Distinct Immunological Landscapes Characterize Inherited and Sporadic Mismatch Repair Deficient Endometrial Cancer.

Neal C Ramchander,D G Evans,Lauren Harries,James Bolton,Emma J Crosbie,Tjalling Bosse,Neil A J Ryan,Thomas D J Walker

doi:10.3389/fimmu.2019.03023

Abstract

Around 30% of endometrial cancers (EC) are mismatch repair (MMR) deficient, mostly as a consequence of mutations acquired during tumorigenesis, but a significant minority is caused by Lynch syndrome (LS). This inherited cancer predisposition syndrome primes an anti-cancer immune response, even in healthy carriers. We sought to explore the intra-tumoral immunological differences between genetically confirmed LS-associated MMR-deficient (MMRd), sporadic MMR-deficient, and MMR-proficient (MMRp) EC. Endometrial tumors from women with known LS were identified (n = 25). Comparator tumors were recruited prospectively and underwent microsatellite instability (MSI) testing, immunohistochemistry (IHC) for MMR expression and MLH1 methylation testing. Those found to have MLH1 hypermethylation formed the sporadic MMR-deficient group (n = 33). Those found to be mismatch repair proficient and microsatellite stable formed the MMR-proficient group (n = 35). A fully automated monoplex IHC panel was performed on sequential formalin-fixed paraffin-embedded tumor sections to identify CD3+, CD8+, CD45RO+, FoxP3+, and PD-1+ immune cells, and PD-L1 expression by tumor/immune cells. Two independent observers quantified immune marker expression at the tumor center and invasive margin. Mean and overall compartmental T-cell counts generated standard (binary: Low/High) and higher resolution (quaternary: 0–25, 25–50, 50–75, 75–100%) immune scores, which were used as explanatory features in neural network, support vector machine, and discriminant predictive modeling. Overall T-cell counts were significantly different between the three cohorts: CD3+ (p = <0.0001), CD8+ (p = <0.0001), CD45RO+ (<0.0001), FoxP3+ (p = <0.0001), and PD1+ (p = <0.0001), with LS-associated MMR-deficient tumors having highest infiltrations. There were significant differences in CD8+ (p = 0.02), CD45RO+ (p = 0.007), and PD-1+ (p = 0.005) T-cell counts at the invasive margin between LS-associated and sporadic MMR-deficient tumors, but not between sporadic MMR-deficient and MMR-proficient tumors. Predictive modeling could accurately determine MMR status based on CD8+ T-cell counts within the tumor center alone. This study shows that LS-associated and sporadic MMR-deficient EC are distinct immunological entities, which has important implications for treatment and prognosis.

Highlights

In the UK, endometrial cancer (EC) is the fourth most common malignancy in women, and its incidence is rising [1]
There was no significant difference between the three cohorts with respect to histological subtype, grade or stage of disease, or whether the tumor sample derived from the hysterectomy specimen or the diagnostic biopsy
The Lynch syndrome (LS)-associated cohort was significantly younger at diagnosis than the sporadic MMRdeficient and mismatch repair (MMR)-proficient cohorts; there was no significant difference between the sporadic MMRdeficient and MMR-proficient cohorts (p = 0.14 Student ttest)

Summary

Introduction

In the UK, endometrial cancer (EC) is the fourth most common malignancy in women, and its incidence is rising [1]. Microsatellite instable EC tumors are characterized by dense immune infiltrates [9, 10] due to the translation of neoantigens, called frameshift peptides (FSP), derived from non-synonymous point and frameshift mutations in protein-coding DNA [11, 12]. Some of these FSPs are processed into major histocompatibility complex (MHC) compatible FSP-epitopes that are recognized by T-cells. The upregulation of FoxP3+ regulatory T-Cells (Tregs) has been described in MSI tumors [26]; together, these mechanisms prevent the priming of activated, cytotoxic T cells [27]

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