Engineered CD47 protects T cells for enhanced antitumour immunity.

Adoptively transferred T cells and agents designed to block the CD47-SIRPα axis are promising cancer therapeutics that activate distinct arms of the immune system1,2. Here we administered anti-CD47 antibodies in combination with adoptively transferred T cells with the goal of enhancing antitumour efficacy but observed abrogated therapeutic benefit due to rapid macrophage-mediated clearance of T cells expressing chimeric antigen receptors (CARs) or engineered T cell receptors. Anti-CD47-antibody-mediated CAR T cell clearance was potent and rapid enough to serve as an effective safety switch. To overcome this challenge, we engineered the CD47 variant CD47(Q31P) (47E), which engages SIRPα and provides a 'don't eat me' signal that is not blocked by anti-CD47 antibodies. TCR or CAR T cells expressing 47E are resistant to clearance by macrophages after treatment with anti-CD47 antibodies, and mediate substantial, sustained macrophage recruitment to the tumour microenvironment. Although many of the recruited macrophages manifested an M2-like profile3, the combined therapy synergistically enhanced antitumour efficacy. Our study identifies macrophages as major regulators of T cell persistence and illustrates the fundamental challenge of combining T-cell-directed therapeutics with those designed to activate macrophages. It delivers a therapeutic approach that is capable of simultaneously harnessing the antitumour effects of T cells and macrophages, offering enhanced potency against solid tumours.

CD22-directed CAR T-cell therapy induces complete remissions in CD19-directed CAR-refractory large B-cell lymphoma.

The prognosis of patients with large B-cell lymphoma (LBCL) that progresses after treatment with chimeric antigen receptor (CAR) T-cell therapy targeting CD19 (CAR19) is poor. We report on the first 3 consecutive patients with autologous CAR19-refractory LBCL who were treated with a single infusion of autologous 1 × 106 CAR+ T cells per kilogram targeting CD22 (CAR22) as part of a phase 1 dose-escalation study. CAR22 therapy was relatively well tolerated, without any observed nonhematologic adverse events higher than grade 2. After infusion, all 3 patients achieved complete remission, with all responses continuing at the time of last follow-up (mean, 7.8 months; range, 6-9.3). Circulating CAR22 cells demonstrated robust expansion (peak range, 85.4-350 cells per microliter), and persisted beyond 3 months in all patients with continued radiographic responses and corresponding decreases in circulating tumor DNA beyond 6 months after infusion. Further accrual at a higher dose level in this phase 1 dose-escalation study is ongoing and will explore the role of this therapy in patients in whom prior CAR T-cell therapies have failed. This trial is registered on clinicaltrials.gov as #NCT04088890.

Cryopreservation and storage patterns of hematopoietic progenitor stem cells for multiple myeloma.

Autologous hematopoietic stem cell transplantation (HCT) has been a standard of care treatment for eligible patients with newly diagnosed multiple myeloma (MM). Guidelines generally recommend hematopoietic progenitor cell (HPC) harvest for two potential HCT. There is a paucity of data reporting use of such collections in the era of novel approved therapies. In this single-center retrospective study, our goal was to determine the HPC utilization rate and costs associated with leukocytapheresis, collection, storage, and disposal to guide future HPC collection planning. We included 613 patients with MM who underwent HPC collection over a nine-year period. The patients were separated into four groups based on HPC utilization: 1) patients who never proceeded to HCT, or Harvest and Hold (14.8 %), 2) patients who proceeded to one HCT with banked HPC remaining (76.8 %), 3) patients who proceeded to one HCT without HPC remaining (5.1 %), and 4) patients who proceeded to two HCTs (3.3 %). After collection, 73.9 % of patients underwent HCT within 30 days. Of patients with banked HPC, defined as not undergoing HCT within 30 days of leukocytapheresis, the overall utilization rate was 14.9 %. At 2- and 5-years post HPC collection, utilization rate was 10.4 % and 11.5 %, respectively. In conclusion, our results suggest very low utilization of stored HPC, raising into question the current HPC collection targets. Given advances in MM therapy, as well as significant costs associated with harvest and storage, collection for unplanned future use warrants reconsideration. As a result of our analysis, our institution has reduced our HPC collection targets.

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.

Incidence and outcomes of cytomegalovirus reactivation after chimeric antigen receptor T-cell therapy.

ABSTRACT: Cytomegalovirus (CMV) reactivation is a major complication among seropositive allogeneic hematopoietic cell transplantation recipients; however, data on CMV reactivation after chimeric antigen receptor (CAR) T-cell therapy are limited. We report the incidence and outcomes of 95 adult CMV-seropositive patients who received CAR T-cell therapy between February 2018 and February 2023. CMV outcomes were CMV reactivation (any viremia) and clinically significant CMV infection (cs-CMV). Thirty-one patients (33%) had evidence of CMV reactivation (any viremia), and 10 patients (11%) had cs-CMV. The median time from CAR T-cell infusion to CMV reactivation was 19 days (interquartile range [IQR], 9-31). The cumulative incidence of CMV (any viremia) was significantly higher among patients with grade 3 to 4 cytokine release syndrome (67 vs 28%; P = .01), and those who received corticosteroids (39 vs 21%; P = .03), anakinra (56 vs 28%; P = .02), or ≥2 immunosuppressants (41 vs 21%; P = .02). Receipt of corticosteroids (18 vs 0%; P = .004), tocilizumab (14 vs 0%; P = .04), anakinra (33 vs 7%; P = .008), and ≥2 immunosuppressants (20 vs 0%; P = .001) were all associated with cs-CMV. Receiving ≥2 immunosuppressants was associated with a twofold increase in CMV reactivation in multivariate analyses (adjusted odds ratio [aOR], 2.27; 95% confidence interval, 1.1-4.8; P = .03). Overall, the 1-year mortality was significantly higher in those with CMV reactivation (57% vs 23%; P = .001). Immunosuppression, particularly with corticosteroids, for the management of CAR T-cell toxicities, is a major risk factor for CMV reactivation.

Bridging therapy with axicabtagene ciloleucel for large B-cell lymphoma: results from the US Lymphoma CAR-T Consortium.

ABSTRACT: During the manufacturing period of autologous chimeric antigen receptor (CAR) T-cell therapy, patients may experience a decline in their condition due to cancer progression. In this study, we investigated the impact of bridging therapy (BT) on the outcome of patients with relapsed/refractory large B-cell lymphoma who received antilymphoma treatment between leukapheresis and axicabtagene ciloleucel (axi-cel) infusion. We conducted our analysis using data from the multicenter US Lymphoma CAR-T Consortium, with a median follow-up of 33 months (range, 4.3-42.1). Out of the 298 patients who underwent leukapheresis, 275 patients received axi-cel. A total 52% of patients (n = 143) who received BT had a higher baseline risk profile than patients who did not receive BT, and these patients, as a group, had inferior outcomes compared with those who did not receive BT. However, after propensity score matching between the 2 groups, there were no statistically significant differences in overall response rate (77% vs 87%; P = .13), complete response rate (58% vs 70%; P = .1), progression-free survival (hazard ratio [HR], 1.25; P = .23), and overall survival (HR, 1.39; P=.09) between the BT group and the no-BT group, respectively. Analyzing the effects of BT in the whole cohort that underwent leukapheresis regardless of receiving axi-cel (intention-to-treat analysis) showed similar results. Radiation BT resulted in outcomes similar to those observed with nonradiation BT. Our findings suggest that BT may be safe without a significant impact on long-term survival for patients who require disease stabilization during the manufacturing period. Moreover, our results suggest that there is no clear advantage to using radiation-based BT over nonradiation-based BT.

Continuous EEG monitoring detects nonconvulsive seizure and Ictal-Interictal Continuum abnormalities in moderate to severe ICANS following systemic CAR-T therapy.

Background and Purpose: Immune Cell Effector Associated Neurotoxicity Syndrome (ICANS) is common amongst patients receiving CD19 targeted Chimeric Antigen Receptor T-cell (CAR-T) therapy. The purpose of this study is to characterize the incidence of seizures and ictal-interictal continuum (IIC) abnormalities in patients with ICANS. Methods: Retrospective review of consecutive patients treated with axicabtagene ciloleucel (axi-cel) for recurrent high-grade systemic lymphoma at Stanford Medical Center between 2/2016-6/2019. Electronic medical records (EMR) were reviewed for clinical features, treatment information, EEG data, CRS (cytokine release syndrome)/ICANS severity, and clinical outcomes. Results: Fifty-six patients met inclusion criteria. 85.7% of patients developed CRS, and 58.9% developed ICANS. Twenty-eight patients had EEG monitoring, of whom 26 had ICANS. Median duration of EEG monitoring was 30 hours (range .5-126 hours). Four patients (7.1%) had seizures (1 patient had a clinical generalized seizure, 2 patients had clinical and nonconvulsive seizures, and 1 patient had an isolated non-convulsive seizure). Ictal-interictal continuum abnormalities were common, of which generalized periodic discharges (GPDs) with triphasic morphology and GPDs with epileptiform morphology were most frequently seen. Generalized periodic discharges with triphasic wave morphology were found across Grade 2-3 peak ICANS severity, however the majority (86%) of patients with epileptiform GPDs had Grade 3 peak ICANS severity. Conclusions: Among patients receiving axi-cel, seizure occurred in 7.1% of the total cohort, representing 12% of patients with ICANS. Ictal-interictal continuum abnormalities are also seen in patients with ICANS, most commonly GPDs. 75% of patients with seizures had nonconvulsive seizures supporting the use of continuous video EEG monitoring in this population.

Determinants of resistance to engineered T cell therapies targeting CD19 in large B cell lymphomas.

Most relapsed/refractory large B cell lymphoma (r/rLBCL) patients receiving anti-CD19 chimeric antigen receptor (CAR19) T cells relapse. To characterize determinants of resistance, we profiled over 700 longitudinal specimens from two independent cohorts (n = 65 and n = 73) of r/rLBCL patients treated with axicabtagene ciloleucel. A method for simultaneous profiling of circulating tumor DNA (ctDNA), cell-free CAR19 (cfCAR19) retroviral fragments, and cell-free T cell receptor rearrangements (cfTCR) enabled integration of tumor and both engineered and non-engineered T cell effector-mediated factors for assessing treatment failure and predicting outcomes. Alterations in multiple classes of genes are associated with resistance, including B cell identity (PAX5 and IRF8), immune checkpoints (CD274), and those affecting the microenvironment (TMEM30A). Somatic tumor alterations affect CAR19 therapy at multiple levels, including CAR19 T cell expansion, persistence, and tumor microenvironment. Further, CAR19 T cells play a reciprocal role in shaping tumor genotype and phenotype. We envision these findings will facilitate improved chimeric antigen receptor (CAR) T cells and personalized therapeutic approaches.

Imagining the cell therapist: Future CAR T cell monitoring and intervention strategies to improve patient outcomes.

Chimeric antigen receptor (CAR) T cell therapy is now approved for the standard of care treatment of several types of relapsed or refractory hematologic malignancies. Future advances may extend cellular therapies to solid tumors or even non-malignant diseases. As patient need grows, a clinical specialty of "cell therapy" may emerge. Here, we envision the needs of a clinical cell therapist to monitor and intervene upon patients receiving cell therapies. These include: (1) monitoring patient T cell quality and the host immune environment to ensure optimal timing for cell therapy. (2) Tumor antigen profiling to personalize CAR T cell targeting. (3) Real-time monitoring of CAR T cells and circulating tumor DNA to modulate CAR T cell activity to maximize tumor eradication while mitigating toxicity. (4) Monitoring of CAR rejection and anti-CAR immunity posttreatment to inform re-dosing and subsequent cell therapy strategies. Armed with these tools, the future Cell Therapist may optimize and personalize treatment to avoid toxicity and improve efficacy universally across CAR designs.

Recurrent Status Epilepticus in the Setting of Chimeric Antigen Receptor (CAR)-T Cell Therapy.

Axicabtagene ciloleucel (AC) is an FDA-approved anti-CD19 autologous chimeric antigen receptor T-cell (CAR-T) therapy for refractory diffuse large B cell lymphoma (DLBCL). While its efficacy in DLBCL has been promising, neurotoxicity remains a significant concern. We present a case of a 22-year-old woman with chemotherapy-refractory DLBCL who exhibited Grade IV neurotoxicity in the setting of sepsis, after undergoing AC infusion. Despite prophylactic levetiracetam given per guidelines,1,2 she experienced a precipitous mental status decline on post-infusion day 8 (D8) followed by hypoxic respiratory failure in the setting of clinical status epilepticus on D11 and nonconvulsive status epilepticus (NCSE) on D18. While neuroimaging was unremarkable, EEG demonstrated diffuse slowing and 2.5-3 Hz generalized periodic discharges consistent with NCSE. Seizures were initially refractory to lorazepam, increasing doses of levetiracetam, and phenobarbital, requiring a midazolam drip titrated to 50-70% burst suppression for resolution. Methylprednisolone and tocilizumab were used to treat neurotoxicity and cytokine release syndrome, respectively. Empiric antibiotics were used for sepsis. After cessation of sedatives on D19, mental status improved to near baseline. PET/CT just prior to discharge showed a complete response of the DLBCL (Deauville 3). She was discharged on D37 with no further seizure activity. Unfortunately, a 3-month interval PET/CT demonstrated disease progression which continued through salvage pembrolizumab eventually leading to death 1.2 years post-CAR-T infusion. This case illustrates the clinical management challenges of a complex and rare neurotoxic side effect of CAR-T cell therapy, namely NCSE following status epilepticus.

Severity of Cytokine Release Syndrome Influences Outcome After Axicabtagene Ciloleucel for Large B cell Lymphoma: Results from the US Lymphoma CAR-T Consortium.

BACKGROUND: The majority of patients with large B-cell lymphoma treated with axicabtagene ciloleucel (axi-cel), an anti-CD19 chimeric antigen receptor (CAR) T-cell therapy, develop cytokine release syndrome (CRS). Whether the lack of development of CRS with axi-cel is associated with inferior lymphoma outcomes is unknown. Additionally, relationship between CRS grade and lymphoma outcome is not well established. METHODS: The US Lymphoma CAR T Consortium includes seventeen US academic centers that contribute data independently of manufacturers. We analyzed the modified intent-to-treat population of 275 patients receiving axi-cel in two different ways: 1) Two group analysis comparing no CRS with any grade CRS; 2) Three group analysis comparing grade 0 CRS with grade 1 to 2 CRS, and grade 3-5 CRS. RESULTS: In this large multi-center observational cohort of 275 patients receiving axi-cel, 9% (n = 24) did not develop CRS, 84% (n = 232) developed grade 1-2 CRS, and 7% (n = 19) developed grade 3 to 5 CRS. Patients without CRS, compared with those having any grade CRS, had similar overall response rates (ORR), lower complete response (CR) rates and inferior progression free survival (PFS) with no statistically significant difference in overall survival (OS). Patients experiencing grade 1 to 2 CRS had superior CR rate and PFS, as compared to those without CRS or with grade 3 to 5 CRS. Grade 3 to 5 CRS was associated with a worse OS. CONCLUSION: Overall, durable responses were seen in patients that did not develop CRS, however grade 1 to 2 CRS was associated with better outcomes while those with grade 3 to 5 experienced the worse outcomes.

Post-infusion CAR TReg cells identify patients resistant to CD19-CAR therapy.

Approximately 60% of patients with large B cell lymphoma treated with chimeric antigen receptor (CAR) T cell therapies targeting CD19 experience disease progression, and neurotoxicity remains a challenge. Biomarkers associated with resistance and toxicity are limited. In this study, single-cell proteomic profiling of circulating CAR T cells in 32 patients treated with CD19-CAR identified that CD4+Helios+ CAR T cells on day 7 after infusion are associated with progressive disease and less severe neurotoxicity. Deep profiling demonstrated that this population is non-clonal and manifests hallmark features of T regulatory (TReg) cells. Validation cohort analysis upheld the link between higher CAR TReg cells with clinical progression and less severe neurotoxicity. A model combining expansion of this subset with lactate dehydrogenase levels, as a surrogate for tumor burden, was superior for predicting durable clinical response compared to models relying on each feature alone. These data credential CAR TReg cell expansion as a novel biomarker of response and toxicity after CAR T cell therapy and raise the prospect that this subset may regulate CAR T cell responses in humans.

Incidence and risk factors associated with bleeding and thrombosis following chimeric antigen receptor T-cell therapy.

Bleeding and thrombotic events are an emerging toxicity associated with chimeric antigen receptor (CAR) therapies. To determine their incidence, we retrospectively analyzed consecutive adult patients (N = 127) with large B-cell lymphoma (LBCL) or B-cell acute lymphoblastic leukemia (B-ALL) treated from 2017 through 2020 with axicabtagene ciloleucel (axi-cel; n = 89) or a bispecific CD19/CD22 CAR (n = 38). Twelve (9.4%) and 8 (6.3%) patients developed bleeding and thrombosis within the first 3 months, respectively. In the axi-cel subgroup, these occurred in 11.2% and 6.7%, respectively. Bleeding occurred between days 8 and 30 (median, 17.5) and thrombosis between days 2 and 91 (median, 29). Bleeding sites included genitourinary, soft tissue, intracranial, gastrointestinal, and pulmonary and were associated with features of consumptive coagulopathy. On univariate analysis, patients with bleeding were older, had lower baseline platelets (86 × 103/µL vs 178 × 103/µL; P < .01), lower platelet and fibrinogen nadirs , and elevated lactate dehydrogenase. Immune effector cell (IEC)-associated neurotoxicity syndrome (ICANS) grade ≥3 was associated with increased bleeding (50% vs 15%; P = .01), thrombosis (50% vs 16%; P = .04), prothrombin time prolongation, hypofibrinogenemia, and elevated D-dimer. Low pretreatment platelet counts were associated with bleeding in a multivariate logistic regression model. Patients with thrombocytopenia or severe ICANS are at increased risk of bleeding and should be closely monitored, particularly within the first month after CAR therapy. Future studies in larger cohorts should assess risk factors for systemic coagulopathies in CAR T therapy, including their association with neurotoxicity.

Concordance of peripheral blood and bone marrow measurable residual disease in adult acute lymphoblastic leukemia.

Monitoring of measurable residual disease (MRD) is essential to the management of acute lymphoblastic leukemia (ALL) and is typically performed through repeated bone marrow (BM) assessments. Using a next-generation sequencing (NGS) MRD platform, we performed a prospective observational study evaluating the correlation between peripheral blood (PB) and BM MRD in adults with ALL receiving cellular therapies (hematopoietic cell transplantation [HCT] and chimeric antigen receptor T-cell [CAR-T] therapies). Among the study cohort (N = 69 patients; 126 paired PB/BM samples), we found strong correlation between PB and BM MRD (r = 0.87; P < .001), with a sensitivity and specificity of MRD detection in the PB of 87% and 90%, respectively, relative to MRD in the BM. MRD became detectable in the PB in 100% of patients who subsequently relapsed following HCT, with median time from MRD+ to clinical relapse of 90 days, and in 85% of patients who relapsed following CAR T, with median time from MRD+ to clinical relapse of 60 days. In adult patients with ALL undergoing cellular therapies, we demonstrate strong concordance between NGS-based MRD detected in the PB and BM. Monitoring of ALL MRD in the PB appears to be an adequate alternative to frequent invasive BM evaluations in this clinical setting.

Immune reconstitution and infectious complications following axicabtagene ciloleucel therapy for large B-cell lymphoma.

Chimeric antigen receptor (CAR) T-cell therapy targeting CD19 has significantly improved outcomes in the treatment of refractory or relapsed large B-cell lymphoma (LBCL). We evaluated the long-term course of hematologic recovery, immune reconstitution, and infectious complications in 41 patients with LBCL treated with axicabtagene ciloleucel (axi-cel) at a single center. Grade 3+ cytopenias occurred in 97.6% of patients within the first 28 days postinfusion, with most resolved by 6 months. Overall, 63.4% of patients received a red blood cell transfusion, 34.1% of patients received a platelet transfusion, 36.6% of patients received IV immunoglobulin, and 51.2% of patients received growth factor (granulocyte colony-stimulating factor) injections beyond the first 28 days postinfusion. Only 40% of patients had recovered detectable CD19+ B cells by 1 year, and 50% of patients had a CD4+ T-cell count <200 cells per µL by 18 months postinfusion. Patients with durable responses to axi-cel had significantly longer durations of B-cell aplasia, and this duration correlated strongly with the recovery of CD4+ T-cell counts. There were significantly more infections within the first 28 days compared with any other period of follow-up, with the majority being mild-moderate in severity. Receipt of corticosteroids was the only factor that predicted risk of infection in a multivariate analysis (hazard ratio, 3.69; 95% confidence interval, 1.18-16.5). Opportunistic infections due to Pneumocystis jirovecii and varicella-zoster virus occurred up to 18 months postinfusion in patients who prematurely discontinued prophylaxis. These results support the use of comprehensive supportive care, including long-term monitoring and antimicrobial prophylaxis, beyond 12 months after axi-cel treatment.

Monitoring of Circulating Tumor DNA Improves Early Relapse Detection After Axicabtagene Ciloleucel Infusion in Large B-Cell Lymphoma: Results of a Prospective Multi-Institutional Trial.

PURPOSE: Although the majority of patients with relapsed or refractory large B-cell lymphoma respond to axicabtagene ciloleucel (axi-cel), only a minority of patients have durable remissions. This prospective multicenter study explored the prognostic value of circulating tumor DNA (ctDNA) before and after standard-of-care axi-cel for predicting patient outcomes. METHODS: Lymphoma-specific variable, diversity, and joining gene segments (VDJ) clonotype ctDNA sequences were frequently monitored via next-generation sequencing from the time of starting lymphodepleting chemotherapy until progression or 1 year after axi-cel infusion. We assessed the prognostic value of ctDNA to predict outcomes and axi-cel-related toxicity. RESULTS: A tumor clonotype was successfully detected in 69 of 72 (96%) enrolled patients. Higher pretreatment ctDNA concentrations were associated with progression after axi-cel infusion and developing cytokine release syndrome and/or immune effector cell-associated neurotoxicity syndrome. Twenty-three of 33 (70%) durably responding patients versus 4 of 31 (13%) progressing patients demonstrated nondetectable ctDNA 1 week after axi-cel infusion (P < .0001). At day 28, patients with detectable ctDNA compared with those with undetectable ctDNA had a median progression-free survival and OS of 3 months versus not reached (P < .0001) and 19 months versus not reached (P = .0080), respectively. In patients with a radiographic partial response or stable disease on day 28, 1 of 10 patients with concurrently undetectable ctDNA relapsed; by contrast, 15 of 17 patients with concurrently detectable ctDNA relapsed (P = .0001). ctDNA was detected at or before radiographic relapse in 29 of 30 (94%) patients. All durably responding patients had undetectable ctDNA at or before 3 months after axi-cel infusion. CONCLUSION: Noninvasive ctDNA assessments can risk stratify and predict outcomes of patients undergoing axi-cel for the treatment of large B-cell lymphoma. These results provide a rationale for designing ctDNA-based risk-adaptive chimeric antigen receptor T-cell clinical trials.

Molecular Imaging of Chimeric Antigen Receptor T Cells by ICOS-ImmunoPET.

PURPOSE: Immunomonitoring of chimeric antigen receptor (CAR) T cells relies primarily on their quantification in the peripheral blood, which inadequately quantifies their biodistribution and activation status in the tissues. Noninvasive molecular imaging of CAR T cells by PET is a promising approach with the ability to provide spatial, temporal, and functional information. Reported strategies rely on the incorporation of reporter transgenes or ex vivo biolabeling, significantly limiting the application of CAR T-cell molecular imaging. In this study, we assessed the ability of antibody-based PET (immunoPET) to noninvasively visualize CAR T cells. EXPERIMENTAL DESIGN: After analyzing human CAR T cells in vitro and ex vivo from patient samples to identify candidate targets for immunoPET, we employed a syngeneic, orthotopic murine tumor model of lymphoma to assess the feasibility of in vivo tracking of CAR T cells by immunoPET using the 89Zr-DFO-anti-ICOS tracer, which we have previously reported. RESULTS: Analysis of human CD19-CAR T cells during activation identified the Inducible T-cell COStimulator (ICOS) as a potential target for immunoPET. In a preclinical tumor model, 89Zr-DFO-ICOS mAb PET-CT imaging detected significantly higher signal in specific bone marrow-containing skeletal sites of CAR T-cell-treated mice compared with controls. Importantly, administration of ICOS-targeting antibodies at tracer doses did not interfere with CAR T-cell persistence and function. CONCLUSIONS: This study highlights the potential of ICOS-immunoPET imaging for monitoring of CAR T-cell therapy, a strategy readily applicable to both commercially available and investigational CAR T cells.See related commentary by Volpe et al., p. 911.

CAR T cells with dual targeting of CD19 and CD22 in adult patients with recurrent or refractory B cell malignancies: a phase 1 trial.

Despite impressive progress, more than 50% of patients treated with CD19-targeting chimeric antigen receptor T cells (CAR19) experience progressive disease. Ten of 16 patients with large B cell lymphoma (LBCL) with progressive disease after CAR19 treatment had absent or low CD19. Lower surface CD19 density pretreatment was associated with progressive disease. To prevent relapse with CD19- or CD19lo disease, we tested a bispecific CAR targeting CD19 and/or CD22 (CD19-22.BB.z-CAR) in a phase I clinical trial ( NCT03233854 ) of adults with relapsed/refractory B cell acute lymphoblastic leukemia (B-ALL) and LBCL. The primary end points were manufacturing feasibility and safety with a secondary efficacy end point. Primary end points were met; 97% of products met protocol-specified dose and no dose-limiting toxicities occurred during dose escalation. In B-ALL (n = 17), 100% of patients responded with 88% minimal residual disease-negative complete remission (CR); in LBCL (n = 21), 62% of patients responded with 29% CR. Relapses were CD19-/lo in 50% (5 out of 10) of patients with B-ALL and 29% (4 out of 14) of patients with LBCL but were not associated with CD22-/lo disease. CD19/22-CAR products demonstrated reduced cytokine production when stimulated with CD22 versus CD19. Our results further implicate antigen loss as a major cause of CAR T cell resistance, highlight the challenge of engineering multi-specific CAR T cells with equivalent potency across targets and identify cytokine production as an important quality indicator for CAR T cell potency.