An Observational Study Design to Detect if Co-stimulatory Markers and Vitamin D Status in Anti-PD-1 Treated Advanced Melanoma Patients Can Predict Treatment Outcome

Background Advanced melanoma still is associated with severe disease and early death. New immunotherapies including the checkpoint inhibitors anti-programmed death 1(PD-1) and anti-cytotoxic T-lymphocyte-associated protein 4 (CTLA4) improve survival compared to chemotherapy. It still remains to be elucidated why the treatment only benefits some patients. The tumour cells expression of programmed death ligand 1 (PD-L1) and other co-stimulatory receptors, as well as the presence of soluble isoforms are speculated to influence treatment success. Possible modulators of the PD-1 pathway like vitamin D might also influence the treatment outcome. Investigating these relations could provide useful markers to predict response to anti-PD-1 therapy in advanced melanoma patients.

PD-1, a transmembranous molecule present on activated T, B and natural killer (NK) cells is essential in maintaining self tolerance. PD-1 has two widely expressed ligands, PD-L1 and programmed death ligand 2 (PD-L2). Both PD-1 and its ligands are present in soluble (s) forms. In autoimmune disease like rheumatoid arthritis sPD-1 concentrations are associated with disease markers and scores.

PD-L1 can be highly expressed by cancers and thereby silence the T cell immune attack. Using anti-PD-1 antibodies, the immune cells are not inhibited by the PD-1 pathway, and proliferation, activation and T cell survival increases, improving tumour cells targeting. Soluble PD-1, sPD-L1 and sPD-L2 may be potential markers in melanoma patients who would benefit from the anti- PD1 treatment.

In autoimmune diseases as rheumatoid arthritis, Crohn's disease and in multiple sclerosis vitamin D deficiency is associated with increased disease activity. Active 1.25-dihydroxyvitamin D3 (1.25-vitD) binds to the vitamin D receptor (VDR) and the 1.25-vitD-VDR complex functions as a transcription factor. Regarding melanoma, VDR variants are associated with melanoma risk. In mice, vitamin D stimulation has been shown to increase the PD-L2 expression in dendritic cells (DCs). In humans vitamin D stimulation increased the DC PD-L1 expression and interleukin 10 (IL-10) production and PD-L1 blockage resulted in increased interferon gamma and decreased IL-10 production.

Our preliminary pilot studies have demonstrated that vitamin D initially decreases PD-1 expression in Crohn's disease T cells but after 26 weeks of vitamin D treatment PD-1 expression increases in CD4+CD25+ T cells (unpublished data). These results might indicate that vitamin D treatment initially increase T cell activation replaced by a decreased T cell activation after long-time vitamin D treatment in inflamed patients. This might influence the anti-PD-1 treatment response in advanced melanoma. Improved knowledge of the interaction between anti-PD-1treatment, vitamin-D and sPD-1, PD-L1 and PD-L2 could provide new beneficial modifications to the treatment regimens currently available -for instance as a new predictor of treatment response.