An investigational chimeric antigen receptor T-cell (CAR T-cell) construct targeting two antigens on multiple myeloma cells showed promise in a first-in-humans trial, investigators said.
Among 16 patients with relapsed/refractory, heavily pretreated multiple myeloma who received the dual-targeting construct GC012F, the overall response rate was 93.8%, and all of six patients who received the cells at the highest of three dose levels had stringent complete responses (sCR) and were negative for minimal residual disease (MRD) at 6 months follow-up, reported Weijun Fu, MD, PhD, from Shanghai (China) Changzheng Hospital in an oral abstract presented during the virtual American Society of Hematology annual meeting.
GC012F is a novel CAR-T cell platform targeting both the B-cell maturation antigen (BCMA), which is universally expressed on malignant plasma cells, and CD19, which is expressed on both multiple myeloma cells and progenitors, Dr. Fu said.
“Targeting CD19 can trigger elimination of malignant cells by CAR T. Our preclinical work demonstrated more effective elimination of multiple myeloma clone-forming cells by BCMA and CD19 dual CAR T, so targeting both BCMA and CD19 antigens could improve efficacy and reduce relapse,” he said.
The construct is created using the FasTCAR platform that, according to manufacturer Gracell Biotechnologies (Shanghai), allows for cell culturing and expansion within 24-36 hours, rather than 2-3 weeks required for other CAR T-cell products.
Investigator-initiated trial
In a phase 1 investigator-initiated trial, 16 patients with a median age of 56 (range 27-71) years were enrolled. The patients all had relapsed or refractory multiple myeloma according to 2016 International Myeloma Working Group criteria, with a life expectancy of at least 3 months and adequate organ function.
The median time since diagnosis was 3 years (range 1-10). All but one of the 16 patients had high-risk disease, 3 had double-hit disease (the presence of two deletions, gain of function, or p53 mutation), and 5 patients had one or more extramedullary plasmacytomas. Four of the patients had received therapy with an anti-CD38 monoclonal antibody.
Following lymphodepletion with fludarabine and cyclophosphamide, the patients received the CAR T cells in a single infusion at dose levels of either 1, 2, or 3 times 105 cells/kg.
As of the cutoff date in July 2020, 15 of the 16 patients had a clinical response, including 9 with a CR or sCR, and 6 with a very good partial response (VGPR). As noted before, all of the six patients treated at the highest dose level had a sCR. At the median follow-up of 7.3 months, the median duration of response had not been reached.
Among all patients evaluable for response at month 1 (14 patients), 11 were MRD negative by flow cytometry. At month 3 all 11 evaluable patients were MRD negative, and all of 10 patients evaluable at 6 months were also MRD negative.
As with other CAR T-cell constructs, all patients developed the cytokine-release syndrome (CRS), with grade 1 or 2 severity in 14 patients, and grade 3 in 2 patients. The median time to onset of CRS was 6 days (range 2-10), and the median duration was 4 days (range 1-8 days).
No cases of immune effector cell–associated neurotoxicity syndrome (ICANS) were observed.
One patient treated at the middle dose level presented with fever and died shortly after day 78 of an unknown cause during the COVID-19 pandemic. Two patients died of extramedullary disease; each had achieved MRD negativity.
Investigators continue to follow the patients and are enrolling new patients in the ongoing study.
‘Interesting approach’
Sandy W. Wong, MD, from the Helen Diller Family Comprehensive Cancer Center at the University of California San Francisco, who was not involved in the study, said in an interview that the dual-targeted approach is interesting, in light of a case report presented at ASH 2020 of a patient with multiple myeloma who had a partial response to CAR T-cell therapy with a different construct and who developed a subsequent biallelic loss of BCMA that resulted in resistance to CAR T-cell therapy.
“This raises the idea that, if we perhaps had a dual-targeted CAR T, perhaps we will prolong progression-free survival, in order to avoid antigen escape. So I do think the concept is very interesting and does deserve further study,” she said.
CD19 is thought to be expressed on myeloma stem cells, “so the question is: Are patients not being cured because there is a reservoir of myeloma cells, and targeting CD19 is thought to get at this putative myeloma stem cell? but that remains to be seen,” she added.
Dr. Wong comoderated the session where Dr. Fu presented the data.
The study was supported by participating medical centers and Gracell Biotechnologies. Dr. Fu and Dr. Wong reported no relevant conflicts of interest to disclose.
SOURCE: Jiang H et al. ASH 2020, Abstract 178.