Revolution of Chronic Lymphocytic Leukemia Therapy: the Chemo-Free Treatment Paradigm

Active Hexose-Correlated Compound Shows Direct and Indirect Effects against Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is a disease characterized by the accumulation of mature CD19+CD5+CD23+ B cells in the bloodstream and in lymphoid organs. It usually affects people over 70 years of age, which limits the options for treatments. The disease is typically well-managed, but to date is still incurable. Hence, the need for novel therapeutic strategies remains. Nurse-like cells (NLCs) are major components of the microenvironment for CLL, supporting tumor cell survival, proliferation, and even drug resistance. They are of myeloid lineage, guided toward differentiating into their tumor-supportive role by the CLL cells themselves. As such, they are analogous to tumor-associated macrophages and represent a major therapeutic target. Previously, it was found that a mushroom extract, Active Hexose-Correlated Compound (AHCC), promoted the death of acute myeloid leukemia cells while preserving normal monocytes. Given these findings, it was asked whether AHCC might have a similar effect on the abnormally differentiated myeloid-lineage NLCs in CLL. CLL-patient PBMCs were treated with AHCC, and it was found that AHCC treatment showed a direct toxic effect against isolated CLL cells. In addition, it significantly reduced the number of tumor-supportive NLCs and altered their phenotype. The effects of AHCC were then tested in the Eµ-TCL1 mouse model of CLL and the MllPTD/WT Flt3ITD/WT model of AML. Results showed that AHCC not only reduced tumor load and increased survival in the CLL and AML models, but it also enhanced antitumor antibody treatment in the CLL model. These results suggest that AHCC has direct and indirect effects against CLL and that it may be of benefit when combined with existing treatments.

Health-related quality-of-life in treatment-naive CLL/SLL patients treated with zanubrutinib versus bendamustine plus rituximab

OBJECTIVE

Zanubrutinib is a highly selective, next-generation Bruton's tyrosine kinase inhibitor. In the phase 3 SEQUOIA trial (NCT03336333), treatment with zanubrutinib resulted in significantly improved progression-free survival compared to bendamustine plus rituximab (BR) in adult patients with treatment-naïve chronic lymphocytic leukemia (CLL) and small lymphocytic lymphoma (SLL) without del(17p). The current analysis compared the effects of zanubrutinib versus BR on patients' health-related quality-of-life (HRQoL).

METHODS

In the SEQUOIA trial, patient-reported outcomes (PROs) were assessed at baseline and every 12 weeks (3 cycles) using the EORTC QLQ-C30 and EQ-5D-5L. Descriptive analyses were performed on all the questionnaires' scales and a mixed model for repeated measures was performed using the key QLQ-C30 endpoints of global health status/QoL (GHS/QoL), physical and role functioning, and symptoms of fatigue, pain, diarrhea, and nausea/vomiting at weeks 12 and 24.

RESULTS

Compared with BR-treated patients, those in the zanubrutinib arm experienced greater improvements in HRQoL outcomes at both weeks 12 and 24. By week 24, mean change differences (95% confidence interval) between the arms were significant for GHS/QoL (4.9 [0.9, 9.0]), physical functioning (3.8 [0.8, 6.7]), diarrhea (-6.2 [-10.0, -2.5]), fatigue (-4.5 [-8.9, -0.1]), and nausea/vomiting (-4.5 [-8.9, -0.1]); role functioning (4.8 [-0.2, 9.7]) was marginally better in the zanubrutinib arm and there were no differences in pain symptoms (-0.4 [-4.3, 5.1]) between the arms.

CONCLUSIONS

During the first 24 weeks of treatment, zanubrutinib was associated with better HRQoL outcomes in patients with treatment-naive CLL/SLL without del(17p) compared to BR.

TRIAL REGISTRATION

The SEQUOIA trial is registered on clinicaltrials.gov as SEQUOIA trial (NCT03336333).

CircRNA: a rising star in leukemia

Non-coding RNA are a class of RNA that lack the potential to encode proteins. CircRNAs, generated by a post-splicing mechanism, are a newly discovered type of non-coding RNA with multi-functional covalent loop structures. CircRNAs may play an important role in the occurrence and progression of tumors. Research has shown that circRNAs are aberrantly expressed in various types of human cancers, including leukemia. In this review, we summarize the expression and function of circRNAs and their impact on different types of leukemia. We also illustrate the function of circRNAs on immune modulation and chemoresistance in leukemia and their impact on its diagnosis and prognosis. Herein, we provide an understanding of recent advances in research that highlight the importance of circRNAs in proliferation, apoptosis, migration, and autophagy in different types of leukemia. Furthermore, circRNAs make an indispensable difference in the modulation of the immunity and chemoresistance of leukemia. Increasing evidence suggests that circRNAs may play a vital role in the diagnostic and prognostic markers of leukemia because of their prominent properties. More detailed preclinical studies on circRNAs are needed to explore effective ways in which they can serve as biomarkers for the diagnosis and prognosis of leukemia in vivo.

Impact of Fixed-Duration Oral Targeted Therapies on the Economic Burden of Chronic Lymphocytic Leukemia in Canada

BACKGROUND

Continuous oral targeted therapies (OTT) represent a major economic burden on the Canadian healthcare system, due to their high cost and administration until disease progression/toxicity. The recent introduction of venetoclax-based fixed-duration combination therapies has the potential to reduce such costs. This study aims to estimate the prevalence and the cost of CLL in Canada with the introduction of fixed OTT.

METHODS

A state transition Markov model was developed and included five health states: watchful waiting, first-line treatment, relapsed/refractory treatment, and death. The number of CLL patients and total cost associated with CLL management in Canada for both continuous- and fixed-treatment-duration OTT were projected from 2020 to 2025. Costs included drug acquisition, follow-up/monitoring, adverse event, and palliative care.

RESULTS

The CLL prevalence in Canada is projected to increase from 15,512 to 19,517 between 2020 and 2025. Annual costs were projected at C$880.7 and C$703.1 million in 2025, for continuous and fixed OTT scenarios, respectively. Correspondingly, fixed OTT would provide a total cost reduction of C$213.8 million (5.94%) from 2020 to 2025, compared to continuous OTT.

CONCLUSIONS

Fixed OTT is expected to result in major reductions in cost burden over the 5-year projection, compared to continuous OTT.

Richter Syndrome: From Molecular Pathogenesis to Druggable Targets

Richter syndrome (RS) represents the occurrence of an aggressive lymphoma, most commonly diffuse large B-cell lymphoma (DLBCL), in patients with chronic lymphocytic leukemia (CLL). Most cases of RS originate from the direct transformation of CLL, whereas 20% are de novo DLBCL arising as secondary malignancies. Multiple molecular mechanisms contribute to RS pathogenesis. B-cell receptor (BCR) overreactivity to multiple autoantigens is due to frequent stereotyped BCR configuration. Genetic lesions of TP53, CDKN2A, NOTCH1 and c-MYC deregulate DNA damage response, tumor suppression, apoptosis, cell cycle and proliferation. Hyperactivation of Akt and NOTCH1 signaling also plays a role. Altered expression of PD-1/PD-L1 and of other immune checkpoints leads to RS resistance to cytotoxicity exerted by T-cells. The molecular features of RS provide vulnerabilities for therapy. Targeting BCR signaling with noncovalent BTK inhibitors shows encouraging results, as does the combination of BCL2 inhibitors with chemoimmunotherapy. The association of immune checkpoint inhibitors with BCL2 inhibitors and anti-CD20 monoclonal antibodies is explored in early phase clinical trials with promising results. The development of patient-derived xenograft mice models reveals new molecular targets for RS, exemplified by ROR1. Although RS still represents an unmet medical need, understanding its biology is opening new avenues for precision medicine therapy.

Disruption of Nurse-like Cell Differentiation as a Therapeutic Strategy for Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is the most common adult leukemia, but, despite advances in treatment, many patients still experience relapse. CLL cells depend on interactions with supportive cells, and nurse-like cells (NLCs) are the major such cell type. However, little is known about how NLCs develop. Here, we performed DNA methylation analysis of CLL patient-derived NLCs using the 850K Illumina array, comparing CD14+ cells at day 1 (monocytes) versus day 14 (NLCs). We found a strong loss of methylation in AP-1 transcription factor binding sites, which may be driven by MAPK signaling. Testing of individual MAPK pathways (MEK, p38, and JNK) revealed a strong dependence on MEK/ERK for NLC development, because treatment of patient samples with the MEK inhibitor trametinib dramatically reduced NLC development in vitro. Using the adoptive transfer Eµ-TCL1 mouse model of CLL, we found that MEK inhibition slowed CLL progression, leading to lower WBC counts and to significantly longer survival time. There were also lower numbers of mouse macrophages, particularly within the M2-like population. In summary, NLC development depends on MEK signaling, and inhibition of MEK leads to increased survival time in vivo. Hence, targeting the MEK/ERK pathway may be an effective treatment strategy for CLL.

Long-term follow-up and future direction on the management of chronic lymphocytic leukemia/small lymphocytic leukemia

Objective

Chronic lymphocytic leukemia and small lymphocytic lymphoma remain the most prevalent adult leukemia in Western countries. Novel therapeutics have established long-term efficacy and have changed the landscape in patient management. In contrast, novel approaches pose opportunities for patients to be treated for finite durations. In this manuscript, we highlight long-term safety and efficacy data with Bruton's tyrosine kinase inhibitors and combination BCL2 + anti-CD20 therapies. We also offer key considerations for treatment selection and outline ongoing trials which may continue to expand therapeutic options and approaches.

Data sources

An electronic search of the PubMed database was performed to obtain key literature in chronic lymphocytic leukemia and small lymphocytic lymphoma published using the following search terms: chronic lymphocytic leukemia/small lymphocytic lymphoma, Richter syndrome, and histologic transformation. The search results were narrowed by selecting studies in humans published in English. Results were confined to the following article types: Clinical Trial, Phase II; Clinical Trial, Phase III; Clinical Trial, Phase IV; Guideline; Randomized Controlled Trial; Meta-Analysis; Systematic Reviews; and Validation Studies.

Data summary

Chronic lymphocytic leukemia and small lymphocytic lymphoma are different manifestations of the same disease and are managed in much the same way. Bruton's tyrosine kinase inhibitors have demonstrated long and durable efficacy benefits in patients with newly diagnosed chronic lymphocytic leukemia/small lymphocytic lymphoma and in the relapsed/refractory setting. Despite these benefits, long terms adverse events have posed challenges for patients and have led to treatment discontinuations. Additionally, the use of monotherapy Bruton's tyrosine kinase inhibitor's requires chronic use of the medications leading to added financial implications. BCL2 inhibition with venetoclax in combination with anti-CD20 monoclonal antibodies has offered a novel and finite treatment approach in frontline and relapsed chronic lymphocytic leukemia/small lymphocytic lymphoma. Ongoing clinical trials are in investigating this modality further to enhance durable responses utilizing a combination Bruton's tyrosine kinase inhibitor's and BCL2 inhibitors.

Conclusion

The treatment armamentarium of chronic lymphocytic leukemia/small lymphocytic lymphoma continues to evolve. Despite the long term, durable responses with Bruton's tyrosine kinase inhibitor's, it is likely that finite treatment durations could become the standard of care as a result of continued, long-term responses.

Novel Approaches for the Treatment of Patients with Richter's Syndrome

OPINION STATEMENT

In the last 10-15 years, the way to treat cancers has dramatically changed towards precision medicine approaches. These treatment options are mainly based on selective targeting against signaling pathways critical for or detrimentally activated in cancer cells in cancer cells, as well as exploiting molecules that are specifically expressed on neoplastic cells, also known as tumor-associated antigens. These considerations hold true also in the hematological field where a plethora of novel targeted agents have reached patients' bedside, significantly improving clinical responses. Chronic lymphocytic leukemia (CLL) is an example of how targeted therapies, such as BTK, PI3K, or Bcl-2 inhibitors as well as anti-CD20 antibodies, have improved patients' management, even when adopted as frontline treatment. However, these advancements do not apply to Richter's syndrome (RS), the transformation of CLL into a very aggressive and fatal lymphoma, occurring in 2-10% of patients. RS is usually a fast-growing lymphoma of the diffuse large B cell or the Hodgkin's variant, with a dismal prognosis. Despite advancements in depicting and understanding the genetic background of RS and its pathogenesis, no significant clinical results have been registered. In the last couple of years, several studies have started to investigate the impact of novel drugs or drug combinations and some of them have opened for clinical trials, currently in phase I or II, whose results will be soon available. This review will present an overview of current and most recent therapeutic options in RS, discussing also how results coming from xenograft models may help in designing and identifying novel treatment opportunities to overcome the lack of effective therapies.

O-GlcNAcylation in Chronic Lymphocytic Leukemia and Other Blood Cancers

In the past decade, aberrant O-GlcNAcylation has emerged as a new hallmark of cancer. O-GlcNAcylation is a post-translational modification that results when the amino-sugar β-D-N-acetylglucosamine (GlcNAc) is made in the hexosamine biosynthesis pathway (HBP) and covalently attached to serine and threonine residues in intracellular proteins by the glycosyltransferase O-GlcNAc transferase (OGT). O-GlcNAc moieties reflect the metabolic state of a cell and are removed by O-GlcNAcase (OGA). O-GlcNAcylation affects signaling pathways and protein expression by cross-talk with kinases and proteasomes and changes gene expression by altering protein interactions, localization, and complex formation. The HBP and O-GlcNAcylation are also recognized to mediate survival of cells in harsh conditions. Consequently, O-GlcNAcylation can affect many of the cellular processes that are relevant for cancer and is generally thought to promote tumor growth, disease progression, and immune escape. However, recent studies suggest a more nuanced view with O-GlcNAcylation acting as a tumor promoter or suppressor depending on the stage of disease or the genetic abnormalities, proliferative status, and state of the p53 axis in the cancer cell. Clinically relevant HBP and OGA inhibitors are already available and OGT inhibitors are in development to modulate O-GlcNAcylation as a potentially novel cancer treatment. Here recent studies that implicate O-GlcNAcylation in oncogenic properties of blood cancers are reviewed, focusing on chronic lymphocytic leukemia and effects on signal transduction and stress resistance in the cancer microenvironment. Therapeutic strategies for targeting the HBP and O-GlcNAcylation are also discussed.

A novel class of oxazepine-based anti-cancer agents induces cell death in primary human CLL cells and efficiently reduces tumor growth in Eμ-TCL1 mice through the JNK/STAT4/p66Shc axis

Survival and expansion of malignant B cells in chronic lymphocytic leukemia (CLL) are highly dependent both on intrinsic defects in the apoptotic machinery and on the interactions with cells and soluble factors in the lymphoid microenvironment. The adaptor protein p66Shc is a negative regulator of antigen receptor signaling, chemotaxis and apoptosis whose loss in CLL B cells contributes to their extended survival and poor prognosis. Hence, the identification of compounds that restore p66Shc expression and function in malignant B cells may pave the way to a new therapeutic approach for CLL. Here we show that a novel oxazepine-based compound (OBC-1) restores p66Shc expression in primary human CLL cells by promoting JNK-dependent STAT4 activation without affecting normal B cells. Moreover, we demonstrate that the potent pro-apoptotic activity of OBC-1 in human leukemic cells directly correlates with p66Shc expression levels and is abrogated when p66Shc is genetically deleted. Preclinical testing of OBC-1 and the novel analogue OBC-2 in Eμ-TCL1 tumor-bearing mice resulted in a significantly longer overall survival and a reduction of the tumor burden in the spleen and peritoneum. Interestingly, OBCs promote leukemic cell mobilization from the spleen to the blood, which correlates with upregulation of sphingosine-1-phosphate receptor expression. In summary, our work identifies OBCs as a promising class of compounds that, by boosting p66Shc expression through the activation of the JNK/STAT4 pathway, display dual therapeutic effects for CLL intervention, namely the ability to mobilize cells from secondary lymphoid organs and a potent pro-apoptotic activity against circulating leukemic cells.

MyPal ADULT study protocol: a randomised clinical trial of the MyPal ePRO-based early palliative care system in adult patients with haematological malignancies

INTRODUCTION

The systematic collection of electronic patient-reported outcome (ePRO) in the routine care of patients with chronic haematological malignancies such as chronic lymphocytic leukaemia (CLL) and myelodysplasia syndromes (MDS) can constitute a very ambitious but worthwhile challenge. MyPal is a Horizon 2020 Research & Innovation Action aiming to meet this challenge and foster palliative care for patients with CLL or MDS by leveraging ePRO systems to adapt to the personal needs of patients and caregiver(s).

METHODS AND ANALYSIS

In this interventional randomised trial, 300 patients with CLL or MDS will be recruited across Europe. Patients will be randomly allocated to early palliative care using the MyPal system (n=150) versus standard care including general palliative care if needed (n=150). Patients in the experimental arm will be given access to the MyPal digital health platform which consists of purposely designed software available on smartphones and/or tablets. The platform entails different functionalities including physical and psychoemotional symptom reporting via regular questionnaire completion, spontaneous self-reporting, motivational messages, medication management and a personalised search engine for health information. Data on patients' activity (daily steps and sleep quality) will be automatically collected via wearable devices.

ETHICS AND DISSEMINATION

The integration of ePROs via mobile applications has raised ethical concerns regarding inclusion criteria, information provided to participants, free and voluntary consent, and respect for their autonomy. These have been carefully addressed by a multidisciplinary team. Data processing, dissemination and exploitation of the study findings will take place in full compliance with European Union data protection law. A participatory design was adopted in the development of the digital platform involving focus groups and discussions with patients to identify needs and preferences. The protocol was approved by the ethics committees of San Raffaele (8/2020), Thessaloniki 'George Papanikolaou' Hospital (849), Karolinska Institutet (20.10.2020), University General Hospital of Heraklion (07/15.4.2020) and University of Brno (01-120220/EK).

TRIAL REGISTRATION NUMBER

NCT04370457.

Treatment strategies for a rapidly evolving landscape in chronic lymphocytic leukemia management

With the advent of targeted therapies for chronic lymphocytic leukemia (CLL), treatment choice has expanded and patients are living longer. Careful consideration is needed regarding treatment duration and sequence, how best to meet patients' needs, balancing toxicities while improving long-term survival and maximizing depth of response. This review addresses these considerations and discusses current targeted treatment dilemmas. Targeted therapies have dramatically transformed the CLL treatment landscape. Two treatment paradigms have emerged using B-cell lymphoma 2 inhibitors (BCL2i) and Bruton's tyrosine kinase (BTK): (i) fixed duration and (ii) continuous treatment. The BCL2i venetoclax can attain deep remissions with a fixed-duration approach, resulting in high rates of undetectable minimal residual disease (uMRD) in treatment-naïve and relapsed/refractory (R/R) patients with CLL. BTKis such as ibrutinib and acalabrutinib achieve high objective response rates and long-term disease control, although they rarely attain complete response or uMRD status as monotherapy. Numerous studies are evaluating the clinical utility of BTKi and BCL2i as combination therapies, where deep remissions have been found to occur. MRD status may also be a useful marker for deciding when to stop continuous therapy, and randomized trials on MRD-guided treatment strategies are currently ongoing. The current treatment choice between continuous or fixed-duration therapy should be based on comorbidities, risks, preferences, and treatment goals, whilst areas of emerging clinical interest include the potential utility of BTKi-BCL2i combination therapies, as well as an MRD-guided treatment strategies in the future.

Current and future treatment strategies in chronic lymphocytic leukemia

Treatment decisions for patients with chronic lymphocytic leukemia (CLL) are dependent on symptoms and classification into high-, medium-, or low-risk categories. The prognosis for CLL hinges, in part, on the presence or absence of less-favorable genetic aberrations, including del(17p), del(11q), TP53 dysfunction, and IGHV mutations, as these markers are associated with worse treatment response. Promising results from multiple clinical trials show emerging therapies targeting Burton tyrosine kinase, B-cell leukemia/lymphoma 2, and phosphatidylinositol 4,5-bisphosphate 3-kinase catalytic subunit delta result in better outcomes and prolonged progression-free survival for patients both with and without certain high-risk aberrations. Favorable outcomes using these novel oral targeted therapies, either alone or in combination with other treatments such as anti-CD20 antibodies, has led to their use almost entirely supplanting chemoimmunotherapy in the treatment of CLL. In this narrative review, we summarize the current clinical evidence for the use of targeted mono- and combination therapies for CLL, discuss new and next-generation treatment approaches currently in development, and provide insight into areas of unmet need for the treatment of patients with CLL.

Recurrent XPO1 mutations alter pathogenesis of chronic lymphocytic leukemia

BACKGROUND

Exportin 1 (XPO1/CRM1) is a key mediator of nuclear export with relevance to multiple cancers, including chronic lymphocytic leukemia (CLL). Whole exome sequencing has identified hot-spot somatic XPO1 point mutations which we found to disrupt highly conserved biophysical interactions in the NES-binding groove, conferring novel cargo-binding abilities and forcing cellular mis-localization of critical regulators. However, the pathogenic role played by change-in-function XPO1 mutations in CLL is not fully understood.

METHODS

We performed a large, multi-center retrospective analysis of CLL cases (N = 1286) to correlate nonsynonymous mutations in XPO1 (predominantly E571K or E571G; n = 72) with genetic and epigenetic features contributing to the overall outcomes in these patients. We then established a mouse model with over-expression of wildtype (wt) or mutant (E571K or E571G) XPO1 restricted to the B cell compartment (Eµ-XPO1). Eµ-XPO1 mice were then crossed with the Eµ-TCL1 CLL mouse model. Lastly, we determined crystal structures of XPO1 (wt or E571K) bound to several selective inhibitors of nuclear export (SINE) molecules (KPT-185, KPT-330/Selinexor, and KPT-8602/Eltanexor).

RESULTS

We report that nonsynonymous mutations in XPO1 associate with high risk genetic and epigenetic features and accelerated CLL progression. Using the newly-generated Eµ-XPO1 mouse model, we found that constitutive B-cell over-expression of wt or mutant XPO1 could affect development of a CLL-like disease in aged mice. Furthermore, concurrent B-cell expression of XPO1 with E571K or E571G mutations and TCL1 accelerated the rate of leukemogenesis relative to that of Eµ-TCL1 mice. Lastly, crystal structures of E571 or E571K-XPO1 bound to SINEs, including Selinexor, are highly similar, suggesting that the activity of this class of compounds will not be affected by XPO1 mutations at E571 in patients with CLL.

CONCLUSIONS

These findings indicate that mutations in XPO1 at E571 can drive leukemogenesis by priming the pre-neoplastic lymphocytes for acquisition of additional genetic and epigenetic abnormalities that collectively result in neoplastic transformation.

Molecular Remission Using Low-Dose Immunotherapy with Minimal Toxicities for Poor Prognosis IGHV- Unmutated Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) accounts for 10% of hematologic malignancies. CLL is a malignancy of CD5+ B cells and it is characterized by the accumulation of small, mature-appearing neoplastic lymphocytes in the blood, bone marrow, and secondary lymphoid tissues. In the present case, a middle-aged female patient with poor prognosis unmutated IGHV CLL achieved cytogenetic and molecular remission with minimal adverse events following six cycles of low dose recombinant human IL-2 (rIL-2) in combination with low dose targeted venetoclax. Personalized low dose rIL-2 in combination with either lenalidomide or venetoclax mediates natural killer stimulation and is an effective non-toxic immunotherapy administered in the outpatient setting for poor prognosis CLL.

Neutralization of B-Cell Activating Factor (BAFF) by Belimumab Reinforces Small Molecule Inhibitor Treatment in Chronic Lymphocytic Leukemia

Simple Summary

Chronic lymphocytic leukemia (CLL) is the most common form of leukemia in Western countries. Despite the substantial progress achieved by the recent introduction of the novel small molecule inhibitors idelalisib, ibrutinib and venetoclax in CLL treatment, therapy resistance occurs frequently and the disease so far remains incurable. In the present study we report that BAFF, a member of the TNF protein family, protects CLL cells from treatment-induced cell death. In turn, the therapeutic effects of idelalisib, ibrutinib and venetoclax can be reinforced by neutralizing BAFF with belimumab, an antibody which presently is clinically approved for treatment of systemic lupus erythematosus. Based on the data presented in this study, a clinical study to evaluate whether drug repurposing of belimumab for BAFF neutralization can serve to improve response to small molecule inhibitor treatment in CLL is in preparation.

Abstract

The introduction of idelalisib, ibrutinib and venetoclax for treatment of chronic lymphocytic leukemia (CLL) has greatly improved long term survival of patients. However, many patients do not achieve complete remission and suffer from development of resistance upon treatment with these small molecule inhibitors. Here we report that the TNF family member B-cell activating factor (BAFF) mediates resistance of CLL cells to idelalisib, ibrutinib and venetoclax by sustaining survival and preventing apoptosis of the malignant B cells as revealed by analysis of cellular ATP levels and mitochondrial membrane integrity as well as caspase activation, respectively. As BAFF also plays a prominent role in autoimmune diseases, the BAFF-neutralizing antibody belimumab was developed and approved for treatment of systemic lupus erythematosus (SLE). When we employed belimumab in the context of CLL treatment with idelalisib, ibrutinib and venetoclax, BAFF neutralization was found to significantly increase the sensitivity of the leukemic cells to all three small molecule inhibitors. Notably, BAFF neutralization proved to be beneficial independently of clinical stage according to Binet and Rai or IgVH mutational status. Our results identify drug repurposing of belimumab for neutralization of BAFF to complement small molecule inhibitor treatment as a promising therapeutic approach in CLL that is presently undergoing clinical evaluation.