Chimeric-antigen receptor T-cell (CAR-T) therapy is a novel cellular therapy whereby T-cells are collected via apheresis and genetically modified to target specific antigens, e.g. CD19 on B cells, then reinfused after lymphodepleting chemotherapy [1]. The first adult patient received CAR-T therapy in 2010 for refractory chronic lymphocytic leukaemia and the first paediatric patient received CAR-T therapy in 2012 for refractory B-cell acute lymphoblastic leukaemia (ALL) [1]. In the 14 years since, CAR-T therapy has grown substantially with research aiming to expand its usage into other indications. However, generating CAR-T to target antigens other than those on B-cells poses various challenges. Exciting new results in the development of novel cellular therapies and CAR-T for both paediatric and adult patients were presented at the 50th annual European Society for Blood and Marrow Transplantation (EBMT) Congress in Glasgow, Scotland in April 2024.
Relapsed or refractory paediatric T-cell ALL has poor outcomes with <50% five-year overall survival [2] and relapsed T-ALL after allogeneic hematopoietic stem cell transplantation (HSCT) has <15% long-term survival [3]. However, as discussed in the 'Paediatric Diseases Working Party' session [4] use of CAR-T therapy in T-ALL is complicated by shared antigen expression on both normal and leukaemic T-cells resulting in fratricide (self-killing) of CAR-T cells and subsequent limitation of in vivo CAR-T proliferation. Successful CAR-T expansion and persistence then results in T-cell aplasia with severe consequences of profound immunodeficiency. Furthermore, collection of autologous T-cells risks product contamination resulting in accidental generation of CAR-modified leukaemic T-cells [Fig. 1]. Chiesa [5] from Great Ormond Street Hospital, United Kingdom presented initial results of an open-label, single-centre phase 1 trial of allogeneic base-edited (BE) CD7 CAR-T therapy for relapsed T-ALL (NCT05397184). Donor T-cells have no risk of leukaemic contamination and via CRISPR base-editing technology were modified to knock out genes for TCR alpha-beta to prevent graft versus host disease, CD7 to prevent fratricide effect and CD52 to evade alemtuzumab lymphodepletion. Cells were transduced with lentiviral vectors encoding CAR7 to produce anti-CD7 CAR-T (BE-CAR7). This whole process took 10-12 days and on analysis BECAR7 had normal karyotypes with no detectable translocations. BE-CAR7 (0.2-2 × 10 cells/kg) were infused after lymphodepleting chemotherapy with fludarabine and cyclophosphamide. If in molecular remission at day +28 post BE-CAR7 infusion, patients proceeded to allogeneic HSCT to deplete remaining BE-CAR7 and allow for normal immune and T-cell reconstitution. Three children have been treated so far, two of whom remain in clinical remission 12- and 24-months post BE-CAR7 followed by HSCT and one passed away from a fungal infection at day +33 post BE-CAR7 infusion [5]. The study demonstrated good CAR-T clinical safety profile, no off-target toxicities, normal immune reconstitution post HSCT and good preliminary anti-leukaemic response in this high-risk population. Audiences at the conference were privileged to hear from an inspiring young woman about her experiences and unique insights from undergoing BE-CAR7 therapy [6].
Efficacy of CAR-T therapy in solid tumours is also challenging, hindered by the often heterogenous markers on solid tumour cells, physical and biochemical barriers preventing trafficking of CAR-T to the tumour, and the immunosuppressive effects of the hostile tumour micro-environment, often being hypoxic and acidic [7] [Fig. 2]. Potency and persistence of CAR-T is directly related to response durability, but sessions during the 'Cell Therapy Day' reflected how this has been a key barrier in solid tumours.
Naldini et al. [8] described the efficient engineering of a population of tumour-associated Tie-2 expressing monocytes/macrophages (TEMs) naturally infiltrating the tumour micro-environment (TME) to precisely deliver Interferon-α (IFN-α). By transplanting hematopoietic stem and progenitor cells (HSPC) transduced with a lentiviral vector expressing IFN-α, under the positive regulation of the Tie-2 enhancer/promoter, a specific release of IFN-α in the TME was assessed, favouring immune activation and therapeutic activity in different preclinical tumour models [9,10,11]. Based on these findings, Birocchi and colleagues [12] described an inducible platform for a precise, spatial-temporal regulated cytokine delivery within the TME. This has been combined with adoptive T-cell therapies such as CAR-T and tumour targeted gene therapy in preclinical models with promising results [13], paving the way for clinical trials.
During the session 'New/other indications for cell therapy products' [7] Gentner presented updates from a Phase 1/2a dose-escalating non-randomised open label study in newly diagnosed glioblastoma multiforme (GBM) with unmethylated MGMT gene promoter, involving injection of autologous CD34+ HSPC genetically modified with a lentiviral vector encoding for human IFN-α2 (Temferon, NCT03866109) [Fig. 3]. By exploiting cutting-edge technologies on patients' samples such as single-cell RNA sequencing, the presence of engineered cells and immune activation within the TME were documented. Farina [14] presented initial evidence of safety and tolerability of Temferon, with potential efficacy to counteract disease progression in patients affected by GBM.
Neuroblastoma is the commonest extracranial solid tumour of childhood, but high-risk disease has five-year overall survival (OS) 40-50% despite aggressive multimodal therapy and relapsed or refractory neuroblastoma portends even worse outcomes [15]. Locatelli [16] and Del Bufalo [17] from Bambino Gesù Children's Hospital in Italy presented results from a phase 1/2 trial of third generation autologous anti-GD2 CAR-T to target relapsed or refractory neuroblastoma (NCT03373097). GD2 CAR-T were manufactured with two additional molecules, 4-1BB and CD28 to enhance potency and persistence of CAR-T, along with an inducible caspase 9 (iC9) as an apoptotic safety switch. 27 children with heavily pre-treated neuroblastoma (12 refractory disease, 14 relapsed disease, and one complete response after front-line therapy) underwent lymphodepleting chemotherapy with fludarabine and cyclophosphamide, then received GD2 CAR-T at dosages of 1-10 × 10 cells/kg with no dose-limiting toxicities. GD2 CAR-T populations peaked in the blood between days +7 and +14; distributed in the bone marrow, central nervous system (CNS) and peritoneal fluid from week 6 onwards; and persisted for up to 3 years. The overall response rate in this high-risk population was 63% (nine patients had complete response and eight partial response) and in patients who received the recommended 10 × 10 CAR-T cells/kg, three-year OS was 60% and event-free survival (EFS) 36%. Common side effects included cytokine release syndrome, cytopenias and immune effector cell associated-neurotoxicity syndrome (ICANS), the latter benefiting from activation of iC9 which effectively removed circulating GD2 CAR-T.
Del Bufalo [17] presented updated but unpublished data with excellent results in neuroblastoma patients with low disease burden or in clinical remission treated with autologous GD2 CAR-T. There also appeared to be no significant difference in EFS or OS between patients with or without MYC-N amplification, nor those with or without prior anti-GD2 therapy i.e. dinutuximab beta. The only statistically significant factor improving survival was a lower number of lines of chemotherapy prior to GD2 CAR-T. A European multicentre phase 2 trial of GD2 CAR-T therapy is planned for relapsed or progressive neuroblastoma after first line therapy to confirm results.
GD2 is also expressed on the cell surface of many different CNS tumours. A 2023 study [18] described outcomes of four paediatric and four adult patients infused with autologous GD2 CAR-T for H3K27 mutated glioblastoma multiforme (GBM), demonstrating no unexpected toxicities and median OS ten months from infusion. GD2 CAR-T therapy is also efficacious for medulloblastoma with reduction in tumour size and improved OS demonstrated in vivo in orthotopic mouse models [19].
Bambino Gesù Children's Hospital in Italy recently opened a phase 1 dose-escalation trial in January 2024 using GD2 CAR-T for paediatric CNS tumours including medulloblastoma, GBM and other high-grade gliomas. During the 'Cell Therapy Day,' Locatelli [16] shared initial results from the first two patients treated to date without any unexpected toxicities.
Anti-CD19 CAR-T can achieve complete and frequently long-lasting B-cell aplasia, targeting B-cell lineage from early-stage to late-stage cells [Fig. 4], representing a strong rationale for its use in the treatment of autoimmune diseases refractory to conventional immunosuppressant therapies [20]. This is supported by robust pre-clinical evidence [21].
Mackensen et al. [22] and Mougiakakos et al. [23] presented the first clinical evidence of CAR-T activity in patients affected by refractory systemic lupus erythematosus. From that pivotal work, their group and others reported clinical efficacy of CAR-T across several diverse autoimmune disorders [24,25,-26], with incredible response rates and very low toxicities [27].
Mackensen et al. [22] presented results on the use of anti-CD19 CAR-T for autoimmune diseases, including follow up data of the first treated patient with refractory systemic lupus erythematosus confirming prolonged disease control. They also shared initial data from an open phase 1/2 clinical trial of CD19 CAR-T in other autoimmune diseases such as systemic sclerosis, dermatomyositis, polymyositis and anti-synthetase syndrome (NCT06347718).
An update on anti-CD19 CAR-T for myositis was presented by Henes during the 'Autoimmune Diseases Working Party' session [28] and Mougiakakos [29] presented a case of refractory anti-AchR antibody positive myasthenia gravis treated successfully by CAR-T during the oral session 'Cellular therapy for autoimmune and inflammatory diseases.' These promising results suggest CAR-T therapy will likely play a crucial role in the future treatment of autoimmune diseases.
The joint EBMT/WBMT session 'CAR T-cell and advanced cellular and gene therapies, minimising disparities, regulatory issues and global collaboration to improve access' [30] facilitated a pivotal discussion about inequities in accessing advanced therapy medicinal products (ATMP) worldwide and considered possible solutions. Koh and Chabannon discussed challenges of CAR-T cell accessibility, affordability and shortage of manufacturing facilities. Ahmed gave an important update on the challenges, opportunities and state of the art technologies surrounding CAR-T and advanced cellular therapies in emerging economies.
During the joint EBMT/CIBMTR/ASTCT/APBMT/LABMT session 'Exploring the contributions of laboratory, translational, and big data science in HSCT/CAR-T within our organisations and meetings' [31] an interesting debate took place on the role and challenges of data analysis and artificial intelligence (AI) in the field of transplantation and cellular therapies.
Finally, three sessions were dedicated to the GoCART coalition, a multi-stakeholder coalition co-founded by EBMT and European Haematology Association (EHA) [32]. This includes patient representatives, health care professionals, pharmaceutical companies, regulators, health technology assessment bodies, reimbursement agencies and medical organisations, collaborating to maximise the potential of cellular therapies manufactured from haematopoietic origin. During the first session, preliminary data from ongoing studies were presented; the second session was dedicated to the updates on national CAR-T networks across different European countries; and in the last session new initiatives for standardisation, harmonisation, and education in the field of CAR-T therapy and ATMP were proposed.
CAR-T therapy shows exciting new results in a wide range of paediatric haematologic, solid organ and CNS malignancies. Among the innovative cellular therapies for adult patients, tumoral macrophage engineering has advanced cancer immunotherapy and promising results of CAR-T therapies for autoimmune diseases are emerging. Moreover, challenges in the development of ATMP, and the role of data analysis and AI were considered. While there are unique challenges posed by each indication for CAR-T, researchers are developing innovative methods to overcome these and provide much needed options for patients with difficult-to-treat malignancies or autoimmune conditions.
