Anti-CD19 CAR T Cells Administered after Low-Dose Chemotherapy Can Induce Remissions of Chemotherapy-Refractory Diffuse Large B-Cell Lymphoma

We have treated a total of 30 patients with autologous T cells genetically modified to express a chimeric antigen receptor (CAR) targeting the B-cell antigen CD19; 22 of 27 evaluable patients obtained either complete remissions (CR) or partial remissions (PR). Ten patients remain in ongoing CRs of 1 to 37 months duration. The CAR was encoded by a gammaretroviral vector and included the variable regions of an anti-CD19 antibody along with CD28 and CD3-zeta moieties. The first 21 patients treated on this protocol have been reported (Kochenderfer et al. Blood 2010, Blood 2012, and Journal of Clinical Oncology 2014). To enhance the activity of the transferred CAR T cells, T-cell infusions in the previously reported patients were preceded by a chemotherapy regimen of high-dose cyclophosphamide (60-120 mg/kg) plus fludarabine. In an attempt to reduce the overall toxicity of our anti-CD19 CAR treatment protocol, we substantially reduced the doses of chemotherapy administered before CAR T-cell infusions. This abstract communicates results from 9 patients with B-cell lymphoma who received a single infusion of 1x10⁶ anti-CD19-CAR-expressing T cells/kg bodyweight preceded by a low-dose chemotherapy regimen consisting of cyclophosphamide 300 mg/m² and fludarabine 30 mg/m² (Table). Each chemotherapy agent was administered daily for 3 days. Eight of the 9 treated patients had DLBCL (diffuse large B-cell lymphoma) that was refractory to chemotherapy (chemo-refractory) or that had relapsed less than 1 year after autologous stem cell transplantation (ASCT). Both of these clinical situations carry a grim prognosis, with median overall survivals of only a few months. Despite the very poor prognoses of our patients, one patient with DLBCL obtained a CR and 4 DLBCL patients obtained PRs. In some patients, PRs included resolution of large lymphoma masses. Compared to our previous experience with anti-CD19 CAR T cells preceded by high-dose chemotherapy, toxicity was reduced when CAR T cells were infused after low-dose chemotherapy. None of the 9 patients treated with low-dose chemotherapy and CAR T cells required vasopressor drugs or mechanical ventilation, although some patients did have short-term neurological toxicity. Cytopenias were mild with a mean of only 1.4 days of blood neutrophils<500/microliter. Blood anti-CD19 CAR T-cell levels were assessed in 6 patients with a quantitative PCR assay; we detected CAR+ cells in the blood of all 6 patients. The mean peak absolute number of blood CAR+ T cells was 73 cells/microliter. Six months after infusion, persisting CAR+ T cells were detected in a lymphoma-involved lymph node by flow cytometry. These results demonstrate that anti-CD19 CAR T cells administered after low-dose chemotherapy have significant activity against chemo-refractory DLBCL and could potentially become a standard treatment for aggressive lymphoma.