Diminished durability of <scp>chimeric antigen receptor</scp> T‐cell efficacy with severe or prolonged <scp>postinfusion</scp> cytopenias
Authors: Nadeem Tabbara, Jack Sharp, Daria Gaut, Thanh Thuy Dan Pham, Kevin Tang, Caspian Oliai, Myung Shin Sim, Gary Schiller, Patricia Young, Joshua P. Sasine
Journal: American Journal of Hematology (2022)

To the Editor: Chimeric antigen receptor (CAR) T-cell therapy is an exciting advance in the treatment of patients with hematologic malignancies. However, associated toxicities, including cytokine release syndrome (CRS), immune effector cell-associated neurotoxicity syndrome (ICANS), and prolonged cytopenias are central drawbacks of the platform. Systemic inflammation drives hematopoietic stem cell exhaustion1 and this inflammation, especially when it occurs immediately following genotoxic CAR T conditioning treatment, can lead to severe and long-lasting cytopenias. Postinfusion cytopenias are common and often lead to infections, need for transfusions, or administration of granulocyte-colony stimulating factor (G-CSF). Because the intensity of conditioning chemotherapy before CAR T is directly associated with CAR T response2 and more intense conditioning chemotherapy induces deeper myelosuppression, we analyzed the relationship between the postinfusion cytopenias and CAR T efficacy. In this single-institution retrospective study, we examined all patients who had received axicabtagene ciloleucel for relapsed–refractory diffuse large B cell lymphoma (DLBCL) between March 2018 and April 2021. Prior to CAR T-cell infusion, all patients received conditioning with fludarabine 30 mg/m2/day and cyclophosphamide 500 mg/m2/day on days −5 through −3, except for one patient who received reduced doses for chronic kidney disease (fludarabine 15 mg/m2/day and cyclophosphamide 375 mg/m2/day). Tocilizumab and/or corticosteroids were given for grade 2 or higher CRS or ICANS based on the American Society for Transplantation and Cellular Therapy consensus grading system.3 Each patient was evaluated for degree of cytopenias during treatment, defined as a nadir, day 28 measurements, or need for prolonged interventions (requiring supplemental G-CSF, red blood cell [pRBC] or platelet [plt] transfusion beyond day 28 after CAR T infusion). No institutional guidelines were in place for G-CSF use post-CAR T; however, in general, G-CSF was used if the absolute neutrophil count (ANC) was below 0.5 × 103/μL after day 28. Some patients received G-CSF earlier than day 28 and we have previously published those outcomes.4 The institutional threshold for pRBC transfusions was 8 g/dL; the threshold for plt transfusions was 10 × 103/μL for afebrile inpatients and 20 × 103/μL otherwise. We compared response to CAR T 6 weeks postinfusion, progression-free survival (PFS), and overall survival (OS) among patients based on cytopenias. A univariate logistic regression model and Cox proportional hazard regression model were used in analyzing response to CAR T and time to event (PFS and OS) data, respectively. Comparison of proportions was performed using Chi-squared or Fisher's exact tests. Kaplan–Meier survival estimates were compared using log-rank test. p values <.05 were considered statistically significant and all tests were two-sided. All analyses were performed using SAS 9.4 (Cary, NC). Prior to initiation of the study, collection and analysis of the patient data were approved by the Institutional Review Board (IRB). All studies were performed in accordance with the Declaration of Helsinki. The study included 54 patients, the median age was 59 years (range, 17–83 years), and the patients had received a median of 3 (range, 2–8) prior therapies (Table 1). Most patients (55.6%) had advanced-stage disease at the time of CAR T treatment. CD19-directed CAR T cells were manufactured to the target cell dose for all patients. As defined by need for G-CSF or a transfusion beyond day 28, 31 (57.4%) patients met criteria for prolonged cytopenias. Of the 31 patients who required G-CSF or transfusions beyond day 28, 19 (61.3%) received G-CSF and at least one transfusion, 9 (29.0%) received only G-CSF and no transfusions beyond day 28, 1 (3.2%) received pRBCs only, 1 (3.2%) received plts only, and 1 (3.2%) received both pRBCs and platelets without G-CSF beyond day 28. Duration of cytopenias was stratified based on the patients who died with ongoing cytopenias, were treated for relapse without resolution of cytopenias, or neither (Table 2). Patients who did not have a radiographic response to CAR T at first assessment were more likely to require G-CSF past day 28 or have a platelet count below the median at day 28 (Figure 1A). Other measurements of cytopenias shared that trend without reaching statistical significance. Patients with a day 28 ANC below the median (0.6 × 103/μL, HR = 2.07, p = .039), platelet nadir below the median (25 × 103/μL, HR = 3.10, p = .013), or day 28 platelet count below the median (39 × 103/μL, HR = 4.06, p = .0004) had a significantly lower PFS (Figure 1B–D). All patients who died during this study did so due to progressive lymphoma, except one patient with prolonged cytopenias who died of fungal pneumonia at 9.3 months post-CAR T. Patients requiring G-CSF administration beyond day 28 (HR = 2.89, p = .031), or who had a day 28 ANC below the median (HR = 2.67, p = .019) had a significantly lower OS (Figure 1E,F). Those who had a platelet nadir below the median (25 × 103/μL, HR = 3.55, p = .005) or a day 28 platelet count below the median (39 × 103/μL, HR = 3.50, p = .005) also had significantly a lower OS (Figure 1G,H). No significant differences with regard to risk of progression or death were observed based on transfusion requirements or other metrics of cytopenias, though the trends were the same (Figure S1). Baseline peripheral blood cell counts are listed in Table 1. No difference was observed in PFS or OS based on baseline cytopenias (Figure S1) except for an association with OS and baseline Hg below the median (7.8 g/dL, HR = 2.52, p = .033). Forty-one (75.9%) patients developed CRS after CAR T-cell infusion, including 5 (9.3%) with grade ≥3 CRS. Any grade ICANS developed in 23 (42.6%) patients and grade ≥3 neurotoxicity developed in 15 (27.8%) patients. There was an association between cytopenias and CAR T inflammatory toxicities, CRS and ICANS (Figure 1I,J). These associations, which are not necessarily causal, were also reported from other groups.5, 6 Eighty-three percent of patients with prolonged cytopenias developed CRS compared to 56% of patients without prolonged cytopenias (OR = 4.00, p = .03). Fifty-three percent of patients with prolonged cytopenias developed ICANS compared to 26% of patients without prolonged cytopenias (OR = 4.02, p = .04). Importantly, given the retrospective nature of the data, it does not imply causality. Number of prior lines of therapy did not associate with objective response to CAR T (p = .134) or risk of progression (HR = 1.15, p = .24), however, number of lines of therapy was associated with an increased risk of death, with each additional line of therapy representing a hazard ratio of 1.41 for OS (p = .006). This is likely reflective of the difficulty in treating patients who relapse with few treatment options remaining. Lines of therapy did not associate with baseline cytopenias or day 28 cytopenias; some baseline cytopenias were associated with development of post-CAR T cytopenias (Table 3). A multivariable analysis identified factors associated with OS and PFS. The covariates considered were age, sex, CRS, ICANS, infection, radiographic response at 6 weeks, baseline cytopenias by lineage (ANC, Hg, and platelets), nadir cytopenias by lineage, day 28 cytopenias by lineage, G-CSF given past day 28, red blood cell transfusions past day 28, platelet transfusions past day 28, and number of prior therapies. The final model was constructed using forward selection method confirmed by stepwise selection method. Development of infection, radiographic response at 6 weeks, and day 28 ANC were significantly associated with OS. For PFS, only day 28 platelet count was significantly associated in the multivariable model (Tables 4 and 5). Given that intensity of conditioning chemotherapy for CAR T correlates with CAR T expansion and efficacy,2 and that more intense conditioning causes deeper and longer cytopenias, it is surprising that cytopenias are associated with reduced CAR T efficacy. One explanation is that postinfusion cytopenias reflect general hematopoietic health, including T cells. If so, cytopenias after CAR T might merely be a useful biomarker of CAR T efficacy. However, the immune system functions in concert so a causal, actionable relationship cannot be excluded. Indeed, macrophages play a key role in CAR T toxicity7, 8 and animal studies support the notion that normal myeloid cells are critical for durability of CAR T response.9 That data, along with ours, begs a question: would augmenting myeloid recovery after CAR T aid anticancer activity? This could be accomplished through early use of G-CSF though we have previously reported the association of filgrastim and the development of severe CRS,4 suggesting that G-CSF should not be routinely used in the early period after CAR T infusion. Thrombopoietin receptor agonists augment hemopoietic stem cell regeneration and could be studied post-CAR T. Our group has reported other hematopoietic stem cell regenerative factors.10, 11 These, as well as autologous hematopoietic cell infusion post-CAR T, could be the subjects of clinical trials. CAR T-cell redosing is an ongoing area of investigation. Importantly, our study identifies a key confounder in redosing trials. Patients who are candidates for a second round of conditioning chemotherapy and CAR T dose by virtue of adequate bone marrow function are already poised to have a better outcome from the first dose of CAR T cells. Overall, patients with severe or prolonged cytopenias following CAR T therapy are at higher risk for relapse and might benefit from interventions to enhance the durability of CAR T function. Gary Schiller: Research funding and speaker's bureau—Kite Pharma, a Gilead Company. Joshua Sasine: Consulting—Kite Pharma, a Gilead Company. Nadeem Tabbara, Jack Sharp, Daria Gaut, and Joshua P. Sasine conceived and designed the study. Nadeem Tabbara, Jack Sharp, Daria Gaut, Kevin Tang, Caspian Oliai, and Patricia Young extracted the primary data. Myung Shin Sim provided statistical expertise and analysis. Nadeem Tabbara, Jack Sharp, Joshua P. Sasine, Gary Schiller, and Thanh Thuy Dan Pham analyzed the data and wrote the manuscript with input from all authors. The data supportive the findings of this study are available on request to the corresponding author. The data are not publicly available due to privacy or ethical restrictions. Figure S1. Clinical outcomes based on cytopenias. (A,B) Kaplan-Meier analyses of PFS and OS by median ANC nadir. (C,D) Kaplan-Meier analyses of PFS and OS by baseline ANC. (E,F) Kaplan-Meier analyses of PFS and OS by baseline Hg. (G,H) Kaplan-Meier analyses of PFS and OS by baseline platelet count. Log-rank analyses for Kaplan-Meier curves. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.