Background: Tertiary lymphoid structures (TLS) are ectopic lymphoid formations within or around tumours. They are emerging as important predictors of prognosis and response to immune checkpoint inhibitors (ICIs) in various cancers. However, in Merkel cell carcinoma (MCC), the correlation between TLS and ICI response has not yet been evaluated. Furthermore, the criteria for assessing TLS maturity vary by report, and there is no unified consensus.
Objectives: To investigate the relationship between TLS and ICI responsiveness in MCC using spatial proteomics at the single-cell level. By comparing the spatial characteristics of TLS in people whose disease responds to ICI and those whose disease does not, we also aimed to identify features related to functionality of TLS, distinct from the previously reported maturity of TLS.
Methods: We analysed 24 TLS from 13 patients with MCC treated with the anti-programmed cell death ligand 1 antibody avelumab, using the PhenoCyclerTM platform with 16 oligonucleotide-labelled antibodies. Infiltrating immune cells and tumour cells were phenotyped based on machine learning, and spatial single-cell analysis was performed, including cellular neighbourhood analysis and cell-cell correlation analysis.
Results: Our findings revealed that the number of TLS positively correlated with survival and ICI response (P = 0.03). The number of TLS observed in tumours was significantly higher in those whose disease responded to the ICI compared with those whose disease did not (P = 0.004). Cellular neighbourhood analysis and cell-cell correlation analysis demonstrated that in functional TLS in those whose disease responded to treatment, T cells infiltrated densely within B-cell clusters, extending close to follicular dendritic cells, and that CD4+ T cells adjacent to CD8+ T cells express programmed cell death protein 1 (PD-1). In contrast, in TLS in those whose disease did not respond to treatment, although the B-cell density was high, T cells did not infiltrate B-cell cluster areas but instead resided in the peripheral areas. Furthermore, it was found that CD8+ T cells and CD4+ T cells approaching B cells expressed PD-1.
Conclusions: We found a significant positive correlation between the number of TLS and ICI response in MCC. Additionally, our results suggest that the immune composition and spatial configuration within TLS may be important determinants of ICI efficacy.
Merkel cell carcinoma is a rare and aggressive type of skin cancer. It only affects a small number of people worldwide. It grows quickly and can spread to other parts of the body. Some patients benefit from a type of treatment called immunotherapy. In some people, this treatment helps the body’s immune system recognize and attack cancer cells. Unfortunately, it does not work for every patient. This study was carried out in Japan. We wanted to find out whether small clusters of immune cells called ‘tertiary lymphoid structures’ help patients benefit from immunotherapy or not. The are called ‘TLS’ for short and they form inside or around tumours. These structures contain two different types of immune cells called T cells and B cells. T cells can kill cancer cells and B cells help with the immune response and organize immune attacks against cancer cells. We studied 13 patients with Merkel cell carcinoma treated with immunotherapy. Using special analytical techniques, we looked at 23 TLS in detail. We examined which types of immune cells were present and how they were arranged. We found that patients with more TLS in their tumours benefited more from immunotherapy. In TLS in these patients, immune cells were organized so that T cells closely interacted with B cells. In the TLS of patients who did not benefit from immunotherapy, T cells stayed mostly at the edge of the TLS and did not interact well with B cells. Our findings suggest that the number of TLS and the way immune cells are arranged inside them may influence the success of immunotherapy. Understanding this could help doctors predict which patients are most likely to benefit from treatment.
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