Impact of Psoralen/UVA-Treatment on Survival, Activation, and Immunostimulatory Capacity of Monocyte-Derived Dendritic Cells

Efficacy of a 365 nm Ultraviolet A1 light Emitting Diode (UVA1-LED) in in vitro Extracorporeal Photopheresis

Extracorporeal photochemotherapy (ECP) is one of the more effective cell therapies for graft-versus-host disease (GvHD). ECP is a widely recommended therapeutic approach for the treatment of chronic GvHD, particularly steroid-refractory GVHD. In recent years, the use of a light emitting diode (LED) in the clinic has attracted considerable interest. In this study, we examined the issue of whether an ultraviolet A1-light emitting diode (UVA1-LED) can be used as a light source in ECP. To compare the efficacy of ECP with conventional UVA lamp and a UVA1-LED, we established an in vitro ECP model. Treatment efficacy was evaluated by measuring the % apoptosis and the inhibition of T-cell proliferation. To investigate the effect of ECP on the innate immune reaction, THP-1 cells with a luciferase reporter gene driven by a NF-kB response element (THP-1 luc NF-kB) were treated with ECP. The LED-ECP induced apoptosis and inhibition of T-cell proliferation as efficiently as a conventional ECP. However, LED-ECP induced less innate immunity in THP-1. Since LED devices are more compact compared with conventional UVA irradiation devices, the use of a UVA1-LED in the treatment of ECP may be a better alternative to conventional ECP therapy.

Pathogenesis and Therapy of Primary Cutaneous T-Cell Lymphoma: Collegium Internationale Allergologicum (CIA) Update 2020

Cutaneous T-cell lymphoma (CTCL) is a heterogeneous disease group of unknown etiology with a complex immunological background. As CTCL arises from T cells that have a vital role in the antitumor response, their therapy is largely aimed at reversing the immunological mechanisms leading to or manifesting during this malignancy. Early disease stages can be controlled with skin-directed therapy in most CTCL cases. Still, advanced CTCL has a dismal prognosis and warrants systemic therapy. Despite considerable progress in understanding the pathophysiology of the disease and the numerous systemic treatment options available, long-term remission rates with conventional treatments alone are still low. Allogeneic hematopoietic stem cell transplantation is currently the only curative option for advanced CTCL, including mycosis fungoides and Sézary syndrome. The aims of this review is to summarize the recent findings on the immunology of this heterogeneous disease and to present the advances in its clinical management.

Extracorporeal Photopheresis: A Case of Immunotherapy Ahead of Its Time

Extracorporeal photopheresis (ECP) is a cell-based immunotherapy that involves the reinfusion of autologous leukocytes after exposure to psoralen and UVA. The treatment has been used for over 30 years, at first on patients with cutaneous T-cell lymphoma (CTCL) and later for the management of patients with graft-versus-host disease (GvHD), sclerosing disorders, atopic dermatitis, and other diseases that may share the common driving factor of a pathogenic T-cell clone or clones in blood circulation. Patients with clinical improvement mount an antigen-specific immune response that may have tolerance traits in the case of GvHD or anticlonal cytotoxic characteristics in the case of CTCL. The exact mechanisms that dictate one response or the other are not fully understood, but the evidence accumulated so far indicates that multiple events occur simultaneously and consequentially contribute to the end result. These include contact of cells with the outside (plastics and tubing of the ECP apparatus), exposure to psoralen and UVA that activates platelets, monocytes, and other myeloid cells, the release of damage-associated molecular patterns, differentiation of monocytes into dendritic cells, and generation and successive presentation of numerous antigens after the phagocytosis of apoptotic cells. Once reintroduced, the ECP product increases the frequency and activity of regulatory T cells (Tregs), shifts the systemic cytokine balance, and promotes extravasation of immune cells that together shape the effects of this treatment. In this review, we summarize the seminal work and most recent literature of the therapeutic mechanisms and reflect on future avenues of improvements and applications of ECP.

Retrospective Multicenter Study of Extracorporeal Photopheresis in Steroid-Refractory Acute and Chronic Graft-versus-Host Disease

Extracorporeal photopheresis (ECP) is an established treatment strategy in steroid-refractory graft-versus-host disease (GVHD). This study's main objective was to analyze the clinical response and impact of ECP therapy in steroid dose reduction. A retrospective observational series of 113 patients from 7 transplantation centers was analyzed. Sixty-five patients (58%) had acute GVHD (aGVHD), and 48 (42%) had chronic GVHD (cGVHD). All ECP procedures were performed with the off-line system. The median number of procedures until achievement of initial response was 3 for both patients with aGVHD and those with cGVHD. ECP was the second-line therapy in 48% of the aGVHD cases and in 50% of the cGVHD cases. 71% of the cases of aGVHD were grade III-IV, and 69% of the cases of cGVHD were severe. The overall response rate on day 28 was 53% (complete response [CR] rate, 45%) in the patients with aGVHD and 67% (CR, 23%) in those with cGVHD. Skin was the most frequently involved organ, with a response rate of 58% (CR, 49%) in the patients with aGVHD and 69% (CR 29%) in those with cGVHD. At the end of ECP treatment, 60% of patients treated for aGVHD who responded were able to stop steroid therapy, with a median dose reduction of 100%. Significant differences in overall survival were observed for patients responding to ECP with aGVHD (hazard ratio [HR], 4.3; P < .001) and with cGVHD (HR, 4.8; P = .003). Our data indicate that ECP is a valid therapeutic alternative in patients with steroid-refractory aGVHD and cGVHD, permitting significant steroid dosage reductions.

A standardized methodical approach to characterize the influence of key parameters on the in vitro efficacy of extracorporeal photopheresis

Extracorporeal photopheresis (ECP) is an autologous immunomodulatory cell therapy that consists of the ex vivo collection of mononuclear cells (MNCs), which are irradiated with UVA in the presence of the photosensitizing agent 8-methoxypsoralen (8-MOP) to induce cell apoptosis. This photoactivated cell preparation is then reinfused into the patient. While the clinical benefits of ECP are well-demonstrated, no study has yet characterized the influence of variations in the composition of the cell preparation on the efficacy of ECP in vitro. Here, we describe a standardized methodology for the in vitro assessment of ECP that uses the human lymphoma T-cell line and mimics the clinical procedure. By quantifying cell apoptosis, inhibition of cell proliferation, and 8-MOP consumption, we used this approach to characterize the specific influence of key variables on the cellular response to ECP. We found that (i) increases in hematocrit and plasma concentrations attenuated the cellular response to ECP; (ii) plasma concentration was the only variable tested that influenced 8-MOP consumption; and (iii) the loss of efficacy due to variations in the concentration of certain blood components could be counteracted by modulating the UVA dose. This methodology may enable evaluation of other leukapheresis preparation protocols and better determination of the optimal working parameters for ECP.

Monocytes show immunoregulatory capacity on CD4+ T cells in a human in-vitro model of extracorporeal photopheresis

Extracorporeal photopheresis (ECP) is a widely used immunomodulatory therapy for the treatment of various T cell-mediated disorders such as cutaneous T cell lymphoma (CTCL), graft-versus-host disease (GvHD) or systemic sclerosis. Although clinical benefits of ECP are already well described, the underlying mechanism of action of ECP is not yet fully understood. Knowledge on the fate of CD14⁺ monocytes in the context of ECP is particularly limited and controversial. Here, we investigated the immunoregulatory function of ECP treated monocytes on T cells in an in-vitro ECP model. We show that ECP-treated monocytes significantly induce proinflammatory T cell types in co-cultured T cells, while anti-inflammatory T cells remain unaffected. Furthermore, we found significantly reduced proliferation rates of T cells after co-culture with ECP-treated monocytes. Both changes in interleukin secretion and proliferation were dependent on cell-contact between monocytes and T cells. Interestingly, blocking interactions of programmed death ligand 1 (PD-L1) to programmed death 1 (PD-1) in the in-vitro model led to a significant recovery of T cell proliferation. These results set the base for further studies on the mechanism of ECP, especially the regulatory role of ECP-treated monocytes.

Extracoporeal photopheresis treatment of acute graft-versus-host disease following allogeneic haematopoietic stem cell transplantation

Acute graft-versus-host disease (aGvHD) continues to be a major obstacle to allogeneic haematopoietic stem cell transplantation. Thymic damage secondary to aGvHD along with corticosteroids and other non-selective T lymphocyte-suppressive agents used in the treatment of aGvHD concurrently impair thymopoiesis and negatively impact on immunoreconstitution of the adaptive immune compartment and ultimately adversely affect clinical outcome. Extracorporeal photopheresis (ECP) is an alternative therapeutic strategy that appears to act in an immunomodulatory fashion, potentially involving regulatory T lymphocytes and dendritic cells. By promoting immune tolerance and simultaneously avoiding systemic immunosuppression, ECP could reduce aGvHD and enable a reduction in other immunosuppression, allowing thymic recovery, restoration of normal T lymphopoiesis, and complete immunoreconstitution with improved clinical outcome. Although the safety and efficacy of ECP has been demonstrated, further randomised controlled studies are needed as well as elucidation of the underlying mechanisms responsible and the effect of ECP on thymic recovery.

Extracorporeal photopheresis promotes IL-1β production

Extracorporeal photopheresis (ECP) is a widely used clinical cell-based therapy exhibiting efficacy in heterogenous immune-mediated diseases such as cutaneous T cell lymphoma, graft-versus-host disease, and organ allograft rejection. Despite its documented efficacy in cancer immunotherapy, little is known regarding the induction of immunostimulatory mediators by ECP. In this article, we show that ECP promotes marked release of the prototypic immunostimulatory cytokine IL-1β. ECP primes IL-1β production and activates IL-1β maturation and release in the context of caspase-1 activation in monocytes and myeloid dendritic cells. Of interest, IL-1β maturation by ECP was fully intact in murine cells deficient in caspase-1, suggesting the predominance of an inflammasome-independent pathway for ECP-dependent IL-1β maturation. Clinically, patient analysis revealed significantly increased IL-1β production in stimulated leukapheresis concentrates and peripheral blood samples after ECP. Collectively, these results provide evidence for promotion of IL-1β production by ECP and offer new insight into the immunostimulatory capacity of ECP.

Blue light irradiation suppresses dendritic cells activation in vitro

Blue light is a UV-free irradiation suitable for treating chronic skin inflammation, for example, atopic dermatitis, psoriasis, and hand- and foot eczema. However, a better understanding of the mode of action is still missing. For this reason, we investigated whether dendritic cells (DC) are directly affected by blue light irradiation in vitro. Here, we report that irradiation neither induced apoptosis nor maturation of monocyte-derived and myeloid DC. However, subsequent DC maturation upon LPS/IFNγ stimulation was impaired in a dose-dependent manner as assessed by maturation markers and cytokine release. Moreover, the potential of this DC to induce cytokine secretion from allogeneic CD4 T cells was reduced. In conclusion, unlike UV irradiation, blue light irradiation at high and low doses only resulted in impaired DC maturation upon activation and a reduced subsequent stimulatory capacity in allogeneic MLRs with strongest effects at higher doses.

Activation of GILZ gene by photoactivated 8-methoxypsoralen: potential role of immunoregulatory dendritic cells in extracorporeal photochemotherapy

Extracorporeal photochemotherapy (ECP) is a widely used method for either immunization against cutaneous T cell lymphoma or immunosuppression of graft-versus-host disease and organ transplant rejection (OTR). Leukapheresed blood is routed through a chamber, in which 8-methoxypsoralen is activated by ultraviolet energy (PUVA), thereby causing DNA crosslinks in processed leukocytes. Return of ECP-processed mononuclear leukocytes to the patient then modulates aberrant T cell immunity. Since interaction with the ECP flow chamber induces monocyte-to-dendritic antigen presenting cell (DC) maturation, we examined the possibility that PUVA may direct the most heavily exposed monocytes to differentiate into tolerogenic DC, while the least exposed DC might remain immunogenic. Expression of the glucocorticoid-induced leucine zipper (GILZ) gene is a distinguishing marker of tolerogenic DC. We report that PUVA directly stimulates GILZ expression. PUVA-exposed DC up-regulated GILZ, down-regulated costimulatory CD80 and CD86, became resistant to Toll-like receptor-induced maturation, increased IL-10 production and decreased IL-12p70 production, all features of immunosuppressive DC. Knockdown of GILZ with siRNA reduced IL-10 and increased IL-12p70 production, demonstrating that GILZ is critical for this profile. PUVA-induction of GILZ expression by DC may help explain how ECP suppresses GVHD and OTR. Conversely, those ECP-processed monocytes minimally exposed to PUVA may mediate ECP's immunogenic effects.

Extracorporeal photopheresis in 62 patients with acute and chronic GVHD: results of treatment with the COBE Spectra System

In this retrospective analysis, 30 patients with acute GVHD (aGVHD) and 32 patients with chronic GVHD (cGVHD) treated with extracorporeal photopheresis (ECP) performed by the COBE Spectra System were evaluated. After 3 months of ECP treatment, a CR and PR were observed in 9 (30%) and 6 (20%) patients with aGVHD and in 2 (6%) and 12 (38%) patients with cGVHD. In 16 (53%) patients with aGVHD and 9 (28%) with cGVHD ECP treatment was already stopped after 3 months. One (3%) patient with aGVHD and 7 (22%) patients with cGVHD received new additional immunosuppressive therapy started during the first 3 months of ECP treatment and were classified as 'nonresponder' with regard to ECP. Of these patients a PR was achieved in one patient with aGVHD and in three patients with cGVHD. Steroids could be tapered by 50 in 83% of patients with aGVHD and in 29% of patients with cGVHD after 3 months of ECP treatment. Patients with aGVHD achieving a CR or PR showed a significant improved OS after allo-SCT (P=0.019). ECP is associated with significant response rates and successful reduction of steroids in patients with GVHD.

Sun exposure rapidly reduces plasmacytoid dendritic cells and inflammatory dermal dendritic cells in psoriatic skin

BACKGROUND

Interferon (IFN)-α-producing plasmacytoid dendritic cells (pDCs), inflammatory CD11c+CD1c- myeloid dendritic cells (mDCs) and macrophages have been found to contribute to the pathogenesis of psoriasis. Heliotherapy is a well-established treatment modality of this disease, although the details of how the effects are mediated are unknown.

OBJECTIVES

To test the hypothesis that exposure to natural sun affects pathogenic DC subsets in lesional skin.

METHODS

Skin biopsies were obtained from lesional and nonlesional skin in 10 patients with moderate to severe psoriasis subjected to controlled sun exposure on Gran Canaria. Biopsies were obtained at baseline, day 2 and day 16 and examined by immunohistochemistry.

RESULTS

Sixteen days of heliotherapy had excellent clinical effect on patients with psoriasis, with significant reductions in Psoriasis Area and Severity Index (PASI) scores. In lesional skin pDC numbers and expression of MxA, a surrogate marker for IFN-α, were rapidly reduced. Inflammatory CD11c+CD1c- mDCs were significantly reduced whereas resident dermal CD11c+CD1c+ mDCs were unaffected. Expression levels of the maturation marker DC-LAMP (CD208) on mDCs were significantly reduced after sun exposure, as were the numbers of lesional dermal macrophages. A decrease of dermal DC subsets and macrophages was already observed after 1 day of sun exposure. An additional finding was that DC-SIGN (CD209) is primarily expressed on CD163+ macrophages and not DCs.

CONCLUSIONS

The clinical improvement in psoriasis following sun exposure is associated with rapid changes in dermal DC populations and macrophages in lesional skin, preceding the clinical effect. These findings support the concept that these DC subsets are involved in the pathogenesis of psoriasis and suggest that sun-induced clinical benefit may partly be explained by its effect on dermal DCs.

Circulating B-cell activating factor level predicts clinical response of chronic graft-versus-host disease to extracorporeal photopheresis

Extracorporeal photopheresis (ECP) is an important therapeutic option in steroid-refractory chronic graft-versus-host disease (cGVHD). Few biomarkers predicting response exist. We measured serum B-cell activating factor (BAFF) in 46 cGVHD patients receiving ECP before and during treatment course. BAFF level at 1 month of ECP predicted 3- and 6-month skin disease response, with BAFF less than 4 ng/mL associated with significant skin improvement and complete resolution in 11 of 20 patients. High BAFF at 1-month ECP associated with a worsening median 6-month skin score and resolution in 1 of 10 patients. BAFF level at 3 months also predicted the likelihood of maintaining skin disease improvement at 6 months. BAFF level was not correlated directly with extracutaneous cGVHD response, although full cutaneous responders exhibited improved extracutaneous organ response rates compared with skin nonresponders (65% vs 35%). This study suggests that early BAFF measurement during ECP for cGVHD represents a potentially useful biomarker in prediction of treatment outcome.

Insulin-like growth factor-1 in psoriatic plaques treated with PUVA and methotrexate

BACKGROUND

The pathogenesis of psoriasis is thought to depend on the activation of immune cells and their secreted cytokines, chemokines and growth factors like IGF-1 which may contribute to the epidermal hyperplasia of psoriasis. Treatment of psoriasis with PUVA and methotrexate are associated with clinical improvement and decrease in epidermal hyperplasia.

OBJECTIVE

To examine the effects of PUVA and methotrexate therapy on IGF-1 expression in psoriatic plaques and whether this change correlates with clinical response.

METHODS

For 24 psoriatic patients, the PASI score and levels of lesional IGF-1 and its mRNA were determined by RT-PCR before and after treatment with either methotrexate or PUVA. Skin biopsies from 12 healthy volunteers served as control for IGF-1 levels in normal skin.

RESULTS

Lesional skin of psoriatic patients showed a statistically significant elevation in IGF-1 and its mRNA levels in comparison to control (P = 0.0001). Both methotrexate and PUVA treatment were associated with a significant decrease in both PASI scores and lesional IGF-1 after 10 month treatment.

CONCLUSION

Both methotrexate and PUVA therapy for psoriasis are associated with a decrease in PASI score and IGF-1. The IGF-1 down-regulation may possibly be a consequence of the decrease in cytokines and inflammatory cellular infiltrate that occur following treatment with either modalities or due to their effect on local fibroblast activity and proliferation.

Apoptotic cell-based therapies against transplant rejection: role of recipient's dendritic cells

One of the ultimate goals in transplantation is to develop novel therapeutic methods for induction of donor-specific tolerance to reduce the side effects caused by the generalized immunosuppression associated to the currently used pharmacologic regimens. Interaction or phagocytosis of cells in early apoptosis exerts potent anti-inflammatory and immunosuppressive effects on antigen (Ag)-presenting cells (APC) like dendritic cells (DC) and macrophages. This observation led to the idea that apoptotic cell-based therapies could be employed to deliver donor-Ag in combination with regulatory signals to recipient’s APC as therapeutic approach to restrain the anti-donor response. This review describes the multiple mechanisms by which apoptotic cells down-modulate the immuno-stimulatory and pro-inflammatory functions of DC and macrophages, and the role of the interaction between apoptotic cells and APC in self-tolerance and in apoptotic cell-based therapies to prevent/treat allograft rejection and graft-versus-host disease in murine experimental systems and in humans. It also explores the role that in vivo-generated apoptotic cells could have in the beneficial effects of extracorporeal photopheresis, donor-specific transfusion, and tolerogenic DC-based therapies in transplantation.

Predictors of response to extracorporeal photopheresis in advanced mycosis fungoides and Sézary syndrome

BACKGROUND

Extracorporeal photopheresis (ECP) has been utilized for more than 20 years to treat cutaneous T-cell lymphoma (CTCL), but a clinical response can take up to 9 months to manifest. This study was undertaken to determine whether clinical features, laboratory values, cytokine levels, or gene expression levels of tumor markers are useful to predict the subsequent response to ECP in CTCL patients with blood involvement.

METHODS

Twenty-one patients with CTCL treated with ECP as monotherapy for at least 6 months were retrospectively identified. Laboratory and clinical data and blood obtained at baseline, 3, and 6 months of treatment were used for analysis.

RESULTS

In pretreatment blood specimens, a lower percentage of Sézary cells and a higher absolute eosinophil count were associated with a favorable clinical response. Clinical evidence of an early response after 3 months of ECP did not reliably predict a favorable response at 6 months or beyond. Comparison of cytokines, gene transcripts, and other laboratory measures of disease did not correlate with the subsequent clinical response, although lactate dehydrogenase levels tended to decrease progressively in ECP-responsive cases and increase progressively in ECP-non-responsive cases. Additionally, serum levels of TNF-alpha significantly increased from baseline to 6 months of ECP, but was not found to correlate with the clinical response.

CONCLUSIONS

Although we found that increased eosinophils and decreased percentage of Sézary cells were associated with a favorable clinical response to ECP, we were not able to identify the predictors of ECP response within the first 3 months of treatment.

Dendritic cell apoptosis: regulation of tolerance versus immunity

Dendritic cell (DC) apoptosis is an important event that regulates the balance between tolerance and immunity through multiple pathways, and defects in DC apoptosis can trigger autoimmunity. DC apoptosis is also associated with immunosuppression and has been observed under several pathologies and infections. Recent studies indicate that apoptotic DCs can also play an active role in induction of tolerance. This review discusses the regulatory pathways of DC apoptosis, stimuli inducing DC apoptosis, and the implications of DC apoptosis in the induction of immunosuppression and/or tolerance.

Photochemotherapy induces the apoptosis of monocytes without impairing their function

BACKGROUND

Extracorporeal photopheresis (ECP) is a powerful therapy currently used to treat various hematological disorders as in graft versus host disease. Clinical data clearly demonstrate its efficacy and immunomodulation toward the pathogenic T cells. However, ECP mechanism of action is still poorly understood. Monocytes represent up to 30% of the total amount of treated cells and are known to play an important role in adaptive immunity. However, data from previous reports analyzing the effect of psoralen and UV-A irradiation (PUVA) on their functions are heterogeneous. In this study, we focused on the effect of PUVA on human monocytes functions in adaptive immunity.

DESIGN AND METHODS

Purified human monocytes were treated in vitro by PUVA. We measured their kinetic of apoptosis after the treatment. We also determine whether their phenotype and functionalities were modified. Finally, we assessed the functionalities of PUVA-treated monocytes-derived dendritic cells (DC).

RESULTS

PUVA treatment sentenced purified monocytes to die in 6 days and immediately altered their migratory capacities without impairing their ability of endocytosis. It also up-regulated co-stimulatory molecules and production of inflammatory cytokines on activation and consequently stimulated allogeneic or autologous T cells as efficiently as untreated monocytes. Moreover, PUVA-treated monocytes retained their ability to differentiate into fully functional DC that maturated and stimulated T cells as well as normal DC.

CONCLUSIONS

Our data demonstrate that monocytes undergo apoptosis and loose a part of their migratory capacity after ECP and the surviving cell functionalities are not impaired, suggesting that monocytes have a minor effect on ECP-mediated immunomodulation.

Extracorporeal photopheresis-induced immune tolerance: a focus on modulation of antigen-presenting cells and induction of regulatory T cells by apoptotic cells

PURPOSE OF REVIEW

This review is intended to introduce recent advances in the research surrounding extracorporeal photopheresis (ECP) with a focus on how apoptotic cells modulate antigen-presenting cells and induce regulatory T cells, given that ECP therapy induces apoptosis of leukocytes collected through leukapheresis.

RECENT FINDINGS

It has been suggested that ECP therapy, unlike other immunosuppressive regimens, does not cause global immunosuppression, but induces immune tolerance. Recent clinical and animal studies demonstrate that ECP therapy induces antigen-specific regulatory T cells, including CD4+CD25+FoxP3+ T cells and IL-10-producing Tr1 cells, that may arise secondarily to the induction of tolerogenic antigen-presenting cells (APCs) by infusion of apoptotic cells. It has also been suggested that ECP therapy may induce IL-10-producing regulatory B cells and regulatory CD8+ T cells. Finally, several recent studies, which examined the cellular elements involved in the uptake of apoptotic cells, demonstrated that apoptotic cells modulate APCs through binding to specific receptors, particularly TAM receptors that provide inhibitory signals that block APC activation.

SUMMARY

ECP therapy induces immune tolerance through modulation of antigen-presenting cells as well as induction of regulatory T cells. ECP therapy has great potential in the management of allogeneic transplantation and autoimmune diseases.

Extracorporeal photopheresis efficiently impairs the proinflammatory capacity of human 6-sulfo LacNAc dendritic cells

BACKGROUND

Extracorporeal photopheresis (ECP) emerged as a promising treatment modality for steroid-refractory graft-versus-host disease (GVHD), which represents a major complication of allogeneic hematopoietic stem-cell transplantation. Dendritic cells (DCs) display an extraordinary capacity to induce T-cell responses and play a crucial role in the initiation and maintainance of GVHD. This study evaluated the direct impact of ECP on the proinflammatory capacity of 6-sulfo LacNAc (slan) DCs, representing a major subpopulation of human blood DCs.

METHODS

SlanDCs were isolated from ECP-treated or untreated blood of healthy donors or GVHD patients by immunomagnetic isolation. The maturation of slanDC was determined by flow cytometry. Cytokine production of slanDCs was measured by enzyme-linked immunosorbent assay. SlanDC-mediated T-cell proliferation was evaluated by H-thymidine incorporation. SlanDC-mediated T-cell programming was determined by flow cytometry.

RESULTS

ECP efficiently impairs the spontaneous maturation and secretion of proinflammatory tumor necrosis factor-alpha, interleukin-1beta, and interleukin-12 by slanDCs. Furthermore, ECP markedly inhibits slanDC-induced proliferation of CD4 and CD8 T cells and polarization of naïve CD4 T lymphocytes into Th1 cells.

CONCLUSIONS

These novel findings indicate that ECP efficiently impairs the proinflammatory capacity of slanDCs, which may represent an important mechanism for the therapeutic efficiency of ECP in GVHD.

A novel paradigm for dendritic cells as effectors of cartilage destruction

OBJECTIVE

Dendritic cells (DCs) are enriched in RA synovium and have been implicated in the pathogenesis of RA primarily through their ability to present autoantigen and activate T cells. However, whether DCs play an effector role in cartilage destruction is unknown. The aim of this study was to investigate whether DCs can induce collagen release from cartilage and the mechanism involved.

METHODS

Human monocyte-derived DCs (mDCs) were activated with CD40 ligand (CD40L) to mimic DC-T-cell interaction, and supernatants were incubated with cartilage explants. Hydroxyproline was assessed as a measure of collagen release and collagenolytic activity was measured by a bioassay using tritiated collagen. TNF-alpha in DC supernatants was measured by specific ELISA.

RESULTS

Supernatants from CD40L-activated mDCs, but not unstimulated mDCs, strongly induced the destruction of cartilage collagen. mDC supernatants did not contain collagenases but did induce collagenolytic activity in cartilage explants. Neutralization of TNF-alpha in mDC supernatants completely abolished collagenolysis.

CONCLUSIONS

This study shows that mDCs, upon CD40-ligation, induce cartilage collagen degradation through an indirect mechanism via the production of TNF-alpha. Our data suggest a potential important role for mDC-derived TNF-alpha in RA, which is in line with the previously reported observations that DCs are a major source of TNF-alpha in early autoimmune lesions and that anti-TNF-alpha therapeutics effectively suppress joint damage in RA patients. We propose that DCs can act as effectors in cartilage destruction, adding a new aspect to the functional role of DCs in RA pathogenesis.