Optimizing early phase clinical trial washout periods: a report from the therapeutic advances in childhood leukemia and lymphoma (TACL) consortium.

PURPOSE: The National Cancer Institute (NCI) issued a 2021 memorandum adopting the American Society of Clinical Oncology (ASCO) and Friends of Cancer Research (Friends) task force recommendations to broaden clinical study eligibility criteria. They recommended that washout periods be eliminated for most prior cancer therapy and when required, to utilize evidence/rationale-based criteria. The Therapeutic Advances in Childhood Leukemia and Lymphoma (TACL) consortium responded to this guidance. PROCESS: A TACL task force reviewed the consortium's research portfolio, the relevant literature and guidance documents from ASCO-Friends, NCI, and US Food and Drug Administration (FDA) to make expert consensus and evidence-based recommendations for modernizing, broadening and codifying TACL-study washout periods while ensuring consistency with pediatric ethics and federal regulations. TACL's screening log was reviewed to estimate the impact that updated washout periods would have on patient inclusivity and recruitment. RESULTS: Over a 19-year period, 42 patients (14.6% of all screened ineligible (n = 287) patients), were identified as excluded from TACL early-phase studies exclusively due to not meeting washout criteria. An additional six (2.1%) did not meet washout and at least one other exclusion criterion. A new TACL washout guidance document was developed/adopted for use. Where washout criteria were not eliminated, rationale/evidenced-based criteria were established with citation. CONCLUSION: In an effort to reduce unnecessary exclusion from clinical trials, TACL created rationale/evidenced-based washout period standards largely following guidance from the NCI/ASCO-Friends recommendations. These new, expanded eligibility criteria are expected to increase access to TACL clinical trials while maintaining safety and scientific excellence.

INSPIRED Symposium Part 2: Prevention and Management of Relapse Following Chimeric Antigen Receptor T Cell Therapy for B Cell Acute Lymphoblastic Leukemia.

Although CD19-directed chimeric antigen receptor (CAR) T cell therapy (CAR-T) for relapsed/refractory B cell acute lymphoblastic leukemia (B-ALL) has been transformative in inducing and sustaining remission, relapse rates remain unacceptably high, with approximately 50% of children and young adults experiencing relapse within the first year postinfusion. Emerging strategies to extend the durability of remission involve the use of prognostic biomarkers to identify those at high risk of relapse or incorporate strategies aimed to enhancing functional CAR T cell persistence. Nonetheless, with antigen loss/down-regulation or evolution to lineage switch as major mechanisms of relapse, optimizing single antigen targeting alone is insufficient. Here, with a focus on relapse prevention strategies, including postinfusion surveillance and treatment approaches being explored to optimize post-CAR-T management (eg, combinatorial antigen targeting strategies, preemptive hematopoietic cell transplantation), we review the current state of the art in the prevention and management of post CAR-T relapse. We highlight the advancements in the field and identify gaps in the literature to guide future research in optimizing the prevention and management of post-CAR-T relapse in children and young adults with B-ALL.

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.

Potential clinical use of azacitidine and MEK inhibitor combination therapy in PTPN11-mutated juvenile myelomonocytic leukemia.

Juvenile myelomonocytic leukemia (JMML) is a rare myeloproliferative neoplasm of childhood. The molecular hallmark of JMML is hyperactivation of the Ras/MAPK pathway with the most common cause being mutations in the gene PTPN11, encoding the protein tyrosine phosphatase SHP2. Current strategies for treating JMML include using the hypomethylating agent, 5-azacitidine (5-Aza) or MEK inhibitors trametinib and PD0325901 (PD-901), but none of these are curative as monotherapy. Utilizing an Shp2E76K/+ murine model of JMML, we show that the combination of 5-Aza and PD-901 modulates several hematologic abnormalities often seen in JMML patients, in part by reducing the burden of leukemic hematopoietic stem and progenitor cells (HSC/Ps). The reduced JMML features in drug-treated mice were associated with a decrease in p-MEK and p-ERK levels in Shp2E76K/+ mice treated with the combination of 5-Aza and PD-901. RNA-sequencing analysis revealed a reduction in several RAS and MAPK signaling-related genes. Additionally, a decrease in the expression of genes associated with inflammation and myeloid leukemia was also observed in Shp2E76K/+ mice treated with the combination of the two drugs. Finally, we report two patients with JMML and PTPN11 mutations treated with 5-Aza, trametinib, and chemotherapy who experienced a clinical response because of the combination treatment.

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.

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.

Chimeric Antigen Receptor T-cell Therapy: Current Status and Clinical Outcomes in Pediatric Hematologic Malignancies.

Chimeric antigen receptor T-cell (CART) therapy has transformed the treatment paradigm for pediatric patients with relapsed/refractory B-cell acute lymphoblastic leukemia (B-ALL), with complete remission rates in key pivotal CD19-CART trials ranging from 65% to 90%. Alongside this new therapy, new toxicity profiles and treatment limitations have emerged, necessitating toxicity consensus grading systems, cooperative group trials, and novel management approaches. This review highlights the results of key clinical trials of CART for pediatric hematologic malignancies, discusses the most common toxicities seen to date, and elucidates challenges, opportunities, and areas of active research to optimize this therapy.

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.

Beyond the storm - subacute toxicities and late effects in children receiving CAR T cells.

As clinical advances with chimeric antigen receptor (CAR) T cells are increasingly described and the potential for extending their therapeutic benefit grows, optimizing the implementation of this therapeutic modality is imperative. The recognition and management of cytokine release syndrome (CRS) marked a milestone in this field; however, beyond the understanding gained in treating CRS, a host of additional toxicities and/or potential late effects of CAR T cell therapy warrant further investigation. A multicentre initiative involving experts in paediatric cell therapy, supportive care and/or study of late effects from cancer and haematopoietic stem cell transplantation was convened to facilitate the comprehensive study of extended CAR T cell-mediated toxicities and establish a framework for new systematic investigations of CAR T cell-related adverse events. Together, this group identified six key focus areas: extended monitoring of neurotoxicity and neurocognitive function, psychosocial considerations, infection and immune reconstitution, other end organ toxicities, evaluation of subsequent neoplasms, and strategies to optimize remission durability. Herein, we present the current understanding, gaps in knowledge and future directions of research addressing these CAR T cell-related outcomes. This systematic framework to study extended toxicities and optimization strategies will facilitate the translation of acquired experience and knowledge for optimal application of CAR T cell therapies.

EEG Correlates of Delirium in Children and Young Adults With CD19-Directed CAR T Cell Treatment-Related Neurotoxicity.

INTRODUCTION: EEG patterns in chimeric antigen receptor T cell treatment-associated neurotoxicity (immune effector cell-associated neurotoxicity syndrome) have not yet been systematically studied. We tested the hypothesis that EEG background abnormalities in immune effector cell-associated neurotoxicity syndrome correlate with clinical signs of neurotoxicity. In addition, we describe ictal and interictal EEG patterns to better understand the natural history of immune effector cell-associated neurotoxicity syndrome-associated seizures. METHODS: EEGs were obtained in 19 of 100 subjects in a prospective cohort study of children and young adults undergoing CD19-directed chimeric antigen receptor T cell therapy. We classified the EEG background on a severity scale of 0 to 5 during 30-minute epochs. EEG grades were compared with neurotoxicity scored by Common Terminology Criteria for Adverse Events and Cornell Assessment of Pediatric Delirium scores. Descriptive analysis was conducted for ictal and interictal EEG abnormalities. RESULTS: EEG background abnormality scores correlated well with Common Terminology Criteria for Adverse Events neurotoxicity scores (P = 0.0022) and Cornell Assessment of Pediatric Delirium scores (P = 0.0085). EEG was better able to differentiate the severity of coma patterns compared with the clinical scores. The EEG captured electroclinical seizures in 4 of 19 subjects, 3 of whom had additional electrographic-only seizures. Seizures most often arose from posterior head regions. Interictal epileptiform discharges were focal, multifocal, or lateralized periodic discharges. No seizures or interictal epileptiform abnormalities were seen in subjects without previous clinical seizures. CONCLUSIONS: Continuous EEG monitoring is high yield for seizure detection in high-risk chimeric antigen receptor T cell patients, and electrographic-only seizures are common. Increasing severity of EEG background abnormalities correlates with increasing neurotoxicity grade.

Allopurinol use during pediatric acute lymphoblastic leukemia maintenance therapy safely corrects skewed 6-mercaptopurine metabolism, improving inadequate myelosuppression and reducing gastrointestinal toxicity.

BACKGROUND: Inadequate myelosuppression during maintenance therapy for acute lymphoblastic leukemia (ALL) is associated with an increased risk of relapse. One mechanism is skewed metabolism of 6-mercaptopurine (6MP), a major component of maintenance therapy, which results in preferential formation of the hepatotoxic metabolite (6-methyl mercaptopurine [6MMP]) with low levels of the antileukemic metabolite, 6-thioguanine nucleotides (6TGN). Allopurinol can modify 6MP metabolism to favor 6TGN production and reduce 6MMP. METHODS: Patients in maintenance were considered for allopurinol treatment who had the following features: (a) Grade ≥3 hepatotoxicity; (b) Grade ≥2 nonhepatic gastrointestinal (GI) toxicity; or (c) persistently elevated absolute neutrophil count (ANC) despite >150% protocol dosing of oral chemotherapy. RESULTS: From 2013 to 2017, 13 ALL patients received allopurinol: nine for hepatotoxicity, five for inadequate myelosuppression, and three for nonhepatic GI toxicity (four met multiple criteria). Allopurinol was well tolerated, without significant adverse events. Allopurinol resulted in a significant decrease in the average 6MMP/6TGN ratio (mean reduction 89.1, P = .0001), with a significant increase in 6TGN (mean 550.4, P = .0008) and a significant decrease in 6MMP (mean 13 755, P = .0013). Patients with hepatotoxicity had a significant decrease in transaminase elevation after starting allopurinol (alanine transaminase [ALT] mean decrease 22.1%, P = .02), and all with nonhepatic GI toxicity had improved symptoms. Those with inadequate myelosuppression had a significant increase in the time with ANC in goal (mean increase 26.4%, P = .0004). CONCLUSIONS: Allopurinol during ALL maintenance chemotherapy is a safe, feasible, and effective intervention for those who have altered metabolism of 6MP causing toxicity or inadequate myelosuppression.

Pediatric Acute Lymphoblastic Leukemia, Version 2.2020, NCCN Clinical Practice Guidelines in Oncology.

Acute lymphoblastic leukemia (ALL) is the most common pediatric malignancy. Advancements in technology that enhance our understanding of the biology of the disease, risk-adapted therapy, and enhanced supportive care have contributed to improved survival rates. However, additional clinical management is needed to improve outcomes for patients classified as high risk at presentation (eg, T-ALL, infant ALL) and who experience relapse. The NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines) for pediatric ALL provide recommendations on the workup, diagnostic evaluation, and treatment of the disease, including guidance on supportive care, hematopoietic stem cell transplantation, and pharmacogenomics. This portion of the NCCN Guidelines focuses on the frontline and relapsed/refractory management of pediatric ALL.

Preemptive mitigation of CD19 CAR T-cell cytokine release syndrome without attenuation of antileukemic efficacy.

Immunotherapy with the adoptive transfer of T cells redirected with CD19-specific chimeric antigen receptors (CARs) for B-lineage acute lymphoblastic leukemia (ALL) can salvage >80% of patients having relapsed/refractory disease. The therapeutic index of this emerging modality is attenuated by the occurrence of immunologic toxicity syndromes that occur upon CAR T-cell engraftment. Here, we report on the low incidence of severe cytokine release syndrome (CRS) in a subject treated with a CAR T-cell product composed of a defined ratio CD4:CD8 T-cell composition with a 4-1BB:zeta CAR targeting CD19 who also recieved early intervention treatment. We report that early intervention with tocilizumab and/or corticosteroids may reduce the frequency at which subjects transition from mild CRS to severe CRS. Although early intervention doubled the numbers of subjects dosed with tocilizumab and/or corticosteroids, there was no apparent detrimental effect on minimal residual disease-negative complete remission rates or subsequent persistence of functional CAR T cells compared with subjects who did not receive intervention. Moreover, early intervention therapy did not increase the proportion of subjects who experience neurotoxicity or place subjects at risk for infectious sequelae. These data support the contention that early intervention with tocilizumab and/or corticosteroids in subjects with early signs of CRS is without negative impact on the antitumor potency of CD19 CAR T cells. This intervention serves to enhance the therapeutic index in relapsed/refractory patients and provides the rationale to apply CAR T-cell therapy more broadly in ALL therapy. This trial was registered at www.clinicaltrials.gov as #NCT020284.

Knock-in of the Wt1 R394W mutation causes MDS and cooperates with Flt3/ITD to drive aggressive myeloid neoplasms in mice.

Wilms tumor 1 (WT1) is a zinc finger transcriptional regulator, and has been implicated as both a tumor suppressor and oncogene in various malignancies. Mutations in the DNA-binding domain of the WT1 gene are described in 10-15% of normal-karyotype AML (NK-AML) in pediatric and adult patients. Similar WT1 mutations have been reported in adult patients with myelodysplastic syndrome (MDS). WT1 mutations have been independently associated with treatment failure and poor prognosis in NK-AML. Internal tandem duplication (ITD) mutations of FMS-like tyrosine kinase 3 (FLT3) commonly co-occur with WT1-mutant AML, suggesting a cooperative role in leukemogenesis. The functional role of WT1 mutations in hematologic malignancies appears to be complex and is not yet fully elucidated. Here, we describe the hematologic phenotype of a knock-in mouse model of a Wt1 mutation (R394W), described in cases of human leukemia. We show that Wt1 +/R394W mice develop MDS which becomes 100% penetrant in a transplant model, exhibit an aberrant expansion of myeloid progenitor cells, and demonstrate enhanced self-renewal of hematopoietic progenitor cells in vitro. We crossbred Wt1 +/R394W mice with knock-in Flt3 +/ITD mice, and show that mice with both mutations (Flt3 +/ITD/Wt1 +/R394W) develop a transplantable MDS/MPN, with more aggressive features compared to either single mutant mouse model.

Lymphocyte apheresis for chimeric antigen receptor T-cell manufacturing in children and young adults with leukemia and neuroblastoma.

BACKGROUND: The first step in the production of chimeric antigen receptor T cells is the collection of autologous T cells using apheresis technology. The procedure is technically challenging, because patients often have low leukocyte counts and are heavily pretreated with multiple lines of chemotherapy, marrow transplantation, and/or radiotherapy. Here, we report our experience of collecting T lymphocytes for chimeric antigen receptor T-cell manufacturing in pediatric and young adult patients with leukemia, non-Hodgkin lymphoma, or neuroblastoma. STUDY DESIGN AND METHODS: Apheresis procedures were performed on a COBE Spectra machine using the mononuclear cell program, with a collection target of 1 × 109 total mononuclear cells per kilogram. Data were collected regarding preapheresis and postapheresis blood counts, apheresis parameters, products, and adverse events. RESULTS: Ninety-nine patients (ages 1.3-25.7 years) and 102 apheresis events were available for analysis. Patients underwent apheresis at a variety of absolute lymphocyte cell counts, with a median absolute lymphocyte count of 944 cells/µL (range, 142-6944 cells/µL). Twenty-two patients (21.6%) had absolute lymphocyte counts less than 500 cells/µL. The mononuclear cell target was obtained in 100% of all apheresis harvests, and chimeric antigen receptor T-cell production was possible from the majority of collections (94%). Mononuclear cell collection efficiency was 65.4%, and T-lymphocyte collection efficiency was 83.4%. Ten patients (9.8%) presented with minor adverse events during the 102 apheresis procedures, with one exception of a severe allergy. CONCLUSIONS: Mononuclear cell apheresis for chimeric antigen receptor T-cell therapy is well tolerated and safe, and it is possible to obtain an adequate quantity of CD3+ lymphocytes for chimeric antigen receptor T-cell manufacturing in heavily pretreated patients who have low lymphocyte counts.