Melanoma growth and lymph node metastasis is independent of host CD169 expression

Metastasis to the lymph node is a frequent and early event in tumour dissemination. Tumour soluble factors, including extracellular vesicles, condition host organs for metastatic tumour spread, thereby facilitating tumour cell migration and survival. In the peripheral lymphatics, extracellular vesicles are captured via their sialic acids by lymph node macrophages expressing the CD169 (sialoadhesin) molecule, thereby suppressing the immune response. We hypothesised that the CD169 molecule could modulate primary tumour growth and invasion into the regional lymph node by altering the immune response to tumour extracellular vesicles, or by directly interacting with invading tumour cells. No significant difference was noted in primary tumour growth between wild-type and CD169^-/- mice, and protection against tumour challenge with tumour extracellular vesicle immunisation was similar between the strains. Subcutaneous implantation of B16 (F1 or F10) into the ventral-carpal aspect of forelimb resulted in melanoma infiltration into the axillary and brachial lymph nodes. CD169^-/- mice displayed a lower level of metastatic lymph node lesions, however this failed to reach statistical significance. Although CD169 participates in the immune response to tumour antigen and appears to be a positive prognostic marker for human cancers, its role in modulating melanoma growth and metastasis is less clear.