Safe and Effective Re-Induction Of Complete Remissions In Adults With Relapsed B-ALL Using 19-28z CAR CD19-Targeted T Cell Therapy

Although most adults diagnosed with B-ALL can be induced into a first complete remission (CR1 rates of approximately 80-90%), a majority will relapse and develop chemorefractory disease. Novel, non-chemotherapy based treatments are needed for this group of patients.

We have developed a novel CD19-targeted T cell-based therapy for patients with B cell malignancies. We isolate T cells from patients with relapsed/refractory B-ALL and genetically modify them with a chimeric antigen receptor (CAR) construct, termed 19-28z, which comprises a CD19 binding domain fused to the signaling domains of the CD28 costimulatory receptor and the ζ chain of the CD3 complex. CD19 is a universal B cell antigen expressed on all normal and malignant B cells. Expression of the 19-28z CAR by a T cell promotes binding of the CD19 antigen and triggers cytotoxicity, cytokine release and proliferation upon engagement of CD19.

We are conducting a Phase I clinical protocol in adults with relapsed/refractory B-ALL (NCT01044069). Enrolled patients are leukapheresed and then re-induced with salvage chemotherapy. A T cell infusion (3 x 10⁶ 19-28z CAR T cells/kg) is administered following conditioning chemotherapy. We now describe the results from this Phase I protocol. Thirteen adults have been treated to date: eleven were enrolled with relapsed/refractory disease, while the other 2 were enrolled and leukapheresed during CR1, but not treated until they relapsed. The age of the patients ranged from 23 to 74 with a median age of 42. Three of the 13 patients had Philadelphia-chromosome positive B-ALL, which is considered the most negative genetic risk factor for adults with B-ALL. We were able to achieve the required T cell dose, despite collecting patients with high blast counts or marked lymphopenias, in all but one patient. Seven of the 13 patients were infused with 19-28z CAR T cells while they had gross residual disease (>5 to 70% blasts in the BM). The remaining patients had MRD, detected by flow cytometry or deep sequencing, at the time of 19-28z CAR T cell infusion.

Six patients developed toxicities including high-grade fevers (>40°C), hypotension, hypoxia, mental status changes, and seizures. These episodes ran for approximately one week before they were halted by treatment with steroids or tocilizumab. The other 7 patients did not experience toxicities. All patients completely recovered and were able to leave the hospital. The occurrence of toxicities correlated with tumor burden so that patients with gross residual disease (>5% blasts in BM) developed toxicities, while patients with MRD had no evidence of toxicities.

Ten out of the 12 patients with detectable disease before T cell infusion developed MRD- responses such that 5 of the patients with gross residual disease (blasts > 5% in BM) became MRD- and 5 MRD+ patients became MRD-. The rapidity of the responses was quite remarkable with MRD- results obtained as early as 7 -14 days after T cell infusion. Furthermore, despite the poor predicted outcomes of relapsed Ph+ B-ALL we were able to get these patients MRD-, as detected by both deep sequencing for the IgH rearrangement and qPCR for the bcr-abl transcript.