IL-17–Induced CD70 expression promotes T-cell suppression in DLBCL: Implications for immune escape and T-cell exhaustion

Abstract Background: Diffuse Large B-cell Lymphoma (DLBCL) is one of the most aggressive types of non-Hodgkin B-cell lymphomas, characterized by the presence of large neoplastic B cells infiltrating lymph nodes and other extranodal sites. Contemporary treatment regimens for DLBCL involving various R-CHOP–based protocols show a success rate of 50-70% while the remaining fail due to disease relapse following complete remission. The abundance of immunosuppressive factors—such as cancer-associated fibroblasts (CAFs), CD4⁺ regulatory T cells (Tregs), and, most importantly, IL-17–producing Th17 cells—in the tumor microenvironment (TME) contributes to immune escape and is a major driver of relapsed/refractory disease. Several studies have reported that IL-17, a potent pro-inflammatory cytokine, is capable of inducing resistance to rituximab, thereby correlating its abundance with poor survival and prognosis in DLBCL patients (Zhong et al., 2017). However, the precise mechanism remains poorly understood. We hypothesized that an IL-17–mediated signalling pathway operates in the DLBCL tumor microenvironment (TME), facilitating tumor immune escape and thus serving as a potential target for therapies aimed at overcoming resistance. Methods and Results: Through immunofluorescence, flow cytometric analysis, and other functional assays, we aimed to demonstrate a previously unexplored IL-17–based signalling network operating in DLBCL that potentially contributes to immune suppression and exhaustion of infiltrating T-cells. High-throughput global proteomics analysis of the IL-17–treated malignant B-cell line Raji, a model for DLBCL, identified CD70—a regulator of immune responses (Fliewasser et al., 2022)—as one of the most significantly upregulated proteins (abundance ratio: 7.29), which was subsequently validated by in vitro staining, immunofluorescence (p = 0.003), and flow cytometric analysis (p = 0.02). To support the clinical relevance of this finding, formalin-fixed paraffin-embedded (FFPE) sections of lymph node biopsies from DLBCL patients (n=5) and healthy individuals (n=5) were used for immunofluorescence staining that revealed a 2-fold increase (p = 0.004) in the expression of CD70 and co-localization of CD70 with CD19high B cells in DLBCL patient samples, as compared to healthy controls. To decipher the underlying mechanism of the IL-17/CD70 pathway, we co-cultured IL-17–treated and untreated tumor cells with primary T cells and observed a substantial increase (p = 0.003) in the population of CD4⁺ FoxP3⁺ regulatory T cells (Tregs) under IL-17–treated conditions, indicating a shift toward an immunosuppressive environment. Furthermore, ELISA performed on the cell-free supernatants from these co-cultures revealed an 80% increase in the secretion of immunosuppressive cytokine IL-10 (Mean ± SEM; 57.78 ± 9.271 pg/ml, control; 88.31 ± 18.78 pg/ml, IL-17-treated) under IL-17–rich condition. In addition, primary T cells co-cultured with IL-17–treated tumor cells exhibited higher expression of T-cell exhaustion markers TIM-3 and PD-1. ELISA-based analysis of cytokine secretion profiles further revealed a 40-50% reduction in the secretion of pro-inflammatory cytokines TNF-α (18.32 ± 3.312 pg/ml, control; 9.319 ± 3.573 pg/ml, IL-17-treated) and IL-2 (39.92 ± 5.53 pg/ml, control; 28.82 ± 8.72 pg/ml, IL-17-treated), in the presence of IL-17–treated malignant B cells—another hallmark of T-cell exhaustion. Primary T cells treated with IL-17 in the absence of CD70+ tumor cell challenge showed non-significant change in Treg population size, cytokine secretion, or expression levels of exhaustion markers. Conclusion: Collectively, our data demonstrate a previously unidentified IL-17/CD70 axis that plays a critical role in regulating immune escape in DLBCL cells. Based on our findings, we propose the repurposing of FDA orphan drug CD70 neutralizing antibody Cusatuzumab (ARGX-110) for DLBCL treatment to reduce the risk of relapse and improve outcomes following R-CHOP therapy. Furthermore, this discovery may contribute to a better understanding of the potential outcomes and treatment responses of DLBCL patients to conventional chemotherapy regimens.