While treatment with CD19-directed chimeric antigen receptor (CAR) T cells has demonstrated impressive response rates of over 80% in select patients with B-cell malignancies, the associated toxicities – including severe neurotoxicity and cytokine release syndrome (CRS) – are serious concerns.
To better understand the kinetics of CRS and identify biomarkers of its severity, Kevin A. Hay, MD, MSc, from the Clinical Research Division at the Fred Hutchinson Cancer Research Center in Seattle, Washington, and researchers conducted a phase I/II study of patients who received lymphodepletion followed by anti-CD19 CAR T-cell therapy to treat relapsed/refractory B-cell malignancies. Their analysis, published in Blood, identified several independent predictors of CRS, including lymphodepletion using cyclophosphamide and fludarabine, higher CAR T-cell dose, and the presence of thrombocytopenia before lymphodepletion.
The study enrolled 133 adult patients (median age = 54 years; range = 43-62 years) with CD19-positive B-cell malignancies, including acute lymphocytic leukemia (n=47), non-Hodgkin lymphoma (n=62), and chronic lymphocytic leukemia (n=24). Patients had received a median of four prior therapies (range = 1-11 therapies); 25 (19%) had undergone allogeneic hematopoietic cell transplantation (HCT), 22 (17%) had undergone autologous HCT, and three (2%) had undergone both.
Patients received lymphodepletion chemotherapy with a cyclophosphamide-based regimen with (n=104; 78%) or without (n=29; 22%) fludarabine. Two to four days later, they received an infusion of CD19-directed CAR T cells (formulated in a 1:1 ratio of CD4+:CD8+) at one of three dose levels:
- 2×105 cells/kg (n=35; 26%)
- 2×106 cells/kg (n=86; 65%)
- 2×107 cells/kg (n=12; 9%)
The researchers collected blood samples before lymphodepletion, on day zero before CAR T-cell infusion, and at regular intervals after CAR T-cell infusion to evaluate CAR T-cell counts and serum biomarkers.
A total of 93 patients (70%) developed CRS, graded according to modified National Cancer Institute Common Terminology Criteria for Adverse Events. Most patients had grade 2 CRS (32%; defined as symptoms that require or respond to moderate intervention), followed by grade 1 (26%; defined as symptoms that are not life-threatening and require symptomatic treatment only) and grade 3 (4.5%; defined as symptoms that require or respond to aggressive intervention). Ten patients (7.5%) developed grade ≥4 CRS with life-threatening symptoms, half of whom (n=5) died within the first 30 days after CAR T-cell infusion because of complications associated with CRS and/or neurotoxicity. Another patient died four months after treatment because of irreversible neurotoxicity.
Neurologic adverse events (AEs) were also common: 53 patients (40%) experienced one or more grade ≥1 neurologic AE, and the severity of those events was associated with the severity of CRS (p<0.0001). All patients with grade ≥4 CRS developed grade ≥3 neurotoxicity, which typically presented after CRS (p=0.003), with the first neurologic AE presenting a median of four days (range = 2-7 days) after CAR T-cell infusion.
“Fever [≥100.4°F] was the first objective sign of CRS,” the authors noted, “with the exception of one patient who presented with hypotension without fever.”
Fever occurred a median of 2.2 days (range = 0.9-5.6 days) after CAR T-cell infusion and lasted for a median of three days (range = 1.2-4.8 days). Compared with patients with grade 1-3 CRS, patients who developed grade ≥4 CRS had fevers that presented earlier after infusion (p<0.001), peaked earlier (p=0.001), reached a higher maximum temperature (p<0.0001), and lasted longer (p=0.03).
Most patients (n=109; 82%) received both lymphodepletion chemotherapy and CAR T-cell infusion in the outpatient setting and were only admitted at the onset of fever. Seventeen patients (13%) required admission to the intensive care unit (ICU) because of CRS and/or neurologic AEs, with a median length of stay of three days (range = 2-7 days).
The authors noted that, because CRS reached peak severity a median of 3.4 days after onset of fever (range = 1.4-4.7 days), “there was sufficient time for hospital admission and therapeutic interventions to mitigate CRS progression.” Twenty patients with CRS and/or neurotoxicity were treated with both tocilizumab and dexamethasone, five received dexamethasone alone, and one received tocilizumab alone. Fever resolved within a median of 0.4 days (interquartile range = 0.2-2.0 days) after the first dose of either drug.
Multivariable analyses revealed several risk factors for CRS (see TABLE 1), including those indicative of more robust CAR T-cell expansion (such as a higher bone marrow CD19+ tumor burden), and baseline and treatment-related factors that could be addressed early to reduce the risk of CRS (such as the presence of thrombocytopenia and CAR T-cell dose level).