Vascular E-Selectin Expression Correlates with CD8 Lymphocyte Infiltration and Improved Outcome in Merkel Cell Carcinoma

Abstract

Merkel cell carcinoma (MCC) is an aggressive, polyomavirus-linked skin cancer. While CD8 lymphocyte infiltration into the tumor is strongly correlated with improved survival, these cells are absent or sparse in most MCCs. We investigated whether specific mechanisms of T-cell migration may be commonly disrupted in MCC tumors with poor CD8 lymphocyte infiltration. Intratumoral vascular E-selectin, critical for T-cell entry into skin, was downregulated in the majority (52%) of MCCs (n=56), and its loss was associated with poor intratumoral CD8 lymphocyte infiltration (p<0.05; n=45). Importantly, survival was improved in MCC patients whose tumors had higher vascular E-selectin expression (p<0.05). Local nitric oxide (NO) production is one mechanism of E-selectin downregulation and it can be tracked by quantifying nitrotyrosine, a stable biomarker of NO-induced reactive nitrogen species (RNS). Indeed, increasing levels of nitrotyrosine within MCC tumors were associated with low E-selectin expression (p<0.05; n=45) and decreased CD8 lymphocyte infiltration (p<0.05, n=45). These data suggest that one mechanism of immune evasion in MCC may be restriction of T cell entry into the tumor. Existing therapeutic agents that modulate E-selectin expression and/or RNS generation may restore T cell entry and could potentially synergize with other immune-stimulating therapies.

The Role of the Tumor Vasculature in the Host Immune Response: Implications for Therapeutic Strategies Targeting the Tumor Microenvironment

“…However, this inflammatory environment appears to fail to induce the expression of vascular adhesion molecules on intratumoral vessels. This has been demonstrated in experimental models of melanoma and carcinoma (81), as well as in human cutaneous squamous cell carcinoma, Merkel cell carcinoma, and metastatic melanoma tissue (74, 75, 82). This lack of responsiveness to inflammatory signals has been termed endothelial anergy (83) and may play an important role in the exclusion of antitumor immune effector cells from the tumor microenvironment.…”

“…Expression of vascular adhesion molecules in intratumoral blood vessels is correlated with the number of TILs. E-selectin is required for T cell extravasation in skin, and expression of E-selectin in cutaneous squamous cell carcinoma and Merkel cell carcinoma correlates with infiltration by CD8 + T cells and better prognosis (74, 75). Medullary breast carcinomas are defined in part by a florid lymphocytic infiltrate and showed a higher expression of ICAM-1 on intratumoral blood vessels than ductal breast carcinomas of no special type (76).…”

PD-L1 Expression in the Merkel Cell Carcinoma Microenvironment: Association with Inflammation, Merkel Cell Polyomavirus, and Overall Survival

“…We postulate that high lymphocyte infiltration and consequent PD-L1 up-regulation in a subset of virus-positive tumors reflects both enhanced antigenicity associated with viral infection and virus independent factors, such as E-selectin expression on vascular endothelium that promotes lymphocyte egress. (40) Of note, Rodig and colleagues, in a recently published study using ultra-sensitive IHC and quantitative molecular techniques, demonstrated that MCPyV DNA was detectable in almost all MCC specimens analyzed. (3) It may be that integration of MCPyV DNA into host DNA – and subsequent expression of oncogenic viral proteins – beyond a certain threshold is required for immune activation of the tumor microenvironment.…”

Rationale For Immune-Based Therapies in Merkel Polyomavirus-Positive and -Negative Merkel Cell Carcinomas

“…In squamous cell carcinomas, E-selectin downregulation is mediated through nitric oxide (NO) signaling that is released by tumor-associated myeloid derived suppressor cells [63]. Nitration of proteins is a marker of NO production and evaluation of nitrotyrosine expression in MCCs indicated that increased levels of nitrotyrosine was associated with decreased E-selectin expression and CD8 T cell infiltration, suggesting that a similar mechanism is being employed within MCC tumors (Figure 2: process 'C') [64]. Notably, elevated expression of E-selectin was correlated with improved survival in MCC patients, implying that T-cell extravasation into the tumor microenvironment is critical for optimal immune function against MCC [64].…”