The induction of human myeloid derived suppressor cells through hepatic stellate cells is dose-dependently inhibited by the tyrosine kinase inhibitors nilotinib, dasatinib and sorafenib, but not sunitinib.

Increased numbers of immunosuppressive myeloid derived suppressor cells (MDSCs) correlate with a poor prognosis in cancer patients. Tyrosine kinase inhibitors (TKIs) are used as standard therapy for the treatment of several neoplastic diseases. However, TKIs not only exert effects on the malignant cell clone itself but also affect immune cells. Here, we investigate the effect of TKIs on the induction of MDSCs that differentiate from mature human monocytes using a new in vitro model of MDSC induction through activated hepatic stellate cells (HSCs). We show that frequencies of monocytic CD14(+)HLA-DR(-/low) MDSCs derived from mature monocytes were significantly and dose-dependently reduced in the presence of dasatinib, nilotinib and sorafenib, whereas sunitinib had no effect. These regulatory effects were only observed when TKIs were present during the early induction phase of MDSCs through activated HSCs, whereas already differentiated MDSCs were not further influenced by TKIs. Neither the MAPK nor the NFκB pathway was modulated in MDSCs when any of the TKIs was applied. When functional analyses were performed, we found that myeloid cells treated with sorafenib, nilotinib or dasatinib, but not sunitinib, displayed decreased suppressive capacity with regard to CD8+ T cell proliferation. Our results indicate that sorafenib, nilotinib and dasatinib, but not sunitinib, decrease the HSC-mediated differentiation of monocytes into functional MDSCs. Therefore, treatment of cancer patients with these TKIs may in addition to having a direct effect on cancer cells also prevent the differentiation of monocytes into MDSCs and thereby differentially modulate the success of immunotherapeutic or other anti-cancer approaches.

Variable resistance to freezing and thawing of CD34-positive stem cells and lymphocyte subpopulations in leukapheresis products.

BACKGROUND AIMS: Leukapheresis products for hematopoietic stem cell transplantation can be cryopreserved for various indications. Although it is known that CD34(+) cells tolerate cryopreservation well, a significant loss of CD3(+) cells has been observed, which has been ascribed to several factors, including transport, storage conditions and granulocyte-colony stimulating factor (G-CSF) administration. METHODS: To assess the tolerance of CD34(+) cells and lymphocyte subpopulations for cryopreservation and thawing, the post-thaw recoveries of CD34(+) cells, CD3(+)CD4(+) cells, CD3(+)CD8(+) cells, CD19(+) cells and CD16(+)CD56(+) cells were determined in 90 cryopreserved apheresis products, among which 65 were from G-CSF-mobilized donors, and 34 from unrelated donors that underwent transport before cryopreservation at our center. A controlled rate freezer and 5% dimethyl sulfoxide were used for cryopreservation. RESULTS: We could detect statistically significant differences for CD34(+) cell recovery (93.0 ± 20.7%) when compared to CD3(+)CD4(+) cell (83.1 ± 15.4%, P = 0.014), and CD3(+)CD8(+) cell recovery (83.3 ± 13.9%, P = 0.001). Similarly, CD19(+) cell recovery (98.6 ± 15.1%) was higher than CD3(+)CD4(+) cell (P = 2.5 × 10(-7)) and CD3(+)CD8(+) cell recovery (P = 1.2 × 10(-8)). Post-thaw recovery rates of all cell populations were not impaired in G-CSF-mobilized products compared with non-mobilized products nor in unrelated compared with related donor products. DISCUSSION: Our data suggest a lower tolerance of CD3(+) cells for cryopreservation and demonstrate that freezing-thawing resistance thawing is cell-specific and independent from other factors that affect post-thaw recovery of cryopreserved cells. Thus, a clinical consequence may be the monitoring of post-thaw CD3(+) cell doses of cryopreserved products, such as donor lymphocyte infusions.

The JAK-inhibitor ruxolitinib impairs dendritic cell function in vitro and in vivo.

The Janus kinase (JAK)-inhibitor ruxolitinib decreases constitutional symptoms and spleen size of myelofibrosis (MF) patients by mechanisms distinct from its anticlonal activity. Here we investigated whether ruxolitinib affects dendritic cell (DC) biology. The in vitro development of monocyte-derived DCs was almost completely blocked when the compound was added throughout the differentiation period. Furthermore, when applied solely during the final lipopolysaccharide-induced maturation step, ruxolitinib reduced DC activation as demonstrated by decreased interleukin-12 production and attenuated expression of activation markers. Ruxolitinib also impaired both in vitro and in vivo DC migration. Dysfunction of ruxolitinib-exposed DCs was further underlined by their impaired induction of allogeneic and antigen-specific T-cell responses. Ruxolitinib-treated mice immunized with ovalbumin (OVA)/CpG induced markedly reduced in vivo activation and proliferation of OVA-specific CD8⁺ T cells compared with vehicle-treated controls. Finally, using an adenoviral infection model, we show that ruxolitinib-exposed mice exhibit delayed adenoviral clearance. Our results demonstrate that ruxolitinib significantly affects DC differentiation and function leading to impaired T-cell activation. DC dysfunction may result in increased infection rates in ruxolitinib-treated patients. However, our findings may also explain the outstanding anti-inflammatory and immunomodulating activity of JAK inhibitors currently used in the treatment of MF and autoimmune diseases.

Imatinib mesylate and nilotinib affect MHC-class I presentation by modulating the proteasomal processing of antigenic peptides.

Imatinib (IM) has been described to modulate the function of dendritic cells and T lymphocytes and to affect the expression of antigen in CML cells. In our study, we investigated the effect of the tyrosine kinase inhibitors IM and nilotinib (NI) on antigen presentation and processing by analyzing the proteasomal activity in CML cell lines and patient samples. We used a biotinylated active site-directed probe, which covalently binds to the proteasomally active beta-subunits in an activity-dependent fashion. Additionally, we analyzed the cleavage and processing of HLA-A3/11- and HLA-B8-binding peptides derived from BCR-ABL by IM- or NI-treated isolated 20S immunoproteasomes using mass spectrometry. We found that IM treatment leads to a reduction in MHC-class I expression which is in line with the inhibition of proteasomal activity. This process is independent of BCR-ABL or apoptosis induction. In vitro digestion experiments using purified proteasomes showed that generation of epitope-precursor peptides was significantly altered in the presence of NI and IM. Treatment of the immunoproteasome with these compounds resulted in an almost complete reduction in the generation of long precursor peptides for the HLA-A3/A11 and -B8 epitopes while processing of the short peptide sequences increased. Treatment of isolated 20S proteasomes with serine-/threonine- and tyrosine-specific phosphatases induced a significant downregulation of the proteasomal activity further indicating that phosphorylation of the proteasome regulates its function and antigen processing. Our results demonstrate that IM and NI can affect the immunogenicity of malignant cells by modulating proteasomal degradation and the repertoire of processed T cell epitopes.

Regulation of dectin-1-mediated dendritic cell activation by peroxisome proliferator-activated receptor-gamma ligand troglitazone.

Dectin-1 is the major receptor for fungal ß-glucans. The activation of Dectin-1 leads to the up-regulation of surface molecules on dendritic cells (DCs) and cytokine secretion. Furthermore, Dectin-1 is important for the recruitment of leukocytes and the production of inflammatory mediators. Peroxisome proliferator-activated receptor-γ (PPAR-γ) and its ligands, cyclopentenone prostaglandins or thiazolidinediones, have modulatory effects on B-cell, T-cell, and DC function. In the present study, we analyzed the effects of troglitazone (TGZ), a high-affinity synthetic PPAR-γ ligand, on the Dectin-1-mediated activation of monocyte-derived human DCs. Dectin-1-mediated activation of DCs was inhibited by TGZ, as shown by down-regulation of costimulatory molecules and reduced secretion of cytokines and chemokines involved in T-lymphocyte activation. Furthermore, TGZ inhibited the T-cell-stimulatory capacity of DCs. These effects were not due to a diminished expression of Dectin-1 or to a reduced phosphorylation of spleen tyrosine kinase; they were mediated by the inhibition of downstream signaling molecules such as mitogen-activated protein kinases and nuclear factor-κB. Furthermore, curdlan-mediated accumulation of caspase recruitment domain 9 (CARD9) in the cytosol was inhibited by TGZ. Our data demonstrate that the PPAR-γ ligand TGZ inhibits Dectin-1-mediated activation by interfering with CARD9, mitogen-activated protein kinase, and nuclear factor-κB signaling pathways. This confirms their important role as negative-feedback regulators of potentially harmful inflammatory responses.

Spoilt for choice: different immunosuppressive potential of anaplastic lymphoma kinase inhibitors for non small cell lung cancer.

Introduction: Several anaplastic lymphoma kinase (ALK)-inhibitors (ALKi) have been approved for the treatment of ALK-translocated advanced or metastatic Non Small Cell Lung Cancer (NSCLC), amongst crizotinib and alectinib. This forces physicians to choose the most suitable compound for each individual patient on the basis of the tumor´s genetic profile, but also in regard to toxicities and potential co-treatments. Moreover, targeted therapies might be combined with or followed by immunotherapy, which underlines the importance to gain detailed knowledge about potential immunomodulatory effects of these inhibitors. We here aimed to 1.) determine whether ALKi display an immunosuppressive effect on human dendritic cells (DCs) as important mediators of antigen-specific immunity and to 2.) dissect whether this immunosuppression differs among ALKi. Methods: We investigated the effect of alectinib and crizotinib on human monocyte-derived DCs (moDC) as most powerful antigen-presenting cells. We performed immunophenotyping by flow cytometry, migration, antigen uptake and cytokine assays. Results: Crizotinib-treated DCs showed reduced activation markers, such as CD83, decreased chemokine-guided migration, lower antigen uptake and produced inferior levels of pro-inflammatory cytokines, especially Interleukin-12. In contrast, the immunosuppressive potential of alectinib was significantly less pronounced. This indicates that crizotinib might profoundly dampen anti-tumor immunity, while alectinib had no unfavourable immunosuppressive effects. Conclusions: Our results implicate that current ALKi differ in their capacity to suppress the activation, migration and cytokine production of DCs as essential mediators of T cell immunity. We show that crizotinib, but not alectinib, had immunosuppressive effects on DCs phenotype and reduced DC function, thereby potentially impairing anti-tumor immunity.

Baseline immune signature score of Tregs × HLA-DR+CD4+ T cells × PD1+CD8+ T cells predicts outcome to immunotherapy in cancer patients.

Background: The use of immunotherapy (IT) is rapidly increasing across different tumor entities. PD-L1 expression is primarily used for therapy evaluation. The disadvantages of PD-L1 status are spatial and temporal heterogeneity as well as tumor type-dependent variation of predictive value. To optimize patient selection for IT, new prediction markers for therapy success are needed. Based on the systemic efficacy of IT, we dissected the immune signature of peripheral blood as an easily accessible predictive biomarker for therapeutic success. Methods: We conducted a retrospective clinical study of 62 cancer patients treated with IT. We assessed peripheral immune cell counts before the start of IT via flow cytometry. The predictive value for therapy response of developed immune signature scores was tested by ROC curve analyses and scores were correlated with time to progression (TTP). Results: High score values of "Tregs ÷ (CD4+/CD8+ ratio)" (Score A) and high score values of "Tregs × HLA-DR+CD4+ T cells × PD1+CD8+ T cells" (Score B) significantly correlated with response at first staging (p = 0.001; p < 0.001). At the optimal cutoff point, Score A correctly predicted 79.1% and Score B correctly predicted 89.3% of the staging results (sensitivity: 86.2%, 90.0%; specificity: 64.3%, 87.5%). A high Score A and Score B statistically correlated with prolonged median TTP (6.13 vs. 2.17 months, p = 0.025; 6.43 vs. 1.83 months, p = 0.016). Cox regression analyses for TTP showed a risk reduction of 55.7% (HR = 0.44, p = 0.029) for Score A and an adjusted risk reduction of 73.2% (HR = 0.27, p = 0.016) for Score B. Conclusion: The two identified immune signature scores showed high predictive value for therapy response as well as for prolonged TTP in a pan-cancer patient population. Our scores are easy to determine by using peripheral blood and flow cytometry, apply to different cancer entities, and allow an outcome prediction before the start of IT.

RNA vaccines in cancer treatment.

The Cancer Report from the World Health Organization states that in the year 2000 12% of all death cases worldwide were caused by cancer. In the western world, the cancer death rates are often devastating, being at about 25%. This fact stresses the urgency to find effective cures against malignant diseases. New approaches in the treatment of cancer focus on the development of immunotherapies to fight the disease. Besides other methods, the usage of tumor-specific RNA as part of vaccines is investigated lately. RNA, administered alone or used for transfection of dendritic cells, shows several advantages as a vaccine including feasibility, applicability, safeness, and effectiveness when it comes to the generation of immune responses. This review concentrates on results from in vitro experiments and recent trials using RNA vaccines to present an overview about this specific strategy.

Dexamethasone induced inhibition of Dectin-1 activation of antigen presenting cells is mediated via STAT-3 and NF-κB signaling pathways.

Treatment of patients with glucocorticoids can result in an increased risk of infection with pathogens such as fungi. Dectin-1 is a member of the C-type lectin receptor superfamily and was shown to be one of the major receptors for fungal beta-glucans. Activation of Dectin-1 increases the production of cytokines and chemokines and T-cell stimulatory capacity of DC and mediates resolution of fungal infections. Here we show that antigen-presenting cells generated in the presence of dexamethasone (Dex-DC) have a reduced capacity to stimulate T-cell proliferation and decreased expression of costimulatory molecules, that can not be enhanced upon stimulation with Dectin-1 ligands. Stimulation of Dex-DC with beta-glucans induced a strong upregulation of Syk phosphorylation and increased secretion of IL-10, while the production of IL-12, IL-23 and TNF-alpha was reduced. Downstream of Syk stimulation of Dectin-1 on Dex-DC resulted in phosphorylation of STAT3 and reduced nuclear localization of transcription factors involved in DC activation and function.

Generation and functional characterization of MDSC-like cells.

Myeloid-derived suppressor cells (MDSC) are critical in regulating immune responses by suppressing antigen presenting cells (APC) and T cells. We previously observed that incubation of peripheral blood monocytes with interleukin (IL)-10 during their differentiation to monocyte-derived dendritic cells (moDCs) results in the generation of an APC population with a CD14+HLA-DRlowphenotype (IL-10-APC) with reduced stimulatory capacity similar to human MDSC. Co-incubation experiments now revealed that the addition of IL-10-APC to moDC caused a reduction of DC-induced T-cell proliferation, of the expression of maturation markers, and of secreted cytokines and chemokines such as TNF-α, IL-6, MIP-1α and Rantes. Addition of IL-10-APC increased the immunosuppressive molecule osteoactivin and its corresponding receptor syndecan-4 on moDC. Moreover, CD14+HLA-DRlow MDSC isolated from healthy donors expressed high levels of osteoactivin, which was even further upregulated by the auxiliary addition of IL-10. Using transcriptome analysis, we identified a set of molecules and pathways mediating these effects. In addition, we found that IL-10-APC as well as human isolated MDSC expressed higher levels of programmed death (PD)-1, PD-ligand-1 (PD-L1), glucocorticoid-induced-tumor-necrosis-factor-receptor-related-protein (GITR) and GITR-ligand. Inhibition of osteoactivin, syndecan-4, PD-1 or PD-L1 on MDSC by using blocking antibodies restored the stimulatory capacity of DC in co-incubation experiments. Activation of MDSC with Dectin-1 ligand curdlan reduced the expression of osteoactivin and PD-L1. Our results demonstrate that osteoactivin/syndecan-4 and PD-/PD-L1 are key molecules that are profoundly involved in the inhibitory effects of MDSC on DC function and might be promising tools for clinical application.

Interferon gamma modulates sensitivity of CML cells to tyrosine kinase inhibitors.

Immune effector cells such as T and NK cells can efficiently eliminate tumor cells. However, when activating oncogenic signaling pathways or protective mechanisms against cell death are active, immune cells can also confer therapy resistance. Here, we analyzed the role of activated T and NK cells and released cytokines on tyrosine kinase inhibitors imatinib and nilotinib - mediated apoptosis induction and proliferation of chronic myelogenous leukemia (CML) cells. Incubation of CML cells with activated, but not with resting CD3+ T cells or with activated NK cells significantly inhibited TKI-induced apoptosis induction in CML cells as quantified by nuclear fragmentation assays. Transwell experiments revealed a critical role for T or NK cell-derived cytokines for CML cell protection. Accordingly, CML cells treated with IFNγ also showed a clearly reduced sensitivity to TKI-mediated cell death induction and inhibition of proliferation. In contrast, IFNα or other pro-inflammatory mediators and cytokines, such as TNFα and GM-CSF did not impair TKI-induced apoptosis in CML cells. On a molecular level, IFNγ-exposed CML cells showed a significantly reduced caspase-3 activation and PARP-1 cleavage as well as an increased expression of anti-apoptotic molecule xIAP. Finally, IFNγ diminished TKI-induced downregulation of Jak-2 and STAT-5 phosphorylation and increased nuclear expression of RUNX-1, which may at least in part contribute to the reduced sensitivity to TKI effects. Our results demonstrate that IFNγ released by activated T or NK cells may interfere with the therapeutic effects of TKI in CML. Our findings may have important implications for the understanding of inflammation-mediated BCR-ABL independent resistance mechanisms.

The VEGF-Receptor Inhibitor Axitinib Impairs Dendritic Cell Phenotype and Function.

Inhibitors of VEGF receptor (VEGFR) signaling such as sorafenib and sunitinib that are currently used in the treatment of malignant diseases have been shown to affect immunological responses by inhibition of the function of antigen presenting cells and T lymphocytes. The VEGFR-inhibitor axitinib has recently been approved for second line therapy of metastatic renal cell carcinoma. While there is some evidence that axitinib might interfere with the activation of T cells, not much is known about the effects of axitinib on dendritic cell (DC) phenotype and function. We here show that the addition of axitinib during the final Toll-like receptor-4-induced maturation step of monocyte-derived human DCs results in a reduced DC activation characterized by impaired expression of activation markers and co-stimulatory molecules such as CD80, CD83 and CD86. We further found a decreased secretion of interleukin-12 which was accompanied by reduced nuclear expression of the transcription factor cRel. In addition, we found a dose-dependent reduced activation of p38 and STAT3 in axitinib-exposed DCs, whereas the expression was not affected. The dysfunction of axitinib-exposed DCs was further underlined by their impaired induction of allogeneic T cell proliferation in a mixed lymphocyte reaction assay and inhibition of DC migration. Our results demonstrate that axitinib significantly affects DC differentiation and function primarily via the inhibition of the nuclear factor kappa B signaling pathway leading to impaired T cell activation. This will be of importance for the design of future vaccination protocols and therapeutic approaches aiming at combining different treatment strategies, eg such as programmed death-1 inhibitors with axitinib.

Analysis of the anti-proliferative and the pro-apoptotic efficacy of Syk inhibition in multiple myeloma.

BACKGROUND: Multiple myeloma (MM) is a clonal B cell malignancy characterized by proliferation of malignant plasma cells in the bone marrow. Despite high-dose melphalan therapy with autologous stem cell transplantation (ASCT) and the introduction of immunomodulatory drugs like bortezomib or lenalidomide, that have been associated with improved survival, MM is still incurable and new treatment options are needed. In B cell malignancies such as chronic lymphocytic leukaemia (CLL) or diffuse large B cell lymphoma (DLBCL), Syk (spleen tyrosine kinase) inhibitors have shown promising in vitro and first clinical results. In our study, we analyzed the potential of Syk as a target in MM. METHODS: The MM cell lines AMO-1, U266 and RPMI8226 and primary MM cells were treated with the Syk inhibitors BAY61-3606, R406 or Piceatannol and proliferation, migration and apoptosis induction were analyzed. Effects on involved intracellular signaling cascades were determined by Western blotting. Furthermore, we analyzed synergistic and additive effects of Syk inhibitors in combination with established anti-myeloma drugs and experimental inhibitors (e.g. PI-3-Kinase inhibitor NVP-BEZ235). RESULTS: Incubation of MM cell lines as well as primary MM cells with Syk inhibitors resulted in a reduced proliferation and stromal cell-derived factor-1 alpha (SDF-1 alpha) induced migration that was accompanied by a concentration dependent inhibition of the MAP-Kinase, characterized by reduced phosphorylation of ERK an p38 molecules, and NF-kappaB signalling pathways. Furthermore, Syk inhibition induced apoptosis in MM cells in a dose-dependent manner, characterized by reduced expression of pro-caspase 3, increased PARP-1 cleavage and enhanced release of cytochrome c. In addition combined treatment of MM cells with Syk inhibitors and NVP-BEZ235 (dual PI3-kinase/mTOR inhibitor) or MAPK inhibitors (PD98059, SP600125, U0126, SB203580) resulted in increased apoptotic activity of the drugs. CONCLUSIONS: Our results show that Syk inhibition might represent a promising new treatment option in MM with an increased efficacy when combined with MAP kinase inhibitors. Furthermore, our study strongly underlines the potency of Syk inhibitors as a potential therapeutic treatment option for MM patients.

Advances in immunotherapy of chronic myeloid leukemia CML.

Tyrosine kinase inhibitors induce sustained disease remissions in chronic myeloid leukemia by exploiting the addiction of this type of leukemia to the activity of the fusion oncogene BCR-ABL. However, these agents fail to eradicate CML stem cells which are ultimately responsible for disease relapses upon treatment discontinuation. Evidence that the immune system can effectively reject CML stem cells potentially leading to patient cure is provided by the experience with patients receiving allogeneic bone marrow transplantations. Compelling evidence indicates that more modern, antigen-specific immunotherapeutic approaches are also feasible and hold strong potential to be clinically effective. Amongst these, particularly promising is the use of autologous dendritic cells pulsed with antigens or direct application of in vitro transcribed RNA encoding for leukemia-associated antigens, since this approach allows to circumvent HLA-restriction of the leukemia-associated T cell epitopes that have been eventually identified. Combining these strategies with monoclonal antibodies, such as anti-CTLA-4 or anti-PD-1, may help to obtain even stronger immune responses and better clinical results. This narrative review addresses this topic by focusing in particular on the cell-based immunotherapeutic strategies for CML and on the issue of the leukemia-associated antigens to be selected for targeting.