Microbiota-dependent activation of the myeloid calcineurin-NFAT pathway inhibits B7H3- and B7H4-dependent anti-tumor immunity in colorectal cancer.

Bacterial sensing by intestinal tumor cells contributes to tumor growth through cell-intrinsic activation of the calcineurin-NFAT axis, but the role of this pathway in other intestinal cells remains unclear. Here, we found that myeloid-specific deletion of calcineurin in mice activated protective CD8+ T cell responses and inhibited colorectal cancer (CRC) growth. Microbial sensing by myeloid cells promoted calcineurin- and NFAT-dependent interleukin 6 (IL-6) release, expression of the co-inhibitory molecules B7H3 and B7H4 by tumor cells, and inhibition of CD8+ T cell-dependent anti-tumor immunity. Accordingly, targeting members of this pathway activated protective CD8+ T cell responses and inhibited primary and metastatic CRC growth. B7H3 and B7H4 were expressed by the majority of human primary CRCs and metastases, which was associated with low numbers of tumor-infiltrating CD8+ T cells and poor survival. Therefore, a microbiota-, calcineurin-, and B7H3/B7H4-dependent pathway controls anti-tumor immunity, revealing additional targets for immune checkpoint inhibition in microsatellite-stable CRC.

CD38 promotes hematopoietic stem cell dormancy.

A subpopulation of deeply quiescent, so-called dormant hematopoietic stem cells (dHSCs) resides at the top of the hematopoietic hierarchy and serves as a reserve pool for HSCs. The state of dormancy protects the HSC pool from exhaustion throughout life; however, excessive dormancy may prevent an efficient response to hematological stresses. Despite the significance of dHSCs, the mechanisms maintaining their dormancy remain elusive. Here, we identify CD38 as a novel and broadly applicable surface marker for the enrichment of murine dHSCs. We demonstrate that cyclic adenosine diphosphate ribose (cADPR), the product of CD38 cyclase activity, regulates the expression of the transcription factor c-Fos by increasing the release of Ca2+ from the endoplasmic reticulum (ER). Subsequently, we uncover that c-Fos induces the expression of the cell cycle inhibitor p57Kip2 to drive HSC dormancy. Moreover, we found that CD38 ecto-enzymatic activity at the neighboring CD38-positive cells can promote human HSC quiescence. Together, CD38/cADPR/Ca2+/c-Fos/p57Kip2 axis maintains HSC dormancy. Pharmacological manipulations of this pathway can provide new strategies to improve the success of stem cell transplantation and blood regeneration after injury or disease.

BRAF and MEK inhibitor combinations induce potent molecular and immunological effects in NRAS-mutant melanoma cells: Insights into mode of action and resistance mechanisms.

About 25% of melanoma harbor activating NRAS mutations, which are associated with aggressive disease therefore requiring a rapid antitumor intervention. However, no efficient targeted therapy options are currently available for patients with NRAS-mutant melanoma. MEK inhibitors (MEKi) appear to display a moderate antitumor activity and also immunological effects in NRAS-mutant melanoma, providing an ideal backbone for combination treatments. In our study, the MEKi binimetinib, cobimetinib and trametinib combined with the BRAF inhibitors (BRAFi) encorafenib, vemurafenib and dabrafenib were investigated for their ability to inhibit proliferation, induce apoptosis and alter the expression of immune modulatory molecules in sensitive NRAS-mutant melanoma cells using two- and three-dimensional cell culture models as well as RNA sequencing analyses. Furthermore, NRAS-mutant melanoma cells resistant to the three BRAFi/MEKi combinations were established to characterize the mechanisms contributing to their resistance. All BRAFi induced a stress response in the sensitive NRAS-mutant melanoma cells thereby significantly enhancing the antiproliferative and proapoptotic activity of the MEKi analyzed. Furthermore, BRAFi/MEKi combinations upregulated immune relevant molecules, such as ICOS-L, components of antigen-presenting machinery and the "don't eat me signal" molecule CD47 in the melanoma cells. The BRAFi/MEKi-resistant, NRAS-mutant melanoma cells counteracted the molecular and immunological effects of BRAFi/MEKi by upregulating downstream mitogen-activated protein kinase pathway molecules, inhibiting apoptosis and promoting immune escape mechanisms. Together, our study reveals potent molecular and immunological effects of BRAFi/MEKi in sensitive NRAS-mutant melanoma cells that may be exploited in new combinational treatment strategies for patients with NRAS-mutant melanoma.

Guidelines for visualization and analysis of DC in tissues using multiparameter fluorescence microscopy imaging methods.

This article is part of the Dendritic Cell Guidelines article series, which provides a collection of state-of-the-art protocols for the preparation, phenotype analysis by flow cytometry, generation, fluorescence microscopy, and functional characterization of mouse and human dendritic cells (DC) from lymphoid organs and various non-lymphoid tissues. Here, we provide detailed procedures for a variety of multiparameter fluorescence microscopy imaging methods to explore the spatial organization of DC in tissues and to dissect how DC migrate, communicate, and mediate their multiple functional roles in immunity in a variety of tissue settings. The protocols presented here entail approaches to study DC dynamics and T cell cross-talk by intravital microscopy, large-scale visualization, identification, and quantitative analysis of DC subsets and their functions by multiparameter fluorescence microscopy of fixed tissue sections, and an approach to study DC interactions with tissue cells in a 3D cell culture model. While all protocols were written by experienced scientists who routinely use them in their work, this article was also peer-reviewed by leading experts and approved by all co-authors, making it an essential resource for basic and clinical DC immunologists.

Bone marrow-derived mesenchymal stromal cells obstruct AML-targeting CD8+ clonal effector and CAR T-cell function while promoting a senescence-associated phenotype.

Bone marrow mesenchymal stromal cells (MSCs) have been described as potent regulators of T-cell function, though whether they could impede the effectiveness of immunotherapy against acute myeloid leukemia (AML) is still under investigation. We examine whether they could interfere with the activity of leukemia-specific clonal cytotoxic T-lymphocytes (CTLs) and chimeric antigen receptor (CAR) T cells, as well as whether the immunomodulatory properties of MSCs could be associated with the induction of T-cell senescence. Co-cultures of leukemia-associated Wilm's tumor protein 1 (WT1) and tyrosine-protein kinase transmembrane receptor 1 (ROR1)-reactive CTLs and of CD123-redirected switchable CAR T cells were prepared in the presence of MSCs and assessed for cytotoxic potential, cytokine secretion, and expansion. T-cell senescence within functional memory sub-compartments was investigated for the senescence-associated phenotype CD28-CD57+ using unmodified peripheral blood mononuclear cells. We describe inhibition of expansion of AML-redirected switchable CAR T cells by MSCs via indoleamine 2,3-dioxygenase 1 (IDO-1) activity, as well as reduction of interferon gamma (IFNγ) and interleukin-2 (IL-2) release. In addition, MSCs interfered with the secretory potential of leukemia-associated WT1- and ROR1-targeting CTL clones, inhibiting the release of IFNγ, tumor necrosis factor alpha, and IL-2. Abrogated T cells were shown to retain their cytolytic activity. Moreover, we demonstrate induction of a CD28loCD27loCD57+KLRG1+ senescent T-cell phenotype by MSCs. In summary, we show that MSCs are potent modulators of anti-leukemic T cells, and targeting their modes of action would likely be beneficial in a combinatorial approach with AML-directed immunotherapy.

Correlation of microscopic tumor extension with tumor microenvironment in esophageal cancer patients.

OBJECTIVE: In the era of image-guided adaptive radiotherapy, definition of the clinical target volume (CTV) is a challenge in various solid tumors, including esophageal cancer (EC). Many tumor microenvironmental factors, e.g., tumor cell proliferation or cancer stem cells, are hypothesized to be involved in microscopic tumor extension (MTE). Therefore, this study assessed the expression of FAK, ILK, CD44, HIF-1α, and Ki67 in EC patients after neoadjuvant radiochemotherapy followed by tumor resection (NRCHT+R) and correlated these markers with the MTE. METHODS: Formalin-fixed paraffin-embedded tumor resection specimens of ten EC patients were analyzed using multiplex immunofluorescence staining. Since gold fiducial markers had been endoscopically implanted at the proximal and distal tumor borders prior to NRCHT+R, correlation of the markers with the MTE was feasible. RESULTS: In tumor resection specimens of EC patients, the overall percentages of FAK+, CD44+, HIF-1α+, and Ki67+ cells were higher in tumor nests than in the tumor stroma, with the outcome for Ki67+ cells reaching statistical significance (p < 0.001). Conversely, expression of ILK+ cells was higher in tumor stroma, albeit not statistically significantly. In three patients, MTE beyond the fiducial markers was found, reaching up to 31 mm. CONCLUSION: Our findings indicate that the overall expression of FAK, HIF-1α, Ki67, and CD44 was higher in tumor nests, whereas that of ILK was higher in tumor stroma. Differences in the TME between patients with residual tumor cells in the original CTV compared to those without were not found. Thus, there is insufficient evidence that the TME influences the required CTV margin on an individual patient basis. TRIAL REGISTRATION NUMBER AND DATE: BO-EK-148042017 and BO-EK-177042022 on 20.06.2022, DRKS00011886, https://drks.de/search/de/trial/DRKS00011886 .

Cyclosporin A-Based PROTACs Can Deplete Abundant Cellular Cyclophilin A without Suppressing T Cell Activation.

Cyclophilin A (CypA), the cellular receptor of the immunosuppressant cyclosporin A (CsA), is an abundant cytosolic protein and is involved in a variety of diseases. For example, CypA supports cancer proliferation and mediates viral infections, such as the human immunodeficiency virus 1 (HIV-1). Here, we present the design of PROTAC (proteolysis targeting chimera) compounds against CypA to induce its intracellular proteolysis and to investigate their effect on immune cells. Interestingly, upon connecting to E3 ligase ligands, both peptide-based low-affinity binders and CsA-based high-affinity binders can degrade CypA at nM concentration in HeLa cells and fibroblast cells. As the immunosuppressive effect of CsA is not directly associated with the binding of CsA to CypA but the inhibition of phosphatase calcineurin by the CypA:CsA complex, we investigated whether a CsA-based PROTAC compound could induce CypA degradation without affecting the activation of immune cells. P3, the most efficient PROTAC compound discovered from this study, could deplete CypA in lymphocytes without affecting cell proliferation and cytokine production. This work demonstrates the feasibility of the PROTAC approach in depleting the abundant cellular protein CypA at low drug dosage without affecting immune cells, allowing us to investigate the potential therapeutic effects associated with the endogenous protein in the future.

Tailored immunotherapy approach with nivolumab with or without ipilimumab in patients with advanced transitional cell carcinoma after platinum-based chemotherapy (TITAN-TCC): a multicentre, single-arm, phase 2 trial.

BACKGROUND: Nivolumab is used after platinum-based chemotherapy in patients with metastatic urothelial carcinoma. Studies suggest improved outcomes for dual checkpoint inhibition with high ipilimumab doses. We aimed to examine the safety and activity of nivolumab induction and high-dose ipilimumab as an immunotherapeutic boost as a second-line treatment for patients with metastatic urothelial carcinoma. METHODS: TITAN-TCC is a multicentre, single-arm, phase 2 trial done at 19 hospitals and cancer centres in Germany and Austria. Adults aged 18 years or older with histologically confirmed metastatic or surgically unresectable urothelial cancer of the bladder, urethra, ureter, or renal pelvis were eligible. Patients had to have progression during or after first-line platinum-based chemotherapy and up to one more second-line or third-line treatment, a Karnofsky Performance Score of 70 or higher, and measurable disease as per Response Evaluation Criteria in Solid Tumors version 1.1. After four doses of intravenous nivolumab 240 mg induction monotherapy every 2 weeks, patients with a partial or complete response at week 8 continued maintenance nivolumab, whereas those with stable or progressive disease (non-responders) at week 8 received a boost of two or four doses of intravenous nivolumab 1 mg/kg plus ipilimumab 3 mg/kg every 3 weeks. Patients who subsequently had progressive disease during nivolumab maintenance also received a boost, using this schedule. The primary endpoint was the confirmed investigator-assessed objective response rate in the intention-to-treat population and had to exceed 20% for the null hypothesis to be rejected (based on the objective response rate with nivolumab monotherapy in the CheckMate-275 phase 2 trial). This study is registered with ClinicalTrials.gov, NCT03219775, and is ongoing. FINDINGS: Between April 8, 2019, and Feb 15, 2021, 83 patients with metastatic urothelial carcinoma were enrolled and all received nivolumab induction treatment (intention-to-treat population). The median age of enrolled patients was 68 years (IQR 61-76), and 57 (69%) were male and 26 (31%) were female. 50 (60%) patients received at least one boost dose. A confirmed investigator-assessed objective response was recorded in 27 (33%) of 83 patients in the intention-to-treat population, including six (7%) patients who had a complete response. This objective response rate was significantly higher than the prespecified threshold of 20% or less (33% [90% CI 24-42]; p=0·0049). The most common grade 3-4 treatment-related adverse events were immune-mediated enterocolitis (nine [11%] patients) and diarrhoea (five [6%] patients). Two (2%) treatment-related deaths were reported, both due to immune-mediated enterocolitis. INTERPRETATION: Treatment with nivolumab and nivolumab plus ipilimumab boosts in early non-responders and patients who progress late significantly improved objective response rate after previous platinum-based chemotherapy compared with the rate reported with nivolumab in the CheckMate-275 trial. Our study provides evidence for the added value of high-dose ipilimumab 3 mg/kg and suggests a potential role for the combination as a rescue strategy in platinum-pretreated patients with metastatic urothelial carcinoma. FUNDING: Bristol Myers Squibb.

Tailored immunotherapy approach with nivolumab with or without nivolumab plus ipilimumab as immunotherapeutic boost in patients with metastatic renal cell carcinoma (TITAN-RCC): a multicentre, single-arm, phase 2 trial.

BACKGROUND: Nivolumab plus ipilimumab is approved as first-line regimen for intermediate-risk or poor-risk metastatic renal cell carcinoma, and nivolumab monotherapy as second-line therapy for all risk groups. We aimed to examine the efficacy and safety of nivolumab monotherapy and nivolumab plus ipilimumab combination as an immunotherapeutic boost after no response to nivolumab monotherapy in patients with intermediate-risk and poor-risk clear-cell metastatic renal cell carcinoma. METHODS: TITAN-RCC is a multicentre, single-arm, phase 2 trial, done at 28 hospitals and cancer centres across Europe (Austria, Belgium, Czech Republic, France, Germany, Italy, Spain, and the UK). Adults (aged ≥18 years) with histologically confirmed intermediate-risk or poor-risk clear-cell metastatic renal cell carcinoma who were formerly untreated (first-line population) or pretreated with one previous systemic therapy (anti-angiogenic or temsirolimus; second-line population) were eligible. Patients had to have a Karnofsky Performance Status score of at least 70 and measurable disease per Response Evaluation Criteria in Solid Tumours (version 1.1). Patients started with intravenous nivolumab 240 mg once every 2 weeks. On early progressive disease (week 8) or non-response at week 16, patients received two or four doses of intravenous nivolumab (3 mg/kg) and ipilimumab (1 mg/kg) boosts (once every 3 weeks), whereas responders continued with intravenous nivolumab (240 mg, once every 2 weeks), but could receive two to four boost doses of nivolumab plus ipilimumab for subsequent progressive disease. The primary endpoint was confirmed investigator-assessed objective response rate in the full analysis set, which included all patients who received at least one dose of study medication; safety was also assessed in this population. An objective response rate of more than 25% was required to reject the null hypothesis and show improvement, on the basis of results from the pivotal phase 3 CheckMate-025 trial. This study is registered with ClinicalTrials.gov, NCT02917772, and is complete. FINDINGS: Between Oct 28, 2016, and Nov 30, 2018, 207 patients were enrolled and all received nivolumab induction (109 patients in the first-line group; 98 patients in the second-line group). 60 (29%) of 207 patients were female and 147 (71%) were male. 147 (71%) of 207 patients had intermediate-risk metastatic renal cell carcinoma and 51 (25%) had poor-risk disease. After median follow-up of 27·6 months (IQR 10·5-34·8), 39 (36%, 90% CI 28-44; p=0·0080) of 109 patients in the first-line group and 31 (32%, 24-40; p=0·083) of 98 patients in the second-line group had a confirmed objective response for nivolumab with and without nivolumab plus ipilimumab. Confirmed response to nivolumab at week 8 or 16 was observed in 31 (28%) of 109 patients in the first-line group and 18 (18%) of 98 patients in the second-line group. The most frequent grade 3-4 treatment-related adverse events (reported in ≥5% of patients) were increased lipase (15 [7%] of 207 patients), colitis (13 [6%]), and diarrhoea (13 [6%]). Three deaths were reported that were deemed to be treatment-related: one due to possible ischaemic stroke, one due to respiratory failure, and one due to pneumonia. INTERPRETATION: In treatment-naive patients, nivolumab induction with or without nivolumab plus ipilimumab boosts significantly improved the objective response rate compared with that reported for nivolumab monotherapy in the CheckMate-025 trial. However, overall efficacy seemed inferior when compared with approved upfront nivolumab plus ipilimumab. For second-line treatment, nivolumab plus ipilimumab could be a rescue strategy on progression with approved nivolumab monotherapy. FUNDING: Bristol Myers Squibb.

Tumor-associated human dendritic cell subsets: Phenotype, functional orientation, and clinical relevance.

DCs play a pivotal role in orchestrating innate and adaptive antitumor immunity. Activated DCs can produce large amounts of various proinflammatory cytokines, initiate T-cell responses, and exhibit direct cytotoxicity against tumor cells. They also efficiently enhance the antitumoral properties of NK cells and T lymphocytes. Based on these capabilities, immunogenic DCs promote tumor elimination and are associated with improved survival of patients. Furthermore, they can essentially contribute to the clinical efficacy of immunotherapeutic strategies for cancer patients. However, depending on their intrinsic properties and the tumor microenvironment, DCs can be rendered dysfunctional and mediate tolerance by producing immunosuppressive cytokines and activating Treg cells. Such tolerogenic DCs can foster tumor progression and are linked to poor prognosis of patients. Here, we focus on recent studies exploring the phenotype, functional orientation, and clinical relevance of tumor-infiltrating conventional DC1, conventional DC2, plasmacytoid DCs, and monocyte-derived DCs in translational and clinical settings. In addition, recent findings demonstrating the influence of DCs on the efficacy of immunotherapeutic strategies are summarized.

Targeting intracellular WT1 in AML with a novel RMF-peptide-MHC-specific T-cell bispecific antibody.

Antibody-based immunotherapy is a promising strategy for targeting chemoresistant leukemic cells. However, classical antibody-based approaches are restricted to targeting lineage-specific cell surface antigens. By targeting intracellular antigens, a large number of other leukemia-associated targets would become accessible. In this study, we evaluated a novel T-cell bispecific (TCB) antibody, generated by using CrossMAb and knob-into-holes technology, containing a bivalent T-cell receptor-like binding domain that recognizes the RMFPNAPYL peptide derived from the intracellular tumor antigen Wilms tumor protein (WT1) in the context of HLA-A*02. Binding to CD3ε recruits T cells irrespective of their T-cell receptor specificity. WT1-TCB elicited antibody-mediated T-cell cytotoxicity against AML cell lines in a WT1- and HLA-restricted manner. Specific lysis of primary acute myeloid leukemia (AML) cells was mediated in ex vivo long-term cocultures by using allogeneic (mean ± standard error of the mean [SEM] specific lysis, 67 ± 6% after 13-14 days; n = 18) or autologous, patient-derived T cells (mean ± SEM specific lysis, 54 ± 12% after 11-14 days; n = 8). WT1-TCB-treated T cells exhibited higher cytotoxicity against primary AML cells than an HLA-A*02 RMF-specific T-cell clone. Combining WT1-TCB with the immunomodulatory drug lenalidomide further enhanced antibody-mediated T-cell cytotoxicity against primary AML cells (mean ± SEM specific lysis on days 3-4, 45.4 ± 9.0% vs 70.8 ± 8.3%; P = .015; n = 9-10). In vivo, WT1-TCB-treated humanized mice bearing SKM-1 tumors exhibited a significant and dose-dependent reduction in tumor growth. In summary, we show that WT1-TCB facilitates potent in vitro, ex vivo, and in vivo killing of AML cell lines and primary AML cells; these results led to the initiation of a phase 1 trial in patients with relapsed/refractory AML (#NCT04580121).

Concluding remarks: Carbon dioxide utilization: where are we now? and where are we going?

This publication is reminiscent of the 12 principles of CO2 chemistry as formulated in the first Faraday Discussion on CO2 utilization in 2015. Their visionary significance at the time is brought into context with the current developments in society and industry. "What has changed since then?" and "is our enthusiasm still enough?" are only a few questions that are to be answered in the following from today's perspective. The synergy of the use of carbon dioxide (CCU) with the concepts of green chemistry as well as the connection to the energy sector is demonstrated using selected examples from industry and research.

T Cell Mediated Conversion of a Non-Anti-La Reactive B Cell to an Autoreactive Anti-La B Cell by Somatic Hypermutation.

Since the first description of nuclear autoantigens in the late 1960s and early 1970s, researchers, including ourselves, have found it difficult to establish monoclonal antibodies (mabs) against nuclear antigens, including the La/SS-B (Sjögrens' syndrome associated antigen B) autoantigen. To date, only a few anti-La mabs have been derived by conventional hybridoma technology; however, those anti-La mabs were not bona fide autoantibodies as they recognize either human La specific, cryptic, or post-translationally modified epitopes which are not accessible on native mouse La protein. Herein, we present a series of novel murine anti-La mabs including truly autoreactive ones. These mabs were elicited from a human La transgenic animal through adoptive transfer of T cells from non-transgenic mice immunized with human La antigen. Detailed epitope and paratope analyses experimentally confirm the hypothesis that somatic hypermutations that occur during T cell dependent maturation can lead to autoreactivity to the nuclear La/SS-B autoantigen.

And Yet It Moves: Oxidation of the Nuclear Autoantigen La/SS-B Is the Driving Force for Nucleo-Cytoplasmic Shuttling.

Decades ago, we and many other groups showed a nucleo-cytoplasmic translocation of La protein in cultured cells. This shuttling of La protein was seen after UV irradiation, virus infections, hydrogen peroxide exposure and the Fenton reaction based on iron or copper ions. All of these conditions are somehow related to oxidative stress. Unfortunately, these harsh conditions could also cause an artificial release of La protein. Even until today, the shuttling and the cytoplasmic function of La/SS-B is controversially discussed. Moreover, the driving mechanism for the shuttling of La protein remains unclear. Recently, we showed that La protein undergoes redox-dependent conformational changes. Moreover, we developed anti-La monoclonal antibodies (anti-La mAbs), which are specific for either the reduced form of La protein or the oxidized form. Using these tools, here we show that redox-dependent conformational changes are the driving force for the shuttling of La protein. Moreover, we show that translocation of La protein to the cytoplasm can be triggered in a ligand/receptor-dependent manner under physiological conditions. We show that ligands of toll-like receptors lead to a redox-dependent shuttling of La protein. The shuttling of La protein depends on the redox status of the respective cell type. Endothelial cells are usually resistant to the shuttling of La protein, while dendritic cells are highly sensitive. However, the deprivation of intracellular reducing agents in endothelial cells makes endothelial cells sensitive to a redox-dependent shuttling of La protein.

Two Be or Not Two Be: The Nuclear Autoantigen La/SS-B Is Able to Form Dimers and Oligomers in a Redox Dependent Manner.

According to the literature, the autoantigen La is involved in Cap-independent translation. It was proposed that one prerequisite for this function is the formation of a protein dimer. However, structural analyses argue against La protein dimers. Noteworthy to mention, these structural analyses were performed under reducing conditions. Here we describe that La protein can undergo redox-dependent structural changes. The oxidized form of La protein can form dimers, oligomers and even polymers stabilized by disulfide bridges. The primary sequence of La protein contains three cysteine residues. Only after mutation of all three cysteine residues to alanine La protein becomes insensitive to oxidation, indicating that all three cysteines are involved in redox-dependent structural changes. Biophysical analyses of the secondary structure of La protein support the redox-dependent conformational changes. Moreover, we identified monoclonal anti-La antibodies (anti-La mAbs) that react with either the reduced or oxidized form of La protein. Differential reactivities to the reduced and oxidized form of La protein were also found in anti-La sera of autoimmune patients.

Reliable isolation of human mesenchymal stromal cells from bone marrow biopsy specimens in patients after allogeneic hematopoietic cell transplantation.

Isolation of mesenchymal stromal cells (MSCs) from pretreated, hematologic patients is challenging. Especially after allogeneic hematopoietic cell transplantation (HCT), standard protocols using bone marrow aspirates fail to reliably recover sufficient cell numbers. Because MSCs are considered to contribute to processes that mainly affect the outcome after transplantation, such as an efficient lymphohematopoietic recovery, extent of graft-versus-host disease as well as the occurrence of leukemic relapse, it is of great clinical relevance to investigate MSC function in this context. Previous studies showed that MSCs can be isolated by collagenase digestion of large bone fragments of hematologically healthy patients undergoing hip replacement or knee surgeries. We have now further developed this procedure for the isolation of MSCs from hematologic patients after allogeneic HCT by using trephine biopsy specimens obtained during routine examinations. Comparison of aspirates and trephine biopsy specimens from patients after allogeneic HCT revealed a significantly higher frequency of clonogenic MSCs (colony-forming unit-fibroblast [CFU-F]) in trephine biopsy specimens (mean, 289.8 ± standard deviation 322.5 CFU-F colonies/1 × 106 total nucleated cells versus 4.2 ± 9.9; P < 0.0001). Subsequent expansion of functional MSCs isolated from trephine biopsy specimen was more robust and led to a significantly higher yield compared with control samples expanded from aspirates (median, 1.6 × 106; range, 0-2.3 × 107 P0 MSCs versus 5.4 × 104; range, 0-8.9 × 106; P < 0.0001). Using trephine biopsy specimens as MSC source facilitates the investigation of various clinical questions.

Midostaurin abrogates CD33-directed UniCAR and CD33-CD3 bispecific antibody therapy in acute myeloid leukaemia.

Combinatory therapeutic approaches of different targeted therapies in acute myeloid leukaemia are currently under preclinical/early clinical investigation. To enhance anti-tumour effects, we combined the tyrosine kinase inhibitor (TKI) midostaurin and T-cell mediated immunotherapy directed against CD33. Clinically relevant concentrations of midostaurin abrogated T-cell mediated cytotoxicity both after activation with bispecific antibodies and chimeric antigen receptor T cells. This information is of relevance for clinicians exploring T-cell mediated immunotherapy in early clinical trials. Given the profound inhibition of T-cell functionality and anti-tumour activity, we recommend specific FLT3 TKIs for further clinical testing of combinatory approaches with T-cell based immunotherapy.

PRAME peptide-specific CD8+ T cells represent the predominant response against leukemia-associated antigens in healthy individuals.

Antigen-specific T cells isolated from healthy individuals (HIs) have shown great therapeutic potential upon adoptive transfer for the treatment of viremia in immunosuppressed patients. The lack of comprehensive data on the prevalence and characteristics of leukemia-associated antigen (LAA)-specific T cells in HIs still limits such an approach for tumor therapy. Therefore, we have investigated T-cell responses against prominent candidates comprising Wilms' tumor protein 1 (WT1), preferentially expressed antigen in melanoma (PRAME), Survivin, NY-ESO, and p53 by screening PBMCs from HIs using intracellular IFN-γ staining following provocation with LAA peptide mixes. Here, we found predominantly poly-functional effector/effector memory CCR7- /CD45RA+/- /CD8+ LAA peptide-specific T cells with varying CD95 expression in 34 of 100 tested HIs, whereas CD4+ T cells responses were restricted to 5. Most frequent LAA peptide-specific T cell responses were directed against WT1 and PRAME peptides with a prevalence of 20 and 17%, respectively, showing the highest magnitude (0.16% ± 0.22% (mean ± SD)) for PRAME peptides. Cytotoxicity of PRAME peptide-specific T cells was demonstrated by specific killing of PRAME peptide-pulsed T2 cells. Furthermore, the proliferative capacity of PRAME peptide-specific T cells was confined to HIs responsive toward PRAME peptide challenge corroborating the accuracy of the screening results. In conclusion, we identified PRAME as a promising target antigen for adoptive leukemia therapy.

Engrafting human regulatory T cells with a flexible modular chimeric antigen receptor technology.

As regulatory T cells (Tregs) play a fundamental role in immune homeostasis their adoptive transfer emerged as a promising treatment strategy for inflammation-related diseases. Preclinical animal models underline the superiority of antigen-specific Tregs compared to polyclonal cells. Here, we applied a modular chimeric antigen receptor (CAR) technology called UniCAR for generation of antigen-specific human Tregs. In contrast to conventional CARs, UniCAR-endowed Tregs are indirectly linked to their target cells via a separate targeting module (TM). Thus, transduced Tregs can be applied universally as their antigen-specificity is easily adjusted by TM exchange. Activation of UniCAR-engrafted Tregs occurred in strict dependence on the TM, facilitating a precise control over Treg activity. In order to augment efficacy and safety, different intracellular signaling domains were tested. Both 4-1BB (CD137) and CD28 costimulation induced strong suppressive function of genetically modified Tregs. However, in light of safety issues, UniCARs comprising a CD137-CD3ζ signaling domain emerged as constructs of choice for a clinical application of redirected Tregs. In that regard, Tregs isolated from patients suffering from autoimmune or inflammatory diseases were, for the first time, successfully engineered with UniCAR 137/ζ and efficiently suppressed patient-derived effector cells. Overall, the UniCAR platform represents a promising approach to improve Treg-based immunotherapies for tolerance induction.

Immunomodulatory effects of BRAF and MEK inhibitors: Implications for Melanoma therapy.

Targeted therapy with BRAF inhibitors (BRAFi) and MEK inhibitors (MEKi) provides rapid disease control with high response rates in patients with BRAF-mutant metastatic melanoma. However, the majority of patients develop resistance to therapy during the course of therapy. Immune checkpoint inhibitors show a slower onset of action with lower response rates, with responders showing sustained response. The combination of BRAFi/MEKi and immune checkpoint inhibitors combines the hope for a fast, reliable and lasting response to therapy. Preclinical data supports this hypothesis. With the help of the PubMed database, a comprehensive search and analysis of preclinical and clinical studies on the combination of BRAFi/MEKi with immune checkpoint inhibitors was performed and yielded the following results: 1) In vivo, BRAFi and MEKi have no negative effects on immune cells; BRAFi and MEKi generate 2) an immune stimulating tumor microenvironment, 3) an increased infiltration of immune cells into the tumors, 4) a better recognition of melanoma cells by immune effector cells, and 5) a better functionality of the immune effector cells. In addition, in vivo experiments 6) demonstrated a superiority of the combination treatment compared to the individual strategies in both BRAF-mutant and BRAF wild-type melanomas. In summary, available data show that both BRAFi and MEKi have beneficial effects on the antitumor immunity and the tumor microenvironment as a whole, which is mediated by different mechanisms. Currently, clinical studies are underway to investigate combinations of BRAFi and MEKi with immune checkpoint inhibitors. The results of these studies are eagerly awaited.