Investigating the role of CD38 and functionally related molecular risk factors in the CLL NOD/SCID xenograft model

Mouse models of CLL: In vivo modeling of disease initiation, progression, and transformation to Richter transformation

Chronic lymphocytic leukemia (CLL) is a highly complex disease characterized by the proliferation of CD5+ B cells in lymphoid tissues. Current modern treatments have brought significant clinical benefits to CLL patients. However, there are still unmet needs. Patients relapse on Bruton's tyrosine kinase inhibitors and BCL2 inhibitors and often develop more aggressive diseases including Richter transformation (RT), an incurable complication of up to ∼10% patients. This evidence underscores the need for improved immunotherapies, combination treatment strategies, and predictive biomarkers. A mouse model that can recapitulate human CLL disease and certain components of the tumor immune microenvironment represents a promising preclinical tool for such purposes. In this review, we provide an overview of CRISPR-engineered and xenograft mouse models utilizing either cell lines, or primary CLL cells suitable for studies of key events driving the disease onset, progression and transformation of CLL. We also review how CRISPR/Cas9 established mouse models carrying loss-of-function lesions allow one to study key mutations driving disease progression. Finally, we discuss how next generation humanized mice might improve to generation of faithful xenograft mouse models of human CLL.

In Vitro and In Vivo Models of CLL–T Cell Interactions: Implications for Drug Testing

Simple Summary

Chronic lymphocytic leukemia (CLL) cells in the peripheral blood and lymphoid microenvironment display substantially different gene expression profiles and proliferative capaci-ty. It has been suggested that CLL–T-cell interactions are key pro-proliferative stimuli in immune niches. We review in vitro and in vivo model systems that mimic CLL-T-cell interactions to trigger CLL proliferation and study therapy resistance. We focus on studies describing the co-culture of leukemic cells with T cells, or supportive cell lines expressing T-cell factors, and simplified models of CLL cells’ stimulation with recombinant factors. In the second part, we summarize mouse models revealing the role of T cells in CLL biology and implications for generating patient-derived xenografts by co-transplanting leukemic cells with T cells.

Abstract

T cells are key components in environments that support chronic lymphocytic leukemia (CLL), activating CLL-cell proliferation and survival. Here, we review in vitro and in vivo model systems that mimic CLL–T-cell interactions, since these are critical for CLL-cell division and resistance to some types of therapy (such as DNA-damaging drugs or BH3-mimetic venetoclax). We discuss approaches for direct CLL-cell co-culture with autologous T cells, models utilizing supportive cell lines engineered to express T-cell factors (such as CD40L) or stimulating CLL cells with combinations of recombinant factors (CD40L, interleukins IL4 or IL21, INFγ) and additional B-cell receptor (BCR) activation with anti-IgM antibody. We also summarize strategies for CLL co-transplantation with autologous T cells into immunodeficient mice (NOD/SCID, NSG, NOG) to generate patient-derived xenografts (PDX) and the role of T cells in transgenic CLL mouse models based on TCL1 overexpression (Eµ-TCL1). We further discuss how these in vitro and in vivo models could be used to test drugs to uncover the effects of targeted therapies (such as inhibitors of BTK, PI3K, SYK, AKT, MEK, CDKs, BCL2, and proteasome) or chemotherapy (fludarabine and bendamustine) on CLL–T-cell interactions and CLL proliferation.

A Detailed Analysis of Parameters Supporting the Engraftment and Growth of Chronic Lymphocytic Leukemia Cells in Immune-Deficient Mice

Patient-derived xenograft models of chronic lymphocytic leukemia (CLL) can be created using highly immunodeficient animals, allowing analysis of primary tumor cells in an in vivo setting. However, unlike many other tumors, CLL B lymphocytes do not reproducibly grow in xenografts without manipulation, proliferating only when there is concomitant expansion of T cells. Here we show that in vitro pre-activation of CLL-derived T lymphocytes allows for a reliable and robust system for primary CLL cell growth within a fully autologous system that uses small numbers of cells and does not require pre-conditioning. In this system, growth of normal T and leukemic B cells follows four distinct temporal phases, each with characteristic blood and tissue findings. Phase 1 constitutes a period during which resting CLL B cells predominate, with cells aggregating at perivascular areas most often in the spleen. In Phase 2, T cells expand and provide T-cell help to promote B-cell division and expansion. Growth of CLL B and T cells persists in Phase 3, although some leukemic B cells undergo differentiation to more mature B-lineage cells (plasmablasts and plasma cells). By Phase 4, CLL B cells are for the most part lost with only T cells remaining. The required B-T cell interactions are not dependent on other human hematopoietic cells nor on murine macrophages or follicular dendritic cells, which appear to be relatively excluded from the perivascular lymphoid aggregates. Notably, the growth kinetics and degree of anatomic localization of CLL B and T cells is significantly influenced by intravenous versus intraperitoneal administration. Importantly, B cells delivered intraperitoneally either remain within the peritoneal cavity in a quiescent state, despite the presence of dividing T cells, or migrate to lymphoid tissues where they actively divide; this dichotomy mimics the human condition in that cells in primary lymphoid tissues and the blood are predominately resting, whereas those in secondary lymphoid tissues proliferate. Finally, the utility of this approach is illustrated by documenting the effects of a bispecific antibody reactive with B and T cells. Collectively, this model represents a powerful tool to evaluate CLL biology and novel therapeutics in vivo.

Maltotriose-modified poly(propylene imine) Glycodendrimers as a potential novel platform in the treatment of chronic lymphocytic Leukemia. A proof-of-concept pilot study in the animal model of CLL

Cancer nanotherapeutics have shown promise in resolving some of the limitations of conventional drug delivery systems such as nonspecific biodistribution and targeting, lack of water solubility, and low therapeutic indices, Among the various nanoparticles that are available, dendrimers, highly branched macromolecules with a specific size and shape, are one of the most promising ones. In this preliminary study, we tested the anti-tumor activity of maltotriose-modified fourth-generation poly(propylene imine) glycodendrimers (PPI-G4-M3) in vivo in the subcutaneous MEC-1 xenograft model of human chronic lymphocytic leukemia (CLL) in NOD scid gamma mice. Fludarabine was used for model validation and as a positive treatment control. The anti-tumor response was calculated as tumor volume, tumor control ratio, and tumor growth inhibition. The study showed that PPI-G4-M3 inhibited subcutaneous tumor growth more efficiently than fludarabine. The anti-tumor response was dose-dependent. Cationic PPI-G4-M3 showed the highest anti-tumor activity but also higher toxicity than the neutral dendrimers and fludarabine. These first promising results warrant further studies in the optimization of dendrimers charge, dose, route and schedule of administration to combat CLL.

Optimized Xenograft Protocol for Chronic Lymphocytic Leukemia Results in High Engraftment Efficiency for All CLL Subgroups

Preclinical drug development for human chronic lymphocytic leukemia (CLL) requires robust xenograft models recapitulating the entire spectrum of the disease, including all prognostic subgroups. Current CLL xenograft models are hampered by inefficient engraftment of good prognostic CLLs, overgrowth with co-transplanted T cells, and the need for allogeneic humanization or irradiation. Therefore, we aimed to establish an effective and reproducible xenograft protocol which allows engraftment of all CLL subtypes without the need of humanization or irradiation. Unmanipulated NOD.Cg-Prkdc^scidIl2rg^tm1Sug/JicTac (NOG) mice in contrast to C.Cg-Rag2^tm1Fwa-/-Il2rg^tm1Sug/JicTac (BRG) mice allowed engraftment of all tested CLL subgroups with 100% success rate, if CLL cells were fresh, injected simultaneously intra-peritoneally and intravenously, and co-transferred with low fractions of autologous T cells (2%–4%). CLL transplanted NOG mice (24 different patients) developed CLL pseudofollicles in the spleen, which increased over 4–6 weeks, and were then limited by the expanding autologous T cells. Ibrutinib treatment studies were performed to validate our model, and recapitulated treatment responses seen in patients. In conclusion, we developed an easy-to-use CLL xenograft protocol which allows reliable engraftment for all CLL subgroups without humanization or irradiation of mice. This protocol can be widely used to study CLL biology and to explore novel drug candidates.

Method for Generating a Patient-Derived Xenograft Model of CLL

Patient-derived xenograft (PDX) models are created by implantation of tumor cells into immunodeficient mice. These models maintain similar morphology and molecular profiling of the original tumors, and therefore have been extensively used in cancer research in both the basic and preclinical fields. Here, we describe a PDX model of CLL using autologous activated T cells to support CLL B-cell growth in lymphoid tissues such as spleen and bone marrow. This model allows one to perform in vivo preclinical and biological studies for this clinically and molecularly heterogeneous disease.

CD49d associates with nodal presentation and subsequent development of lymphadenopathy in patients with chronic lymphocytic leukaemia

CD49d is a surface integrin that is expressed on chronic lymphocytic leukaemia (CLL) cells, and strongly correlates with more aggressive disease. Given its association with cell-cell adhesion and leucocyte trafficking, we hypothesized that patients with high CD49d expression would experience a clinical course dominated by lymphadenopathy. CD49d expression was measured by flow cytometry and considered positive if expressed by ≥30% of CLL cells. The study included 797 newly diagnosed CLL/small lymphocytic leukaemia patients; 279 (35%) were CD49d positive. CD49d-positive patients were more likely to present with lymphadenopathy (P < 0·001); a finding that persisted after adjusting for fluorescence in situ hybridisation (FISH) and IGHV mutation status [odds ratio (OR) 2·51; 95% confidence interval (CI) 1·64-3·83; P < 0·001]. Among CLL Rai 0 patients, CD49d positivity was associated with shorter time to development of lymphadenopathy (3·2 years vs not reached, P < 0·01). This association was maintained after adjusting for either FISH [hazard ratio (HR) 2·18; 95% CI 1·25-3·81; P = 0·006) or IGHV status (HR 2·02; 95% CI 1·11-3·69; P = 0·02) individually, but was attenuated when adjusting by both (HR 1·72; 95% CI 0·88-3·38; P = 0·11).These data demonstrate that CD49d-positive CLL patients experience a disease course dominated by lymphadenopathy. These findings could have implications for therapy selection and disease monitoring.

Overview of the Use of Murine Models in Leukemia and Lymphoma Research

Murine models have been adopted as a significant and powerful tool in the study of cancer. The applications of murine models of cancer are numerous: mechanism discovery, oncogenesis, molecular genetics, microenvironment, metastasis, and therapeutic efficacy. Leukemias and lymphomas are a group of highly heterogeneous hematologic malignancies that affect people of all ages and ethnicities. Leukemia and lymphoma arise from hematopoietic and immune cells and usually spread widely throughout the body. The liquid nature of many of these malignancies, as well as the complex microenvironment from which they arise and their multifaceted genetic basis, has added to the difficulty in generating appropriate and translational models to study them. Murine models of leukemia and lymphoma have made substantial contributions to our understanding of the pathobiology of these disorders in humans. However, while there are many advantages to these models, limitations remain. In this review, we discuss the mouse as a model to study leukemia and lymphoma, and the importance of choosing the correct methodology. Specific examples of murine models of leukemias and lymphomas are provided, with particular attention to those that are highly translational to their human counterpart. Finally, future applications of murine models and potential for better models are discussed.

Humanized mouse G6 anti-idiotypic monoclonal antibody has therapeutic potential against IGHV1-69 germline gene-based B-CLL

In 10-20% of the cases of chronic lymphocytic leukemia of B-cell phenotype (B-CLL), the IGHV1-69 germline is utilized as VH gene of the B cell receptor (BCR). Mouse G6 (MuG6) is an anti-idiotypic monoclonal antibody discovered in a screen against rheumatoid factors (RFs) that binds with high affinity to an idiotope expressed on the 51p1 alleles of IGHV1-69 germline gene encoded antibodies (G6-id(+)). The finding that unmutated IGHV1-69 encoded BCRs are frequently expressed on B-CLL cells provides an opportunity for anti-idiotype monoclonal antibody immunotherapy. In this study, we first showed that MuG6 can deplete B cells encoding IGHV1-69 BCRs using a novel humanized GTL mouse model. Next, we humanized MuG6 and demonstrated that the humanized antibodies (HuG6s), especially HuG6.3, displayed ∼2-fold higher binding affinity for G6-id(+) antibody compared to the parental MuG6. Additional studies showed that HuG6.3 was able to kill G6-id(+) BCR expressing cells and patient B-CLL cells through antibody-dependent cell-mediated cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC). Finally, both MuG6 and HuG6.3 mediate in vivo depletion of B-CLL cells in NSG mice. These data suggest that HuG6.3 may provide a new precision medicine to selectively kill IGHV1-69-encoding G6-id(+) B-CLL cells.

NOD/SCID IL2Rγ-null mouse xenograft model of human p53-mutated chronic lymphocytic leukemia and ATM-mutated mantle cell lymphoma using permanent cell lines

Xenograft models represent a promising tool to study the pathogenesis of hematological malignancies. To establish a reliable and appropriate in vivo model of aggressive human B-cell leukemia and lymphoma we xenotransplanted four p53-mutated cell lines and one ATM-mutated cell line into immunodeficient NOD/SCID IL2Rγ-null mice. The cell lines MEC-1, SU-DHL-4, JEKO-1, REC-1, and GRANTA-519 were transplanted intraperitoneally or subcutaneously and the engraftment was investigated using immunohistochemistry and flow cytometry. We found significant differences in engraftment efficiency. MEC-1, JEKO-1 and GRANTA-519 cell lines engrafted most efficiently, while SU-DHL-4 cells did not engraft at all. MEC-1 and GRANTA-519 massively infiltrated organs and the whole intraperitoneal cavity showing very aggressive growth. In addition, GRANTA-519 cells massively migrated to the bone marrow regardless of the transplantation route. The MEC-1 and GRANTA-519 cells can be especially recommended for in vivo study of p53-mutated chronic lymphocytic leukemia and ATM-mutated mantle cell lymphoma, respectively.

Microenvironment dependency in Chronic Lymphocytic Leukemia: The basis for new targeted therapies

Chronic Lymphocytic Leukemia (CLL) is a prototype microenvironment-dependent B-cell malignancy, in which the neoplastic B cells co-evolve together with a supportive tissue microenvironment, which promotes leukemia cell survival, growth, and drug-resistance. Chemo-immunotherapy is an established treatment modality for CLL patients, resulting in high rates of responses and improved survival, especially in low-risk CLL. New, alternative treatments target B-cell receptor (BCR) signaling and the Chemokine (C-X-C motif) Receptor 4 (CXCR4)-Chemokine (C-X-C motif) Ligand 12 (CXCL12) axis, which are key pathways of CLL-microenvironment cross talk. The remarkable clinical efficacy of inhibitors targeting the BCR-associated kinases Bruton's tyrosine kinase (BTK) and phosphoinositide 3-kinase delta (PI3Kδ) challenges established therapeutic paradigms and corroborates the central role of BCR signaling in CLL pathogenesis. In this review, we discuss the cellular and molecular components of the CLL microenvironment. We also describe the emerging therapeutic options for CLL patients, with a focus on inhibitors of CXCR4-CXCL12 and BCR signaling.

Murine genetically engineered and human xenograft models of chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is a genetically complex disease, with multiple factors having an impact on onset, progression, and response to therapy. Genetic differences/abnormalities have been found in hematopoietic stem cells from patients, as well as in B lymphocytes of individuals with monoclonal B-cell lymphocytosis who may develop the disease. Furthermore, after the onset of CLL, additional genetic alterations occur over time, often causing disease worsening and altering patient outcomes. Therefore, being able to genetically engineer mouse models that mimic CLL or at least certain aspects of the disease will help us understand disease mechanisms and improve treatments. This notwithstanding, because neither the genetic aberrations responsible for leukemogenesis and progression nor the promoting factors that support these are likely identical in character or influences for all patients, genetically engineered mouse models will only completely mimic CLL when all of these factors are precisely defined. In addition, multiple genetically engineered models may be required because of the heterogeneity in susceptibility genes among patients that can have an effect on genetic and environmental characteristics influencing disease development and outcome. For these reasons, we review the major murine genetically engineered and human xenograft models in use at the present time, aiming to report the advantages and disadvantages of each.

The pathogenic relevance of the prognostic markers CD38 and CD49d in chronic lymphocytic leukemia

The interactions of chronic lymphocytic leukemia cells with the microenvironment in secondary lymphoid tissues and the bone marrow are known to promote CLL cell survival and proliferation. CD38 and CD49d are both independent prognostic risk parameters in CLL with important roles in shaping these interactions. Both are reported to influence CLL cell trafficking between blood and lymphoid organs as well as their survival and proliferation within the lymphoid organs, thereby impacting the pathophysiology of the disease. The expression of CD38 and CD49d is associated in the majority of cases, and they exist as part of macromolecular complexes. Here, we review the current evidence for the individual and associated contributions of these molecules to CLL pathophysiology.

Animal models of leukemia: any closer to the real thing?

Animal models have been invaluable in the efforts to better understand and ultimately treat patients suffering from leukemia. While important insights have been gleaned from these models, limitations must be acknowledged. In this review, we will highlight the various animal models of leukemia and describe their contributions to the improved understanding and treatment of these cancers.

Biology of chronic lymphocytic leukemia in different microenvironments: clinical and therapeutic implications

Chronic lymphocytic leukemia (CLL) is characterized by the accumulation of mature monoclonal B cells in peripheral blood, bone marrow, spleen, and lymph nodes. The trafficking, survival, and proliferation of CLL cells is tightly regulated by the surrounding tissue microenvironment and is mediated by antigenic stimulation, close interaction with various accessory cells and exposure to different cytokines, chemokines, and extracellular matrix components. In the last decade there have been major advances in the understanding of the reciprocal interactions between CLL cells and the various microenvironmental compartments. This article discusses the role of the microenvironment in the context of efforts to develop novel therapeutics that target the biology of CLL.

Modeling tumor-host interactions of chronic lymphocytic leukemia in xenografted mice to study tumor biology and evaluate targeted therapy

Chronic lymphocytic leukemia (CLL) cells depend on microenvironmental factors for proliferation and survival. In particular, the B-cell receptor (BCR) and NF-κB pathways are activated in the lymph node microenvironment. Thus, model systems mimicking tumor-host interactions are important tools to study CLL biology and pathogenesis. We investigated whether the recently established NOD/scid/γc^null (NSG) mouse xenograft model can recapitulate the effects of the human microenvironment. We assessed, therefore, tumor characteristics previously defined in lymph node-resident CLL cells, including proliferation, and activation of the BCR and NF-κB pathways. We found that the murine spleen microenvironment supported CLL cell proliferation and activation to a similar degree than the human lymph node, including induction of BCR and NF-κB signaling in the xenografted cells. Next, we used this model to study ibrutinib, a Bruton's tyrosine kinase inhibitor in clinical development. Ibrutinib inhibited BCR and NF-κB signaling induced by the microenvironment, decreased proliferation, induced apoptosis, and reduced the tumor burden in vivo. Thus, our data demonstrate that the spleen of xenografted NSG mice can, in part, recapitulate the role of the human lymph node for CLL cells. In addition, we show that ibrutinib effectively disrupts tumor-host interactions essential for CLL cell proliferation and survival in vivo.

Carbonyl group serum levels are associated with CD38 expression in patients with B chronic lymphocytic leukemia

OBJECTIVES

To evaluate carbonyl groups (CG) serum levels in B-chronic lymphocytic leukemia (B-CLL) patients.

DESIGN AND METHODS

CG serum levels were assessed in 48 B-CLL patients and in 30 control subjects.

RESULTS

CG were increased in B-CLL patients. We found a positive correlation between CG with CD38 expression and a negative correlation with ZAP 70 expression.

CONCLUSIONS

B-CLL patients displayed an unbalance of the oxidative stress. CG serum levels could be considered as a prognostic factor in B-CLL.