Correlation of Serum Vitamin D Level with the Development of Endocrine Autoimmune Complications During Treatment with Immune Checkpoint Inhibitors

Until 2011 no therapy with proven overall survival benefit was Food and Drug Administration (FDA) approved for the treatment of stage IV (disseminated) melanoma. In 2011 ipilimumab, an inhibitor of CTLA-4, was FDA approved for the treatment of stage IV melanoma representing the first immunotherapy to confer an increase in overall survival. CTLA-4 is expressed on the surface of activated T cells and binds to B7 on antigen-presenting cells with higher affinity than the co-stimulatory protein CD28. By competing for and disrupting the binding of CD28 to B7, CTLA-4 prevents T-cell co-stimulation which leads to a dampening of the immune response. Ipilimumab is an IgG1 monoclonal antibody that binds CTLA-4 in an inhibitory manner. Treating stage IV melanoma with ipilimumab confers an overall survival benefit when compared in randomized fashion to peptide vaccine treatment, with median survival increasing from 6 to 10 months and 2-year survival increasing from 14% to 24%. Benefit is durable as the overall survival rate plateauing at 21% by year 3 with follow-up extending up to 10 years.

The regulation of immune T-cell activity is complex involving multiple activating and inhibitory protein interactions with antigen presenting cells. T-cells express the protein programmed death-1 (PD-1) which when bound to its ligand PD-L1 normally expressed on peripheral tissues inhibits T-cell activity. Many melanomas select for aberrant expression of PD-L1. When T-cells infiltrate the melanoma metastasis tumor microenvironment the PD-1 on the infiltrating T-cells binds the tumor expressed PD-L1 leading to inhibition of T-cell activity. Blocking the interaction of PD-1 to PD-L1 in stage IV melanoma leads to clinical efficacy. Two inhibitors of PD-1, nivolumab and pembrolizumab, were FDA approved in 2014 for the treatment stage IV melanoma with response rates approximating 40% and 5-year survival post-nivolumab treatment of 35%. In 2015 concurrent treatment with ipilimumab and nivolumab was FDA-approved on the basis of a 57.6% response rate.

Ipilimumab is infused intravenously as a single agent every 3 weeks for a total of four treatments. Nivolumab is administered intravenously every two weeks at dose of 240 mg or every four weeks at a dose of 480 mg while pembrolizumab is infused every three weeks at dose of 200 mg or every 6 weeks at 400 mg per dose. With concurrent ipilimumab and nivolumab treatment the combination is administered every three weeks for 4 doses and then nivolumab is infused as a single agent every two weeks.

The inhibition of immune cell activity in the tumor microenvironment through the selection of PD-L1 expression on tumor cells is not specific to melanoma. Clinical efficacy has been appreciated in a range of malignancies leading to multiple FDA approvals for stage IV disease. Specifically pembrolizumab is also FDA approved for treatment of stage IV non-small cell lung cancer and recurrent or metastatic HNSCC. Nivolumab is also FDA approved for the treatment of metastatic non-small cell lung cancer, advanced renal cell carcinoma, classical Hodgkin lymphoma, and recurrent or metastatic squamous cell carcinoma of the head and neck.

Given the mechanism of action of CTLA-4 and PD-1 inhibitors toxicity is largely immune mediated. The incidence of grade3 or higher immune mediated toxicity following single agent ipilimumab treatment is approximately 25%. Following nivolumab or pembrolizumab treatment the risk of such toxicity is 17-20% while following combined ipilimumab and nivolumab treatment the risk is 55-59%. Toxicity can manifest based on organ or tissue involved such as rash, colitis, hepatitis, nephritis, pancreatitis, myocarditis, pneumonitis uveitis, neurologic or endocrine.