CD19 Chimeric Antigen Receptor Therapy for Refractory Aggressive B-Cell Lymphoma

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1 biology of neoplasia CD19 Chimeric Antigen Receptor Therapy for Refractory Aggressive B-Cell Lymphoma Caron A. Jacobson, MD 1 ABSTRACT PURPOSE Anti-CD19 directed chimeric antigen receptor (CAR) T-cell therapy has had a resounding effect on the treatment of chemotherapy-insensitive aggressive B-cell non-hodgkin lymphoma (B-NHL). There are now two US Food and Drug Administration (FDA) approved products available for treating these patients, and a third product is expected to be approved in the coming months. The question remains: Is there a preferred or best product for my patient? However, answering that question is more complicated than simply balancing the reported efficacy and toxicity results. DESIGN This review outlines potential confounding factors involving the three products and their pivotal clinical trials and highlights additional considerations of manufacturing reliability and overall cost that must be considered when weighing one product against another. It will also review the directions in which the field is moving and strategies being examined to improve efficacy as well as toxicity. CONCLUSION Because a randomized three-arm clinical trial is unlikely, a product may have to be chosen on the basis of results from treatment centers that have experience with all three products. But by the time those results are available, they are likely to be outdated because, given the rapid evolution of the field, the next product will probably have been identified. J Clin Oncol by American Society of Clinical Oncology Author affiliations and support information (if applicable) appear at the end of this article. Accepted on October 30, 2018 and published at jco.org on December 13, 2018: DOI org/ /jco INTRODUCTION Anti-CD19 chimeric antigen receptor (CAR) T cells have had a marked impact on the management of chemotherapy refractory aggressive B-cell non- Hodgkin lymphoma (B-NHL), thus establishing a new and effective standard of care for patients for whom no standard previously existed. Since the first report of anti-cd19 CAR T cells in B-NHL in 2010, three anti-cd19 CAR T-cell constructs have been tested in pivotal phase II clinical trials, and they have demonstrated durable remissions in up to 40% of patients. 1 6 The result has been the US Food and Drug Administration (FDA) approval of two of these products, axicabtagene ciloleucel (axi-cel) and tisagenlecleucel (t-cel), and the anticipated FDA approval of the third, lisocabtagene maraleucel (liso-cel). These drugs have been clinically successful in spite of considerable toxicity, namely cytokine release syndrome (CRS) and neurotoxicity (NT), which limits their general applicability. How to balance efficacy against high-grade and potentially life-threatening, toxicities is of considerable interest because cellular therapy specialists are confronting a field in which three competitive products will likely exist. But looking at the final efficacy and toxicity results does not tell the whole story. These therapies differ with respect to costimulatory domains, routes of transfection, manufacturing procedures, and composition of the T-cell product. Beyond the product itself, the trials differ with regard to patient eligibility and management. As a result, any comparison across studies is limited and must be performed with extreme caution. Although a randomized three-arm trial is unlikely, institutional experiences with each of the three products may shed light on their relative benefits and costs. ANTI-CD19 CAR T-CELL EFFICACY IN AGGRESSIVE B-NHL The National Cancer Institute published the first report of an anti-cd19 CAR T-cell product for treating B-NHL in This product contained a CD28 costimulatory molecule and was the basis for the development of axi-cel (Fig 1). This was followed by a phase I trial in 15 patients with B-NHL who demonstrated an overall objective response rate (ORR) of 92% and an 86% response rate in diffuse large B-cell lymphoma (DLBCL). 2 More than half the patients with DLBCL achieved a complete response (CR; 57%), and many responses were durable through the 22-month followup. These results were corroborated by the pivotal multicenter phase II study of axi-cel in aggressive B-NHL, including DLBCL, high-grade B-cell lymphoma (HGBL), primary mediastinal large B-cell lymphoma (PMBL), and transformed follicular lymphoma (tfl), which also demonstrated the feasibility of delivering this therapy to large numbers of patients across the globe and of using a centralized manufacturing process. 3 Among the 101 patients who received axi-cel 1

2 Jacobson Axicabtagene ciloleucel Tisagenecleucel Lisocabtagene maraleucel scfv FMC63 scfv Hinge CD28 CD8 4-1BB Spacer 4-1BB FIG 1. Depictions of three anti-cd19 CAR T-cell constructs in clinical development. Axicabtagene ciloleucel (left) contains a CD28 costimulatory domain in addition to a CD3 zeta domain, whereas tisagenecleucel (middle) and lisocabtagene maraleucel (right) contain a 4-1BB costimulatory domain in addition to a CD3 zeta costimulatory domain. scfv, signal chain variable fragment. CD3 zeta CD3 zeta CD3 zeta on that study, the ORR was 82% (82% in DLBCL and HGBL; 83% in PMBL and tfl), and 54% of patients achieved a CR (49% in DLBCL and HGBL; 71% in PMBL and tfl; Table 1). 7 Responses were seen across all risk groups and were durable in up to 70% of patients in CR, or 42% of patients overall, at a median follow-up of 15.4 months. On the basis of these results, axi-cel is now FDA approved for treating relapsed or refractory aggressive B-NHL, including PMBL, after two or more lines of systemic therapy that were unsuccessful. Simultaneously, a second anti-cd19 CAR T-cell product, t-cel, was being developed at the University of Pennsylvania, and it would become the second FDA-approved CAR T-cell therapy for B-NHL. The t-cel product contains a 4-1BB costimulatory domain, which distinguishes it from axi-cel; it is also FDA approved for pediatric and young adult patients with B-cell acute lymphoblastic leukemia (Fig 1). It was tested in a pilot study of 28 patients with DLBCL (n = 14) or FL (n = 14). 4 Among patients with DLBCL, the ORR was 50%, and the CR rate was 43%. At a median 28.6 months of follow-up, 43% of patients with DLBCL remain in response. Again, there was no difference in response rates by conventional DLBCL risk stratification. As with axi-cel, t-cel was then tested in a multicenter, international pivotal phase II TABLE 1. Efficacy of Anti-CD19 CAR T Cells in Aggressive B-NHL Variable ZUMA-1 (axi-cel [KTE-C19]) 3 JULIET (t-cel [CTL019]) 6 JULIET Package Insert (t-cel [CTL019]) 7 TRANSCEND-NHL-001 (full cohort; liso-cel [JCAR017]) 5 TRANSCEND-NHL-001 (core cohort; liso-cel [JCAR017]) 5 No. pheresed NR No. treated NR No. evaluable No. never treated (%) 10 (9) of (31) of (30) of (15) of 134 NR Bridging treatment, % NR NR ORR, % CR, % Month ORR, % 41 37* NR NR 47 6-Month CR, % 36 30* NR NR 41 ITT ORR (%) 83 (75) of (30) of 161 N/A 77 (63) of 122 NA Abbreviations: axi-cel, axicabtagene ciloleucel; B-NHL, B-cell non-hodgkin lymphoma; CAR, chimeric antigen receptor; CR, complete response; ITT, intent-to-treat; liso-cel, lisocabtagene ciloleucel; NA, not applicable; NR, not reported; ORR, objective response rate; t-cel, tisageneleucel. *Numbers reflect an earlier presentation of the JULIET trial by American Society of Clinical Oncology

3 CD19 Therapy for Refractory Aggressive B-Cell Lymphoma trial, the JULIET (ClinicalTrials.gov identifier: NCT ) study, which treated 111 patients with DLBCL, HGBL, and tfl. Among the 68 evaluable patients reviewed by the FDA (see discussion of this subset in the section on bridging therapy), there was an ORR of 50%, with approximately 32% of patients achieving a CR. 7 When considering all patients treated with sufficient follow-up (n = 93), responses seem to be durable, with 83% of patients in partial response (PR) or CR at 3 months and in ongoing CR at 12 months (approximately 40% of patients overall), with more than half the patients with PRs converting to CRs over the course of the 1-year follow-up. 6 Finally, a third anti-cd19 CAR T-cell product, liso-cel, is anticipated to be approved by the FDA in the coming year. Like t-cel, liso-cel has a 4-1BB costimulatory domain, but unlike either t-cel or axi-cel, it is engineered so that the final product has a defined composition of CD4 and CD8 T cells (Fig 1). Liso-cel was tested in the pivotal TRANSCEND- NHL-001 (ClinicalTrials.gov identifier: NCT ) trial, which initially enrolled a broad group of patients with B-NHL and tested different T-cell doses and dosing schedules. The core cohort, which included patients with DLBCL, HGBL, and tfl, was later defined to represent the pivotal and registration study. 5 In this cohort, 73 patients were treated, resulting in an ORR of 80% and a CR rate of 59%. At a median follow-up of 6 months, 41% of patients remained in response and once again, response was independent of adverse prognostic factors. ANTI-CD19 CAR T-CELL TOXICITY IN AGGRESSIVE B-NHL The efficacy of anti-cd19 CAR T-cells in chemotherapy refractory aggressive B-NHL, regardless of conventional high-risk features, is remarkable but is not without cost. These therapies carry unique and potentially life-threatening risks of CRS and NT that limit the number of patients who are eligible for treatment. The pathophysiology of CRS is generally well understood and results from the rapid expansion and activation of CAR T cells upon reinfusion and the release of proinflammatory cytokines. This leads to the clinical syndrome of high fevers, fatigue, and malaise that can progress to shock, capillary leak, respiratory compromise, and end organ dysfunction. In the ZUMA-1 (ClinicalTrials.gov identifier: NCT ) trial, CRS occurred in 93% of patients, but it was grade 3 or higher (using the Lee criteria) in only 13% of the patients (Table 2). 3,9 There were two cases of fatal CRS, one the result of hemophagocytic lymphohistiocytosis and the other a result of cardiac arrest; all other cases of CRS were fully reversible. The use of antidotes to CRS (ie, the anti-interleukin-6r [IL-6R] antibody tocilizumab and corticosteroids) evolved over the course of the study as data emerged showing that these antidotes had little effect on CAR T-cell efficacy, and rates of high-grade CRS decreased as the study progressed. Ultimately, 43% of patients received tocilizumab, and 27% of patients received steroids. On this study CRS occurred early, after a median of 2 days, and lasted a median of 8 days. This timing differs from those for t-cel or liso-cel, for which the median time to onset of CRS was 3 and 5 days, respectively, and it is hypothesized that this is potentially because of the differential kinetics of the co-stimulatory domains. 5,6 The delayed onset of CRS had an impact on the feasibility of outpatient CAR T-cell dosing, which was performed as part of the JULIET and TRANSCEND-NHL-001 trials, but not the ZUMA-1 trial. Rates of CRS were also different on the JULIET and TRANSCEND-NHL-001 trials compared with the ZUMA-1 trial. On the JULIET trial, 74% of patients experienced CRS of any kind. 7 An updated analysis, however, reported a rate of CRS (any grade) of 58%. 6 Although 22% to 23% of patients (depending on the subset reported) experienced grade 3 or higher CRS, that study used an alternate grading scale in which fluidresponsive hypotension (grade 2 by Lee criteria) was TABLE 2. Toxicity of Anti-CD19 CAR T Cells in Aggressive B-NHL Variable ZUMA-1 (axi-cel [KTE-C19]) 3 JULIET (t-cel [CTL019]) 6 JULIET Package Insert (t-cel [CTL019]) 7 TRANSCEND-NHL-001 (full cohort; liso-cel [JCAR017]) 5 TRANSCEND-NHL-001 (core cohort; liso-cel [JCAR017]) 5 No. pheresed NR No. treated NR No. evaluable No. never treated (%) 10 (9) of (31) of (30) of (15) of 134 NR Bridging treatment, % NR NR CRS, % Grade $ 3 CRS, % NT, % Grade $ 3 NT, % Abbreviations: axi-cel, axicabtagene ciloleucel; B-NHL, B-cell non-hodgkin lymphoma; CAR, chimeric antigen receptor; CRS: cytokine release syndrome; liso-cel, lisocabtagene ciloleucel; NR, not reported; NT: neurotoxicity; t-cel, tisageneleucel. Journal of Clinical Oncology 3

4 Jacobson considered grade 3. Up to this point, less than 10% of patients required vasopressor support. 10 As on the ZUMA-1 trial, CRS lasted a median of 8 days. 7 Tocilizumab was used in 15% of patients to treat CRS. In the CORE cohort of the TRANSCEND-NHL-001 trial, CRS was observed in 37% of patients, and grade 3 or higher CRS was seen in only 3% of patients. 5 Up to 7% of patients were managed with tocilizumab, and 10% received corticosteroids. Although much is understood about the mechanisms of CRS (allowing for successful treatment), the biology and management of NT remains more elusive. NT can manifest itself in many ways ranging from mild confusion, tremors, and language difficulties to complete aphasia, seizures, obtundation, and coma. What is known is that inflammatory cytokines, CAR-positive and CAR-negative T cells, monocytes, and other myeloid cells cross the blood-brain barrier (BBB) and lead to inflammation of the brain and meninges Whether this is the result of passive diffusion across the BBB or facilitated by active BBB disruption remains to be elucidated. This will inform the management of NT which, to date, is largely with corticosteroids alone. However, in extreme and rare cases, this inflammation can cause cerebral edema and brain herniation and is therefore of great concern to cellular therapy specialists when treating patients. On the ZUMA-1 trial, the rate of NT was 64%, with 28% of patients experiencing grade 3 or greater NT. 3 Median onset of NT was 5 days, resolving by day 17 in half the patients. These numbers are similar to those reported in the t-cel package insert, which showed an incidence rate of 58% for NT, with grade 3 or greater NT in 18% of patients. This rate is higher than the rate reported on the JULIET trial, with NT of any grade occurring in 21% of patients and grade 3 or greater NT occurring in 12% of patients. 6,7,16 This may be the result of the stricter FDA definition of NT, which considered symptoms such as headache a manifestation of NT rather than being attributable to something else. Similar to reports from the JULIET trial, reports from the TRANSCEND-NHL-001 trial noted that NT was seen in one quarter of patients in the CORE cohort; in 15% of patients in the CORE cohort, NT was grade 3 or greater. 5 WEIGHING EFFICACY AGAINST TOXICITY ACROSS ANTI-CD19 CAR T CELLS FOR TREATING AGGRESSIVE B-NHL With the anticipated availability of three anti-cd19 CAR T-cell therapies for treating aggressive B-NHL, the obvious questions are, Which therapy is right for which patient? and Is there a best therapy? Clearly the most effective product with the least toxicity should win, but can we discern which product this would be from the available data? It would be easy to look across the studies and compare the rates of ongoing durable remissions and the rates of high-grade CRS and NT and then select a preferred treatment. But there are more questions: Are we comparing apples to apples? and Is that comparison relevant across all eligible patients? Caution must be used when comparing across any two, or in this case three, independent studies, but perhaps even more so in this situation. That these products differ with respect to their co-stimulatory domains and the composition of their final T-cell products is how the companies are hoping to distinguish themselves, but this alone may not be responsible for the differences observed on the trials. Instead, it may be differences in the way the trial was conducted (ie, patient eligibility and patient management) as well as manufacturing procedures and turnaround time that have the greatest impact. Reported Results Versus Intent-to-Treat Results Perhaps the best evidence for supporting trial design and determining the impact of product manufacturing procedures is the difference between the reported results and intent-to-treat (ITT) analyses. Each of the studies reports outcomes only in patients who were treated; however, each had patients drop out between enrollment (leukapheresis) and product infusion (Table 1). On the ZUMA-1 trial, 10 (9%) of 111 patients enrolled were not treated because of the inability to manufacture product (1%), adverse events (6%), or an absence of measurable disease (2%). 11 Up to 31% of patients enrolled on the JULIET trial did not receive therapy because cells could not be manufactured (7%) or because of issues related to patients status (24%). 6 On the TRANSCEND-NHL-001 trial, 15% of patients were not treated after leukapheresis because cells could not be manufactured (1%), adverse events (10%), or physician or patient decision (4%). 5 Although product was manufactured in 99% of cases, 12 of 134 products did not meet product specifications and were administered under separate investigational new drug off-trial protocols (9%). This tells us that among eligible patients or in an ITT population (assuming disease progression in patients not treated), the ORRs are lower than those reported: 75% versus 82% on the ZUMA-1 trial, 3 30% versus 52% on the JULIET trial, 6 and 63% versus 75% on the TRANSCEND-NHL-001 (full cohort, excluding the patients treated with a nonconforming product). 5 Although it is valid to say that the power of this therapy is in those who receive it, the choice of therapy for the patient you are treating should be the one most likely to be administered and the one most likely to be effective. There are a variety of reasons for the differences between reported results and ITT results. One is the time to manufacture cells; on the ZUMA-1 trial, it was 17 days; on the JULIET trial, the time was longer but it was not specifically reported. Part of this difference is the result of differences in transfection and manufacturing procedures: axi-cel used lentiviral transfection, and t-cel and liso-cel used retroviral transfection. Part of this difference is also the result of how the cells were received and placed in queue for manufacturing: fresh cells were received and placed directly into manufacturing for the ZUMA-1 trial, and for the JULIET trial, frozen cells waited in a queue for manufacturing. The by American Society of Clinical Oncology

5 CD19 Therapy for Refractory Aggressive B-Cell Lymphoma patients had progressive aggressive B-NHL, so any delay in manufacturing could affect whether the patient remained well and fit enough to receive his or her cells. Another more obvious reason is a differential ability to manufacture cells, which was quite good on the ZUMA-1 and TRANSCEND-NHL-001 trials but slightly lower on the JULIET trial. Finally, these differences may reflect differences in patient eligibility, that is, healthier patients with lower-risk and/or more slowly progressive lymphomas more likely to tolerate the manufacturing time and therefore more likely to be treated. By this argument, one would expect patients on the ZUMA-1 trial to be the fittest on the basis of the lowest drop-out rates. This is a difficult variable to measure, and rates of high-risk prognostic factors seem to be evenly distributed across all three trials. Bridging Therapy The trials also differ with respect to allowing bridging therapy between leukapheresis and CAR T-cell infusion (Tables 1 and 2). On the ZUMA-1 trial, bridging therapy was not allowed; on the JULIET and TRANSCEND-NHL-001 trials, bridging therapy was allowed and was administered to as many as 92% of patients (JULIET trial). 6 In this chemotherapy refractory population, it was doubtful that bridging therapy would result in long-term benefit and thus have an impact on efficacy in the study. It was much more likely that the rates of durable remission reflected the activity of the engineered T cells. However, even a chemotherapyrefractory patient may experience a transient benefit from additional chemotherapy with a reduction in tumor burden just before T-cell infusion. Evidence of this was the differential data set reviewed by the FDA compared with what was ultimately included in the t-cel package insert. Efficacy data from 68 of a total of 92 treated patients is included in the t-cel package insert, because 15 patients had not been restaged after bridging therapy, and eight patients who had been restaged had had a CR to bridging therapy. Although bridging therapy is unlikely to have an impact on efficacy in these studies, it may have an impact on rates of toxicity. Good risk models for CRS and NT are not yet available, but several risk factors have been defined. Risk of CRS has been correlated with tumor burden and high levels of inflammation pretreatment, whereas risk of NT has been correlated with tumor burden, high levels of inflammation pretreatment, younger age, and a history of early and/or high-grade CRS. 3,11,12 On the ZUMA-1 trial, for example, tumor volume (as estimated by the sum of products of diameter of target lesions) correlated with an increased risk of grade 3 or greater NT, with only 4% of patients in the lowest quartile of the sum of products of diameter data experiencing grade 3 or greater NTcompared with 56% of patients in the third quartile. 16 On the JULIET trial, tumor volume was associated with an increased risk of CRS and NT of any grade. 6 Of course there are other ways in which bridging therapy could have an impact on subsequent CAR T-cell therapy. One way is through its positive or negative effects on a patient s pretreatment inflammatory state and subsequent CAR T-cell expansion, which could have an impact on both toxicity and efficacy. This makes it impossible to say whether the variable allowance for bridging therapy favors or harms a given study; all that can be said definitively is that it has an impact on the ability to compare results across these trials. The impact of different bridging therapies, ranging from chemotherapy to targeted agents to radiation therapy, should be studied to improve durable remission rates while minimizing toxicity after CAR T-cell therapy. Outpatient Therapy As mentioned earlier, the differential kinetics of CRS after axi-cel compared with t-cel or liso-cel, which may reflect differential rates of CAR T-cell expansion and activation as a result of CD28 versus 4-1BB co-stimulation, has practical implications for the administration of this therapy. It is estimated that the cost for a patient treated with axi-cel who experiences grade 3 or greater CRS is $531, Applying this cost algorithm to the approximately 7,500 eligible patients annually in the United States, this amounts to an annual amount of more than $3 billion. Thus, many centers are exploring ways to minimize financial losses while continuing to deliver this revolutionary new therapy. One solution is to treat patients in the outpatient setting, admitting them only if and when they develop toxicity that requires inpatient care. The earlier onset of CRS after treatment with axi-cel (within 2 days) complicates outpatient dosing, whereas the delayed onset of CRS after treatment with t-cel or liso-cel makes outpatient treatment feasible. On the JULIET trial, up to 77% of patients treated as outpatients remained outpatients for 3 or more days. 8 Although this does not have an impact on the results of the study, it may have an impact on the product choice for physicians and centers moving forward. FUTURE DIRECTIONS FOR CAR T-CELL THERAPY IN B-NHL The success of targeting CD19 with CAR T cells is unlikely to be limited to aggressive B-NHL, but the balance of efficacy and toxicity for more indolent lymphomas with longer survival and more well-tolerated treatment options is a potential challenge. We await the results of several ongoing trials in indolent B-NHL, mantle cell lymphoma, and chronic lymphocytic leukemia (ClinicalTrials.gov identifiers: NCT , NCT , NCT , NCT , and NCT ; Table 3). Another outstanding question is the optimal timing of treatment with CAR T-cells in aggressive B-NHL and whether it is more effective than existing therapies for high-risk patients in the second-line setting. It is plausible that CAR T-cells may work even better in earlier lines of therapy because the patient s T cells may be healthier since they have been exposed to less therapy. Although this may translate to improved efficacy, it may also mean worse toxicity. There Journal of Clinical Oncology 5

6 Jacobson TABLE 3. Ongoing and Future Studies of Anti-CD19 CAR T Cells in B-NHL Disease Trial Product Product Description Line of Therapy Indolent B-NHL NCT axi-cel CD28 anti-cd19 autologous CAR Third line and beyond NCT t-cel 4-1BB anti-cd19 autologous CAR Third line and beyond Mantle cell lymphoma NCT axi-cel CD28 anti-cd19 autologous CAR Third line and beyond NCT liso-cel 4-1BB anti-cd19 autologous CAR Second line and beyond CLL/SLL NCT liso-cel with or without ibrutinib 4-1BB anti-cd19 autologous CAR Second or third line and beyond NCT axi-cel CD28 anti-cd19 autologous CAR Third line and beyond Aggressive B-NHL NCT axi-cel CD28 anti-cd19 autologous CAR Second line, randomized against standard of care NCT liso-cel 4-1BB anti-cd19 autologous CAR Second line, randomized against standard of care NCT t-cel 4-1BB anti-cd19 autologous CAR Second line, randomized against standard of care B-NHL, multiple subtypes NCT axi-cel + atezolizumab CD28 anti-cd19 autologous CAR + anti-pd-l1 antibody NCT liso-cel combinations (ie, durvalumab, cc-122) 4-1BB anti-cd19 autologous CAR + combinations (ie, durvalumab, CC-122) Refractory disease, second line and beyond Third line and beyond NCT Pembrolizumab Anti-PD-1 antibody Post-CAR T-cell relapse NCT PBCAR BB anti-cd19 allogeneic CAR Third line and beyond NCT EGFR, t19-28z, 4-1BBL CAR T cells CD28 anti-cd19 armored CAR, secrete 4-1BBL NCT CAR 20/19 T cells Tandem 4-1BB anti-cd19 and anti-cd20 CAR T cells Second or third line and beyond No standard of care therapies available Abbreviations: axi-cel, axicabtagene ciloleucel; B-NHL, B-cell non-hodgkin lymphoma; CAR, chimeric antigen receptor; CLL, chronic lymphocytic leukemia; liso-cel, lisocabtagene maraleucel; SLL, small lymphocytic lymphoma; t-cel, tisagenecleucel. are randomized trials in the second-line setting comparing anti-cd19 CAR T cells with salvage chemotherapy followed by autologous stem cell transplantation in responding patients that will hopefully answer these questions (ClinicalTrials.gov identifiers: NCT , NCT , and NCT ). Finally, off-the-shelf or allogeneic CAR T cells are being developed, and hopefully they will allow for more immediate and less costly treatment of patients whose disease cannot wait for the time it takes to manufacture autologous CAR T cells (ClinicalTrials.gov identifier: NCT ). Many researchers are looking at patient and disease characteristics and cytokine and immune profiles to develop better predictive models for CRS and NT. If we can predict which patients are likely to experience high-grade CRS and/or NT, we could risk-stratify patients for inpatient versus outpatient therapy. If we can develop ways to better remotely monitor patients, we may be able to determine not only who can be treated as an outpatient, but also who can remain as an outpatient after developing low-grade toxicity. This has implications for the cost of care mentioned earlier. Furthermore, such models may identify risk factors that are intervenable, either before or during treatment, to further reduce the risk of toxicity. Finally, safety is being addressed by engineering safer CAR T cells, which strengthen the interaction and specificity at the immunologic synapse while taking advantage of innate T-cell signaling molecules, resulting in more controlled and less tonic signaling. Such strategies include switch-mediated CAR T cells, Booleangated CAR T cells, and T-cell antigen coupler T cells In addition to defining risk models for NT, we also need to better understand the principle mechanism of this toxicity to develop better therapies and prophylactic strategies. Existing animal and human studies have identified cytokines that are differentially present in the cerebrospinal fluid after CAR T-cell infusion and have documented the presence of both CAR-positive and CAR-negative T cells in the cerebrospinal fluid In addition, there is a correlation between markers of disseminated intravascular coagulation and endothelial activation and injury and risk of high-grade NT. 11 It some cases, it seems that it is not the T cells themselves producing the cytokines of interest, but monocytes and macrophages. 13 These investigations highlight several targetable interventions to be used in by American Society of Clinical Oncology

7 CD19 Therapy for Refractory Aggressive B-Cell Lymphoma the treatment and prevention of NT, including anti-granulocytemacrophage colony-stimulating factor antibodies and cytokine inhibitors and drugs that have an impact on the health of endothelial cells. Finally, and perhaps most importantly, efforts are underway to improve efficacy for the 20% of patients with primary resistance and the 40% of patients with secondary resistance. There are two main mechanisms of resistance that are currently understood: loss of target antigen and T-cell exhaustion. The former is likely the result of alternative splicing of the gene for CD19 such that the cell has a truncated CD19 that is not detected by immunostains or the CAR itself but that is sufficient to prevent cell death. 21 Bivalent CARs targeted against two tumor antigens are in clinical development to try to overcome CD19 loss (ClinicalTrials.gov identifier: NCT ). With regard to T-cell exhaustion, there are several studies that combine CAR T-cell therapy with checkpoint inhibitors such as atezolizumab, pembrolizumab, or durvalumab and immune agonists such as utomilumab or ibrutinib, to improve expansion, activation, and/or persistence of CAR T cells (ClinicalTrials.gov identifiers: NCT , NCT , and NCT ). Advances in gene editing allow for the generation of CAR T cells that either knock out genes for PD-1 and other inhibitory receptors or the creation of armored CARs, which have an inducible or constitutive cytokine gene construct (eg, IL-12) to improve CAR T-cell activation and/or persistence (ClinicalTrials.gov identifier: NCT ). Finally, the profile of the preinfusion engineered T-cell product itself is important for tumor response; products enriched for early memory differentiation, higher STAT3 signaling, and higher levels of CD8 + CD45RO CD27 + memory-like T cells are associated with disease response whereas products enriched for late memory/effector T-cell differentiation and high PD-1, LAG3, and TIM3 expression correlate with tumor resistance. 22 In chronic lymphocytic leukemia, treatment with 6 months or more of ibrutinib before leukapheresis results in improved T-cell expansion, decreased PD-1 expression and, in a pilot study, a rate of minimal residual disease negative response of 89%. 23 The impact of prior therapies and precollection and treatment T-cell health may then have an important impact on results. In conclusion, directly comparing the efficacy and toxicity results from the ZUMA-1, JULIET, and TRANSCEND- NHL-001 trials is more imperfect than usual, given the complexity of the therapy, differences in manufacturing procedures and turnaround time, and differences in patient eligibility and management, all of which have an impact on the likelihood that a patient will be treated and the outcomes from that treatment. It is not possible to know whether patients treated on the ZUMA-1 trial, who were more likely to receive their CAR T cells, were healthier and more fit than patients on other studies, or because they were not allowed to receive bridging therapy were actually sicker with a higher tumor burden and were therefore at risk for greater toxicity. It is not possible to know whether the slightly lower efficacy between the JULIET trial compared with the ZUMA-1 and TRANSCEND-NHL- 001 trials or the higher toxicity seen on the ZUMA-1 trial compared with the JULIET and TRANSCEND-NHL-001 trials are statistically meaningful. A randomized trial of the therapies used in these three trials is unlikely, so perhaps the best answers will come from institutions that have experience with all three products. And in these cases, physicians and institutions will have to decide to what extent they would sacrifice efficacy for improved safety or sacrifice safety for improved reliability and consistency of treatment delivery. The added financial complexity of this therapy adds a third variable to the equation, in which the ability to maximize reimbursement through outpatient administration may have an impact on the choice of therapy. Given the pace with which the field is moving, however, the resolution of these choices will likely be outdated, because the next new generation of therapies is already underway. AFFILIATION 1 Dana-Farber Cancer Institute, Boston, MA CORRESPONDING AUTHOR Caron A. Jacobson, MMSc, Dana-Farber Cancer Institute, 450 Brookline Ave, Boston, MA 02215; caron_jacobson@dfci.harvard.edu. AUTHORS DISCLOSURES OF POTENTIAL CONFLICTS OF INTEREST AND DATA AVAILABILITY STATEMENT Disclosures provided by the authors and data availability statement (if applicable) are available with this article at DOI JCO REFERENCES 1. Kochenderfer JN, Wilson WH, Janik JE, et al: Eradication of B-lineage cells and regression of lymphoma in a patient treated with autologous T cells genetically engineered to recognize CD19. 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9 CD19 Therapy for Refractory Aggressive B-Cell Lymphoma AUTHOR S DISCLOSURES OF POTENTIAL CONFLICTS OF INTEREST CD19 Chimeric Antigen Receptor Therapy for Refractory Aggressive B-Cell Lymphoma The following represents disclosure information provided by authors of this manuscript. All relationships are considered compensated. Relationships are self-held unless noted. I = Immediate Family Member, Inst = My Institution. Relationships may not relate to the subject matter of this manuscript. For more information about ASCO s conflict of interest policy, please refer to or ascopubs.org/jco/site/ifc. Caron A. Jacobson Honoraria: Kite Pharma/Gilead Sciences Consulting or Advisory Role: Kite Pharma/Gilead Sciences, Bayer AG, Pfizer, Precision BioSciences, Novartis, Celgene Speakers Bureau: Cowen Travel, Accommodations, Expenses: Kite Pharma/Gilead Sciences, Novartis, Pfizer, Bayer, Cowen Journal of Clinical Oncology