Background: The transmembrane protease serine 2 (TMPRSS2) proteolytically activates the envelope proteins of several viruses for viral entry via membrane fusion and is therefore an interesting and promising target for the development of broad-spectrum antivirals. However, the use of a host protein as a target may lead to potential side effects, especially on the immune system. We examined the effect of a genetic deletion of TMPRSS2 on dendritic cells. Methods: Bone marrow cells from wild-type (WT) and TMPRSS2-deficient mice (TMPRSS2^−/−) were differentiated to plasmacytoid dendritic cells (pDCs) and classical DCs (cDCs) and activated with various toll-like receptor (TLR) agonists. We analyzed the released cytokines and the mRNA expression of chemokine receptors, TLR7, TLR9, IRF7 and TCF4 stimulation. Results: In cDCs, the lack of TMPRSS2 led to an increase in IL12 and IFNγ in TLR7/8 agonist resiquimod or TLR 9 agonist ODN 1668-activated cells. Only IL-10 was reduced in TMPRSS2^−/− cells in comparison to WT cells activated with ODN 1668. In resiquimod-activated pDCs, the lack of TMPRSS2 led to a decrease in IL-6, IL-10 and INFγ. ODN 1668 activation led to a reduction in IFNα. The effect on receptor expression in pDCs and cDCs was low. Conclusion: The effect of TMPRSS2 on pDCS and cDCs depends on the activated TLR, and TMPRSS2 seems to affect cytokine release differently in pDCs and cDCs. In cDCs, TMPRSS2 seems to suppress cytokine release, whereas in pDCS TMPRSS2 possibly mediates cytokine release.

The zoonotic transmission of influenza A viruses (IAVs) and coronaviruses (CoVs) may result in severe disease. Cleavage of the surface glycoproteins hemagglutinin (HA) and spike protein (S), respectively, is essential for viral infectivity. The transmembrane serine protease 2 (TMPRSS2) is crucial for cleaving IAV HAs containing monobasic cleavage sites and severe acute respiratory syndrome (SARS)-CoV-2 S in human airway cells. Here, we analysed and compared the TMPRSS2-dependency of SARS-CoV, Middle East respiratory syndrome (MERS)-CoV, the 1918 pandemic H1N1 IAV and IAV H12, H13 and H17 subtypes in human airway cells. We used the peptide-conjugated morpholino oligomer (PPMO) T-ex5 to knockdown the expression of active TMPRSS2 and determine the impact on virus activation and replication in Calu-3 cells. The activation of H1N1/1918 and H13 relied on TMPRSS2, whereas recombinant IAVs carrying H12 or H17 were not affected by TMPRSS2 knockdown. MERS-CoV replication was strongly suppressed in T-ex5 treated cells, while SARS-CoV was less dependent on TMPRSS2. Our data underline the importance of TMPRSS2 for certain (potentially) pandemic respiratory viruses, including H1N1/1918 and MERS-CoV, in human airways, further suggesting a promising drug target. However, our findings also highlight that IAVs and CoVs differ in TMPRSS2 dependency and that other proteases are involved in virus activation.

Background: TMPRSS2 plays an important role in the viral entry mechanisms of influenza viruses and coronaviruses. Therefore, TMPRSS2 seems to be a suitable antiviral drug target. To exclude possible side effects of TMPRSS2 truncation in an early stage of drug in-vitro testing, this study aims to analyze the impact of TMPRSS2 truncation via antisense peptide-conjugated phosphorodiamidate morpholino oligomer (PPMO) targeting immune cells, using the example of regulatory T cells (Treg). Methods: TMPRSS2 was truncated in human Tregs using a splice-modulating PPMO. Effects on Treg function were analyzed by evaluation of surface marker and transcription factor expression, cytokine secretion, and effector cell suppression capability. Results: PPMO treatment led to a slight concentration-dependent toxicity in Tregs. Tregs with truncated TMPRSS2 behave similarly to untreated and control PPMO-treated cells in the analyzed assays. Conclusions: Treg function is not altered after TMPRSS2 truncation and therefore, no unwanted side effects in regard of Tregs are expected when using TMPRSS2-truncating PPMO as an anti-viral drug.