Checkpoint inhibitors are relatively inefficacious in head and neck cancers, despite an abundance of genetic alterations and a T cell-inflamed phenotype. One significant barrier to efficacy may be the recruitment of myeloid-derived suppressor cells (MDSC) into the tumor microenvironment. Here we demonstrate functional inhibition of MDSC with IPI-145, an inhibitor of PI3Kδ and PI3Kγ isoforms which enhances responses to PD-L1 blockade. Combination therapy induced CD8+ T lymphocyte-dependent primary tumor growth delay and prolonged survival only in T cell-inflamed tumor models of head and neck cancers. However, higher doses of IPI-145 reversed the observed enhancement of anti-PD-L1 efficacy due to off-target suppression of the activity f tumor-infiltrating T lymphocytes. Together, our results offer a preclinical proof of concept for the low dose use of isoform-specific PI3Kδ/γ inhibitors to suppress MDSC to enhance responses to immune checkpoint blockade.

No adverse effects were observed in HIV-uninfected children with in utero and neonatal exposure to zidovudine followed up for as long as 5.6 years. Continued prospective evaluations of children born to HIV-infected women who are exposed to antiretroviral or immunotherapeutic agents are critical to assess the long-term safety of interventions that prevent perinatal HIV transmission.

Head and neck squamous cell carcinoma (HNSCC) has been treated for decades with cisplatin chemotherapy, and anti–PD-1 immunotherapy has recently been approved for the treatment of this disease. However, preclinical studies of how antitumor immunity in HNSCC is affected by cisplatin alone or in combination with immunotherapies are lacking. Here, we show that sublethal doses of cisplatin may enhance antigen presentation and T-cell killing in vitro, though cisplatin also upregulates tumor cell expression of PD-L1 and may impair T-cell function at higher doses. In a syngeneic mouse model of HNSCC, concurrent use of cisplatin and anti–PD-L1/PD-1 delayed tumor growth and enhanced survival without significantly reducing the number or function of tumor-infiltrating immune cells or increasing cisplatin-induced toxicities. These results suggest that moderate doses of cisplatin may enhance antitumor immunity by mechanisms other than direct tumor cell killing, which may be further enhanced by anti–PD-L1/PD-1 therapy.

Patients with head and neck squamous cell carcinoma harbor T-cell inflamed and non-T-cell inflamed tumors. Despite this, only 20% of patients respond to checkpoint inhibitor immunotherapy. Lack of induction of innate immunity through pattern-recognition receptors such as the stimulator of interferon (IFN) genes (STING) receptor may represent a significant barrier to the development of effective antitumor immunity. Here, we demonstrate robust control of a T-cell inflamed (MOC1), but not non-T-cell inflamed (MOC2), model of head and neck cancer by activation of the STING pathway with the synthetic cyclic dinucleotide RP,RP dithio-c-di-GMP. Rejection or durable tumor control of MOC1 tumors was dependent upon a functional STING receptor and CD8 T lymphocytes. STING activation resulted in increased tumor microenvironment type 1 and type 2 IFN and greater expression of PD-1–pathway components in vivo. Established MOC1 tumors were rejected and distant tumors abscopally controlled, after adaptive immune resistance had been reversed by the addition of PD-L1 mAb. These findings suggest that PD-1-pathway blockade may reverse adaptive immune resistance following cyclic dinucleotide treatment, enhancing both local and systemic antitumor immunity.