Kathy Forner

Mesenchymal Stromal Cells Ameliorate Experimental Autoimmune Encephalomyelitis by Inhibiting CD4 Th17 T Cells in a CC Chemokine Ligand 2-Dependent Manner

The administration of ex vivo culture-expanded mesenchymal stromal cells (MSCs) has been shown to reverse symptomatic neuroinflammation observed in experimental autoimmune encephalomyelitis (EAE). The mechanism by which this therapeutic effect occurs remains unknown. In an effort to decipher MSC mode of action, we found that MSC conditioned medium inhibits EAE-derived CD4 T cell activation by suppressing STAT3 phosphorylation via MSC-derived CCL2. Further analysis demonstrates that the effect is dependent on MSC-driven matrix metalloproteinase proteolytic processing of CCL2 to an antagonistic derivative. We also show that antagonistic CCL2 suppresses phosphorylation of AKT and leads to a reciprocal increased phosphorylation of ERK associated with an up-regulation of B7.H1 in CD4 T cells derived from EAE mice. CD4 T cell infiltration of the spinal cord of MSC-treated group was robustly decreased along with reduced plasma levels of IL-17 and TNF-α levels and in vitro from restimulated splenocytes. The key role of MSC-derived CCL2 was confirmed by the observed loss of function of CCL2−/− MSCs in EAE mice. In summary, this is the first report of MSCs modulating EAE biology via the paracrine conversion of CCL2 from agonist to antagonist of CD4 Th17 cell function.

Mesenchymal stromal cell-derived CCL2 suppresses plasma cell immunoglobulin production via STAT3 inactivation and PAX5 induction

We demonstrate that the secretome of mesenchymal stromal cells (MSCs) suppresses plasma cell (PC) immunoglobulin (Ig) production, induces plasmablast proliferation, and leads to interleukin-10-mediated blockade in vitro. We found that these effects are the result of MSC-derived CC chemokine ligands CCL2 and CCL7. More specifically, MSCs further processed these CC chemokines by the activity of matrix metalloproteinases (MMPs), leading to the generation of proteolytically processed antagonistic CCL2 variant. Neutralizing CCL2 or inhibiting MMP enzymatic activity abolished the PC-suppressive effect of MSCs. We also observed that MMP-processed CCL2 suppresses signal transducer and activator of transcription 3 (STAT3) activation in PC. As a result, the transcription factor PAX5 is induced, thus explaining the inhibition of Ig synthesis. The absence of inhibitory effects by MSC on the humoral response of CCR2(-/-) mice to xenoantigen suggests that MMP-cleaved CCL2/CCR2 interaction as well as downstream phosphatase activity is necessary for antagonistic effect. We tested syngeneic MSCs in hemophilic B6 mice with predeveloped antihuman factor VIII (hFVIII) antibodies and demonstrated a robust decrease in hFVIII-specific IgG levels. Thus, MSCs may play a role in modulating Ig production by PCs via MMP processing of CCL2 and may represent an appealing cell therapy approach for pathologic humoral responses.

Human marrow-derived mesenchymal stromal cells decrease cisplatin renotoxicity in vitro and in vivo and enhance survival of mice post-intraperitoneal injection

Acute kidney injury (AKI) can occur from the toxic side-effects of chemotherapeutic agents such as cisplatin. Bone marrow-derived mesenchymal stromal cells (MSCs) have demonstrated wide therapeutic potential often due to beneficial factors they secrete. The goal of this investigation was to evaluate in vitro the effect of human MSCs (hMSCs) secretome on cisplatin-treated human kidney cells, and in vivo the consequence of hMSCs intraperitoneal (ip) implantation in mice with AKI. Our results revealed that hMSCs-conditioned media improved survival of HK-2 human proximal tubular cells exposed to cisplatin in vitro. This enhanced survival was linked to increased expression of phosphorylated Akt (Ser473) and was reduced by a VEGF-neutralizing antibody. In vivo testing of these hMSCs established that ip administration in NOD-SCID mice decreased cisplatin-induced kidney function impairment, as demonstrated by lower blood urea nitrogen levels and higher survival. In addition, blood phosphorous and amylase levels were also significantly decreased. Moreover, hMSCs reduced the plasma levels of several inflammatory cytokines/chemokines. Immunohistochemical examination of kidneys showed less apoptotic and more proliferating cells. Furthermore, PCR indicated the presence of hMSCs in mouse kidneys, which also showed enhanced expression of phosphorylated Akt. In conclusion, our study reveals that hMSCs can exert prosurvival effects on renal cells in vitro and in vivo, suggests a paracrine contribution for kidney protective abilities of hMSCs delivered ip, and supports their clinical potential in AKI.

Novel TGF-β Antagonist Inhibits Tumor Growth and Angiogenesis by Inducing IL-2 Receptor-Driven STAT1 Activation

Carcinoma derived TGF-β acts as a potent pro-oncogenic factor and suppresses antitumor immunity. To antagonize TGF-β–mediated effects in tandem with a proinflammatory immune stimulus, we generated a chimeric protein borne of the fusion of IL-2 and the soluble extracellular domain of TGF-βR II (FIST). FIST acts as a decoy receptor trapping active TGF-β in solution and interacts with IL-2–responsive lymphoid cells, inducing a distinctive hyperactivation of STAT1 downstream of IL-2R, which in turn promotes SMAD7 overexpression. Consequently, FIST-stimulated lymphoid cells are resistant to TGF-β–mediated suppression and produce significant amounts of proinflammatory cytokines. STAT1 hyperactivation further induces significant secretion of angiostatic CXCL10. Moreover, FIST upregulates T-bet expression in NK cells promoting a potent Th1-mediated antitumor response. As a result, FIST stimulation completely inhibits pancreatic cancer (PANC02) and melanoma (B16) tumor growth in immunocompetent C57BL/6 mice. In addition, melanoma cells expressing FIST fail to form tumors in CD8−/−, CD4−/−, B cell-deficient (μMT), and beige mice, but not in NOD-SCID and Rag2/γc knockout mice, consistent with the pivotal role of FIST-responsive, cancer-killing NK cells in vivo. In summary, FIST constitutes a novel strategy of treating cancer that targets both the host’s angiogenic and innate immune response to malignant cells.

Selective Inhibition of CCR2 Expressing Lymphomyeloid Cells in Experimental Autoimmune Encephalomyelitis by a GM-CSF-MCP1 Fusokine

We describe the generation of a fusion cytokine consisting of GM-CSF in tandem with N-terminal-truncated MCP-1 (6-76), hereafter GMME1. Treatment of activated T cells with recombinant GMME1 protein leads to proinflammatory cytokine reduction and apoptosis via a CCR2-restricted pathway. Similarly, cell death is triggered in macrophages cultured with GMME1, while an inhibition of Ab production from plasma cells is observed. Treatment of CD4 T cells derived from experimental autoimmune encephalomyelitis mice with GMME1 leads to p38 hyperphosphorylation, inhibition of p44/42, AKT and STAT3 phosphorylation, and caspase-3 activation. GMME1 administration to experimental autoimmune encephalomyelitis mice suppresses symptomatic disease and correlates with decreased levels of inflammatory cytokines including IL-17, MOG-specific Ab titers, and blockade of CD4 and CD8 T cell infiltration in spinal cords. We propose that GMME1 defines a new class of agents for the treatment of autoimmune ailments by selectively targeting lymphomyeloid cells expressing CCR2.

A Dendritic Cell Population Generated by a Fusion of GM-CSF and IL-21 Induces Tumor-Antigen–Specific Immunity

We have previously shown that the fusion of GM-CSF and IL-21 (GIFT-21) possesses a potent immune stimulatory effect on myeloid cells. In this study, we define the effect of GIFT-21 on naive murine monocytes (GIFT-21 dendritic cells [DCs]), which express increased levels of Gr-1, CD45R, MHC class I, CD80, CD86, and CXCR4 and suppress CD11c and MHC class II. Compared with conventional dendritic cells, GIFT-21 DCs produced substantially more CCL2, IL-6, TNF-α, and IFN-α and induced significantly greater production of IFN-γ by CD8+ T cells in MHC class I-restricted Ag presentation assays. B16 melanoma and D2F2 Neu breast cancer growth was inhibited in mice treated with Ag-naive GIFT-21 DCs. This effect was lost in CD8−/− and CCR2−/− mice and when mice were treated with β2-microglobulin–deficient GIFT-21 DCs, indicating that GIFT-21 DCs migrated to and sampled from the tumors to present tumor Ags to CCL2 recruited CD8+ T cells via MHC class I. We propose that autologous GIFT-21 DCs may serve as a cell therapy platform for the treatment of cancer.

Mesenchymal Stromal Cells Expressing ErbB-2/neu Elicit Protective Anti–Breast Tumor Immunity In vivo, which is Paradoxically Suppressed by IFN-γ and Tumor Necrosis Factor-α Priming

It is unknown whether mesenchymal stromal cells (MSC) can regulate immune responses targeting tumor autoantigens of low immunogenicity. We tested here whether immunization with MSC could break immune tolerance towards the ErbB-2/HER-2/neu tumor antigen and the effects of priming with IFN-γ and tumor necrosis factor-α (TNF-α) on this process. BALB/c- and C57BL/6-derived MSC were lentivirally transduced to express a kinase-inactive rat neu mutant (MSC/Neu). Immunization of BALB/c mice with nontreated or IFN-γ-primed allogeneic or syngeneic MSC/Neu induced similar levels of anti-neu antibody titers; however, only syngeneic MSC/Neu induced protective neu-specific CD8(+) T cell responses. Compared to immunization with nontreated or IFN-γ-primed syngeneic MSC/Neu, the number of circulating neu-specific CD8(+) T cells and titers of anti-neu antibodies were observed to be decreased after immunizations with IFN-γ- plus TNF-α-primed MSC/Neu. In addition, syngeneic MSC/Neu seemed more efficient than IFN-γ-primed MSC/Neu at inducing a protective therapeutic antitumor immune response resulting in the regression of transplanted neu-expressing mammary tumor cells. In vitro antigen-presenting cell assays performed with paraformaldehyde-fixed or live MSC showed that priming with IFN-γ plus TNF-α, compared to priming with IFN-γ alone, increased antigen presentation as well as the production of immunosuppressive factors. These data suggest that whereas MSC could effectively serve as antigen-presenting cells to induce immune responses aimed at tumor autoantigens, these functions are critically regulated by IFN-γ and TNF-α.

B Effector Cells Activated by a Chimeric Protein Consisting of IL-2 and the Ectodomain of TGF-β Receptor II Induce Potent Antitumor Immunity

We have previously shown that interleukin (IL)-2 receptor-expressing lymphoid cells stimulated with a chimeric protein linking IL-2 to the ectodomain of TGF-β receptor II (also known as FIST) become resistant to TGF-β-mediated suppression and produce significant amounts of proinflammatory cytokines. In this study, we have characterized the antigen presentation properties of FIST-stimulated B cells (hereafter inducible B effector cells, iBEC). FIST converts naïve splenic B cells to B effector cells characterized by potent antigen presentation properties and production of TNFα and IFNγ. iBECs display hyperphosphorylation of STAT3 and STAT5 downstream of the IL-2 receptor and upregulation of T-bet expression. iBECs maintain B-cell identity based on the expression of PAX5 and CD19 and overexpress Smad7, which confers resistance to TGF-β-mediated suppression of B-cell activation. iBEC antitumor immunity was determined by a mouse model of lymphoma-expressing ovalbumin (E.G7-OVA) as a specific tumor antigen. OVA-pulsed iBECs function as antigen-presenting cells (APC) in vitro by inducing the activation of OVA-specific CD4(+) and CD8(+) T cells, respectively, and in vivo by conferring complete protective immunity against E.G7-OVA tumor challenge. In addition, OVA-pulsed iBECs promote tumor regression in immunocompetent C57Bl/6 mice bearing E.G7-OVA tumors. In conclusion, iBECs represent an entirely novel B cell-derived APC for immune therapy of cancer.