Human MSLN Stable Cell Line - HEK293

Mesothelin (MSLN) is a cell-surface tumor antigen expressed in various subtypes of both breast and non-breast cancers. Given that recent studies have validated MSLN as a biomarker for a subset of triple-negative breast tumors, it has emerged as a highly attractive therapeutic target; currently, antibody-drug conjugates (ADCs) and CAR-T cell therapies targeting MSLN are undergoing clinical trials. The advent of MSLN-retargeted oncolytic viruses holds promise as a biotherapeutic agent capable of effectively complementing current immunotherapy regimens used to treat HER2-negative breast cancers and non-breast malignancies. In this study, researchers utilized a panel of MSLN-positive cancer cell lines-derived from tumors of the breast and female reproductive system-to validate the specific infectivity and cytotoxicity of these MSLN-retargeted viruses. Furthermore, the researchers successfully developed a second-generation oncolytic virus, MSLN-THV (encoding IL-12), designed to further enhance the immunotherapeutic potential of the viral backbone. To optimize viral production yields, they also engineered a non-tumor cell line that not only expresses a chimeric MSLN/Nectin-1 receptor but also features a genetically inactivated the Stimulator of Interferon Genes (STING)-dependent signaling pathway, thereby attenuating the cellular antiviral immune response to viral infection. Consequently, MSLN-retargeted herpesviruses show promise as potential cancer immunotherapeutics and warrant further evaluation in preclinical models of MSLN-positive tumors.

Varying doses of the THV_SS1 virus were inoculated into wild-type cells (Figure 1a) and HEK293-MSLN cells (Fig. 3b), and viral spread was continuously monitored until the infection covered the entire cell monolayer. The wild-type R-LM55 HSV-1 was used as a positive control for infection (Figure 1a). As expected, HEK293 cells were efficiently infected by the wild-type R-LM55; however, due to the absence of mesothelin (MSLN)-which serves as the ligand for SS1-these cells failed to be infected by the THV_SS1 virus (Figure 1a). In contrast, THV_SS1 efficiently infected HEK293-MSLN cells; at various time points post-infection, the complete cytopathic effect (CPE) induced by the virus exhibited a distinct dose-dependent pattern (Figure 1b). Beyond the process of viral entry, the researchers also investigated viral replication by quantifying viral genome copy numbers. They evaluated the replication capabilities of THV_SS1 and its parental virus, R-LM55, within the HEK293-MSLN cell line. The results demonstrated that both the wild-type virus and the retargeted virus exhibited similar replication efficiencies in these mesothelin-expressing cells (Figure 1c).

Figure 1. Cytopathic effect of THV_SS1 is tightly dependent on MSLN positive cells. (Froechlich G, et al., 2021)