CCL21 and lymphoma: Cross-talk with resident stromal and accessory cells at these sites contributed to the creation and preservation of pro-tumor niches that conferred a survival advantage to CCR7-positive lymphoma cells over CCR7-deficient lymphoma cells (9). In a proposed model, stromal cells (e.g. fibroblastic reticular cells, FRC, and HEV endothelial cells) secrete CCL21 through which CCR7-expressing lymphoma cells home through HEV into the LN (or spleen) and migrate towards FRC in the T-cell region.