Enhancing Fc-mediated effector functions of monoclonal antibodies: The example of HexaBodies.

Since the approval of the CD20-targeting monoclonal antibody (mAb) rituximab for the treatment of lymphoma in 1997, mAb therapy has significantly transformed cancer treatment. With over 90 FDA-approved mAbs for the treatment of various hematological and solid cancers, modern cancer treatment relies heavily on these therapies. The overwhelming success of mAbs as cancer therapeutics is attributed to their broad applicability, high safety profile, and precise targeting of cancer-associated surface antigens. Furthermore, mAbs can induce various anti-tumor cytotoxic effector mechanisms including antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP), and complement-dependent cytotoxicity (CDC), all of which are mediated via their fragment crystallizable (Fc) domain. Over the past decades, these effector mechanisms have been substantially improved through Fc domain engineering. In this review, we will outline the different approaches to enhance Fc effector functions via Fc engineering of mAbs, with a specific emphasis on the so-called "HexaBody" technology, which is designed to enhance the hexamerization of mAbs on the target cell surface, thereby inducing greater complement activation, CDC, and receptor clustering. The review will summarize the development, preclinical, and clinical testing of several HexaBodies designed for the treatment of B-cell malignancies, as well as the potential use of the HexaBody technology beyond Fc-mediated effector functions.

Response to DA-EPOCH-R is associated with activation of 'fitter' cytotoxic T-cells in patients with newly diagnosed double and triple hit high-grade B-cell lymphoma.

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CD38 knockout natural killer cells expressing an affinity optimized CD38 chimeric antigen receptor successfully target acute myeloid leukemia with reduced effector cell fratricide.

There is a strong biological rationale for the augmentation of allogeneic natural killer (NK) cell therapies with a chimeric antigen receptor (CAR) to enhance acute myeloid leukemia (AML) targeting. CD38 is an established immunotherapeutic target in multiple myeloma and under investigation as a target antigen in AML. CD38 expression on NK cells and its further induction during ex vivo NK cell expansion represents a barrier to the development of a CD38 CAR-NK cell therapy. We set out to develop a CD38 CAR-NK cell therapy for AML, first by using an NK cell line which has low baseline CD38 expression and subsequently healthy donor expanded NK cells. To overcome anticipated fratricide due to NK cell CD38 expression when using primary expanded NK cells, we applied CRISPR/Cas9 genome editing to disrupt the CD38 gene during expansion achieving a mean knockdown efficiency of 84%. The resulting CD38 KD expanded NK cells, after expression of an affinity optimized CD38 CAR, showed reduced NK cell fratricide and an enhanced ability to target primary AML blasts. Furthermore, the cytotoxic potential of CD38 CAR-NK cells was augmented by pre-treatment of the AML cells with all-trans retinoic acid which drove enhanced CD38 expression offering a rational combination therapy. These findings support the further investigation of CD38 KD - CD38 CAR-NK cells as a viable immunotherapeutic approach to the treatment of AML.

Preclinical Evaluation of Invariant Natural Killer T Cells Modified with CD38 or BCMA Chimeric Antigen Receptors for Multiple Myeloma.

Due to the CD1d restricted recognition of altered glycolipids, Vα24-invariant natural killer T (iNKT) cells are excellent tools for cancer immunotherapy with a significantly reduced risk for graft-versus-host disease when applied as off-the shelf-therapeutics across Human Leukocyte Antigen (HLA) barriers. To maximally harness their therapeutic potential for multiple myeloma (MM) treatment, we here armed iNKT cells with chimeric antigen receptors (CAR) directed against the MM-associated antigen CD38 and the plasma cell specific B cell maturation antigen (BCMA). We demonstrate that both CD38- and BCMA-CAR iNKT cells effectively eliminated MM cells in a CAR-dependent manner, without losing their T cell receptor (TCR)-mediated cytotoxic activity. Importantly, iNKT cells expressing either BCMA-CARs or affinity-optimized CD38-CARs spared normal hematopoietic cells and displayed a Th1-like cytokine profile, indicating their therapeutic utility. While the costimulatory domain of CD38-CARs had no influence on the cytotoxic functions of iNKT cells, CARs containing the 4-1BB domain showed a better expansion capacity. Interestingly, when stimulated only via CD1d+ dendritic cells (DCs) loaded with α-galactosylceramide (α-GalCer), both CD38- and BCMA-CAR iNKT cells expanded well, without losing their CAR- or TCR-dependent cytotoxic activities. This suggests the possibility of developing an off-the-shelf therapy with CAR iNKT cells, which might even be boostable in vivo by administration α-GalCer pulsed DCs.

Monoclonal antibodies targeting CD38 in hematological malignancies and beyond.

CD38 is a multifunctional cell surface protein that has receptor as well as enzyme functions. The protein is generally expressed at low levels on various hematological and solid tissues, while plasma cells express particularly high levels of CD38. The protein is also expressed in a subset of hematological tumors, and shows especially broad and high expression levels in plasma cell tumors such as multiple myeloma (MM). Together, this triggered the development of various therapeutic CD38 antibodies, including daratumumab, isatuximab, and MOR202. Daratumumab binds a unique CD38 epitope and showed strong anti-tumor activity in preclinical models. The antibody engages diverse mechanisms of action, including complement-dependent cytotoxicity, antibody-dependent cellular cytotoxicity, antibody-dependent cellular phagocytosis, programmed cell death, modulation of enzymatic activity, and immunomodulatory activity. CD38-targeting antibodies have a favorable toxicity profile in patients, and early clinical data show a marked activity in MM, while studies in other hematological malignancies are ongoing. Daratumumab has single agent activity and a limited toxicity profile, allowing favorable combination therapies with existing as well as emerging therapies, which are currently evaluated in the clinic. Finally, CD38 antibodies may have a role in the treatment of diseases beyond hematological malignancies, including solid tumors and antibody-mediated autoimmune diseases.

High-Parameter Mass Cytometry Evaluation of Relapsed/Refractory Multiple Myeloma Patients Treated with Daratumumab Demonstrates Immune Modulation as a Novel Mechanism of Action.

Daratumumab is a CD38-targeted human monoclonal antibody with direct anti-myeloma cell mechanisms of action. Flow cytometry in relapsed and/or refractory multiple myeloma (RRMM) patients treated with daratumumab revealed cytotoxic T-cell expansion and reduction of immune-suppressive populations, suggesting immune modulation as an additional mechanism of action. Here, we performed an in-depth analysis of the effects of daratumumab on immune-cell subpopulations using high-dimensional mass cytometry. Whole-blood and bone-marrow baseline and on-treatment samples from RRMM patients who participated in daratumumab monotherapy studies (SIRIUS and GEN501) were evaluated with high-throughput immunophenotyping. In daratumumab-treated patients, the intensity of CD38 marker expression decreased on many immune cells in SIRIUS whole-blood samples. Natural killer (NK) cells were depleted with daratumumab, with remaining NK cells showing increased CD69 and CD127, decreased CD45RA, and trends for increased CD25, CD27, and CD137 and decreased granzyme B. Immune-suppressive population depletion paralleled previous findings, and a newly observed reduction in CD38+ basophils was seen in patients who received monotherapy. After 2 months of daratumumab, the T-cell population in whole-blood samples from responders shifted to a CD8 prevalence with higher granzyme B positivity (P = 0.017), suggesting increased killing capacity and supporting monotherapy-induced CD8+ T-cell activation. High-throughput cytometry immune profiling confirms and builds upon previous flow cytometry data, including comparable CD38 marker intensity on plasma cells, NK cells, monocytes, and B/T cells. Interestingly, a shift toward cytolytic granzyme B+ T cells was also observed and supports adaptive responses in patients that may contribute to depth of response. © 2018 The Authors. Cytometry Part A published by Wiley Periodicals, Inc. on behalf of International Society for Advancement of Cytometry.

CD20 and CD37 antibodies synergize to activate complement by Fc-mediated clustering.

CD20 monoclonal antibody therapies have significantly improved the outlook for patients with B-cell malignancies. However, many patients acquire resistance, demonstrating the need for new and improved drugs. We previously demonstrated that the natural process of antibody hexamer formation on targeted cells allows for optimal induction of complement-dependent cytotoxicity. Complement-dependent cytotoxicity can be potentiated by introducing a single point mutation such as E430G in the IgG Fc domain that enhances intermolecular Fc-Fc interactions between cell-bound IgG molecules, thereby facilitating IgG hexamer formation. Antibodies specific for CD37, a target that is abundantly expressed on healthy and malignant B cells, are generally poor inducers of complement-dependent cytotoxicity. Here we demonstrate that introduction of the hexamerization-enhancing mutation E430G in CD37-specific antibodies facilitates highly potent complement-dependent cytotoxicity in chronic lymphocytic leukemia cells ex vivo Strikingly, we observed that combinations of hexamerization-enhanced CD20 and CD37 antibodies cooperated in C1q binding and induced superior and synergistic complement-dependent cytotoxicity in patient-derived cancer cells compared to the single agents. Furthermore, CD20 and CD37 antibodies colocalized on the cell membrane, an effect that was potentiated by the hexamerization-enhancing mutation. Moreover, upon cell surface binding, CD20 and CD37 antibodies were shown to form mixed hexameric antibody complexes consisting of both antibodies each bound to their own cognate target, so-called hetero-hexamers. These findings provide novel insights into the mechanisms of synergy in antibody-mediated complement-dependent cytotoxicity and provide a rationale to explore Fc-engineering and antibody hetero-hexamerization as a tool to enhance the cooperativity and therapeutic efficacy of antibody combinations.

Daratumumab depletes CD38+ immune regulatory cells, promotes T-cell expansion, and skews T-cell repertoire in multiple myeloma.

Daratumumab targets CD38-expressing myeloma cells through a variety of immune-mediated mechanisms (complement-dependent cytotoxicity, antibody-dependent cell-mediated cytotoxicity, and antibody-dependent cellular phagocytosis) and direct apoptosis with crosslinking. These mechanisms may also target nonplasma cells that express CD38, which prompted evaluation of daratumumab's effects on CD38-positive immune subpopulations. Peripheral blood (PB) and bone marrow (BM) from patients with relapsed/refractory myeloma from 2 daratumumab monotherapy studies were analyzed before and during therapy and at relapse. Regulatory B cells and myeloid-derived suppressor cells, previously shown to express CD38, were evaluated for immunosuppressive activity and daratumumab sensitivity in the myeloma setting. A novel subpopulation of regulatory T cells (Tregs) expressing CD38 was identified. These Tregs were more immunosuppressive in vitro than CD38-negative Tregs and were reduced in daratumumab-treated patients. In parallel, daratumumab induced robust increases in helper and cytotoxic T-cell absolute counts. In PB and BM, daratumumab induced significant increases in CD8(+):CD4(+) and CD8(+):Treg ratios, and increased memory T cells while decreasing naïve T cells. The majority of patients demonstrated these broad T-cell changes, although patients with a partial response or better showed greater maximum effector and helper T-cell increases, elevated antiviral and alloreactive functional responses, and significantly greater increases in T-cell clonality as measured by T-cell receptor (TCR) sequencing. Increased TCR clonality positively correlated with increased CD8(+) PB T-cell counts. Depletion of CD38(+) immunosuppressive cells, which is associated with an increase in T-helper cells, cytotoxic T cells, T-cell functional response, and TCR clonality, represents possible additional mechanisms of action for daratumumab and deserves further exploration.

CD38 expression and complement inhibitors affect response and resistance to daratumumab therapy in myeloma.

The anti-CD38 monoclonal antibody daratumumab is well tolerated and has high single agent activity in heavily pretreated relapsed and refractory multiple myeloma (MM). However, not all patients respond, and many patients eventually develop progressive disease to daratumumab monotherapy. We therefore examined whether pretreatment expression levels of CD38 and complement-inhibitory proteins (CIPs) are associated with response and whether changes in expression of these proteins contribute to development of resistance. In a cohort of 102 patients treated with daratumumab monotherapy (16 mg/kg), we found that pretreatment levels of CD38 expression on MM cells were significantly higher in patients who achieved at least partial response (PR) compared with patients who achieved less than PR. However, cell surface expression of the CIPs, CD46, CD55, and CD59, was not associated with clinical response. In addition, CD38 expression was reduced in both bone marrow-localized and circulating MM cells, following the first daratumumab infusion. CD38 expression levels on MM cells increased again following daratumumab discontinuation. In contrast, CD55 and CD59 levels were significantly increased on MM cells only at the time of progression. All-trans retinoic acid increased CD38 levels and decreased CD55 and CD59 expression on MM cells from patients who developed daratumumab resistance, to approximately pretreatment values. This resulted in significant enhancement of daratumumab-mediated complement-dependent cytotoxicity. Together, these data demonstrate an important role for CD38 and CIP expression levels in daratumumab sensitivity and suggest that therapeutic combinations that alter CD38 and CIP expression levels should be investigated in the treatment of MM. These trials were registered at www.clinicaltrials.gov as #NCT00574288 (GEN501) and #NCT01985126 (SIRIUS).

Phase 1/2 study of lenalidomide combined with low-dose cyclophosphamide and prednisone in lenalidomide-refractory multiple myeloma.

The prognosis of multiple myeloma (MM) patients who become refractory to lenalidomide and bortezomib is very poor, indicating the need for new therapeutic strategies for these patients. Next to the development of new drugs, the strategy of combining agents with synergistic activity may also result in clinical benefit for patients with advanced myeloma. We have previously shown in a retrospective analysis that lenalidomide combined with continuous low-dose cyclophosphamide and prednisone (REP) had remarkable activity in heavily pretreated, lenalidomide-refractory MM patients. To evaluate this combination prospectively, we initiated a phase 1/2 study to determine the optimal dose and to assess its efficacy and safety in lenalidomide-refractory MM patients. The maximum tolerated dose (MTD) was defined as 25 mg lenalidomide (days 1-21/28 days), combined with continuous cyclophosphamide (50 mg/d) and prednisone (20 mg/d). At the MTD (n = 67 patients), the overall response rate was 67%, and at least minimal response was achieved in 83% of the patients. Median progression-free survival and overall survival were 12.1 and 29.0 months, respectively. Similar results were achieved in the subset of patients with lenalidomide- and bortezomib-refractory disease as well as in patients with high-risk cytogenetic abnormalities, defined as t(4;14), t(14;16), del(17p), and/or ampl(1q) as assessed by fluorescence in situ hybridization. Neutropenia (22%) and thrombocytopenia (22%) were the most common grade 3-4 hematologic adverse events. Infections (21%) were the most common grade 3-5 nonhematologic adverse events. In conclusion, the addition of continuous low-dose oral cyclophosphamide to lenalidomide and prednisone offers a new therapeutic perspective for multidrug refractory MM patients. This trial was registered at www.clinicaltrials.gov as #NCT01352338.

A Rational Strategy for Reducing On-Target Off-Tumor Effects of CD38-Chimeric Antigen Receptors by Affinity Optimization.

Chimeric antigen receptors (CARs) can effectively redirect cytotoxic T cells toward highly expressed surface antigens on tumor cells. The low expression of several tumor-associated antigens (TAAs) on normal tissues, however, hinders their safe targeting by CAR T cells due to on-target/off-tumor effects. Using the multiple myeloma (MM)-associated CD38 antigen as a model system, here, we present a rational approach for effective and tumor-selective targeting of such TAAs. Using "light-chain exchange" technology, we combined the heavy chains of two high-affinity CD38 antibodies with 176 germline light chains and generated ∼124 new antibodies with 10- to >1,000-fold lower affinities to CD38. After categorizing them into three distinct affinity classes, we incorporated the single-chain variable fragments of eight antibodies from each class into new CARs. T cells carrying these CD38-CARs were extensively evaluated for their on-tumor/off-tumor cytotoxicity as well as CD38-dependent proliferation and cytokine production. We identified CD38-CAR T cells of ∼1,000- fold reduced affinity, which optimally proliferated, produced Th1-like cytokines, and effectively lysed CD382+ MM cells, but spared CD38+ healthy hematopoietic cells in vitro and in vivo. Thus, this systematic approach is highly suitable for the generation of optimal CARs for effective and selective targeting of TAAs.

A genome-wide association study identifies a functional ERAP2 haplotype associated with birdshot chorioretinopathy.

Birdshot chorioretinopathy (BSCR) is a rare form of autoimmune uveitis that can lead to severe visual impairment. Intriguingly, >95% of cases carry the HLA-A29 allele, which defines the strongest documented HLA association for a human disease. We have conducted a genome-wide association study in 96 Dutch and 27 Spanish cases, and 398 unrelated Dutch and 380 Spanish controls. Fine-mapping the primary MHC association through high-resolution imputation at classical HLA loci, identified HLA-A*29:02 as the principal MHC association (odds ratio (OR) = 157.5, 95% CI 91.6-272.6, P = 6.6 × 10(-74)). We also identified two novel susceptibility loci at 5q15 near ERAP2 (rs7705093; OR = 2.3, 95% CI 1.7-3.1, for the T allele, P = 8.6 × 10(-8)) and at 14q32.31 in the TECPR2 gene (rs150571175; OR = 6.1, 95% CI 3.2-11.7, for the A allele, P = 3.2 × 10(-8)). The association near ERAP2 was confirmed in an independent British case-control samples (combined meta-analysis P = 1.7 × 10(-9)). Functional analyses revealed that the risk allele of the polymorphism near ERAP2 is strongly associated with high mRNA and protein expression of ERAP2 in B cells. This study further defined an extremely strong MHC risk component in BSCR, and detected evidence for a novel disease mechanism that affects peptide processing in the endoplasmic reticulum.

Pre-clinical evaluation of CD38 chimeric antigen receptor engineered T cells for the treatment of multiple myeloma.

Adoptive transfer of chimeric antigen receptor-transduced T cells is a promising strategy for cancer immunotherapy. The CD38 molecule, with its high expression on multiple myeloma cells, appears a suitable target for antibody therapy. Prompted by this, we used three different CD38 antibody sequences to generate second-generation retroviral CD38-chimeric antigen receptor constructs with which we transduced T cells from healthy donors and multiple myeloma patients. We then evaluated the preclinical efficacy and safety of the transduced T cells. Irrespective of the donor and antibody sequence, CD38-chimeric antigen receptor-transduced T cells proliferated, produced inflammatory cytokines and effectively lysed malignant cell lines and primary malignant cells from patients with acute myeloid leukemia and multi-drug resistant multiple myeloma in a cell-dose, and CD38-dependent manner, despite becoming CD38-negative during culture. CD38-chimeric antigen receptor-transduced T cells also displayed significant anti-tumor effects in a xenotransplant model, in which multiple myeloma tumors were grown in a human bone marrow-like microenvironment. CD38-chimeric antigen receptor-transduced T cells also appeared to lyse the CD38(+) fractions of CD34(+) hematopoietic progenitor cells, monocytes, natural killer cells, and to a lesser extent T and B cells but did not inhibit the outgrowth of progenitor cells into various myeloid lineages and, furthermore, were effectively controllable with a caspase-9-based suicide gene. These results signify the potential importance of CD38-chimeric antigen receptor-transduced T cells as therapeutic tools for CD38(+) malignancies and warrant further efforts to diminish the undesired effects of this immunotherapy using appropriate strategies.

Outcome of allogeneic transplantation in newly diagnosed and relapsed/refractory multiple myeloma: long-term follow-up in a single institution.

Allogeneic stem cell transplantation (allo-SCT) has the potential to induce long-term remission in multiple myeloma (MM), but the role of allo-SCT in MM is controversial due to the high rate of treatment-related mortality (TRM). However, although proteasome inhibitors and immunomodulatory drugs have improved the outcome of patients with MM, high-risk patients still have a very poor prognosis. This indicates the need for new treatment strategies and identification of patients who might benefit from allo-SCT. We therefore analyzed the outcome of one hundred and forty-seven patients with MM who received an allo-SCT at our institution (58 in first line, 89 in relapsed/refractory setting) after a median follow-up of 88.8 months. For the first-line setting, median progression-free survival (PFS) and overall survival (OS) were remarkably good, with a CR rate of 48.3%, median PFS of 30.2 months, and 10-yr OS of 51%. We found no difference in outcome for patients with high-risk metaphase cytogenetics or FISH del(13q14), but efficacy in current standard high-risk patients could not be determined. The outcome in the relapsed/refractory setting was poor, especially in the subgroup of patients relapsing within 18 months after auto-SCT. Therefore, if applied at all in these patients, improvement of allo-SCT is needed, focusing on reduction of TRM and more effective immunotherapy.

Altered peptide ligands revisited: vaccine design through chemically modified HLA-A2-restricted T cell epitopes.

Virus or tumor Ag-derived peptides that are displayed by MHC class I molecules are attractive starting points for vaccine development because they induce strong protective and therapeutic cytotoxic T cell responses. In thus study, we show that the MHC binding and consequent T cell reactivity against several HLA-A*02 restricted epitopes can be further improved through the incorporation of nonproteogenic amino acids at primary and secondary anchor positions. We screened more than 90 nonproteogenic, synthetic amino acids through a range of epitopes and tested more than 3000 chemically enhanced altered peptide ligands (CPLs) for binding affinity to HLA-A*0201. With this approach, we designed CPLs of viral epitopes, of melanoma-associated Ags, and of the minor histocompatibility Ag UTA2-1, which is currently being evaluated for its antileukemic activity in clinical dendritic cell vaccination trials. The crystal structure of one of the CPLs in complex with HLA-A*0201 revealed the molecular interactions likely responsible for improved binding. The best CPLs displayed enhanced affinity for MHC, increasing MHC stability and prolonging recognition by Ag-specific T cells and, most importantly, they induced accelerated expansion of antitumor T cell frequencies in vitro and in vivo as compared with the native epitope. Eventually, we were able to construct a toolbox of preferred nonproteogenic residues with which practically any given HLA-A*02 restricted epitope can be readily optimized. These CPLs could improve the therapeutic outcome of vaccination strategies or can be used for ex vivo enrichment and faster expansion of Ag-specific T cells for transfer into patients.

Daratumumab-mediated lysis of primary multiple myeloma cells is enhanced in combination with the human anti-KIR antibody IPH2102 and lenalidomide.

Despite recent treatment improvements, multiple myeloma remains an incurable disease. Since antibody-dependent cell-mediated cytotoxicity is an important effector mechanism of daratumumab, we explored the possibility of improving daratumumab-mediated cell-mediated cytotoxicity by blocking natural killer cell inhibitory receptors with the human monoclonal anti-KIR antibody IPH2102, next to activation of natural killer cells with the immune modulatory drug lenalidomide. In 4-hour antibody-dependent cell-mediated cytotoxicity assays, IPH2102 did not induce lysis of multiple myeloma cell lines, but it did significantly augment daratumumab-induced myeloma cell lysis. Also in an ex vivo setting, IPH2102 synergistically improved daratumumab-dependent lysis of primary myeloma cells in bone marrow mononuclear cells (n=21), especially in patients carrying the FcγRIIIa-158F allele or the FcγRIIa-131R allele, who bind IgG1 with lower affinity than patients carrying the FcγRIIIa-158V allele or the FcγRIIa-131H allele. Finally, a further synergistically improved myeloma cell lysis with the daratumumab-IPH2102 combination was observed by adding lenalidomide, which suggests that more effective treatment strategies can be designed for multiple myeloma by combining daratumumab with agents that independently modulate natural killer cell function.

Reconstructing the human hematopoietic niche in immunodeficient mice: opportunities for studying primary multiple myeloma.

Interactions within the hematopoietic niche in the BM microenvironment are essential for maintenance of the stem cell pool. In addition, this niche is thought to serve as a sanctuary site for malignant progenitors during chemotherapy. Therapy resistance induced by interactions with the BM microenvironment is a major drawback in the treatment of hematologic malignancies and bone-metastasizing solid tumors. To date, studying these interactions was hampered by the lack of adequate in vivo models that simulate the human situation. In the present study, we describe a unique human-mouse hybrid model that allows engraftment and outgrowth of normal and malignant hematopoietic progenitors by implementing a technology for generating a human bone environment. Using luciferase gene marking of patient-derived multiple myeloma cells and bioluminescent imaging, we were able to follow pMM cells outgrowth and to visualize the effect of treatment. Therapeutic interventions in this model resulted in equivalent drug responses as observed in the corresponding patients. This novel human-mouse hybrid model creates unprecedented opportunities to investigate species-specific microenvironmental influences on normal and malignant hematopoietic development, and to develop and personalize cancer treatment strategies.