The function of the complement system remains fully intact throughout the course of allogeneic stem cell transplantation.

Introduction: Hematopoietic stem cell transplantation (HSCT) is associated with immune complications and endothelial dysfunction due to intricate donor-recipient interactions, conditioning regimens, and inflammatory responses. Methods: This study investigated the role of the complement system during HSCT and its interaction with the cytokine network. Seventeen acute myeloid leukemia patients undergoing HSCT were monitored, including blood sampling from the start of the conditioning regimen until four weeks post-transplant. Clinical follow-up was 200 days. Results: Total complement functional activity was measured by WIELISA and the degree of complement activation by ELISA measurement of sC5b-9. Cytokine release was measured using a 27-multiplex immuno-assay. At all time-points during HSCT complement functional activity remained comparable to healthy controls. Complement activation was continuously stable except for two patients demonstrating increased activation, consistent with severe endotheliopathy and infections. In vitro experiments with post-HSCT whole blood challenged with Escherichia coli, revealed a hyperinflammatory cytokine response with increased TNF, IL-1ß, IL-6 and IL-8 formation. Complement C3 inhibition markedly reduced the cytokine response induced by Staphylococcus aureus, Aspergillus fumigatus, and cholesterol crystals. Discussion: In conclusion, HSCT patients generally retained a fully functional complement system, whereas activation occurred in patients with severe complications. The complement-cytokine interaction indicates the potential for new complement-targeting therapeutic strategies in HSCT.

The impact of individual clinical features in cold agglutinin disease: hemolytic versus non-hemolytic symptoms.

INTRODUCTION: During the last decades, the pathogenesis of cold agglutinin disease (CAD) has been well elucidated and shown to be complex. Several documented or investigational therapies have been made available. This development has resulted in major therapeutic advances, but also in challenges in choice of therapy. AREAS COVERED: In this review, we address each step in pathogenesis: bone marrow clonal lymphoproliferation, composition and effects of monoclonal cold agglutinin, non-complement mediated erythrocyte agglutination, complement-dependent hemolysis, and other effects of complement activation. We also discuss the heterogeneous clinical features and their relation to specific steps in pathogenesis, in particular with respect to the impact of complement involvement. CAD can be classified into three clinical phenotypes with consequences for established treatments as well as development of new therapies. Some promising future treatment approaches - beyond chemoimmunotherapy and complement inhibition - are reviewed. EXPERT OPINION: The patient's individual clinical profile regarding complement involvement and hemolytic versus non-hemolytic features is important for the choice of treatment. Further development of treatment approaches is encouraged, and some candidate drugs are promising irrespective of clinical phenotype. Patients with CAD requiring therapy should be considered for inclusion in clinical trials.

Long-lasting severe anemia following treatment with natalizumab for relapsing-remitting multiple sclerosis: a case report.

BACKGROUND: Natalizumab is a monoclonal antibody used to treat patients with relapsing-remitting multiple sclerosis. Anemia is a recognized side effect, but it is usually mild and of a short duration when natalizumab is stopped. Here, we describe a case of a young woman with severe and especially long lasting anemia associated with treatment with natalizumab, persisting up to a year after treatment was stopped. CASE PRESENTATION: A 24 year-old Caucasian woman with relapsing-remitting multiple sclerosis developed severe transfusion dependent anemia after 27 infusions with natalizumab, which was her first and only treatment for her multiple sclerosis. Extensive hematologic diagnostics did not reveal any malignant cause or any other plausible non-malignant cause for her anemia. The bone marrow was found to be hypercellular, with a maturation arrest of the erythropoiesis and with grade 1-2 fibrosis. No specific treatment for the anemia was given. The hemoglobin level showed signs of spontaneous increase after nearly one year after natalizumab was discontinued. CONCLUSION: Severe anemia can be caused by treatment with natalizumab. This case adds information to the few other similar reported cases, demonstrating the potential duration of the anemia, as well as detailed description of hematologic findings. The mechanism is most likely due to inhibition of α4 subunit of the α4ß1-integrin, which is present on both lymphocytes and erythroid precursor cells.

Allogeneic stem cell transplant recipients surviving at least 2 years without relapse: outcome and risk factors.

Outcomes of 2-year survivours undergoing allo-haematopoietic stem cell transplantation at Oslo University Hospital were retrospectively assessed with the objectives of identification of risk factors for late death as possible means for precautionary measures and interventions to improve long-term survival. 421 patients with haematological malignancy, transplanted between 2005 and 2019, alive and free of disease after 2 years were included with data reported from The OUS-HSCT registry. Median follow-up was 6.2 years (2.016.1), and 232 patients (55%) were observed for minimum 5 years. The probability of being alive 5 and 10 years after HSCT was 86% and 76%. Primary risk factors for late death included initial diagnosis of age ≥ 60 years, chronic lymphocytic leukaemia (CLL), previous blood stream- or invasive fungal infection (BSI, IFI), and chronic graft-versus-host disease (cGVHD). Transplant-related mortality (TRM) and relapse at 5 years were 9.0% and 7.7%, respectively. Two factors were associated with the latter: cytomegalovirus (CMV) seronegative donor and CLL. Compared with the age- and gender-matched Norwegian general population, life expectancy was lower for each disease, except for CML. The prospect for the long-term survival is good for 2-year survivors of the allogeneic hematopoietic stem cell transplantation. However, life expectancy remains inferior to the age- and gender-matched general population. Optimising prophylaxis and treatment for chronic GVHD, BSI and IFI are needed along with the improved adherence to guidelines for early detection of secondary malignancies. Measures to improve immune reconstitution, possibly the microbiota, and the use of CMV seropositive donors regardless of recipient sero-status may be warranted and should be addressed in further studies.

Transcriptome analysis of primary adult B-cell lineage acute lymphoblastic leukemia identifies pathogenic variants and gene fusions, and predicts subtypes for in depth molecular diagnosis.

BACKGROUND: B-cell acute lymphoblastic leukemia (B-ALL) is classified into subgroups based on known driver oncogenes and molecular lesions, including translocations and recurrent mutations. However, the current diagnostic tests do not identify subtypes or oncogenic lesions for all B-ALL samples, creating a heterogeneous B-ALL group of unknown subtypes. METHODS: We sorted primary adult B-ALL cells and performed transcriptome analysis by bulk RNA sequencing (RNA-seq). RESULTS: Transcriptomic analysis of an adult B-ALL cohort allowed the classification of four patient samples with subtypes that were not previously revealed by standard gene panels. The leukemia of two patients were of the DUX4 subtype and two were CRLF2+ Ph-like B-ALL. Furthermore, single nucleotide variant analysis detected the oncogenic NRAS-G12D, KRAS-G12D, and KRAS-G13D mutations in three of the patient samples, presenting targetable mutations. Additional oncogenic variants and gene fusions were uncovered, as well as multiple variants in the PDE4DIP gene across five of the patient samples. CONCLUSION: We demonstrate that RNA-seq is an effective tool for precision medicine in B-ALL by providing comprehensive molecular profiling of leukemia cells, identifying subtype and oncogenic lesions, and stratifying patients for appropriate therapy.

Health-related quality of life and physical activity in Nordic patients with moderate haemophilia A and B (the MoHem study).

INTRODUCTION: The impact of moderate haemophilia on health-related quality of life (HRQoL) and physical activity (PA) is not well known. In previous studies, persons with factor VIII/factor IX activity (FVIII/FIX:C) below 3 IU/dL were associated with a more severe bleeding phenotype than predicted. AIM: To explore HRQoL and PA in patients with moderate haemophilia A (MHA) and B (MHB). METHODS: A cross-sectional, multicentre study covering patients with MHA and MHB in Sweden, Finland, and Norway. HRQoL was assessed with the EuroQoL 5-Dimensions (EQ-5D) form and PA with the International Physical Activity Questionnaire among participants aged ≥15 years. RESULTS: We report on 104 patients aged 15-84 years from the MoHem study. Overall, EQ-5D utility was .85 (median) (Q1-Q3 0.73-1.0) with corresponding visual analogue scale (VAS) 80 (70-90), which were similar regardless of treatment modality, FVIII/FIX:C, and MHA or MHB. Pain and mobility were most frequently affected dimensions. Utility (r = -.54), VAS (r = -.42), and PA (r = -.32) correlated negatively with arthropathy (HJHS). Only patients aged 41-50 years displayed lower utility (p = .02) and VAS (p < .01) than the Norwegian population norm. Patients on prophylaxis aged 35-54 years reported higher PA than those treated on-demand (p = .01). CONCLUSION: Haemophilic arthropathy had negative impact on HRQoL and PA in Nordic patients with moderate haemophilia. Middle-aged patients captured lower utility and VAS than observed in the general population. Tailored prophylaxis and improved joint health may influence positively on HRQoL and PA also in moderate haemophilia.

Gene expression analysis revealed downregulation of complement receptor 1 in clonal B cells in cold agglutinin disease.

Cold agglutinin disease (CAD) is a rare B-cell lymphoproliferative disorder of the bone marrow, manifested by autoimmune hemolytic anemia caused by binding of monoclonal IgM autoantibodies to the I antigen. Underlying genetic changes have previously been reported, but their impact on gene expression profile has been unknown. Here, we define differentially expressed genes in CAD B cells. To unravel downstream alteration in cellular pathways, gene expression by RNA sequencing was undertaken. Clonal B-cell samples from 12 CAD patients and IgM-expressing memory B cells from 4 healthy individuals were analyzed. Differential expression analysis and filtering resulted in 93 genes with significant differential expression. Top upregulated genes included SLC4A1, SPTA1, YBX3, TESC, HBD, AHSP, TRAF1, HBA2, RHAG, CA1, SPTB, IL10, UBASH3B, ALAS2, HBA1, CRYM, RGCC, KANK2, and IGHV4-34. They were upregulated at least 8-fold, while complement receptor 1 (CR1/CD35) was downregulated 11-fold in clonal CAD B cells compared to control B cells. Flow cytometry analyses further confirmed reduced CR1 (CD35) protein expression by clonal CAD IgM+ B cells compared to IgM+ memory B cells in controls. CR1 (CD35) is an important negative regulator of B-cell activation and differentiation. Therefore, reduced CR1 (CD35) expression may increase activation, proliferation, and antibody production in CAD-associated clonal B cells.

Report on 4 cases with decreased recovery due to neutralizing antibodies specific for PEGylated recombinant factor VIII.

BACKGROUND: The immunogenicity, safety, and efficacy of recombinant factor VIII (rFVIII) have gained increasing interest after the introduction of extended half-life products with various modifications of the rFVIII molecule, such as covalent attachment of polyethylene glycol (PEG). Anti-PEG antibodies may be associated with a temporary reduction of FVIII recovery, but according to previous studies, they usually disappear after continuous dosing. Anti-PEG antibodies with an inhibitory capacity have never been demonstrated in patients treated with PEGylated rFVIII products. OBJECTIVES: To routinely switch from standard half-life to PEGylated extended half-life rFVIII products in patients with hemophilia A. METHODS: From December 2022 until May 2023, 83 adults with hemophilia A attending Oslo Haemophilia Comprehensive Care Centre received a test dose with a PEGylated rFVIII product to switch treatment. Four patients presented with decreased recovery without the presence of an FVIII inhibitor. Accordingly, we performed a variant inhibitor test utilizing different rFVIII concentrates as a source of FVIII and enzyme-linked immunosorbent assay to search for anti-PEG antibodies. RESULTS: We found inhibitory anti-PEG/anti-PEGylated rFVIII antibodies in 4 patients (5%), both persistent and transient, explaining the impaired recovery. The patients had neutralizing anti-PEG antibodies prior to the first dosing of PEGylated rFVIII. We demonstrated neutralizing antibodies (mainly immunoglobuline G) specific for PEG and all 3 commercially available PEGylated rFVIII products. CONCLUSION: The number of patients with inhibitory anti-PEG antibodies was significant, and the presence of inhibitors against PEGylated rFVIII emphasizes the importance of individual monitoring when switching FVIII concentrates to ensure safety and efficacy of the treatment.

Chronic neutropenia in adults. / Kronisk nøytropeni hos voksne.

Neutrophils are an important component of the innate immune system, and they prevent bacterial and fungal infections by phagocytosis and killing of pathogens. Neutropenia is defined as an abnormally low number of circulating neutrophils, and the term chronic neutropenia is used when it lasts more than three months. The objective of this clinical review is to raise awareness among doctors in Norway of chronic neutropenia and possible causes. A patient with severe neutropenia and fever requires immediate admission to hospital and initiation of empiric sepsis treatment before the cause of neutropenia has been determined, but patients with chronic neutropenia do not always require rapid and extensive workup.

A tumor microenvironment model of chronic lymphocytic leukemia enables drug sensitivity testing to guide precision medicine.

The microenvironment of chronic lymphocytic leukemia (CLL) cells in lymph nodes, spleen, and bone marrow provides survival, proliferation, and drug resistance signals. Therapies need to be effective in these compartments, and pre-clinical models of CLL that are used to test drug sensitivity must mimic the tumor microenvironment to reflect clinical responses. Ex vivo models have been developed that capture individual or multiple aspects of the CLL microenvironment, but they are not necessarily compatible with high-throughput drug screens. Here, we report on a model that has reasonable associated costs, can be handled in a regularly equipped cell lab, and is compatible with ex vivo functional assays including drug sensitivity screens. The CLL cells are cultured with fibroblasts that express the ligands APRIL, BAFF and CD40L for 24 h. The transient co-culture was shown to support survival of primary CLL cells for at least 13 days, and mimic in vivo drug resistance signals. Ex vivo sensitivity and resistance to the Bcl-2 antagonist venetoclax correlated with in vivo responses. The assay was used to identify treatment vulnerabilities and guide precision medicine for a patient with relapsed CLL. Taken together, the presented CLL microenvironment model enables clinical implementation of functional precision medicine in CLL.

The prognostic value of patient-reported outcomes in allogeneic hematopoietic stem cell transplantation: exploratory analysis of a randomized nutrition intervention trial.

Whether patient-reported outcomes (PROs) can predict overall survival (OS) and non-relapse mortality (NRM) among recipients of allogeneic stem cell transplantation (allo-HSCT), is unclear. We performed an exploratory analysis of the prognostic value of patient-reported outcomes (PROs) among 117 recipients of allogeneic stem cell transplantation (allo-HSCT) who participated in a randomized nutrition intervention trial. Cox proportional hazards models were used to investigate possible associations between PROs collected pre-allo-HSCT (baseline) using scores from the EORTC Quality of Life Questionnaire-Core 30 (QLQ-C30) and 1-year overall survival (OS), whereas logistic regression was used to study associations between these PROs and 1-year non-relapse mortality (NRM). Multivariable analyses indicated that only the Hematopoietic Cell Transplantation Comorbidity Index (HCT-CI) and the European Bone Marrow Transplantation (EBMT) risk score were associated with 1-year OS. In the multivariable model including clinical-sociodemographic factors for 1-year NRM, our analysis showed that living alone (p=0.009), HCT-CI (p=0.016), EBMT risk score (p=0.002), and stem cell source (p=0.046) could be associated with 1-year NRM. Moreover, in the multivariable model, our analysis showed that only appetite loss from the QLQ-C30 was associated with 1-year NRM (p=0.026). In conclusion, in this specific setting, our analysis suggests that the commonly used HCT-CI and EBMT risk scores could be predictive for both 1-year OS and 1-year NRM, whereas baseline PROs in general were not.

Allogeneic stem cell transplantation in adults 2015-21. / Allogen stamcelletransplantasjon hos voksne 2015­21.

BACKGROUND: Allogeneic stem cell transplantation is the only curative treatment for several malignant and non-malignant haematological diseases, and is associated with a risk of serious complications. In recent years, several changes have been introduced with the aim of reducing treatment-related complications. This retrospective study reviews quality indicators for patients who underwent transplantation in the period 2015-21. MATERIAL AND METHOD: The study included 589 adult patients who were treated with allogeneic stem cell transplantation for the first time at Oslo University Hospital in the period May 2015 to May 2021. Three two-year periods are compared using descriptive methods. RESULTS: In the period 2015-2021, the number of first-time transplant patients per year increased from 85 to 113. One-year survival increased from 68 % in the first two-year period to 74 % in the second period and 82 % in the last period. Both acute and chronic GVHD were reduced, and one-year GVHD-free and relapse-free survival increased from 42 % to 60 % during the study period. INTERPRETATION: Since 2015, the number of transplants has increased, while survival has improved and the risk of complications is lower.

Extracorporeal Photopheresis as Graft-versus-Host Disease Prophylaxis: A Randomized Controlled Trial.

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is the sole curative option for many patients diagnosed with hematologic malignancies. A major obstacle is graft-versus-host disease (GVHD), causing significant morbidity and mortality. Extracorporeal photopheresis (ECP) is an increasingly applied treatment for GVHD, owing in part to its favorable safety profile. In contrast, reports on the use of ECP to prevent GVHD are rare, and randomized controlled trials (RCTs) are lacking. We conducted an RCT to assess whether ECP applied post-transplantation could prevent the development of GVHD within the first year of transplantation. We enrolled 157 patients (age 18 to 74 years) with a hematologic malignancy undergoing their first allo-HSCT, randomized as 76 to the intervention group and 81 to the control group. ECP was initiated directly on engraftment and was planned twice weekly for 2 weeks, then once weekly for 4 weeks. GVHD, relapse, and death were analyzed by Cox regression analysis. During the first year, 45 patients in the intervention group and 52 control patients developed GVHD (hazard ratio [HR], .82; 95% confidence interval [CI], .55 to 1.22; P = .32). There were no differences in acute or chronic GVHD or its organ distribution in this intention-to-treat RCT. A per-protocol analysis revealed a significant difference in GVHD between the intervention group (per-protocol; n = 39 of 76) and the control group (n = 77), 46% versus 68%, respectively (HR, .47; 95% CI, .27 to .80; P = .006). Relapse occurred in 15 patients in the intervention group and in 11 control patients (HR, 1.38; 95% CI, .64 to 3.01; P = .42). GVHD-free relapse-free survival, event-free survival, overall survival, and nonrelapse mortality did not differ significantly between the 2 study groups. There also was no significant difference in immune reconstitution between the 2 groups. This first intention-to-treat RCT investigating ECP as GVHD prophylaxis in allo-HSCT for hematologic malignancy does not support the use of ECP as an adjunct to standard drug-based GVHD prophylaxis.

Graft-Versus-Host-Disease and Health-Related Quality of Life in Young Long-term Survivors of Cancer and Allogeneic Hematopoietic Stem Cell Transplantation.

Purpose: Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is an established treatment predominantly for malignancies. Chronic graft-versus-host disease (cGVHD) is the leading long-term complication after allo-HSCT, but knowledge on cGVHD and health-related quality of life (HRQOL) in long-term survivors of allo-HSCT performed in childhood, adolescence, and young adulthood (CAYA) is scarce. Therefore, we aimed to (1) assess prevalence and risk factors of active cGVHD using the 2014 National Institutes of Health-Consensus criteria, (2) investigate associations between cGVHD severity, patient-reported symptom burden, and HRQOL, and (3) compare HRQOL of survivors to population norms. Methods: We conducted a nationwide cross-sectional study in long-term survivors of CAYA allo-HSCT combining clinical examinations and patient-reported outcome measures. Results: We included 103 survivors, 55 (53%) females, median age of 19.6 years [range 0.3-29.9] at HSCT, 16.8 years [6.0-32.0] from HSCT, and 77 (75%) with underlying malignancy. Overall, 32 (31%) survivors were diagnosed with active cGVHD. The risk of active cGVHD was increased with prior acute GVHD and reduced with in vivo T cell depletion. cGVHD severity was associated with increased symptom burden, but not with adverse HRQOL. Compared to Norwegian population norms, allo-HSCT survivors reported significantly lower HRQOL. Conclusion: These results indicate a high prevalence of cGVHD in long-term survivors of CAYA allo-HSCT. Although we did not find an association between cGVHD severity and HRQOL, survivors reported significantly poorer HRQOL compared to population norms. Knowledge on the long-term consequences of cGVHD will be important for optimizing treatment and long-term follow-up care after CAYA allo-HSCT.

Adaptive single-KIR+NKG2C+ NK cells expanded from select superdonors show potent missing-self reactivity and efficiently control HLA-mismatched acute myeloid leukemia.

BACKGROUND: Natural killer (NK) cells hold great promise as a source for allogeneic cell therapy against hematological malignancies, including acute myeloid leukemia (AML). Current treatments are hampered by variability in NK cell subset responses, a limitation which could be circumvented by specific expansion of highly potent single killer immunoglobulin-like receptor (KIR)+NKG2C+ adaptive NK cells to maximize missing-self reactivity. METHODS: We developed a GMP-compliant protocol to expand adaptive NK cells from cryopreserved cells derived from select third-party superdonors, that is, donors harboring large adaptive NK cell subsets with desired KIR specificities at baseline. We studied the adaptive state of the cell product (ADAPT-NK) by flow cytometry and mass cytometry as well as cellular indexing of transcriptomes and epitopes by sequencing (CITE-Seq). We investigated the functional responses of ADAPT-NK cells against a wide range of tumor target cell lines and primary AML samples using flow cytometry and IncuCyte as well as in a mouse model of AML. RESULTS: ADAPT-NK cells were >90% pure with a homogeneous expression of a single self-HLA specific KIR and expanded a median of 470-fold. The ADAPT-NK cells largely retained their adaptive transcriptional signature with activation of effector programs without signs of exhaustion. ADAPT-NK cells showed high degranulation capacity and efficient killing of HLA-C/KIR mismatched tumor cell lines as well as primary leukemic blasts from AML patients. Finally, the expanded adaptive NK cells had preserved robust antibody-dependent cellular cytotoxicity potential and combination of ADAPT-NK cells with an anti-CD16/IL-15/anti-CD33 tri-specific engager led to near-complete killing of resistant CD45dim blast subtypes. CONCLUSIONS: These preclinical data demonstrate the feasibility of off-the-shelf therapy with a non-engineered, yet highly specific, NK cell population with full missing-self recognition capability.

Current Treatment Options in Cold Agglutinin Disease: B-Cell Directed or Complement Directed Therapy?

Two major steps are identified in the pathogenesis of cold agglutinin disease; clonal B-cell lymphoproliferation and complement-mediated hemolysis. Each of these steps constitutes a target for treatment. In this focused review, we address 2 successful therapeutic approaches; the bendamustine plus rituximab combination as a highly efficacious B-cell directed therapy and the anti-C1s monoclonal antibody sutimlimab as the most extensively studied complement-targeting therapy. We describe and discuss the prospective study of bendamustine plus rituximab and 2 recent, prospective studies of sutimlimab. Bendamustine-rituximab results in a high response rate, frequent complete responses and long median response duration, and the treatment is temporary. However, this therapy is relatively slow-acting and associated with some toxicity. Sutimlimab is also highly efficacious, is far more rapidly acting, and is low-toxic. Disadvantages of sutimlimab are the lack of effect on circulatory symptoms, the probable need for indefinite treatment, and the very high costs. In cold agglutinin disease patients who require treatment, the choice should be based on an individual assessment.

Determining drug dose in the era of targeted therapies: playing it (un)safe?

Targeted therapies against phosphatidylinositol 3-kinase (PI3K), Bruton's tyrosine kinase (BTK), and B-cell lymphoma-2 (BCL-2) are approved for chronic lymphocytic leukemia (CLL). Since approval of the first-in-class drugs, next-generation agents have become available and are continuously under development. While these therapies act on well-characterized molecular targets, this knowledge is only to some extent taken into consideration when determining their dose in phase I trials. For example, BTK occupancy has been assessed in dose-finding studies of various BTK inhibitors, but the minimum doses that result in full BTK occupancy were not determined. Although targeted agents have a different dose-response relationship than cytotoxic agents, which are more effective near the maximum tolerated dose, the traditional 3 + 3 toxicity-driven trial design remains heavily used in the era of targeted therapies. If pharmacodynamic biomarkers were more stringently used to guide dose selection, the recommended phase II dose would likely be lower as compared to the toxicity-driven selection. Reduced drug doses may lower toxicity, which in some cases is severe for these agents, and are supported by retrospective studies demonstrating non-inferior outcomes for patients with clinically indicated dose reductions. Here, we review strategies that were used for dose selection in phase I studies of currently approved and select investigational targeted therapies in CLL, and discuss how our initial clinical experience with targeted therapies have pointed to dose reductions, intermittent dosing, and drug combinations as strategies to overcome treatment intolerance and resistance.

Functional Testing to Characterize and Stratify PI3K Inhibitor Responses in Chronic Lymphocytic Leukemia.

PURPOSE: PI3K inhibitors (PI3Ki) are approved for relapsed chronic lymphocytic leukemia (CLL). Although patients may show an initial response to these therapies, development of treatment intolerance or resistance remain clinical challenges. To overcome these, prediction of individual treatment responses based on actionable biomarkers is needed. Here, we characterized the activity and cellular effects of 10 PI3Ki and investigated whether functional analyses can identify treatment vulnerabilities in PI3Ki-refractory/intolerant CLL and stratify responders to PI3Ki. EXPERIMENTAL DESIGN: Peripheral blood mononuclear cell samples (n = 51 in total) from treatment-naïve and PI3Ki-treated patients with CLL were studied. Cells were profiled against 10 PI3Ki and the Bcl-2 antagonist venetoclax. Cell signaling and immune phenotypes were analyzed by flow cytometry. Cell viability was monitored by detection of cleaved caspase-3 and the CellTiter-Glo assay. RESULTS: pan-PI3Kis were most effective at inhibiting PI3K signaling and cell viability, and showed activity in CLL cells from both treatment-naïve and idelalisib-refractory/intolerant patients. CLL cells from idelalisib-refractory/intolerant patients showed overall reduced protein phosphorylation levels. The pan-PI3Ki copanlisib, but not the p110δ inhibitor idelalisib, inhibited PI3K signaling in CD4+ and CD8+ T cells in addition to CD19+ B cells, but did not significantly affect T-cell numbers. Combination treatment with a PI3Ki and venetoclax resulted in synergistic induction of apoptosis. Analysis of drug sensitivities to 73 drug combinations and profiling of 31 proteins stratified responders to idelalisib and umbralisib, respectively. CONCLUSIONS: Our findings suggest novel treatment vulnerabilities in idelalisib-refractory/intolerant CLL, and indicate that ex vivo functional profiling may stratify PI3Ki responders.