Rebekka Wehner

Identification of SOX2 as a novel glioma-associated antigen and potential target for T cell-based immunotherapy.

Prognosis for patients suffering from malignant glioma has not substantially improved. Specific immunotherapy as a novel treatment concept critically depends on target antigens, which are highly overexpressed in the majority of gliomas, but the number of such antigens is still very limited. SOX2 was identified by screening an expression database for transcripts that are overexpressed in malignant glioma, but display minimal expression in normal tissues. Expression of SOX2 mRNA was further investigated in tumour and normal tissues by real-time PCR. Compared to cDNA from pooled normal brain, SOX2 was overexpressed in almost all (9 out of 10) malignant glioma samples, whereas expression in other, non-malignant tissues was almost negligible. SOX2 protein expression in glioma cell lines and tumour tissues was verified by Western blot and immunofluorescence. Immunohistochemistry demonstrated SOX2 protein expression in all malignant glioma tissues investigated ranging from 6 to 66% stained tumour cells. Human leucocyte antigen-A*0201-restricted SOX2-derived peptides were tested for the activation of glioma-reactive CD8+ cytotoxic T lymphocytes (CTLs). Specific CTLs were raised against the peptide TLMKKDKYTL and were capable of lysing glioma cells. The abundant and glioma-restricted overexpression of SOX2 and the generation of SOX2-specific and tumour-reactive CTLs may recommend this antigen as target for T-cell-based immunotherapy of glioma.

Immunomodulatory Properties of Mesenchymal Stromal Cells and Their Therapeutic Consequences for Immune-Mediated Disorders

Bone marrow-derived mesenchymal stromal cells (MSCs) represent a population of nonhematopoietic cells, which play a crucial role in supporting hematopoiesis and can differentiate into various cell types such as osteocytes, chondrocytes, adipocytes, and myocytes. Due to their differentiation capability, MSCs emerge as promising candidates for therapeutic applications in tissue engineering. In addition, they display immunomodulatory properties that have prompted consideration of their potential use for treatment modalities aimed at the inhibition of immune responses. In this context, MSCs efficiently inhibit maturation, cytokine production, and T-cell stimulatory capacity of dendritic cells (DCs). They also markedly impair proliferation, cytokine secretion, and cytotoxic potential of natural killer cells and T lymphocytes. Furthermore, MSCs are able to inhibit the proliferation of B cells and their capacity to produce antibodies. Various animal models confirm the immunomodulatory properties of MSCs. Thus, administered MSCs prolong the survival of skin and cardiac allografts and ameliorate acute graft-versus-host disease (GVHD) as well as experimental autoimmune encephalomyelitis. Clinical studies enrolling patients with severe acute GVHD reveal that the administration of MSCs results in significant clinical responses. Due to their immunomodulatory capability and their low immunogenicity, MSCs represent promising candidates for the prevention and treatment of immune-mediated diseases.

Chimeric Antigen Receptor-Engineered T Cells for Immunotherapy of Cancer

CD4+ and CD8+ T lymphocytes are powerful components of adaptive immunity, which essentially contribute to the elimination of tumors. Due to their cytotoxic capacity, T cells emerged as attractive candidates for specific immunotherapy of cancer. A promising approach is the genetic modification of T cells with chimeric antigen receptors (CARs). First generation CARs consist of a binding moiety specifically recognizing a tumor cell surface antigen and a lymphocyte activating signaling chain. The CAR-mediated recognition induces cytokine production and tumor-directed cytotoxicity of T cells. Second and third generation CARs include signal sequences from various costimulatory molecules resulting in enhanced T-cell persistence and sustained antitumor reaction. Clinical trials revealed that the adoptive transfer of T cells engineered with first generation CARs represents a feasible concept for the induction of clinical responses in some tumor patients. However, further improvement is required, which may be achieved by second or third generation CAR-engrafted T cells.

The bidirectional crosstalk between human dendritic cells and natural killer cells.

Dendritic cells (DCs) are professional antigen-presenting cells, which display an extraordinary capacity to induce T-cell responses. Recent findings revealed that DCs also play a crucial role in the activation of natural killer (NK) cells representing important effectors in the innate immune defense against viruses and tumors. Here, we summarize various studies investigating the bidirectional crosstalk between human DCs and NK cells. In this context, it has been reported that DCs efficiently enhance CD69 expression, proliferation, interferon (IFN)-γ secretion and cytotoxic activity of NK cells. Cell membrane-associated molecules as well as soluble factors such as interleukin-12, tumor necrosis factor-α and type I IFNs contributed to DC-mediated NK cell activation. Reciprocally, the ability of human NK cells to enhance the immunostimulatory capacity of DCs was shown. Thus, NK cells promoted the maturation of DCs and markedly augmented their capacity to produce proinflammatory cytokines and to stimulate T-cell responses. The NK cell-mediated effects on DCs were dependent on cell membrane-associated molecules such as NKp30 and soluble factors such as tumor necrosis factor-α and IFN-γ. In conclusion, the reciprocal activating interaction between human DCs and NK cells may play a pivotal role in the immune defense against viruses and tumors.

Tumoricidal Potential of Native Blood Dendritic Cells: Direct Tumor Cell Killing and Activation of NK Cell-Mediated Cytotoxicity

Dendritic cells (DCs) are characterized by their unique capacity for primary T cell activation, providing the opportunity for DC-based cancer vaccination protocols. Novel findings reveal that besides their role as potent inducers of tumor-specific T cells, human DCs display additional antitumor effects. Most of these data were obtained with monocyte-derived DCs, whereas studies investigating native blood DCs are limited. In the present study, we analyze the tumoricidal capacity of M-DC8+ DCs, which represent a major subpopulation of human blood DCs. We demonstrate that IFN-γ-stimulated M-DC8+ DCs lyse different tumor cell lines but not normal cells. In addition, we show that tumor cells markedly enhance the production of TNF-α by M-DC8+ DCs via cell-to-cell contact and that this molecule essentially contributes to the killing activity of M-DC8+ DCs. Furthermore, we illustrate the ability of M-DC8+ DCs to promote proliferation, IFN-γ production, and tumor-directed cytotoxicity of NK cells. The M-DC8+ DC-mediated enhancement of the tumoricidal potential of NK cells is mainly dependent on cell-to-cell contact. These results reveal that, in addition to their crucial role in activating tumor-specific T cells, blood DCs exhibit direct tumor cell killing and enhance the tumoricidal activity of NK cells. These findings point to the pivotal role of DCs in triggering innate and adaptive immune responses against tumors.

Dendritic Cell-Based Immunotherapy for Prostate Cancer

Dendritic cells (DCs) are professional antigen-presenting cells (APCs), which display an extraordinary capacity to induce, sustain, and regulate T-cell responses providing the opportunity of DC-based cancer vaccination strategies. Thus, clinical trials enrolling prostate cancer patients were conducted, which were based on the administration of DCs loaded with tumor-associated antigens. These clinical trials revealed that DC-based immunotherapeutic strategies represent safe and feasible concepts for the induction of immunological and clinical responses in prostate cancer patients. In this context, the administration of the vaccine sipuleucel-T consisting of autologous peripheral blood mononuclear cells including APCs, which were pre-exposed in vitro to the fusion protein PA2024, resulted in a prolonged overall survival among patients with metastatic castration-resistent prostate cancer. In April 2010, sipuleucel-T was approved by the United States Food and Drug Administration for prostate cancer therapy.

Mesenchymal stromal cells from patients with myelodyplastic syndrome display distinct functional alterations that are modulated by lenalidomide

The contribution of the bone marrow microenvironment in myelodysplastic syndrome is controversial. We therefore analyzed the functional properties of primary mesenchymal stromal cells from patients with myelodysplastic syndrome in the presence or absence of lenalidomide. Compared to healthy controls, clonality and growth were reduced across all disease stages. Furthermore, differentiation defects and particular expression of adhesion and cell surface molecules (e.g. CD166, CD29, CD146) were detected. Interestingly, the levels of stromal derived factor 1-alpha in patients’ cells culture supernatants were almost 2-fold lower (P<0.01) than those in controls and this was paralleled by a reduced induction of migration of CD34+ hematopoietic cells. Co-cultures of mesenchymal stromal cells from patients with CD34+ cells from healthy donors resulted in reduced numbers of cobblestone area-forming cells and fewer colony-forming units. Exposure of stromal cells from patients and controls to lenalidomide led to a further reduction of stromal derived factor 1-alpha secretion and cobblestone area formation, respectively. Moreover, lenalidomide pretreatment of mesenchymal stromal cells from patients with low but not high-risk myelodysplastic syndrome was able to rescue impaired erythroid and myeloid colony formation of early hematopoietic progenitors. In conclusion, our analyses support the notion that the stromal microenvironment is involved in the pathophysiology of myelodysplastic syndrome thus representing a potential target for therapeutic interventions.

Bortezomib significantly impairs the immunostimulatory capacity of human myeloid blood dendritic cells

Bortezomib is a potent drug for the treatment of multiple myeloma. Its anti-tumor activity is mediated by proteasome inhibition leading to decreased cell proliferation and induction of apoptosis. However, an unimpaired proteasomal function plays a crucial role for the induction of anti-tumor immunity by dendritic cells (DCs), which are currently used for therapeutic vaccination against various tumors including myeloma. In the present study, we investigated the impact of bortezomib on the immunostimulatory capacity of 6-sulfo LacNAc (slan) DCs, which represent a major subset of human blood DCs. We demonstrated that this proteasome inhibitor efficiently impairs the spontaneous in vitro maturation of slanDCs and the release of tumor necrosis factor (TNF)-α as well as interleukin (IL)-12 upon lipopolysaccharide (LPS) stimulation. Functional data revealed that bortezomib profoundly inhibits slanDC-induced proliferation and differentiation of CD4+ T cells. In addition, the capacity of slanDCs to promote interferon-γ secretion and tumor-directed cytotoxicity of natural killer (NK) cells is markedly impaired by bortezomib. These results provide evidence that bortezomib significantly reduces the ability of native human blood DCs to regulate innate and adaptive anti-tumor immunity and may have implications for the design of therapeutic strategies combining DC vaccination and bortezomib treatment.

Retargeting of T cells to prostate stem cell antigen expressing tumor cells: comparison of different antibody formats.

Prostate cancer (PCa) is the most common malignant disease in men. Novel treatment options are needed for patients after development of metastatic, hormone‐refractory disease or for those who have failed a local treatment. The prostate stem cell antigen (PSCA) is expressed in >80% of primary PCa samples and bone metastases. Its expression is increased both in androgen‐dependent and independent prostate tumors, particularly in carcinomas of high stages and Gleason scores. Therefore, PSCA is an attractive target for immunotherapy of PCa by retargeting of T cells to tumor cells.

Prophylactic transfer of BCR-ABL–, PR1-, and WT1-reactive donor T cells after T cell–depleted allogeneic hematopoietic cell transplantation in patients with chronic myeloid leukemia

Donor lymphocyte infusions have been effective in patients with chronic myeloid leukemia (CML) relapsing after allogeneic stem cell transplantation, but their use is associated with the risk of graft-versus-host disease. We investigated the effects of prophylactic infusion of in vitro-generated donor T cells reactive against peptides derived from CML-associated antigens. Fourteen CML patients received conditioning therapy followed by CD34(+)-selected peripheral blood stem cells from matched siblings (n = 7) or unrelated (n = 7) donors. Donor-derived mature dendritic cells generated in vitro from CD14(+) monocytes were loaded with human leukocyte Ag-restricted peptides derived from PR1, WT1, and/or B-cell receptor-ABL and used to repetitively stimulate donor CD8(+) T cells in the presence of IL-2 and IL-7. Stimulated T cells were infused 28, 56, and 112 days after transplantation. Thirteen patients are alive and 7 remain in molecular remission (median follow-up, 45 months). Interestingly, all 4 patients receiving CD8(+) T cells displaying marked cytotoxic activity in vitro and detectable peptide-reactive CD8(+) T cells during follow-up have not experienced graft-versus-host disease or relapse. Our study reveals that prophylactic infusion of allogeneic CD8(+) T cells reactive against peptides derived from CML-associated antigens is a safe and promising therapeutic strategy. This trial was registered at www.clinicaltrials.gov as #NCT00460629.