As interest in chimeric antigen receptor (CAR) T-cell therapy continues to grow with more promising data coming out and approvals from the FDA in various hematologic malignancies, the role of this cellular therapy has yet to be defined in multiple myeloma, but recent data have inspired hope for this therapy in the relapsed/refractory population.

The B-cell maturation antigen (BCMA)directed CAR T-cell therapy idecabtagene vicleucel (ide-cel; bb2121) has generated excitement in this population following the submission of a Biologics License Application (BLA) in March 2020, seeking approval of ide-cel in patients with multiple myeloma who have received at least 3 prior therapies, including an immunomodulatory drug (IMiD), a proteasome inhibitor (PI), and an anti-CD38 antibody, and a Priority Review designation granted in September 2020. Following delays in the review due to coronavirus disease 2019, the Prescription Drug User Fee Act action date has been set as March 27, 2021.

Deep and durable responses were observed with ide-cel as treatment of heavily pretreated patients with relapsed/refractory multiple myeloma, according to updated results from the CRB-401 study presented by Yi Lin, MD, PhD, assistant professor of oncology and associate professor of medicine at Mayo Clinic, during the 2020 American Society of Hematology (ASH) Annual Meeting. The efficacy and safety findings were consistent with prior findings and supported a favorable clinical risk-benefit profile at target dose levels 150 x 106.1

The median overall survival with ide-cel was 34.2 months (95% CI, 19.2-not evaluable) among all patients in this triple-classexposed population, and half of the patients who had ongoing responses achieved a duration of response >2 years. The median progression-free survival (PFS) was 8.8 months (95% CI, 5.9-11.9). The objective response rate (ORR) overall was 75.8%, which included complete responses (CRs) in 38.7%.

These results from CRB-401 are comparable to the findings from the pivotal phase 2 KarMMa study (NCT03361748), which were presented earlier this year during the 2020 American Society of Clinical Oncology (ASCO) Virtual Scientific Program and support the Biologics License Application. The median OS for this study was 19.4 months, and the median PFS was 8.8 months. The ORR was 73%, which included a CR rate of 33%, and the median duration of response was 10.7 months.2

Ide-cel is being explored in several ongoing studies as well, including the phase 2 KarMMa-2 (NCT-3601078), phase 3 KarMMa-3 (NCT03651128), and phase 1 KarMMa-4 (NCT04196491) clinical trials. These phase 2 and 3 studies are evaluating ide-cel in patients with triple-classexposed disease, and the phase 1 study will explore the use of this CAR T-cell therapy in patients with high-risk newly diagnosed multiple myeloma.

These data have also set the stage for other BCMA-directed CAR T-cell therapies in development for the treatment of patients with multiple myeloma.

In an interview with Targeted Oncology, Lin discussed the updated findings from the CRB-401 study of ide-cel as treatment of patients with relapsed/refractory multiple myeloma.

TARGETED ONCOLOGY: What historical data have we seen with BCMA-directed CAR T-cell therapy in patients with relapsed/refractory multiple myeloma?

Lin: With the CAR T approach in multiple myeloma, the very first case report was actually with CD19-targeted CAR T because there was already experience with that particular antigen in leukemia and lymphomas. There's some ongoing effort in terms of dual targeting with CD19 and BCMA, but BCMA very quickly emerged as an ideal candidate for the myeloma space. This is an antigen that is more uniformly expressed on plasma cells, including myeloma cells, and maybe a small subset of mature B cells, but otherwise BCMA is not expressed on healthy tissues.

There have been some single-center clinical trials with the BCMA-targeted CAR T approach prior to the CRB-401 study, both with National Cancer Institute and the University of Pennsylvania with slightly different constructs. With those early phase 1 studies, there was a little bit more toxicity seen, although there was certainly some response, but the response wasn't particularly durable. CRB-401 is the first in a series of now industry-sponsored multicenter studies, in which we are now seeing a much more encouraging durable response rate and also a more favorable side effect profile as well. At ASH this year, I presented the longer follow-up on the phase 1 CRB-401 study. There is a pivotal phase 2 KarMMa study using the same CAR T construct that had been presented at ASCO earlier this year.

TARGETED ONCOLOGY: Please describe the design of the trial and what was different about the study.

Lin: The CRB-401 study has 2 parts. The first part is the dose-escalation part, and the second part is the dose expansion. The dose escalation is basically testing the range of a fixed dose of 50 million all the way up to 800 million of ide-cel CAR T cells in a relatively small number of patients, basically looking for signs of severe side effects to identify a safe dose. The dose expansion cohort is where we take the more promising doses in terms of response, and also safety profile, and test them in more patients to get a better safety signal, which is then moved forward for phase 2 testing in the KarMMa study.

In the dose-expansion portion of CRB-401, we required that each patient must have had exposure to an anti-CD38 antibody. That was allowed in a dose escalation but not required for everybody. [To be included in the study,] the patient must have had become refractory to the most recent line of treatment before they came on the study. The other thing that was different was that in the dose-escalation cohort, all patients had their myeloma cells in the bone marrow reviewed centrally by immunohistochemistry staining, and they were required to have at least 50% of these cells having BCMA expression in a dose-expansion cohort, to better understand the clinical efficacy and safety profiles of this treatment. We also included some patients that had BCMA expression below that to even levels that were not detectable by immunohistochemistry.

TARGETED ONCOLOGY: What were the results from this study?

Lin: The study [included] a total of 62 patients. The results from the first 33 patients were already published in the New England Journal of Medicine last year, and this year at ASH, data were presented for outcomes of the entire 62-patient cohort, with a median follow-up of now 18.1 months. What we have seen so far is in this entire treated patient cohort these are patients with very high-risk features of myeloma, and close to a third of these patients had high-risk cytogenetics, 37% of these patients had extra modularity plasma effect, and almost half of these patients needed some type of systemic therapy while their CAR T cells are being made. These patients, on average, had 6 lines of prior therapy, and in close to 70% or higher, these patients are either triple-refractory or were refractory to the most recent line of therapy.

For this group of patients that was treated overall, the safety signal was very tolerable, which is not surprising with CAR T therapy because these patients also do get lymphodepletion chemotherapy as part of the treatment with CAR T. We do see that low blood count is the most common side effect, including the more severe low blood counts, but on average, the recovery of these blood counts can be seen well under the first 3 months after CAR T infusion. The other most common side effects that we need to watch for with CAR T are cytokine release syndrome (CRS) and neurotoxicity. What we have seen in this study is that, on average, about 76% of these patients had some type of CRS. However, those that had grade 3 or higher, that is only [seen] in 6.5% of the patients, so much lower, and that's also reflected in the relative lower use of tocilizumab and steroids, as well, to manage the side effects. About 35% of these patients had some type of neurologic side effect, but again, only 1 patient had a more severe form of neurotoxicity. Compared to what we have seen with the CAR T experience in the lymphoma/leukemia space, this is a very, very encouraging safety profile.

We have also now seen that the ORR is quite high. It's 75.8% with a CR and stringent CR rate of about 38.7%. Many of these patients that had bone marrow that were evaluable for minimal residual disease (MRD) response were MRD-negative. We are seeing, since we tested many doses, that there is a dose-related increase in response with increasing [the] dose, and we have also seen that the duration of response is 10.3 months. When we look at the dose that was tested as well in those expansions [in] the 150 to 450 range, what we have seen is that the duration of response is comparable, so not significantly decreased, for patients with high-risk features like those with extramedullary disease for older patients, as well as patients who needed to get bridging therapy during treatment. The median PFS is 8.8 months, and the median OS is 34.2 months.

So far, the response rate, duration of response, and PFS seem to be comparable to what we also now see in the KarMMa study, which has less follow-up, but we are seeing a very nice median OS for a treatment in which we're just giving a 1 dose infusion and no follow-up maintenance therapy.

TARGETED ONCOLOGY: In terms of CAR T-cell therapy, how do you see this strategy impacting this patient population in the future?

Lin: I think there's definitely a role for this in the practice. The BLA for ide-cel has been submitted to the FDA, so we're anticipating review sometime in early 2021. This is very exciting because this could very well be the first CAR T for multiple myeloma. I think this would definitely be a treatment option for these patients. Based on how KarMMa is designed, we anticipate that the FDA approval will be in the space of patients who [have] had at least 3 lines of prior therapy and have been exposed to the currently approved 3 main backbones of treatmenta PI, IMiD, and the CD38 antibody. The full detail is pending final FDA review and the label. However, in that space, certainly looking at the demographic of the patient that's been treated so far as CRB-401 and KarMMa, that's a wider group of patients. Based on the fact that this is a treatment that is a basically living active cells, I perceive that the earlier that patient could get this therapy in the earliest possible approved indication, there would likely be potentially more benefit for the patients.

TARGETED ONCOLOGY: Do you think there is hope for this treatment in other hematologic malignancies outside of lymphomas and leukemias as well?

Lin: That is actually a very interesting question because what we're seeing in terms of the severity of CRS and neurotoxicity is a reflection of our evolving learning about how to manage the toxicity, as well. There is a component to the CAR design, the disease, the nature of the disease, the kinetics of the CAR T actions, in the manifestation of these symptoms. What we are seeing now, with even the prior CAR and next-generation CAR coming on, we will likely see an ongoing improvement in terms of a reduction of severity of these symptoms and also in the ways that we could manage these symptoms.

The fact that myeloma would be the next disease that has an FDA-approved CAR T also relates to the fact that the BCMA antigen is more restricted on the cell type where the malignancy is involved, similar to CD19 for lymphoid malignancy. We are seeing that there are some challenges, for example with acute myeloid leukemia or myeloid neoplasms where a number of antigens could overlap with stem cells, which we wouldn't want to try to hurt. There are some novel CAR approaches to try to overcome that, and those are in very early phase testing, so we'll need to see how those results evolve.

References

1. Lin Y, Raje NS, Berdeja JG, et al. Idecabtagene vicleucel (ide-cel, bb2121), a BCMA-directed CAR T cell therapy, in patients with relapsed and refractory multiple myeloma: updated results from phase 1 CRB-401 study. Presented at: 2020 ASH Annual Meeting & Exposition; December 5-8, 2020; Virtual. Abstract 131.

2. Munshi NC, Anderson Jr LD, Jagannath S, et al. Idecabtagene vicleucel (ide-cel; bb2121), a BCMA-targeted CAR T-cell therapy, in patients with relapsed and refractory multiple myeloma (RRMM): Initial KarMMa results.J Clin Oncol. 2020;38(suppl):8503. doi:10.1200/JCO.2020.38.15_suppl.8503

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Updated Findings Show Continued Efficacy for CAR T-Cell Therapy in Heavily Pretreated Myeloma - Targeted Oncology