Kaposi's sarcoma-associated herpesvirus replication and transcription activator protein activates CD274/PD-L1 gene promoter.

Kaposi's sarcoma-associated herpesvirus (KSHV) is responsible for the pathogenesis of Kaposi's sarcoma, primary effusion lymphoma, and multicentric Castleman disease. The expression of immunosuppressive genes, such as IL-10 and CD274/PD-L1 is observed during KSHV-associated pathogenesis, and the modulation of the host immune system by KSHV contributes to establishing viral persistence in the host. Understanding the mechanism that allows the virus to evade host cell immunity would be helpful in order to develop therapeutic strategies for KSHV malignancy. In this study, we show that KSHV replication and transcriptional activator (K-RTA), an essential activator of the viral lytic cycle, transactivates the CD274/PD-L1 gene promoter. Mechanistically, we demonstrate that the binding of K-RTA to the cellular specificity protein 1 (SP1) is critical for K-RTA-mediated CD274/PD-L1 promoter activation. These findings suggest that K-RTA cooperates with intracellular SP1 to activate the expression of CD274/PD-L1, which helps the virus regulate immune checkpoints to escape and survive.

Gene code CD274/PD-L1: from molecular basis toward cancer immunotherapy.

The programmed death 1 receptor (PD-1) and its ligand (PD-L1) are key molecules of immune checkpoint mechanisms in cancer and actually represent one of the main targets of immunotherapy. The predictive and prognostic values of PD-L1 expression alone in cancer patients is currently under debate due to the methodological assessment of PD-L1 expression and its temporal variations. Better detailed studies about the molecular basis of immunotherapy biomarkers are necessary. Here we summarize the current knowledge of PD-L1 gene modifications at genetic and epigenetic levels in different tumors, thus highlighting their reported correlation with cellular processes and potential impact on patient outcomes.

Histopathological and genotypic characterization of metastatic colorectal carcinoma with PD-L1 (CD274)-expression: Possible roles of tumour micro environmental factors for CD274 expression.

Aberrant PD-L1 (CD274) expression has been described in different types of tumour and linked to tumour aggressiveness and a poor prognosis. In primary colorectal carcinomas (CRCs), CD274 expression was reported to be associated with mismatch repair (MMR)-deficiency, BRAF mutation, and "stem-like" immunophenotype defined by down-regulation of homeobox protein CDX2 and membranous expression of activated leukocyte cell adhesion molecule (ALCAM). However, the immunophenotype and genotype of CD274-positive metastatic CRC have not been extensively analysed. In this study, 189 CRC metastases were evaluated immunohistochemically for CD274, MMR proteins, CDX2, and ALCAM expression. Immunostaining for CD4, CD8, and FOXP3 was also performed to characterize tumour-associated immune cells. In addition, 34 arbitrarily selected lesions were genotyped using Sanger- and next-generation sequencing. Univariate analyses showed no clear association between CD274 expression and clinicopathological parameters including MMR-deficiency or "stem-like" immunophenotype after adjustment for multiple testing. Comparison of the clinicopathological profiles of CD274-positive primary and metastatic tumours revealed in the latter younger age of occurrence (60.9 ± 13.3 versus 72.6 ± 13.1 years, p = 0.001), cytoplasm-dominant CD274 expression (p < 0.001), infrequent MMR-deficiency (p < 0.001), and common KRAS mutations (54%, p < 0.001). In five cultured colon cancer cell lines, CD274 was expressed and modulated after exogenous exposure to IFNγ and TGF-ß1. Thus, CD274 regulation mechanisms might include tumour micro environmental factors. Based on significantly different characteristics in CD274-positive metastatic and primary CRCs, evaluation of metastases should also be considered when planning immune checkpoint inhibitor therapy.

Immune checkpoint inhibition in lymphoid disease.

It has long been understood that the immune system has intrinsic anti-tumour activity in humans, and that a key mechanism of tumour progression is the ability of a tumour to escape this immune surveillance. A number of attempts have been made to harness this anti-tumour immunity in both solid tumour oncology and haematological malignancies with variable success. Examples include the use of allogeneic stem cell transplantation and donor lymphocyte infusion in haematological cancer and vaccine studies in solid tumours. Enhanced signalling of the Programmed cell death-1 (PDCD1, PD-1)/cytotoxic T-lymphocyte-associated protein 4 (CTLA4) 'immune checkpoint' pathway has emerged recently as a critical mechanism by which tumours can escape the natural anti-tumour immune response. As such, novel therapies have been developed to help enhance this natural immunity by switching off the PDCD1/CTLA4 immune checkpoint pathway. The following review will discuss the pathobiology of these pathways and the exciting new data now available in lymphoid malignancies.