Floris Foijer

Spatiotemporal Immune Landscape and Long-term Immune Memory in POLE-Mutant Endometrial Cancer at the Single-Cell Level

Abstract Polymerase epsilon–mutant (POLE-mut) endometrial cancers are characterized by a near 100% disease-specific survival rate, even when treated with surgery alone. This survival, combined with the ultramutated genome and high level of neoantigens in these tumors, indicates a substantial degree of immune control in preventing disease spread and recurrence. Although these features are intriguing, the analysis of immune infiltration in POLE-mut endometrial cancers has predominantly been confined to IHC studies. In this study, we used single-cell RNA and T-cell receptor sequencing to characterize the immune landscape of POLE-mut endometrial cancers. Moreover, we analyzed patient blood samples taken 2 to 8 years after curative treatment to assess the formation of long-term immune memory in circulation. We identified specialized tumor-infiltrating myeloid subsets at different stages of maturation, an array of lymphocytes ranging from immature to cytotoxic, and adaptive NK cells, as well as tumor-reactive exhausted and effector T cells, all contributing to a highly inflammatory antitumor response. Our analysis of blood samples taken years after curative treatment uncovered the presence of tumor-reactive T-cell clones that matched the primary tumor. This indicates the formation of systemic long-term memory immune responses in POLE-mut endometrial cancer survivors. Our study highlights the distinctive immunogenicity of POLE-mut endometrial cancer and identifies key features associated with persistent antitumor immunity that may contribute to prolonged, relapse-free survival.

TP53 loss initiates chromosomal instability in fallopian tube epithelial cells

ABSTRACT High-grade serous ovarian cancer (HGSOC) originates in the fallopian tube epithelium and is characterized by ubiquitous TP53 mutation and extensive chromosomal instability (CIN). However, direct causes of CIN, such as mutations in DNA replication and mitosis genes, are rare in HGSOC. We therefore asked whether oncogenic mutations that are common in HGSOC can indirectly drive CIN in non-transformed human fallopian tube epithelial cells. To model homologous recombination deficient HGSOC, we sequentially mutated TP53 and BRCA1 then overexpressed MYC. Loss of p53 function alone was sufficient to drive the emergence of subclonal karyotype alterations. TP53 mutation also led to global gene expression changes, influencing modules involved in cell cycle commitment, DNA replication, G2/M checkpoint control and mitotic spindle function. Both transcriptional deregulation and karyotype diversity were exacerbated by loss of BRCA1 function, with whole-genome doubling events observed in independent p53/BRCA1-deficient lineages. Thus, our observations indicate that loss of the key tumour suppressor TP53 is sufficient to deregulate multiple cell cycle control networks and thereby initiate CIN in pre-malignant fallopian tube epithelial cells. This article has an associated First Person interview with the first author of the paper.

Neoadjuvant immune checkpoint blockade in women with mismatch repair deficient endometrial cancer: a phase I study

Neoadjuvant immune checkpoint blockade (ICB) has shown unprecedented activity in mismatch repair deficient (MMRd) colorectal cancers, but its effectiveness in MMRd endometrial cancer (EC) remains unknown. In this investigator-driven, phase I, feasibility study (NCT04262089), 10 women with MMRd EC of any grade, planned for primary surgery, received two cycles of neoadjuvant pembrolizumab (200 mg IV) every three weeks. A pathologic response (primary objective) was observed in 5/10 patients, with 2 patients showing a major pathologic response. No patient achieved a complete pathologic response. A partial radiologic response (secondary objective) was observed in 3/10 patients, 5/10 patients had stable disease and 2/10 patients were non-evaluable on magnetic resonance imaging. All patients completed treatment without severe toxicity (exploratory objective). At median duration of follow-up of 22.5 months, two non-responders experienced disease recurrence. In-depth analysis of the loco-regional and systemic immune response (predefined exploratory objective) showed that monoclonal T cell expansion significantly correlated with treatment response. Tumour-draining lymph nodes displayed clonal overlap with intra-tumoural T cell expansion. All pre-specified endpoints, efficacy in terms of pathologic response as primary endpoint, radiologic response as secondary outcome and safety and tolerability as exploratory endpoint, were reached. Neoadjuvant ICB with pembrolizumab proved safe and induced pathologic, radiologic, and immunologic responses in MMRd EC, warranting further exploration of extended neoadjuvant treatment.