Received: 01.06.2023 Accepted: 02.06.2023 Early publication date: 15.06.2023
Over the last decade, the use of chimeric antigen receptor (CAR) T cells has emerged as a new strategy in the treatment of relapsed/refractory (R/R) acute lymphoblastic leukemia (ALL). The immune activation plays a pivotal role, both in the therapeutic effect of CAR-T cells and the side effects of the therapy.
The most common toxicities related to CAR-T cell treatment, which are cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity syndrome (ICANS), are caused by the excessive activation of effector cells and the release of high levels of cytokines [1, 2]. We here report the profile of immunological response in a patient treated with CAR-T cells due to primary refractory ALL.
The patient, a 5-year-old girl, was diagnosed with B-common ALL with co-expression of CD36 in December 2022. After the diagnosis, she received treatment according to the AIEOP-BFM-2017-Poland therapeutic protocol. On the 15th day of treatment, the therapy response was unsatisfactory, with 49.5% blast cells in the bone marrow. On the 33rd day, minimal residual disease (MRD) was measured at 3 × 10–1. Due to the identification of activating aberrations of the ABL-kinase family in blast cells, the therapy was switched to the imatinib-based EsPHALL-2017 protocol. At that point, a bone marrow aspirate biopsy was repeated, revealing 29.5% blast cells. She was subsequently diagnosed with primary refractory ALL and qualified for CAR-T cell therapy.
The bridging therapy was based on the FRALLPOST-2004 protocol with the addition of imatinib. Prior to the CAR-T cell infusion, a lymphodepleting regimen consisting of fludarabine and cyclophosphamide was administered. Subsequently, in May 2023 the patient received an infusion of anti-CD19 CAR-T cells (tisagenlecleucel, Novartis). No immediate infusion-related toxic effects were observed. The post CAR-T cell infusion course was complicated by grade I CRS and grade II ICANS which occurred at day +4 after the CAR-T cell infusion and required treatment with tocilizumab and dexamethasone. After a temporary improvement, on day +7 after the infusion, fever and neurological symptoms were observed. The child was diagnosed with grade I CRS and grade III ICANS, with complete remission after treatment with four doses of tocilizumab and dexamethasone. Laboratory test results, including complete blood morphology, C-reactive protein, ferritin, cytokine profiles and flow cytometry of lymphocyte subpopulation, were monitored daily from day –1 to day +14 after the CAR-T cell infusion. Flow cytometry of CAR-T cells was performed on specific days (days 0, +1, +2, +3, +6, +10, and +14). The changes in the cytokine profiles and proinflammatory mediators are set out in Figure 1. Despite the observed toxicities, C-reactive protein (CRP) was <5 mg/L during the entire observation period. The girl was discharged on day +17 after the infusion in good general condition, with scheduled follow-up appointments in the outpatient clinic.
The in vivo kinetics of CAR-T cells have provided crucial insights into the therapeutic response and its associated side effects [3]. Although the CAR-T cell count was initially low in the first few days after infusion in our described case, a similar trend has been observed in other studies, with an exponential increase in CAR-T cells levels being observed between days +7 and +11 [4, 5]. Furthermore, the expansion of CAR-T cells happened at the same time as the occurrence of CRS and ICANS. It is still not fully understood whether the peak of CAR-T cells is the cause of the toxicities itself, or an effect of immune-related CAR-T cell expansion [4, 6, 7]. Incidences of those toxicities were associated also with an increase in both proinflammatory mediators (IL-6 and ferritin) and a slight increase in anti-inflammatory cytokines (IL-10). After anti-inflammatory therapy with tocilizumab and steroids, a rapid decrease in cytokine levels, but not CAR-T cells, occurred.
Treatment of CRS (with tocilizumab) and ICANS (with steroids) was successfully applied [8]. However, there is a subset of patients who experience therapy-resistant CRS/ICANS, highlighting the need to identify new targets for toxicity treatment [2]. In our patient, the second episode of CRS and ICANS coincided with a significant peak in tumor necrosis factor alpha (TNF-α) levels accompanied by a peak in CAR-T cell count. This finding is in line with the results of early studies of CAR-T cell therapy, where toxicities were related to a notable increase in TNF-α level, making TNF-α a potential target for CRS and ICANS therapy [1, 9]. In some severe cases, TNF-α blockade, in combination with tocilizumab, could effectively reverse CRS [10].
In conclusion, the monitoring of kinetics of CAR-T cells and cytokine profile provided a valuable evaluation of the therapeutic response and its associated adverse effects. Understanding the underlying mechanisms of CAR-T cell-related immune responses is crucial for improving therapy outcomes, and for the early detection of toxicities and their better management. The presence of CAR-T cells might be a good prognostic factor for continuous remission in ALL.
Acknowledgements
Authors thank Paweł Wojtylak, Director of Regional Blood Transfusion Center (RCKiK), Bydgoszcz for his continuous support and investment in CAR-T and HCT programs in Bydgoszcz.
Authors’ contributions
JaS, MRP — design of study. MRP, KC, RD, AM, ED — clinical data. JoS, JaS — writing manuscript. MK, BKR, RD — laboratory analysis. EM, KG, MRP, ŁL — CAR-T handling. JaS, MRP, KC — critical review. All authors — final approval.
Conflict of interest
The authors declare no conflict of interest.
Financial support
None.
Ethics
The work described in this article has been carried out in accordance with The Code of Ethics of the World Medical Association (Declaration of Helsinki) for experiments involving humans; EU Directive 2010/63/EU for animal experiments and uniform requirements for manuscripts submitted to biomedical journals.