Human mesenchymal stromal cells (MSC) have been shown to dampen immune response and promote tissue repair, but the underlying mechanisms are still under investigation. Herein, we demonstrate that umbilical cord-derived MSC (UC-MSC) alter the phenotype and function of monocyte-derived dendritic cells (DC) through lactate-mediated metabolic reprogramming. UC-MSC can secrete large quantities of lactate and, when present during monocyte-to-DC differentiation, induce instead the acquisition of M2-macrophage features in terms of morphology, surface markers, migratory properties and antigen presentation capacity. Microarray expression profiling indicates that UC-MSC modify the expression of metabolic-related genes and induce a M2-macrophage expression signature. Importantly, monocyte-derived DC obtained in presence of UC-MSC, polarize naïve allogeneic CD4+ T-cells into Th2 cells. Treatment of UC-MSC with an inhibitor of lactate dehydrogenase strongly decreases lactate concentration in culture supernatant and abrogates the effect on monocyte-to-DC differentiation. Metabolic analysis further revealed that UC-MSC decrease oxidative phosphorylation in differentiating monocytes while strongly increasing the spare respiratory capacity proportional to the amount of secreted lactate. Because both MSC and monocytes are recruited in vivo at the site of tissue damage and inflammation, we propose the local increase of lactate concentration induced by UC-MSC and the consequent enrichment in M2-macrophage generation as a mechanism to achieve immunomodulation.

Following the entry into the host cell, SARS‐CoV‐2 replication is mediated by the replication transcription complex (RTC) assembled through a number of nonstructural proteins (Nsps). A monomeric form of Nsp9 is particularly important for RTC assembly and function. In the present study, 136 unique nanobodies targeting Nsp9 are generated. Several nanobodies belonging to different B‐cell lineages are expressed, purified, and characterized. Results from immunoassays applied to purified Nsp9 and neat saliva from coronavirus disease (COVID‐19) patients show that these nanobodies effectively and specifically recognize both recombinant and endogenous Nsp9. Nuclear magnetic resonance analyses supported by molecular dynamics reveal a composite Nsp9 oligomerization pattern and demonstrate that both nanobodies stabilize the tetrameric form of wild‐type Nsp9 also identifying the epitopes on the tetrameric assembly. These results can have important implications in the potential use of these nanobodies to combat viral replication.

BackgroundVpu is a multifunctional accessory protein that enhances the release of HIV-1 by counteracting the entrapment of nascent virions on infected cell surface mediated by BST2/Tetherin. Vpu-mediated BST2 antagonism involves physical association with BST2 and subsequent mislocalization of the restriction factor to intracellular compartments followed by SCF(β-TrCP) E3 ligase-dependent lysosomal degradation. Apart from BST2 antagonism, Vpu also induces down regulation of several immune molecules, including CD4 and SLAMF6/NTB-A, to evade host immune responses and promote viral dissemination. However, it should be noted that the multiple functions of Vpu have been studied in cell-based assays, and thus it remains unclear how Vpu influences the dynamic of HIV-1 infection in in vivo conditions.ResultsUsing a humanized mouse model of acute infection as well as CCR5-tropic HIV-1 that lack Vpu or encode WT Vpu or Vpu with mutations in the β-TrCP binding domain, we provide evidence that Vpu-mediated BST2 antagonism plays a crucial role in establishing early plasma viremia and viral dissemination. Interestingly, we also find that efficient HIV-1 release and dissemination are directly related to functional strength of Vpu in antagonizing BST2. Thus, reduced antagonism of BST2 due to β-TrCP binding domain mutations results in decreased plasma viremia and frequency of infected T cells, highlighting the importance of Vpu-mediated β-TrCP-dependent BST-2 degradation for optimal initial viral propagation.ConclusionsOverall, our findings suggest that BST2 antagonism by Vpu is critical for efficient early viral expansion and dissemination during acute infection and as such is likely to confer HIV-1 increased transmission fitness.

The efficacy of IVIG in preventing GvHD has not been definitely demonstrated clinically. Using a xenogeneic model of GvHD in NOD/SCID/ccÀ (NSG) mice, we showed that weekly administration of IVIG significantly reduced the incidence and associated mortality of GvHD to a degree similar to CsA. Unlike CsA and OKT3, IVIG were not associated with inhibition of human T-cell proliferation in mice. Instead, IVIG significantly inhibited the secretion of human IL-17, IL-2, IFN-c and IL-15 suggesting that IVIG prevented GvHD by immunomodulation. Furthermore, the pattern of modification of the human cytokine storm differed from that observed with CsA and OKT3. Finally, in a humanized mouse model of immune reconstitution, in which NSG mice were engrafted with human CD34 þ stem cells, IVIG transiently inhibited B-cell reconstitution, whereas peripheral T-cell reconstitution and thymopoiesis were unaffected. Together these in vivo data raise debate related to the appropriateness of IVIG in GvHD prophylaxis. In addition, this model provides an opportunity to further elucidate the precise mechanism(s) by which IVIG inhibit GvHD.

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