Solid-type poorly differentiated adenocarcinoma of the stomach: A characteristic morphology reveals a distinctive immunoregulatory tumor microenvironment

The tumor immune composition of mismatch repair deficient and Epstein-Barr virus-positive gastric cancer: A systematic review

BACKGROUND

Gastric cancer (GC), known for its unfavorable prognosis, has been classified in four distinct molecular subtypes. These subtypes not only exhibit differences in their genome and transcriptome but also in the composition of their tumor immune microenvironment. The microsatellite instable (MSI) and Epstein-Barr virus (EBV) positive GC subtypes show clear clinical benefits from immune checkpoint blockade, likely due to a neoantigen-driven and virus-driven antitumor immune response and high expression of immune checkpoint molecule PD-L1. However, even within these subtypes response to checkpoint inhibition is variable, which is potentially related to heterogeneity in the tumor immune microenvironment (TIME) and expression of co-inhibitory molecules. We conducted a systematic review to outline the current knowledge about the immunological features on the TIME of MSI and EBV + GCs.

METHODS

A systematic search was performed in PubMed, EMBASE and Cochrane Library. All articles from the year 1990 and onwards addressing immune features of gastric adenocarcinoma were reviewed and included based on predefined in- and exclusion criteria.

RESULTS

In total 5962 records were screened, of which 139 were included that reported immunological data on molecular GC subtypes. MSI and EBV + GCs were reported to have a more inflamed TIME compared to non-MSI and EBV- GC subtypes. Compared to microsatellite stable (MSS) tumors, MSI tumors were characterized by higher numbers of CD8 + and FoxP3 + T cells, and tumor infiltrating pro- and anti-inflammatory macrophages. HLA-deficiency was most common in MSI tumors compared to other molecular GC subtypes and associated with lower T and B cell infiltrates compared to HLA-proficient tumors. EBV + was associated with a high number of CD8 + T cells, Tregs, NK cells and macrophages. Expression of PD-L1, CTLA-4, Granzyme A and B, Perforin and interferon-gamma was enriched in EBV + tumors. Overall, MSI tumors harbored a more heterogeneous TIME in terms of immune cell composition and immune checkpoints compared to the EBV + tumors.

DISCUSSION AND CONCLUSION

MSI and EBV + GCs are highly Handbook for Conducting a Literature-Based Health Assessment Using OHAT Approach for Systematic Review and Evidence Integration.; 2019pro-inflammatory immune cell populations. Although studies on the direct comparison of EBV + and MSI tumors are limited, EBV + tumors show less intra-subgroup heterogeneity compared to MSI tumors. More studies are needed to identify how Intra-subgroup heterogeneity impacts response to immunotherapy efficacy.

Clinicopathological significance of microsatellite instability and immune escape mechanism in patients with gastric solid-type poorly differentiated adenocarcinoma

BACKGROUND

In gastric solid-type poorly differentiated adenocarcinoma (PDA), the role of microsatellite instability and immune escape mechanism remains unclear. The current study aimed to elucidate the clinical significance of mismatch repair (MMR) status, genome profile, C-X-C motif chemokine receptor 2 (CXCR2) expression, and myeloid-derived suppressor cell (MDSC) infiltration in solid-type PDA.

METHODS

In total, 102 primary solid-type PDA cases were retrieved, and classified into 46 deficient-MMR (dMMR) and 56 proficient-MMR (pMMR) cases based on immunohistochemistry (IHC) and polymerase chain reaction-based molecular testing results. The mRNA expression profiles (NanoString nCounter Assay) of stage-matched dMMR (n = 6) and pMMR (n = 6) cases were examined. The CXCR2 expression and MDSC infiltration (CD11b- and CD33-positive cells) were investigated via IHC in all solid-type PDA cases.

RESULTS

mRNA analysis revealed several differentially expressed genes and differences in biological behavior between the dMMR (n = 46) and pMMR (n = 56) groups. In the multivariate analysis, the dMMR status was significantly associated with a longer disease-free survival (hazard ratio = 5.152, p = 0.002) and overall survival (OS) (hazard ratio = 5.050, p = 0.005). CXCR2-high expression was significantly correlated with a shorter OS in the dMMR group (p = 0.018). A high infiltration of CD11b- and CD33-positive cells was significantly correlated with a shorter OS in the pMMR group (p = 0.022, 0.016, respectively).

CONCLUSIONS

dMMR status can be a useful prognostic predictor, and CXCR2 and MDSCs can be novel therapeutic targets in patients with solid-type PDA.

Clinical significance of the expression of FOXP3 and TIGIT in Merkel cell carcinoma

The pathogenesis of 80% of Merkel cell carcinoma (MCC) cases is associated with Merkel cell polyomavirus (MCPyV). Forkhead helix transcription factor P3 (FOXP3) and the T cell immunoreceptor with immunoglobulin and immunoreceptor tyrosine-based inhibition motif domains (TIGIT)-CD155 pathway, which are targets for immunotherapy, were assessed as prognostic factors of MCC. We analyzed mRNA expression data of 111 patients with MCC and performed immunohistochemical analysis to detect the expression of programmed death ligand 1 (PD-L1), CD8, FOXP3, TIGIT, and CD155 in 65 cases of MCC. In CD8 and FOXP3 immunostaining, the number of expressing-infiltrating cells was determined by dividing the region into tumor center and invasive front areas. FOXP3 expression was evaluated separately in cells with high and low intensities. Aberrant TIGIT expression and weak CD155 staining were observed in MCC cells. CD8- and FOXP3-positive cell infiltrations were higher in the invasive front than in the tumor center. Multivariate Cox hazard analysis revealed that high infiltration of cells with low-intensity FOXP3 expression in the invasive front is a favorable prognostic factor (p = 0.025). Thus, targeting TIGIT-CD155 signaling and FOXP3 as well as PD-L1 may be a therapeutic strategy for MCC.

The Correlation of Ten Immune Checkpoint Gene Expressions and Their Association with Gastric Cancer Development

In the immunotherapy based on immune checkpoint inhibition (IC), additional ICs are being studied to increase its effectiveness. An almost unstudied feature is the possible co-expression of ICs, which can determine the therapeutic efficacy of their inhibition. For the selection of promising ICs, information on the association of their expression with cancer development may be essential. We have obtained data on the expression correlation of ADAM17, PVR, TDO2, CD274, CD276, CEACAM1, IDO1, LGALS3, LGALS9, and HHLA2 genes in gastric cancer (GC). All but one, TDO2, have other IC genes with co-expression at some stage. At the metastatic stage, the expression of the IDO1 does not correlate with any other gene. The correlations are positive, but the expressions of the CD276 and CEACAM1 genes are negatively correlated. The expression of TDO2 and LGALS3 is associated with GC metastasis. The expression of TDO2 four-fold higher in metastatic tumors than in non-metastatic tumors, but LGALS3 was two-fold lower. The differentiation is associated with IDO1. The revealed features of TDO2, with a significant increase in expression at the metastatic stage and the absence of other IC genes with correlated expression indicates that the prospect of inhibiting TDO2 in metastatic GC. IDO1 may be considered for inhibition in low-differentiated tumors.