BITES and CARS and checkpoints, oh my! Updates regarding immunotherapy for myeloid malignancies from the 2018 annual ASH meeting

T cells with split CARs specific for NKG2D ligands and PD-L1 exhibit improved selectivity towards monocyte-derived cells while effective in eliminating acute myeloid leukaemia in vivo

PURPOSE

The expression of NKG2D ligands and PD-L1 has been detected on acute myeloid leukaemia (AML) cells, as well as normal cells of the myeloid lineage. To target leukemic cells while minimizing collateral damage to normal cells, we constructed a split dual CAR system based on the AND-gate logic.

METHODS

The NKG2D extracellular domain linked with DAP12 without a co-stimulatory signal was used for the basal activation of T cells, and used together with the PD-L1-specific chimeric costimulatory receptor containing the 4-1BB activating domain for co-stimulatory signal 2 input. This dual CAR displayed cell-type specificity and activity similar as a 2nd generation NKG2D ligand-specific CAR.

RESULTS

When compared to CD64 and PD-L1-specific 2nd generation CARs, we observed that the split dual CAR offered an improved myeloid cell type selectivity. For example, PD-L1-specific CAR-T cells lysed all tested myeloid cell types that expressed PD-L1, including M0 macrophages (Mø0), LPS-polarized Mø1, IFN-γ polarized Mø1, IL-4 polarized Mø2, monocytes, immature dendritic cells (imDCs), mature DCs, as well as KG-1 AML cells, while the dual CAR-T cells displaying killing activity only towards LPS polarized Mø1, mature DCs and KG-1 cells that expressed both NKG2D ligands and PD-L1. In a mouse liquid tumor model, the dual CAR-T cells were effective in eradicating established KG-1 AML xenografts.

CONCLUSION

The improved cell type specificity offered by our split dual CAR-T cell system targeting paired antigens would favour the reduction of the on-target off-tumor toxicity towards normal myeloid cells during the treatment of myeloid leukaemia.

Immune Checkpoint Inhibitors in Acute Myeloid Leukemia: A Meta-Analysis

Background

Experience with immune checkpoint inhibitors (ICIs) in the treatment of acute myeloid leukemia (AML) is still limited and based on early clinical trials, with no reported randomized clinical data. In this study, we reviewed the available evidence on the use of ICIs, either in monotherapy or in combination with other treatments, in different AML settings, including newly diagnosed AML, relapsed or refractory (R/R) AML and maintenance treatment after allogeneic-HSCT (allo-HSCT).

Materials and Methods

A systematic literature review was conducted using PubMed electronic database as primary source to identify the studies involving immune checkpoint inhibitors in first-line and R/R AML. We recorded Overall Response (ORR), Complete Response (CR) and Complete Response with incomplete count recovery (CRi) rates, overall survival (OS) and immune-related adverse events ≥ grade 3 (irAEs). Hereafter, we analyzed the overall profile of these ICIs by performing a meta-analysis of the reported outcomes.

Results

A total of 13 studies were identified where ICI was used in patients with AML. ORR across these studies was 42% (IC95%, 31% - 54%) and CR/CRi was 33% (IC95%, 22%-45%). Efficacy was also assessed considering the AML setting (first-line vs. relapsed/refractory) and results pointed to higher response rates in first-line, compared to R/R. Mean overall survival was 8.9 months [median 8 months, (IC95%, 3.9 - 15.5)]. Differences between first line and R/R settings were observed, since average overall survival in first line was 12.0 months, duplicating the OS in R/R which was 7.3 months. Additionally, the most specific adverse events (AEs) of these therapies are immune-related adverse events (irAEs), derived from their inflammatory effects. Grade ≥3 irAEs rate was low and similar among studies [12% (95%CI 8% - 16%)].

Conclusion

ICIs in combination with intensive chemotherapy, hypomethylating agents or other targeted therapies are gaining interest in the management of hematological malignancies such as AML. However, results obtained from clinical trials are modest and limited by both, the type of design and the clinical trial phase. Hopefully, the prospective study of these therapies in late-stage development could help to identify patients who may benefit from ICI therapy.

Immunotherapeutic Targeting of Mesothelin Positive Pediatric AML Using Bispecific T Cell Engaging Antibodies

Advances in the treatment of pediatric AML have been modest over the past four decades. Despite maximally intensive therapy, approximately 40% of patients will relapse. Novel targeted therapies are needed to improve outcomes. We identified mesothelin (MSLN), a well-validated target overexpressed in some adult malignancies, to be highly expressed on the leukemic cell surface in a subset of pediatric AML patients. The lack of expression on normal bone marrow cells makes MSLN a viable target for immunotherapies such as T-cell engaging bispecific antibodies (BsAbs) that combine two distinct antibody-variable regions into a single molecule targeting a cancer-specific antigen and the T-cell co-receptor CD3. Using antibody single-chain variable region (scFv) sequences derived from amatuximab-recognizing MSLN, and from either blinatumomab or AMG330 targeting CD3, we engineered and expressed two MSLN/CD3-targeting BsAbs: MSLNAMA-CD3L2K and MSLNAMA-CD3AMG, respectively. Both BsAbs promoted T-cell activation and reduced leukemic burden in MV4;11:MSLN xenografted mice, but not in those transplanted with MSLN-negative parental MV4;11 cells. MSLNAMA-CD3AMG induced complete remission in NTPL-146 and DF-5 patient-derived xenograft models. These data validate the in vivo efficacy and specificity of MSLN-targeting BsAbs. Because prior MSLN-directed therapies appeared safe in humans, MSLN-targeting BsAbs could be ideal immunotherapies for MSLN-positive pediatric AML patients.

Precision medicine in myeloid malignancies

Myeloid malignancies have always been at the forefront of an improved understanding of the molecular pathogenesis of cancer. In accordance, over the last years, basic research focusing on the aberrations underlying malignant transformation of myeloid cells has provided the basis for precision medicine approaches and subsequently has led to the development of powerful therapeutic strategies. In this review article, we will recapitulate what has happened since in the 1980s the use of all-trans retinoic acid (ATRA), as a first targeted cancer therapy, has changed one of the deadliest leukemia subtypes, acute promyelocytic leukemia (APL), into one that can be cured without classical chemotherapy today. Similarly, imatinib, the first molecularly designed cancer therapy, has revolutionized the management of chronic myeloid leukemia (CML). Thus, targeted treatment approaches have become the paradigm for myeloid malignancy, but many questions still remain unanswered, especially how identical mutations can be associated with different phenotypes. This might be linked to the impact of the cell of origin, gene-gene interactions, or the tumor microenvironment including the immune system. Continuous research in the field of myeloid neoplasia has started to unravel the molecular pathways that are not only crucial for initial treatment response, but also resistance of leukemia cells under therapy. Ongoing studies focusing on leukemia cell vulnerabilities do already point to novel (targetable) "Achilles heels" that can further improve myeloid cancer therapy.

Induced dendritic cells co-expressing GM-CSF/IFN-α/tWT1 priming T and B cells and automated manufacturing to boost GvL

Acute myeloid leukemia (AML) patients with minimal residual disease and receiving allogeneic hematopoietic stem cell transplantation (HCT) have poor survival. Adoptive administration of dendritic cells (DCs) presenting the Wilms tumor protein 1 (WT1) leukemia-associated antigen can potentially stimulate de novo T and B cell development to harness the graft-versus-leukemia (GvL) effect after HCT. We established a simple and fast genetic modification of monocytes for simultaneous lentiviral expression of a truncated WT1 antigen (tWT1), granulocyte macrophage-colony-stimulating factor (GM-CSF), and interferon (IFN)-α, promoting their self-differentiation into potent “induced DCs” (iDCtWT1). A tricistronic integrase-defective lentiviral vector produced under good manufacturing practice (GMP)-like conditions was validated. Transduction of CD14⁺ monocytes isolated from peripheral blood, cord blood, and leukapheresis material effectively induced their self-differentiation. CD34⁺ cell-transplanted Nod.Rag.Gamma (NRG)- and Nod.Scid.Gamma (NSG) mice expressing human leukocyte antigen (HLA)-A∗0201 (NSG-A2)-immunodeficient mice were immunized with autologous iDCtWT1. Both humanized mouse models showed improved development and maturation of human T and B cells in the absence of adverse effects. Toward clinical use, manufacturing of iDCtWT1 was up scaled and streamlined using the automated CliniMACS Prodigy system. Proof-of-concept clinical-scale runs were feasible, and the 38-h process enabled standardized production and high recovery of a cryopreserved cell product with the expected identity characteristics. These results advocate for clinical trials testing iDCtWT1 to boost GvL and eradicate leukemia.

Acute Myeloid Leukemia: From Biology to Clinical Practices Through Development and Pre-Clinical Therapeutics

Recent studies have provided several insights into acute myeloid leukemia. Studies based on molecular biology have identified eight functional mutations involved in leukemogenesis, including driver and passenger mutations. Insight into Leukemia stem cells (LSCs) and assessment of cell surface markers have enabled characterization of LSCs from hematopoietic stem and progenitor cells. Clonal evolution has been described as having an effect similar to that of microenvironment alterations. Such biological findings have enabled the development of new targeted drugs, including drug inhibitors and monoclonal antibodies with blockage functions. Some recently approved targeted drugs have resulted in new therapeutic strategies that enhance standard intensive chemotherapy regimens as well as supportive care regimens. Besides the progress made in adoptive immunotherapy, since allogenic hematopoietic stem cell transplantation enabled the development of new T-cell transfer therapies, such as chimeric antigen receptor T-cell and transgenic TCR T-cell engineering, new promising strategies that are investigated.

Advances in Acute Myeloid Leukemia: Recently Approved Therapies and Drugs in Development

Acute myeloid leukemia (AML) is a genetically heterogeneous malignancy comprised of various cytogenetic and molecular abnormalities that has notoriously been difficult to treat with an overall poor prognosis. For decades, treatment options were limited to either intensive chemotherapy with anthracycline and cytarabine-based regimens (7 + 3) or lower intensity regimens including hypomethylating agents or low dose cytarabine, followed by either allogeneic stem cell transplant or consolidation chemotherapy. Fortunately, with the influx of rapidly evolving molecular technologies and new genetic understanding, the treatment landscape for AML has dramatically changed. Advances in the formulation and delivery of 7 + 3 with liposomal cytarabine and daunorubicin (Vyxeos) have improved overall survival in secondary AML. Increased understanding of the genetic underpinnings of AML has led to targeting actionable mutations such as FLT3, IDH1/2 and TP53, and BCL2 or hedgehog pathways in more frail populations. Antibody drug conjugates have resurfaced in the AML landscape and there have been numerous advances utilizing immunotherapies including immune checkpoint inhibitors, antibody-drug conjugates, bispecific T cell engager antibodies, chimeric antigen receptor (CAR)-T therapy and the development of AML vaccines. While there are dozens of ongoing studies and new drugs in the pipeline, this paper serves as a review of the advances achieved in the treatment of AML in the last several years and the most promising future avenues of advancement.