Analyses of tertiary lymphoid structures observed in cases of Merkel cell carcinoma showing spontaneous regression.

Merkel cell carcinoma (MCC) is a high-grade skin cancer, but spontaneous regression is observed at a markedly higher frequency than in other carcinomas. Although spontaneous regression is a phenomenon that greatly impacts treatment planning, we still cannot predict it. We previously reported on the prognostic impact of the presence or absence of tertiary lymphoid structures (TLS) and of Merkel cell polyomavirus (MCPyV) infection. To learn more about the spontaneous regression of MCC, detailed analyses were performed focusing on spontaneous regression cases. We collected 71 Japanese patients with MCC including 6 cases of spontaneous regression. Samples were analysed by immunostaining, spatial single-cell analysis using PhenoCycler, and RNA sequencing using the next-generation sequencer (NGS). All 6 cases of spontaneous regression were positive for MCPyV. TLS was positive in all 5 cases analysed. Spatial single-cell analyses revealed that PD-L1-positive tumour cells were in close proximity to CD20-positive B cell and CD3-, 4-positive T cells. Gene set enrichment analysis between MCPyV-positive and TLS-positive samples and other samples showed significantly high enrichment of "B-cell-mediated immunity" gene sets in the MCPyV-positive and TLS-positive groups. In conclusion, TLS may play an important role in the spontaneous regression of MCC.

Blockade of glucose-6-phosphate dehydrogenase induces immunogenic cell death and accelerates immunotherapy.

BACKGROUND: Enhanced glucose metabolism has been reported in many cancers. Glucose-6-phosphate dehydrogenase (G6PD) is a rate-limiting enzyme involved in the pentose phosphate pathway, which maintains NADPH levels and protects cells from oxidative damage. We recently found that low G6PD expression correlates with active tumor immunity. However, the mechanism involving G6PD and tumor immunity remained unclear. METHODS: We conducted in vitro studies using G6PD-knocked down malignant melanoma cells, pathway analysis using the GEO dataset, in vivo studies in combination with immune checkpoint inhibitors (ICIs) using a mouse melanoma model, and prognostic analysis in 42 melanoma patients and 30 lung cancer patients who were treated with ICIs. RESULTS: Inhibition of G6PD, both chemically and genetically, has been shown to decrease the production of NADPH and reduce their oxidative stress tolerance. This leads to cell death, which is accompanied by the release of high mobility group box 1 and the translocation of calreticulin to the plasma membrane. These findings suggested that inhibiting G6PD can induce immunogenic cell death. In experiments with C57BL/6 mice transplanted with G6PD-knockdown B16 melanoma cells and treated with anti-PD-L1 antibody, a significant reduction in tumor size was observed. Interestingly, inhibiting G6PD in only a part of the lesions increased the sensitivity of other lesions to ICI. Additionally, out of 42 melanoma patients and 30 lung cancer patients treated with ICIs, those with low G6PD expression had a better prognosis than those with high G6PD expression (p=0.0473; melanoma, p=0.0287; lung cancer). CONCLUSION: G6PD inhibition is a potent therapeutic strategy that triggers immunogenic cell death in tumors, significantly augmenting the efficacy of immunotherapies.