytotoxicity of HER2/neu-expressing cells. Thus, combinations of CD4⁺ Th1 immune interventions and multivalent targeting of HER family members may be required for optimal anti-HER2/neu CD8⁺ T-cell-directed immunotherapy.