Systemic effects of melanoma-secreted MIDKINE in the inhibition of dendritic cell differentiation and function

Cutaneous melanomas are a prime example of potentially immunogenic tumors, and as such, ideal targets for immune therapy. These lesions have the largest mutational burden described to date, and accumulate a broad spectrum of post-transcriptional and translational alterations that could conceptually result in a plethora of neoantigens for immune recognition. However, a significant fraction of metastatic melanoma patients is or becomes resistant to current immunotherapeutic agents. How lesions that should represent an inherently hot milieu for immune attack shift into immunologically cold or irresponsive neoplasms is not well understood. Combining cellular systems, mouse models and clinical datasets, here we identify the growth factor Midkine (MDK) as a multipronged blocker of antigen presentation. Mechanistically, we found MDK to repress all main aspects of the maturation, activation and function of dendritic cells, particularly of conventional type 1 (cDC1). These roles of MDK were found to involve primary tumors and lymph nodes, and were traced back to suppressive effects on myeloid precursor cells in the bone marrow. Moreover, MDK shifted the transcriptional profile of DCs towards a tolerogenic state that prevented and bypassed CD8+ T cell activation. Blocking MDK enhanced the response to DC-based vaccination and improved the response to immune checkpoint blockade.Together, these data provide insight into how melanomas overcome immune surveillance and support MDK as a target for therapeutic intervention.