Immune checkpoint CD161/LLT1‐associated immunological landscape and diagnostic value in oral squamous cell carcinoma

Abstract

An active host adaptive response is characterized by the existence of programmed cell death protein 1 (PD‐1)+/IFN‐γ+ cytotoxic T cells and IFN‐γ‐induced PD‐L1+ tumor cells (TCs), which predicts high response rate to anti‐PD‐1/L1 therapy. Recently, CD161 and its ligand LLT1 (CLEC2D) have been identified as an emerging checkpoint for immunotherapy. Clarifying its heterogeneous clinical expression pattern and its immune landscape is a prerequisite for maximizing the response rate of CD161 blockade therapy in a specific population of oral squamous cell carcinoma (OSCC) patients. Here, we investigated the expression pattern of CD161/LLT1 and its association with major immunocytes (T cells, B cells, NK cells, and macrophages) by multiplex immunofluorescence, immunohistochemistry, and flow cytometry in 109 OSCC tissues and 102 peripheral blood samples. TCs showed higher LLT1 levels than tumor infiltrating lymphocytes (TILs), whereas CD161 was highly expressed in CD8+ T cells at the tumor front, which was decreased in paracancerous tissue. High expression of TC‐derived LLT1 (LLT1TC) conferred poor clinical outcomes, whereas higher CD161+ and LLT1+ TILs were associated with better prognosis. Meanwhile, patients with high LLT1TC showed a decreased ratio of CD8+/Foxp3+ T cells in situ, but CD161+ TILs correlated with more peripheral CD3+ T cells. Interestingly, treatment of OSCC patients with nivolumab (anti‐PD‐1) could restore tumoral CD161/LLT1 signal. Furthermore, an OSCC subgroup characterized by high LLT1+ TCs and low CD161+CD8+ T cells showed fewer peripheral T cells and a higher risk of lymph node metastasis, leading to a shorter 5‐year survival time (29%). More LLT1TC at the invasive front was another risk characteristic of exhausted T cells. In conclusion, in view of this heterogeneity, the LLT1/CD161 distribution pattern should be determined before CD161‐based immunotherapy.

Lectin-like Transcript-1 (LLT1) Expression in Oral Squamous Cell Carcinomas: Prognostic Significance and Relationship with the Tumor Immune Microenvironment

“…The partial inconsistencies between our findings and those by Hu et al [19] could be due to differences in the activation state of cells [34], different antibodies [28], methodologies/ cut-off points used, and differences between the patient cohorts studied in terms of risk factors or clinical and biological characteristics.…”

“…Regarding the prognostic significance of LLT1 expression, our findings are in line with those recently reported by Hu et al [19], consistently revealing that tumor-intrinsic LLT1 expression was associated with poor clinical outcomes in OSCC, whereas positive LLT1 expression in TILs was associated with a favorable prognosis. The study by Hu et al [19] was performed in a Chinese cohort of 109 OSCC patients with several demographic, etiological, and clinicopathological differences from our studied Spanish patient cohort. The Hu series is composed of 63% of patients older than 60 years, 50% with positive neck lymph node metastasis, and 78% of their tumors were moderately or poorly differentiated.…”

“…These results are in line with our previous observations in head and neck cutaneous squamous cell carcinomas [32] and HPV-negative oropharyngeal squamous cell carcinomas [33]. A recent study by Hu et al [19] reported that fewer CD8 + T cells were present in those OSCC patients harboring high LLT1 expression in tumor cells (both at the front and the center of tumor tissue), although these differences were not statistically significant. Moreover, these authors also found that tumors with high LLT1+ lymphocyte infiltration showed significantly higher absolute counts of CD3 + and CD4 + T cells.…”

“…To date, only one study has been recently published by Hu et al [19] that examined the expression patterns of CD161/LLT1 in OSCC and the impact on patient prognosis. This prompted us to investigate the clinical relevance of LLT1 expression in the OSCC TIME.…”