Foreskin-derived mesenchymal stromal cells with aldehyde dehydrogenase activity: isolation and gene profiling.

BACKGROUND: Mesenchymal stromal cells (MSCs) become an attractive research topic because of their crucial roles in tissue repair and regenerative medicine. Foreskin is considered as a valuable tissue source containing immunotherapeutic MSCs (FSK-MSCs). RESULTS: In this work, we used aldehyde dehydrogenase activity (ALDH) assay (ALDEFLUOR™) to isolate and therefore characterize subsets of FSK-MSCs. According to their ALDH activity, we were able to distinguish and sort by fluorescence activated cell sorting (FACS) two subsets of FSK-MSCs (referred as ALDH+ and ALDH-). Consequently, these subsets were characterized by profiling the gene expression related to the main properties of MSCs (proliferation, response to hypoxia, angiogenesis, phenotype, stemness, multilineage, hematopoiesis and immunomodulation). We thus demonstrated by Real Time PCR several relevant differences in gene expression based on their ALDH activity. CONCLUSION: Taken together, this preliminary study suggests that distinct subsets of FSK-MSCs with differential gene expression profiles depending of ALDH activity could be identified. These populations could differ in terms of biological functionalities involving the selection by ALDH activity as useful tool for potent therapeutic applications. However, functional studies should be conducted to confirm their therapeutic relevance.

Extracellular vesicles of bone marrow stromal cells rescue chronic lymphocytic leukemia B cells from apoptosis, enhance their migration and induce gene expression modifications.

Interactions between chronic lymphocytic leukemia (CLL) B cells and the bone marrow (BM) microenvironment play a major function in the physiopathology of CLL. Extracellular vesicles (EVs), which are composed of exosomes and microparticles, play an important role in cell communication. However, little is known about their role in CLL / microenvironment interactions. In the present study, EVs purified by ultracentrifugation from BM mesenchymal stromal cell (BM-MSC) cultures were added to CLL B cells. After their integration into CLL B cells, we observed a decrease of leukemic cell spontaneous apoptosis and an increase in their chemoresistance to several drugs, including fludarabine, ibrutinib, idelalisib and venetoclax after 24 hours. Spontaneous (P=0.0078) and stromal cell-derived factor 1α -induced migration capacities of CLL B cells were also enhanced (P=0.0020). A microarray study highlighted 805 differentially expressed genes between leukemic cells cultured with or without EVs. Of these, genes involved in the B-cell receptor pathway such as CCL3/4, EGR1/2/3, and MYC were increased. Interestingly, this signature presents important overlaps with other microenvironment stimuli such as B-cell receptor stimulation, CLL/nurse-like cells co-culture or those provided by a lymph node microenvironment. Finally, we showed that EVs from MSCs of leukemic patients also rescue leukemic cells from spontaneous or drug-induced apoptosis. However, they induce a higher migration and also a stronger gene modification compared to EVs of healthy MSCs. In conclusion, we show that EVs play a crucial role in CLL B cells/BM microenvironment communication.

Opposite Prognostic Significance of Cellular and Serum Circulating MicroRNA-150 in Patients with Chronic Lymphocytic Leukemia.

MicroRNAs (or miRs) play a crucial role in chronic lymphocytic leukemia (CLL) physiopathology and prognosis. In addition, circulating microRNAs in body fluids have been proposed as new biomarkers. We investigated the expression of matched cellular and serum circulating microRNA-150 by quantitative real-time PCR (qPCR) from purified CD19(+) cells or from CLL serums obtained at diagnosis in a cohort of 273/252 CLL patients with a median follow-up of 78 months (range 7-380) and correlated it to other biological or clinical parameters. We showed that miR-150 was significantly overexpressed in CLL cells/serums compared with healthy subjects (P < 0.0001). Among CLL patients, a low cellular miR-150 expression level was associated with tumor burden, disease aggressiveness and poor prognostic factors. In contrast, a high level of serum miR-150 was associated with tumor burden markers and some markers of poor prognosis. Similarly, cellular and serum miR-150 also predicted treatment-free survival (TFS) and overall survival (OS) in an opposite manner: patients with low cellular/serum miR-150 levels have median TFS of 40/111 months compared with high-level patients who have a median TFS of 122/60 months (P < 0.0001/P = 0.0066). Similar results were observed for OS. We also found that cellular and serum miR-150 levels vary in an opposite manner during disease progression and that cellular miR-150 could be regulated by its release into the extracellular space. Cellular and serum levels of miR-150 are associated with opposite clinical prognoses and could be used to molecularly monitor disease evolution as a new prognostic factor in CLL.

ETx-22: a novel nectin-4-directed antibody drug conjugate, demonstrates safety and potent antitumor activity in low nectin-4 expressing tumors.

Nectin-4 is a cell-adhesion molecule expressed at various levels in many solid tumors, including urothelial cancer. As means to reduce on-target skin toxicity observed with enfortumab vedotin, an anti-nectin-4-MMAE ADC approved for patients with advanced urothelial cancer, 15A7.5, an anti-nectin-4 monoclonal antibody that exhibited differential nectin-4 binding between tumor and primary keratinocytes, was selected for the development of ETx-22. Exatecan, a topoisomerase I inhibitor, was chosen as payload. ETx-22 ADC induced rapid and long-lasting tumor regression in various patient derived xenograft models expressing low to high levels of nectin-4 and also in MonoMethyl Auristatin-E resistant xenograft model. ETx-22 has a highest non severely toxic dose of over 20 mg/kg in non-human primates without signs of important skin toxicity. ETx-22 represents a valuable therapy, for the treatment of patients with nectin-4 expressing tumors including those that have become resistant to enfortumab vedotin treatment.

Overcoming Resistance to Anti-Nectin-4 Antibody-Drug Conjugate.

Antibody-drug conjugates (ADC) represent a fast-growing drug class in oncology. However, ADCs are associated with resistance, and therapies able to overcome it are of utmost importance. Recently, enfortumab vedotin-ejfv (EV) was approved in nectin-4+ metastatic urothelial cancer. We previously described PVRL4/nectin-4 as a new therapeutic target in breast cancer and produced an efficient EV-like ADC comprising a human anti-nectin-4 mAb conjugated to monomethyl auristatin-E (MMAE) named N41mab-vcMMAE. To study the consequence of the long-term treatment with this ADC, we developed a preclinical breast cancer model in mice, and report a mechanism of resistance to N41mab-vcMMAE after 9-month treatment and a way to reverse it. RNA-sequencing pointed to an upregulation in resistant tumors of ABCB1 expression, encoding the multidrug resistance protein MDR-1/P-glycoprotein (P-gp), associated with focal gene amplification and high protein expression. Sensitivity to N41mab-vcMMAE of the resistant model was restored in vitro by P-gp pharmacologic inhibitors, like tariquidar. P-gp is expressed in a variety of normal tissues. By delivering the drug to the tumor more specifically than classical chemotherapy, we hypothesized that the combined use of ADC with P-gp inhibitors might reverse resistance in vivo without toxicity. Indeed, we showed that the tariquidar/N41mab-vcMMAE combination was well tolerated and induced a rapid regression of ADC-resistant tumors in mice. In contrast, the tariquidar/docetaxel combination was toxic and poorly efficient. These results show that ABC transporter inhibitors can be safely used with ADC to reverse ADC-induced resistance and open new opportunities in the fight against multidrug resistance.

Quantitative immunohistochemical fingerprinting of adhesion/growth-regulatory galectins in salivary gland tumours: divergent profiles with diagnostic potential.

AIMS: This study tests the hypothesis that histopathological fingerprinting of galectins, which are emerging multifunctional effectors in cell sociology, could refine the differential diagnosis of salivary tumours. METHODS AND RESULTS: We applied non-crossreactive polyclonal antibodies against galectin-1 (Gal-1), galectin-3 (Gal-3), galectin-7 (Gal-7) and galectin-8 (Gal-8) for immunohistochemical analysis of salivary gland tumours (72 cases with benign disease and 39 cases with malignancy) and 29 control specimens. The principal positivity of cases, the site of signal presence and the quantitative parameters concerning percentage of positive cells and labelling intensity were determined. Acinic cell and adenoid cystic carcinomas (specifically tubular and cribriform types) shared the expression signature of Gal-1, Gal-3 and Gal-8 presence combined with Gal-7 absence. Mucoepidermoid carcinomas presented a unique profile based on cytoplasmic Gal-1, Gal-3, Gal-7 and Gal-8 localization in the intermediate cells. Adenomas were separable from malignancy by a consistent decrease in the labelling index (LI) for Gal-7 and Gal-8 (LI Gal-7, P<10(-6) ; LI Gal-8, P=0.001). When present, staining for the tumour suppressor p16(INK4a) coincided with Gal-1 presence. CONCLUSIONS: Expression profiling of the four tested galectins in salivary gland tumours revealed non-uniform staining patterns with discriminatory potential based on intracellular localization and quantitative aspects.

Importance of Crosstalk Between Chronic Lymphocytic Leukemia Cells and the Stromal Microenvironment: Direct Contact, Soluble Factors, and Extracellular Vesicles.

Chronic lymphocytic leukemia (CLL) is caused by the accumulation of malignant B cells due to a defect in apoptosis and the presence of small population of proliferating cells principally in the lymph nodes. The abnormal survival of CLL B cells is explained by a plethora of supportive stimuli produced by the surrounding cells of the microenvironment, including follicular dendritic cells (FDCs), and mesenchymal stromal cells (MSCs). This crosstalk between malignant cells and normal cells can take place directly by cell-to-cell contact (assisted by adhesion molecules such as VLA-4 or CD100), indirectly by soluble factors (chemokines such as CXCL12, CXCL13, or CCL2) interacting with their receptors or by the exchange of material (protein, microRNAs or long non-coding RNAs) via extracellular vesicles. These different communication methods lead to different activation pathways (including BCR and NFκB pathways), gene expression modifications (chemokines, antiapoptotic protein increase, prognostic biomarkers), chemotaxis, homing in lymphoid tissues and survival of leukemic cells. In addition, these interactions are bidirectional, and CLL cells can manipulate the normal surrounding stromal cells in different ways to establish a supportive microenvironment. Here, we review this complex crosstalk between CLL cells and stromal cells, focusing on the different types of interactions, activated pathways, treatment strategies to disrupt this bidirectional communication, and the prognostic impact of these induced modifications.

Aldehyde dehydrogenase activity of Wharton jelly mesenchymal stromal cells: isolation and characterization.

Mesenchymal stromal cells (MSCs) are promising tools in regenerative medicine and targeted therapies. Although different origins have been described, there is still huge need to find a valuable source harboring specific subpopulations of MSCs with precise therapeutic functions. Here, we isolated by fluorescence activated cell sorting technique, two populations of Wharton's jelly (WJ)-MSCs based on their aldehyde dehydrogenase (ALDH) activity. Two different ALDH activities (low vs. high) were thus observed. We then analyzed their gene expression profile for stemness, phenotype, response to hypoxia, angiogenesis, hematopoietic support, immunomodulation and multilineage differentiation abilities (osteogenesis, adipogenesis, and chondrogenesis). According to ALDH activity, many differences in the mRNA expression of these populations were noticed. In conclusion, we provide evidences that WJ harbors two distinct populations of MSCs with different ALDH activity. These populations seem to display specific functional competences that may be interesting for concise therapeutic applications.

Cytokinome of adult-derived human liver stem/progenitor cells: immunological and inflammatory features.

BACKGROUND: Being non-immunogenic and capable of achieving major metabolic liver functions, adult-derived human liver stem/progenitor cells (ADHLSCs) are of special interest in the field of liver cell therapy. The cytokine repertoire of engrafted cells may have critical impacts on the immune response balance, particularly during cell transplantation. METHODS: In this work, we analyzed the cytokinome of ADHLSCs during hepatogenic differentiation (HD) following stimulation with a mixture of inflammatory cytokines (I) in vitro and compared it to that of mature hepatocytes. RESULTS: Independent of their hepatic state, ADHLSCs showed no constitutive expression of pro-inflammatory cytokines, which were significantly induced by inflammation (IL-1ß, IL-6, IL-8, TNFα, CCL5, IL-12a, IL-12b, IL-23p19, IL-27p28 and EBI-3). IL1-RA and IDO-1, as immunoregulatory cytokines, were highly induced in undifferentiated ADHLSCs, whereas TGF-ß was downregulated by both hepatic and inflammatory events. Interestingly, TDO-1 was exclusively expressed in ADHLSCs after hepatic differentiation and enhanced by inflammatory cytokines. Compared to mature hepatocytes, hepatic-differentiated ADHLSCs showed significantly different cytokine expression patterns. CONCLUSIONS: By establishing the cytokinome of ADHLSCs and highlighting their immunological and inflammatory features, we can enhance our knowledge about the safety and efficiency of the transplantation strategy.

Aldehyde Dehydrogenase Activity in Adipose Tissue: Isolation and Gene Expression Profile of Distinct Sub-population of Mesenchymal Stromal Cells.

Thanks to their relative abundance and easier collection, adipose tissue (AT) is considered an alternative source for the isolation of mesenchymal stromal cells (MSCs). MSCs have great therapeutic values and are thus under investigations for several clinical indications such as regenerative medicine and immunomodulation. In this work, we aimed to identify, isolate and characterize AT-MSCs based on their aldehyde dehydrogenase (ALDH) activity known to be a classical feature of stem cells. FACS technology allowed to isolate two different populations of AT-MSCs according to their ALDH activity (referred as ALDH+ and ALDH-). Depending on their ALDH activity, the transcriptome analysis of both cell populations demonstrated a differential pattern of genes related to the main properties of MSCs (proliferation, response to hypoxia, angiogenesis, phenotype, stemness, multilineage, hematopoiesis, immunomodulation). Based on these profiling, both AT-MSC populations could differ in terms of biological responses and functionalities. Collectively, the use of ALDH for isolating and identifying sub-populations of MSCs with specific gene profile may represent an alternative method to provide solutions for targeted therapeutic applications.

Isolation and Characterization of Bone Marrow Mesenchymal Stromal Cell Subsets in Culture Based on Aldehyde Dehydrogenase Activity.

Mesenchymal stromal cells (MSCs) have particular properties that allow their use as therapeutic strategies for several cell-based applications. Historically, bone marrow (BM)-MSCs are isolated by culture adherence since specific cell surface markers are yet to be developed. This original work aimed to identify and characterize isolating expanded BM-MSCs based on their aldehyde dehydrogenase (ALDH) activity known to be a hallmark of stem cells and relevant for their isolation. We thus isolated by fluorescence-activated cell sorting technology two functionally different populations of BM-MSCs depending on their ALDH activity (ALDH+ and ALDH-). Transcriptome analysis and profiling clearly demonstrated that both populations of BM-MSCs present distinct pattern of genes related to the main properties of MSCs (proliferation, response to hypoxia, angiogenesis, phenotype, stemness, multilineage, hematopoiesis, immunomodulation) in an ALDH activity dependent manner. Both BM-MSC populations look to significantly differ in terms of biological responses and functionalities. More functional analyses are needed to understand and characterize the properties of these ALDH populations. Collectively, our results highlight ALDH activity as a potential feature for isolating and segregating functional and/or competent subset of BM-MSC populations, which may account for better and more efficient therapeutic issue.

The Light Chain IgLV3-21 Defines a New Poor Prognostic Subgroup in Chronic Lymphocytic Leukemia: Results of a Multicenter Study.

Purpose: Unmutated (UM) immunoglobulin heavy chain variable region (IgHV) status or IgHV3-21 gene usage is associated with poor prognosis in chronic lymphocytic leukemia (CLL) patients. Interestingly, IgHV3-21 is often co-expressed with light chain IgLV3-21, which is potentially able to trigger cell-autonomous BCR-mediated signaling. However, this light chain has never been characterized independently of the heavy chain IgHV3-21.Experimental Design: We performed total RNA sequencing in 32 patients and investigated IgLV3-21 prognostic impact in terms of treatment-free survival (TFS) and overall survival (OS) in 3 other independent cohorts for a total of 813 patients. IgLV3-21 presence was tested by real-time PCR and confirmed by Sanger sequencing.Results: Using total RNA sequencing to characterize 32 patients with high-risk CLL, we found a high frequency (28%) of IgLV3-21 rearrangements. Gene set enrichment analysis revealed that these patients express higher levels of genes responsible for ribosome biogenesis and translation initiation (P < 0.0001) as well as MYC target genes (P = 0.0003). Patients with IgLV3-21 rearrangements displayed a significantly shorter TFS and OS (P < 0.05), particularly those with IgHV mutation. In each of the three independent validation cohorts, we showed that IgLV3-21 rearrangements-similar to UM IgHV status-conferred poor prognosis compared with mutated IgHV (P < 0.0001). Importantly, we confirmed by multivariate analysis that this was independent of IgHV mutational status or subset #2 stereotyped receptor (P < 0.0001).Conclusions: We have demonstrated for the first time that a light chain can affect CLL prognosis and that IgLV3-21 light chain usage defines a new subgroup of CLL patients with poor prognosis. Clin Cancer Res; 24(20); 5048-57. ©2018 AACR.

Comparison and immunobiological characterization of retinoic acid inducible gene-I-like receptor expression in mesenchymal stromal cells.

Due to their immunomodulatory and regenerative properties, Mesenchymal stromal cells (MSC) have generated major interests in several clinical settings including transplantation and inflammatory diseases. MSC functions can be influenced by their tissue origin. Their microenvironment strongly affects their biology notably through TLR sensing. In this study, we show that MSC isolated from four different sources express another type of cytosolic pathogen recognition receptors known as retinoic acid inducible gene-I (RIG-I)-like receptors (RLR). RLR activation in MSC induces the production of Type I IFN (IFN-ß) and Type III IFN (IFN-λ1). The highest producers are adipose tissue(AT)-MSC. We further show that Interferon production is induced through TBK1/IKK-ε signaling and IRF7 phosphorylation. Depending on MSC source, the knockdown of TLR3 and/or RIG-I decreases the MSC response to RLR ligand poly(I:C)/Lyovec. Among the different MSC types, AT-MSCs display the highest sensitivity to viral stimuli as shown by the alteration of their viability after prolonged stimulation. Our work indicates that this could be linked to an increase of pro-apoptotic Noxa expression. Finally, the expression of IDO1 and LIF upon RLR activation indicate the increase of MSC immunomodulatory potential, especially in AT-MSCs. Altogether, these data should be considered when designing MSC-based therapy in clinical settings where inflammation or infection are present.

The Immunomodulatory Potential of Mesenchymal Stromal Cells: A Story of a Regulatory Network.

Mesenchymal stromal cells (MSCs) have recently been the subject of great interest in the fields of regenerative medicine and immunotherapy due to their unique biological properties. In particular, MSCs possess immunoregulatory properties that can modulate immune as well as inflammatory responses. Although there are many studies about MSC immunomodulation, several complex and conflicting mechanisms have been reported. Herein, we aim to review these mechanisms and identify a link between these pathways. We focus on human studies in which bone marrow-derived MSCs and T cells were investigated. We propose that MSC-induced immunomodulation exists as a network where converging regulatory pathways compete to establish a tolerogenic state. As interleukin-10 seems to play a central role in this network, we also discuss the relationship between this cytokine and other regulatory factors in the context of immunomodulation.

Characterization of TET and IDH gene expression in chronic lymphocytic leukemia: comparison with normal B cells and prognostic significance.

BACKGROUND: Chronic lymphocytic leukemia (CLL) is the most common hematological malignancy in western countries, characterized by a heterogeneous clinical course. Although genetic studies have identified chromosomal aberrations or specific mutations, epigenetic changes have been poorly characterized in CLL. METHODS: We assessed ten-eleven translocations (TET) 1, 2, and 3, isocitrate dehydrogenase (IDH) 1, and 2 messenger RNA (mRNA) expression using real-time PCR on purified leukemic B cells from 214 CLL patients (median follow-up = 75 months, range 1-380), normal peripheral blood B cells (n = 20), and umbilical cord blood B cells (n = 21). The microenvironment influence was assessed after 24 h co-culture of CLL cells with bone marrow mesenchymal stromal cells (BMSC). Finally, 5-hydroxymethylcytosine level (%5-hmC) was assessed by ELISA in CLL cells alone or with microenvironment stimuli. RESULTS: TET 1 and 3 and IDH2 were decreased in CLL cells compared with healthy B cells (P = 0.0221, 0.0013, <0.0001, respectively), while IDH1 was overexpressed (P = 0.0037). TET2 and IDH1 were significantly correlated with treatment-free survival (TFS); patients with high TET2/IDH1 expression had a higher median TFS (111 months) than patients with low expression (78 months, P = 0.0071/0.0123). Moreover, TET1 expression decreased (P = 0.0371), while TET3 and IDH2 expression increased (P = 0.0273/0.0039) in co-cultures. However, %5-hmC was not correlated with clinical data and was unchanged following microenvironment stimuli. CONCLUSIONS: Despite a slight deregulation in CLL cells compared with normal B cells, we identified a significant association between TET/IDH gene expression and prognosis, suggesting that epigenetic changes could potentially be associated with disease progression. Moreover, despite an identical %5-hmC, TET gene expression was influenced by contact with BMSC confirming the crucial role of the microenvironment in CLL pathogenesis.

Avoiding false positive antigen detection by flow cytometry on blood cell derived microparticles: the importance of an appropriate negative control.

BACKGROUND: Microparticles (MPs), also called microvesicles (MVs) are plasma membrane-derived fragments with sizes ranging from 0.1 to 1µm. Characterization of these MPs is often performed by flow cytometry but there is no consensus on the appropriate negative control to use that can lead to false positive results. MATERIALS AND METHODS: We analyzed MPs from platelets, B-cells, T-cells, NK-cells, monocytes, and chronic lymphocytic leukemia (CLL) B-cells. Cells were purified by positive magnetic-separation and cultured for 48h. Cells and MPs were characterized using the following monoclonal antibodies (CD19,20 for B-cells, CD3,8,5,27 for T-cells, CD16,56 for NK-cells, CD14,11c for monocytes, CD41,61 for platelets). Isolated MPs were stained with annexin-V-FITC and gated between 300nm and 900nm. The latex bead technique was then performed for easy detection of MPs. Samples were analyzed by Transmission (TEM) and Scanning Electron microscopy (SEM). RESULTS: Annexin-V positive events within a gate of 300-900nm were detected and defined as MPs. Our results confirmed that the characteristic antigens CD41/CD61 were found on platelet-derived-MPs validating our technique. However, for MPs derived from other cell types, we were unable to detect any antigen, although they were clearly expressed on the MP-producing cells in the contrary of several data published in the literature. Using the latex bead technique, we confirmed detection of CD41,61. However, the apparent expression of other antigens (already deemed positive in several studies) was determined to be false positive, indicated by negative controls (same labeling was used on MPs from different origins). CONCLUSION: We observed that mother cell antigens were not always detected on corresponding MPs by direct flow cytometry or latex bead cytometry. Our data highlighted that false positive results could be generated due to antibody aspecificity and that phenotypic characterization of MPs is a difficult field requiring the use of several negative controls.

Global histone deacetylase enzymatic activity is an independent prognostic marker associated with a shorter overall survival in chronic lymphocytic leukemia patients.

Histone deacetylases (HDAC) play a crucial role in transcriptional regulation and are often deregulated in many cancers. However, global HDAC enzymatic activity has never been investigated in Chronic Lymphocytic Leukemia (CLL). We measured HDAC activity in protein extracts from CD19+ B-cells purified from 114 CLL patients with a median follow-up of 91 months (range: 11-376). HDAC activity was equivalent in CLL and normal B-cells but higher in patients who died during the study than in living patients (152.1 vs. 65.04 pmol; P = 0.0060). Furthermore, HDAC activity correlated with treatment-free survival (TFS; P = 0.0156) and overall survival (OS; P < 0.0001): patients with low HDAC activity (n = 75) had a median TFS and OS of 101 and > 376 months, respectively, whereas patients with high HDAC activity (n = 39) had a median TFS and OS of 47 and 137 months, respectively. Multivariate analyses indicated that HDAC activity is an independent predictor of OS (hazard ratio = 7.68; P = 0.0017). Finally, HDAC activity increased after B-cell receptor stimulation using IgM, suggesting a role for microenvironment stimuli (n = 10; P = 0.0371). In conclusion, high HDAC activity in CLL B-cells is associated with shorter TFS and OS and is an independent marker of OS, refining the use of other prognostic factors. This work provides a biological base for the use of HDAC inhibitors in CLL treatment.

HDAC isoenzyme expression is deregulated in chronic lymphocytic leukemia B-cells and has a complex prognostic significance.

Histone deacetylases (HDACs) play a crucial role in chromatin structure and, consequently, gene expression. Their deregulation has been reported in various cancers. We performed a complete and comprehensive study of the expression of 18 HDACs (including Sirtuin; SIRT) by real-time PCR in a cohort of 200 chronic lymphocytic leukemia (CLL) patients with a median follow-up of 77 mo, and compared it with the results obtained from normal B cells. We also compared HDAC expression at diagnosis and after relapse. We observed significant deregulation (mostly upregulation) of HDACs in CLL. In terms of clinical significance, only HDAC6 was significantly correlated with treatment-free survival (TFS), whereas HDAC3 and SIRT2, 3 and 6 were correlated with overall survival (OS). A multivariate Cox regression stepwise analysis indicated that HDAC6, 7 and 10 and SIRT3 were TFS independent predictors. Interestingly, poor prognosis was associated with an overexpression of HDAC7 and 10 but an underexpression of HDAC6 and SIRT3. Therefore, these factors were combined in a TFS score: patients with a score of 0-1-2, 3 and 4 had a median TFS of 107, 57 and 26 mo, respectively (HR = 4.03, p < 0.0001). For OS, SIRT5 and 6 allowed stratification into 3 groups, with a median OS of > 360, 237 and 94 mo (HR = 6.38, p < 0.0001). However, we could not find statistical differences in HDAC expression after relapse. These results, validated by a 5-fold cross-validation, highlight the complex impact of HDAC expression in CLL clinical course.