ACT To Sustain: Adoptive Cell Therapy To Sustain Access to Non-Commercialized Genetically Modified Cell Therapies.

Genetically modified cell therapies (GMCT), particularly immune effector cells (IEC) such as chimeric receptor antigen (CAR) T cells, have shown promise in curing cancer and rare diseases after a single treatment course. Following close behind CAR T approvals are GMCT based on hematopoietic stem cells, such as products developed for hemoglobinopathies and other disorders. Academically sponsored GMCT products, often developed in academic centers without industry involvement, face challenges in sustaining access after completion of early phase studies when there is no commercial partner invested in completing registration trials for marketing applications. The American Society for Transplantation and Cellular Therapy (ASTCT) formed a task force named ACT To Sustain (Adoptive Cell Therapy to Sustain) to address the "valley of death" of academic GMCT products. This paper presents the task force's findings and considerations regarding financial sustainability of academically sponsored GMCT products in the absence of commercial development. We outline case scenarios illustrating barriers to maintaining access to promising GMCT developed by academic centers. The paper also delves into the current state of GMCT development, commercialization, and reimbursement, citing examples of abandoned products, cost estimates associated with GMCT manufacturing and real-world use of cost recovery. We propose potential solutions to address the financial, regulatory, and logistical challenges associated with sustaining access to academically sponsored GMCT products and to ensure that products with promising results do not languish in a "valley of death" due to financial or implementational barriers. The suggestions include aligning US Food and Drug Administration (FDA) designations with benefit coverage, allowing for cost recovery of certain products as a covered benefit, and engaging with regulators and policy makers to discuss alternative pathways for academic centers to provide access. We stress the importance of sustainable access to GMCT and call for collaborative efforts to develop regulatory pathways that support access to academically sponsored GMCT products.

Drug-regulated CD33-targeted CAR T cells control AML using clinically optimized rapamycin dosing.

Chimeric antigen receptor (CAR) designs that incorporate pharmacologic control are desirable; however, designs suitable for clinical translation are needed. We designed a fully human, rapamycin-regulated drug product for targeting CD33+ tumors called dimerizaing agent-regulated immunoreceptor complex (DARIC33). T cell products demonstrated target-specific and rapamycin-dependent cytokine release, transcriptional responses, cytotoxicity, and in vivo antileukemic activity in the presence of as little as 1 nM rapamycin. Rapamycin withdrawal paused DARIC33-stimulated T cell effector functions, which were restored following reexposure to rapamycin, demonstrating reversible effector function control. While rapamycin-regulated DARIC33 T cells were highly sensitive to target antigen, CD34+ stem cell colony-forming capacity was not impacted. We benchmarked DARIC33 potency relative to CD19 CAR T cells to estimate a T cell dose for clinical testing. In addition, we integrated in vitro and preclinical in vivo drug concentration thresholds for off-on state transitions, as well as murine and human rapamycin pharmacokinetics, to estimate a clinically applicable rapamycin dosing schedule. A phase I DARIC33 trial has been initiated (PLAT-08, NCT05105152), with initial evidence of rapamycin-regulated T cell activation and antitumor impact. Our findings provide evidence that the DARIC platform exhibits sensitive regulation and potency needed for clinical application to other important immunotherapy targets.

Development of a Safety Surveillance Plan for the Academic Medicine Sponsor Performing First-in-Human Cellular Therapy Clinical Trials: A Report from the Consortium for Pediatric Cellular Immunotherapy.

Pharmacovigilance (PV), also known as drug safety, is the science of risk management involving the detection, assessment, understanding, and prevention of adverse effects related to a medication. This discipline has traditionally focused on the postmarketing period, with less attention to early-phase clinical trials. However, during the immunotherapy and cellular therapy investigational stage, regulatory agencies are increasingly emphasizing the need to identify and characterize safety signals earlier in clinical development as part of a comprehensive safety surveillance plan. Compliance with PV and safety regulations are further heightened as cell and gene therapy (CGT) trials grow in complexity and scope owing to ever-changing and increasingly rigorous regulatory mandates. Based on this changing landscape, a critical aspect of early-phase trials of cellular products where significant safety events are anticipated is to ensure that every effort is made to protect clinical trial participants by maximizing attention to the risk-versus-benefit profile. This includes the development of robust plans for safety surveillance that provide a continual assessment of safety signals to enable safety reporting to regulatory bodies and the Food and Drug Administration, a regular analysis of aggregate safety data, and a plan to communicate safety findings. This report focuses on PV in early-phase clinical trials of first-in-human investigational products sponsored by academic centers in which the availability of PV resources and subject matter experts is limited. To more fully understand the challenges of CGT PV oversight within pediatric academic medical centers conducting early-phase clinical trials, a working group from institutions participating in the Consortium for Pediatric Cellular Immunotherapy composed of faculty and regulatory professionals was convened to compare experiences, identify best practices, and review published literature to identify commonalities and opportunities for alignment. Here we present guidelines on PV planning in early-phase CGT clinical trials occurring in academic medical centers and offer strategies to mitigate risk to trial participants. Standards to address regulatory requirements and governance for safety signal identification and risk assessment are discussed.

How Many Tests Does It Take to Diagnose a Triple-Hit B-Lymphoblastic Lymphoma? (Hint, It's A Lot).

B-lymphoblastic leukemia/lymphoma (B-ALL/LBL) is a precursor B-cell neoplasm that often harbors specific cytogenetic/molecular abnormalities with distinctive clinical, phenotypic, and prognostic characteristics. Subcategorization of B-ALL/LBL therefore requires extensive cytogenetic and/or molecular testing to determine the appropriate classification and therapeutic interventions for these patients. Herein, we present a case of a 17-year-old young woman diagnosed with B-LBL harboring not only an IGH::MYC rearrangement but also BCL2 and BCL6 rearrangements (so-called "triple-hit") and somatic biallelic TP53 inactivation. MYC rearrangements are relatively rare in B-ALL/LBL, and the identification of a "triple-hit" elicited an initial diagnostic dilemma. However, a multimodal approach allowed for the classification of this complex case and helped guide selection of an appropriate therapeutic regimen.

Chimeric Antigen Receptor T Cells as Salvage Therapy for Post-Chimeric Antigen Receptor T Cell Failure.

Outcomes for post-chimeric antigen receptor (CAR) T cell therapy (CART) relapse are poor. The utilization of a unique CAR T cell construct for post-CART failure is increasing, but this approach is not well described. In this study, with CART-A the first unique CAR T cell construct received and CART-B the second, the primary objective was to characterize outcomes following CART-B. Secondary objectives included evaluating safety and toxicity with sequential CART infusions; investigating the impact of potential factors, such as antigen modulation and interval therapy, on CART-B response; and characterizing long-term outcomes in patients receiving multiple CARTs. This was a retrospective review (NCT03827343) of children and young adults with B cell acute lymphoblastic leukemia (B-ALL) undergoing CART therapy who received at least 2 unique CART constructs, excluding interim CART reinfusions of the same product. Of 135 patients, 61 (45.1%) received 2 unique CART constructs, including 13 who received >2 CARTs over time. Patients included in this analysis received 14 distinct CARTs targeting CD19 and/or CD22. The median age at CART-A was 12.6 years (range, 3.3 to 30.4 years). The median time from CART-A to CART-B was 302 days (range, 53 to 1183 days). CART-B targeted a different antigen than CART-A in 48 patients (78.7%), owing primarily to loss of CART-A antigen target. The rate of complete remission (CR) was lower with CART-B (65.5%; 40 of 61) than with CART-A (88.5%; 54 of 61; P = .0043); 35 of 40 (87.5%) CART-B responders had CART-B targeting a different antigen than CART-A. Among the 21 patients with a partial response or nonresponse to CART-B, 8 (38.1%) received CART-B with the same antigen target as CART-A. Of 40 patients with CART-B complete response (CR), 29 (72.5%) relapsed. For the 21 patients with evaluable data, the relapse immunophenotype was antigennegative in 3 (14.3%), antigendim in 7 (33.3%), antigenpositive in 10 (47.6%), and lineage switch in 1 (4.8%). The median relapse-free survival following CART-B CR was 9.4 months (95% confidence interval [CI], 6.1 to 13.2 months), and overall survival was 15.0 months (95% CI, 13.0 to 22.7 months). Given the limited salvage options for post-CART relapse, identifying optimizing strategies for CART-B is critical. We raise awareness about the emerging use of CART for post-CART failure and highlight clinical implications accompanying this paradigm shift.

Anti-HLA antibodies in recipients of CD19 versus BCMA-targeted CAR T-cell therapy.

Antibodies against foreign human leukocyte antigen (HLA) molecules are barriers to successful organ transplantation. B cell-depleting treatments are used to reduce anti-HLA antibodies but have limited efficacy. We hypothesized that the primary source for anti-HLA antibodies is long-lived plasma cells, which are ineffectively targeted by B cell depletion. To study this, we screened for anti-HLA antibodies in a prospectively enrolled cohort of 49 patients who received chimeric antigen receptor T-cell therapy (CARTx), targeting naïve and memory B cells (CD19-targeted, n = 21) or plasma cells (BCMA-targeted, n = 28) for hematologic malignancies. Longitudinal samples were collected before and up to 1 year after CARTx. All individuals were in sustained remission. We identified 4 participants with anti-HLA antibodies before CD19-CARTx. Despite B cell depletion, anti-HLA antibodies and calculated panel reactive antibody scores were stable for 1 year after CD19-CARTx. Only 1 BCMA-CARTx recipient had pre-CARTx low-level anti-HLA antibodies, with no follow-up samples available. These data implicate CD19neg long-lived plasma cells as an important source for anti-HLA antibodies, a model supported by infrequent HLA sensitization in BCMA-CARTx subjects receiving previous plasma cell-targeted therapies. Thus, plasma cell-targeted therapies may be more effective against HLA antibodies, thereby enabling improved access to organ transplantation and rejection management.

Paving the Road for Chimeric Antigen Receptor T Cells: American Society for Transplantation and Cellular Therapy 80/20 Task Force Consensus on Challenges and Solutions to Improving Efficiency of Clinical Center Certification and Maintenance of Operations for Commercially Approved Immune Effector Cell Therapies.

As the number and type of regulatory authority-approved cellular therapies grow, clinical treatment centers face a heavy burden of duplicative documentation around initial qualification, ongoing auditing, and reporting, with overlapping requirements from each manufacturer to ensure safe use of their specific product, which in the United States are stipulated under individual Food and Drug Administration (FDA) Biologic License Applications. The American Society for Transplantation and Cellular Therapy (ASTCT) convened the 80/20 Task Force to consider challenges and potential solutions to these issues. The Task Force proposed that 80% of manufacturers' requirements for onboarding and ongoing operations of commercially available products could be standardized and streamlined. Task Force members interviewed dozens of stakeholders, including clinicians at large academic medical centers already using commercial and investigational immune effector cell (IEC) products, regulators, members of accrediting bodies and professional cellular therapy societies, and manufacturers of IEC therapies for oncologic indications. In November 2021, the Task Force organized and led virtual discussions in a public forum and at a private ASTCT 80/20 Workshop at the online AcCELLerate Forum, a cellular-therapy stakeholders' meeting organized by the ASTCT, National Marrow Donor Program (NMDP), and Center for International Blood and Marrow Transplant Research (CIBMTR). At the workshop, approximately 60 stakeholders worked to identify and prioritize common challenges in onboarding and maintenance of operations at clinical sites for commercial FDA-approved and future IEC therapies and ways to streamline the process. It was agreed that standardization would improve efficiency of onboarding, allowing more cost-effective, sustainable growth of approved IEC therapies at treatment centers, and facilitate wider access while maintaining safety and clinical success. This early but extensive survey of stakeholders resulted in 5 overarching suggestions for both established and emerging treatment centers: (1) eliminate duplication in accreditation and auditing of clinical sites; (2) define expectations for the education about and management of CAR-T therapy toxicities to potentially replace product-specific REMS programs; (3) streamline current REMS education, testing, and data reporting; (4) standardize information technology (IT) platforms supporting enrollment, clinical site-manufacturer communication, and logistics of maintaining chain of identity/chain of custody across multiple transportation steps; and (5) encourage the use of universal nomenclature by cell therapy manufacturers. Future discussions need to engage a broader range of stakeholders, including administrators, pharmacists, nurses, data coordinators, surgeons, pathologists, and those developing promising cellular therapies for solid tumors, as well as teams from smaller academic or community cancer center settings. Continued collaboration with stakeholders outside of clinical sites will include accrediting bodies/auditors, established and emerging cell therapy companies, software developers, professional societies, and the patients who receive these therapies. Active dialog with government regulators remains essential. Such joint efforts are critical as the number of IEC therapies for myriad oncologic and nononcologic indications grows.

A stem cell epigenome is associated with primary nonresponse to CD19 CAR T cells in pediatric acute lymphoblastic leukemia.

CD19 chimeric antigen receptor T-cell therapy (CD19-CAR) has changed the treatment landscape and outcomes for patients with pre-B-cell acute lymphoblastic leukemia (B-ALL). Unfortunately, primary nonresponse (PNR), sustained CD19+ disease, and concurrent expansion of CD19-CAR occur in 20% of the patients and is associated with adverse outcomes. Although some failures may be attributable to CD19 loss, mechanisms of CD19-independent, leukemia-intrinsic resistance to CD19-CAR remain poorly understood. We hypothesize that PNR leukemias are distinct compared with primary sensitive (PS) leukemias and that these differences are present before treatment. We used a multiomic approach to investigate this in 14 patients (7 with PNR and 7 with PS) enrolled in the PLAT-02 trial at Seattle Children's Hospital. Long-read PacBio sequencing helped identify 1 PNR in which 47% of CD19 transcripts had exon 2 skipping, but other samples lacked CD19 transcript abnormalities. Epigenetic profiling discovered DNA hypermethylation at genes targeted by polycomb repressive complex 2 (PRC2) in embryonic stem cells. Similarly, assays of transposase-accessible chromatin-sequencing revealed reduced accessibility at these PRC2 target genes, with a gain in accessibility of regions characteristic of hematopoietic stem cells and multilineage progenitors in PNR. Single-cell RNA sequencing and cytometry by time of flight analyses identified leukemic subpopulations expressing multilineage markers and decreased antigen presentation in PNR. We thus describe the association of a stem cell epigenome with primary resistance to CD19-CAR therapy. Future trials incorporating these biomarkers, with the addition of multispecific CAR T cells targeting against leukemic stem cell or myeloid antigens, and/or combined epigenetic therapy to disrupt this distinct stem cell epigenome may improve outcomes of patients with B-ALL.

Locoregional CAR T cells for children with CNS tumors: Clinical procedure and catheter safety.

Central nervous system (CNS) tumors are the most common solid malignancy in the pediatric population. Based on adoptive cellular therapy's clinical success against childhood leukemia and the preclinical efficacy against pediatric CNS tumors, chimeric antigen receptor (CAR) T cells offer hope of improving outcomes for recurrent tumors and universally fatal diseases such as diffuse intrinsic pontine glioma (DIPG). However, a major obstacle for tumors of the brain and spine is ineffective T cell chemotaxis to disease sites. Locoregional CAR T cell delivery via infusion through an intracranial catheter is currently under study in multiple early phase clinical trials. Here, we describe the Seattle Children's single-institution experience including the multidisciplinary process for the preparation of successful, repetitive intracranial T cell infusion for children and the catheter-related safety of our 307 intracranial CAR T cell doses.

Preinfusion factors impacting relapse immunophenotype following CD19 CAR T cells.

Relapse following chimeric antigen receptor (CAR) T-cell therapy directed against CD19 for relapsed/refractory B-acute lymphoblastic leukemia (r/r B-ALL) remains a significant challenge. Three main patterns of relapse predominate: CD19 positive (CD19pos) relapse, CD19 negative (CD19neg) relapse, and lineage switch (LS). Development and validation of risk factors that predict relapse phenotype could help define potential pre- or post-CAR T-cell infusion interventions aimed at decreasing relapse. Our group sought to extensively characterize preinfusion risk factors associated with the development of each relapse pattern via a multicenter, retrospective review of children and young adults with r/r B-ALL treated with a murine-based CD19-CAR construct. Of 420 patients treated with CAR, 166 (39.5%) relapsed, including 83 (50%) CD19pos, 68 (41%) CD19neg, and 12 (7.2%) LS relapses. A greater cumulative number of prior complete remissions was associated with CD19pos relapses, whereas high preinfusion disease burden, prior blinatumomab nonresponse, older age, and 4-1BB CAR construct were associated with CD19neg relapses. The presence of a KMT2A rearrangement was the only preinfusion risk factor associated with LS. The median overall survival following a post-CAR relapse was 11.9 months (95% CI, 9-17) and was particularly dismal in patients experiencing an LS, with no long-term survivors following this pattern of relapse. Given the poor outcomes for those with post-CAR relapse, study of relapse prevention strategies, such as consolidative hematopoietic stem cell transplantation, is critical and warrants further investigation on prospective clinical trials.

Intraventricular B7-H3 CAR T Cells for Diffuse Intrinsic Pontine Glioma: Preliminary First-in-Human Bioactivity and Safety.

Diffuse intrinsic pontine glioma (DIPG) remains a fatal brainstem tumor demanding innovative therapies. As B7-H3 (CD276) is expressed on central nervous system (CNS) tumors, we designed B7-H3-specific chimeric antigen receptor (CAR) T cells, confirmed their preclinical efficacy, and opened BrainChild-03 (NCT04185038), a first-in-human phase I trial administering repeated locoregional B7-H3 CAR T cells to children with recurrent/refractory CNS tumors and DIPG. Here, we report the results of the first three evaluable patients with DIPG (including two who enrolled after progression), who received 40 infusions with no dose-limiting toxicities. One patient had sustained clinical and radiographic improvement through 12 months on study. Patients exhibited correlative evidence of local immune activation and persistent cerebrospinal fluid (CSF) B7-H3 CAR T cells. Targeted mass spectrometry of CSF biospecimens revealed modulation of B7-H3 and critical immune analytes (CD14, CD163, CSF-1, CXCL13, and VCAM-1). Our data suggest the feasibility of repeated intracranial B7-H3 CAR T-cell dosing and that intracranial delivery may induce local immune activation. SIGNIFICANCE: This is the first report of repeatedly dosed intracranial B7-H3 CAR T cells for patients with DIPG and includes preliminary tolerability, the detection of CAR T cells in the CSF, CSF cytokine elevations supporting locoregional immune activation, and the feasibility of serial mass spectrometry from both serum and CSF. This article is highlighted in the In This Issue feature, p. 1.

GFAP and NfL increase during neurotoxicity from high baseline levels in pediatric CD19-CAR T-cell patients.

There is a need for biomarkers to predict and measure the severity of immune effector cell-associated neurotoxicity syndrome (ICANS). Glial fibrillary acidic protein (GFAP) and neurofilament light chain (NfL) are well-validated biomarkers of astroglial and neuronal injury, respectively. We hypothesized that pretreatment GFAP and NfL levels can predict the risk of subsequent ICANS and that increases in GFAP and NfL levels during treatment reflect ICANS severity. We measured cerebrospinal fluid GFAP (cGFAP) and NfL (cNfL) along with serum NfL (sNfL) levels at pretreatment and day 7 to 10 after chimeric antigen receptor (CAR) T-cell infusion in 3 pediatric cohorts treated with CD19- or CD19/CD22-directed CAR T cells. cGFAP and cNfL levels increased during grade ≥1 ICANS in patients treated with CD19-directed CAR T cells but not in those who received CD19/CD22-directed CAR T cells. The sNfL levels did not increase during ICANS. Prelymphodepletion cGFAP, cNfL, and sNfL levels were not predictive of subsequent ICANS. Elevated baseline cGFAP levels were associated with a history of transplantation. Patients with prior central nervous system (CNS) radiation had higher cNfL levels, and elevated baseline sNfL levels were associated with a history of peripheral neuropathy. Thus, cGFAP and cNfL may be useful biomarkers for measuring the severity of CNS injury during ICANS in children. Elevated baseline levels of cGFAP, cNfL, and sNfL likely reflect the cumulative injury to the central and peripheral nervous systems from prior treatment. However, levels of any of the 3 biomarkers before CAR T-cell infusion did not predict the risk of ICANS.

Nelarabine, etoposide, and cyclophosphamide in relapsed pediatric T-acute lymphoblastic leukemia and T-lymphoblastic lymphoma (study T2008-002 NECTAR).

Children with relapse of T-cell acute lymphoblastic leukemia (T-ALL) or lymphoblastic lymphoma (T-LBL) have a dismal prognosis, largely due to difficulty attaining second remission. We hypothesized that adding etoposide and cyclophosphamide to the nucleoside analog nelarabine could improve response rates over single-agent nelarabine for relapsed T-ALL and T-LBL. This phase I dose-escalation trial's primary objective was to evaluate the dose and safety of nelarabine given in combination with etoposide at 100 mg/m2 /day and cyclophosphamide at 330-400 mg/m2 /day, each for 5 consecutive days in children with either T-ALL (13 patients) or T-LBL (10 patients). Twenty-three patients were treated at three dose levels; 21 were evaluable for dose-limiting toxicities (DLT) and response. The recommended phase II doses (RP2D) for this regimen, when given daily ×5 every 3 weeks, were nelarabine 650 mg/m2 /day, etoposide 100 mg/m2 /day, and cyclophosphamide 400 mg/m2 /day. DLTs included peripheral motor and sensory neuropathies. An expansion cohort to evaluate responses at the RP2D was terminated early due to slow accrual. The overall best response rate was 38% (8/21), with 33% (4/12) responses in the T-ALL cohort and 44% (4/9) responses in the T-LBL cohort. These response rates are comparable to those seen with single-agent nelarabine in this setting. These data suggest that the addition of cyclophosphamide and etoposide to nelarabine does not increase the incidence of neurologic toxicities or the response rate beyond that obtained with single-agent nelarabine in children with first relapse of T-ALL and T-LBL.

Modified Manufacturing Process Modulates CD19CAR T-cell Engraftment Fitness and Leukemia-Free Survival in Pediatric and Young Adult Subjects.

T cells modified to express a chimeric antigen receptor (CAR) targeting CD19 can induce potent and sustained responses in children with relapsed/refractory acute lymphoblastic leukemia (ALL). The durability of remission is related to the length of time the CAR T cells persist. Efforts to understand differences in persistence have focused on the CAR construct, in particular the costimulatory signaling module of the chimeric receptor. We previously reported a robust intent-to-treat product manufacturing success rate and remission induction rate in children and young adults with recurrent/refractory B-ALL using the SCRI-CAR19v1 product, a second-generation CD19-specific CAR with 4-1BB costimulation coexpressed with the EGFRt cell-surface tag (NCT02028455). Following completion of the phase I study, two changes to CAR T-cell manufacturing were introduced: switching the T-cell activation reagent and omitting midculture EGFRt immunomagnetic selection. We tested the modified manufacturing process and resulting product, designated SCRI-CAR19v2, in a cohort of 21 subjects on the phase II arm of the trial. Here, we describe the unanticipated enhancement in product performance resulting in prolonged persistence and B-cell aplasia and improved leukemia-free survival with SCRI-CAR19v2 as compared with SCRI-CAR19v1.

Hematopoietic Cell Transplantation after CD19 Chimeric Antigen Receptor T Cell-Induced Acute Lymphoblastic Lymphoma Remission Confers a Leukemia-Free Survival Advantage.

Consolidative hematopoietic cell transplantation (HCT) after CD19 chimeric antigen receptor (CAR) T cell therapy is frequently performed for patients with refractory/ relapsed B cell acute lymphoblastic leukemia (B-ALL). However, there is controversy regarding the role of HCT following remission attainment. We evaluated the effect of consolidative HCT on leukemia-free survival (LFS) in pediatric and young adult subjects following CD19 CAR T cell induced remission. We evaluated the effect of consolidative HCT on LFS in pediatric and young adult subjects treated with a 41BB-CD19 CAR T cell product on a phase 1/2 trial, Pediatric and Young Adult Leukemia Adoptive Therapy (PLAT)-02 (ClinicalTrials.gov identifier NCT02028455), using a time-dependent Cox proportional hazards statistical model. Fifty of 64 subjects enrolled in PLAT-02 phase 1 and early phase 2 were evaluated, excluding 14 subjects who did not achieve remission, relapsed, or died before day 63 post-CAR T cell therapy. An improved LFS (P = .01) was observed in subjects who underwent consolidative HCT after CAR T cell therapy versus watchful waiting. Consolidative HCT improved LFS specifically in subjects who had no prior history of HCT, with a trend toward significance (P = .09). This benefit was not evident when restricted to the cohort of 34 subjects with a history of prior HCT (P = .45). However, for subjects who had CAR T cell functional persistence of 63 days or less, inclusive of those with a history of prior HCT, HCT significantly improved LFS outcomes (P = .01). These data support the use of consolidative HCT following CD19 CAR T cell-induced remission for patients with no prior history of HCT and those with short functional CAR T cell persistence.

Blinatumomab Nonresponse and High-Disease Burden Are Associated With Inferior Outcomes After CD19-CAR for B-ALL.

PURPOSE: CD19-targeted chimeric antigen receptor T cells (CD19-CAR) and blinatumomab effectively induce remission in relapsed or refractory B-cell acute lymphoblastic leukemia (ALL) but are also associated with CD19 antigen modulation. There are limited data regarding the impact of prior blinatumomab exposure on subsequent CD19-CAR outcomes. PATIENTS AND METHODS: We conducted a multicenter, retrospective review of children and young adults with relapsed or refractory ALL who received CD19-CAR between 2012 and 2019. Primary objectives addressed 6-month relapse-free survival (RFS) and event-free survival (EFS), stratified by blinatumomab use. Secondary objectives included comparison of longer-term survival outcomes, complete remission rates, CD19 modulation, and identification of factors associated with EFS. RESULTS: Of 420 patients (median age, 12.7 years; interquartile range, 7.1-17.5) treated with commercial tisagenlecleucel or one of three investigational CD19-CAR constructs, 77 (18.3%) received prior blinatumomab. Blinatumomab-exposed patients more frequently harbored KMT2A rearrangements and underwent a prior stem-cell transplant than blinatumomab-naïve patients. Among patients evaluable for CD19-CAR response (n = 412), blinatumomab nonresponders had lower complete remission rates to CD19-CAR (20 of 31, 64.5%) than blinatumomab responders (39 of 42, 92.9%) or blinatumomab-naive patients (317 of 339, 93.5%), P < .0001. Following CD19-CAR, blinatumomab nonresponders had worse 6-month EFS (27.3%; 95% CI, 13.6 to 43.0) compared with blinatumomab responders (66.9%; 95% CI, 50.6 to 78.9; P < .0001) or blinatumomab-naïve patients (72.6%; 95% CI, 67.5 to 77; P < .0001) and worse RFS. High-disease burden independently associated with inferior EFS. CD19-dim or partial expression (preinfusion) was more frequently seen in blinatumomab-exposed patients (13.3% v 6.5%; P = .06) and associated with lower EFS and RFS. CONCLUSION: With the largest series to date in pediatric CD19-CAR, and, to our knowledge, the first to study the impact of sequential CD19 targeting, we demonstrate that blinatumomab nonresponse and high-disease burden were independently associated with worse RFS and EFS, identifying important indicators of long-term outcomes following CD19-CAR.