Tregs from human blood differentiate into nonlymphoid tissue-resident effector cells upon TNFR2 costimulation.

Tregs can facilitate transplant tolerance and attenuate autoimmune and inflammatory diseases. Therefore, it is clinically relevant to stimulate Treg expansion and function in vivo and to create therapeutic Treg products in vitro. We report that TNF receptor 2 (TNFR2) is a unique costimulus for naive, thymus-derived Tregs (tTregs) from human blood that promotes their differentiation into nonlymphoid tissue-resident (NLT-resident) effector Tregs, without Th-like polarization. In contrast, CD28 costimulation maintains a lymphoid tissue-resident (LT-resident) Treg phenotype. We base this conclusion on transcriptome and proteome analysis of TNFR2- and CD28-costimulated CD4+ tTregs and conventional T cells (Tconvs), followed by bioinformatic comparison with published transcriptomic Treg signatures from NLT and LT in health and disease, including autoimmunity and cancer. These analyses illuminate that TNFR2 costimulation promoted tTreg capacity for survival, migration, immunosuppression, and tissue regeneration. Functional studies confirmed improved migratory ability of TNFR2-costimulated tTregs. Flow cytometry validated the presence of the TNFR2-driven tTreg signature in effector/memory Tregs from the human placenta, as opposed to blood. Thus, TNFR2 can be exploited as a driver of NLT-resident tTreg differentiation for adoptive cell therapy or antibody-based immunomodulation in human disease.

CD4+ T cells produce IFN-I to license cDC1s for induction of cytotoxic T-cell activity in human tumors.

CD4+ T cells can "help" or "license" conventional type 1 dendritic cells (cDC1s) to induce CD8+ cytotoxic T lymphocyte (CTL) anticancer responses, as proven in mouse models. We recently identified cDC1s with a transcriptomic imprint of CD4+ T-cell help, specifically in T-cell-infiltrated human cancers, and these cells were associated with a good prognosis and response to PD-1-targeting immunotherapy. Here, we delineate the mechanism of cDC1 licensing by CD4+ T cells in humans. Activated CD4+ T cells produce IFNß via the STING pathway, which promotes MHC-I antigen (cross-)presentation by cDC1s and thereby improves their ability to induce CTL anticancer responses. In cooperation with CD40 ligand (L), IFNß also optimizes the costimulatory and other functions of cDC1s required for CTL response induction. IFN-I-producing CD4+ T cells are present in diverse T-cell-infiltrated cancers and likely deliver "help" signals to CTLs locally, according to their transcriptomic profile and colocalization with "helped/licensed" cDCs and tumor-reactive CD8+ T cells. In agreement with this scenario, the presence of IFN-I-producing CD4+ T cells in the TME is associated with overall survival and the response to PD-1 checkpoint blockade in cancer patients.

Proteomics reveals unique identities of human TGF-ß-induced and thymus-derived CD4+ regulatory T cells.

The CD4+ regulatory T (Treg) cell lineage, defined by FOXP3 expression, comprises thymus-derived (t)Treg cells and peripherally induced (p)Treg cells. As a model for Treg cells, studies employ TGF-ß-induced (i)Treg cells generated from CD4+ conventional T (Tconv) cells in vitro. Here, we describe how human iTreg cells relate to human blood-derived tTreg and Tconv cells according to proteomic analysis. Each of these cell populations had a unique protein expression pattern. iTreg cells had very limited overlap in protein expression with tTreg cells, regardless of cell activation status and instead shared signaling and metabolic proteins with Tconv cells. tTreg cells had a uniquely modest response to CD3/CD28-mediated stimulation. As a benchmark, we used a previously defined proteomic signature that discerns ex vivo naïve and effector Treg cells from Tconv cells and includes conserved Treg cell properties. iTreg cells largely lacked this Treg cell core signature and highly expressed e.g. STAT4 and NFATC2, which may contribute to inflammatory responses. We also used a proteomic signature that distinguishes ex vivo effector Treg cells from Tconv cells and naïve Treg cells. iTreg cells contained part of this effector Treg cell signature, suggesting acquisition of pTreg cell features. In conclusion, iTreg cells are distinct from tTreg cells and share limited features with ex vivo Treg cells at the proteomic level.

Cytokine Mixtures Mimicking the Local Milieu in Patients with Inflammatory Bowel Disease Impact Phenotype and Function of Mesenchymal Stromal Cells.

Locally applied mesenchymal stromal cells (MSCs) have the capacity to promote the healing of perianal fistulas in Crohn's disease (CD) and are under clinical development for the treatment of proctitis in ulcerative colitis (UC). Despite these clinical advances, the mechanism of action of local MSC therapy in inflammatory bowel disease (IBD) is largely unknown. We hypothesized that the local cytokine environment in IBD patients affects the immunomodulatory properties of MSCs. To evaluate this, 11 cytokines were analyzed in inflamed tissues obtained from CD and UC patients. Based on the identified cytokine profiles 4 distinct cytokine mixtures that mimic various inflammatory IBD environments were established. Next, MSCs were cultured in the presence of either of these 4 cytokine mixtures after which the expression of immunomodulatory and tissue regenerative molecules and the capacity of MSCs to modulate T-cell proliferation and dendritic cell (DC) differentiation were assessed. Our data show that MSCs respond, in a cytokine-specific manner, by upregulation of immunomodulatory and tissue regenerative molecules, including cyclooxygenase-2, indoleamine 2,3-dioxygenase, and transforming growth factor-ß1. Functional studies indicate that MSCs exposed to a cytokine profile mimicking one of the 2 UC cytokine milieus were less effective in inhibition of DC differentiation. In conclusion, our data indicate that cytokine mixes mimicking the local cytokine milieus of inflamed UC colonic or CD fistulas tissues can differentially affect the immunomodulatory and tissue regenerative characteristics of MSCs. These data support the hypothesis that the local intestinal cytokine milieu serves as a critical factor in the efficacy of local MSC treatment.

TNFR2 Costimulation Differentially Impacts Regulatory and Conventional CD4+ T-Cell Metabolism.

CD4+ conventional T cells (Tconvs) mediate adaptive immune responses, whereas regulatory T cells (Tregs) suppress those responses to safeguard the body from autoimmunity and inflammatory diseases. The opposing activities of Tconvs and Tregs depend on the stage of the immune response and their environment, with an orchestrating role for cytokine- and costimulatory receptors. Nutrient availability also impacts T-cell functionality via metabolic and biosynthetic processes that are largely unexplored. Many data argue that costimulation by Tumor Necrosis Factor Receptor 2 (TNFR2) favors support of Treg over Tconv responses and therefore TNFR2 is a key clinical target. Here, we review the pertinent literature on this topic and highlight the newly identified role of TNFR2 as a metabolic regulator for thymus-derived (t)Tregs. We present novel transcriptomic and metabolomic data that show the differential impact of TNFR2 on Tconv and tTreg gene expression and reveal distinct metabolic impact on both cell types.

Multipotent stromal cells induce human regulatory T cells through a novel pathway involving skewing of monocytes toward anti-inflammatory macrophages.

Multipotent stromal cells (MSC) have been shown to possess immunomodulatory capacities and are therefore explored as a novel cellular therapy. One of the mechanisms through which MSC modulate immune responses is by the promotion of regulatory T cell (Treg) formation. In this study, we focused on the cellular interactions and secreted factors that are essential in this process. Using an in vitro culture system, we showed that culture-expanded bone marrow-derived MSC promote the generation of CD4(+) CD25(hi) FoxP3(+) T cells in human PBMC populations and that these populations are functionally suppressive. Similar results were obtained with MSC-conditioned medium, indicating that this process is dependent on soluble factors secreted by the MSC. Antibody neutralization studies showed that TGF-ß1 mediates induction of Tregs. TGF-ß1 is constitutively secreted by MSC, suggesting that the MSC-induced generation of Tregs by TGF-ß1 was independent of the interaction between MSC and PBMC. Monocyte-depletion studies showed that monocytes are indispensable for MSC-induced Treg formation. MSC promote the survival of monocytes and induce differentiation toward macrophage type 2 cells that express CD206 and CD163 and secrete high levels of IL-10 and CCL-18, which is mediated by as yet unidentified MSC-derived soluble factors. CCL18 proved to be responsible for the observed Treg induction. These data indicate that MSC promote the generation of Tregs. Both the direct pathway through the constitutive production of TGF-ß1 and the indirect novel pathway involving the differentiation of monocytes toward CCL18 producing type 2 macrophages are essential for the generation of Tregs induced by MSC.

The impact of cell source, culture methodology, culture location, and individual donors on gene expression profiles of bone marrow-derived and adipose-derived stromal cells.

Bone marrow (BM) stromal cells (MSCs), also known as mesenchymal stem cells, display a high degree of heterogeneity. To shed light on the causes of this heterogeneity, MSCs were collected from either human BM (n=5) or adipose tissue (AT) (n=5), and expanded using 2 different culture methods: one based on fetal calf serum, and one based on human platelet lysate. After initial expansion, MSCs were frozen, and the vials were transported to 3 different laboratories and grown for 1 passage using the same brand of culture plastic, medium, and supplements. Subsequently, the cells were harvested and assayed for their gene expression profile using the Affymetrix exon microarray platform. Based on gene expression profiles, the most discriminative feature was the anatomical harvesting site, followed by culture methodology. Remarkably, genes in the WNT pathway were expressed at higher levels in BM-derived MSCs than in AT-derived MSCs. Although differences were found between laboratories, cell culture location only slightly affects heterogeneity. Furthermore, individual donors contributed marginally to the observed differences in transcriptomes. Finally, BM-derived MSCs displayed the highest level of similarity, irrespective their culture conditions, when compared to AT-derived cells.

Transmaternal cell flow leads to antigen-experienced cord blood.

Umbilical cord blood (UCB) is used for HSCT. It is known that UCB can comprise Ag-specific T cells. Here we question whether solely transmaternal cell flow may immunize UCB. Twenty-three female UCB samples were collected from healthy mothers and analyzed for minor histocompatibility Ag HY-specific responses. Forty-two of 104 tetramer(pos) T-cell clones, isolated from 16 of 17 UCB samples, showed male-specific lysis in vitro. Male microchimerism was present in 6 of 12 UCB samples analyzed. In conclusion, female UCB comprises HY-specific cytotoxic T cells. The immunization is presumably caused by transmaternal cell flow of male microchimerism present in the mother. The presence of immune cells in UCB that are not directed against maternal foreign Ags is remarkable and may explain the reported clinical observation of improved HSCT outcome with younger sibling donors.

In situ detection of HY-specific T cells in acute graft-versus-host disease-affected male skin after sex-mismatched stem cell transplantation.

HY-specific T cells are presumed to play a role in acute graft-versus-host disease (aGVHD) after female-to-male stem cell transplantation (SCT). However, infiltrates of these T cells in aGVHD-affected tissues have not yet been reported. We evaluated the application of HLA-A2/HY dextramers for the in situ detection of HY-specific T cells in cryopreserved skin biopsy specimens. We applied the HLA-A2/HY dextramers on cryopreserved skin biopsy specimens from seven male HLA-A2(+) pediatric patients who underwent stem cell transplantation with confirmed aGVHD involving the skin. The dextramers demonstrated the presence of HY-specific T cells. In skin biopsy specimens of three male recipients of female grafts, 68% to 78% of all skin-infiltrating CD8(+) T cells were HY-specific, whereas these cells were absent in biopsy specimens collected from sex-matched patient-donor pairs. Although this study involved a small and heterogeneous patient group, our results strongly support the hypothesis that HY-specific T cells are actively involved in the pathophysiology of aGVHD after sex-mismatched stem cell transplantation.

Exogenous Addition of Minor H Antigen HA-1+ Dendritic Cells to Skin Tissues Ex Vivo Causes Infiltration and Activation of HA-1-Specific Cytotoxic T Cells.

T cells specific for hematopoietic system restricted minor Histocompatibility (H) antigens target normal and malignant hematopoietic cells. Thus, cellular immune responses against the latter miHAS eradicate the recipient's hematopoiesis including residual leukemic cells after HLA-matched minor H antigen-mismatched stem-cell transplantation (SCT). However, there are controversial reports on the role of HA-1 in the development of graft-versus-host-disease (GVHD) as well. Here, we address the behavior of HA-1-specific cytotoxic T cells (CTLs) in an ex vivo in situ skin explant model wherein HA-1-expressing dendritic cells (DCs) were added as antigen-presenting cells (APCs). Infiltration and activation of HA-1 CTLs occurred only in those cases where both HLA-A2 and HA-1 were expressed, either by the skin or by the DCs, or by the combination of HLA-A2(+) skin and HA-1(+) DCs. These results point toward the role of recipient's HA-1(+) DCs in the chimeric patient suffering from GVHD after HA-1-mismatched SCT. Although in our model the infiltrated and activated CTLs did not cause skin tissue destruction, our results provide a first step in understanding the reported association of HA-1 mismatching with clinical GVHD.

Gene therapy with IgG-HY fusion proteins to reduce male-specific T-cell reactivity in vitro.

Graft-versus-host disease is still a major complication in stem-cell transplantation. In HLA-identical stem-cell transplantation, mismatches in minor histocompatibility antigens contribute to the development of graft-versus-host disease. As treatment of graft-versus-host disease with immunosuppressive drugs potentially also reduces the graft-versus-leukemia responses, antigen-specific tolerance induction may be used to reduce graft-versus-host disease while leaving the graft-versus-leukemia responses intact. In mouse models, induction of antigen-specific tolerance using IgG-antigen-transduced B cells can prevent and ameliorate autoimmunity. In this study, the principle of the in vivo animal model has been applied to a human in vitro model wherein induction of tolerance against the HLA class II-restricted male-specific minor histocompatibility antigen RPS4Y1 has been analyzed. T cells precultured in the presence of B cells expressing the IgG-coupled HY antigen showed reduced responsiveness selectively against the minor HY antigen RPS4Y1 in different in vitro protocols. These first observations serve as a basis for further studying and understanding the tolerizing potential of IgG constructs with human T cells.

In situ visualization of antigen-specific T cells in cryopreserved human tissues.

Tetrameric MHC/peptide complexes are important tools for analyzing antigen-specific T cells. The in situ use of tetrameric MHC/peptide complexes in viable tissue sections has several shortcomings: it does not allow the execution of multiple analyses on one single biopsy, the storage of the biopsies, and the co-staining of the tetramer-positive cells for various intracellular molecules. We have developed a novel approach using overnight pre-labeling of viable human tissues with MHC/peptide tetramers, followed by cryopreservation and labeling of the cryosections. The visualization of antigen-specific T cells, combined with detection of other membrane, cytoplasmic, or nuclear markers is now feasible.

Efficient induction of minor histocompatibility antigen HA-1-specific cytotoxic T-cells using dendritic cells retrovirally transduced with HA-1-coding cDNA.

Cytotoxic T-cells (CTLs) specific for the hematopoietic system-restricted minor histocompatibility antigen (mHag) HA-1 efficiently lyse HA-1-positive leukemic cells without affecting nonhematopoietic cells. HA-1-specific CTLs are thus potential tools for adoptive immunotherapy of relapsed leukemia after HLA-matched-HA-1-mismatched stem cell transplantation (SCT). In vitro generation of HA-1-specific CTLs from SC donors is possible using dendritic cells (DCs) pulsed with synthetic HA-1 peptide as stimulator cells. However, this approach requires at least 6 weeks of in vitro culturing under GMP (good manufacturing practice) conditions. Our data show that in vitro induction of HA-1-specific CTLs is more rapid with the use of DCs that are retrovirally transduced with the HA-1 complementary DNA. Retrovirally transduced DCs showed functional and long-term stable expression of the HA-1 CTL epitope in primary CTL cultures. In 4 SC donors, HA-1-transduced DCs induced HA-1-specific CTLs in 14 to 21 days. The in vitro-generated CTL lines contained 6% to 9% T-cells that stained brightly with tetrameric HLA-A2/HA-1 peptide complexes (HA-1(A2) tetramer) and showed significant lysis of HA-1+ leukemic cells. The CTL induction procedure using peptide-pulsed DCs was less effective and required 28 to 35 days of T-cell culture. Thus, sustained presentation of mHag HA-1 by retrovirally transduced DCs facilitates the in vitro induction of HA-1-specific CTLs.

Generation of minor histocompatibility antigen HA-1-specific cytotoxic T cells restricted by nonself HLA molecules: a potential strategy to treat relapsed leukemia after HLA-mismatched stem cell transplantation.

Successful stem cell transplantation (SCT) across HLA barriers can be performed with cord blood, megadoses of stem cells, or with nonmyeloablative conditioning strategies. Because the HLA-mismatched transplants are often T-cell depleted, leukemia relapse rates are high. Treatment of relapsed leukemia after HLA-mismatched SCT is difficult. A novel potential strategy to treat relapsed leukemia after HLA-mismatched SCT is the use of patients' mismatched HLA molecules as antigen-presenting molecules to generate hematopoietic system-specific cytotoxic T cells (CTLs) from the stem cell donor. Adoptive transfer of these hematopoietic system-specific CTLs that are restricted by nonself HLA molecules may eliminate leukemia without affecting the patient's nonhematopoietic cells or donor hematopoietic cells. We investigated the feasibility of this strategy using the hematopoietic system-specific minor histocompatibility antigen HA-1, which is known to induce HLA-A2-restricted CTLs. HLA-A2(-) peripheral blood mononuclear cells were stimulated with HLA-A2(+) T2 cells pulsed with synthetic HA-1 peptide or with dendritic cells transduced with the HA-1 cDNA. Tetrameric HLA-A2/HA-1 peptide complexes were used to monitor and enrich HA-1-specific CTLs. In the alloreactive cultures, HA-1-specific CTLs were enriched up to 7% by 3 rounds of antigen-specific stimulations and up to 87% by fluorescence-activated cell sorting of tetramer-positive T cells. The HA-1-specific CTLs showed specific lysis of the relevant target cells, including leukemic cells. Because the polyclonal CTL cultures also contained natural killer cells and allo-HLA-A2-specific CTLs, CTL clones were generated that showed the expected HA-1 specificity only. Thus, HA-1-specific CTLs restricted by nonself HLA-A2 molecules can be generated in an HLA-A2-mismatched setting.

Exclusive TCRVbeta chain usage of ex vivo generated minor Histocompatibility antigen HA-1 specific cytotoxic T cells: implications for monitoring of immunotherapy of leukemia by TCRBV spectratyping.

Tissue expression of minor Histocompatibility antigens HA-1 and HA-2 is limited to the hematopoietic system. Therefore, ex vivo generated HA-1/HA-2 specific cytotoxic T lymphocytes (CTLs) can be applied for adoptive immunotherapy of relapsed leukemia after HLA-matched HA-1/HA-2 mismatched stem cell transplantation. Here we used T cell receptor beta variable chain (TCRBV) spectratyping and/or TCRBV sequencing to monitor the specific TCR usage in eleven HA-1/HA-2 CTLs that were induced ex vivo with peptide pulsed dendritic cells. The HA-2 induced CTLs used different TCRBV. In contrast, the development of HA-1 specific CTLs coincided with prominent skewing of TCRBV7 spectratypes. Sequencing of the TCRBV7 specific PCR products used by these ex vivo generated HA-1 CTLs revealed the exclusive usage of TCRBV7-9*03, identical to the TCRBV used by HA-1 specific CTLs induced in vivo after stem cell transplantation. Thus, monitoring of immunotherapy with HA-1 specific CTLs is now also feasible by TCRBV spectratyping.