Immune regulatory cell infusion for graft-versus-host disease prevention and therapy

Helios+ and Helios- Treg subpopulations are phenotypically and functionally distinct and express dissimilar TCR repertoires

The transcription factor Helios is expressed in a large subset of Foxp3⁺ Tregs. We previously proposed that Helios is a marker of thymic derived Treg (tTreg), while Helios^- Treg were induced from Foxp3^- T conventional (Tconv) cells in the periphery (pTreg). To compare the two Treg subpopulations, we generated Helios-GFP reporter mice and crossed them to Foxp3-RFP reporter mice. The Helios⁺ Treg population expressed a more activated phenotype, had a slightly higher suppressive capacity in vitro and expressed a more highly demethylated TSDR but were equivalent in their ability to suppress inflammatory bowel disease in vivo. However, Helios⁺ Treg more effectively inhibited the proliferation of activated, autoreactive splenocytes from scurfy mice. When Helios⁺ and Helios^- Treg were transferred to lymphoreplete mice, both populations maintained comparable Foxp3 expression, but Foxp3 expression was less stable in Helios^- Treg when transferred to lymphopenic mice. Gene expression profiling demonstrated a large number of differentially expressed genes and showed that Helios^- Treg expressed certain genes normally expressed in CD4⁺ Foxp3^- T cells. TCR repertoire analysis indicated very little overlap between Helios⁺ and Helios^- Treg. Thus, Helios⁺ and Helios^- Treg subpopulations are phenotypically and functionally distinct and express dissimilar TCR repertoires.

Transiently Activated Human Regulatory T Cells Upregulate BCL-XL Expression and Acquire a Functional Advantage in vivo

Regulatory T cells (Tregs) can control excessive or undesirable immune responses toward autoantigens, alloantigens, and pathogens. In transplantation, host immune responses against the allograft are suppressed through the use of immunosuppressive drugs, however this often results in life-threatening side effects including nephrotoxicity and an increased incidence of cancer and opportunistic infections. Tregs can control graft-vs.-host disease and transplant rejection in experimental models, providing impetus for the use of Tregs as a cellular therapy in clinical transplantation. One of the major barriers to the widespread use of Treg cellular therapy is the requirement to expand cells ex vivo to large numbers in order to alter the overall balance between regulatory and effector cells. Methods that enhance suppressive capacity thereby reducing the need for expansion are therefore of interest. Here, we have compared the function of freshly-isolated and ex vivo-manipulated human Tregs in a pre-clinical humanized mouse model of skin transplantation. Sorted human CD127^loCD25⁺CD4⁺ Tregs were assessed in three different conditions: freshly-isolated, following transient in vitro activation with antiCD3/antiCD28 beads or after ex vivo-expansion for 2 weeks in the presence of antiCD3/antiCD28 beads and recombinant human IL2. While ex vivo-expansion of human Tregs increased their suppressive function moderately, transient in vitro-activation of freshly isolated Tregs resulted in a powerful enhancement of Treg activity sufficient to promote long-term graft survival of all transplants in vivo. In order to investigate the mechanisms responsible for these effects, we measured the expression of Treg-associated markers and susceptibility to apoptosis in activated Tregs. Transiently activated Tregs displayed enhanced survival and proliferation in vitro and in vivo. On a molecular level, Treg activation resulted in an increased expression of anti-apoptotic BCL2L1 (encoding BCL-XL) which may be at least partially responsible for the observed enhancement in function. Our results suggest that in vitro activation of human Tregs arms them with superior proliferative and survival abilities, enabling them to more effectively control alloresponses. Importantly, this transient activation results in a rapid functional enhancement of freshly-isolated Tregs, thereby providing an opportunity to eliminate the need for in vitro expansion in select circumstances. A protocol employing this technique would therefore benefit from a reduced requirement for large cell numbers for effective therapy.

Strategies for Enhancing and Preserving Anti-leukemia Effects Without Aggravating Graft-Versus-Host Disease

Allogeneic stem cell transplantation (allo-SCT) is a curable method for the treatment of hematological malignancies. In the past two decades, the establishment of haploidentical transplant modalities make “everyone has a donor” become a reality. However, graft-versus-host disease (GVHD) and relapse remain the major two causes of death either in the human leukocyte antigen (HLA)-matched transplant or haploidentical transplant settings, both of which restrict the improvement of transplant outcomes. Preclinical mice model showed that both donor-derived T cells and natural killer (NK) cells play important role in the pathogenesis of GVHD and the effects of graft-versus-leukemia (GVL). Hence, understanding the immune mechanisms of GVHD and GVL would provide potential strategies for the control of leukemia relapse without aggravating GVHD. The purpose of the current review is to summarize the biology of GVHD and GVL responses in preclinical models and to discuss potential novel therapeutic strategies to reduce the relapse rate after allo-SCT. We will also review the approaches, including optimal donor selection and, conditioning regimens, donor lymphocyte infusion, BCR/ABL-specific CTL, and chimeric antigen receptor-modified T cells, which have been successfully used in the clinic to enhance and preserve anti-leukemia activity, especially GVL effects, without aggravating GVHD or alleviate GVHD.

Effects of mesenchymal stem cell therapy on alopecia areata in cellular and hair follicle organ culture models

Mesenchymal stem cell therapy (MSCT) has been suggested as a new therapeutic strategy for immunological disorders. There have been only a few attempts to treat alopecia areata (AA) with MSCT. MSCT efficacy and mechanism of action in treating AA are not known. We sought to investigate the effect of human hematopoietic mesenchymal stem cells (hHMSCs) on an in vitro model of AA and to explore relevant mechanisms that regulate efficacy. An AA-like environment was induced by pretreatment of human dermal papilla cells (hDPCs) with interferon gamma (IFN-γ). hHMSCs were administered to the hDPCs, and cell viability was determined. Similar studies were also conducted with human hair follicles (HFs) in culture. The change in expression of the Wnt/β-catenin pathway and JAK/STAT pathway-related molecules and growth factors in hHMSC-treated hDPCs was also examined by reverse transcription-PCR, Western blot assay and growth factor array. Immune privilege-related molecules were examined by immunohistochemistry in HF culture models. hHMSCs enhanced the cell viability of the hDPCs. hHMSCs activated several molecules in the Wnt/β-catenin signalling pathway, including ß-catenin and phosphorylated GSK3b, and decreased IFN-γ-induced expression of DKK1 in hDPCs. hHMSCs suppressed IFN-γ-induced expression of caspase-1, caspase-3 and IFN-γ receptor. hHMSCs induced the phosphorylation of STAT1 and STAT3 compared to controls and IFN-γ-pretreated hDPCs. hHMSC-treated HFs enhanced several growth factor mRNAs. hHMSC pretreatment modulated IFN-γ-induced expression of molecules related to HF immune privilege on HFs in organ culture. These data suggest MSCT may be a new potential therapeutic option in treating AA.

Donor-derived marrow mesenchymal stromal cell co-transplantation following a haploidentical hematopoietic stem cell transplantation trail to treat severe aplastic anemia in children

Haploidentical hematopoietic stem cell transplantation (haplo-HSCT) is associated with an increased risk of graft failure and severe graft-versus-host disease (GVHD). Recent studies have shown that mesenchymal stromal cells (MSCs) display potent immunosuppressive effects and can support normal hematopoiesis. In a multi-center trial, we co-transplanted culture-expanded donor-derived bone marrow MSCs (BM-MSCs) into 35 children with severe aplastic anemia (SAA) undergoing haplo-HSCT. All 35 patients (100%) achieved hematopoietic reconstitution and showed sustained full donor chimerism. The median time for myeloid engraftment was 14 days (range 10-22 days), while that for platelet engraftment was 18 days (range 9-36 days). The incidence of grade II-IV acute GVHD and chronic GVHD was 25.71 and 22.86%, respectively. The overall survival rate was 85.71% with a median of 22 months (range 3.5-37 months). The combined transplantation of haploidentical HSCs and BM-MSCs into children with SAA without an HLA-identical sibling donor is relatively safe and may represent an effective new therapy to improve survival rates and reduce the risk of graft failure.

Stabilization of Foxp3 by Targeting JAK2 Enhances Efficacy of CD8 Induced Regulatory T Cells in the Prevention of Graft-versus-Host Disease

CD8⁺ induced regulatory T cells (iTregs) have been identified to suppress alloreactive immune responses and expressed regulatory T cell (Treg) ontological markers as similar as CD4⁺ iTregs. However, adoptive transfer of CD8⁺ iTreg-based therapy is hampered by the instability of Treg specific-transcription factor, Foxp3. As CD8⁺ iTregs were previously demonstrated to possess superior tumor-killing ability to CD4⁺ iTregs, adoptive transfer of stabilized CD8⁺ iTregs would be a potential therapy to prevent tumor relapse during graft-versus-leukemia disease (GVHD) treatment. In the current study, we generated alloantigen reactive CD8⁺ iTregs from JAK2^-/- T cells and adoptively transferred them to MHC-mismatched and haploidentical murine models of allogeneic bone marrow transplantation. JAK2^-/- CD8⁺ iTregs not only attenuated GVHD but also preserved graft-versus-leukemia effect. Mechanistic analysis revealed that JAK2^-/- CD8⁺ iTregs upregulated natural Treg marker (neuropilin-1), and augmented DNA demethylation of CNS2 region within Foxp3 gene. These properties licensed JAK2^-/- CD8⁺ iTregs to retain high Foxp3 expression resulting in less conversion to type 1 CTLs; as a result, JAK2^-/- CD8⁺ iTregs were able to maintain their suppressive and cytolytic function. Thus, our findings provide a strong rationale and means to stabilize CD8⁺ iTregs by targeting JAK2, and the stabilized CD8⁺ iTregs exhibit therapeutic potential for alleviating GVHD and preserving the graft-versus-leukemia effect.