Study design and participants
We conducted a real-world study incorporating data from 400 patients with hematologic malignancies who underwent continuous CAR T treatment at the First Affiliated Hospital of Suzhou University (Jiangsu, China) between November 1, 2015 and January 1, 2019. The end date of the follow-up visit is September 1, 2019. The validation cohort consisted of an independent series of 39 patients from Hongci Hematology Hospital. Patient data were collected in accordance with the standards for registration tracking (NCT03919240). Patients who were on antithrombotic therapy, had severe renal or hepatic insufficiency or hemorrhagic disease, lacked information on bleeding complications or had no follow-up information were excluded. A flowchart of the patient enrollment process is shown (Figure 1). Electronic medical records are used to obtain demographic variables. Gender; sex; age; diagnosis; percentage of vesicle cells in bone marrow; type of CAR T cell therapy; application of IL-6 knockout; hypertension and diabetes status; CAR T cell count; CRS staging; use of hematopoietic stem cell transplantation (HSCT); efficacy (complete remission); transfusion application; DIC incidence; platelet count before and after CAR T cell therapy; white blood cell count; hemoglobin levels. Active partial thrombinogen time (APTT); thrombinogen time (PT); thrombinogen time (TT); IL-2, IL-4, IL-6, IL-6, IL-10, IL-17A, TNF-α, and interferon gamma (IFN-γ) levels. Bleeding risk was estimated from modified outpatient bleeding risk index (MOBRI) and levels of hypertension, abnormal renal/hepatic function, stroke, history or susceptibility to bleeding, IL-2-4, IL-6, IL-10, TNF-17A, TNF-α and IFN-γ; as well as bleeding site and bleeding grade. Details of the above variants are given in Part III of the supplementary information. The mortality data are derived from the hospital death registers, and the time of death is confirmed through access to electronic medical records or telephone follow-up visits. The median follow-up time was 9.2 months. The creation of the database was carried out by an independent researcher who was not involved in the care of the patients. Informed consent was obtained from all patients or their immediate family members. All research programmes are in line with the guidelines of the Ethics Committee of Soochow University and follow the Declaration of Helsinki.
CRS grading system
The CRS stage was evaluated by the CAR T-cell therapy-associated TOXicity Working Group[17]. Grade 1 organ toxicities were: temperature ≥ 38.0°C, systolic blood pressure ≥ 90 mmHg, and arterial oxygen saturation > 90%. Grade 2 organ toxicities were: hypotension with systolic blood pressure < 90 mmHg, responding to IV fluids or vasopressors at doses not meeting the criteria for grade 3 and hypoxia requiring supplemental oxygen, and fraction of inspired oxygen < 40%. Grade 3 organ toxicities were: hypotension requiring multiple or high dose vasopressors (as defined by norepinephrine ≥ 20 μg/min, dopamine ≥ 10 μg/kg/min, phenylephrine ≥ 200 μg/min, epinephrine ≥ 10 μg/min, vasopressin + norepinephrine ≥ 10 μg/min, and other vasopressor dose equivalent to norepinephrine ≥ 20 μg/min), and hypoxia requiring supplemental oxygen ≥ 40%. Grade 4 organ toxicities were: life-threatening hypotension and requirement for ventilator support. Grade 0 was defined as not meeting all conditions above.
Definition of bleeding class
Bleeding levels are determined according to World Health Organization scales. Patients without bleeding were defined as Grade 0. Grade 1 included stasis/suppurative/suppurative confined to one or two dependent sites, or sparse/uninflatable, oropharyngeal bleeding with epistaxis lasting <30 min. Grade 2 included syphilis, hematemesis, hemoptysis, fecal bleeding, blood in stool, musculoskeletal bleeding or soft tissue bleeding not requiring red blood cell transfusion within 24 h of onset, no hemodynamic instability, extensive epistaxis or oropharyngeal bleeding (i.e., duration >30 min), asymptomatic oral blood blisters, multiple petechiae, >2 cm each or any >10 cm, diffuse or multiple or >5 significant purpuric lesions, visible blood in the urine, invasive or abnormal bleeding at the surgical site, unexpected vaginal bleeding within 24 hours, more than two pieces of vaginal bleeding within 24 hours, macroscopically significant intracavitary bleeding, retinal bleeding, with or without visual impairment.Grade 3 includes: trichiasis, hematemesis, hematuria, including intermittent hemorrhage without clots, abnormal vaginal bleeding, bloody stool, epistaxis and oropharyngeal bleeding, traumatic bleeding, etc. Musculoskeletal hemorrhage or soft tissue hemorrhage requiring red blood cell transfusion within 24 hours of onset and without hemodynamic instability, significant intracorporeal hemorrhage visible, cerebral hemorrhage observed on computed tomography, and no neurologic symptoms.Grade 4 includes debilitating hemorrhage, including retinal hemorrhage and visual impairment (defined as visual impairment; patients with suspected visual impairment require ophthalmologist consultation), nonfatal cerebral hemorrhage with neurologic signs and symptoms, hemorrhage associated with hemodynamic instability (hypotension, systolic or diastolic blood pressure changes >30 mmHg), and fatal hemorrhage of any origin. Bleeding levels 0 to 2 were classified as low bleeding levels, while levels 3 and 4 were classified as high bleeding levels [18].
Assays for plasma cytokines
Peripheral blood specimens from patients treated with CAR T cells were collected and all specimens were treated with EDTA as an anticoagulant. The peripheral blood specimens were then centrifuged at 800×g for 10 min at room temperature to collect plasma. Plasma levels of IL-2, IL-4, IL-6, IL-10, IL-17A, TNF-α and IFN-γ were determined by flow cytometry using the corresponding antibodies (BD Biosciences, Franklin Lakes, NJ, USA) according to manufacturer's instructions. Details of this antibody are given in the supplementary material. Flow cytometry was performed using the BD FACSCalibur system (BD Biosciences).
Statistical analysis
Sample size assessment was performed using NCSS-PASS software (https://www.ncss.com/software/pass/) version 11.0. Power was set as 0.90 and alpha was 0.5. Mortality rates (0.40 and 0.029) for the severe and non-severe bleeding groups from previous data were entered into PASS. the actual hazard ratio was set to 10. sample size was then calculated using PASS and the minimum sample size was found to be 233 (control group = 203 and experimental group = 30). Our sample size of 400 (363 in the control group and 37 in the experimental group) is more appropriate. The sample size assessment report (Supplementary Material Part II) was also presented. Missing data were estimated and a random forest algorithm using the mouse package in RStudio (R version 3.6.1). Continuous variables with skewed and normal distributions are expressed as median to interval mean and mean ± standard deviation. The Mann-Whitney U test and unpaired t test were used for intergroup comparisons. Categorical variables were expressed as percentages and compared using the κ² test. Cumulative mortality was shown using Kaplan-Meier curves and analyzed using the log-rank test. Univariate and multivariate survival analyses for total survival (OS) were assessed using Cox regression models. The significance of covariates on prognosis was visually analyzed using forest plots. Restricted stereo spline analysis was performed using Harrell's Regression Modelling Strategies (rms) package.
To build a bleeding risk model, Lasso regression was used to identify factors associated with bleeding. The contribution of each covariate was quantified and presented in the form of a Nomogram plot with 1000 self-directed internal validations. The consistency of the model created was assessed using a calibration assay. The net clinical benefit of the model compared with traditional bleeding scores was evaluated using decision curve analysis (DCAs). The coordination of each model was visualized using scatterplots and analyzed using 1000 bootstrapping. The association between bleeding grade and survival endpoint was analyzed using Kaplan-Meier curve and log-rank test. Statistical analyses were performed using RStudio (R version 3.6.1) with rms, risk regression, ggplot2, PredictABLE and surminer packages.