Toxicity of CART19 Cells
The cell infusions had no acute toxic effects. The only serious adverse event noted was the grade 3 tumor lysis syndrome described previously. The patient had the expected disappearance of blood B-lymphocytes beginning on day 1 and continuing through the most recent follow-up visit, 10 months after treatment. The patient had transiently low platelets from day 19 through day 26 and neutropenia from day 17 through day 33. Other signs and symptoms that were probably related to the study treatment included mild elevations in aminotransferase and alkaline phosphatase levels, which developed 17 days after the first infusion and resolved by day 33. Mild constitutional symptoms consisted of fevers, chills, feeling 'shocky', muscle pains, headache, and fatigue. Mild hypogammaglobulinemia was corrected with infusions of ivIg.
Analysis of Serum and Bone Marrow Cytokines
The patient's clinical response was accompanied by an increase in levels of inflammatory cytokines with levels of interferon-γ, the interferon-γ–responsive chemokines CXCL9 and CXCL10, and interleukin-6 that were 160 times as high as baseline levels. The temporal rise in cytokine levels paralleled the clinical symptoms, peaking 17 to 23 days after the first CART19-cell infusion.
The supernatants from serial bone marrow aspirates were measured for cytokines and showed evidence of immune activation. Significant increases in interferon-γ, CXCL9, interleukin-6, and soluble interleukin-2 receptor were noted, as compared with the baseline levels on the day before the T-cell infusion; the values peaked on day 23 after the first CART19-cell infusion. The increase in bone marrow cytokines coincided with the elimination of leukemia cells from the marrow. Serum and marrow tumor necrosis factor α remained unchanged.
Expansion and Persistence of Chimeric Antigen Receptor T Cells
DNA encoding anti-CD19 chimeric antigen receptor (CAR19) could be detected beginning on day 1 after the first infusion. More than a 1000 fold expansion of the cells in the patient was noted by day 21 after the infusion. At peak levels, CART19 cells in blood accounted for more than 20% of circulating lymphocytes; these peak levels coincided with the occurrence of constitutional symptoms, the tumor lysis syndrome and elevations in serum cytokine levels. CART19 cells remained detectable at high levels 6 months after the infusions, though the values decreased by a factor of 10 from peak levels. The doubling time of CART19 cells in blood was approximately 1.2 days, with an elimination half-life of 31 days.
Chimeric Antigen Receptor T Cells in Bone Marrow
CART19 cells were identified in bone marrow specimens beginning 23 days after the first infusion and persisted for at least 6 months, with a decay half-life of 34 days. The highest levels of CART19 cells in the bone marrow were identified at the first assessment 23 days after the first infusion and coincided with induction of an immune response, as indicated by cytokine-secretion profiles. Flow-cytometric analysis of bone marrow aspirates indicated a clonal expansion of CD5+CD19+ cells at baseline that was absent 1 month after infusion and in a sample obtained 3 months after infusion. Normal B cells were not detected after treatment