Mesenchymal stem cells express serine protease inhibitor to evade the host immune response.

Clinical trials using mesenchymal stem cells (MSCs) have been initiated worldwide. An improved understanding of the mechanisms by which allogeneic MSCs evade host immune responses is paramount to regulating their survival after administration. This study has focused on the novel role of serine protease inhibitor (SPI) in the escape of MSCs from host immunosurveillance through the inhibition of granzyme B (GrB). Our data indicate bone marrow-derived murine MSCs express SPI6 constitutively. MSCs from mice deficient for SPI6 (SPI6(-/-)) exhibited a 4-fold higher death rate by primed allogeneic cytotoxic T cells than did wild-type MSCs. A GrB inhibitor rescued SPI6(-/-) MSCs from cytotoxic T-cell killing. Transduction of wild-type MSCs with MigR1-SPI6 also protected MSCs from cytotoxic T cell-mediated death in vitro. In addition, SPI6(-/-) MSCs displayed a shorter lifespan than wild-type MSCs when injected into an allogeneic host. We conclude that SPI6 protects MSCs from GrB-mediated killing and plays a pivotal role in their survival in vivo. Our data could serve as a basis for future SPI-based strategies to regulate the survival and function of MSCs after administration and to enhance the efficacy of MSC-based therapy for diseases.

The novel role of SERPINB9 in cytotoxic protection of human mesenchymal stem cells.

Clinical trials using allogeneic mesenchymal stem cells (MSCs) are ongoing for the purpose of providing therapeutic benefit for a variety of human disorders. Pertinent to their clinical use are the accessibility to sufficient quantities of these cells allowing for repetitive administration, as well as a better understanding of the specific mechanisms by which allogeneic MSCs evade host immune responses that in turn influence their life span following administration. In this report, we sought to characterize and compare human peripheral blood MSCs (hPB-MSCs) with bone marrow-derived MSCs. hPB-MSCs met the established criteria to characterize this cellular lineage, including capacity for self-renewal, differentiation into tissues of mesodermal origin, and expression of phenotypic surface markers. In addition, hPB-MSCs suppressed alloreactive proliferation as well as the production of proinflammatory cytokines. Examination of the mechanisms by which allogeneic MSCs evade the host immune response, which is crucial for their therapeutic use, demonstrated that constitutive expression of serine protease inhibitor 9 (PI-9) on hPB-MSCs and bone marrow-derived MSCs is a major defense mechanism against granzyme B-mediated destruction by NK cells. Similarly, MSCs treated with small interfering RNA for PI-9 increased MSC cellular death, whereas expression of transgenic PI-9 following retroviral transduction protected MSCs. These data significantly advance our understanding of the immunomodulatory role for hPB-MSCs as well as the mechanisms by which they evade host immune responses. These findings contribute to the development of MSC-based therapies for diseases.

Polylactide-cyclosporin A nanoparticles for targeted immunosuppression.

Polymeric nanoparticles (NPs), prepared via coprecipitation of drugs and polymers, are promising drug delivery vehicles for treating diseases with improved efficacy and reduced toxicity. Here, we report an unprecedented strategy for preparing polylactide-cyclosporine A (PLA-CsA) NPs (termed CsA-NPs) through CsA-initiated ring-opening polymerization of lactide (LA) followed by nanoprecipitation. The resulting CsA-NPs have sub-100 nm sizes and narrow particle size distributions, and release CsA in a sustained manner without a "burst"-release effect. Both free CsA and CsA-NPs displayed comparable suppression of T-cell proliferation and production of inflammatory cytokines in various T-cell assays in a dose-dependent manner. The IC(50) values for CsA and CsA-NPs were 27.5 and 72.0 ng/ml, respectively. As lymph nodes are the main loci for T-cell activation, we coupled dendritic cells (DCs) with CsA-NPs and successfully delivered CsA selectively to the lymph nodes. Our studies indicated that CsA-NPs could be internalized in the DCs with a sustained release of CsA to the culture medium, suppressing alloreactive T-cell proliferation. Allogeneic DCs loaded with CsA-NPs were able to migrate to the draining lymph nodes where the T-cell priming was significantly reduced without any systemic release. This innovative nanoparticulate CsA delivery technology constitutes a strong basis for future targeted delivery of immunosuppressive drugs with improved efficiency and reduced toxicity.

The novel therapeutic effect of phosphoinositide 3-kinase-γ inhibitor AS605240 in autoimmune diabetes.

Type 1 diabetes (T1D) remains a major health problem worldwide, with a steadily rising incidence yet no cure. Phosphoinositide 3-kinase-γ (PI3Kγ), a member of a family of lipid kinases expressed primarily in leukocytes, has been the subject of substantial research for its role in inflammatory diseases. However, the role of PI3Kγ inhibition in suppressing autoimmune T1D remains to be explored. We tested the role of the PI3Kγ inhibitor AS605240 in preventing and reversing diabetes in NOD mice and assessed the mechanisms by which this inhibition abrogates T1D. Our data indicate that the PI3Kγ pathway is highly activated in T1D. In NOD mice, we found upregulated expression of phosphorylated Akt (PAkt) in splenocytes. Notably, T regulatory cells (Tregs) showed significantly lower expression of PAkt compared with effector T cells. Inhibition of the PI3Kγ pathway by AS605240 efficiently suppressed effector T cells and induced Treg expansion through the cAMP response element-binding pathway. AS605240 effectively prevented and reversed autoimmune diabetes in NOD mice and suppressed T-cell activation and the production of inflammatory cytokines by autoreactive T cells in vitro and in vivo. These studies demonstrate the key role of the PI3Kγ pathway in determining the balance of Tregs and autoreactive cells regulating autoimmune diabetes.

Immunohistochemical markers of tissue injury in biopsies with transplant glomerulitis.

Transplant glomerulitis is associated with suboptimal graft function. To understand its pathogenesis and to assess the parameters of potential prognostic value, we immunostained 25 paraffin-embedded allograft biopsies showing glomerulitis for markers of complement activation (C4d), cytotoxicity (Granzyme-B), apoptosis (Bcl-XL, Bcl-2, and Fas-L), and endothelial injury (von Willebrand factor). Staining was semiquantitatively assessed in different anatomical compartments, and comparison was made with 40 control allograft biopsies without glomerulitis. Biopsies with glomerulitis had more frequent incidence of "mixed" T-cell and antibody-mediated rejection compared with controls [8/25 (32%) versus 4/40 (10%), P = .046]. Furthermore, they had higher glomerular capillary-C4d scores (1.9 ± 1.1 versus 1.2 ± 1.2, P = .015), which tended to persist when biopsies showing transplant glomerulopathy were excluded. Higher glomerular capillary-C4d scores were observed in samples with versus without donor-specific antibody (2.5 ± 0.9 versus 1.2 ± 1.2, P = .01). Compared with controls, biopsies with glomerulitis had more intraglomerular (4.8 ± 4.5 versus 0.9± 0.8 cells/glomerulus, P < .001) and interstitial mainly peritubular capillary (6.1 ± 4.1 versus 3.2 ± 3.4 cells/hpf, P = .002) Granzyme-B(+) leukocytes. Higher mesangial-von Willebrand factor scores were noted in the glomerulitis group (1.8 ± 1.0 versus 0.8 ± 0.8, P = .003) and correlated with the percentage of inflamed glomeruli (r = 0.54, P < .001). Interstitial-von Willebrand factor was associated with a higher peritubular capillaritis score (interstitial-von Willebrand factor: 1.6 ± 1.2 versus no interstitial-von Willebrand factor: 0.6 ± 0.9, P = .02). Glomerular capillary-Bcl-XL was not associated with accommodation. Finally, no difference in Bcl-2 or Fas-L was observed upon comparing glomerulitis to controls. In conclusion, glomerular injury in transplant glomerulitis appears to be mediated by complement activation and cellular cytotoxicity. Mesangial- or interstitial-von Willebrand factor identified cases with more severe microcirculation injury.