Increased Vascular Permeability in the Bone Marrow Microenvironment Contributes to Disease Progression and Drug Response in Acute Myeloid Leukemia

The biological and clinical behaviors of hematological malignancies can be influenced by the active crosstalk with an altered bone marrow (BM) microenvironment. In the present study, we provide a detailed picture of the BM vasculature in acute myeloid leukemia using intravital two-photon microscopy. We found several abnormalities in the vascular architecture and function in patient-derived xenografts (PDX), such as vascular leakiness and increased hypoxia. Transcriptomic analysis in endothelial cells identified nitric oxide (NO) as major mediator of this phenotype in PDX and in patient-derived biopsies. Moreover, induction chemotherapy failing to restore normal vasculature was associated with a poor prognosis. Inhibition of NO production reduced vascular permeability, preserved normal hematopoietic stem cell function, and improved treatment response in PDX.

Role of the tumor microenvironment in mature B-cell lymphoid malignancies

The tumor microenvironment is the cellular and molecular environment in which the tumor exists and with which it continuously interacts. In B-cell lymphomas, this microenvironment is intriguing in that it plays critical roles in the regulation of tumor cell survival and proliferation, fostering immune escape as well as the development of treatment resistance. The purpose of this review is to summarize the proceedings of the Second Annual Summit on the Immune Microenvironment in Hematologic Malignancies that took place on September 11-12, 2014 in Dublin, Ireland. We provide a timely overview of the composition and biological relevance of the cellular and molecular microenvironment interface and discuss the role of interactions between the microenvironment and neoplastic cells in a variety of B-cell lymphomas. In addition, we focus on various novel therapeutic strategies that target the tumor microenvironment, including agents that modulate B-cell receptor pathways and immune-checkpoints, chimeric antigen receptor T cells and immunomodulatory agents.

International Working Group consensus response evaluation criteria in lymphoma (RECIL 2017)

In recent years, the number of approved and investigational agents that can be safely administered for the treatment of lymphoma patients for a prolonged period of time has substantially increased. Many of these novel agents are evaluated in early-phase clinical trials in patients with a wide range of malignancies, including solid tumors and lymphoma. Furthermore, with the advances in genome sequencing, new "basket" clinical trial designs have emerged that select patients based on the presence of specific genetic alterations across different types of solid tumors and lymphoma. The standard response criteria currently in use for lymphoma are the Lugano Criteria which are based on [18F]2-fluoro-2-deoxy-D-glucose positron emission tomography or bidimensional tumor measurements on computerized tomography scans. These differ from the RECIST criteria used in solid tumors, which use unidimensional measurements. The RECIL group hypothesized that single-dimension measurement could be used to assess response to therapy in lymphoma patients, producing results similar to the standard criteria. We tested this hypothesis by analyzing 47 828 imaging measurements from 2983 individual adult and pediatric lymphoma patients enrolled on 10 multicenter clinical trials and developed new lymphoma response criteria (RECIL 2017). We demonstrate that assessment of tumor burden in lymphoma clinical trials can use the sum of longest diameters of a maximum of three target lesions. Furthermore, we introduced a new provisional category of a minor response. We also clarified response assessment in patients receiving novel immune therapy and targeted agents that generate unique imaging situations.

Prognostic relevance of CD163 and CD8 combined with EZH2 and gain of chromosome 18 in follicular lymphoma: a study by the Lunenburg Lymphoma Biomarker Consortium

In follicular lymphoma, studies addressing the prognostic value of microenvironment-related immunohistochemical markers and tumor cell-related genetic markers have yielded conflicting results, precluding implementation in practice. Therefore, the Lunenburg Lymphoma Biomarker Consortium performed a validation study evaluating published markers. To maximize sensitivity, an end of spectrum design was applied for 122 uniformly immunochemotherapy-treated follicular lymphoma patients retrieved from international trials and registries. The criteria were: early failure, progression or lymphoma-related death <2 years versus long remission, response duration of >5 years. Immunohistochemical staining for T cells and macrophages was performed on tissue microarrays from initial biopsies and scored with a validated computer-assisted protocol. Shallow whole-genome and deep targeted sequencing was performed on the same samples. The 96/122 cases with complete molecular and immunohistochemical data were included in the analysis. EZH2 wild-type (P=0.006), gain of chromosome 18 (P=0.002), low percentages of CD8+ cells (P=0.011) and CD163+ areas (P=0.038) were associated with early failure. No significant differences in other markers were observed, thereby refuting previous claims of their prognostic significance. Using an optimized study design, this Lunenburg Lymphoma Biomarker Consortium study substantiates wild-type EZH2 status, gain of chromosome 18, low percentages of CD8+ cells and CD163+ area as predictors of early failure to immunochemotherapy in follicular lymphoma treated with rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP [-like]), while refuting the prognostic impact of various other markers.

Dietary practices in isovaleric acidemia: A European survey

Background

In Europe, dietary management of isovaleric acidemia (IVA) may vary widely. There is limited collective information about dietetic management.

Aim

To describe European practice regarding the dietary management of IVA, prior to the availability of the E-IMD IVA guidelines (E-IMD 2014).

Methods

A cross-sectional questionnaire was sent to all European dietitians who were either members of the Society for the Study of Inborn Errors of Metabolism Dietitians Group (SSIEM-DG) or whom had responded to previous questionnaires on dietetic practice (n = 53). The questionnaire comprised 27 questions about the dietary management of IVA.

Results

Information on 140 patients with IVA from 39 centres was reported. 133 patients (38 centres) were given a protein restricted diet. Leucine-free amino acid supplements (LFAA) were routinely used to supplement protein intake in 58% of centres. The median total protein intake prescribed achieved the WHO/FAO/UNU [2007] safe levels of protein intake in all age groups. Centres that prescribed LFAA had lower natural protein intakes in most age groups except 1 to 10 y. In contrast, when centres were not using LFAA, the median natural protein intake met WHO/FAO/UNU [2007] safe levels of protein intake in all age groups. Enteral tube feeding was rarely prescribed.

Conclusions

This survey demonstrates wide differences in dietary practice in the management of IVA across European centres. It provides unique dietary data collectively representing European practices in IVA which can be used as a foundation to compare dietary management changes as a consequence of the first E-IMD IVA guidelines availability.

Versatile humanized niche model enables study of normal and malignant human hematopoiesis

The BM niche comprises a tightly controlled microenvironment formed by specific tissue and cells that regulates the behavior of hematopoietic stem cells (HSCs). Here, we have provided a 3D model that is tunable in different BM niche components and useful, both in vitro and in vivo, for studying the maintenance of normal and malignant hematopoiesis. Using scaffolds, we tested the capacity of different stromal cell types to support human HSCs. Scaffolds coated with human mesenchymal stromal cells (hMSCs) proved to be superior in terms of HSC engraftment and long-term maintenance when implanted in vivo. Moreover, we found that hMSC-coated scaffolds can be modulated to form humanized bone tissue, which was also able to support human HSC engraftment. Importantly, hMSC-coated humanized scaffolds were able to support the growth of leukemia patient cells in vivo, including the growth of samples that would not engraft the BM of immunodeficient mice. These results demonstrate that an s.c. implantation approach in a 3D carrier scaffold seeded with stromal cells is an effective in vivo niche model for studying human hematopoiesis. The various niche components of this model can be changed depending on the context to improve the engraftment of nonengrafting acute myeloid leukemia (AML) samples.

Chronic lymphocytic leukaemia

Chronic lymphocytic leukaemia (CLL) is a malignancy of CD5+ B cells that is characterized by the accumulation of small, mature-appearing lymphocytes in the blood, marrow and lymphoid tissues. Signalling via surface immunoglobulin, which constitutes the major part of the B cell receptor, and several genetic alterations play a part in CLL pathogenesis, in addition to interactions between CLL cells and other cell types, such as stromal cells, T cells and nurse-like cells in the lymph nodes. The clinical progression of CLL is heterogeneous and ranges from patients who require treatment soon after diagnosis to others who do not require therapy for many years, if at all. Several factors, including the immunoglobulin heavy-chain variable region gene (IGHV) mutational status, genomic changes, patient age and the presence of comorbidities, should be considered when defining the optimal management strategies, which include chemotherapy, chemoimmunotherapy and/or drugs targeting B cell receptor signalling or inhibitors of apoptosis, such as BCL-2. Research on the biology of CLL has profoundly enhanced our ability to identify patients who are at higher risk for disease progression and our capacity to treat patients with drugs that selectively target distinctive phenotypic or physiological features of CLL. How these and other advances have shaped our current understanding and treatment of patients with CLL is the subject of this Primer.

Comparison of the impact of cancer between British and US long-term non-Hodgkin lymphoma survivors

PURPOSE

The aims of this study were to examine quality of life, using the Impact of Cancer version 2 (IOCv2), in British non-Hodgkin lymphoma (NHL) survivors and investigate differences between survivors in the UK and the USA.

METHODS

NHL survivors (326 UK and 667 US) completed the 37-item IOCv2 and psychological distress, fatigue and social support questionnaires.

RESULTS

The IOCv2 showed good reliability in the British sample with higher internal consistency (Cronbach alpha 0.7-0.9) and no floor and ceiling effects. UK survivors showed significantly higher negative (p < 0.001) and higher positive (p = 0.003) IOC compared to US survivors. Younger survivors (p = 0.003), those with shorter time since diagnosis (p < 0.001) and with lower levels of social support (p = 0.001), showed more negative IOC in both groups. Higher negative IOC was also significantly associated with fatigue (p < 0.001) and depressive symptoms (p < 0.001) in both countries. Higher positive IOC was associated with female gender (p < 0.001), longer time since diagnosis (p = 0.02), those diagnosed at later stage (p < 0.05) and with greater social support (p = 0.004). Whereas significantly lower positive IOC was associated with white ethnicity (p < 0.001), higher education levels (p < 0.05) and fatigue (p = 0.001).

CONCLUSIONS

The IOCv2 is reliable and applicable in UK and US populations. Both negative and positive IOC scores were higher in British compared to US survivors. However, in both countries, psychosocial factors consistently showed the greatest impact on QOL irrespective of clinical characteristics. Recognition and treatment of individuals with these risk factors is a high priority for improving QOL in long-term cancer survivors, as is the development of modular interventions aimed at increasing positive IOC as well as decreasing negative impact. The IOCv2 shows great potential both as a screening and assessment measure for examining cancer-related outcomes among survivors.

T-cell acute leukaemia exhibits dynamic interactions with bone marrow microenvironments

It is widely accepted that complex interactions between cancer cells and their surrounding microenvironment contribute to disease development, chemo-resistance and disease relapse. In light of this observed interdependency, novel therapeutic interventions that target specific cancer stroma cell lineages and their interactions are being sought. Here we studied a mouse model of human T-cell acute lymphoblastic leukaemia (T-ALL) and used intravital microscopy to monitor the progression of disease within the bone marrow at both the tissue-wide and single-cell level over time, from bone marrow seeding to development/selection of chemo-resistance. We observed highly dynamic cellular interactions and promiscuous distribution of leukaemia cells that migrated across the bone marrow, without showing any preferential association with bone marrow sub-compartments. Unexpectedly, this behaviour was maintained throughout disease development, from the earliest bone marrow seeding to response and resistance to chemotherapy. Our results reveal that T-ALL cells do not depend on specific bone marrow microenvironments for propagation of disease, nor for the selection of chemo-resistant clones, suggesting that a stochastic mechanism underlies these processes. Yet, although T-ALL infiltration and progression are independent of the stroma, accumulated disease burden leads to rapid, selective remodelling of the endosteal space, resulting in a complete loss of mature osteoblastic cells while perivascular cells are maintained. This outcome leads to a shift in the balance of endogenous bone marrow stroma, towards a composition associated with less efficient haematopoietic stem cell function. This novel, dynamic analysis of T-ALL interactions with the bone marrow microenvironment in vivo, supported by evidence from human T-ALL samples, highlights that future therapeutic interventions should target the migration and promiscuous interactions of cancer cells with the surrounding microenvironment, rather than specific bone marrow stroma, to combat the invasion by and survival of chemo-resistant T-ALL cells.

NCRI phase II study of CHOP in combination with ofatumumab in induction and maintenance in newly diagnosed Richter syndrome

Richter syndrome (RS) is associated with chemotherapy resistance and a poor historical median overall survival (OS) of 8-10 months. We conducted a phase II trial of standard CHOP-21 (cyclophosphamide, doxorubicin, vincristine, prednisolone every 21 d) with ofatumumab induction (Cycle 1: 300 mg day 1, 1000 mg day 8, 1000 mg day 15; Cycles 2-6: 1000 mg day 1) (CHOP-O) followed by 12 months ofatumumab maintenance (1000 mg given 8-weekly for up to six cycles). Forty-three patients were recruited of whom 37 were evaluable. Seventy-three per cent were aged >60 years. Over half of the patients received a fludarabine and cyclophosphamide-based regimen as prior CLL treatment. The overall response rate was 46% (complete response 27%, partial response 19%) at six cycles. The median progression-free survival was 6·2 months (95% confidence interval [CI] 4·9-14·0 months) and median OS was 11·4 months (95% CI 6·4-25·6 months). Treatment-naïve and TP53-intact patients had improved outcomes. Fifteen episodes of neutropenic fever and 46 non-neutropenic infections were observed. There were no treatment-related deaths. Seven patients received platinum-containing salvage at progression, with only one patient obtaining an adequate response to proceed to allogeneic transplantation. CHOP-O with ofatumumab maintenance provides minimal benefit beyond CHOP plus rutuximab. Standard immunochemotherapy for RS remains wholly inadequate for unselected RS. Multinational trials incorporating novel agents are urgently needed.

Clinical Practice Recommendations for Use of Allogeneic Hematopoietic Cell Transplantation in Chronic Lymphocytic Leukemia on Behalf of the Guidelines Committee of the American Society for Blood and Marrow Transplantation

We sought to establish clinical practice recommendations to redefine the role of allogeneic hematopoietic cell transplantation (allo-HCT) for patients with chronic lymphocytic leukemia (CLL) in an era of highly active targeted therapies. We performed a systematic review to identify prospective randomized controlled trials comparing allo-HCT against novel therapies for treatment of CLL at various disease stages. In the absence of such data, we invited physicians with expertise in allo-HCT and/or CLL to participate in developing these recommendations. We followed the Grading of Recommendations Assessment, Development and Evaluation methodology. For standard-risk CLL we recommend allo-HCT in the absence of response or if there is evidence of disease progression after B cell receptor (BCR) inhibitors. For high-risk CLL an allo-HCT is recommended after failing 2 lines of therapy and showing an objective response to BCR inhibitors or to a clinical trial. It is also recommended for patients who fail to show an objective response or progress after BCR inhibitors and receive BCL-2 inhibitors, regardless of whether an objective response is achieved. For Richter transformation, we recommend allo-HCT upon demonstration of an objective response to anthracycline-based chemotherapy. A reduced-intensity conditioning regimen is recommended whenever indicated. These recommendations highlight the rapidly changing treatment landscape of CLL. Newer therapies have disrupted prior paradigms, and allo-HCT is now relegated to later stages of relapsed or refractory CLL.

Obinutuzumab plus bendamustine versus bendamustine monotherapy in patients with rituximab-refractory indolent non-Hodgkin lymphoma (GADOLIN): a randomised, controlled, open-label, multicentre, phase 3 trial

BACKGROUND

Patients with indolent non-Hodgkin lymphoma who fail to achieve adequate disease control with rituximab-based treatment have few treatment options and a poor prognosis. We aimed to assess a combination of obinutuzumab (GA101), a novel glyco-engineered type II anti-CD20 monoclonal antibody, and bendamustine in this patient population.

METHODS

In this open-label, randomised, phase 3 study (GADOLIN), patients aged 18 years or older with histologically documented, CD20-positive indolent non-Hodgkin lymphoma refractory to rituximab were enrolled at 83 hospital and community sites in 14 countries in Europe, Asia, and North and Central America. Patients were randomly assigned (1:1) using a hierarchical dynamic randomisation scheme stratified by indolent non-Hodgkin lymphoma subtype, rituximab-refractory type, number of previous therapies, and geographical region, to receive induction treatment (six 28-day cycles) with obinutuzumab plus bendamustine or bendamustine monotherapy, both given intravenously. Obinutuzumab plus bendamustine dosing was obinutuzumab 1000 mg (days 1, 8, and 15, cycle 1; day 1, cycles 2-6) plus bendamustine 90 mg/m(2) per day (days 1 and 2, cycles 1-6), and bendamustine monotherapy dosing was 120 mg/m(2) per day (days 1 and 2, all cycles). Non-progressing patients in the obinutuzumab plus bendamustine group received obinutuzumab maintenance (1000 mg every 2 months) for up to 2 years. The primary endpoint was progression-free survival in all randomised patients, as assessed by an independent review committee. Safety was assessed in all patients who received any amount of obinutuzumab or bendamustine. This study is registered with ClinicalTrials.gov, number NCT01059630, and has stopped recruiting patients.

FINDINGS

Between April 15, 2010, and Sept 1, 2014, when the study was stopped after a pre-planned interim analysis, 396 patients were randomly assigned (194 to obinutuzumab plus bendamustine and 202 to bendamustine monotherapy). After a median follow-up time of 21·9 months (IQR 12·1-31·0) in the obinutuzumab plus bendamustine group and 20·3 months (9·5-29·7) in the bendamustine monotherapy group, progression-free survival was significantly longer with obinutuzumab plus bendamustine (median not reached [95% CI 22·5 months-not estimable]) than with bendamustine monotherapy (14·9 months [12·8-16·6]; hazard ratio 0·55 [95% CI 0·40-0·74]; p=0·0001). Grade 3-5 adverse events occurred in 132 (68%) of 194 patients in the obinutuzumab plus bendamustine group and in 123 (62%) of 198 patients in the bendamustine monotherapy group. The most frequent grade 3 or worse adverse events were neutropenia (64 [33%] in the obinutuzumab plus bendamustine group vs 52 [26%] in the bendamustine monotherapy group), thrombocytopenia (21 [11%] vs 32 [16%]), anaemia (15 [8%] vs 20 [10%]) and infusion-related reactions (21 [11%] vs 11 [6%]). Serious adverse events occurred in 74 patients (38%) in the obinutuzumab plus bendamustine group and in 65 patients (33%) in the bendamustine monotherapy group, and deaths due to adverse events occurred in 12 patients (6%) and 12 patients (6%), respectively. Three (25%) of 12 adverse event-related deaths in the obinutuzumab plus bendamustine group and five (42%) of 12 in the bendamustine monotherapy group were treatment related.

INTERPRETATION

Obinutuzumab plus bendamustine followed by obinutuzumab maintenance has improved efficacy over bendamustine monotherapy in rituximab-refractory patients with indolent non-Hodgkin lymphoma, with manageable toxicity, and is a new treatment option for patients who have relapsed after or are no longer responding to rituximab-based therapy.

FUNDING

F Hoffmann-La Roche Ltd.

Allogeneic Transplantation for Chronic Lymphocytic Leukemia in the Age of Novel Treatment Strategies

Hematopoietic stem cell transplantation (HSCT) is the only established potentially curative treatment option for chronic lymphocytic leukemia (CLL) to date. However, this approach is associated with high toxicity and significant treatment-related morbidity and mortality; thus, it is suitable for only a minority of high-risk patients, given that most persons with CLL have comorbidities and are of advanced age. Until very recently, international guidelines recommended HSCT for physically fit patients who displayed poor-risk features or had only a short response to immunochemotherapy. In the wake of novel treatment approaches that offer high efficacy and highly durable responses with little toxicity, our approach to HSCT in CLL needs to be re-evaluated. While we wait for data on the long-term efficacy of novel therapies to inform the choice of HSCT or alternative treatment, strategies must be assessed individually for every patient, and treatment must be conducted in the setting of randomized clinical trials whenever possible.

Autologous Hematopoetic Stem Cell Transplantation for Refractory Crohn Disease: A Randomized Clinical Trial

IMPORTANCE

Case reports and series suggest hematopoietic stem cell transplantation (HSCT) may benefit some patients with Crohn disease.

OBJECTIVE

To evaluate the effect of autologous HSCT on refractory Crohn disease.

DESIGN, SETTING, AND PARTICIPANTS

Parallel-group randomized clinical trial conducted in 11 European transplant units from July 2007 to September 2011, with follow-up through March 2013. Patients were aged 18 to 50 years with impaired quality of life from refractory Crohn disease not amenable to surgery despite treatment with 3 or more immunosuppressive or biologic agents and corticosteroids.

INTERVENTIONS

All patients underwent stem cell mobilization before 1:1 randomization to immunoablation and HSCT (n = 23) or control treatment (HSCT deferred for 1 year [n = 22]). All were given standard Crohn disease treatment as needed.

MAIN OUTCOMES AND MEASURES

Sustained disease remission at 1 year, a composite primary end point comprising clinical remission (Crohn Disease Activity Index (CDAI) <150 [range, 0-600]), no use of corticosteroids or immunosuppressive or biologic drugs for at least the last 3 months, and no endoscopic or radiological evidence of active (erosive) disease anywhere in the gastrointestinal (GI) tract. Secondary outcomes were individual components of the primary composite outcome and other measures of disease activity, laboratory results, quality of life and functional status, and GI tract imaging.

RESULTS

Twenty-three patients underwent HSCT and 22 received standard Crohn disease treatment (controls). Sustained disease remission was achieved in 2 patients undergoing HSCT (8.7%) vs 1 control patient (4.5%) (absolute difference, 4.2% [95% CI, -14.2% to 22.6%]; P = .60). Fourteen patients undergoing HSCT (61%) vs 5 control patients (23%) had discontinued immunosuppressive or biologic agents or corticosteroids for at least 3 months (difference, 38.1% [95% CI, 9.3% to 59.3%]; P = .01). Ten vs 2 patients had a CDAI less than 150 (remission) at the final evaluation, 8 (34.8%) vs 2 (9.1%) for 3 or more months (difference, 25.7% [95% CI, 1.1% to 47.1%]; P = .052). Eight (34.8%) vs 2 (9.1%) patients were adjudicated free of active disease on endoscopy and radiology at final assessment (difference, 25.7% [95% CI, 1.1% to 47.1%]; P = .054). There were 76 serious adverse events in patients undergoing HSCT vs 38 in controls. One patient undergoing HSCT died.

CONCLUSIONS AND RELEVANCE

Among adult patients with refractory Crohn disease not amenable to surgery who had impaired quality of life, HSCT, compared with conventional therapy, did not result in a statistically significant improvement in sustained disease remission at 1 year and was associated with significant toxicity. These findings do not support the widespread use of HSCT for patients with refractory Crohn disease.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00297193.

New insights into hematopoietic stem cell transplantation for chronic lymphocytic leukemia: a 2015 perspective

A considerable body of evidence demonstrates that allogeneic hematopoietic stem cell transplantation (HSCT) offers the only potentially curative treatment option for patients with chronic lymphocytic leukemia (CLL). However, this approach is suitable for only a minority of CLL patients, owing to its significant treatment-related mortality and morbidity. Until recently, internationally accepted guidelines suggested that HSCT should be considered in physically fit CLL patients who carry poor-risk features, such as TP53 abnormalities, or who had a short response to previous immunochemotherapy. However, several new agents and alternative treatment strategies are available that demonstrate impressive and durable responses, even in CLL patients who previously might have been candidates for transplant. The decision about which patients merit HSCT therefore remains important, and HSCT must now be considered in light of other less toxic therapies. Until data on the long-term efficacy of novel treatment approaches mature, the choice of HSCT vs alternative strategies must be assessed on a patient-by-patient basis, and treatment in the setting of randomized clinical trials should be pursued whenever possible.

Targeting dysfunctional myeloid cells delays disease development and improves immune function in a CLL mouse model (TUM6P.1009)

Previous in vitro studies have shown that myeloid cells play a key role in apoptosis-resistance in chronic lymphocytic leukemia (CLL). However, their composition and function have not been thoroughly investigated in vivo. Using the Eµ-TCL1 mouse model of CLL, we observed severe skewing of myeloid cell populations along with CLL development. Monocytes and M2-like macrophages infiltrated the peritoneal cavity of leukemic mice. Monocytes expressing high levels of inflammatory factors like IL-10, TNFα and CXCL9 accumulated also in the spleen, the main site of disease, and were severely skewed towards Ly6Clow phenotype. Along with that, the percentage of MHC-IIhi dendritic cells (DCs) and macrophages significantly dropped in the spleen, suggesting monocyte differentiation arrest. Myeloid cell depletion using liposomal clodronate resulted in a significant control of CLL development, repair of innate immune cell phenotypes and partial resolution of systemic inflammation. Also, CLL-induced loss of naive T cells was resolved. CLL-associated monocytes and DCs aberrantly express high PD-L1 levels suggesting their contribution in T cell defects. Importantly, PD-L1 blockade very effectively prevented CLL development and was accompanied with a re-activation of immune effector cells. This included restoration of mature macrophages and MHC-IIhi DCs. Our preclinical data suggests that targeting myeloid cell survival and immunosuppression can serve as a novel strategy for CLL immunotherapy.