We report one of the first real-life cohorts of RRMM patients treated with commercial ide-cel at a single Swiss academic center between June and October 2022, following the administrative approval of ide-cel in April 2022. Our patient population was comparable to the patient population of previously published trial data on ide-cel (19), with 38% of patients harboring high-risk cytogenetics, 19%, R-ISS stage III, 31%, extramedullary disease, and a median number of previous treatment lines of 6 (range: 3–12). Similarly, safety and primary response results were comparable to the previous study experiences.
In our patient cohort, we performed a first BM response assessment 2 weeks after ide-cel treatment (median: 12 days, range: 10–35), and further assessments at 3 and 6 months. Remarkably, 44% of patients achieved CR (including 25% of sCRs by multiparameter flow cytometry) as early as 2 weeks after ide-cel infusion. Additionally, we observed an increased depth of responses at 3 months follow-up, with 2 additional patients with initial CR and PR, respectively, further improving to an sCR. Moreover, patients showing an early sCR or CR in the first BM biopsy assessment, maintained this response status in the following response assessment 3 months after ide-cel infusion.
In line with ide-cel trial data, peak CAR T expansion in the peripheral blood occurred between week + 1 and + 3 after ide-cel infusion (9). Similar CAR T expansion dynamics have been observed for CD19-targeting CAR T-cell agents in diffuse large B-cell lymphoma (DLBCL) and B-acute lymphoblastic leukemia (B-ALL) studies (20–23). Interestingly, in our cohort, we observed sCR and CR more frequently in patients with a higher CAR T expansion in the peripheral blood (> 105 copies/µg cfDNA) as documented by ddPCR, and all patients with PD only achieved a low CAR T expansion (< 105 copies/µg cfDNA).
Additionally, we performed longitudinal monitoring of circulating sBCMA levels in peripheral blood, and found lack of progressive decrease or plateau levels in patients with PD. In contrast, responders showed constantly decreasing sBCMA levels with a nadir between week + 8 and + 12 following ide-cel infusion. This suggests that circulating sBCMA levels can be potentially used as additional biomarker to monitor MM responses following CAR T-cell therapy.
In this cohort, CAR T-associated toxicity was manageable. However, we observed expected adverse events frequently, requiring complex and timely multidisciplinary management (23–25). Similarly to previous reports, the vast majority of patients (94%) presented CRS, mainly grade 1 (88%), and required the administration of at least one dose of tocilizumab. Thus, albeit neurotoxic adverse events presented less frequently in our cohort than previously described in patients receiving ide-cel (9), with only one (6%) patient presenting an ICANS grade 2, adequate and timely management of CAR T patients in experienced centers is essential. For instance, one patient developed refractory CRS and ICANS grade 2 requiring the administration of tocilizumab, dexamethasone and siltuximab. The same patient presented the highest CAR T expansion in the peripheral blood observed in our cohort, reaching a peak of 757’927 copies /µg cfDNA 2 weeks after ide-cel infusion, which also correlated with CR and MRD negativity in the early BM assessment.
Hematologic toxicity of any grade presented in all patients, and most patients presented grade 3 or higher events. Relevantly, 38% of patients presented prolonged grade 3 or higher hematologic toxicity, persisting at 3 months follow-up after ide-cel treatment. This prolonged toxicity, especially in patients with severe pancytopenia, may represent a major clinical challenge. Prolonged hematologic toxicities persisting at > 90 days post-CAR T-cell therapy, mainly thrombocytopenia and neutropenia, have been reported in 7–38% and 0–33%, respectively, in DLBCL and B-ALL studies with tisagenlecleucel (20, 21), axicabtagene ciloleucel (26) and lisocabtagene maraleucel (27). In the KarMMa trial, 41% of patients showed at least grade 3 persistent neutropenia, and 49% thrombocytopenia, with a median time to recovery of 1.9 and 2.1 months, respectively (9, 28). Moreover, in the KarMMa trial 3/127 (0.2%) of patients required stem cell support due to prolonged pancytopenia (9). The physiopathology of this post CAR-T persistent cytopenia is incompletely understood, and the clinical management relies on supportive measures, mainly transfusions, use of hematopoietic growth factors and hematopoietic stem cell boost (29).
Regarding the ide-cel manufacturing process, the median time from lymphapheresis to ide-cel infusion was 7 (7–11) weeks. This seemed acceptable, since most patients (68.8%) were able to receive a bridging therapy, while patients with lower tumor burden did not require bridging. Manufacturing success rate was 88%, which is clearly lower as compared to previously published data (14). In the KarMMa phase 2 trial, only one case of production failure out of 140 included patients was reported (99.3% production success rate) (14). In this trial, the number of previous treatment lines, as well as the proportion of patients with a history of HDCT with ASCT, was comparable to our cohort. Thus, we hypothesized that the lower real-life manufacturing success rate was not related to a more heavily pretreated patient population. For tisagenlecleucel, the latest reported manufacturing success rates were around 96%, with less than 3% of patients receiving OOS products (30). Further reports from real-life cohorts could clarify the maximal expected production success rate for MM CAR-Ts and the possible underlying factors.