The CIpP activator, TR-57, is highly effective as a single agent and in combination with venetoclax against CLL cells in vitro

Despite advances in treatment, a significant proportion of patients with chronic lymphocytic leukemia (CLL) will relapse with drug-resistant disease. The imipridones, ONC-201 and ONC-212, are effective against a range of different cancers, including acute myeloid leukemia (AML) and tumors of the brain, breast, and prostate. These drugs induce cell death through activation of the mitochondrial protease, caseinolytic protease (CIpP), and the unfolded protein response (UPR). Here we demonstrate that the novel imipridone analog, TR-57, has efficacy as a single agent and synergises with venetoclax against CLL cells under in vitro conditions that mimic the tumor microenvironment. Changes in protein expression suggest TR-57 activates the UPR, inhibits the AKT and ERK1/2 pathways and induces pro-apoptotic changes in the expression of proteins of the BCL-2 family. The study suggests that TR-57, as a single agent and in combination with venetoclax, may represent an effective treatment option for CLL.

CXCR4 overexpression in chronic lymphocytic leukemia associates with poorer prognosis: A prospective, single-center, observational study

Controversial data have been reported on the prognostic value of C-X-C motif chemokine receptor 4 (CXCR4) in chronic lymphocytic leukemia (CLL). This prospective, single-center, observational study aimed to evaluate the role of CXCR4 in the pathophysiology of CLL and its prognostic role. A total of 158 patients of CLL were enrolled, and CXCR4 expression on CLL cells was detected by flow cytometry (FCM) at initial diagnosis. The patients were divided into 2 groups according to the CXCR4 mean fluorescence intensity (MFI) median. Also, four patient specimens from the CXCR4low and CXCR4high groups were selected for RNASeq analysis. The progression-free survival (PFS) of CLL patients in the CXCR4high group was significantly shorter than the CXCR4low group, with a median follow-up time of 27 months (log-rank P < 0.001). Moreover, CXCR4 overexpression (MFI > 3376) was an independent marker of poor PFS in CLL patients (P < 0.001). Analysis of RNASeq results revealed that CXCR4 plays an important role in the migration of CLL. Collectively, CXCR4 expression levels on leukemia cells can be detected rapidly by FCM. CXCR4 overexpression was significantly associated with poorer prognosis in CLL patients within a shorter follow-up time.

Targeting the NTSR2/TrkB oncogenic pathway in chronic lymphocytic leukemia

Current therapies that target the B-cell receptor pathway or the inhibition of anti-apoptotic proteins do not prevent the progressive forms of chronic lymphocytic leukemia (CLL), have low long-term efficacy and are subject to therapeutic resistance. Deciphering the mechanisms of leukemic cell survival and searching for new specific targets therefore remain major challenges to improve the management of this disease. It was evidenced that NTSR2 (neurotensin receptor 2), through the recruitment of TRKB (tropomyosin related kinase B), induces survival pathways in leukemic B cells. We have investigated the therapeutic potential of this protein complex as a new target. The binding domain of NTSR2 and TRKB was identified and a peptide targeting the latter was designed. The peptide binds TRKB and efficiently decreases the interaction of the two proteins. It is also effectively internalized by CLL-B cells in which it notably affects Src family kinase signaling and anti-apoptotic proteins levels. It demonstrated a cytotoxic effect both in vitro on the MEC-1 cell line and ex vivo on a cohort of 30 CLL patients. Altogether, these results underline the therapeutic potential of the NTSR2/TRKB protein complex as a target in CLL and open new perspectives for the development of targeted therapies.

Persistence of Chronic Lymphocytic Leukemia Stem-like Populations under Simultaneous In Vitro Treatment with Curcumin, Fludarabine, and Ibrutinib: Implications for Therapy Resistance

Leukemic stem cells (LSCs) possess similar characteristics to normal hematopoietic stem cells, including self-renewal capacity, quiescence, ability to initiate leukemia, and drug resistance. These cells play a significant role in leukemia relapse, persisting even after apparent remission. LSCs were first described in 1994 by Lapidot et al. Although they have been extensively studied in acute leukemia, more LSC research is still needed in chronic lymphocytic leukemia (CLL) to understand if reduced apoptosis in mature cells should still be considered as the major cause of this disease. Here, we provide new evidence suggesting the existence of stem-like cell populations in CLL, which may help to understand the disease as well as to develop effective treatments. In this study, we identified a potential leukemic stem cell subpopulation using the tetraploid CLL cell line I83. This subpopulation is characterized by diploid cells that were capable of generating the I83 tetraploid population. Furthermore, we adapted a novel flow cytometry analysis protocol to detect CLL subpopulations with stem cell properties in peripheral blood samples and primary cultures from CLL patients. These cells were identified by their co-expression of CD19 and CD5, characteristic markers of CLL cells. As previously described, increased alkaline phosphatase (ALP) activity is indicative of stemness and pluripotency. Moreover, we used this method to investigate the potential synergistic effect of curcumin in combination with fludarabine and ibrutinib to deplete this subpopulation. Our results confirmed the effectiveness of this ALP-based analysis protocol in detecting and monitoring leukemic stem-like cells in CLL. This analysis also identified limitations in eradicating these populations using in vitro testing. Furthermore, our findings demonstrated that curcumin significantly enhanced the effects of fludarabine and ibrutinib on the leukemic fraction, exhibiting synergistic effects (combination drug index, CDI 0.97 and 0.37, respectively). Our results lend support to the existence of potential stem-like populations in CLL cell lines, and to the idea that curcumin could serve as an effective adjuvant in therapies aimed at eliminating these populations and improving treatment efficacy.

The effect of HYPE knock-out on the AMPylome of human OSU-CLL leukemia cells

In humans, AMPylation of cellular proteins is carried out by Huntingtin yeast-interacting protein E (HYPE), activated under conditions of endoplasmic reticulum stress, such as in cancer cells. Extracts of the human chronic lymphocytic leukemia cell line, OSU-CLL, were fractionated using immuno-precipitation with antibodies against adenosine-phosphate and then AMP-Tyr. The proteins isolated were modified with AMP, the 'AMPylome.' AMP-labelled peptides isolated from HYPE wild-type (WT) and HYPE knock-out (KO) cells were identified using tandem mass spectrometry. A total of 213 proteins were identified from WT cell extracts, while only 23 of these were pulled down from KO cells, consistent with the presence of another AMPylator, besides HYPE. The KO cells were more sensitive to fludarabine nucleoside (2-FaraA) than WT cells. Ingenuity Pathway Analysis of the AMPylated proteins identified in WT cells clustered actin binding proteins of the cytoskeleton, and proteins of the RHO GTPase pathway that would jointly stimulate cell proliferation.

USF2 promotes autophagy and proliferation in chronic lymphocytic leukemia by inhibiting STUB1-induced NFAT5 ubiquitination

Chronic lymphocytic leukemia (CLL) mainly affects the health of older adults and is difficult to cure. Upstream stimulatory factor 2 (USF2) has been implicated in several diseases and conditions including cancers. However, the effect of USF2 on CLL has not been elucidated. To investigate the effect of USP2 on proliferation and autophagy of CLL, and to explore the underlying mechanism. The mRNA of USF2 and STIP1 homology and U-Box containing protein 1 (STUB1) was analyzed using qRT-PCR. Western blots were used to evaluate the expression level of USF2, LC3II, Beclin-1, P62, STUB1, and NFAT5. The cell proliferation was evaluated using CCK-8 and EdU assays. The cell apoptosis was evaluated using flow cytometry. Indirect fluorescent assay (IFA) was performed to analyze LC3 signal. Nuclear factor of activated T-cells 5 (NFAT5) ubiquitination was detected using immunoprecipitation (IP) assay. The CLL progression was evaluated in xenotransplantation model of nude mice. USF2 was highly expressed in CLL tissues and cell lines. USF2 knockdown suppressed the cell viability and EdU incorporation, while promoting cell apoptosis. Meanwhile, USF2 knockdown reduced the level of LC3II and Beclin-1, but increased P62, illustrating USF2 knockdown inhibiting autophagy. USF2 induced NFAT5 ubiquitination and promoted NFAT5 protein level via repressing STUB1. The downregulation of USF2 weakened CLL progression in xenotransplantation model of nude mice. CLL survival and autophagy was dependent on highly expressed USF2 which promoted the expression and ubiquitination of NFAT5 through inhibiting the transcription of STUB1, which makes USF2 a promising therapeutic candidate for CLL treatment.

Tandem bispecific CD123/CLL-1 CAR-T cells exhibit specific cytolytic effector functions against human acute myeloid leukaemia

OBJECTIVES

The treatment of refractory and recurrent acute myeloid leukaemia (AML) is still a challenge with poor response rates and short survival times. In an attempt to solve this problem, we constructed a tandem bispecific chimeric antigen receptor (CAR) targeting CD123 and C-type lectin-like molecule 1 (CLL-1), two different AML antigens, and verified its cytotoxic effects in vitro.

METHODS

We established and cultured K562 cell lines expressing both CD123 and CLL1 antigens. Single-target CAR-T cells specific to CD123 and CLL1 were engineered, alongside tandem CD123/CLL1 bispecific CAR-T cells. Flow cytometry was used to determine cell phenotypes, transfection efficiencies, cytokine release, and CAR-T-cell proliferation, and an lactate dehydrogenase assay was used to detect the cytotoxicity of CD123/CLL-1 bispecific tandem CAR-T cells in vitro.

RESULTS

Two types of tandem CAR-T cells exhibited significant killing effects on CLL-1 + CD123+ leukaemia cell lines and primary AML tumour cells. The killing efficiency of tandem CAR-T cells in the case of single antigen expression is comparable to that of single target CAR-T cells. When faced with dual target tumour cells, dual target CAR-T cells significantly surpass single target CAR-T cells. CD123/CLL-1 CAR-T cells in tandem targeted and killed CD123- and CLL-1-positive leukaemia cell lines and released a large number of cytokines.

CONCLUSIONS

CD123/CLL-1 CAR-T cells in tandem can simultaneously target CD123 and CLL-1 on AML cells, demonstrating a significant ability to kill single antigens and multi-target tumour cells. This suggests that CD123/CLL-1 CAR-T cells exhibit significant advantages in the expression of multiple antigens in a wide range of target cells, which may help overcome the challenges posed by tumour heterogeneity and evasion mechanisms.

Targeting TP53 disruption in chronic lymphocytic leukemia: Current strategies and future directions

In the modern era of Chronic Lymphocytic Leukemia (CLL) targeted therapy, the loss of p53 function due to genetic abnormalities remains a significant challenge. This is because even targeted agents, which are currently the mainstay of treatment for CLL, do not directly target p53 or restore its disrupted pathway. Consequently, resistance to therapy and unfavorable clinical outcomes often accompany these p53-related abnormalities. An essential goal of future clinical research should be to address the ostensibly "undruggable" p53 pathway. Currently, multiple therapeutic approaches are being explored to tackle TP53 dysfunction and improve outcomes in high-risk CLL. These approaches include the use of oncoprotein murine double minute 2 inhibitors, small-molecule p53 reactivators, exportin 1 (XPO1) inhibitors, and ataxia-telangiectasia mutated and Rad3-related (ATR) inhibitors. Combinations of these p53-targeting strategies, along with established novel therapies such as B-cell receptor or B-cell lymphoma-2 (BCL-2) inhibitors, may shape the future of therapeutic trials in this challenging-to-treat disease.

mTORC1-selective activation of translation elongation promotes disease progression in chronic lymphocytic leukemia

Targeted deletion of Raptor, a component of mechanistic target of rapamycin complex 1 (mTORC1), reveals an essential role for mTORC1 in initiation/maintenance of leukemia in a CLL model, resulting from a failure for haemopoietic stem/progenitor cells (HSPCs) to commit to the B cell lineage. Induction of Raptor-deficiency in NSG mice transplanted with Mx1-Raptor CLL progenitor cells (PKCα-KR-transduced HSPCs) after disease establishment revealed a reduction in CLL-like disease load and a significant increase in survival in the mice. Interestingly in an aggressive CLL-like disease model, rapamycin treatment reduced disease burden more effectively than AZD2014 (dual mTORC1/2 inhibitor), indicating a skew towards mTORC1 sensitivity with more aggressive disease. Rapamycin, but not ibrutinib, efficiently targeted the eEF2/eEF2K translation elongation regulatory axis, downstream of mTORC1, resulting in eEF2 inactivation through induction of eEF2T56 phosphorylation. mTOR inhibitor treatment of primary patient CLL cells halted proliferation, at least in part through modulation of eEF2K/eEF2 phosphorylation and expression, reduced protein synthesis and inhibited expression of MCL1, Cyclin A and Cyclin D2. Our studies highlight the importance of translation elongation as a driver of disease progression and identify inactivation of eEF2 activity as a novel therapeutic target for blocking CLL progression.

Toll-like receptor 9 signaling in chronic lymphocytic leukemia cell lines

Chronic lymphocytic leukemia (CLL) is a prototypic neoplasia in which malignant cells strongly depend on microenvironmental stimulations in the lymphoid tissues where they accumulate; leukemic cells are exposed to interaction with bystander and accessory cells, as well as inflammatory soluble mediators. Cell lines are frequently used to model the pathobiology of this disease; however, they do not always recapitulate leukemic cell growth and response to stimulation, and no data are available on Toll-like receptors (TLR) signaling in CLL cell lines. To address this gap, we analyzed HG3, MEC2, and PCL12 cell lines, before and after CpG stimulation, by RNA-sequencing followed by bioinformatic analyses and validation experiments. We identified NFKBIZ mRNA and the corresponding IkBz protein as robust markers of TLR9 activation in both MEC2 and PCL12, but not in HG3 cells. Next, we compared our current results with previous results obtained with primary CLL patient samples and were able to conclude that MEC2 is most similar to the patients' cells in terms of global responsiveness to TLR stimulation; in particular, MEC2 better resembles the samples of patients, as it is characterized by high expression levels of IkBz, but with a lower number of genes regulated.

NOD2 silencing promotes cell apoptosis and inhibits drug resistance in chronic lymphocytic leukemia by inhibiting the NF-κB signaling pathway

Recent years have witnessed increasing studies on the effect of epigenetic silencing of genes in the progression of chronic lymphocytic leukemia (CLL). This study investigates whether the nucleotide binding oligomerization domain containing 2 (NOD2) participates in the cell apoptosis and drug resistance of CLL cells. Cells were treated with adriamycin (ADR), etoposide, aclacinomycin and daunorubicin. After treatment, drug resistance and cell proliferation were examined to detect the inhibitory effect of ADR on cell proliferation; flow cytometry to identify ADR accumulation, the cell cycle distribution and apoptosis after transfection, and rhodamine 123 accumulation and efflux tests to assess P-glycoprotein (P-gp) function. NOD2 silencing or inhibition of the nuclear factor kappa-B (NF-κB) signaling pathway suppressed the multidrug resistance level in CLL, the inhibition rate, and cell proliferation caused by ADR at concentrations of approximately 0.25-1.5 μmol/L. Greater accumulation of ADR was observed in the CLL-AAT cell line than in the CLL-AAT/A02 cell line, but NOD2 silencing or inhibition of the NF-κB signaling pathway further increased the accumulation of ADR drugs in the CLL-AAT cell line and inhibited the drug efflux pump function of P-gp. Additionally, NOD2 silencing or NF-κB signaling pathway inhibition increased the apoptotic rate. The results of this study indicate that NOD2 promotes cell apoptosis and reduces the drug resistance of CLL by inhibiting the NF-κB signaling pathway.

Measurement of Trogocytosis: Quantitative Analyses Validated with Rigorous Controls

Trogocytosis is a process in which receptors on acceptor cells remove and internalize cognate ligands from donor cells. Trogocytosis has a profound and negative impact on mAb-based cancer immunotherapy, as seen in the treatment of chronic lymphocytic leukemia (CLL) with CD20 mAbs, such as rituximab (RTX) and ofatumumab (OFA). Our clinical observations of RTX/OFA-mediated loss of the CD20 target from circulating CLL cells have been replicated in our in vitro studies. Here we describe flow cytometry and fluorescence microscopy experiments, which demonstrate that acceptor cells, such as monocytes/macrophages that express FcγR, remove and internalize both antigen and donor cell-bound cognate IgG mAbs for several different mAb-donor cell pairs. Fluorescent mAbs and portions of the plasma cell membrane are transferred from donor cells to acceptor cells, which include the THP-1 monocytic cell line as well as freshly isolated monocytes. We describe rigorous controls to validate the reactions and eliminate dissociation or internalization as alternative mechanisms. Trogocytosis is likely to contribute to neutropenia, thrombocytopenia, and liver damage associated with use of antibody-drug conjugates. The methods we have described should allow for examination of strategies focused on blocking trogocytosis and its adverse effects. © 2023 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Trogocytosis of mAb-opsonized donor cells mediated by adherent THP-1 cells Alternate Protocol: Application of fluorescence microscopy to examine THP-1 cell-mediated trogocytosis Support Protocol 1: Alexa labeling of mAbs and determination of F/P ratios Support Protocol 2: Standard washing procedure Support Protocol 3: Labeling and opsonization of cells Basic Protocol 2: Trogocytosis mediated by human monocytes as acceptor cells Support Protocol 4: Isolation of human monocytes Basic Protocol 3: Trogocytosis mediated by THP-1 cells in solution Support Protocol 5: Retinoic acid treatment of THP-1 cells Support Protocol 6: Culturing of SCC-25, BT-474, MOLT-4 and THP-1 cell lines.

The Use of CD200 in the Differential Diagnosis of B-Cell Lymphoproliferative Disorders

Background: B-Cell Lymphoproliferative Disorders (B-LPDs) are a group of heterogenous disorders characterised by the accumulation of B-cells in peripheral blood, bone marrow, lymph nodes and spleen. They have a variable disease course and outcome and many share similar features making differential diagnosis challenging. Therefore, accurate diagnosis is fundamental in particular for determining treatment options. Immunophenotyping by flow cytometry plays a crucial role in the diagnosis of B-LPDs. However, overlapping immunophenotyping patterns exist and the use of novel monoclonal antibodies has become increasingly important in immunophenotyping analysis. More recently differential expression of CD200 has been reported in various B-LPDs and that CD200 may improve the differentiation between chronic lymphocytic leukaemia (CLL) and mantle cell lymphoma (MCL). In this study CD200 expression is evaluated in different B-LPDs. Methods: A total of 100 samples were collected and analysed by immunophenotyping flow cytometry over a period of 1 year (2017-2018), by a panel of monoclonal antibodies including CD200. The percentage of CD200 and its expression intensity was evaluated and compared between different groups of B-LPDs. Results: All of the 50 cases of CLL expressed CD200 with moderate to bright intensity, 6 MCL cases lacked the expression of CD200. Furthermore, all 5 cases of hairy cell leukaemia (HCL) expressed CD200. Out of all B-LPDs evaluated, CD200 expression in HCL cases was noted to be the brightest. The other 39 cases were not found to be B-LPDs. Conclusion: CD200 has an important role in differentiating CLL from MCL, HCL has a consistent bright expression of CD200. By adding CD200 to the combinations of markers in routine testing panel, Immunophenotyping by flow cytometry can be an effective tool in the diagnosis of B-LPDs especially in cases with atypical immunophenotyping pattern. Our result support that CD200 can be added to routine testing panel as it is useful in differentiating them.

BCR/Integrin Interaction in CLL: A Physiologic Remnant with Clinical Relevance

CD49d, the alpha chain of the very late antigen-4 (VLA-4) integrin, has a negative prognostic impact in chronic lymphocytic leukemia treated with the Bruton's tyrosine kinase (BTK) inhibitors, ibrutinib and acalabrutinib. Despite BTK inhibition, VLA-4 remains inside-out activated via B-cell receptor, an activation dampened by phosphoinositide 3-kinase inhibitors. Evaluation of CD49d expression in patients starting BTK inhibitor therapy may improve their prognostic stratification. See related article by Alsadhan et al., p. 3612.

AKAP12 and IGFBP4 Are Prognostic Factors for Chronic Lymphocytic Leukemia

INTRODUCTION

The aim of this study was to develop a prognostic model for chronic lymphocytic leukemia (CLL).

METHODS

GEO2R was used to retrieve the gene expression data of CLL and normal B cells from the Gene Expression Omnibus (GEO; GSE22529 and GSE50006 datasets) database. Practical Extraction and Report Language was used to extract the gene expression and overall survival (OS) data of CLL patients from the Chronic Lymphocytic Leukemia - ES (CLLE-ES) project in the International Cancer Genome Consortium (ICGC) database. Cox regression with Lasso was used to create and validate a prognostic model for CLL.

RESULTS

A total of 267 genes exhibited differential expression between CLL and normal B cells. Cox univariate analysis identified 14 DEGs that correlated with OS. Lasso multivariate evaluation demonstrated that AKAP12 and IGFBP4 are independent prognostic factors for CLL. Kaplan-Meier survival analysis revealed a significant association between the estimated risk score and survival. The area under the receiver operating characteristic curve was calculated to be 0.97, indicating high predictive accuracy. In addition, high AKAP12 and IGFBP4 risk scores were associated with the high incidence of trisomy 12q.

CONCLUSION

Taken together, AKAP12 and IGFBP4 are independent prognostic factors for CLL.

B-cell Receptor Pathway Mutations Are Infrequent in Patients with Chronic Lymphocytic Leukemia on Continuous Ibrutinib Therapy

PURPOSE

Acquired mutations in Bruton's tyrosine kinase (BTK) or phospholipase C-γ2 (PLCG2) genes are associated with clinical progressive disease (PD) in patients with chronic lymphocytic leukemia (CLL) treated with BTK inhibitors. Data on mutation rates in patients without PD on ibrutinib treatment are limited.

EXPERIMENTAL DESIGN

We evaluated frequency and time to detection of BTK and PLCG2 mutations in peripheral blood samples from 388 patients with previously untreated (n = 238) or relapsed/refractory (n = 150) CLL across five clinical trials.

RESULTS

With median follow-up of 35 months (range, 0-72) without PD at last sampling, mutations in BTK (3%), PLCG2 (2%), or both genes (1%) were rare in previously untreated patients. With median follow-up of 35 months (range, 1-70) without PD at last sample, mutations in BTK (30%), PLCG2 (7%), or both genes (5%) were more common in patients with relapsed/refractory CLL. Median time to first detection of BTK C481S mutation was not reached in previously untreated patients and was >5 years in patients with relapsed/refractory CLL. Among patients evaluable at PD, previously untreated patients (n = 12) had lower rates than those with relapsed/refractory disease (n = 45) of BTK (25% vs. 49%) and PLCG2 mutations (8% vs. 13%). Time from first detection of BTK C481S mutation to PD was 11.3 months in 1 previously untreated patient and median 8.5 months (range, 0-35.7) among 23 patients with relapsed/refractory CLL.

CONCLUSIONS

This systematic investigation describes development of mutations over time in patients without PD and informs the potential clinical opportunity to optimize ongoing benefits for such patients.

Using Human 'Personalized' Cybrids to Identify Drugs/Agents That Can Regulate Chronic Lymphoblastic Leukemia Mitochondrial Dysfunction

This study uses personalized chronic lymphoblastic leukemia (CLL) cybrid cells to test various drugs/agents designed to improve mitochondrial function and cell longevity. Age-matched control (NL) and CLL cybrids were created. The NL and CLL cybrids were treated with ibrutinib (Ibr-10 μM), mitochondrial-targeted nutraceuticals such as alpha lipoic acid (ALA-1 mM), amla (Aml-300 μg), melatonin (Mel-1 mM), resveratrol (Res-100 μM) alone, or a combination of ibrutinib with nutraceuticals (Ibr + ALA, Ibr + Aml, Ibr + Mel, or Ibr + Res) for 48 h. MTT (3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazoliumbromide), H2DCFDA(2',7' Dichlorodihydrofluorescein diacetate), and JC1 assays were used to measure the cellular metabolism, intracellular ROS levels, and mitochondrial membrane potential (∆ψm), respectively. The expression levels of genes associated with antioxidant enzymes (SOD2, GPX3, and NOX4), apoptosis (BAX and CASP3), and inflammation (IL6, IL-1β, TNFα, and TGFβ) were measured using quantitative real-time PCR (qRT-PCR). CLL cybrids treated with Ibr + ALA, Ibr + Aml, Ibr + Mel, and Ibr + Res had (a) reduced cell survivability, (b) increased ROS production, (c) increased ∆ψm levels, (d) decreased antioxidant gene expression levels, and (e) increased apoptotic and inflammatory genes in CLL cybrids when compared with ibrutinib-alone-treated CLL cybrids. Our findings show that the addition of nutraceuticals makes the CLL cybrids more pro-apoptotic with decreased cell survival compared with CLL cybrids exposed to ibrutinib alone.

Valproic acid increases CAR T cell cytotoxicity against acute myeloid leukemia

The treatment of B cell malignancies has dramatically changed with the introduction of immunotherapy, especially chimeric antigen receptor T (CAR-T) cell therapy. However, only limited efficacy is observed in acute myeloid leukaemia (AML). In the study, We detected CD123 and CLL-1 expression on leukaemia cells from Relapsed/Refractory AML (R/R AML) patients. Then, we constructed anti-CD123 CAR and CLL-1 CAR with different co-stimulation domains (CD28 or 4-1BB) and detected their anti-AML effects. To increase the efficacy of CAR-T cell therapy, we tested different strategies, including application of combined checkpoint inhibitors and histone deacetylase inhibitors (HDACi) in vivo and in vitro We found CD123 and CLL-1 were highly expressed on AML cells. The proportions of T cell subsets and NK cells involved in anti-tumour or anti-inflammation processes in AML patients significantly decreased when compared with healthy donors. Both CD123 CAR and CLL-1 CAR displayed specific anti-AML effects in vitro To improve the lysis effects of CAR-T cells, we combined CAR-T cell therapy with different agents. PD-1/PD-L1 antibodies only slightly improved the potency of CAR-T cell therapy (CD123 CAR-T 60.92% ± 2.9087% vs. 65.43% ± 2.1893%, 60.92% ± 2.9087% vs. 67.43% ± 3.4973%; 37.37% ± 3.908% vs. 41.89% ± 5.1568%, 37.37% ± 3.908% vs. 42.84% ± 4.2635%). However, one HDACi (valproic acid [VPA]) significantly improved CAR-T cell potency against AML cells (CLL-1 CAR-T 34.97% ± 0.3051% vs. 88.167% ± 1.5327%, p < 0.0001; CD123 CAR-T 26.87% ± 2.7010% vs. 82.56% ± 3.086%, p < 0.0001 in MV411; CLL-1 CAR-T 78.77% ± 1.2061% vs. 93.743% ± 1.2333%, p < 0.0001; CD123 CAR-T 64.10% ± 1.5130% vs. 94.427% ± 0.142%, p = 0.0001 in THP-1). Combination therapy prolonged the overall survival of mice when compared with single CD123 CAR-T cell therapy (median survival: 180 days vs. unfollowed). A possible mechanism is that activated CD8+T cells upregulate natural-killer group 2 member D (NKG2D), and VPA upregulates NKG2D ligand expression in AML cells, contributing to NKG2D-mediated cytotoxicity of CAR-T cells against tumour cells. In conclusion, CD123 and CLL-1 are promising targets for AML CAR-T cell therapy. A combination of VPA pre-treatment and CAR-T against AML exhibits synergic effects.

Prognostic Value of Plasma miR-29a Evaluation in Chronic Lymphocytic Leukemia Patients

OBJECTIVE

Dysregulation of microRNA expression could attenuate the course of chronic lymphocytic leukemia (CLL). Therefore, the aim of our study is to address the association between miR-29a expression and other prognostic markers in CLL patients.

METHODS

miR-29a expression was determined by quantitative real-time PCR in the plasma of 158 CLL patients at diagnosis beside 21 healthy controls in a prospective study.

RESULTS

The levels of miR-29a expression were found to be significantly higher in CLL patients as compared to healthy controls (P<0.001). Moreover, a significant association between high miR-29a expression and poor prognostic markers (high expression of CD38 and ZAP70, high LDH levels, Stage III Rai stage, unfavorable cytogenetic finding, time to first treatment (TTFT) and patients outcome (P<0.001 for All). Using ROC curve, we have reported that miR-29a expression levels (29a<0.76 vs >0.76) is able to discriminate severity subgroups of CLL patients.

CONCLUSION

Up regulation of miR-29a expression at CLL diagnosis was detected. Determination of miR-29a expression concentration levels at diagnosis could be demonstrated as a prognostic biomarker in CLL patients.

Inhibition of MYC translation through targeting of the newly identified PHB-eIF4F complex as a therapeutic strategy in CLL

Dysregulation of messenger RNA (mRNA) translation, including preferential translation of mRNA with complex 5' untranslated regions such as the MYC oncogene, is recognized as an important mechanism in cancer. Here, we show that both human and murine chronic lymphocytic leukemia (CLL) cells display a high translation rate, which is inhibited by the synthetic flavagline FL3, a prohibitin (PHB)-binding drug. A multiomics analysis performed in samples from patients with CLL and cell lines treated with FL3 revealed the decreased translation of the MYC oncogene and of proteins involved in cell cycle and metabolism. Furthermore, inhibiting translation induced a proliferation arrest and a rewiring of MYC-driven metabolism. Interestingly, contrary to other models, the RAS-RAF-(PHBs)-MAPK pathway is neither impaired by FL3 nor implicated in translation regulation in CLL cells. Here, we rather show that PHBs are directly associated with the eukaryotic initiation factor (eIF)4F translation complex and are targeted by FL3. Knockdown of PHBs resembled FL3 treatment. Importantly, inhibition of translation controlled CLL development in vivo, either alone or combined with immunotherapy. Finally, high expression of translation initiation-related genes and PHBs genes correlated with poor survival and unfavorable clinical parameters in patients with CLL. Overall, we demonstrated that translation inhibition is a valuable strategy to control CLL development by blocking the translation of several oncogenic pathways including MYC. We also unraveled a new and direct role of PHBs in translation initiation, thus creating new therapeutic opportunities for patients with CLL.

Relative Expression of BATF and CD112 in PBMC of Patients with Chronic Lymphocytic Leukemia

OBJECTIVE

BATF, as a transcription factor, and CD112, as a receptor for TIGIT, are involved in T-cell exhaustion. We investigated BATF and CD112 gene expression in the peripheral blood mononuclear cells from CLL patients and healthy subjects.

METHODS

In a case-control study, 33 patients with CLL and 20 sex- and age-matched healthy individual were enrolled. Diagnosis and classification of patients was done according to immunophenotyping via flow cytometry and RAI staging system, respectively. Relative mRNA expression of BATF and CD112 was measured using qRT-PCR.

RESULT

Our results showed that the expression of BATF and CD112 in CLL samples were significantly decreased in comparison those of the healthy controls (P = 0.0236 and P = 0.0002, respectively).

CONCLUSION

These findings suggest the role of BATF and CD112 not only as a role in T cell exhaustion, but in effector differentiation program in CLL, which warrants further studies in future.

Pirtobrutinib targets BTK C481S in ibrutinib-resistant CLL but second-site BTK mutations lead to resistance

Covalent inhibitors of Bruton tyrosine kinase (BTK) have transformed the therapy of chronic lymphocytic leukemia (CLL), but continuous therapy has been complicated by the development of resistance. The most common resistance mechanism in patients whose disease progresses on covalent BTK inhibitors (BTKis) is a mutation in the BTK 481 cysteine residue to which the inhibitors bind covalently. Pirtobrutinib is a highly selective, noncovalent BTKi with substantial clinical activity in patients whose disease has progressed on covalent BTKi, regardless of BTK mutation status. Using in vitro ibrutinib-resistant models and cells from patients with CLL, we show that pirtobrutinib potently inhibits BTK-mediated functions including B-cell receptor (BCR) signaling, cell viability, and CCL3/CCL4 chemokine production in both BTK wild-type and C481S mutant CLL cells. We demonstrate that primary CLL cells from responding patients on the pirtobrutinib trial show reduced BCR signaling, cell survival, and CCL3/CCL4 chemokine secretion. At time of progression, these primary CLL cells show increasing resistance to pirtobrutinib in signaling inhibition, cell viability, and cytokine production. We employed longitudinal whole-exome sequencing on 2 patients whose disease progressed on pirtobrutinib and identified selection of alternative-site BTK mutations, providing clinical evidence that secondary BTK mutations lead to resistance to noncovalent BTKis.

Empirical Study on Exploring the Role of CD180 and MD-1 Prognostic Indicators for the Chronic Lymphocytic Leukaemia (CLL) Disease

&lt;b&gt;Background and Objective:&lt;/b&gt; Chronic Lymphocytic Leukaemia (CLL) is a frequent type of leukaemia disease. This study was focused on investigating the role of prognostic indicators, such as CD180 and MD-1 for Chronic Lymphocytic Leukaemia (CLL) pathogenesis because they involve cell signalling and proliferation. &lt;b&gt;Materials and Methods:&lt;/b&gt; A total of 12 normal controls and 52 patients were taken to determine the expressions of CD180 and MD-1 with different variations in comparison with the IgVH (Immunoglobulin Heavy Chain variable region gene) mutational status, FISH (fluorescence &lt;i&gt;in situ&lt;/i&gt; hybridization) and Rai staging. &lt;b&gt;Results:&lt;/b&gt; The quantitative data findings were evident that CD180 and MD-1 expressions showed insignificant differences among CLL patients at the protein level based on SPSS results. On the contrary, they resulted in significant differences for subgroups of established biomarkers like Rai staging (stages 0, I, II and III), FISH (13q and non-13q deletions) and IgVH (mutated and unmutated). &lt;b&gt;Conclusion:&lt;/b&gt; The CD180 and MD-1 have been used as prognostic indicators to evaluate the outcomes relevant to the cell cycle and survival rate of CLL cells.

CCL3 as Possible Negative Prognostic Factor in Chronic Lymphocytic Leukemia

INTRODUCTION

Both microenvironmental signals from surrounding cells and changes in the genome of leukemic cells play essential role in the development of chronic lymphocytic leukemia. Nurse-like cells (NLCs) are one of the important elements of the microenvironment of CLL cells. The key role in the interactions of leukemic cells with NLCs is played by chemokines, which may interfere with the programmed cell death process in the leukemic lymphocytes. The aim of our study was analysis of selected microenvironmental factors having a potential impact on the leukemic cells survival, as well as their association with clinical, cytogenetic, and molecular parameters. For this study, we selected three types of molecules which can modulate microenvironment: chemokines IL-8 and CCL3 (which are classically secreted to extracellular matrix), soluble forms of adhesion molecules JAG1 and CD163, and secreted form of endogenous protein BIRC5. We assessed their expression in the serum of CLL patients as well as in medium of long-term NLCs cultures.

METHODS

Long-term cell culture was prepared from mononuclear cells derived from the blood of 34 patients with CLL. Number of NLCs cells was evaluated, under a light inverted microscope. The concentration of IL-8, CCL3, sBIRC5, sCD163, and sJAG1 in culture medium and serum was assessed by enzyme-linked immunosorbent assays.

RESULTS

There were significant differences in the concentration of IL-8, sBIRC5, CCL3, sCD163, and sJAG1 between the patient's blood serum and the culture medium. The concentrations of IL-8, CCL3, and JAG1 were higher in the culture medium, which confirmed the role of the microenvironment in the production of these proteins. In addition, the concentration of CCL3 chemokine in both patient's blood serum and in the culture medium correlated with the number of NLCs and with known prognostic factors in the course of CLL, e.g., Rai stage, WBC, expression of ZAP-70, CD38, and CD5/19.

CONCLUSION

The microenvironment of CLL cells, which includes NLCs, plays an important role in the pathogenesis of CLL. The CCL3 chemokine seems to be a good factor representing microenvironment of CLL cells. Chronic lymphocytic leukemia is a complex and very heterogeneous disease; therefore, its progress should be considered both in the context of genetic changes and the interaction with microenvironmental cells.

Study of the Utility of Myeloid Cell Nuclear Differentiation Antigen (MNDA) in the Diagnosis of Marginal Zone Lymphoma

Myeloid cell nuclear differentiation antigen (MNDA) is normally expressed on myelomonocytic cells and a subset of B lymphocytes. It was found to be differentially expressed between nodal marginal zone lymphoma (MZL) and follicular lymphoma (FL). However, MNDA has not been widely used as a diagnostic marker in clinical practice. To validate its utility, we studied the expression of MNDA by immunohistochemistry in 313 cases of small B-cell lymphomas. Our results showed that MNDA was positive in 77.9% of MZL, 21.9% of mantle cell lymphoma, 28.9% of small lymphocytic lymphoma/chronic lymphocytic leukemia, 2.6% of FL, and 25% of lymphoplasmacytic lymphoma. MNDA positivity varied from 68.0% to 84.0% among the 3 MZL subtypes, with extranodal MZL having the highest percentage. There was a statistically significant difference in MNDA expression between MZL and FL, mantle cell lymphoma, small lymphocytic lymphoma/chronic lymphocytic leukemia, or lymphoplasmacytic lymphoma. CD43 expression was slightly more frequent in MNDA-negative MZL than in MNDA-positive MZL. Combined use of CD43 and MNDA improved the diagnostic sensitivity for MZL from 77.9% to 87.8%. There was a trend of positive correlation between MNDA and p53 in MZL. In conclusion, MNDA is preferentially expressed in MZL among small B-cell lymphomas and it is a useful marker for the differentiation of MZL and FL.

Interferon gamma regulates a complex pro-survival signal network in chronic lymphocytic leukemia

BACKGROUND

It is known that the microenvironmental cytokine interferon gamma (IFN-γ) provides a survival advantage for chronic lymphocytic leukemia (CLL) cells. However, the mechanisms involved in this effect have not been properly investigated.

METHODS

Herein, we conducted a comprehensive screening of the effects of IFN-γ on signaling pathways and gene expression profiles in CLL cells by using western blotting, real-time quantitative reverse transcription (RT-qPCR) and high-throughput RNA sequencing (RNA-seq).

RESULTS

We found that IFN-γ not only activated the pro-survival signal transducer and activator of transcription 3 (STAT3), but also activated the protein kinase B and extracellular signal-regulated kinase signaling pathways. RNA-seq analysis showed that IFN-γ stimulation changed the expression profiles of more than 500 genes, with 391 being up-regulated and 123 down-regulated. These genes are involved in numerous biological processes, including anti-apoptosis, cell migration, and proliferation. IFN-γ significantly up-regulated the expression of CD38, BCL6, CXCL9, BCL2A1, SCOS3, IL-10, HGF, EGFR, THBS-1, FN1, and MUC1, which encode proteins potentially associated with disease progression, worse prognosis or poor response to treatment. Blocking janus kinases1/2 (JAK1/2) or STAT3 signal by specific inhibitors affected the expression of most genes, suggesting a pivotal role of the JAK1/2-STAT3 pathway in IFN-γ pro-survival effects in CLL.

CONCLUSIONS

Our data demonstrate that IFN-γ regulates a complex pro-survival signal network in CLL through JAK1/2-STAT3, which provides a rational explanation for IFN-γ promoting CLL cells survival and drug resistance.

NRX-0492 degrades wild-type and C481 mutant BTK and demonstrates in vivo activity in CLL patient-derived xenografts

Bruton tyrosine kinase (BTK) is essential for B-cell receptor (BCR) signaling, a driver of chronic lymphocytic leukemia (CLL). Covalent inhibitors bind C481 in the active site of BTK and have become a preferred CLL therapy. Disease progression on covalent BTK inhibitors is commonly associated with C481 mutations. Here, we investigated a targeted protein degrader, NRX-0492, that links a noncovalent BTK-binding domain to cereblon, an adaptor protein of the E3 ubiquitin ligase complex. NRX-0492 selectively catalyzes ubiquitylation and proteasomal degradation of BTK. In primary CLL cells, NRX-0492 induced rapid and sustained degradation of both wild-type and C481 mutant BTK at half maximal degradation concentration (DC50) of ≤0.2 nM and DC90 of ≤0.5 nM, respectively. Sustained degrader activity was maintained for at least 24 hours after washout and was equally observed in high-risk (deletion 17p) and standard-risk (deletion 13q only) CLL subtypes. In in vitro testing against treatment-naïve CLL samples, NRX-0492 was as effective as ibrutinib at inhibiting BCR-mediated signaling, transcriptional programs, and chemokine secretion. In patient-derived xenografts, orally administered NRX-0492 induced BTK degradation and inhibited activation and proliferation of CLL cells in blood and spleen and remained efficacious against primary C481S mutant CLL cells collected from a patient progressing on ibrutinib. Oral bioavailability, >90% degradation of BTK at subnanomolar concentrations, and sustained pharmacodynamic effects after drug clearance make this class of targeted protein degraders uniquely suitable for clinical translation, in particular as a strategy to overcome BTK inhibitor resistance. Clinical studies testing this approach have been initiated (NCT04830137, NCT05131022).

VIP152 is a selective CDK9 inhibitor with pre-clinical in vitro and in vivo efficacy in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is effectively treated with targeted therapies including Bruton tyrosine kinase inhibitors and BCL2 antagonists. When these become ineffective, treatment options are limited. Positive transcription elongation factor complex (P-TEFb), a heterodimeric protein complex composed of cyclin dependent kinase 9 (CDK9) and cyclin T1, functions to regulate short half-life transcripts by phosphorylation of RNA Polymerase II (POLII). These transcripts are frequently dysregulated in hematologic malignancies; however, therapies targeting inhibition of P-TEFb have not yet achieved approval for cancer treatment. VIP152 kinome profiling revealed CDK9 as the main enzyme inhibited at 100 nM, with over a 10-fold increase in potency compared with other inhibitors currently in development for this target. VIP152 induced cell death in CLL cell lines and primary patient samples. Transcriptome analysis revealed inhibition of RNA degradation through the AU-Rich Element (ARE) dysregulation. Mechanistically, VIP152 inhibits the assembly of P-TEFb onto the transcription machinery and disturbs binding partners. Finally, immune competent mice engrafted with CLL-like cells of Eµ-MTCP1 over-expressing mice and treated with VIP152 demonstrated reduced disease burden and improvement in overall survival compared to vehicle-treated mice. These data suggest that VIP152 is a highly selective inhibitor of CDK9 that represents an attractive new therapy for CLL.

Search for Synergistic Drug Combinations to Treat Chronic Lymphocytic Leukemia

Finding synergistic drug combinations is an important area of cancer research. Here, we sought to rationally design synergistic drug combinations with an inhibitor of BTK kinase, ibrutinib, which is used for the treatment of several types of leukemia. We (a) used a pooled shRNA screen to identify genes that protect cells from the drug, (b) identified protective pathways via bioinformatics analysis of these gene sets, and (c) identified drugs that inhibit these pathways. Based on this analysis, we established that inhibitors of proteasome and mTORC1 could synergize with ibrutinib both in vitro and in vivo. We suggest that FDA-approved inhibitors of these pathways could be effectively combined with ibrutinib for the treatment of chronic lymphocytic leukemia (CLL).

Learning from TCR Signaling and Immunological Synapse Assembly to Build New Chimeric Antigen Receptors (CARs)

Chimeric antigen receptor (CAR) T cell immunotherapy is a revolutionary pillar in cancer treatment. Clinical experience has shown remarkable successes in the treatment of certain hematological malignancies but only limited efficacy against B cell chronic lymphocytic leukemia (CLL) and other cancer types, especially solid tumors. A wide range of engineering strategies have been employed to overcome the limitations of CAR T cell therapy. However, it has become increasingly clear that CARs have unique, unexpected features; hence, a deep understanding of how CARs signal and trigger the formation of a non-conventional immunological synapse (IS), the signaling platform required for T cell activation and execution of effector functions, would lead a shift from empirical testing to the rational design of new CAR constructs. Here, we review current knowledge of CARs, focusing on their structure, signaling and role in CAR T cell IS assembly. We, moreover, discuss the molecular features accounting for poor responses in CLL patients treated with anti-CD19 CAR T cells and propose CLL as a paradigm for diseases connected to IS dysfunctions that could significantly benefit from the development of novel CARs to generate a productive anti-tumor response.

Single-cell multiomics reveal the scale of multilayered adaptations enabling CLL relapse during venetoclax therapy

Venetoclax (VEN) inhibits the prosurvival protein BCL2 to induce apoptosis and is a standard therapy for chronic lymphocytic leukemia (CLL), delivering high complete remission rates and prolonged progression-free survival in relapsed CLL but with eventual loss of efficacy. A spectrum of subclonal genetic changes associated with VEN resistance has now been described. To fully understand clinical resistance to VEN, we combined single-cell short- and long-read RNA-sequencing to reveal the previously unappreciated scale of genetic and epigenetic changes underpinning acquired VEN resistance. These appear to be multilayered. One layer comprises changes in the BCL2 family of apoptosis regulators, especially the prosurvival family members. This includes previously described mutations in BCL2 and amplification of the MCL1 gene but is heterogeneous across and within individual patient leukemias. Changes in the proapoptotic genes are notably uncommon, except for single cases with subclonal losses of BAX or NOXA. Much more prominent was universal MCL1 gene upregulation. This was driven by an overlying layer of emergent NF-κB (nuclear factor kappa B) activation, which persisted in circulating cells during VEN therapy. We discovered that MCL1 could be a direct transcriptional target of NF-κB. Both the switch to alternative prosurvival factors and NF-κB activation largely dissipate following VEN discontinuation. Our studies reveal the extent of plasticity of CLL cells in their ability to evade VEN-induced apoptosis. Importantly, these findings pinpoint new approaches to circumvent VEN resistance and provide a specific biological justification for the strategy of VEN discontinuation once a maximal response is achieved rather than maintaining long-term selective pressure with the drug.

Dual checkpoint blockade of CD47 and LILRB1 enhances CD20 antibody-dependent phagocytosis of lymphoma cells by macrophages

Antibody-dependent cellular phagocytosis (ADCP) by macrophages, an important effector function of tumor targeting antibodies, is hampered by ‘Don´t Eat Me!’ signals such as CD47 expressed by cancer cells. Yet, human leukocyte antigen (HLA) class I expression may also impair ADCP by engaging leukocyte immunoglobulin-like receptor subfamily B (LILRB) member 1 (LILRB1) or LILRB2. Analysis of different lymphoma cell lines revealed that the ratio of CD20 to HLA class I cell surface molecules determined the sensitivity to ADCP by the combination of rituximab and an Fc-silent variant of the CD47 antibody magrolimab (CD47-IgGσ). To boost ADCP, Fc-silent antibodies against LILRB1 and LILRB2 were generated (LILRB1-IgGσ and LILRB2-IgGσ, respectively). While LILRB2-IgGσ was not effective, LILRB1-IgGσ significantly enhanced ADCP of lymphoma cell lines when combined with both rituximab and CD47-IgGσ. LILRB1-IgGσ promoted serial engulfment of lymphoma cells and potentiated ADCP by non-polarized M0 as well as polarized M1 and M2 macrophages, but required CD47 co-blockade and the presence of the CD20 antibody. Importantly, complementing rituximab and CD47-IgGσ, LILRB1-IgGσ increased ADCP of chronic lymphocytic leukemia (CLL) or lymphoma cells isolated from patients. Thus, dual checkpoint blockade of CD47 and LILRB1 may be promising to improve antibody therapy of CLL and lymphomas through enhancing ADCP by macrophages.

Phase 1 clinical trial of CRISPR-engineered CAR19 universal T cells for treatment of children with refractory B cell leukemia

Genome editing of allogeneic T cells can provide "off-the-shelf" alternatives to autologous chimeric antigen receptor (CAR) T cell therapies. Disruption of T cell receptor α chain (TRAC) to prevent graft-versus-host disease (GVHD) and removal of CD52 (cluster of differentiation 52) for a survival advantage in the presence of alemtuzumab have previously been investigated using transcription activator-like effector nuclease (TALEN)-mediated knockout. Here, we deployed next-generation CRISPR-Cas9 editing and linked CAR expression to multiplexed DNA editing of TRAC and CD52 through incorporation of self-duplicating CRISPR guide RNA expression cassettes within the 3' long terminal repeat of a CAR19 lentiviral vector. Three cell banks of TT52CAR19 T cells were generated and cryopreserved. A phase 1, open-label, non-randomized clinical trial was conducted and treated six children with relapsed/refractory CD19-positive B cell acute lymphoblastic leukemia (B-ALL) (NCT04557436). Lymphodepletion included fludarabine, cyclophosphamide, and alemtuzumab and was followed by a single infusion of 0.8 × 106 to 2.0 × 106 CAR19 T cells per kilogram with no immediate toxicities. Four of six patients infused with TT52CAR19 T cells exhibited cell expansion, achieved flow cytometric remission, and then proceeded to receive allogeneic stem cell transplantation. Two patients required biological intervention for grade II cytokine release syndrome, one patient developed transient grade IV neurotoxicity, and one patient developed skin GVHD, which resolved after transplant conditioning. Other complications were within expectations, and primary safety objectives were met. This study provides a demonstration of the feasibility, safety, and therapeutic potential of CRISPR-engineered immunotherapy.

ROR1: an orphan becomes apparent

Since its initial identification in 1992 as a possible class 1 cell-surface receptor without a known parent ligand, receptor tyrosine kinase-like orphan receptor 1 (ROR1) has stimulated research, which has made apparent its significance in embryonic development and cancer. Chronic lymphocytic leukemia (CLL) was the first malignancy found to have distinctive expression of ROR1, which can help distinguish leukemia cells from most noncancer cells. Aside from its potential utility as a diagnostic marker or target for therapy, ROR1 also factors in the pathophysiology of CLL. This review is a report of the studies that have elucidated the expression, biology, and evolving strategies for targeting ROR1 that hold promise for improving the therapy of patients with CLL or other ROR1-expressing malignancies.

The rs1001179 SNP and CpG methylation regulate catalase expression in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is an incurable disease characterized by an extremely variable clinical course. We have recently shown that high catalase (CAT) expression identifies patients with an aggressive clinical course. Elucidating mechanisms regulating CAT expression in CLL is preeminent to understand disease mechanisms and develop strategies for improving its clinical management. In this study, we investigated the role of the CAT promoter rs1001179 single nucleotide polymorphism (SNP) and of the CpG Island II methylation encompassing this SNP in the regulation of CAT expression in CLL. Leukemic cells harboring the rs1001179 SNP T allele exhibited a significantly higher CAT expression compared with cells bearing the CC genotype. CAT promoter harboring the T -but not C- allele was accessible to ETS-1 and GR-β transcription factors. Moreover, CLL cells exhibited lower methylation levels than normal B cells, in line with the higher CAT mRNA and protein expressed by CLL in comparison with normal B cells. Methylation levels at specific CpG sites negatively correlated with CAT levels in CLL cells. Inhibition of methyltransferase activity induced a significant increase in CAT levels, thus functionally validating the role of CpG methylation in regulating CAT expression in CLL. Finally, the CT/TT genotypes were associated with lower methylation and higher CAT levels, suggesting that the rs1001179 T allele and CpG methylation may interact in regulating CAT expression in CLL. This study identifies genetic and epigenetic mechanisms underlying differential expression of CAT, which could be of crucial relevance for the development of therapies targeting redox regulatory pathways in CLL.

High surface IgM levels associate with shorter response to ibrutinib and BTK bypass in patients with CLL

Chronic lymphocytic leukemia (CLL) cells have variably low surface IgM (sIgM) levels/signaling capacity, influenced by chronic antigen engagement at tissue sites. Within these low levels, CLL with relatively high sIgM (CLLhigh) progresses more rapidly than CLL with low sIgM (CLLlow). During ibrutinib therapy, surviving CLL cells redistribute into the peripheral blood and can recover sIgM expression. Return of CLL cells to tissue may eventually recur, where cells with high sIgM could promote tumor growth. We analyzed time to new treatment (TTNT) following ibrutinib in 70 patients with CLL (median follow-up of 66 months) and correlated it with pretreatment sIgM levels and signaling characteristics. Pretreatment sIgM levels correlated with signaling capacity, as measured by intracellular Ca2+ mobilization (iCa2+), in vitro (r = 0.70; P < .0001). High sIgM levels/signaling strongly correlated with short TTNT (P < .05), and 36% of patients with CLLhigh vs 8% of patients with CLLlow progressed to require a new treatment. In vitro, capacity of ibrutinib to inhibit sIgM-mediated signaling inversely correlated with pretherapy sIgM levels (r = -0.68; P = .01) or iCa2+ (r = -0.71; P = .009). In patients, sIgM-mediated iCa2+ and ERK phosphorylation levels were reduced by ibrutinib therapy but not abolished. The residual signaling capacity downstream of BTK was associated with high expression of sIgM, whereas it was minimal when sIgM expression was low (P < .05). These results suggested that high sIgM levels facilitated CLL cell resistance to ibrutinib in patients. The CLL cells, surviving in the periphery with high sIgM expression, include a dangerous fraction that is able to migrate to tissue and receive proliferative stimuli, which may require targeting by combined approaches.

Decreased TCF1 and BCL11B expression predicts poor prognosis for patients with chronic lymphocytic leukemia

T cell immune dysfunction is a prominent characteristic of chronic lymphocytic leukemia (CLL) and the main cause of failure for immunotherapy and multi-drug resistance. There remains a lack of specific biomarkers for evaluating T cell immune status with outcome for CLL patients. T cell factor 1 (TCF1, encoded by the TCF7 gene) can be used as a critical determinant of successful anti-tumor immunotherapy and a prognostic indicator in some solid tumors; however, the effects of TCF1 in CLL remain unclear. Here, we first analyzed the biological processes and functions of TCF1 and co-expressing genes using the GEO and STRING databases with the online tools Venny, Circos, and Database for Annotation, Visualization, and Integrated Discovery (DAVID). Then the expression and prognostic values of TCF1 and its partner gene B cell leukemia/lymphoma 11B (BCL11B) were explored for 505 CLL patients from 6 datasets and validated with 50 CLL patients from Henan cancer hospital (HNCH). TCF1 was downregulated in CLL patients, particularly in CD8+ T cells, which was significantly correlated with poor time-to-first treatment (TTFT) and overall survival (OS) as well as short restricted mean survival time (RMST). Function and pathway enrichment analysis revealed that TCF1 was positively correlated with BCL11B, which is involved in regulating the activation and differentiation of T cells in CLL patients. Intriguingly, BCL11B was highly consistent with TCF1 in its decreased expression and prediction of poor prognosis. More importantly, the combination of TCF1 and BCL11B could more accurately assess prognosis than either alone. Additionally, decreased TCF1 and BCL11B expression serves as an independent risk factor for rapid disease progression, coinciding with high-risk indicators, including unmutated IGHV, TP53 alteration, and advanced disease. Altogether, this study demonstrates that decreased TCF1 and BCL11B expression is significantly correlated with poor prognosis, which may be due to decreased TCF1+CD8+ T cells, impairing the effector CD8+ T cell differentiation regulated by TCF1/BCL11B.

Revealing a Phenotypical Appearance of Ibrutinib Resistance in Patients With Chronic Lymphocytic Leukaemia by Flow Cytometry

Background: Ibrutinib is widely known as an effective and well-tolerated therapeutical choice of the chronic lymphocytic leukaemia (CLL). However, acquired resistance may occur during the treatment, causing relapse. Early detection of ibrutinib resistance is an important issue, therefore we aimed to find phenotypic markers on CLL cells the expression of which may correlate with the appearance of ibrutinib resistance.

Methods: We examined 28 patients’ peripheral blood (PB) samples (treatment naïve, ibrutinib sensitive, clinically ibrutinib resistant). The surface markers’ expression (CD27, CD69, CD86, CD184, CD185) were measured by flow cytometry. Furthermore, the BTK^C481S resistance mutation was assessed by digital droplet PCR. Moreover, the CLL cells’ phenotype of a patient with acquired ibrutinib resistance was observed during the ibrutinib treatment.

Results: The expression of CD27 (p = 0.030) and CD86 (p = 0.031) became higher in the clinically resistant cohort than in the ibrutinib sensitive cohort. Besides, we found that high CD86 and CD27 expressions were accompanied by BTK^C481S mutation. Our prospective study showed that the increase of the expression of CD27, CD69 and CD86 was noticed ahead of the clinical resistance with 3 months.

Conclusion: Our study suggests that the changes of the expression of these markers could indicate ibrutinib resistance and the examination of these phenotypic changes may become a part of the patients’ follow-up in the future.

The pyroptosis-related gene signature predicts prognosis and indicates the immune microenvironment status of chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is the most common leukemia in the Western world with great heterogeneity. Pyroptosis has recently been recognized as an inflammatory form of programmed cell death (PCD) and shares a close relationship with apoptosis. Although the role of apoptosis in CLL was comprehensively studied and successfully applied in clinical treatment, the relationship between pyroptosis genes and CLL remained largely unknown. In this study, eight differentially expressed pyroptosis-related genes (PRGs) were identified between CLL and normal B cells. In order to screen out the prognostic value of differentially expressed PRGs, univariate and multivariate Cox regression analyses were conducted and a risk model with three PRG signatures (GSDME, NLRP3, and PLCG1) was constructed. All CLL samples were stratified into high- and low-risk subgroups according to risk scores. The risk model showed high efficacy in predicting both overall survival (OS) and time to first treatment (TTFT). Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and Gene Set Enrichment Analysis (GSEA) showed the dysregulation of immune and inflammatory response in the high-risk group. Single-sample GSEA (ssGSEA) of immune cell infiltration and the activity of immune-related pathways also displayed decreased antitumor immunity in the high-risk group. In conclusion, PRGs are of prognostic value in CLL and may play important roles in tumor immunity, and the underlying relationship between PRGs and CLL needs to be explored further.

Increased serum level of alpha-2 macroglobulin and its production by B-lymphocytes in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL), the most common adult’s leukemia in the western world, is caused in 95% of the cases by uncontrolled proliferation of monoclonal B-lymphocytes. The complement system in CLL is chronically activated at a low level via the classical pathway (CP). This chronic activation is induced by IgG-hexamers, which are formed after binding to alpha-2-macroglobulin (A2M). The study investigated for the first time the serum levels of A2M in CLL patients, their association with the disease severity, and A2M production by the malignant B-lymphocytes. Blood samples were collected from 65 CLL patients and 30 normal controls (NC) subjects, and used for quantifications of the A2M levels, the complement activation marker (sC5b-9), the complement components C2, C3 and C4, and clinical biochemistry and hematology parameters. The production of A2M was studied in B-lymphocytes isolated from blood samples as well as in CLL and non-CLL cell lines.The serum A2M levels were significantly higher in CLL patients vs NCs, showing values of 3.62 ± 0.22 and 1.97 ± 0.10 mg/ml, respectively. Within the CLL group, A2M levels correlated significantly with the disease stage, with sC5b-9, and with clinical indicators of the disease severity. Increased A2M production was showed in three out of four CLL B-lymphocytic lines that were studied, as compared to non-CLL lines, to a non-lymphocytic line, and to blood-derived primary B-lymphocytes. A2M production was further increased both in primary cells and in the CLL cell-line after incubation with CLL sera, compared to NC sera. This study shows for the first time that serum A2M levels in CLL are significantly increased, likely due to A2M production by the malignant B-lymphocytes, and are correlated with the disease severity and with chronic complement activation. The moderate change in A2M production after incubation with NC sera in-vitro supports the hypothesis that inhibition of excess A2M production can be achieved, and that this may potentially down-regulate the IgG-hexamerization and the resulting chronic CP activation. This may also help restore complement system activity, and eventually improve complement activity and immunotherapy outcomes in CLL.

Effects of ibrutinib on T-cell immunity in patients with chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL), a highly heterogeneous B-cell malignancy, is characterized by tumor microenvironment disorder and T-cell immune dysfunction, which play a major role in the proliferation and survival of CLL cells. Ibrutinib is the first irreversible inhibitor of Bruton’s tyrosine kinase (BTK). In addition to targeting B-cell receptor (BCR) signaling to kill tumor cells, increasing evidence has suggested that ibrutinib regulates the tumor microenvironment and T-cell immunity in a direct and indirect manner. For example, ibrutinib not only reverses the tumor microenvironment by blocking cytokine networks and toll-like receptor signaling but also regulates T cells in number, subset distribution, T-cell receptor (TCR) repertoire and immune function by inhibiting interleukin-2 inducible T-cell kinase (ITK) and reducing the expression of inhibitory receptors, and so on. In this review, we summarize the current evidence for the effects of ibrutinib on the tumor microenvironment and cellular immunity of patients with CLL, particularly for the behavior and function of T cells, explore its potential mechanisms, and provide a basis for the clinical benefits of long-term ibrutinib treatment and combined therapy based on T-cell-based immunotherapies.

Spatial organization and early signaling of the B-cell receptor in CLL

Most chronic lymphocytic leukemia (CLL) clones express B-cell receptors (BcR) of both IgM/IgD isotypes; however, 5%–10% of CLL cases express isotype-switched immunoglobulin G (IgG). The early signaling and spatial patterning of the various BcRs at steady state and after activation are still fully unresolved. Herein, we show higher expression of the BcR signalosome elements and a more robust constitutive cell-intrinsic proximal BcR signaling in CLL with unmutated IGHV expressing IgM isotype (IgM U-CLL), compared with IGHV-mutated CLL (M-CLL) expressing either IgM or IgG isotypes. IgM in U-CLL is frequently located in the membrane plane in polarized patches, occasionally in caps, and sometimes inside the cells. Among M-CLL, IgM is scattered laterally in the membrane plane in a similar pattern as seen in normal B cells, whereas IgG is dispersed around the cell membrane in smaller clusters than in IgM U-CLL. Upon BcR engagement, both IgG and IgM expressing M-CLL showed attenuated signaling and only slight spatial reorganization dynamics of BcR microclusters and internalization, compared with the extensive reorganization and internalization of the BcR in IgM expressing U-CLL. The global gene signature of IgG M-CLL was closely related to that of IgM M-CLL rather than IgM U-CLL. Overall, we report fundamental differences in the basal composition, biochemical status, and spatial organization of the BcR in the three examined immunogenetic CLL subtypes that correlate with their clinical behavior. On the basis of our findings, IgG class-switched M-CLL likely represents the same disease as IgM M-CLL rather than a different biological and/or clinical entity.

Idelalisib activates AKT via increased recruitment of PI3Kδ/PI3Kβ to BCR signalosome while reducing PDK1 in post-therapy CLL cells

Idelalisib targets PI3Kδ in the BCR pathway generating only a partial response in CLL patients, indicating that the leukemic cells may have evolved escape signals. Indeed, we detected increased activation of AKT accompanied by upregulation of MYC/BCL2 in post-therapy CLL cells from patients treated with idelalisib/ofatumumab. To unravel the mechanism of increased AKT-activation, we studied the impact of idelalisib on a CLL-derived cell line, MEC1, as a model. After an initial inhibition, AKT-activation level was restored in idelalisib-treated MEC1 cells in a time-dependent manner. As BCAP (B-cell adaptor for PI3K) and CD19 recruit PI3Kδ to activate AKT upon BCR-stimulation, we examined if idelalisib-treatment altered PI3Kδ-recruitment. Immunoprecipitation of BCAP/CD19 from idelalisib-treated MEC1 cells showed increased recruitment of PI3Kδ in association with PI3Kβ, but not PI3Kα or PI3Kγ and that, targeting both PI3Kδ with PI3Kβ inhibited AKT-reactivation. We detected similar, patient-specific recruitment pattern of PI3K-isoforms by BCAP/CD19 in post-idelalisib CLL cells with increased AKT-activation. Interestingly, a stronger inhibitory effect of idelalisib on P-AKT (T308) than S473 was discernible in idelalisib-treated cells despite increased recruitment of PI3Kδ/PI3Kβ and accumulation of phosphatidylinositol-3,4,5-triphosphate; which could be attributed to reduced PDK1 activity. Thus, administration of isoform-specific inhibitors may prove more effective strategy for treating CLL patients.

B cell receptor signaling drives APOBEC3 expression via direct enhancer regulation in chronic lymphocytic leukemia B cells

Constitutively activated B cell receptor (BCR) signaling is a primary biological feature of chronic lymphocytic leukemia (CLL). The biological events controlled by BCR signaling in CLL are not fully understood and need investigation. Here, by analysis of the chromatin states and gene expression profiles of CLL B cells from patients before and after Bruton's tyrosine kinase inhibitor (BTKi) ibrutinib treatment, we show that BTKi treatment leads to a decreased expression of APOBEC3 family genes by regulating the activity of their enhancers. BTKi treatment reduces enrichment of enhancer marks (H3K4me1 and H3K27ac) and chromatin accessibility at putative APOBEC3 enhancers. CRISPR-Cas9 directed deletion or inhibition of the putative APOBEC3 enhancers leads to reduced APOBEC3 expression. We further find that transcription factor NFATc1 couples BCR signaling with the APOBEC3 enhancer activity to control APOBEC3 expression. We also find that enhancer-regulated APOBEC3 expression contributes to replication stress in malignant B cells. In total we demonstrate a novel mechanism for BTKi suppression of APOBEC3 expression via direct enhancer regulation in an NFATc1-dependent manner, implicating BCR signaling as a potential regulator of leukemic genomic instability.

Soluble Fc Receptor for IgM in Sera From Subsets of Patients With Chronic Lymphocytic Leukemia as Determined by a New Mouse Monoclonal Antibody

The FcR for IgM (FcµR) is the newest member of the FcR family, selectively expressed by lymphocytes, and distinct from FcRs for switched Ig isotypes that are expressed by various immune cell types and non-hematopoietic cells. From studies of Fcmr-ablated mice, FcµR was shown to have a regulatory function in B-cell tolerance, as evidenced by high serum titers of autoantibodies of the IgM and IgG isotypes in mutant mice. In our previous studies, both cell-surface and serum FcµR levels were elevated in patients with chronic lymphocytic leukemia (CLL), where antigen-independent self-ligation of BCR is a hallmark of the neoplastic B cells. This was assessed by sandwich ELISA using two different ectodomain-specific mAbs. To determine whether the serum FcµR is derived from cleavage of its cell-surface receptor (shedding) or its alternative splicing to skip the transmembrane exon resulting in a 70-aa unique hydrophilic C-terminus (soluble), we developed a new mouse IgG1κ mAb specific for human soluble FcμR (solFcμR) by taking advantages of the unique nature of transductant stably producing His-tagged solFcµR and of an in vivo differential immunization. His-tagged solFcμR attached to exosomes and plasma membranes, allowing immunization and initial hybridoma screening without purification of solFcμR. Differential immunization with tolerogen (membrane FcμR) and immunogen (solFcμR) also facilitated to generate solFcμR-specific hybridomas. The resultant solFcμR-specific mAb reacted with serum FcµR in subsets of CLL patients. This mAb, along with another ectodomain-specific mAb, will be used for verifying the hypothesis that the production of solFcµR is the consequence of chronic stimulation of BCR.

Chronic Lymphocytic Leukemia/Small Lymphocytic Lymphoma With Secondary Acquisition of t(11;14)(q13;q32)/CCND1-IGH: A Rare Variant Of Richter Transformation to Mantle Cell Lymphoma

INTRODUCTION

Chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) occasionally undergoes Richter transformation, mostly to diffuse large B-cell lymphoma, but its evolution to other types of B-cell lymphoma is rare. We report a CLL evolved to mantle cell lymphoma by acquiring t(11;14)(q13;q32); CCND1-IGH.

METHOD

A Retrospective review of clinical and laboratory data.

RESULTS

A 39-year-old male patient was diagnosed with CLL/SLL, and was initially followed without specific treatment, but subsequently received chlorambucil/fludarabine/rituximab due to exacerbated lymphocytosis. While his CLL/SLL waned and waxed, the immunophenotype and genotype of neoplastic B-cells remained unchanged, without cyclin D1 expression and CCND1-IGH fusion. Eleven years after the diagnosis, the patient's disease showed evidence of progression. Bone marrow examination demonstrated "CLL" with the morphology and immunophenotype similar to those seen in the previous biopsies. Unexpectedly, the neoplastic B-cells demonstrated cyclin D1 expression and harbored t(11;14)(q13;q32); CCND1-IGH, suggesting a clonal evolution to mantle cell lymphoma. He subsequently received cytoreductive chemotherapy followed by allogenic bone marrow transplant and remained in remission since then.

CONCLUSION

The retention of immunophenotype suggests a clonal relationship between CLL/SLL and mantle cell lymphoma. While the acquisition of t(11;14)(q13;q32); CCND1-IGH likely alters the disease course, the pathogenesis of this illegitimate translocation in CLL remains to be studied.

Overexpression of c-Myc-dependent heterogeneous nuclear ribonucleoprotein A1 promotes proliferation and inhibits apoptosis in NOTCH1-mutated chronic lymphocytic leukemia cells

BACKGROUND

NOTCH1 mutation is an essential molecular biologic aberration in chronic lymphocytic leukemia (CLL). CLL patients with NOTCH1 mutation have shown an unfavorable survival and a poor response to chemoimmunotherapy. This study aims to present the mechanisms of adverse prognosis caused by NOTCH1 mutation from the perspective of the splicing factor heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1).

METHODS

The microarray data in Gene Expression Omnibus datasets were analyzed by bioinformatics and the function of hnRNPA1 was checked by testing the proliferation and apoptosis of CLL-like cell lines. Afterward, quantitative reverse transcription-polymerase chain reaction and Western blotting were applied to explore the relationship among NOTCH1, c-Myc, and hnRNPA1.

RESULTS

RNA splicing was found to play a vital part in NOTCH1-mutated CLL cells; hence, hnRNPA1 was selected as the focus of this study. Higher expression of hnRNPA1 validated in primary NOTCH1-mutated CLL samples could promote proliferation and inhibit apoptosis in CLL. The expression of hnRNPA1 increased when NOTCH1 signaling was activated by transfection with NOTCH1 intracellular domain (NICD)-overexpressed adenovirus vector and declined after NOTCH1 signaling was inhibited by NOTCH1-shRNA. Higher expression of c-Myc was observed in NICD-overexpressed cells and hnRNPA1 expression was downregulated after applying c-Myc inhibitor 10058-F4. Moreover, in NICD-overexpressed cells, hnRNPA1 expression decreased through c-Myc inhibition.

CONCLUSION

Overexpression of c-Myc-dependent hnRNPA1 could promote proliferation and inhibit apoptosis in NOTCH1-mutated CLL cells, which might partly account for the poor prognosis of patients with NOTCH1 mutation.

HIF activation enhances FcγRIIb expression on mononuclear phagocytes impeding tumor targeting antibody immunotherapy

BACKGROUND

Hypoxia is a hallmark of the tumor microenvironment (TME) and in addition to altering metabolism in cancer cells, it transforms tumor-associated stromal cells. Within the tumor stromal cell compartment, tumor-associated macrophages (TAMs) provide potent pro-tumoral support. However, TAMs can also be harnessed to destroy tumor cells by monoclonal antibody (mAb) immunotherapy, through antibody dependent cellular phagocytosis (ADCP). This is mediated via antibody-binding activating Fc gamma receptors (FcγR) and impaired by the single inhibitory FcγR, FcγRIIb.

METHODS

We applied a multi-OMIC approach coupled with in vitro functional assays and murine tumor models to assess the effects of hypoxia inducible factor (HIF) activation on mAb mediated depletion of human and murine cancer cells. For mechanistic assessments, siRNA-mediated gene silencing, Western blotting and chromatin immune precipitation were utilized to assess the impact of identified regulators on FCGR2B gene transcription.

RESULTS

We report that TAMs are FcγRIIbbright relative to healthy tissue counterparts and under hypoxic conditions, mononuclear phagocytes markedly upregulate FcγRIIb. This enhanced FcγRIIb expression is transcriptionally driven through HIFs and Activator protein 1 (AP-1). Importantly, this phenotype reduces the ability of macrophages to eliminate anti-CD20 monoclonal antibody (mAb) opsonized human chronic lymphocytic leukemia cells in vitro and EL4 lymphoma cells in vivo in human FcγRIIb+/+ transgenic mice. Furthermore, post-HIF activation, mAb mediated blockade of FcγRIIb can partially restore phagocytic function in human monocytes.

CONCLUSION

Our findings provide a detailed molecular and cellular basis for hypoxia driven resistance to antitumor mAb immunotherapy, unveiling a hitherto unexplored aspect of the TME. These findings provide a mechanistic rationale for the modulation of FcγRIIb expression or its blockade as a promising strategy to enhance approved and novel mAb immunotherapies.

Clonal hematopoiesis, myeloid disorders and BAX-mutated myelopoiesis in patients receiving venetoclax for CLL

The BCL2 inhibitor venetoclax has established therapeutic roles in chronic lymphocytic leukemia (CLL) and acute myeloid leukemia (AML). As BCL2 is an important determinant of survival of both myeloid progenitor and B cells, we investigated whether clinical and molecular abnormalities arise in the myeloid compartment during long-term continuous venetoclax treatment of CLL in 89 patients (87 with relapsed/refractory CLL). Over a median follow-up of 75 (range 21-98) months, persistent cytopenias (≥1 of neutropenia, thrombocytopenia, anemia) lasting ≥4 months and unrelated to CLL occurred in 25 patients (28%). Of these patients, 20 (80%) displayed clonal hematopoiesis, including 10 with therapy-related myeloid neoplasms (t-MNs). t-MNs occurred exclusively in patients previously exposed to fludarabine-alkylator combination therapy with a cumulative 5-year incidence of 10.4% after venetoclax initiation, consistent with rates reported for patients exposed to fludarabine-alkylator combination therapy without venetoclax. To determine whether the altered myelopoiesis reflected the acquisition of mutations, we analyzed samples from patients with no or minimal bone marrow CLL burden (n = 41). Mutations in the apoptosis effector BAX were identified in 32% (13/41). In cellular assays, C-terminal BAX mutants abrogated outer mitochondrial membrane localization of BAX and engendered resistance to venetoclax killing. BAX-mutated clonal hematopoiesis occurred independently of prior fludarabine-alkylator combination therapy exposure and was not associated with t-MNs. Single-cell sequencing revealed clonal co-occurrence of mutations in BAX with DNMT3A or ASXL1. We also observed simultaneous BCL2 mutations within CLL cells and BAX mutations in the myeloid compartment of the same patients, indicating lineage-specific adaptation to venetoclax therapy.

CD99 in malignant hematopoiesis

The CD99 gene encodes a transmembrane protein that is involved in cell differentiation, adhesion, migration, and protein trafficking. CD99 is differentially expressed on the surface of hematopoietic cells both in the myeloid and lymphoid lineages. CD99 has two isoforms, the long and short isoforms that play different roles depending on the cellular context. There has been extensive evidence supporting the role of CD99 in myeloid and lymphoblastic leukemias. Here we review research findings related to the CD99 in malignant hematopoiesis. We also summarize the significance of CD99 as a therapeutic target in hematological malignancies.