Purpose:

B-cell maturation antigen (BCMA)-targeted chimeric antigen receptor (CAR) T cells (CART-BCMA) are a promising treatment for relapsed/refractory multiple myeloma (r/rMM). We evaluated the safety and feasibility of bridging radiation (RT) in subjects treated on a phase I trial of CART-BCMA.

Experimental Design:

Twenty-five r/rMM subjects were treated in three cohorts with two doses of CART-BCMA cells ± cyclophosphamide. We retrospectively analyzed toxicity, response, and CART manufacturing data based on RT receipt.

Results:

Thirteen subjects received no RT <1 year before CART infusion (Group A). Eight subjects received RT <1 year before CART infusion (Group B) with median time from RT to apheresis of 114 days (range 40–301). Four subjects received bridging-RT (Group C) with a median dose of 22 Gy and time from RT to infusion of 25 days (range 18–35). Group C had qualitatively lower rates of grade 4 (G4) hematologic toxicities (25%) versus A (61.5%) and B (62.5%). G3–4 neurotoxicity occurred in 7.7%, 25%, and 25% in Group A, B, and C, respectively. G3–4 cytokine release syndrome was observed in 38.5%, 25%, and 25% in Group A, B, and C, respectively. Partial response or better was observed in 54%, 38%, and 50% of Group A, B, and C, respectively. RT administered <1 year (P = 0.002) and <100 days (P = 0.069) before apheresis was associated with lower in vitro proliferation during manufacturing; however, in vivo CART-BCMA expansion appeared similar across groups.

Conclusions:

Bridging-RT appeared safe and feasible with CART-BCMA therapy in our r/rMM patients, though larger future studies are needed to draw definitive conclusions.

Translational Relevance

Chimeric antigen receptor (CAR) T cells are promising new therapies for hematologic malignancies. Neurotoxicity and cytokine release syndrome (CRS) are serious, potentially fatal toxicities associated with CAR T-cell therapy. In this study, we did not observe an association between bridging radiation (RT) and CRS, neurotoxicity, or hematologic toxicity in patients with relapsed/refractory multiple myeloma (r/rMM). We also showed that patients receiving bridging-RT achieved similar in vivo peak expansion and persistence of anti-BCMA CAR T cells at day 28 post-infusion. However, larger prospective trials investigating RT with anti-BCMA CART therapy are needed to draw definitive conclusions and may further optimize the safety and long-term efficacy of this novel cellular treatment in r/rMM.

Multiple myeloma (MM) remains incurable. Although immunomodulatory drugs (IMID), proteasome inhibitors (PI), and mAbs have prolonged survival (1, 2), most patients relapse due to drug resistance (3–6). Chimeric antigen receptor (CAR) T-cell therapy can yield durable responses in patients with advanced hematologic malignances (7–10). B-cell maturation antigen (BCMA), a member of the tumor necrosis factor receptor superfamily, is a rational target for MM due to its highly selective expression in plasma cells. Early results of BCMA-specific CAR T cells in heavily pretreated patients with relapsed and/or refractory MM (r/rMM) have demonstrated impressive overall response rates (ORR) of 64% to 95% and induction of minimal residual disease (MRD)-negative complete responses (CR; refs. 11–15).

Patients with r/rMM often require radiotherapy (RT) to palliate symptomatic disease. Apart from its local effects, RT has systemic immunomodulatory effects. RT has been found to upregulate MHC-I expression, give rise to novel peptides, and increase presentation of tumor-associated antigens (16–18). RT can also facilitate homing of antigen-specific T cells and possibly counteract the immunosuppressive tumor microenvironment (16, 19). Thus, RT has the potential to combat the following challenges of CART therapy: (i) cancer evasion by poorly antigenic tumor, (ii) optimization of CAR T-cell trafficking to tumor, and (iii) the immunoinhibitory tumor microenvironment. In fact, preclinical data suggest that RT conditioning may promote susceptibility to CART therapy and decrease antigen-negative tumor relapse (20).

The efficacy of CART therapies comes with risk of toxicity from immune activation, namely cytokine release syndrome (CRS) and neurotoxicity. Current anti-BCMA CART trials have cited CRS rates (any grade) of >60% with grade 3 (G3) CRS reaching up to 40% (11–13, 21). Neurotoxicity (any grade) has been observed in approximately 20% to 30% of patients, with most cases being self-limited or responsive to steroids (11–13, 21). Nonetheless, severe CRS and neurotoxicity can occur and are potentially fatal (11–13, 21).

Additional considerations for CAR T cells include the fitness of patients' endogenous T cells and lymphodepletion. Our institution conducted a phase I trial evaluating autologous T cells expressing a fully human BCMA-specific CAR containing CD3ζ and 4-1BB signaling domains (CART-BCMA) in r/rMM patients, with and without lymphodepleting chemotherapy. Investigators showed a higher frequency of CD8+ naïve or early memory T cells and a higher ratio of CD4+ to CD8+ T cells (CD4/CD8 ratio) in the premanufacturing leukapheresis product were associated with better clinical response and more likely to be found in patients with minimal exposure to systemic therapy (22). Lymphodepletion was also found to enhance the clinical benefit of CART therapy (12, 23–25).

Furthermore, although CART manufacturing protocols on average range from 8 to 12 days, vein to vein time can take 3 to 4 weeks, preventing prompt treatment of aggressive disease. In fact, 8% to 14% of apheresed patients in two recent trials never received CAR T cells due to rapid progression, and 88% of patients in the KarMMA trial required bridging therapy (i.e., treatment between leukapheresis and CART infusion; refs. 12, 13). In some cases, patients may require RT as a bridge to CART infusion for fast relief of symptomatic lesions or maintenance of performance status. However, available literature on peri-CART RT is limited to small, single-institution experiences evaluating CD19-directed CART therapy in non–Hodgkin lymphoma (26–28). Herein, we present the first report looking at safety and feasibility of bridging-RT and pre-apheresis RT in r/rMM patients who received CART-BCMA therapy.

The University of Pennsylvania conducted a phase I, single-center, open-label study (NCT02546167) investigating the safety and efficacy of CART-BCMA in patients with r/rMM after failing at least three prior regimens, or two prior regimens if dual-refractory to a PI or IMID. Twenty-five subjects were treated in three cohorts: cohort 1, 1 × 108 to 5 × 108 CART-BCMA cells alone; cohort 2, cyclophosphamide (Cy) 1.5 g/m2 plus 1 × 107 to 5 × 107 CART-BCMA cells; and cohort 3, Cy 1.5 g/m2 plus 1 × 108 to 5 × 108 CART-BCMA cells. A fully human BCMA-specific CAR construct containing CD3ζ and 4-1BB signaling domains was used. Leukapheresis was performed after enrollment following a 2-week washout from prior myeloma therapy (4 weeks for mAbs). Anti-myeloma therapy could resume during manufacturing until 2 weeks prior to first CART infusion. CART-BCMA cells were administered over 3 days in three dose fractions (10% of dose on day 0, 30% on day 1, and 60% on day 2). The 30% or 60% dose could be held if subjects developed signs of CRS. Cy was administered 3 days prior to first CART-BCMA infusion. This study was conducted in accordance with the Declaration of Helsinki, and written consent was obtained from all subjects. Full eligibility criteria and protocol methods have been published previously (12). Correlative studies, analyzed here in this context, including the qPCR- and flow cytometry–based detection of CAR T cells, flow cytometry for T-cell subsets, and levels of soluble BCMA (solBCMA) were reported previously (12).

The institutional review board at the University of Pennsylvania approved this retrospective study of subjects enrolled on the trial described above. RT plans were accessed to confirm treatment dates, treatment location, total dose delivered, fractionation, modality, and technique. Because the duration of how long RT affects the local environment and immune system is not well established, patient grouping was intended to be inclusive, accounting for radiation recall (a tissue reaction that occurs in previously irradiated area after administration of systemic therapy) and variable recovery time of different lymphocytes. Radiation recall has been observed in patients with a long interval (∼1 year) between the end of RT and delivery of immunotherapy, and restoration of particular lymphocyte subsets post-RT has been shown to take 1 year or longer (29, 30). Thus, subjects were characterized into three groups: Group A, no RT within 1 year before apheresis (n = 13); Group B, RT within 1 year before apheresis (n = 8); and Group C, bridging-RT defined as RT delivered after apheresis but before CART infusion (n = 4). Data from the parent trial were reviewed to document patient baseline demographics, clinicopathologic features, prior therapies, CART manufacturing details, and clinical outcomes. Toxicity data were collected from time of Cy-based lymphodepletion for cohort 2 and 3 or first CART-BCMA infusion for cohort 1. Toxicity was graded per CTCAE version 4.0 with the exception of CRS, which was graded per the University of Pennsylvania CRS Grading System (12). Myeloma responses were scored by the updated International Myeloma Working Group (IMWG) criteria (3).

Statistical analysis is primarily descriptive due to small sample sizes in each group and the pilot nature of the parent trial. Kaplan–Meier analysis was used to estimate progression-free survival (PFS), overall survival (OS), and associated median survival times with follow-up defined relative to first CART-BCMA infusion (designated Day 0). Associations between binary endpoints (e.g., receipt of RT) and continuous variables were assessed using the Wilcoxon rank-sum test. Kruskal–Wallis test was used when more than two groups were compared simultaneously. Exact two-sided P values are reported when applicable. A P value <0.05 was considered significant. Analysis was performed using RStudio version 1.3.1056 and GraphPad Prism 9.

Patient groups: no RT <1 year before apheresis (A), RT <1 year before apheresis (B), and bridging-RT (C)

Twenty-five subjects receiving CART-BCMA between November 2015 and December 2017 for r/rMM were identified. Four subjects received bridging-RT (Group C) ≤35 days before CART infusion, 8 subjects received RT <1 year before apheresis (Group B), and 13 subjects had no RT <1 year before apheresis (Group A). Within Group A, 3 subjects had a history of remote RT before apheresis (range, 853–3,452 days) and 10 subjects never had RT. Twenty-one subjects received all three planned CART-BCMA does fractions whereas 4 subjects (1 in Group A, 2 in Group B, and 1 in Group C) received 40% of planned CART-BCMA dose due to early CRS.

Baseline characteristics per group are summarized in Table 1. Each group was heavily pretreated with a median of seven prior lines of therapy and high rates of prior autologous stem cell transplant. At least one high-risk cytogenetic abnormality was detected in all subjects in Group A and B and 3 of 4 subjects in Group C; baseline tumor burden was high across all groups with comparable ranges of myeloma cells on bone marrow biopsy (Table 1) and serum concentrations of solBCMA prior to cyclophosphamide lymphodepletion (P = 0.58; Supplementary Fig. S1A). Extramedullary disease, a poor prognostic indicator, was absent in Group A but common in Group B (63%) and Group C (50%).

Table 1.

Subject characteristics for Group A (no RT <1 year prior to apheresis), Group B (RT <1 year prior to apheresis), and Group C (bridging-RT).

Patient characteristics
Group A (n = 13)Group B (n = 8)Group C (n = 4)
 Median (range) or % Median (range) or % Median (range) or % 
Age, years 58 (44–73) 59 (47–75) 57 (51–63) 
Sex, M/F 62%/38% 50%/50% 100%/0% 
Cohort 1/2/3 23%/15%/62% 75%/0%/25% 0%/50%/50% 
Median time from diagnosis, years 4.1 (1.8–14.5) 4.8 (1.8–8.8) 4.3 (2.3–9.4) 
High-risk cytogeneticsa 100% 100% 75% 
Del17p or TP53 mutation 77% 63% 50% 
Prior lines of therapy, n 7 (4–13) 7 (3–10) 7 (6–7) 
Len/Bort/Pom/Carf/Dara, % exposed 100%/100%/100%/92%/77% 100%/100%/88%/88%/63% 100%/100%/75%/100%/100% 
Len/Bort/Pom/Carf/Dara, % refractory 85%/92%/100%/69%/69% 75%/88%/75%/75%/63% 50%/75%/75%/100%/100% 
Dual-/Triple-class/Quad-/Penta-refractoryb 100%/69%/69%/54% 88%/50%/38%/25% 100%/100%/25%/25% 
Prior autologous SCT 92% 100% 100% 
Extramedullary disease 0% 63% 50% 
Bone marrow plasma cells 60% (13–90) 85% (0–95) 27% (3–80) 
ALC pre-apheresis, × 103/μL 0.80 (0.40–1.30) 0.65 (0.30–1.80) 1.00 (0.27–1.50) 
% Lymphocytes pre-apheresis 25 (8–39) 21 (11–36) 22 (7–33) 
Absolute CD3+ T-cell count pre-apheresis, cells/μL 538 (295–1,513)c 295 (151–1,529) 507 (376–1,554) 
Baseline LDH, U/l 162 (75–315) 169 (112–385) 196 (130–308) 
Baseline serum creatinine, mg/dL 0.93 (0.64–1.83) 1.0 (0.83–2.87) 0.76 (0.55–1.77) 
Baseline hemoglobin, g/dL 8.9 (6.9–15.2) 9.0 (6.9–12.2) 9.3 (8.8–12.0) 
Baseline platelets, × 103/μL 137 (25–221) 152 (13–193) 124 (41–316) 
Patient characteristics
Group A (n = 13)Group B (n = 8)Group C (n = 4)
 Median (range) or % Median (range) or % Median (range) or % 
Age, years 58 (44–73) 59 (47–75) 57 (51–63) 
Sex, M/F 62%/38% 50%/50% 100%/0% 
Cohort 1/2/3 23%/15%/62% 75%/0%/25% 0%/50%/50% 
Median time from diagnosis, years 4.1 (1.8–14.5) 4.8 (1.8–8.8) 4.3 (2.3–9.4) 
High-risk cytogeneticsa 100% 100% 75% 
Del17p or TP53 mutation 77% 63% 50% 
Prior lines of therapy, n 7 (4–13) 7 (3–10) 7 (6–7) 
Len/Bort/Pom/Carf/Dara, % exposed 100%/100%/100%/92%/77% 100%/100%/88%/88%/63% 100%/100%/75%/100%/100% 
Len/Bort/Pom/Carf/Dara, % refractory 85%/92%/100%/69%/69% 75%/88%/75%/75%/63% 50%/75%/75%/100%/100% 
Dual-/Triple-class/Quad-/Penta-refractoryb 100%/69%/69%/54% 88%/50%/38%/25% 100%/100%/25%/25% 
Prior autologous SCT 92% 100% 100% 
Extramedullary disease 0% 63% 50% 
Bone marrow plasma cells 60% (13–90) 85% (0–95) 27% (3–80) 
ALC pre-apheresis, × 103/μL 0.80 (0.40–1.30) 0.65 (0.30–1.80) 1.00 (0.27–1.50) 
% Lymphocytes pre-apheresis 25 (8–39) 21 (11–36) 22 (7–33) 
Absolute CD3+ T-cell count pre-apheresis, cells/μL 538 (295–1,513)c 295 (151–1,529) 507 (376–1,554) 
Baseline LDH, U/l 162 (75–315) 169 (112–385) 196 (130–308) 
Baseline serum creatinine, mg/dL 0.93 (0.64–1.83) 1.0 (0.83–2.87) 0.76 (0.55–1.77) 
Baseline hemoglobin, g/dL 8.9 (6.9–15.2) 9.0 (6.9–12.2) 9.3 (8.8–12.0) 
Baseline platelets, × 103/μL 137 (25–221) 152 (13–193) 124 (41–316) 

Abbreviations: ALC, absolute lymphocyte count; LDH, lactate dehydrogenase; SCT, stem cell transplant.

aComplex karyotype includes gain 1q, deletion 17p, t(14;16), and/or t(4;14).

bDual-refractory = refractory to both 1 PI and 1 IMID; Triple-class refractory = refractory to at least 1 PI, 1 IMID, and 1 CD38 antibody (usually daratumumab); Quad-refractory = refractory to 2 PIs and 2 IMIDs; Penta-refractory = refractory to 2 PIs, 2 IMIDs, and daratumumab.

cSubjects 1 and 2 in Group A did not have pre-apheresis T-cell counts done (n = 11). Normal range, 900 to 3,245 cells/μL.

Clinical outcomes: response rates, OS, and PFS

Median follow-up for the subjects was 16.3 months (range, 0.8–42.1). At time of data cutoff, 18 subjects had expired, and 7 were still alive. OS was not significantly different between Group A, B, and C (median 667, 295, and 264 days, respectively; P = 0.082; Fig. 1A). At time of data cutoff, 2 subjects (subjects 19, 33), 1 from Group A and 1 from Group B, remained progression free at 728 and 623 days (roughly 30 and 20 months), respectively; all remaining subjects had progressed. PFS was not significantly different between Group A, B, and C (median 64, 71, and 94 days, respectively; P = 0.86; Fig. 1B).

Figure 1.

Clinical outcomes between Group A, B, and C using Kaplan–Meier plot with log-rank test based on group. A, OS (P = 0.08). B, PFS (P = 0.86).

Figure 1.

Clinical outcomes between Group A, B, and C using Kaplan–Meier plot with log-rank test based on group. A, OS (P = 0.08). B, PFS (P = 0.86).

Close modal

Conventional univariate analysis to compare treatment response between groups was not performed due to the limited sample size. Responses [minimal response (MR) or better] were observed in 9 of 13 subjects (69%) in Group A, 4 of 8 subjects (50%) in Group B, and 4 of 4 subjects (100%) in Group C. Objective responses [partial response (PR) or better] were confirmed in 54% in Group A, 38% in Group B, and 50% in Group C (Table 2).

Table 2.

Patient responses for Group A (no RT <1 year prior to apheresis), Group B (RT <1 year prior to apheresis), and Group C (bridging-RT).

Patient Responses
Group A (n = 13)Group B (n = 8)Group C (n = 4)
 n (%) n (%) n (%) 
sCR 1 (8) 0 (0) 0 (0) 
CR 1 (8) 0 (0) 0 (0) 
VGPR 3 (23) 2 (25) 0 (0) 
PR 2 (15) 1 (13) 2 (50) 
MR 2 (15) 1 (13) 2 (50) 
SD 4 (31) 2 (25) 0 (0) 
PD 0 (0) 2 (25) 0 (0) 
≥MR 9 (69) 4 (50) 4 (100) 
≥PR 7 (54) 3 (38) 2 (50) 
Ongoing response 1 (8) 1 (13) 0 (0) 
Patient Responses
Group A (n = 13)Group B (n = 8)Group C (n = 4)
 n (%) n (%) n (%) 
sCR 1 (8) 0 (0) 0 (0) 
CR 1 (8) 0 (0) 0 (0) 
VGPR 3 (23) 2 (25) 0 (0) 
PR 2 (15) 1 (13) 2 (50) 
MR 2 (15) 1 (13) 2 (50) 
SD 4 (31) 2 (25) 0 (0) 
PD 0 (0) 2 (25) 0 (0) 
≥MR 9 (69) 4 (50) 4 (100) 
≥PR 7 (54) 3 (38) 2 (50) 
Ongoing response 1 (8) 1 (13) 0 (0) 

Abbreviations: PD, progressive disease; sCR, stringent complete response; SD, stable disease; VGPR, very good partial response.

Initial results of the parent trial revealed a lower dose of CART-BCMA cells, as delivered in cohort 2, led to the lowest response rate (12). Thus, we compared cohort 2 subjects who did and did not receive bridging-RT to examine if bridging-RT affected response. Subject 13 and subject 16, who underwent bridging-RT, had the two largest in vivo CART expansions in cohort 2 (Fig. 2A). Cohort 2 subjects without bridging-RT (n = 3) had no response whereas those with bridging-RT (n = 2) had either MR or PR, with disease improvement both in and out of the RT field (Fig. 2B).

Figure 2.

In vivo expansion of CART-BCMA cells and radiographic response in cohort 2 subjects who received bridging-RT (Group C). A, Previously published line plots show the frequency of CAR+ T cells within the peripheral blood (12). CD3+ population was assessed by flow cytometry for each subject in cohort 2 (cyclophosphamide 1.5 g/m2 plus 1 × 107 to 5 × 107 CART-BCMA cells). Subjects 13 and 16 who received bridging-RT had the largest expansions in cohort 2, which translated to minimal and partial response, respectively. Remaining cohort 2 subjects (12, 14, and 22) had no response to CART-BCMA therapy. B, PET/CT images from Subject 13 show a thoracic plasmacytoma outside the RT field before CART-BCMA therapy and salvage autologous stem cell transplant (auto-SCT). The plasmacytoma showed partial resolution after auto-SCT and further resolution after CART. MRI images show interval resolution of right cavernous sinus plasmacytoma after RT to skull base and prior to CART. Subject 16 showed interval resolution of a T12 lesion after RT to T7-L1 and before CART. Sacral lesions outside of the RT fields showed interval resolution after CART.

Figure 2.

In vivo expansion of CART-BCMA cells and radiographic response in cohort 2 subjects who received bridging-RT (Group C). A, Previously published line plots show the frequency of CAR+ T cells within the peripheral blood (12). CD3+ population was assessed by flow cytometry for each subject in cohort 2 (cyclophosphamide 1.5 g/m2 plus 1 × 107 to 5 × 107 CART-BCMA cells). Subjects 13 and 16 who received bridging-RT had the largest expansions in cohort 2, which translated to minimal and partial response, respectively. Remaining cohort 2 subjects (12, 14, and 22) had no response to CART-BCMA therapy. B, PET/CT images from Subject 13 show a thoracic plasmacytoma outside the RT field before CART-BCMA therapy and salvage autologous stem cell transplant (auto-SCT). The plasmacytoma showed partial resolution after auto-SCT and further resolution after CART. MRI images show interval resolution of right cavernous sinus plasmacytoma after RT to skull base and prior to CART. Subject 16 showed interval resolution of a T12 lesion after RT to T7-L1 and before CART. Sacral lesions outside of the RT fields showed interval resolution after CART.

Close modal

Bridging-RT indications and radiation treatment planning characteristics in Group B and C

Although no explicit criteria mandated referral to a radiation oncologist, patients in need of immediate symptomatic relief were referred for bridging-RT. Indications included severe/refractory bone pain (n = 2) or functional deficits from local tumors (n = 2). One subject was experiencing progressive diplopia and eye discomfort due to bilateral plasmacytomas of the orbital bones. Another patient presented with cranial nerve VI palsy caused by a progressive plasmacytoma of the ipsilateral cavernous sinus. Two subjects had severe bone pain requiring hospitalization for pain control and/or high risk for pathologic fracture.

Radiation dose, fractionation, and treatment fields were at the discretion of the treating radiation oncologists. Median bridging-RT dose in Group C was 22 Gy (range, 8–30 Gy in 3–8 Gy fractions; Supplementary Table S1). Bridging-RT was started a median of 19 days after apheresis (range, 15–22) and completed a median of 25 days before CART infusion (range, 18–35). The radiation modality used was three-dimensional conformal RT (3DCRT). Treatment sites included skull base (n = 1), thoracic and lumbar spine (n = 1), bilateral hips (n = 1), and bilateral orbits (n = 1).

Median RT dose in Group B was 25 Gy (range, 6–40 Gy in 2–8 Gy fractions; Supplementary Table S1). RT was started a median of 77 and 114 days before apheresis (range, 15–268) and CART infusion (range, 40–301) respectively. The radiation modalities used were 3DCRT to the head and pelvis (n = 5), electrons to sternum and ribs (n = 2), and intensity-modulated RT (IMRT) in a re-irradiation case to the left maxillary sinus (n = 1).

Bridging systemic therapy was delivered in 84% of subjects (Group A: n = 11, Group B: n = 6, Group C: n = 4). Concurrent systemic therapy was administered in 2 subjects in Group C and 4 subjects in Group B (Supplementary Table S1).

Bridging-RT and CART-BCMA–related toxicities

G1 and G2 RT toxicities were observed in 1 of 4 Group C subjects. Overall, G1 and G2 RT side effects consisted of fatigue (n = 1) and alopecia (n = 1). No subject experienced pain flare, and no ≥G3 RT toxicities occurred.

Rates of toxicities related to CART-BCMA were analyzed per group (Table 3). In Group C, 1 subject (25%) experienced G4 hematologic toxicities compared with 8 (62%) and 5 (63%) subjects in Group B and A, respectively. Group A experienced the highest rate of G3 hematologic toxicities at 77% (n = 10) compared with 25% (n = 2) in Group B and 50% (n = 2) in Group C. G2 hematologic toxicities were comparable between Group A (23%) and C (25%) and slightly higher in Group B (38%). No ≥G3 gastrointestinal (GI), infectious, or liver-related toxicities were observed in Group C. In contrast, Group A reported G3–4 liver-related toxicities in 3 subjects (23%) and G4 infections in 1 subject (8%); Group B reported G3 GI toxicities in 1 subject (13%) and G3–4 infections in 3 subjects (38%). G2 infections were equal between Group A and B at 38% and slighter lower in Group C at 25%.

Table 3.

Toxicity rates in Group A (no RT <1 year prior to apheresis), Group B (RT <1 year prior to apheresis), and Group C (bridging-RT).

Group A (n = 13)Group B (n = 8)Group C (n = 4)
Toxicityn (%)n (%)n (%)
Neurotoxicity 
Grade 2 2 (15) 0 (0) 0 (0) 
Grade 3 1 (8) 2 (25) 1 (25) 
Grade 4 0 (0) 2 (25) 0 (0) 
CRS 
Grade 2 6 (46) 5 (63) 2 (50) 
Grade 3 5 (39) 2 (25) 1 (25) 
Grade 4 0 (0) 1 (13) 0 (0) 
Hematologic 
Grade 2 3 (23) 3 (38) 1 (25) 
Grade 3 10 (77) 2 (25) 2 (50) 
Grade 4 8 (62) 5 (63) 1 (25) 
Gastrointestinal 
Grade 2 3 (23) 0 (0) 1 (25) 
Grade 3 0 (0) 1 (13) 0 (0) 
Grade 4 0 (0) 0 (0) 0 (0) 
Abnormalities in LFTs 
Grade 2 1 (8) 1 (13) 0 (0) 
Grade 3 2 (15) 0 (0) 0 (0) 
Grade 4 1 (8) 0 (0) 0 (0) 
Infections 
Grade 2 5 (38) 3 (38) 1 (25) 
Grade 3 0 (0) 2 (25) 0 (0) 
Grade 4 1 (8) 1 (13) 0 (0) 
Group A (n = 13)Group B (n = 8)Group C (n = 4)
Toxicityn (%)n (%)n (%)
Neurotoxicity 
Grade 2 2 (15) 0 (0) 0 (0) 
Grade 3 1 (8) 2 (25) 1 (25) 
Grade 4 0 (0) 2 (25) 0 (0) 
CRS 
Grade 2 6 (46) 5 (63) 2 (50) 
Grade 3 5 (39) 2 (25) 1 (25) 
Grade 4 0 (0) 1 (13) 0 (0) 
Hematologic 
Grade 2 3 (23) 3 (38) 1 (25) 
Grade 3 10 (77) 2 (25) 2 (50) 
Grade 4 8 (62) 5 (63) 1 (25) 
Gastrointestinal 
Grade 2 3 (23) 0 (0) 1 (25) 
Grade 3 0 (0) 1 (13) 0 (0) 
Grade 4 0 (0) 0 (0) 0 (0) 
Abnormalities in LFTs 
Grade 2 1 (8) 1 (13) 0 (0) 
Grade 3 2 (15) 0 (0) 0 (0) 
Grade 4 1 (8) 0 (0) 0 (0) 
Infections 
Grade 2 5 (38) 3 (38) 1 (25) 
Grade 3 0 (0) 2 (25) 0 (0) 
Grade 4 1 (8) 1 (13) 0 (0) 

Note: n (%), number of subjects (frequency of toxicity within group).

Abbreviation: LFT, liver function test.

The rates of neurotoxicity and CRS, including high-grade events, did not appear to differ between the groups. G2–4 neurotoxicity was recorded in 23% (n = 3) in Group A, 50% (n = 4) in Group B, and 25% (n = 1) in Group C. G3 neurotoxicity was observed in 1 subject (8%), 2 subjects (25%), and 1 subject (25%) in Group A, B, and C, respectively. G4 neurotoxicity was observed in 2 subjects (25%) in Group B only. Overall CRS rates were high. G2–4 CRS was experienced by 85% (n = 11) in Group A, 100% (n = 8) in Group B, and 75% (n = 3) in Group C. Specifically, G2 CRS was reported in 6 subjects (46%) in Group A, 5 subjects (63%) in Group B, and 2 subjects (50%) in Group C. G3 CRS, however, was slightly higher in Group A (39% vs. 25% in Group B and C). Only Group B had 1 subject (12.5%) with G4 CRS.

CART-BCMA manufacturing details and characteristics at peak expansion in peripheral blood

To assess the impact of pre-apheresis RT on CART-BCMA manufacturing, we analyzed characteristics of CART product before, during, and after completion of manufacturing (Supplementary Table S2). Groups A, B, and C were similar across the following parameters: absolute lymphocyte count pre-apheresis, percent lymphocytes pre-apheresis, frequency of CD3+ cells in the pre- and post-manufacturing products, CD4/CD8 T-cell ratio in the pre- and post-manufacturing products, and frequency of naïve or early memory CD8+ T cells in the pre-manufacturing product (%CD45RO-CD27+ of the CD8+ population; Fig. 3A; Supplementary Table S2). In vitro fold expansion was significantly lower in Group B (14.7) vs. Group A (38.9) but not Group B vs. Group C (27.2; P = 0.0065). Given that bridging-RT should not affect manufacturing, we performed a parallel analysis of subjects combined from Group A and C versus those from Group B; likewise, Group B had significantly lower in vitro proliferation (fold expansion, P = 0.0015) while remaining parameters were similar (Supplementary Table S2). Because most peripheral T-cell recovery occurs within the first 3 to 4 months following focal RT (30, 31), manufacturing details were also compared between subjects who did (n = 6) and did not (n = 19) receive RT within 100 days preceding apheresis (Fig. 3B). Fold expansion showed a similar reduction that trended towards significance in subjects who received RT <100 days before apheresis (fold expansion 20.3 vs. 31.7, P = 0.069). Despite these potential differences, the minimum target goal of CART-BCMA cells was successfully manufactured from all apheresed subjects, and engraftment was seen in all subjects as well.

Figure 3.

Manufacturing and peripheral blood characteristics of CART-BCMA relative to RT receipt. A and C compare parameters of manufacturing and peripheral blood at peak expansion between Group A (no RT <1 year before apheresis; n = 13), Group B (RT <1 year before apheresis; n = 8), and Group C (bridging-RT; n = 4), respectively. A, Group B had significantly lower fold expansion (P = 0.0065) compared with Group A. B, A similar trend was observed between subjects who received RT <100 days before apheresis (n = 6) relative to those who did not (no RT/RT <100 days before apheresis; n = 19; fold expansion, P = 0.069). Percentage of CD8+ T cells with the CD45RO-CD27+ phenotype in the pre-manufacturing product was comparable between Group A, B, and C (A) as well as between No RT within 100 days before apheresis and RT within 100 days before apheresis (B). All other manufacturing parameters were similar between Group A, B, and C and were not associated with RT delivered closer to time of apheresis. Characteristics of peripheral blood CART-BCMA cells at peak expansion between Group A, B, and C (C) and between No RT/RT <100 days before apheresis (n = 15), RT <100 days before apheresis (n = 6), and bridging-RT (n = 4; D) were similar. The frequency of total CD3+, CD3+CD4+, CD3+CD8+, and CD8+CD45RO-CD27+ cells was assessed by flow cytometry before (“in seed culture”) and after (“at harvest”) manufacturing. The frequency of CART cells within CD3+, CD4+, and CD8+ populations and activation status at peak expansion (as measured by % of CART cells expressing HLA-DR) were also assessed by flow cytometry. Lines represent median values with interquartile ranges. The peak expansion of subject 9 in Group B was determined by qPCR since CAR+ cells were not detectable by flow cytometry. The peak for subject 34 in Group A could not be determined due to lack of sample between days 10 and 21. Subjects 1 (Group A), 3 (Group B), 15 (Group B), and 25 (Group C) received 40% of planned CART-BCMA dose due to early CRS. No RT/RT <100 days before apheresis, no history of RT or no RT <100 days preceding apheresis; %CD45RO-CD27+ of CD8+ cells, naïve or early memory CD8+ T cells in the premanufacturing product.

Figure 3.

Manufacturing and peripheral blood characteristics of CART-BCMA relative to RT receipt. A and C compare parameters of manufacturing and peripheral blood at peak expansion between Group A (no RT <1 year before apheresis; n = 13), Group B (RT <1 year before apheresis; n = 8), and Group C (bridging-RT; n = 4), respectively. A, Group B had significantly lower fold expansion (P = 0.0065) compared with Group A. B, A similar trend was observed between subjects who received RT <100 days before apheresis (n = 6) relative to those who did not (no RT/RT <100 days before apheresis; n = 19; fold expansion, P = 0.069). Percentage of CD8+ T cells with the CD45RO-CD27+ phenotype in the pre-manufacturing product was comparable between Group A, B, and C (A) as well as between No RT within 100 days before apheresis and RT within 100 days before apheresis (B). All other manufacturing parameters were similar between Group A, B, and C and were not associated with RT delivered closer to time of apheresis. Characteristics of peripheral blood CART-BCMA cells at peak expansion between Group A, B, and C (C) and between No RT/RT <100 days before apheresis (n = 15), RT <100 days before apheresis (n = 6), and bridging-RT (n = 4; D) were similar. The frequency of total CD3+, CD3+CD4+, CD3+CD8+, and CD8+CD45RO-CD27+ cells was assessed by flow cytometry before (“in seed culture”) and after (“at harvest”) manufacturing. The frequency of CART cells within CD3+, CD4+, and CD8+ populations and activation status at peak expansion (as measured by % of CART cells expressing HLA-DR) were also assessed by flow cytometry. Lines represent median values with interquartile ranges. The peak expansion of subject 9 in Group B was determined by qPCR since CAR+ cells were not detectable by flow cytometry. The peak for subject 34 in Group A could not be determined due to lack of sample between days 10 and 21. Subjects 1 (Group A), 3 (Group B), 15 (Group B), and 25 (Group C) received 40% of planned CART-BCMA dose due to early CRS. No RT/RT <100 days before apheresis, no history of RT or no RT <100 days preceding apheresis; %CD45RO-CD27+ of CD8+ cells, naïve or early memory CD8+ T cells in the premanufacturing product.

Close modal

At peak expansion of CAR T cells, peripheral blood characteristics were compared between groups (Supplementary Table S2). There was no statistically significant difference in the number of CART-BCMA cells received between Group A, B, and C (Fig. 3C). The median day of peak CART expansion was consistent between groups, ranging from 10 to 11.5 days. At time of peak expansion, the percentage of CAR+ cells within the CD3+, CD4+, and CD8+ populations and the frequency of CAR+CD3+ cells expressing HLA-DR, an activated phenotype, were similar across groups. Although the manufactured product in all groups consisted of predominantly CD4+ T cells, circulating CART-BCMA cells were largely CD8+ and highly activated (median % HLA-DR+ of CAR+ population for Group A, 94.5; B, 94; C, 92.5). Parallel comparisons between subjects who received bridging-RT (Group C, n = 4), RT within 100 days preceding apheresis (n = 6), and no RT within 100 days preceding apheresis (n = 15) revealed no association between RT receipt/timing and the peripheral blood profile of CART-BCMA cells at peak expansion (Fig. 3D). A similar analysis of peak expansion based on qPCR measurement of CAR transgene copy number also failed to reveal any differences between groups based on prior RT exposure (Supplementary Fig. S2).

To assess whether RT affects persistence of CART-BCMA cells, qPCR data from peripheral blood at day 28 (D28) after CART infusion were analyzed on the basis of RT receipt. Subjects who received no/remote RT (Group A) versus RT <1 year before CART infusion (Group B and C) had no statistically significant difference in CAR transgene copy number at D28 (median 5,199 vs. 731 copies/μg genomic DNA, P = 0.46; Supplementary Fig. S3A). RT delivered closer to CART infusion did not significantly impact D28 persistence; subjects who received RT within 100 days before apheresis or the bridging period (n = 10) versus subjects who received no RT/remote RT outside this window had comparable CAR transgene copy numbers at D28 (median 732 vs. 3,478 copies/μg DNA, P = 0.55; Supplementary Fig. S3B). Similarly, no difference was found between subjects who received bridging-RT (n = 4), RT <100 days before apheresis (n = 6), or no/remote RT (n = 14; median 3,102, 732, and 3,478 copies/μg DNA, P = 0.55; Supplementary Fig. S3C).

Prior analysis revealed that peak blood CART-BCMA expansion, as measured by qPCR, was significantly associated with a higher frequency of CD45RO-CD27+CD8+ T cells in the premanufacturing leukapheresis product as well as a partial response or better (12). Reanalysis showed that levels of CART BCMA cells at peak expansion and D28 were in fact associated with any clinical response (median 5,302 copies/μg DNA at peak expansion for ≥MR vs. 39,519 for <MR, P = 0.0028; median 5,947 copies/μg DNA at D28 for ≥MR vs. 67 for <MR, P = 0.0042; Supplementary Figs. S4A–S4C). Within responders (≥MR), RT did not impact in vivo levels of CART-BCMA cells at peak expansion (Supplementary Fig. S4B) or D28 (Supplementary Fig. S4D).

In this report, we sought to characterize the toxicity and disease outcomes of CART-BCMA therapy given either with or without bridging-RT in patients with r/rMM. Moreover, we report the profile of CART-BCMA manufacturing products as well as peripheral blood CART expansion in those who received RT within 1 year before apheresis, 100 days before apheresis, and the bridging period. Bridging-RT was not associated with excessive RT- or CART-related toxicities and did not appear to significantly alter clinical outcomes (OS, PFS). It is worth noting that although OS curves did not meet statistical significance, the bridging-RT group did appear to have poorer survival (P = 0.08). The ALC pre-apheresis, percentage of lymphocytes pre-apheresis, CD4/CD8 ratio, and frequency of naïve or early memory CD8+ T cells (CD45RO-CD27+CD8+) in the premanufactured product did not correlate with RT receipt within 1 year or 100 days before apheresis. However, those who received RT in the year prior to apheresis had less robust in vitro T-cell expansion during CAR T-cell manufacturing compared with those who did not (Group B vs. Group A+C, P = 0.0015). We also observed a trend, which did not reach statistical significance, towards lower in vitro expansion in the subjects receiving RT within 100 days prior to apheresis (P = 0.069). Of note, 75% of subjects who received RT in the year prior to apheresis completed RT within 100 days before apheresis. These suggest RT delivered 100 days prior to leukapheresis may negatively impact in vitro proliferation of seeded cells during manufacturing. Depending on the irradiated volume, sufficient T-cell recovery after RT may take at least 3 to 4 months to maintain the in vitro proliferative capacity of apheresed cells. Alternatively, these particular subjects may have had higher tumor burden which may negatively impact T-cell biology even before apheresis. Although solBCMA levels post-apheresis prior to cyclophosphamide administration (or simply first CART infusion for cohort 1 which received no lymphodepletion) did not significantly differ between groups and was not associated with RT exposure within 100 days before apheresis (Supplementary Fig. S1), Group B had a higher level (885 ng/mL vs. 204 ng/mL in Group A and 151 ng/mL in Group C, P = 0.58). These suggest that baseline tumor burden may have been similar in Group A and C and higher in Group B, and our study was not powered to investigate this relationship. We unfortunately did not collect solBCMA levels at the time of apheresis.

The parent trial showed that in vitro fold expansion correlated with in vivo CART-BCMA peak expansion, and in turn, in vivo CART-BCMA peak expansion correlated with clinical responses (12). These findings suggest ex vivo proliferative capacity may predict for in vivo activity. Although RT <1 year preceding apheresis was associated with lower in vitro fold expansion, which did not correlate with decreased in vivo peak expansion, it had numerically lower CAR transgene copy number (median 6,109 copies/μg DNA) relative to no RT <1 year before apheresis (37,946 copies/μg DNA) and bridging-RT (17,528 copies/μg DNA; Supplementary Fig. S2A). Once again, our study was not powered to examine such a relationship.

We believe this study has significant value given the recent FDA approval of the idecabtagene vicleucel (ide-cel). This study is among the first to explore the outcomes of patients who have received CART-BCMA therapy with bridging-RT or RT within 1 year prior to apheresis. As more patients with r/rMM receive ide-cel, new clinical situations will arise on when and how to best offer bridging-RT to those needing palliation during the manufacturing period. Our report, although imperfect, provides the first characterization of the safety and feasibility of bridging-RT with BCMA-specific CAR T cells, which to the best of our knowledge, has not been described in the literature apart from rare case reports.

Limitations of this study largely result from its retrospective nature and small sample size, which preclude definitive conclusions. Specifically with respect to the association we noted between pre-apheresis RT and manufacturing characteristics, the need for pre-apheresis RT may simply be a marker of other factors, such as more intensive systemic treatment, which may explain slower in vitro T-cell expansion. Although we did not identify obvious differences in the baseline characteristics of our groups apart from the presence of extramedullary disease, the small sample size precluded a formal multivariable analysis; moreover, there may be confounding variables we did not analyze, such as differences in systemic therapy over the year prior to apheresis. Nonetheless, we did our best to characterize the groups and showed they were fairly balanced in regards to following prognostic factors: high-risk cytogenetics, number of prior lines of therapy, renal function, LDH, and prior autologous SCT. Because subjects were prohibited from receiving treatment during the 2-week washout prior to apheresis, we are unable to explore the effects of RT completed within this window on CART-BCMA manufacturing. However, given that RT is lymphodepleting, conventional wisdom points to avoiding its delivery within the few weeks preceding apheresis to ensure adequate ALC.

Similarly, none of the subjects received RT within 20 days following administration of CART-BCMA therapy (Supplementary Table S3). Therefore, we cannot assess if RT delivered within this early post-CART period can augment CART efficacy in patients who demonstrate progression after infusion as indicated by further rise in M-spike or new/growing radiographic lesions. In a case report, palliative RT delivered between day 6 and 20 following anti-BCMA CART therapy (coinciding with time of peak CART expansion) in a MM patient led to a synergistic abscopal effect and expansion of new T-cell receptor (TCR) clones, mediating the eradication of substantial tumor burden, including extraosseous lesions (32). This anecdote supports exploration of peri-CART therapy RT, which perhaps may be particularly useful for patients with extramedullary disease where responses are typically less durable, even after CART therapy (33).

Moreover, our analysis was limited to a cohort of r/rMM patients treated at a single institution with a single CAR T-cell product. The effects of bridging-RT or pre-apheresis RT on toxicity and manufacturing of other anti-BCMA CART products, for example, ide-cel and ciltacabtagene autoleucel (cilta-cel; refs. 11, 21), requires future investigation. However, given that ide-cel and cilta-cel both feature a 4-1BB co-stimulatory moiety like our CART-BCMA construct, bridging-RT may be safe with these products.

Medical oncologists may be hesitant to recommend bridging-RT before CART infusion due to concerns of adding RT-related toxicity to those of lymphodepletion and CART therapy. In this study, we palliatively treated the skull base, thoracic and lumbar spine, bilateral hips, and bilateral orbits. Notably, we observed mild acute RT-related toxicity, predominantly G1 fatigue, despite 2 subjects receiving concurrent chemotherapy. Similarly, patients with relapsed/refractory aggressive B-cell lymphoma who received bridging-RT prior to CD19–CAR T cells experienced no significant acute toxicity in three recent series (26–28). Another concern with bridging therapy, either RT or systemic, is marrow suppression. Routine lymphodepletion chemotherapy can cause protracted cytopenias. So far, published data on RT-related toxicity appear proportional to the dose and size of RT fields used without exacerbation by CART therapy. Nonetheless, larger clinical studies are needed before we can draw conclusions.

Another potential concern is whether bridging-RT may worsen CART-associated toxicities. In our study, CRS and neurotoxicity rates appeared unaffected by bridging-RT. All 3 subjects with severe neurotoxicity (≥G3) had high tumor burden (2 with extramedullary disease) as well as G3 or G4 CRS. Studies of CD19-directed CART therapy in acute lymphocytic leukemia and lymphomas support the notion that tumor burden correlates with CRS severity (34–37). Therefore, bridging-RT may temper the severity of CRS or neurotoxicity by debulking systemic treatment-refractory myeloma. Furthermore, RT has an immune-priming potential to amplify immunomodulatory therapies via exposure of neoantigens. Taken together with the observation that incremental increases in the conditioning intensity improve engraftment and clinical outcomes (25, 38), it is possible that modifying the lymphodepletion (e.g., adding low-dose total-body irradiation to cyclophosphamide plus fludarabine) may augment the activity of BCMA-directed CAR T cells while reducing risk of CART-related toxicities.

How RT influences CART toxicity and efficacy via immunologic mechanisms requires further elucidation. Because CARs lead to MHC-independent T-cell activation, RT may synergize with CART therapy via several potential mechanisms: (i) RT may increase the migration and effector functions of CAR T cells (20, 39, 40), (ii) cytokines secreted by CAR T cells in response to RT may prime endogenous T cells to mount an abscopal-like response (32), and (iii) RT-induced apoptosis of cancer cells leading to the release of antigens that are ultimately presented by antigen-presenting cells may stimulate broader T-cell responses (i.e., both CAR T-cell and endogenous T-cell clonal expansions; ref. 17). We hope this study informs subsequent investigations into radiation as an adjunct to CART therapy.

Conclusions

In our case series of r/rMM patients treated with CART-BCMA cells, bridging-RT seems safe without worsening rates of severe CRS, neurotoxicity, or hematologic toxicity. The time to peak expansion, the activation of CART-BCMA cells, or the frequency of CART-BCMA cells within CD3+, CD4+, and CD8+ populations in vivo at peak expansion appeared similar between those who did and did not receive bridging-RT. Our data suggest RT delivered <100 days before apheresis may negatively impact in vitro proliferation of T cells during manufacturing. However, larger numbers are required to show significant associations. Future prospective trials investigating the impact of bridging-RT on anti-BCMA CAR T-cell response, long-term efficacy, and toxicity in r/rMM patients are warranted.

S.H. Manjunath reports grants from Novartis during the conduct of the study. A.D. Cohen reports grants from Novartis during the conduct of the study. A.D. Cohen also reports personal fees from Janssen, BMS/Celgene, Oncopeptides, Takeda, AstraZeneca, and Genentech/Roche, as well as grants and personal fees from GlaxoSmithKline outside the submitted work; A.D. Cohen also has a patent for 15/757,123 licensed to Novartis. S.F. Lacey reports grants from Tmunity Therapeutics and Cabaletta, as well as personal fees from Gilead/Kite outside the submitted work; S.F. Lacey also has a patent for Markers of Cytokine Release Syndrome pending and licensed to Novartis and a patent for CAR19 issued and licensed to Novartis. M.M. Davis reports grants and personal fees from Tmunity Therapeutics, as well as other support from Cellares Corporation outside the submitted work; M.M. Davis is also involved in research activities that generate intellectual property including patents and know-how related to advancing cell therapies. A.L. Garfall reports grants from Novartis, Tmunity, and CRISPR Therapeutics; grants and personal fees from Janssen; and personal fees from Amgen outside the submitted work. A.L. Garfall also has a patent for 15/757,123 pending and with royalties paid, as well as patents for 16/768,260 and 16/746,459 pending to Novartis. J.J. Melenhorst reports grants from Novartis during the conduct of the study; J.J. Melenhorst also reports grants and personal fees from IASO Biotherapeutics and Kite Pharma, as well as personal fees from Simcere of America, Shanghai Unicar Therapy, Johnson & Johnson, and Poseida Therapeutics outside the submitted work. In addition, J.J. Melenhorst also has patents pending for Methods of Making Chimeric Antigen Receptor-Expressing Cells, Biomarkers Predictive of Therapeutic Responsiveness to Chimeric Antigen Receptor Therapy and Uses Thereof, CAR T-cell Therapies with Enhanced Efficacy, Methods for Improving the Efficacy and Expansion of Chimeric Antigen Receptor-Expressing Cells, Methods for Improving the Efficacy and Expansion of Immune Cells, Biomarkers Predictive of Cytokine Release Syndrome, Combination Therapies of Chimeric Antigen Receptor and PD-1 Inhibitors, Biomarkers and CAR T-cell Therapies with Enhanced Efficacy, BCMA-targeting Chimeric Antigen Receptor and Uses Thereof, and Therapeutic Regimens for Chimeric Antigen Receptor (CAR)-Expressing Cells. E.A. Stadtmauer reports personal fees from Celgene/BMS, Janssen, AbbVie, and GSK outside the submitted work. B.L. Levine reports personal fees from Avectas, In8bio, Vycellix, Immuneel, Immusoft, Ori Biotech, Akron Biotech, and TerumoBCT, as well as other support from Tmunity Therapeutics outside the submitted work. In addition, B.L. Levine also has patents for Methods for Treatment of Cancer (US 8906682, US 8916381, US 9101584), Compositions for Treatment of Cancer (US 8911993, US 9102761, US 9102760), Method for Treating Chronic Lymphocytic Leukemia (CC; US 9161971), Compositions and Methods for Treatment of Cancer (US 9464140, US 9518123, US 9481728, US 9540445), Use of Chimeric Antigen Receptor-Modified T Cells to Treat cancer (US 9328156, US 9499629), and Methods for Assessing the Suitability of Transduced T Cells for Administration (US 9572836) issued, licensed, and with royalties paid from University of Pennsylvania. C.H. June reports other support from Novaratis, Tmunity, AC Immune, BluesphereBio, Cabaletta, Carisma, Cartography, Cellares, Celldex, DeCART, Poseida, Verismo, WIRB Copernicus, and Ziopharm, as well as personal fees from Decheng during the conduct of the study; C.H. June also has a patent for IPR pending and licensed to Novartis. M.C. Milone reports grants from Novartis during the conduct of the study, as well as a patent for US20160046724 pending to Novartis. I. Paydar reports grants from Novartis during the conduct of the study. No disclosures were reported by the other authors.

S.H. Manjunath: Conceptualization, data curation, formal analysis, writing–original draft, writing–review and editing. A.D. Cohen: Conceptualization, resources, supervision, writing–review and editing. S.F. Lacey: Data curation, writing–review and editing. M.M. Davis: Resources, data curation, writing–review and editing. A.L. Garfall: Writing–review and editing. J.J. Melenhorst: Writing–review and editing. R. Maxwell: Formal analysis. W.T. Arscott: Conceptualization, data curation, methodology. A. Maity: Writing–review and editing. J.A. Jones: Writing-review and editing. J.P. Plastaras: Conceptualization, writing–review and editing. E.A. Stadtmauer: Writing–review and editing. B.L. Levine: Writing–review and editing. C.H. June: Conceptualization, resources, writing–review and editing. M.C. Milone: Writing–review and editing. I. Paydar: Supervision, writing–review and editing.

We acknowledge and appreciate the assistance of J. Finklestein, F. Nazimuddin, C. Bartoszek, T. Mikheeva, S. Rajkumar, and B. Menchel for sample processing; I. Kulikovskaya, M. Gupta, and A. Kim for qPCR analyses; D. Ambrose, L. Tian, and H. Parakandi for flow cytometry analyses; F. Chen and N. Koterba for Luminex cytokine analyses; V. Gonzalez and Y. Tanner for data management and quality control; and A. Lamontagne, A. Brennan, A. Malykhin, and members of the Clinical Cell and Vaccine Production Facility for cell manufacturing and testing. We acknowledge the medical and nursing staff of the Apheresis Unit at the Hospital of the University of Pennsylvania for their care and management of patients undergoing leukapheresis. This work was supported by a sponsored research agreement between the University of Pennsylvania and Novartis, as well as NIH Grant No. 1P01CA214278.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

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