Characteristics of Malignant Pleural Effusion Resident CD8+ T Cells from a Heterogeneous Collection of Tumors

Abstract

While T cell-based cancer immunotherapies have shown great promise, there remains a need to understand how individual metastatic tumor environments impart local T cell dysfunction. At advanced stages, cancers that metastasize to the pleural space can result in a malignant pleural effusion (MPE) that harbors abundant tumor and immune cells, often exceeding 108 leukocytes per liter. Unlike other metastatic sites, MPEs are readily and repeatedly accessible via indwelling catheters, providing an opportunity to study the interface between tumor dynamics and immunity. In the current study, we examined CD8+ T cells within MPEs collected from patients with heterogeneous primary tumors and at various stages in treatment to determine (1) if these cells possess anti-tumor activity following removal from the MPE, (2) factors in the MPE that may contribute to their dysfunction, and (3) the phenotypic changes in T cell populations that occur following ex vivo expansion. Co-cultures of CD8+ T cells with autologous CD45― tumor containing cells demonstrated cytotoxicity (p = 0.030) and IFNγ production (p = 0.003) that inversely correlated with percent of myeloid derived suppressor cells, lactate, and lactate dehydrogenase (LDH) within the MPE. Ex vivo expansion of CD8+ T cells resulted in progressive differentiation marked by distinct populations expressing decreased CD45RA, CCR7, CD127, and increased inhibitory receptors. These findings suggest that MPEs may be a source of tumor-reactive T cells and that the cellular and acellular components suppress optimal function.

Malignant Pleural Effusions—A Window Into Local Anti-Tumor T Cell Immunity?

“…Despite this abundance of CD4 + T cells, several studies have shown that the CD4 + /CD8 + T cell ratio in MPEs is similar to matched peripheral blood samples in patients with mesothelioma (54,62). For lung cancer patients, CD8 + T cell frequencies were greater in the peripheral blood compared to the MPE for one study (53) but were similar between both compartments in others (41,63), suggesting CD8 + T cell infiltration in the pleural space may be more cancer or chemotherapy specific.…”

“…The proportion of total T cells in the MPE is greater than in matched peripheral blood samples from both mesothelioma and lung cancer patients ( 53 , 54 ). CD4 + T cells are the predominant T cell subset in MPE both prior to and after chemotherapy ( 41 , 54 – 57 ). Of these CD4 + T cells, an increased proportion of regulatory T cells (CD4 + CD25 + ) are recruited in MPEs by chemokines and pro-inflammatory cytokines, compared to matched peripheral blood ( 58 – 61 ).…”

“…Importantly, tumor antigen-specific T cells can be found in the MPE. Co-culture of MPE-derived lymphocytes with tumor cells or known tumor antigens from lung cancer patients resulted in IFN γ production ( 41 , 69 ) and CD137 expression ( 68 ), suggesting tumor reactivity ( 100 ). In addition, tumor reactive MPE-derived CD8 + T cells displayed a memory phenotype with checkpoint expression (PD-1 + TIM-3 - ) ( 68 ).…”

“…MPEs contain multiple cell types including tumor cells, pleural mesothelial cells, and innate and adaptive immune cells (40). Innate immune cells in the MPE include monocytes, macrophages, neutrophils, mast cells, dendritic cells and natural killer cells (41). These cells release cytokines, growth factors and chemokines including monocyte chemotactic protein (MCP-1), vascular endothelial growth factor (VEGF), IL-8, IL-6, IL-1b, interferon gamma (IFN-g), tumor necrosis factor alpha (TNFa), and transforming growth factor beta (TGFb) (40,(42)(43)(44)(45)(46)(47)(48).…”

“…These cytokines can be proinflammatory and in some cases protumorigenic, promoting angiogenesis, vascular permeability and protecting cancer cells from apoptosis. MPE have increased lactate dehydrogenase, and a lower pH than non-malignant pleural fluid, suggestive of an immunosuppressive environment (11,41,49). The characterization of MPE proteins, cytokine milieu, innate cells, tumor cells, and their relation to overall survival have been extensively reviewed elsewhere (50)(51)(52), so this review will focus on T cells.…”