Evaluation of Human Mesenchymal Stromal Cells as Carriers for the Delivery of Oncolytic HAdV-5 to Head and Neck Squamous Cell Carcinomas

Human multipotent mesenchymal stromal cells (hMSCs) are of significant therapeutic interest due to their ability to deliver oncolytic adenoviruses to tumors. This approach is also investigated for targeting head and neck squamous cell carcinomas (HNSCCs). HAdV-5-HexPos3, a recently reported capsid-modified vector based on human adenovirus type 5 (HAdV-5), showed strongly improved infection of both hMSCs and the HNSCC cell line UM-SCC-11B. Given that, we generated life cycle-unmodified and -modified replication-competent HAdV-5-HexPos3 vector variants and analyzed their replication within bone marrow- and adipose tissue-derived hMSCs. Efficient replication was detected for both life cycle-unmodified and -modified vectors. Moreover, we analyzed the migration of vector-carrying hMSCs toward different HNSCCs. Although migration of hMSCs to HNSCC cell lines was confirmed in vitro, no homing of hMSCs to HNSCC xenografts was observed in vivo in mice and in ovo in a chorioallantoic membrane model. Taken together, our data suggest that HAdV-5-HexPos3 is a potent candidate for hMSC-based oncolytic therapy of HNSCCs. However, it also emphasizes the importance of generating optimized in vivo models for the evaluation of hMSC as carrier cells.

One-year follow-up of the CAPSID randomized trial for high-dose convalescent plasma in severe COVID-19 patients

BACKGROUNDResults of many randomized trials on COVID-19 convalescent plasma (CCP) have been reported, but information on long-term outcome after CCP treatment is limited. The objectives of this extended observation of the randomized CAPSID trial are to assess long-term outcome and disease burden in patients initially treated with or without CCP.METHODSOf 105 randomized patients, 50 participated in the extended observation. Quality of life (QoL) was assessed by questionnaires and a structured interview. CCP donors (n = 113) with asymptomatic to moderate COVID-19 were included as a reference group.RESULTSThe median follow-up of patients was 396 days, and the estimated 1-year survival was 78.7% in the CCP group and 60.2% in the control (P = 0.08). The subgroup treated with a higher cumulative amount of neutralizing antibodies showed a better 1-year survival compared with the control group (91.5% versus 60.2%, P = 0.01). Medical events and QoL assessments showed a consistent trend for better results in the CCP group without reaching statistical significance. There was no difference in the increase in neutralizing antibodies after vaccination between the CCP and control groups.CONCLUSIONThe trial demonstrated a trend toward better outcome in the CCP group without reaching statistical significance. A predefined subgroup analysis showed a significantly better outcome (long-term survival, time to discharge from ICU, and time to hospital discharge) among those who received a higher amount of neutralizing antibodies compared with the control group. A substantial long-term disease burden remains after severe COVID-19.Trial registrationEudraCT 2020-001310-38 and ClinicalTrials.gov NCT04433910.FundingBundesministerium für Gesundheit (German Federal Ministry of Health).

Cytokine levels associated with favorable clinical outcome in the CAPSID randomized trial of convalescent plasma in patients with severe COVID-19

Objectives

To determine the profile of cytokines in patients with severe COVID-19 who were enrolled in a trial of COVID-19 convalescent plasma (CCP).

Methods

Patients were randomized to receive standard treatment and 3 CCP units or standard treatment alone (CAPSID trial, ClinicalTrials.gov NCT04433910). The primary outcome was a dichotomous composite outcome (survival and no longer severe COVID-19 on day 21). Time to clinical improvement was a key secondary endpoint. The concentrations of 27 cytokines were measured (baseline, day 7). We analyzed the change and the correlation between serum cytokine levels over time in different subgroups and the prediction of outcome in receiver operating characteristics (ROC) analyses and in multivariate models.

Results

The majority of cytokines showed significant changes from baseline to day 7. Some were strongly correlated amongst each other (at baseline the cluster IL-1ß, IL-2, IL-6, IL-8, G-CSF, MIP-1α, the cluster PDGF-BB, RANTES or the cluster IL-4, IL-17, Eotaxin, bFGF, TNF-α). The correlation matrix substantially changed from baseline to day 7. The heatmaps of the absolute values of the correlation matrix indicated an association of CCP treatment and clinical outcome with the cytokine pattern. Low levels of IP-10, IFN-γ, MCP-1 and IL-1ß on day 0 were predictive of treatment success in a ROC analysis. In multivariate models, low levels of IL-1ß, IFN-γ and MCP-1 on day 0 were significantly associated with both treatment success and shorter time to clinical improvement. Low levels of IP-10, IL-1RA, IL-6, MCP-1 and IFN-γ on day 7 and high levels of IL-9, PDGF and RANTES on day 7 were predictive of treatment success in ROC analyses. Low levels of IP-10, MCP-1 and high levels of RANTES, on day 7 were associated with both treatment success and shorter time to clinical improvement in multivariate models.

Conclusion

This analysis demonstrates a considerable dynamic of cytokines over time, which is influenced by both treatment and clinical course of COVID-19. Levels of IL-1ß and MCP-1 at baseline and MCP-1, IP-10 and RANTES on day 7 were associated with a favorable outcome across several endpoints. These cytokines should be included in future trials for further evaluation as predictive factors.

Hexon modification of human adenovirus type 5 vectors enables efficient transduction of human multipotent mesenchymal stromal cells

In adenovirus type 5 (HAdV-5)-derived viral vectors, the fiber protein has been the preferred locale for modifications to alter the natural viral tropism. Hexon, the most abundant capsid protein, has rarely been used for retargeting purposes, likely because the insertion of larger targeting peptides into Hexon often interferes with the assembly of the viral capsid. We previously observed that positively charged molecules enhance the transduction of human multipotent mesenchymal stromal cells (hMSCs)—a cell type of significant interest for clinical development but inefficiently transduced by unmodified HAdV-5-based vectors. As efficient HAdV-5-mediated gene transfer would greatly increase the therapeutic potential of hMSCs, we tested the hypothesis that introducing positively charged amino acids into Hexon might enhance the transduction of hMSCs, enabling efficient expression of selected transgenes. From the constructs that could be rescued as functional virions, one (HAdV-5-HexPos3) showed striking transduction of hMSCs with up to 500-fold increased efficiency. Evaluation of the underlying mechanism identified heparan sulfate proteoglycans (HSPGs) to be essential for virus uptake by the cells. The ease and efficiency of transduction of hMSCs with this vector will facilitate the development of genetically modified hMSCs as therapeutic vehicles in different disciplines, including oncology or regenerative medicine.

Randomisierte Studien zum Einsatz von Rekonvaleszentenplasma bei COVID-19: eine Standortbestimmung

Plasma von genesenen Spendern mit COVID-19 (COVID-19 Convalescent Plasma, CCP) wurde als Behandlungsoption für Patienten mit COVID-19 in Betracht gezogen. In der ersten Phase der Pandemie wurden mehrere Fallberichte und Fallkontrollstudien mit Hinweisen auf eine therapeutische Wirkung veröffentlicht. Inzwischen liegen die Ergebnisse zahlreicher randomisierter Studien vor. Die Studien unterscheiden sich in vielen Aspekten, u. a. in den Patientenpopulationen, die von ambulanten Patienten mit mildem COVID-19 bis zu kritisch Kranken reichten, wie auch den Endpunkten. Ebenso war der Behandlungsstandard innerhalb der klinischen Studien sehr unterschiedlich. Vor allem aber unterschied sich das Prüfpräparat CCP erheblich in Bezug auf das Behandlungsschema, das Volumen und den Gehalt an Antikörpern. Im Folgenden werden wir die Ergebnisse der bisher publizierten randomisierten Studien diskutieren. Aus den bisher veröffentlichten Ergebnissen lässt sich eine Wirksamkeit von CCP ableiten, sofern es sehr hohe Titer neutralisierender Antikörper enthält und früh im Krankheitsverlauf verabreicht wird. COVID-19-Rekonvaleszenten-Plasma ist noch keine Routinebehandlung und sollte möglichst weiter in klinischen Studien untersucht werden. Neu konzipierte Studien sollten sich auf die frühe Anwendung von CCP mit einem hohen Gehalt an neutralisierenden Antikörpern bei Patienten mit hohem Risiko für eine Progression zu einer schweren COVID-19-Erkrankung konzentrieren und wichtige Begleitmedikationen kontrollieren.

Transduction Enhancers Enable Efficient Human Adenovirus Type 5-Mediated Gene Transfer into Human Multipotent Mesenchymal Stromal Cells

Human multipotent mesenchymal stromal cells (hMSCs) are currently developed as cell therapeutics for different applications, including regenerative medicine, immune modulation, and cancer treatment. The biological properties of hMSCs can be further modulated by genetic engineering. Viral vectors based on human adenovirus type 5 (HAdV-5) belong to the most frequently used vector types for genetic modification of human cells in vitro and in vivo. However, due to a lack of the primary attachment receptor coxsackievirus and adenovirus receptor (CAR) in hMSCs, HAdV-5 vectors are currently not suitable for transduction of this cell type without capsid modification. Here we present several transduction enhancers that strongly enhance HAdV-5-mediated gene transfer into both bone marrow- and adipose tissue-derived hMSCs. Polybrene, poly-l-lysine, human lactoferrin, human blood coagulation factor X, spermine, and spermidine enabled high eGFP expression levels in hMSCs. Importantly, hMSCs treated with enhancers were not affected in their migration behavior, which is a key requisite for many therapeutic applications. Exemplary, strongly increased expression of tumor necrosis factor (TNF)-stimulated gene 6 (TSG-6) (a secreted model therapeutic protein) was achieved by enhancer-facilitated HAdV-5 transduction. Thus, enhancer-mediated HAdV-5 vector transduction is a valuable method for the engineering of hMSCs, which can be further exploited for the development of innovative hMSC therapeutics.

Characterization of the SARS-CoV-2 Neutralization Potential of COVID-19-Convalescent Donors

The current SARS-CoV-2 pandemic has triggered the development of various SARS-CoV-2 neutralization tests. A wild-type virus (using African green monkey VeroE6 cells), a pseudovirus (using human Caco-2 cells), and a surrogate neutralization test platform were applied to characterize the SARS-CoV-2 neutralization potential of a cohort of 111 convalescent plasma donors over a period of seven months after diagnosis. This allowed an in-depth validation and assay performance analysis of these platforms. More importantly, we found that SARS-CoV-2 neutralization titers were stable or even increased within the observation period, which contradicts earlier studies reporting a rapid waning of Ab titers after three to four months. Moreover, we observed a positive correlation of neutralization titers with increasing age, number of symptoms reported, and the presence of the Rhesus Ag RhD. Validation of the platforms revealed that highest assay performances were obtained with the wild-type virus and the surrogate neutralization platforms. However, our data also suggested that selection of cutoff titers had a strong impact on the evaluation of neutralization potency. When taking strong neutralization potency, as demonstrated by the wild-type virus platform as the gold standard, up to 55% of plasma products had low neutralization titers. However, a significant portion of these products were overrated in their potency when using the surrogate assay with the recommended cutoff titer. In summary, our study demonstrates that SARS-CoV-2 neutralization titers are stable for at least seven months after diagnosis and offers a testing strategy for rapid selection of high-titer convalescent plasma products in a biosafety level 1 environment.

Independent Side-by-Side Validation and Comparison of 4 Serological Platforms for SARS-CoV-2 Antibody Testing

Highly sensitive and specific platforms for the detection of anti-SARS-CoV-2 antibodies are becoming increasingly important for (1) evaluating potential SARS-CoV-2 convalescent plasma donors, (2) studying the spread of SARS-CoV-2 infections and (3) identifying individuals with seroconversion. This study provides a comparative validation of four anti-SARS-CoV-2 platforms. Unique feature of this study is the use of a representative cohort of COVID-19-convalescent patients with mild-to-moderate disease course. All platforms showed significant correlations with a SARS-CoV-2 plaque-reduction-neutralization test, with highest sensitivities for the Euroimmun and the Roche platforms, suggesting their preferential use for screening of persons at increased risk of SARS-CoV-2 infections.

Osteoarthritic Milieu Affects Adipose-Derived Mesenchymal Stromal Cells

The objective of this study was to define the effects of osteoarthritic (OA) milieu on good manufactured practice-adipose-derived mesenchymal stromal cells (GMP-ASC) that are commonly utilized in cell therapies. Two different OA milieu: OA synovial fluid (SF) and OA-conditioned medium (CM) from synoviocytes were used to treat GMP-ASC both in normoxia or hypoxia. GMP-ASC were tested for cell migration, proliferation, cytokine receptors expression (CXCR1, CXCR2, CXCR3, CXCR4, CXCR7, CCR1, CCR2, CCR3, CCR5, IL6R), and cytokines (CXCL8/IL8, CXCL10/IP10, CXCL12/SDF-1, CCL2/MCP1, CCL3/MIP1α, CCL4/MIP1β, CCL5/RANTES, IL6) release. Healthy SF was used as controls. We demonstrated that GMP-ASC show an increase in proliferation, migration, and modulation of CXCR1, CXCR3, CCR1, and CCR5 receptors in hypoxic condition. Moreover, GMP-ASC migration increased 15-fold when treated either with OA-SF or OA-CM compared with healthy SF both in normoxia and hypoxia. GMP-ASC treated in both OA milieu showed an increase in CXCR3, CCR3, and IL6R and a decrease in CCR1 and CCR2 receptors. In OA-SF, we detected higher amount of CXCL10/IP10 than in OA-CM, while CCL2/MCP1 and CCL4/MIP1β were higher in OA-CM compared with OA-SF. CXCL10/IP10 was the only chemokine of the OA milieu, which was down-modulated after treatment with GMP-ASC. In conclusion, we demonstrated specific effects of OA milieu on both GMP-ASC proliferation, migration, and cytokine receptor expression that were strictly dependent on the inflammatory and hypoxic environment. The use of characterized OA milieu is crucial to define the therapeutic effect of GMP-ASC and indicates that CXCL10/IP10-CXCR3 axis is partially involved in the GMP-ASC effect on synovial macrophages. © 2019 The Authors. Journal of Orthopaedic Research® published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 38:336-347, 2020.

Biomarkers of bone healing induced by a regenerative approach based on expanded bone marrow-derived mesenchymal stromal cells

BACKGROUND

Safety and feasibility of a regenerative strategy based on the use of culture-expanded mesenchymal stromal cells (MSCs) have been investigated in phase 2 trials for the treatment of nonunion and osteonecrosis of the femoral head (ONFH). As part of the clinical study, we aimed to evaluate if bone turnover markers (BTMs) could be useful for predicting the regenerative ability of the cell therapy product.

MATERIALS AND METHODS

The bone defects of 39 patients (nonunion: n = 26; ONFH: n = 13) were treated with bone marrow-derived MSCs, expanded using a clinical-grade protocol and combined with biphasic calcium phosphate before implantation. Bone formation markers, bone-resorption markers and osteoclast regulatory proteins were measured before treatment (baseline) and after 12 and 24 weeks from surgery. At the same time-points, clinical and radiological controls were performed to evaluate the bone-healing progression.

RESULTS

We found that C-Propeptide of Type I Procollagen (CICP) and C-terminal telopeptide of type-I collagen (CTX) varied significantly, not only over time, but also according to clinical results. In patients with a good outcome, CICP increased and CTX decreased, and this trend was observed in both nonunion and ONFH. Moreover, collagen biomarkers were able to discriminate healed patients from non-responsive patients with a good diagnostic accuracy.

DISCUSSION

CICP and CTX could be valuable biomarkers for monitoring and predicting the regenerative ability of cell products used to stimulate the repair of refractory bone diseases. To be translated in a clinical setting, these results are under validation in a currently ongoing phase 3 clinical trial.

ATP promotes immunosuppressive capacities of mesenchymal stromal cells by enhancing the expression of indoleamine dioxygenase

Introduction

MSCs are often found within tumors, promote cancer progression and enhance metastasis. MSCs can act as immuosuppressive cells, partially due to the expression of the enzyme indoleamine dioxygenase (IDO) which converts tryptophan to kynurenine. Decreased concentration of tryptophan and increased kynurenine, both interfere with effective immune response. Damage associated molecular patterns (DAMPs) including ATP are found within the tumor microenvironment, attract MSCs, and influence their biology.

Methods

Bone marrow derived MSCs were exposed to ATP for 4 days, in the presence of 100 ng IFNγ/mL. Intracellular expression of IDO in MSCs was assessed by FACS. Conditioned media from thus stimulated MSCs was analyzed for kynurenine content and its suppressive effect on lymphocyte proliferation. Apyrase or P2 × 7‐receptor antagonist (AZ 11645373) were applied in order to inhibit ATP induced effect on MSCs.

Results

We demonstrate, that ATP at concentrations between 0.062 and 0.5 mM increases dose dependently the expression of IDO in MSCs with subsequent increased kynurenine concentrations within the supernatant at about 60%. This effect could be abolished completely in the presence of ATP degrading enzyme (apyrase) or when MSCs were pretreated with a P2 × 7‐receptor antagonist (AZ 11645373). Consistently, supernatants from MSCs stimulated with ATP, inhibited lymphocyte proliferation from 65% to 16%.

Conclusions

We characterized ATP as a DAMP family member responsible for necrosis‐induced immunomodulation. Given the increased concentration of DAMPs within tumor tissue and the fact that DAMPs can act as chemotattractants to MSCs, our results have implications for therapeutic strategies targeting the tumor microenvironment.

Cell therapy induced regeneration of severely atrophied mandibular bone in a clinical trial

Background

Autologous grafting, despite some disadvantages, is still considered the gold standard for reconstruction of maxillofacial bone defects. The aim of this study was to evaluate bone regeneration using bone marrow-derived mesenchymal stromal cells (MSCs) in a clinical trial, a less invasive approach than autologous bone grafting. This comprehensive clinical trial included subjects with severe mandibular ridge resorption.

Methods

The study included 11 subjects aged 52–79 years with severe mandibular ridge resorption. Bone marrow cells were aspirated from the posterior iliac crest and plastic adherent cells were expanded in culture medium containing human platelet lysate. The MSCs and biphasic calcium phosphate granules as scaffolds were inserted subperiosteally onto the resorbed alveolar ridge. After 4–6 months of healing, new bone formation was assessed clinically and radiographically, as were safety and feasibility. Bone at the implant site was biopsied for micro-computed topography and histological analyses and dental implants were placed in the newly regenerated bone. Functional outcomes and patient satisfaction were assessed after 12 months.

Results

The bone marrow cells, expanded in vitro and inserted into the defect together with biphasic calcium phosphate granules, induced significant new bone formation. The regenerated bone volume was adequate for dental implant installation. Healing was uneventful, without adverse events. The patients were satisfied with the esthetic and functional outcomes. No side effects were observed.

Conclusions

The results of this comprehensive clinical trial in human subjects confirm that MSCs can successfully induce significant formation of new bone, with no untoward sequelae. Hence, this novel augmentation procedure warrants further investigation and may form the basis of a valid treatment protocol, challenging the current gold standard.

Trial registration

EudraCT, 2012-003139-50. Registered on 21 August 2013. ClinicalTrials.gov, NCT 02751125. Registered on 26 April 2016.

Mesenchymale Stromazellen auf dem Weg zur klinischen Anwendung: Update 2018

Mesenchymale Stromazellen (MSC) besitzen ein großes therapeutisches Potenzial sowohl für Immunmodulation als auch regenerative Therapie. In einigen Indikationen, z. B. Behandlung der schweren Transplantat-gegen-Empfänger-Reaktion nach allogener Stammzelltransplantation, wurden MSC schon vor mehr als 10 Jahren therapeutisch eingesetzt. In weiteren Indikationen haben die MSC in den letzten Jahren nun das Stadium der klinischen Erprobung erreicht. Hier erfolgt eine Evaluation der Sicherheit und Wirksamkeit einer MSC-Therapie in einem sehr breiten Spektrum von Erkrankungen. Diese Übersichtsarbeit stellt den aktuellen Stand der präklinischen und klinischen Forschung zur Anwendung von MSC in der Behandlung der Transplantat-gegen-Empfänger-Reaktion, von Wundheilungsstörungen, von neurodegenerativen Erkrankungen und Knochen- und Knorpeldefekten dar.

A Subpopulation of Stromal Cells Controls Cancer Cell Homing to the Bone Marrow

Breast and prostate cancer cells home to the bone marrow, where they presumably hijack the hematopoietic stem cell niche. We characterize here the elusive premetastatic niche by examining the role of mesenchymal stromal cells (MSC) in cancer cell homing. Decreasing the number of MSC pharmacologically enhanced cancer cell homing to the bone marrow in mice. In contrast, increasing the number of these MSCs by various interventions including G-CSF administration diminished cancer cell homing. The MSC subpopulation that correlated best with cancer cells expressed stem, endothelial, and pericytic cell markers, suggesting these cells represent an undifferentiated component of the niche with vascular commitment. In humans, a MSC subpopulation carrying markers for endothelial and pericytic cells was lower in the presence of cytokeratin⁺ cells in bone marrow. Taken together, our data show that a subpopulation of MSC with both endothelial and pericytic cell surface markers suppresses the homing of cancer cells to the bone marrow. Similar to the presence of cytokeratin⁺ cells in the bone marrow, this MSC subpopulation could prove useful in determining the risk of metastatic disease, and its manipulation might offer a new possibility for diminishing bone metastasis formation.Significance: These findings establish an inverse relationship between a subpopulation of mesenchymal stromal cells and cancer cells in the bone marrow. Cancer Res; 78(1); 129-42. ©2017 AACR.

Iron-loaded PLLA nanoparticles as highly efficient intracellular markers for visualization of mesenchymal stromal cells by MRI

Monitoring of the fate of cells after injection appears paramount for the further development of cell therapies. In this context magnetic resonance imaging (MRI) is increasing in relevance owing to its unique tissue visualization properties. For assessment of cell trafficking and homing, the cells have to be labeled to become MR visible. The rather low sensitivity of MRI demands dedicated intracellular markers with high payloads of MR contrast agents for ensuring sensitive detection of local cell aggregations. In the presented work the application of custom-designed nanometer-sized iron oxide loaded poly-(l-lactide) (iPLLA) nanoparticles was investigated. The particles were synthesized by the mini-emulsion process and evaluated for labeling of mesenchymal stromal cells (MSCs). The efficient cellular uptake and long intracellular retention times of the particles as well as their nontoxicity are demonstrated. The average cellular iron content was 55 pg iron per cell. Further incorporation of, for example, fluorescent dye enables the generation of multireporter particles, providing the great potential for multimodal imaging. The efficiency of these nanoparticles as MRI contrast agent was evaluated in vitro using relaxation rate mapping, yielding relaxivities r2 = 273.3, r2 (*) = 545.1 mm(-1) s(-1) at 3 T and r2 = 415.7, r2 (*) = 872.3 mm(-1) s(-1) at 11.7 T. The high r2 (*) relaxivity of the iPLLA nanoparticles enabled visualization of a single labeled cell in vitro at 50-µm spatial resolution. In vivo evaluation in a rat injury model revealed the potential of the iPLLA particles to efficiently label MSCs for MRI monitoring of ~20 000-40 000 injected cells at 11.7 T. In conclusion the presented work demonstrates the applicability of iPLLA particles as efficient intracellular marker for MSC labeling for monitoring the fate of the cells by MRI.

Standardization of Good Manufacturing Practice-compliant production of bone marrow-derived human mesenchymal stromal cells for immunotherapeutic applications

BACKGROUND AIMS

Human mesenchymal stem or stromal cells (MSCs) represent a potential resource not only for regenerative medicine but also for immunomodulatory cell therapies. The application of different MSC culture protocols has significantly hampered the comparability of experimental and clinical data from different laboratories and has posed a major obstacle for multicenter clinical trials. Manufacturing of cell products for clinical application in the European Community must be conducted in compliance with Good Manufacturing Practice and requires a manufacturing license. In Germany, the Paul-Ehrlich-Institut as the Federal Authority for Vaccines and Biomedicines is critically involved in the approval process.

METHODS

This report summarizes a consensus meeting between researchers, clinicians and regulatory experts on standard quality requirements for MSC production.

RESULTS

The strategy for quality control testing depends on the product's cell composition, the manufacturing process and the indication and target patient population. Important quality criteria in this sense are, among others, the immunophenotype of the cells, composition of the culture medium and the risk for malignant transformation, as well as aging and the immunosuppressive potential of the manufactured MSCs.

CONCLUSIONS

This position paper intends to provide relevant information to interested parties regarding these criteria to foster the development of scientifically valid and harmonized quality standards and to support approval of MSC-based investigational medicinal products.

Necrosis associated factors (S100A4 and uric acid) promote accumulation of MSCs which induce IL10+/IDO+ lymphocytes (TUM7P.949)

Necrosis with subsequent release of damage-associated molecular patterns (DAMPs) is a characteristic feature of advanced solid tumors. DAMPs impact the tumor-microenvironment stimulating tumor-associated cells like mesenchymal stromal cells (MSCs). Tumor-infiltrating-MSCs are associated with tumor progression and metastasis. Oxidized DAMPs lose their stimulatory capacity on MSCs. As a DAMP-member S100A4 is sensitive to oxidation while uric acid (UA) acts as an antioxidant. We tested these two DAMP-members separately and in combination for their biologic activity on MSCs. S100A4 and UA showed a dose-dependent chemotactic activity on MSCs with synergistic effects when both DAMPs were combined. Substituting for UA, alternative antioxidants (Vitamin-C, dithiothreitol, and acetylcystein) had also a comparable synergistic effect on the chemotactic activity of S100A4, emphasizing the reducing potential of UA being responsible for the observed synergy. Yet, S100A4 and UA inhibited MSC proliferation without impacting their viability. Nevertheless, in the presence of S100A4 or UA, MSCs gained immunosuppressive capacities by inducing IL-10 and indoleamine dioxygenase expressing lymphocytes. We characterized S100A4 and UA as necrosis-associated factors playing a crucial role within MSC biology and thus immunoregulation. Our results have implications for therapeutic approaches targeting the tumor microenvironment and addressing the immunosuppressive nature of necrotic tumor.

Human mesenchymal stem cells constitutively express the serine protease granzyme B. (P1097)

Human mesenchymal stem cells (MSC) are known for their immunoregulatory potential and are allegedly involved in tolerance induction. Several immune cells have been shown to exhibit their regulatory effects via expression of the cytotoxic serine protease granzyme B including regulatory T cells and plasmacytoid dendritic cells. Since MSC were recently found to express the GrB inhibitor PI-9, which is primarily expressed by cytotoxic cells, we hypothesized that MSC may also express GrB. Using various methods including Western immunoblotting, ELISpot, FACS analysis we found that MSC freshly isolated from healthy donor bone marrow biopsies indeed express considerable amounts of GrB protein. ELISpot assays demonstrated that GrB was not only expressed but also secreted by MSC. Moreover, a colorimetric GrB activity assay confirmed that GrB was secreted in its enzymatically active form. Importantly, when testing the effect of various cytokines we found that G-CSF, IFNg and TPO were capable of further enhancing GrB expression in MSC. Future studies have to elucidate which aspects of the suppressive activity of MSC possibly depend on GrB and which culture conditions may support a suppressive phenotype of these cells including GrB expression. Our results may open novel approaches to the use of MSC as immunoregulatory cellular therapeutics in inflammatory conditions such as graft-versus-host disease.

T-cell reconstitution after allogeneic stem cell transplantation: assessment by measurement of the sjTREC/βTREC ratio and thymic naive T cells

The immune reconstitution after allogeneic hematopoietic stem cell transplantation comprises thymus-dependent and thymus-independent pathways. We wanted to improve the understanding of this complex process using two different measurements at definite checkpoints of T-cell neogenesis. We therefore assessed the thymus-dependent pathway by combining measurements of single joint T-cell receptor excision circles (sjTREC) and β T-cell receptor excision circles (βTREC) in an improved quantitative light-cycler hybridization polymerase chain reaction assay. In a subgroup of patients, we additionally assessed the proliferation kinetics of the CD31(+) thymic naïve cell population, which corresponds to recent thymic emigrants by six-color immunostaining. After the establishment of normal values in 22 healthy volunteers, we applied our polymerase chain reaction to 66 patients undergoing allogeneic hematopoietic stem cell transplantation at a median age of 44 years. It took more than 2 years after transplant to restore the pre-transplant thymic proliferation capacity. Only one third of the patients in our longitudinal study reached age-adjusted normal values for both sjTREC and βTREC at a median follow-up of 558 days, with acute graft-versus-host disease being the most prominent negative factor by univariate analysis. We observed several patterns of sjTREC and βTREC recovery suggesting different mechanisms of thymic damage in individual patients. In a comparison of CD31(+) thymic naïve cells between volunteers and patients after transplant we found a significantly higher peak proliferation rate within the latter population in the first year after transplantation. The combination of measurements of sjTREC and βTREC by our simplified polymerase chain reaction assay provides insight about the stage of T-cell development affected by different types of damage and may help to choose the correct therapeutic intervention. Besides the sole thymic T-cell neogenesis, proliferation within the CD31(+) thymic naïve cell compartment contributed to the replenishment of the naïve T-cell pool after transplantation.

Labeling of mesenchymal stromal cells with iron oxide-poly(L-lactide) nanoparticles for magnetic resonance imaging: uptake, persistence, effects on cellular function and magnetic resonance imaging properties

Background aims. Mesenchymal stromal cells (MSC) are the focus of research in regenerative medicine aiming at the regulatory approval of these cells for specific indications. To cope with the regulatory requirements for somatic cell therapy, novel approaches that do not interfere with the natural behavior of the cells are necessary. In this context in vivo magnetic resonance imaging (MRI) of labeled MSC could be an appropriate tool. Cell labeling for MRI with a variety of different iron oxide preparations is frequently published. However, most publications lack a comprehensive assessment of the noninterference of the contrast agent with the functionality of the labeled MSC, which is a prerequisite for the validity of cell-tracking via MRI. Methods.We studied the effects of iron oxide-poly(L-lactide) nanoparticles in MSC with flow cytom-etry, transmission electron microscopy (TEM), confocal laser scanning microscopy (CLSM), Prussian blue staining, CyQuant® proliferation testing, colony-forming unit-fibroblast (CFU-F) assays, flow chamber adhesion testing, immuno-logic tests and differentiation tests. Furthermore iron-labeled MSC were studied by MRI in agarose phantoms and Wistar rats. Results. It could be demonstrated that MSC show rapid uptake of nanoparticles and long-lasting intracellular persistence in the endosomal compartment. Labeling of the MSC with these particles has no influence on viability, differentiation, clonogenicity, proliferation, adhesion, phenotype and immunosuppressive properties. They show excellent MRI properties in agarose phantoms and after subcutaneous implantation in rats over several weeks. Conclusions. These particles qualify for studying MSC homing and trafficking via MRI.

Ewing's sarcoma cells with CD57-associated increase of tumorigenicity and with neural crest-like differentiation capacity

The Ewing family of tumors (EFT) is an important group of pediatric malignancies with a guarded prognosis. Little is known about the heterogeneity of EFT cells, and the cellular origin of EFT is disputed. We now add evidence that EFT are heterogeneous by showing that EFT cells from spheres growing in serum-free medium are markedly more tumorigenic than adherently growing EFT cells. Furthermore, EFT cells strongly expressing CD57 (HNK-1), a surface marker for migrating and proliferating neural crest cells, are more tumorigenic than cells with low expression of CD57, possibly mediated in part by enhanced adhesion and invasion. We contribute to the controversy about the cellular origin of EFT by clonal analysis, showing that EFT cells can differentiate similar to neural crest cells. These data increase our knowledge about the pathogenesis and heterogeneity of EFT.

The tumor antigens RHAMM and G250/CAIX are expressed in head and neck squamous cell carcinomas and elicit specific CD8+ T cell responses

Despite advances in surgery, radio- and chemotherapy, therapeutic approaches for patients with head and neck squamous carcinoma (HNSCC) need to be improved. Immunotherapies eliciting tumor specific immune responses might constitute novel treatment options. We therefore investigated the expression and immunogenicity of two tumor-associated antigens (TAA) the receptor for hyaluronic acid mediated motility (RHAMM) and carboanhydrase IX (G250/CAIX) in HNSCC patients. Twenty-two HNSCC samples were examined for the expression of RHAMM and G250 by Western blotting and immunohistochemistry, 14/22 samples were tested for HLA-A2 expression by flow cytometry. For 8/22 samples single tumor-cell suspensions were generated, and mixed lymphocyte peptide cultures (MLPC) were performed to evaluate the frequencies of cytotoxic T cells specifically recognizing RHAMM and G250 using Tetramer staining/multi-color flow cytometry and enzyme linked immunosorbent spot (ELISPOT) assays. RHAMM and G250 were expressed in 73 and 80% of the HNSCC samples at the protein level. A co-expression of both TAAs could be detected in 60% of the patients. In 4/8 HLA-A2+ patients, 0.06-0.13% of CD8+ effector T cells recognized Tetramers for RHAMM or G250 and secreted IFNgamma and granzyme B in ELISPOT assays. RHAMM and G250 are expressed at high frequency and high protein level in HNSCCs and are recognized by cytotoxic CD8+ effector T cells. Therefore both TAAs constitute interesting targets for T cell based immunotherapies for HNSCC.

Nilotinib hampers the proliferation and function of CD8+ T lymphocytes through inhibition of T cell receptor signalling

The novel selective BCR-ABL Breakpoint cluster region – Abelson murine leukemia viral oncogene homolog 1 (BCR-AML) inhibitor nilotinib (AMN107) is a tyrosine kinase inhibitor that is more potent against leukaemia cells in vitro than imatinib. As nilotinib might be used in the context of allogeneic stem cell transplantation where CD8⁺ T lymphocytes play a pivotal role in the graft-versus-leukaemia (GVL) effect, we investigated effects of nilotinib on this lymphocyte subpopulation. Nilotinib inhibits phytohemagglutinin (PHA)-induced proliferation of CD8⁺T lymphocytes in vitro at therapeutically relevant concentrations (0.5–4 μM). The inhibition of CD8⁺ T lymphocytes specific for leukaemia or viral antigens through nilotinib was associated with a reduced expansion of antigen peptide specific CD8⁺ T lymphocytes and with a decreased release of interferon—γ and granzyme B by these cells as analysed by flow cytometry and enzyme-linked immunospot (ELISPOT) assays. The inhibitory effect caused by nilotinib was two times stronger than by imatinib. These effects were mediated through the inhibition of the phosphorylation of ZAP-70, Lck and ERK 1/2 and the NF-κβ signalling transduction pathway. Taken together, we observed a strong suppressive impact of nilotinib on the CD8⁺ T lymphocyte function which should be considered carefully in the framework of allogeneic stem cell transplantation or other T cell based immunotherapies.

Imatinib impairs the proliferation and function of CD4+CD25+ regulatory T cells in a dose-dependent manner

The tyrosine kinase inhibitor imatinib has been reported to inhibit CD8+ T lymphocytes. Little is known about its effects on CD4+CD25+ regulatory T cells (T(reg) cells) which might regulate the graft-vs.-leukemia (GVL) reaction after allogeneic stem cell transplantation (allo-SCT) and donor lymphocyte infusion (DLI). This is of particular interest in patients with relapse of chronic myeloid leukemia (CML) after allo-SCT, as the two therapeutical options DLI and imatinib might interact reversely. Here, we demonstrate that the proliferation of CD4+CD25+ T(reg) cells and their production of IL-10, TGF-beta1 and granzyme B as markers of activation were significantly down-regulated by imatinib in a dose-dependent manner. In addition, the expression of surface CD69, both surface and intracellular GITR, FoxP3, CD152 (CTLA) of activated CD4+CD25+ T(reg) cells were inhibited by imatinib in a dose-dependent manner. In light of these findings, clinical administration of imatinib might not result in a reduction of the GVL effect on CML patients receiving imatinib after allo-SCT and/or DLI or other CD8+ T lymphocyte based immunotherapies as the function of CD8+ cytotoxic T lymphocytes and CD4+CD25(hi) Treg cells is hampered in a similar way by imatinib.

Imatinib impairs CD8+ T lymphocytes specifically directed against the leukemia-associated antigen RHAMM/CD168 in vitro

The Bcr-Abl tyrosine kinase inhibitor imatinib mesylate is highly effective in the front-line treatment of chronic myeloid leukemia (CML) and is increasingly used in patients with residual disease or relapse after allogeneic stem cell transplantation (allo-SCT). Since an impairment of anti-viral CD8+ T-lymphocyte function by imatinib has been described, we question whether imatinib also affects specific anti-leukemic CD8+ T lymphocytes generated from the peripheral blood of healthy donors, and of CML patients after allo-SCT. Here, we assessed CD8+ T-cell expansion and function from healthy donors and patients with CML. The release of IFN-gamma and granzyme B by CD8+ T-lymphocytes specific for R3, a recently described T-cell epitope peptide derived from a leukemia-associated antigen designated RHAMM/CD168 (receptor for hyaluronic acid mediated motility), was inhibited by imatinib in a dose-dependent fashion (range: 1-25 microM). These T cells were able to lyse cognate peptide labeled T2 cells and CD34+ CML progenitor cells. This lysis was inhibited by imatinib. The inhibitory effect was not associated with an increased rate of apoptosis of T cells and reversible after removal of imatinib. In the light of these findings, clinical administration of imatinib might result in the reduction of efficacy of the graft-versus-leukemia effect or other T-cell-based immunotherapies.

Accelerated telomere shortening in glycosylphosphatidylinositol (GPI)–negative compared with GPI-positive granulocytes from patients with paroxysmal nocturnal hemoglobinuria (PNH) detected by proaerolysin flow-FISH

Telomere length has been linked to disease stage and degree of (pan-)cytopenia in patients with bone marrow failure syndromes. The aim of the current study was to analyze the impact of replicative stress on telomere length in residual glycosylphosphatidylinositol-positive (GPI+) versus GPI– hematopoiesis in patients with paroxysmal nocturnal hemoglobinuria (PNH). Peripheral blood granulocytes from 16 patients and 22 healthy individuals were analyzed. For this purpose, we developed proaerolysin flow-FISH, a novel methodology that combines proaerolysin staining (for GPI expression) with flow-FISH (for telomere length measurement). We found significantly shortened telomeres in GPI– granulocytes (mean ± SE: 6.26 ± 0.27 telomere fluorescence units [TFU]), both compared with their GPI+ counterparts (6.88 ± 0.38 TFU; P = .03) as well as with age-matched healthy individuals (7.73 ± 0.23 TFU; P < .001). Our findings are in support of a selective growth advantage model of PNH assuming that damage to the GPI+ hematopoietic stem-cell (HSC) compartment leads to compensatory hyperproliferation of residual GPI–HSCs.

Depolarisation of the plasma membrane in the arsenic trioxide (As2O3)-and anti-CD95-induced apoptosis in myeloid cells

Depolarisation of the plasma membrane has been shown to be actively regulated during lymphocyte-apoptosis. Here, we present data about anti-Fas and As2O3 induced depolarisation of myeloid U-937 cells. Anti-Fas but not As2O3-induced depolarisation was significantly dependent on caspase-activation. Na+-fluxes contributed to the depolarisation in early stages of As2O3-induced apoptosis, whereas the membrane potential in late stages depended on Cl- -fluxes. Cl- -channels also played an important role in the induction of cell shrinkage in As2O3-induced apoptosis. However, none of these ions contributed significantly to anti-Fas induced depolarisation. This indicates the existence of different mechanisms for apoptotic plasma membrane depolarisation within one cell type.

Paroxysmal nocturnal haemoglobinuria: a replacement of haematopoietic tissue?

Acquired somatic mutations of the PIG-A gene lead to deficient expression of glycosyl-phosphatidyl-inositol-anchored proteins (GPI-AP) by haematopoietic cells and play a causative role in the pathogenesis of paroxysmal nocturnal haemoglobinuria (PNH). However, PIG-A mutations do not explain how the defective PNH clone can expand. It was hypothesized that a selection process conferring a relative advantage to the GPI-AP-deficient population is required. Since GPI-AP-deficient cells are also detectable in a substantial proportion of patients with otherwise typical aplastic anaemia (AA), the mechanisms inducing bone marrow failure might selectively spare the GPI-deficient cells. In order to examine the growth characteristics of GPI-AP-deficient cells in more detail, we performed repeated analyses of GPI-AP expression on peripheral blood cells in 41 patients with AA. We observed four patterns of the course of GPI-AP-deficient populations: (1) 13 patients showed normal expression of GPI-AP in the first analysis and in at least two follow-up studies at a median time of 709 days after the first analysis. (2) Secondary evolution of a GPI-AP-deficient population was a rare event. Only 4 patients with initially normal GPI-AP expression developed a GPI-AP-deficient population during follow up after immunosuppressive treatment. (3) Persistence of GPI-AP-deficient cells was observed in 16 patients during a median follow-up time of 774 days. However, in some patients, the size of the GPI-AP-deficient population increased substantially. (4) Disappearance of a GPI-AP-deficient population was observed in 8 patients. The time course of GPI-AP expression in relation to the treatment suggests that therapeutic interventions might modulate the ratio of normal versus GPI-AP-deficient haematopoiesis. Overall, these data argue against an 'absolute growth advantage' of GPI-AP-deficient cells. Our data are consistent with the hypothesis that haematopoietic failure caused by damage to normal haematopoiesis allows the outgrowth of a GPI-AP-deficient population. Thus, in at least some patients GPI-AP-deficient cells might pre-exist at a very low percentage and replace haematopoiesis after an insult to the normal cells.