Lymph node location and retention properties of DC‐SIGN engagement with the Immunoglobulin Oligomannoses of Follicular Lymphoma

Introduction: The oligomannose-type glycans occupying the surface immunoglobulin antigen-binding site (sIg-Mann) are a tumor-founding post-translational requirement of classic follicular lymphoma (FL). These are universally acquired and a clonal necessity during the entire natural history of FL from the early stages throughout transformation into EZB-DLBCL (Chiodin G, Blood 2021, Odabashian M, Blood 2020). The low-affinity interaction of sIg-Mann with its specific ligand DC-SIGN distinguishes from conventional high-affinity antigen:Ig protein interactions for promoting prolonged low-level growth and prosurvival signals via PI3K/AKT and not endocytosis (Linley A, Blood 2015). However, the location and function of DC-SIGN remains to be further elucidated. Here, we investigated the hypothesis that the specific DC-SIGN:Ig-Mann interaction functions to promote retention of FL cells in tissue niches maintaining selective survival advantage. Methods: Immunofluorescence imaging was used to determine DC-SIGN histological location in primary FL lymph nodes. In WSU-FSCCL cells, DC-SIGN effects on sIg redistribution were measured by dSTORM; adhesion to VCAM-1 in presence/absence of inhibitors was measured by flow cytometry. Results: Immunofluorescence of lymph nodes from FL patients revealed that DC-SIGN was expressed on interfollicular CD163+ macrophages and, remarkably, on CD23+ follicular dendritic cells (FDC), claiming an influence on FL cell retention and survival. dSTORM revealed that DC-SIGN induced less dense and more diffuse surface Ig clusters compared to anti-Ig, reflecting an immature sIg redistribution unable to promote endocytosis and death. However, DC-SIGN efficiently induced adhesion of sIg-Mann+ve lymphoma cells to VCAM-1, known to be expressed on both lymph node macrophages and FDC, and inhibited migration towards SDF-1 in vitro. Blocking of DC-SIGN carbohydrate-recognition domain completely abrogated DC-SIGN-induced adhesion. Although intracellular signals were significantly lower, DC-SIGN induced levels of adhesion similar to those induced by anti-Ig. Adhesion to VCAM-1 was observed at concentrations from 20 µg/ml down to 20 ng/ml, even when AKT and ERK phosphorylation was not detectable. Either proximal inhibition of the PI3K/AKT pathway, or distal inhibition of ARP2/3, formin, and Cdc42 for lamellipodium formation at the surface membrane, suppressed adhesion. Conclusions: These results reveal an important mechanism of the DC-SIGN:sIg-Mann interaction that fine-tunes signals for membrane adaptation towards tumor cell adhesion, without promotion of cell death. This possibly facilitates FL cell retention in the lymph node protected tumor niche where selective growth and survival signals are maintained. Interrupting this interaction will be a novel way towards tumour-specific targeted therapy in FL patients. The research was funded by: This research was funded by Blood Cancer UK (grant 18009), Cancer Research UK (ECRIN-M3 accelerator award C42023/A29370, program C2750/A23669, and BTERP project C36811/A29101). D.T. was funded by the Eyles Cancer Immunology PhD scholarship, G.C. was funded by the Eyles Cancer Immunology Fellowship and the Southampton Cancer Immunology Centre Pump-priming award 2021). Keywords: Indolent non-Hodgkin lymphoma, Microenvironment, Targeting the Tumor Microenvironment Conflicts of interests pertinent to the abstract. F. Forconi Employment or leadership position: University of Siena Consultant or advisory role: Beigene Honoraria: Abbvie, Janssen-cilag, Beigene, Astra-Zeneca Research funding: Cancer Research UK Educational grants: Beigene, Abbvie Other remuneration: BC Platform