Background Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a highly infectious respiratory virus which is responsible for the coronavirus disease 2019 (COVID-19) pandemic. It is increasingly clear that recovered individuals, even those who had mild COVID-19, can suffer from persistent symptoms for many months after infection, a condition referred to as “long COVID”, post-acute sequelae of COVID-19 (PASC), post-acute COVID-19 syndrome, or post COVID-19 condition. However, despite the plethora of research on COVID-19, relatively little is known about the molecular underpinnings of these long-term effects. Methods We have undertaken an integrated analysis of immune responses in blood at a transcriptional, cellular, and serological level at 12, 16, and 24 weeks post-infection (wpi) in 69 patients recovering from mild, moderate, severe, or critical COVID-19 in comparison to healthy uninfected controls. Twenty-one of these patients were referred to a long COVID clinic and > 50% reported ongoing symptoms more than 6 months post-infection. Results Anti-Spike and anti-RBD IgG responses were largely stable up to 24 wpi and correlated with disease severity. Deep immunophenotyping revealed significant differences in multiple innate (NK cells, LD neutrophils, CXCR3+ monocytes) and adaptive immune populations (T helper, T follicular helper, and regulatory T cells) in convalescent individuals compared to healthy controls, which were most strongly evident at 12 and 16 wpi. RNA sequencing revealed significant perturbations to gene expression in COVID-19 convalescents until at least 6 months post-infection. We also uncovered significant differences in the transcriptome at 24 wpi of convalescents who were referred to a long COVID clinic compared to those who were not. Conclusions Variation in the rate of recovery from infection at a cellular and transcriptional level may explain the persistence of symptoms associated with long COVID in some individuals.

The ability of Frzb/secreted Frizzled-related protein 3 (sFRP3) to inhibit Wnt signaling and the localization of Frzb/sFRP3 on chromosome 2q to a region frequently deleted in cancers have led some investigators to hypothesize that Frzb/sFRP3 is a tumor suppressor gene. Here, we examined the biological effects of Frzb/sFRP3 on an androgenindependent prostate cancer cell model. We showed that expression of Frzb/sFRP3 in PC-3 cells resulted in decreased colony formation in soft agar and a dramatic inhibition of tumor growth in a xenograft mouse model. When cellular morphology was examined, PC-3 cells expressing Frzb/sFRP3 exhibited an increase in cell-cell contact formation accompanied by a pronounced induction of epithelial markers E-cadherin and keratin-8 and down-regulation of mesenchymal markers N-cadherin, fibronectin, and vimentin. This phenomenon suggested a reversal of epithelial-to-mesenchymal transition and a less invasive phenotype. Indeed, further in vitro studies with a Matrigel assay showed that Frzb/sFRP3 decreased the invasive capacity of PC-3 cells. These changes in the biology of PC-3 cells are associated with a decrease in the expression and activities of both matrix metalloproteinase (MMP)-2 and MMP-9 as well as decreases in AKT activation, cytosolic B-catenin levels, T-cell factor transcription activity, and expression of Slug and Twist. In addition, transfection of PC-3 with a dominant-negative low-density lipoprotein receptor-related protein 5 (DN-LRP5) coreceptor showed similar biological effects as Frzb/sFRP3 transfection. Together, these data suggest that Frzb/sFRP3 and DN-LRP5 exhibit antitumor activity through the reversal of epithelial-tomesenchymal transition and inhibition of MMP activities in a subset of prostate cancer. (Cancer Res 2005; 65(21): 9762-70)

Interferon-c (IFN-c)-preactivated mesenchymal stem cells (MSC-c) are highly immunosuppressive but immunogenic in vivo due to their inherent expression of major histocompatibility (MHC) molecules. Here, we present an improved approach where we modified human bone marrowderived MSC with interleukin-17A (MSC-17) to enhance T cell immunosuppression but not their immunogenicity. MSC-17, unlike MSC-c, showed no induction or upregulation of MHC class I, MHC class II, and T cell costimulatory molecule CD40, but maintained normal MSC morphology and phenotypic marker expression. SIGNIFICANCE STATEMENTMesenchymal stem cells (MSC) are potent and promising immunomodulatory cell therapy that have progressed into the clinic for allotransplantation. Cytokine modified MSC show superior immunosuppressive properties compared to unmodified MSC. In this study, we describe the enhanced immunosuppressive properties of MSC generated under the influence of the proinflammatory cytokine interleukin-17A (MSC-17) compared to interferon-gamma pre-treated MSC (MSC-c). Specifically these human MSC-17 have translational potential in transplantation protocols because they do not express MHC class II, thereby reducing their immunogenicity, in addition to avidly promote the formation of induced T regulatory cells.