T-cell Localization, Activation, and Clonal Expansion in Human Pancreatic Ductal Adenocarcinoma

Abstract

Pancreatic ductal adenocarcinoma (PDA) is a lethal malignancy resistant to most therapies, including immune checkpoint blockade. To elucidate mechanisms of immunotherapy resistance, we assessed immune parameters in resected human PDA. We demonstrate significant interpatient variability in T-cell number, localization, and phenotype. CD8+ T cells, Foxp3+ regulatory T cells and PD-1+ and PD-L1+ cells were preferentially enriched in tertiary lymphoid structures that were found in most tumors compared to stroma and tumor cell nests. Tumors containing more CD8+ T cells also had increased granulocytes, CD163+ (M2 immunosuppressive phenotype) macrophages, and FoxP3+ regulatory T cells. PD-L1 was rare on tumor cells, but was expressed by CD163+ macrophages and an additional stromal cell subset commonly found clustered together adjacent to tumor epithelium. The majority of tumoral CD8+ T cells did not express molecules suggestive of recent T-cell receptor (TCR) signaling. However, 41BB+PD-1+ T cells were still significantly enriched in tumors compared to circulation. Tumoral PD-1+ CD8+ T cells commonly expressed additional inhibitory receptors, yet were mostly T-bethi and Eomeslo, consistent with a less terminally exhausted state. Analysis of gene expression and rearranged TCR genes by deep sequencing suggested most patients have a limited tumor-reactive T-cell response. Multiplex immunohistochemistry revealed variable T-cell infiltration based on abundance and location, which may result in different mechanisms of immunotherapy resistance. Overall, the data support the need for therapies that either induce endogenous, or provide engineered, tumor-specific T-cell responses and concurrently relieve suppressive mechanisms operative at the tumor site.

Sensitizing the Tumor Microenvironment to Immune Checkpoint Therapy

“…Indeed, there is an association between pre-treatment Foxp3+ T-reg infiltration, followed by a subsequent increase in TILs 3 weeks into treatment in melanoma biopsies which was associated with response to the CTLA4-targeting antibody ipilimumab (48). Whether this is a causal relationship, or a bystander effect of enhanced inflammation remains to be established, as infiltration of the TME with T-regs usually coexists with an inflammatory response that also includes CD8 + T cells, macrophages and granulocytes (49,50). Conversely, T-regs and T effector cells express similar levels of PD-1 (51), and anti-PD-1 antibodies do not deplete cells expressing the target, but the Fc portion can modulate myeloid cell activity (37).…”

Increased Adiposity Enhances the Accumulation of MDSCs in the Tumor Microenvironment and Adipose Tissue of Pancreatic Tumor-Bearing Mice and in Immune Organs of Tumor-Free Hosts

“…Pancreatic adenocarcinoma (PDAC) is an aggressive tumor type, with an overall five-year survival rate of 7% [27]. The infiltration of effector CD8 + T cells into the tumor confers a survival benefit and is predictive of a beneficial response to therapy; however, CD8 + T cells are found infrequently in the tumor microenvironment (TME) of pancreatic cancer patients [28][29][30]. In contrast, myeloid cells are highly prevalent in the TME, play a significant role in immune suppression, and are correlated with poor responses to therapy [31,32].…”

The Immune Microenvironment in Pancreatic Cancer

“…PDAC is characterized by a high immunological heterogeneity, with tumors having variable degrees of T cell infiltration, comprising distinct T-cell subpopulations [ 14 , 135 , 136 , 137 , 138 , 139 , 140 ]. Although it has previously been thought that the immunosuppressive microenvironment consisting of fibroblasts and desmoplastic stroma restricts T cell infiltration [ 141 , 142 ], more recent work indicates that desmoplastic elements might not influence T cell accumulation, revealing a specific spatial distribution of T cells in PDAC [ 139 ].…”