Generation and preclinical characterization of a Fc-optimized GITR-Ig fusion protein for induction of NK cell reactivity against leukemia

Contribution of immune cells to bone metastasis pathogenesis

Bone metastasis is closely related to the survival rate of cancer patients and reduces their quality of life. The bone marrow microenvironment contains a complex immune cell component with a local microenvironment that is conducive to tumor formation and growth. In this unique immune environment, a variety of immune cells, including T cells, natural killer cells, macrophages, dendritic cells, and myeloid-derived suppressor cells, participate in the process of bone metastasis. In this review, we will introduce the interactions between immune cells and cancer cells in the bone microenvironment, obtain the details of their contributions to the implications of bone metastasis, and discuss immunotherapeutic strategies targeting immune cells in cancer patients with bone metastasis.

Immunoprofiling of 4-1BB Expression Predicts Outcome in Chronic Lymphocytic Leukemia (CLL)

Recent success of novel therapies has improved treatment of chronic lymphocytic leukemia (CLL) patients, but most of them still require several treatment regimes. To improve treatment choice, prognostic markers suitable for prediction of disease outcome are required. Several molecular/genetic markers have been established, but accessibility for the entirety of all patients is limited. We here evaluated the relevance of GITR/4-1BB as well as their ligands for the prognosis of CLL patients. Surface expression of GITR/GITRL and 4-1BB/4-1BBL was correlated with established prognostic markers. Next, we separated our patient population according to GITR/GITRL and 4-1BB/4-1BBL expression in groups with high/low expression levels and performed Kaplan-Meier analyses. Interestingly, no correlation was observed with the defined prognostic markers. Whereas no significant difference between high and low expression of GITR, GITRL and 4-1BBL was observed, high 4-1BB levels on leukemic cells were associated with significantly shorter survival. Thereby we identify 4-1BB as prognostic marker for CLL.

An Fc-Optimized CD133 Antibody for Induction of NK Cell Reactivity against B Cell Acute Lymphoblastic Leukemia

Simple Summary

B cell acute lymphoblastic leukemia (B-ALL) is a common blood cancer characterized by proliferating and accumulating malignant, immature B cells within the body. Despite recent successes in B-ALL therapy, there is still a need for new therapeutic options. In the present study, we report on the characterization of 293C3-SDIE for the treatment of B-ALL. 293C3-SDIE is an improved anti-tumor antibody targeting CD133, a common protein on the surface of B-ALL cells. We demonstrated that 293C3-SDIE specifically induces activation of natural killer cells, which leads to lysis of B-ALL cells. Based on this study, we conclude that CD133 serves as a target for immune therapy, and treatment with 293C3-SDIE represents a promising therapeutic option in B-ALL therapy and warrants further preclinical and clinical evaluation.

Abstract

In recent decades, antibody-dependent cellular cytotoxicity (ADCC)-inducing monoclonal antibodies (mAbs) have revolutionized cancer immunotherapy, and Fc engineering strategies have been utilized to further improve efficacy. A promising option is to enhance the affinity of an antibody’s Fc-part to the Fc-receptor CD16 by altering the amino acid sequence. Herein, we characterized an S239D/I332E-modified CD133 mAb termed 293C3-SDIE for treatment of B cell acute lymphoblastic leukemia (B-ALL). Flow cytometric analysis revealed CD133 expression on B-ALL cell lines and leukemic cells of 50% (14 of 28) B-ALL patients. 293C3-SDIE potently induced NK cell reactivity against the B-ALL cell lines SEM and RS4;11, as well as leukemic cells of B-ALL patients in a target antigen-dependent manner, as revealed by analysis of NK cell activation, degranulation, and cytotoxicity. Of note, CD133 expression did not correlate with BCR-ABL, CD19, CD20, or CD22, which are presently used as therapeutic targets in B-ALL, which revealed CD133 as an independent target for B-ALL treatment. Increased CD133 expression was also observed in MLL-AF4-rearranged B-ALL, indicating that 293C3-SDIE may constitute a particularly suitable treatment option in this hard-to-treat subpopulation. Taken together, our results identify 293C3-SDIE as a promising therapeutic agent for the treatment of B-ALL.

Alterations of NK Cell Phenotype in the Disease Course of Multiple Myeloma

Simple Summary

Multiple myeloma (MM) is a deadly cancer localized in the bone marrow, where changes can support progression and therapy resistance. This study examined the expression of numerous biological markers on natural killer (NK) cells in blood and bone marrow of patients with MM. NK cells play key roles in the innate immunosurveillance of MM, so we sought to identify biomarkers on NK cells that may be prognostic for patient outcomes and identify new therapeutic targets in these patients. Biomarker expression was compared on NK cells between MM disease stages and healthy donors, between blood and bone marrow, and associations with disease progression. The study shows that loss of certain biomarkers on NK cells may limit their anti-tumor function in MM patients, that several drug-targetable biomarkers are upregulated on NK cells, and that high expression of the biomarker, SLAMF7, may have prognostic potential to identify patients more likely to show rapid disease progression.

Abstract

Accumulating evidence demonstrates important roles for natural killer (NK) cells in controlling multiple myeloma (MM). A prospective flow cytometry-based analysis of NK cells in the blood and bone marrow (BM) of MM patient subgroups was performed (smoldering (SMM), newly diagnosed (ND), relapsed/refractory, (RR) and post-stem cell transplantation (pSCT)). Assessments included the biomarker expression and function of NK cells, correlations between the expression of receptors on NK cells with their ligands on myeloma cells, and comparisons between MM patient subgroups and healthy controls. The most striking differences from healthy controls were found in RR and pSCT patients, in which NK cells were less mature and expressed reduced levels of the activating receptors DNAM-1, NKG2D, and CD16. These differences were more pronounced in the BM than in blood, including upregulation of the therapeutic targets TIM3, TIGIT, ICOS, and GITR. Their expression suggests NK cells became exhausted upon chronic encounters with the tumor. A high expression of SLAMF7 on blood NK cells correlated with shorter progression-free survival. This correlation was particularly evident in ND patients, including on mature CD56^dim NK cells in the BM. Thus, our NK cell analysis identified possible therapeutic targets in MM and a biomarker with prognostic potential for disease progression.

Natural killer cell-based immunotherapy for acute myeloid leukemia

Despite considerable progress has been achieved in the treatment of acute myeloid leukemia over the past decades, relapse remains a major problem. Novel therapeutic options aimed at attaining minimal residual disease-negative complete remission are expected to reduce the incidence of relapse and prolong survival. Natural killer cell-based immunotherapy is put forward as an option to tackle the unmet clinical needs. There have been an increasing number of therapeutic dimensions ranging from adoptive NK cell transfer, chimeric antigen receptor-modified NK cells, antibodies, cytokines to immunomodulatory drugs. In this review, we will summarize different forms of NK cell-based immunotherapy for AML based on preclinical investigations and clinical trials.

GITR controls intestinal inflammation by suppressing IL-15-dependent NK cell activity

Glucocorticoid-induced TNFR family related gene (GITR) is a member of the TNFR superfamily that is expressed on cells of the immune system. Although the protective and pathogenic roles of GITR in T cell immunity are well characterized, the role of GITR in innate immunity in the intestinal tissues has not been well clarified. In this study, using a dextran sulfate sodium (DSS)-induced colitis model in mice, we found that GITR-deficiency rendered mice more susceptible to acute intestinal inflammation and that a significantly higher number of activated natural killer (NK) cells was accumulated in the colonic lamina propria of Gitr^-/- mice as compared to wild-type mice. Additionally, Rag2^-/- Gitr^-/- mice, which lack T cells but have NK cells, also displayed more severe colonic inflammation than Rag2^-/- mice. In contrast, an anti-GITR agonistic antibody significantly alleviated colitis in Rag2^-/- mice. Engagement of GITR inhibited IL-15-mediated activating signaling events in NK cells, which include cell activation and proliferation, and production of cytokines and cytotoxic granules. Taken together, our results provide the first evidence that GITR negatively controls intestinal inflammation through NK cell functions.

Induction of NK Cell Reactivity against B-Cell Acute Lymphoblastic Leukemia by an Fc-Optimized FLT3 Antibody

Antibody-dependent cellular cytotoxicity (ADCC) is a major mechanism by which antitumor antibodies mediate therapeutic efficacy. At present, we evaluate an Fc-optimized (amino acid substitutions S239D/I332E) FLT3 antibody termed 4G8-SDIEM (FLYSYN) in patients with acute myeloid leukemia (NCT02789254). Here we studied the possibility to induce NK cell ADCC against B-cell acute lymphoblastic leukemia (B-ALL) by Fc-optimized FLT3 antibody treatment. Flow cytometric analysis confirmed that FLT3 is widely expressed on B-ALL cell lines and leukemic cells of B-ALL patients. FLT3 expression did not correlate with that of CD20, which is targeted by Rituximab, a therapeutic monoclonal antibody (mAb) employed in B-ALL treatment regimens. Our FLT3 mAb with enhanced affinity to the Fc receptor CD16a termed 4G8-SDIE potently induced NK cell reactivity against FLT3-transfectants, the B-ALL cell line SEM and primary leukemic cells of adult B-ALL patients in a target-antigen dependent manner as revealed by analyses of NK cell activation and degranulation. This was mirrored by potent 4G8-SDIE mediated NK cell ADCC in experiments with FLT3-transfectants, the cell line SEM and primary cells as target cells. Taken together, the findings presented in this study provide evidence that 4G8-SDIE may be a promising agent for the treatment of B-ALL, particularly in CD20-negative cases.

An Fc-Optimized CD133 Antibody for Induction of Natural Killer Cell Reactivity against Colorectal Cancer

The introduction of monoclonal antibodies (mAbs) has largely improved treatment options for cancer patients. The ability of antitumor mAbs to elicit antibody-dependent cellular cytotoxicity (ADCC) contributes to a large extent to their therapeutic efficacy. Many efforts accordingly aim to improve this important function by engineering mAbs with Fc parts that display enhanced affinity to the Fc receptor CD16 expressed, e.g., on natural killer (NK) cells. Here we characterized the CD133 mAb 293C3-SDIE that contains an engineered Fc part modified by the amino acid exchanges S239D/I332E—that reportedly increase the affinity to CD16—with regard to its ability to induce NK reactivity against colorectal cancer (CRC). 293C3-SDIE was found to be a stable protein with favorable binding characteristics achieving saturating binding to CRC cells at concentrations of approximately 1 µg/mL. While not directly affecting CRC cell growth and viability, 293C3-SDIE potently induced NK cell activation, degranulation, secretion of Interferon-γ, as well as ADCC resulting in potent lysis of CRC cell lines. Based on the preclinical characterization presented in this study and the available data indicating that CD133 is broadly expressed in CRC and represents a negative prognostic marker, we conclude that 293C3-SDIE constitutes a promising therapeutic agent for the treatment of CRC and thus warrants clinical evaluation.

The Uncovered Role of Immune Cells and NK Cells in the Regulation of Bone Metastasis

Bone is one of the main metastatic sites of solid tumors like breast, lung, and prostate cancer. Disseminated tumor cells (DTCs) and cancer stem cells (CSCs) represent the main target to counteract bone metastatization. These cells often localize in bone marrow (BM) at level of pre-metastatic niche: they can remain dormant for years or directly grow and create bone lesion, according to the different stimulations received in BM. The immune system in bone marrow is dampened and represents an appealing site for DTCs/CSCs. NK cells have an important role in controlling tumor progression, but their involvement in bone metastasis formation is an interesting and not fully investigated issue. Indeed, whether NK cells can interfere with CSC formation, kill them at the site of primary tumor, during circulation or in the pre-metastic niche needs to be elucidated. This review focuses on different aspects that regulate DTC/CSC life in bone and how NK cells potentially control bone metastasis formation.

Therapeutic Antibodies for Myeloid Neoplasms-Current Developments and Future Directions

Therapeutic monoclonal antibodies (mAbs) such as antibody-drug conjugates, ligand-receptor antagonists, immune checkpoint inhibitors and bispecific T cell engagers have shown impressive efficacy in the treatment of multiple human cancers. Numerous therapeutic mAbs that have been developed for myeloid neoplasms, including acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS), are currently investigated in clinical trials. Because AML and MDS originate from malignantly transformed hematopoietic stem/progenitor cells-the so-called leukemic stem cells (LSCs) that are highly resistant to most standard drugs-these malignancies frequently relapse and have a high disease-specific mortality. Therefore, combining standard chemotherapy with antileukemic mAbs that specifically target malignant blasts and particularly LSCs or utilizing mAbs that reinforce antileukemic host immunity holds great promise for improving patient outcomes. This review provides an overview of therapeutic mAbs for AML and MDS. Antibody targets, the molecular mechanisms of action, the efficacy in preclinical leukemia models, and the results of clinical trials are discussed. New developments and future studies of therapeutic mAbs in myeloid neoplasms will advance our understanding of the immunobiology of these diseases and enhance current therapeutic strategies.

Prognostic relevance of HER2/neu in acute lymphoblastic leukemia and induction of NK cell reactivity against primary ALL blasts by trastuzumab

The epidermal growth factor receptor HER2/neu is expressed on various cancers and represents a negative prognostic marker, but is also a target for the therapeutic monoclonal antibody Trastuzumab. In about 30% of cases, HER2/neu is expressed on acute lymphoblastic leukemia (ALL) cells and was proposed to be associated with a deleterious prognosis. Here we evaluated clinical data from 65 ALL patients (HER2/neu+, n = 17; HER2/neu-, n = 48) with a median follow-up of 19.4 months (range 0.6-176.5 months) and observed no association of HER2/neu expression with response to chemotherapy, disease free or overall survival. In vitro, treatment of primary ALL cells (CD20+HER2/neu+, CD20+HER2/neu- and CD20-HER2/neu-) with Rituximab and Trastuzumab led to activation of NK cells in strict dependence of the expression of the respective antigen. NK reactivity was more pronounced with Rituximab as compared to Trastuzumab, and combined application could lead to additive effects in cases where both antigens were expressed. Besides providing evidence that HER2/neu expression is no risk factor in ALL patients, our data demonstrates that HER2/neu can be a promising target for Trastuzumab therapy in the subset of ALL patients with the potential to improve disease outcome.

Decitabine Enhances Lymphocyte Migration and Function and Synergizes with CTLA-4 Blockade in a Murine Ovarian Cancer Model

The lack of second-line treatment for relapsed ovarian cancer necessitates the development of improved combination therapies. Targeted therapy and immunotherapy each confer clinical benefit, albeit limited as monotherapies. Ovarian cancer is not particularly responsive to immune checkpoint blockade, so combination with a complementary therapy may be beneficial. Recent studies have revealed that a DNA methyl transferase inhibitor, azacytidine, alters expression of immunoregulatory genes in ovarian cancer. In this study, the antitumor effects of a related DNA methyl transferase inhibitor, decitabine (DAC), were demonstrated in a syngeneic murine ovarian cancer model. Low-dose DAC treatment increases the expression of chemokines that recruit NK cells and CD8(+) T cells, promotes their production of IFNγ and TNFα, and extends the survival of mice bearing subcutaneous or orthotopic tumors. While neither DAC nor immune checkpoint blockade confers durable responses as a monotherapy in this model, the efficacy of anti-CTLA-4 was potentiated by combination with DAC. This combination promotes differentiation of naïve T cells into effector T cells and prolongs cytotoxic lymphocyte responses as well as mouse survival. These results suggest that this combination therapy may be worthy of further consideration for improved treatment of drug-resistant ovarian cancer.

Present and Future of Allogeneic Natural Killer Cell Therapy

Natural killer (NK) cells are innate lymphocytes that are capable of eliminating tumor cells and are therefore used for cancer therapy. Although many early investigators used autologous NK cells, including lymphokine-activated killer cells, the clinical efficacies were not satisfactory. Meanwhile, human leukocyte antigen (HLA)-haploidentical hematopoietic stem cell transplantation revealed the antitumor effect of allogeneic NK cells, and HLA-haploidentical, killer cell immunoglobulin-like receptor ligand-mismatched allogeneic NK cells are currently used for many protocols requiring NK cells. Moreover, allogeneic NK cells from non-HLA-related healthy donors have been recently used in cancer therapy. The use of allogeneic NK cells from non-HLA-related healthy donors allows the selection of donor NK cells with higher flexibility and to prepare expanded, cryopreserved NK cells for instant administration without delay for ex vivo expansion. In cancer therapy with allogeneic NK cells, optimal matching of donors and recipients is important to maximize the efficacy of the therapy. In this review, we summarize the present state of allogeneic NK cell therapy and its future directions.

Impaired NK cells and increased T regulatory cell numbers during cytotoxic maintenance therapy in AML

Cyclic cytotoxic maintenance therapy can be applied to patients with AML in post-remission. We studied the immune status of AML patients in complete remission and the effect of maintenance therapy on different immune cell populations. Patients in complete remission had reduced NK, TH and Treg counts and a reduced NK activation capacity. In the course of cytotoxic maintenance therapy, NK counts further declined, while TH and Treg cells increased, with lower proliferative potential of TH cells. We conclude that immunotherapeutic approaches in post-remission have to consider reduced NK cell function and further impairment of cellular immune responses during cytotoxic therapy.

Combination immune therapies to enhance anti-tumor responses by NK cells

Natural killer (NK) cells are critical innate immune lymphocytes capable of destroying virally infected or cancerous cells through targeted cytotoxicity and further assisting in the immune response by releasing inflammatory cytokines. NK cells are thought to contribute to the process of tumor killing by certain therapeutic monoclonal antibodies (mAb) by directing antibody-dependent cellular cytotoxicity (ADCC) through FcγRIIIA (CD16). Numerous therapeutic mAb have been developed that target distinct cancer-specific cell markers and may direct NK cell-mediated ADCC. Recent therapeutic approaches have combined some of these cancer-specific mAb with additional strategies to optimize NK cell cytotoxicity. These include agonistic mAb targeting NK cell activating receptors and mAbs blocking NK cell inhibitory receptors to enhance NK cell functions. Furthermore, several drugs that can potentiate NK cell cytotoxicity through other mechanisms are being used in combination with therapeutic mAb. In this review, we examine the mechanisms employed by several promising agents used in combination therapies that enhance natural or Ab-dependent cytotoxicity of cancer cells by NK cells, with a focus on treatments for leukemia and multiple myeloma.