Lipid metabolite platelet-activating factor (PAF)-induced immune suppression in sentinel lymph nodes of melanoma patients – PIs: Hongying Hao and Kelly McMasters

Ultraviolet (UV) radiation is a primary cause of skin cancer. Platelet-activating factor (PAF) is one of the lipid mediators in UV-induced immunosuppression signaling. Sentinel lymph nodes (SLNs) are the first organs to receive lymphatic drainage from the primary melanoma. Given the increasing importance of anti-tumor immunity in SLNs, it is critical to understand how PAF may alter the regional immune environment to favor melanoma nodal metastasis. Our rationale is to find the connection between PAF and the immunosuppression status in SLNs in an effort to restore immune function and to control melanoma progression.

To identify the metabolites that might be involved in governing immune microenvironments from melanoma patients, we compared the metabolic changes in lymphatic fluid samples from high-risk patients with nodal metastasis (SLN+) versus low-risk melanoma patients without nodal metastasis (SLN-). The results showed that lymphatic fluid PAF is 2.97- fold greater in high-risk SLN+ melanoma patients compared with low-risk SLN- patients (p=0.0039). Previous studies have shown that PAF can activate numerous pro-inflammatory chemokines. We observed that CCL17 and CCL23 chemokine levels in serum samples from high-risk SLN+ patients are significantly greater than those in low-risk SLN- patients. CCL17 and CCL23 is believed to contribute to the immunosuppressive microenvironment in SLNs of melanoma patients; we have observed elevated levels of these chemokines in patients who undergo recurrence of their melanoma. Based on these data, we hypothesize that upregulation of PAF can activate the downstream chemokines, resulting in an immunosuppressed environment in SLNs that permits nodal metastasis and melanoma progression. We further hypothesize that reducing PAF levels will restore anti-tumor immunity to better control melanoma progression. The objective of this study is to define the role of PAF in immunosuppression of SLN in melanoma patients.

We propose a single specific aim: To delineate how the upregulation of lipid metabolite PAF results in immunosuppression status of SLNs. We will further identify metabolic signatures, especially lipid metabolic profiling in lymph fluid, serum, and SLN samples from high-risk versus low-risk melanoma patients by mass spectrometry (MS). Cytokine and chemokine levels in the lymph fluid and blood samples from the above-matched patients will be compared. Since PAF exerts its biological function by binding to a single specific G-protein-coupled receptor (PAFR), we will observe the expression of PAF and PAFR in different types of immune cells in SLN. CD8+ T cell function from SLN samples will be tested after adding PAF. Tregs isolated from SLN samples will be treated with PAFR agonist carbamoyl-PAF (CPAF), and the function of the Tregs will be examined after CPAF treatment. Further studies will use a mouse model to determine whether PAF administration results in SLN immunosuppression and CPAF can restore immune competency.

The significance of this research is to provide further understanding of lipid metabolite PAF in reduced adaptive anti-tumor immunity in melanoma SLN. Controlling PAF might present a strategy to reconstitute SLN immune function, prevent melanoma progression, and increase the overall survival rate.