A phase 1 first-in-human study demonstrated synthetic T-cell receptor and antigen receptor (STAR) technical feasibility, clinical safety and efficacy in treating CD19+ relapsed/refractory B-cell acute lymphoblastic leukemia (ALL), according to senior study author Peihua Lu, MD, Beijing Lu Daopei Institute of Hematology, Beijing, China. STAR T cells were found to be superior to conventional chimeric antigen receptor (CAR) T cells with respect to signaling capacity, cytokine production and antitumor potency in an animal model study, according to Dr. Lu’s presentation at the annual meeting of the American Society of Hematology.
Remission can be improved
While CAR T-cell therapy has demonstrated high response rates in patients with B-cell malignancies, remission durability and safety can be improved, Dr Lu said. Her team developed STAR, a novel double-chain chimeric receptor consisting of two protein modules, each containing an antibody light or heavy chain variable region, the T cell receptor (TCR) alpha or beta chain constant region fused to the OX-40 costimulatory domain. The 2 modules are linked by a self-cleaving Furin-p2A sequence that allows the modules to be proteolytically separated and reconstituted. In preclinical in vitro research, STAR-T-cells showed a much faster and stronger cell activation, compared with CAR T cells and superior target cell–killing ability, and higher levels of interferon-y after coculture with the CD19+ Raji cell. In a murine in vivo study, STAR-T cells had higher antileukemia activity, compared with CAR-T cells, and significantly inhibited tumor cell growth, Dr. Lu stated. All animals were sustainably tumor free 5 days after STAR-T cell injection.
The first-in-human study included 18 CD19+ relapsed/refractory B-cell ALL (median age 22.5 years) patients, with a median bone marrow blast level pre–CAR T of 15.3%.
The manufacture success rate was 100% and took about 9 days (7-13). Transduction efficacy was 57.4% (41.0%-78.2%). Subjects received a conditioning regimen of intravenous fludarabine (25mg/m2 per day) and cyclophosphamide (250mg/m2 per day) for 3 days followed by a single STAR T-cell infusion. Patients were given the option, after they achieved complete remission (CR), of proceeding to consolidation allogeneic hematopoietic stem cell transplantation (allo-HSCT).
100% MRD negative
On day 14 following transplant, 18/18 had achieved minimal residual disease–negative complete response/CRi (with incomplete hematologic recovery). One patient relapsed after allogeneic transplant, becoming minimal residual disease positive on day 28. After a median follow-up of 105 days, 11/18 bridged into allo-HSCT without relapse. Among the seven patients who did not undergo allo-HSCT, one relapsed on day 58 and died on day 63. The patient had CNS leukemia and 87% bone marrow blasts before receiving STAR T. The others, Dr. Lu said, remain in CR.
Mild cytokine release syndrome (CRS) occurred in only 10 patients (55.6%), with grade 1 CRS in 8 patients and grade 2 in 2 patients. Grade 3 neurotoxicity occurred in two patients.
Reporting cellular kinetics of STAR T cells in peripheral blood by fluorescence-activated cell sorting (FACS)/quantitative PCR showed the highest STAR-T proliferation ratio (STAR/CD3) of 88.1%. Median peak level was 4.9 x 104 copies number/mcg genomic DNA. The peak time was day 8.5 and the longest detection time was 6 months after STAR T infusion (STAR T ratio, 0.46%-1.85%). High in vivo proliferation and persistence was observed regardless of infusion dose.
STAR holds promise
Dr. Lu concluded: “The phase 1 first-in-human study demonstrated technical feasibility, clinical safety and efficacy of STAR T in treating CD19+ relapsed/refractory B-cell acute lymphoblastic leukemia.” She noted also that long-term observation of these patients and studies of larger patient cohorts are warranted to evaluate a beneficial advantage of the STAR T over the conventional CAR T product.
Asked about future directions in the discussion period, Dr. Lu responded that “this product holds great promise, No. 1 because it is actually between a T-cell receptor and a CAR T, and so clearly has fewer side effects. It potentially can recognize and target the tumor intracellular antigen better than a conventional CAR T. It is easier to construct – and holds great promise for treating solid tumors.”
Dr. Lu reported that she had no relevant disclosures.
SOURCE: Lu P et al. ASH 2020, Abstract 270.