CD22 CAR T cells demonstrate high response rates and safety in pediatric and adult B-ALL: Phase 1b results.

Chimeric antigen receptor (CAR) T cells targeting CD22 (CD22-CAR) provide a therapeutic option for patients with CD22+ malignancies with progression after CD19-directed therapies. Using on-site, automated, closed-loop manufacturing, we conducted parallel Phase 1b clinical trials investigating a humanized CD22-CAR with 41BB costimulatory domain in children and adults with heavily treated, relapsed/refractory (r/r) B-ALL. Of 19 patients enrolled, 18 had successful CD22-CAR manufacturing, and 16 patients were infused. High grade (3-4) cytokine release syndrome (CRS) and immune effector-cell-associated neurotoxicity syndrome (ICANS) each occurred in only one patient; however, three patients experienced immune-effector-cell-associated hemophagocytic lymphohistiocytosis-like syndrome (IEC-HS). Twelve of 16 patients (75%) achieved CR with an overall 56% MRD-negative CR rate. Duration of response was overall limited (median 77 days), and CD22 expression was downregulated in 4/12 (33%) available samples at relapse. In summary, we demonstrate that closed-loop manufacturing of CD22-CAR T cells is feasible and is associated with a favorable safety profile and high CR rates in pediatric and adult r/r B-ALL, a cohort with limited CD22-CAR reporting.

Mediport use as an acceptable standard for CAR T cell infusion.

Introduction: Mediport use as a clinical option for the administration of chimeric antigen receptor T cell (CAR T cell) therapy in patients with B-cell malignancies has yet to be standardized. Concern for mediport dislodgement, cell infiltration, and ineffective therapy delivery to systemic circulation has resulted in variable practice with intravenous administration of CAR T cell therapy. With CAR T cell commercialization, it is important to establish practice standards for CAR T cell delivery. We conducted a study to establish usage patterns of mediports in the clinical setting and provide a standard of care recommendation for mediport use as an acceptable form of access for CAR T cell infusions. Methods: In this retrospective cohort study, data on mediport use and infiltration rate was collected from a survey across 34 medical centers in the Pediatric Real-World CAR Consortium, capturing 504 CAR T cell infusion routes across 489 patients. Data represents the largest, and to our knowledge sole, report on clinical CAR T cell infusion practice patterns since FDA approval and CAR T cell commercialization in 2017. Results: Across 34 sites, all reported tunneled central venous catheters, including Broviac® and Hickman® catheters, as accepted standard venous options for CAR T cell infusion. Use of mediports as a standard clinical practice was reported in 29 of 34 sites (85%). Of 489 evaluable patients with reported route of CAR T cell infusion, 184 patients were infused using mediports, with no reported incidences of CAR T cell infiltration. Discussion/Conclusion: Based on current clinical practice, mediports are a commonly utilized form of access for CAR T cell therapy administration. These findings support the safe practice of mediport usage as an accepted standard line option for CAR T cell infusion.

Role of peripheral blood MRD and 18F-FDG PET in the post-CAR relapse setting: a case study of discordant peripheral blood and bone marrow MRD.

BACKGROUND: Chimeric antigen receptor (CAR) T cell therapy is an effective salvage therapy for pediatric relapsed B-cell acute lymphoblastic leukemia (B-ALL), yet is challenged by high rates of post-CAR relapse. Literature describing specific relapse patterns and extramedullary (EM) sites of involvement in the post-CAR setting remains limited, and a clinical standard for post-CAR disease surveillance has yet to be established. We highlight the importance of integrating peripheral blood minimal residual disease (MRD) testing and radiologic imaging into surveillance strategies, to effectively characterize and capture post-CAR relapse. MAIN BODY: Here, we describe the case of a child with multiply relapsed B-ALL who relapsed in the post-CAR setting with gross non-contiguous medullary and EM disease. Interestingly, her relapse was identified first from peripheral blood flow cytometry MRD surveillance, in context of a negative bone marrow aspirate (MRD <0.01%). Positron emission tomography with 18F-fluorodeoxyglucose revealed diffuse leukemia with innumerable bone and lymph node lesions, interestingly sparing her sacrum, the site of her bone marrow aspirate sampling. CONCLUSIONS: We highlight this case as both peripheral blood MRD and 18F-fluorodeoxyglucose positron emission tomography imaging were more sensitive than standard bone marrow aspirate testing in detecting this patient's post-CAR relapse. Clinical/Biologic Insight: In the multiply relapsed B-ALL setting, where relapse patterns may include patchy medullary and/or EM disease, peripheral blood MRD and/or whole body imaging, may carry increased sensitivity at detecting relapse in patient subsets, as compared with standard bone marrow sampling.

GD2-CAR T cell therapy for H3K27M-mutated diffuse midline gliomas.

Diffuse intrinsic pontine glioma (DIPG) and other H3K27M-mutated diffuse midline gliomas (DMGs) are universally lethal paediatric tumours of the central nervous system1. We have previously shown that the disialoganglioside GD2 is highly expressed on H3K27M-mutated glioma cells and have demonstrated promising preclinical efficacy of GD2-directed chimeric antigen receptor (CAR) T cells2, providing the rationale for a first-in-human phase I clinical trial (NCT04196413). Because CAR T cell-induced brainstem inflammation can result in obstructive hydrocephalus, increased intracranial pressure and dangerous tissue shifts, neurocritical care precautions were incorporated. Here we present the clinical experience from the first four patients with H3K27M-mutated DIPG or spinal cord DMG treated with GD2-CAR T cells at dose level 1 (1 × 106 GD2-CAR T cells per kg administered intravenously). Patients who exhibited clinical benefit were eligible for subsequent GD2-CAR T cell infusions administered intracerebroventricularly3. Toxicity was largely related to the location of the tumour and was reversible with intensive supportive care. On-target, off-tumour toxicity was not observed. Three of four patients exhibited clinical and radiographic improvement. Pro-inflammatory cytokine levels were increased in the plasma and cerebrospinal fluid. Transcriptomic analyses of 65,598 single cells from CAR T cell products and cerebrospinal fluid elucidate heterogeneity in response between participants and administration routes. These early results underscore the promise of this therapeutic approach for patients with H3K27M-mutated DIPG or spinal cord DMG.

Identification of dual positive CD19+/CD3+ T cells in a leukapheresis product undergoing CAR transduction: a case report.

BACKGROUND: Chimeric antigen receptor (CAR) therapy and hematopoietic stem cell transplantation (HSCT) are therapeutics for relapsed acute lymphocytic leukemia (ALL) that are increasingly being used in tandem. We identified a non-physiologic CD19+/CD3+ T-cell population in the leukapheresis product of a patient undergoing CAR T-cell manufacturing who previously received a haploidentical HSCT, followed by infusion of a genetically engineered T-cell addback product. We confirm and report the origin of these CD19+/CD3+ T cells that have not previously been described in context of CAR T-cell manufacturing. We additionally interrogate the fate of these CD19-expressing cells as they undergo transduction to express CD19-specific CARs. MAIN BODY: We describe the case of a preteen male with multiply relapsed B-ALL who was treated with sequential cellular therapies. He received an αß T-cell depleted haploidentical HSCT followed by addback of donor-derived T cells genetically modified with a suicide gene for iCaspase9 and truncated CD19 for cell tracking (RivoCel). He relapsed 6 months following HSCT and underwent leukapheresis and CAR T-cell manufacturing. During manufacturing, we identified an aberrant T-cell population dually expressing CD19 and CD3. We hypothesized that these cells were RivoCel cells and confirmed using flow cytometry and PCR that the identified cells were in fact RivoCel cells and were eliminated with iCaspase9 activation. We additionally tracked these cells through CD19-specific CAR transduction and notably did not detect T cells dually positive for CD19 and CD19-directed CARs. The most likely rationale for this is in vitro fratricide of the CD19+ 'artificial' T-cell population by the CD19-specific CAR+ T cells in culture. CONCLUSIONS: We report the identification of CD19+/CD3+ cells in an apheresis product undergoing CAR transduction derived from a patient previously treated with a haploidentical transplant followed by RivoCel addback. We aim to bring attention to this cell phenotype that may be recognized with greater frequency as CAR therapy and engineered αßhaplo-HSCT are increasingly coupled. We additionally suggest consideration towards using alternative markers to CD19 as a synthetic identifier for post-transplant addback products, as CD19-expression on effector T cells may complicate subsequent treatment using CD19-directed therapy.