An analytical biomarker for treatment of patients with recurrent B-ALL after remission induced by infusion of anti-CD19 chimeric antigen receptor T (CAR-T) cells

Anti-CD19 chimeric antigen receptor-modified T (CAR-T-19) cells have emerged as a powerful targeted immunotherapy for B-cell lineage acute lymphoblastic leukemia with a remarkable clinical response in recent trials. Nonetheless, few data are available on the subsequent clinical monitoring and treatment of the patients, especially those with disease recurrence after CAR-T-19 cell infusion. Here, we analyzed three patients who survived after our phase I clinical trial and who were studied by means of biomarkers reflecting persistence of CAR-T-19 cells in vivo and predictive factors directing further treatment. One patient achieved 9-week sustained complete remission and subsequently received an allogeneic hematopoietic stem cell transplant. Another patient who showed relapse after 20 weeks without detectable leukemia in the cerebrospinal fluid after CAR-T-19 cell treatment was able to achieve a morphological remission under the influence of stand-alone low-dose chemotherapeutic agents. The third patient gradually developed extensive extramedullary involvement in tissues with scarce immune-cell infiltration during a long period of hematopoietic remission after CAR-T-19 cell therapy. Long-term and discontinuous increases in serum cytokines (mainly interleukin 6 and C-reactive protein) were identified in two patients (Nos. 1 and 6) even though only a low copy number of CAR molecules could be detected in their peripheral blood. This finding was suggestive of persistent functional activity of CAR-T-19 cells. Combined analyses of laboratory biomarkers with their clinical manifestations before and after salvage treatment showed that the persistent immunosurveillance mediated by CAR-T-19 cells would inevitably potentiate the leukemia-killing effectiveness of subsequent chemotherapy in patients who showed relapse after CAR-T-19-induced remission.