MXD3 as a Determinant of Immunoproliferative Response to Immunotherapy in HNSCC

Introduction: Although immune checkpoint inhibitors have revolutionized cancer treatment, including in Head and Neck Squamous Cell Carcinoma (HNSCC), improving response rates represents a critical need. Additionally, there is an unmet opportunity for predicting whether patients will respond to immunotherapy.

Methods: We used single-cell RNA-sequencing (scRNASeq) data from neoadjuvant pembrolizumab treated HNSCC patients (Oliveira et al., Sci. Immunol, 2023). We used differential expression to identify transcripts increased in non-responder patient T cells. MXD3 expression was analyzed in TCGA HNSCC patients. MXD3 expression was analyzed with quantitative real time PCR and Western blotting. MXD3 knockdown was achieved using siRNA in transgenic OT-1 T cells. Xcellingence real time cell analysis was used to quantify cytotoxicity against anti-PD1 resistant MOC1-esc1-ova.

Results: We identified increased MXD3, or MAX Dimerization Protein, in proliferating CD8+ T-cells only in non-responders to neoadjuvant pembrolizumab. MXD3 was associated with progression and worse outcomes in TCGA HNSCC patients. MXD3 knockdown in antigen specific OT-1 CD8+ T cells sensitized anti-PD1-resistant MOC1-esc1-ova to T-cell killing ( p < 0.001).

Conclusions: MXD3 is overexpressed in proliferating CD8+ T cells in anti-PD1 resistant HNSCC patients. Further mechanistic and biomarker studies of MXD3 are warranted.