DC-SIGN Binding to the Surface Ig Oligomannose-type Glycans Promotes Follicular Lymphoma Cell Adhesion and Survival.

The occupation of the surface immunoglobulin antigen-binding site by oligomannose-type glycans (sIg-Mann) is a tumor-specific post-translational modification of classic follicular lymphoma (FL). SIg-Mann switches binding from antigen to dendritic cell-specific intercellular adhesion molecule 3 grabbing non-integrin (DC-SIGN), known to be expressed on interfollicular macrophages and FL-associated follicular dendritic cells (FDCs). The interaction with DC-SIGN induces reorganization of sIg-Mann in wider and less dense clusters than anti-Ig, consistent with inefficient DC-SIGN-induced endocytosis and a low-level intracellular signaling. However, ligand-specific cell clusters form between sIg-Mann-expressing lymphoma and DC-SIGN-expressing cells, raising a need to understand the functional consequences of the interaction of DC-SIGN with sIg-Mann on primary FL cells. This engagement induces adhesion of FL cells to vascular cell adhesion molecule-1 (VCAM-1) via B-cell receptor proximal kinases and actin regulators in a fashion similar to anti-Ig, but without initiating apoptosis in vitro. Instead, antibody blockade of sIg-Mann contact with DC-SIGN expressed on FDC-derived YK6/SIGN cells inhibits adhesion and survival of primary FL cells in vitro. These data highlight that the specific interaction with DC-SIGN induces FL cell adhesion to VCAM-1, likely allowing FL cell retention in the lymph node, and survival of the FL cells. Adhesion and survival are inhibited by an anti-DC-SIGN blocking antibody, indicating a new early therapeutic approach against FL retention and survival in adaptive tumor tissue niches.