PEGylated IL2 and tumor-targeted radiotherapy augment CD8+ T cell-mediated anti-tumor response to anti-PD-1 in head and neck squamous cell carcinoma.

Combination of immune checkpoint inhibitors (ICI) with either radiotherapy or PEGylated interleukin 2 (pegIL2) has produced limited or no benefits over ICI alone in clinical trials. A triple combination of radiotherapy, pegIL2, and ICI may overcome the limitations of dual treatments. We report a phase II clinical trial evaluating tumor-targeted radiotherapy, pegIL2 (BEMPEG), and ICI (pembrolizumab) in patients with recurrent or metastatic head and neck squamous cell carcinoma (HNSCC), and combination pre-clinically of radiopharmaceutical therapy (RPT), pegIL2, and ICI in HNSCC. Patients received one cycle of pegIL2 (0.006 mg/kg) plus pembrolizumab (200 mg) followed by external beam radiotherapy (EBRT), then two cycles of pegIL2 plus pembrolizumab. Adverse events, objective response rate (ORR), progression-free survival (PFS), overall survival (OS), and immune response from peripheral blood mononuclear cells (PBMCs) and biopsies were evaluated. RPT (90Y-NM600) was evaluated in combination with pegIL2 and anti-PD-L1 in murine MOC2 and SCC7 HNSCC models. We report ORR of 40%, PFS of 4.2 months, OS of 13.6 months, and increased effector:regulatory T-cell ratios and memory CD8+ T cells in 5 patients treated prior to trial discontinuation. In preclinical HNSCC models, combined RPT and pegIL2 augmented memory CD8+ T cells (IL2Rβ+). CD8+ T cell depletion led to loss of anti-tumor responses. PegIL2 restored RPT-driven lymphocyte deficiency earlier, increasing memory CD8+ T cells (IL2Rβ+) in the tumor, and enhanced anti-tumor response through MHC I-dependent TNFα expression. A deficiency of the stimulator of interferon genes (STING) abrogated tumor MHC I expression and antitumor responses. PD-L1-expressing monocytes antagonized CD8+ T cell memory effect in the tumor recurrence stage, and anti-PD-L1 therapy promoted 90Y-NM600 and pegIL2 efficacy. Preclinically, tumor-targeted RPT and pegIL2 augment response to ICI through CD8+ T cell memory acquisition and regulatory monocyte suppression. This study provides preclinical and clinical insight for HNSCC treatment.