Cytokine release syndrome (CRS) is among the most representative toxicities of chimeric antigen receptor T (CART) cell therapies against non-Hodgkin's lymphoma (NHL). However, the mechanism of CRS is not fully elucidated. Interleukin-6 (IL-6) has been reported as a key factor in the development of CRS. We here present a novel mechanism of CRS emphasizing a balance between IL-6 and soluble IL-6 receptors (sIL-6Rs), essential amplifiers for IL-6-mediated inflammatory responses.
A 46-year-old male patient with transformed diffuse large B-cell lymphoma (Bcl-2+/C-Myc+) refractory to 3 lines of prior therapies was enrolled in our CART trial (NCT 03196830). Baseline findings included extensive disease, multiple lesions in the abdomen, bone marrow infiltration, and a large volume of chylous ascetics with malignant cells (ascitic IL-6 baseline level: 6,691 pg/ml). And the patient received a combination of CD19-BBζ CART (8 x 106 CAR+ cells/kg), CD22-BBζ CART (1 x 106 CAR+ cells/kg), and lenalidomide (25 mg, qod, Wang X, et al., Clin Cancer Res. 2018). The patient developed mild toxicities including fever, febrile, and rash on Day 3 which were completed reversed on Day 8 after supportive care without tocilizumab or steroids. Quantitative PCR analysis of the CAR transgene demonstrated rapid expansion of the CART cells in both peripheral blood and ascites. An efficacy assessment on Day 27 revealed that most lesions disappeared or significantly shrank, the ascites nearly completely disappeared, and no malignant cell in ascites or bone marrow was detected. The patient remained in remission for 10 months.
The patient was graded as CRS grade 1 according to the ASBMT scale, and cytokine assays of peripheral blood at various time points before and after CART infusions revealed expected stable levels of cytokines, including IL-6, IL-1β, IL-12, IL-15, interferon-γ, monocyte chemoattractant protein 1 (MCP1), macrophage inflammatory protein 1-alpha (MIP1α), IL-8 and granulocyte-macrophage colony-stimulating factor (GM-CSF). In the ascites, however, soaring IL-6 levels were detected with a peak value of 18,516 pg/ml on Day 7, one of the highest IL-6 levels on our CART trials, whereas no compartmental CRS or other manifestation in local abdomen was observed. The trend of ascitic IL-6 coincided with that of CAR transgene numbers. Furthermore, sIL-6R levels in ascites were lower than in serum (p < 0.0001). Importantly, the ratios of IL-6:sIL-6R were 400 to 1000 fold higher in ascites compared with in serum, highlighting that sIL-6Rs were relatively depleted in the ascites. Indeed, the absolute levels of ascitic IL-6 were close to, or exceeded at some time points, those of sIL-6R, indicating that the bottleneck of the formation of IL-6/sIL-6R signaling complex might switch from IL-6 to sIL-6R in the ascites. Flow analysis demonstrated neutrophils account for 15-20% of the total cells in ascites compared with 40-75% in serum, indicating that lack of neutrophils might be a potential cause of the low sIL-6R levels. Additionally, although sgp130 levels in ascites were also lower than in serum, the absolute values were still overwhelming to those of IL-6 and sIL-6R. Lastly, the levels of MCP1, IL-8 and angiopoietin 2 were significantly elevated, and flow analysis revealed that approximately 25% of the ascitic cells were CD14+CD11b+, indicating monocytes/macrophages might be recruited and/or activated. The levels of MIP1α, GM-CSF, IL-1β, IL-12, IL-15, interferon-γ were low in ascites during the whole period.
In conclusion, our data show that relative depletion of sIL-6R in ascites may completely abolish the development of local CRS in the presence of high IL-6. This is the first report to demonstrate the features of biomarkers in ascites after CART therapy, and to describe the impacts of disproportionately low sIL-6R on IL-6 signaling without drug intervention. These results imply that the unique microenvironments in exudates such as ascites may lead to distinct pathophysiological events following CART therapy, and IL-6:sIL-6R ratio should be considered as an indicative parameter in the toxicity management of CRS.
No relevant conflicts of interest to declare.
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