2.1 Cell lines and primary samples.
The DLBCL cell lines OCI-Ly3, Su-DHL2, Su-DHL4, and OCI-Ly1 were generously gifted by Dr. T. Zhao (Nanfang Hospital, affiliated to Southern Medical University, Guangzhou, China). CY-GCB and ZML-ABC primary cells were isolated from patients with GCB-DLBCL and ABC-DLBCL, respectively (“CY” and “ZML” are the abbreviations of patients’ names). Both types of primary cells were characterized by flow cytometry and immunohistochemistry (Fig. S1). Human macrophages were isolated from peripheral blood mononuclear cells and identified using flow cytometry (Supplementary methods). DLBCL cells were cultured in IMDM (Iscove's Modified Dulbecco's Media) (Invitrogen, USA) with 10% fetal bovine serum (FBS) (Invitrogen, USA). EA.hy926 cells were cultured in RPMI 1640 medium (Invitrogen, USA) with 10% FBS (Invitrogen, CA, USA).
2.2 CAR-T cell generation
The CAR construct contained a CD19-specific scFv, a CD28 costimulatory domain, a 4-1BB costimulatory domain, and a CD3ζ chain. The genes of mCherry fluorescent protein and firefly luciferase were linked with CAR using the P2A sequence peptide to monitor CAR expression in vitro and in vivo. Both genes were cloned into the pHR lentiviral vector.
Blood samples were obtained from patients with DLBCL and healthy volunteers following a protocol approved by the University Institutional Review Board. The T-cells were isolated from the collected samples using a Human CD3+ T-cell Enrichment Kit (Stem Cell, USA) and cultured in AIM-V (Invitrogen, USA) supplemented with 6% AB human serum (GEMINI, US) and 30 IU/mL human interleukin (IL)-2 (Peprotech, US). The T-cells were transduced with lentiviral vectors at a multiplicity of infection (MOI) ≈ 10 after stimulation with CD3/CD28 Dynabeads (Invitrogen, USA) for 72 h. The CAR expression was detected by flow cytometry either with mCherry or anti-F(ab) staining (Jackson ImmunoResearch, USA). The median transduction efficiency was 66%, ranging from 44.2% to 71.6%.
2.3 Flow cytometry
Cells were harvested from in vitro experiments and animals, washed twice with phosphate-buffered saline (PBS), and stained with antibodies (Table S1) for 15-20 min. The cell phenotypes were analyzed using FlowJo 10.0 software (Tree Star, USA).
2.4 Cytotoxicity assay
Lenalidomide (Selleck, USA) was dissolved in DMSO at a concentration of 2 μM, since the therapeutic dose of lenalidomide could not exceed 2.2 μM [16]. The target cells, including OCI-Ly3, OCI-Ly1, Su-DHL2, and Su-DHL4, were co-cultured with CAR-T cells for 7 h. The effector-to-target cell (E/T) ratio was based on the count of CAR-positive cells obtained by flow cytometry. The antitumor effect of the treatment was assessed through the lactate dehydrogenase (LDH) assay, performed using the CytoTox96 Kit (Promega, WI, USA) following the manufacturer’s protocol. Cytotoxicity was calculated in the form of LDH release as follows:
2.5 Degranulation assay
The CAR-T cells were co-cultured with OCI-Ly1 or OCI-Ly3 cells at the effector-to-target ratio of 5:1. Thereafter, a CD107a antibody (BioLegend, USA) was added to each well, followed by the addition of monensin solution (Sigma-Aldrich, USA) after a 1 h incubation. Flow cytometry was performed 5 h later to determine the percentage of CAR+ CD107a+ cells.
2.6 Cell counting kit-8 assay
The cell counting kit-8 (CCK-8) assay (Dojindo, Japan) was used to measure the proliferation of DLBCL and EA.hy926 cells. Cells were seeded in a 96-well plate and cultured in different media, including lenalidomide-supplemented medium and medium supplemented with macrophage cell culture supernatant with or without lenalidomide. Growth inhibition was determined from absorbance measurements obtained using the CCK-8 assay, following the manufacturer’s protocol.
2.7 Cytokine analysis
Secretion of the cytokines IL-2, interferon (IFN)-γ, tumor necrosis factor (TNF)-α, IL-4, IL-6, and IL-10 was assessed using ELISA kits (Mabtech, Sweden) after CD19-CAR-T cells were co-cultured with tumor cells (OCI-Ly3 and OCI-Ly1) for 24 h.
2.8 Carboxyfluorescein succinimidyl ester (CFSE) assay
CAR-T cells were stained with CellTrace CFSE staining solution (ThermoFisher, USA) before co-culturing with DLBCL cells (with or without lenalidomide administration). After 72 h or 96 h of incubation, the cells were harvested and flow cytometry was performed to detect proliferation.
2.9 In vitro migration assay
EA.hy926 cells were first seeded in Transwell inserts (Corning, USA) at a density of 1 × 104 cells per well and incubated for 4 h. These cell-seeded Transwell inserts were transferred into a 24-well plate seeded with macrophages . The co-cultures were cultured in medium with or without 2 μM lenalidomide. After 72 h, the Transwell inserts were moved to a new 24-well plate and incubated in complete medium supplemented with either CLL19 or CLL21. Thereafter, CAR-T cells were seeded above the EA.hy926 cell layer at a density of 5 × 105 cells per insert. After 5 h, the CAR-T cells that had migrated through the EA.hy926 cell layer and reached the bottom wells were harvested, counted, and subjected to flow cytometry for identification.. This protocol has been illustrated in Figure S10.
2.10 Real-time polymerase chain reaction analysis
RNA content of the CAR-T cells was extracted using the ChamQ Universal SYBR qPCR Master Mix (Vazyme Biotech, China), and the corresponding cDNA was synthesized. Genes related to T-cell function were selected and identified using a polymerase chain reaction (PCR) array (Qiagen, Germany). The relative cDNA expression was quantified after normalization.
2.11 Animal experiments
NOD-SCID mice, aged 6-8 weeks, were obtained from the Shanghai Laboratory Animal Center (Shanghai, China). All the experiments were performed following the protocol approved by the Animal Care and Use Committee of Ruijin Hospital, affiliated to the School of Medicine at the Shanghai Jiao Tong University. The mice used in the experiments were sex-matched.
Bone marrow (BM) involvement occurs in 11-34% of DLBCL patients at initial diagnosis[17, 18], which is associated with poor prognosis[19]. Thus, the “lymphoma-leukemia xenograft mouse model” was established in the present study to simulate DLBCL progression by injecting luciferase-positive OCI-Ly3 cells via tail vein. Primary cells isolated from patients or OCI-Ly3 cells were also subcutaneously injected into the right flank of each mouse. Tumor-bearing mice were randomized by tumor burden and infused either with saline, lenalidomide 10 mg/(kg × d), or CAR-T cells with or without LEN 10 mg/(kg × d). Detailed protocol is presented in Figure 4 and Figure 5. Bioluminescent imaging was performed using an in vivo imaging system (PerkinElmer, USA) and analyzed with the help of the Living Imaging software (PerkinElmer, USA) to determine the extent of infiltration of CAR-T cells and the tumor burden. To establish the ABC-DLBCL and GCB-DLBCL patient-derived xenograft mouse model, primary ZML-ABC and CY-GCB cells obtained from patients were subcutaneously injected in the right flanks of NOD-SCID mice. The tumors in PDX mouse mimicked the histology and gene expression observed in ABC/GCB-DLBCL patients.
2.12 Statistical analysis
Statistical analysis was performed with GraphPad Prism Software (GraphPad, CA, USA). The t test was used for comparing two groups, while one-way analysis of variance (ANOVA) was used for comparing more than two groups. Survival analysis was conducted using the Kaplan–Meier method and comparisons were made using the log-tank test. Comparisons for which P < 0.05 were considered to be statistically significant.