Bob Valamehr, PhD
An off-the-shelf, dual-targeted chimeric antigen receptor (CAR) T-cell approach yielded positive results in preclinical specificity, functionality, and efficacy studies, according to findings presented at the 2018 AACR Annual Meeting.
FT819, manufactured by Fate Therapeutics, is an off-the-shelf, T-cell receptor (TCR)-less CD19-targeted CAR T-cell product. “This product is responsive, cytotoxic, and specific,” noted Bob Valamehr, PhD, vice president of cancer immunotherapy at Fate Therapeutics Inc.
The hope is that this product could potentially be more accessible to patients than conventional CAR T-cell therapies, which tend to be highly personalized, time-consuming to produce, and consist of only enough cells for a single-dose treatment with variable quality.
In this new approach, investigators begin with cells from a healthy donor rather than the patient. To generate FT819, they combine reprogramming of peripheral blood-derived T cells with targeted insertion of a CD19 CAR into the T-cell receptor α (TRAC) locus under the transcriptional control of its endogenous regulatory elements to generate a single cell-derived clonal TRAC-targeted CAR-expressing master pluripotent stem cell (iPSC) line.
“Our off-the-shelf vision starts with an iPSC—a pluripotent cell that has the unique ability of unlimited self-renewal and the capacity to differentiate in to 200 cell types. Using this cell, we can effectively place multiple attributes in to a cell at the single cell level and create a master cell bank,” Valamehr explained.
In creating the master line cell, the iPSC line for the production of CAR T-cells provides distinct advantages over autologous and allogeneic approaches. In doing so, the investigators are able to produce large quantities of what Valamehr called “universal CAR19 T cells” that are not patient-restricted.
“This master cell bank, rising from a single-cell iPSC clonal population, can be plugged in to our proprietary differentiation and expansion strategy to make a mass number of T cells that are capable of multi-dose application and can basically begin to address the many challenges as discussed earlier—including creation of a homogenous product, at one time different reprogramming strategy and engineering strategy, a cost-effective process, and starting with material that is from a healthy starting source,” he added.
When using donor T cells, they can attack the patient’s tissues and organs, potentially resulting in graft-versus-host disease (GVHD); therefore, it is critical to deactivate or remove TCR.
During the stage-specific differentiation, the iPSC line dependably converted into CD34-positive cells, which were then differentiated towards CD8-positive cells with uniform CAR expression (95 +/- 5%) in the absence of TCR expression, eliminating the likelihood of GVHD. “The product is pure for CAR expression and has complete elimination of TCR. As we have been told through several clinical trials, even few cells expressing TCR can elicit GVHD. So, this pure product is now safe and highly efficacious,” Valamehr said.
In vitro functional studies showed that FT819 displayed an efficient cytotoxic T-cell response when challenged with CD19-positive tumor cells by producing cytokines (IFN-gamma, TNF-alpha, and interleukin-2) and mediators of cell death (CD107a/b, perforin, and granzyme B). FT819 was also found to be target specific by attacking only CD19-positive tumor cells and sparing CD19-negative tumor cells.
FT819 also has a second targeting receptor designed to broaden the therapy’s efficacy: a CD16 Fc receptor that can bind to tumor cells coated with antibodies, which enables the agent to be administered in combination with other proven cancer treatments, like monoclonal antibodies targeting CD20-positive tumor cells, to potentially overcome tumor antigen escape.
Also in the in vitro studies, FT819 was shown to elicit antibody-dependent cell-mediated cytotoxicity when combined with a therapeutic antibody targeting CD20, all through the expression of CD16 Fc receptor.
Valamehr noted the cells can be can be packaged, stored, and made readily available for treatment of a large number of patients.
“CAR T cells can be robustly manufactured from a multi-point engineered master iPSC line,” he added. “The master iPSC line is self-renewing and can be used repeatedly without sourcing new donor material or re-engineering cells. A single manufacturing campaign yields large quantities of CAR T cells and can be repeated in the same exact manner.”