Since the outbreak of the COVID-19 pandemic, much has been learned regarding its clinical course, prognostic inflammatory markers, disease complications, and mechanical ventilation strategy. Clinically, three stages have been identified based on viral infection, pulmonary involvement with inflammation, and fibrosis. Moreover, low and high elastance phenotypes can be distinguished in mechanically ventilated patients, based on lung mechanics, ventilation-to-perfusion ratio, and CT scans; these two phenotypes have presumed differences in their underlying pathophysiology. Although essential for therapeutic guidance, the pathophysiology of COVID-19 is poorly understood. Here, we systematically reviewed published case reports and case series in order to increase our understanding of COVID-19 pathophysiology by constructing a timeline and correlating histopathological findings with clinical stages of COVID-19. Using PRISMA-IPD guidelines, 42 articles reporting 198 individual cases were included in our analysis. In lung samples (n = 131 cases), we identified three main histological patterns: epithelial (n = 110, 85%), with reactive epithelial changes and DAD; vascular (n = 76, 59%) with microvascular damage, (micro)thrombi, and acute fibrinous and organizing pneumonia; and fibrotic (n = 28, 22%) with interstitial fibrosis. The epithelial and vascular patterns can present in all stages of symptomatic COVID-19, whereas the fibrotic pattern presents starting at~3 weeks. Moreover, patients can present with more than one pattern, either simultaneously or consecutively. These findings are consistent with knowledge regarding clinical patterns of viral infection, development of hyperinflammation and hypercoagulability, and fibrosis. Close collaboration among medical staff is necessary in order to translate this knowledge and classification of pathophysiological mechanisms into clinical stages of disease in individual patients. Moreover, further research, including histopathological studies, is warranted in order to develop reliable, clinically relevant biomarkers by correlating these pathological findings with laboratory results and radiological findings, thus, increasing our understanding of COVID-19 and facilitating the move to precision medicine for treating patients.

Although it has long been recognized that the exonucleolytic proofreading activity intrinsic to the replicative DNA polymerases Pol δ and Pol ε is essential for faithful replication of DNA, evidence that defective DNA polymerase proofreading contributes to human malignancy has been limited. However, recent studies have shown that germline mutations in the proofreading domains of Pol δ and Pol ε predispose to cancer, and that somatic Pol ε proofreading domain mutations occur in multiple sporadic tumours, where they underlie a phenotype of 'ultramutation' and favourable prognosis. In this Review, we summarize the current understanding of the mechanisms and consequences of polymerase proofreading domain mutations in human malignancies, and highlight the potential utility of these variants as novel cancer biomarkers and therapeutic targets.

Purpose Recent studies have shown that 7-12% of endometrial cancers (ECs) are ultramutated due to somatic mutation in the proofreading exonuclease domain of the DNA replicase POLE. Interestingly, these tumors have an excellent prognosis. In view of the emerging data linking mutation burden, immune response and clinical outcome in cancer, we investigated whether POLE-mutant ECs showed evidence of increased immunogenicity. Experimental design We examined immune infiltration and activation according to tumor POLE proofreading mutation in a molecularly defined EC cohort including 47 POLE-mutant tumors. We sought to confirm our results by analysis of RNAseq data from the TCGA EC series and used the same series to examine whether differences in immune infiltration could be explained by an enrichment of immunogenic neoepitopes in POLE-mutant ECs. Results Compared to other ECs, POLE-mutants displayed an enhanced cytotoxic T cell response, evidenced by increased numbers of CD8+ tumor infiltrating lymphocytes and CD8A expression, enrichment for a tumor-infiltrating T cell gene signature, and strong upregulation of the T cell cytotoxic differentiation and effector markers T-bet, Eomes, IFNG, PRF and granzyme B. This was accompanied by upregulation of T cell exhaustion markers, consistent with chronic antigen exposure. In-silico analysis confirmed that POLE-mutant cancers are predicted to display more antigenic neo-epitopes than other ECs, providing a potential explanation for our findings. Conclusions Ultramutated POLE proofreading-mutant ECs are characterized by a robust intratumoral T cell response, which correlates with, and may be caused by an enrichment of antigenic neo-peptides. Our study provides a plausible mechanism for the excellent prognosis of these cancers.

A transcriptionally distinct CXCL13+CD103+CD8+ T-cell population is associated with B-cell recruitment and neoantigen load in human cancer de Bruyn, M. (2019). A transcriptionally distinct CXCL13+CD103+CD8+ T-cell population is associated with B-cell recruitment and neoantigen load in human cancer. Cancer immunology research, 7(5), 784-796. AbstractThe chemokine CXCL13 mediates recruitment of B cells to tumors and is essential for the formation of tertiary lymphoid structures (TLSs). TLSs are thought to support antitumor immunity and are associated with improved prognosis. However, it remains unknown whether TLSs are formed in response to the general inflammatory character of the tumor microenvironment, or rather, are induced by (neo)antigen-specific adaptive immunity. We here report on the finding that the transforming growth factor beta (TGFβ)-dependent CD103 + CD8 + tumor-infiltrating T-cell (TIL) subpopulation expressed and produced CXCL13. Accordingly, CD8 + T cells from peripheral blood activated in the presence of TGFβ upregulated CD103 and secreted CXCL13. Conversely, inhibition of TGFβ receptor signaling abrogated CXCL13 production. CXCL13 + CD103 + CD8 + TILs correlated with B-cell recruitment, TLSs, and neoantigen burden in six cohorts of human tumors. Altogether, our findings indicated that TGFβ plays a non-canonical role in coordinating immune responses against human tumors and suggest a potential role for CXCL13 + CD103 + CD8 + TILs in mediating B-cell recruitment and TLS formation in human tumors.

Studies in early-stage, predominantly low- and intermediate-risk endometrial cancer have demonstrated that L1 cell adhesion molecule (L1CAM) overexpression identifies patients at increased risk of recurrence, yet its prognostic significance in high-risk endometrial cancer is unclear. To evaluate this, its frequency, and the relationship of L1CAM with the established endometrial cancer biomarker p53, we analyzed the expression of both markers by immunohistochemistry in a pilot series of 116 endometrial cancers (86 endometrioid, 30 non-endometrioid subtype) with high-risk features (such as high tumor grade and deep myometrial invasion) and correlated results with clinical outcome. We used The Cancer Genome Atlas (TCGA) endometrial cancer series to validate our findings. Using the previously reported cutoff of 10% positive staining, 51/116 (44%) tumors were classified as L1CAM-positive, with no significant association between L1CAM positivity and the rate of distant metastasis (P=0.195). However, increasing the threshold for L1CAM positivity to 50% resulted in a reduction of the frequency of L1CAM-positive tumors to 24% (28/116), and a significant association with the rate of distant metastasis (P=0.018). L1CAM expression was strongly associated with mutant p53 in the high-risk and TCGA series (P<0.001), although a substantial fraction (36% of endometrioid, 10% of non-endometrioid morphology) of p53-mutant endometrial cancers displayed <10% L1CAM positivity. Moreover, 30% of p53-wild-type non-endometrioid endometrial cancers demonstrated diffuse L1CAM staining, suggesting p53-independent mechanisms of L1CAM overexpression. In conclusion, the previously proposed threshold for L1CAM positivity of >10% does not predict prognosis in high-risk endometrial cancer, whereas an alternative threshold (>50%) does. L1CAM expression is strongly, but not universally, associated with mutant p53, and may be strong enough for clinical implementation as prognostic marker in combination with p53. The high frequency of L1CAM expression in high-risk endometrial cancers suggests that it may also be a promising therapeutic target in this tumor subset.