Initial Findings of the Phase 1 Trial of PBCAR0191, a CD19 Targeted Allogeneic CAR-T Cell Therapy

Background:

Adoptive engineered autologous cellular immunotherapy has had a significant impact on the lives of some patients with advanced hematologic malignancies. However, the use of these therapies on a larger proportion of patients has been limited by variability of the final cell product, feasibility concerns, cost, and toxicity. Off-the-shelf allogeneic (allo) products offer the opportunity to address some of these concerns. Allo products have their own theoretical limitations, including the potential for graft-versus-host disease (GvHD) causing additional toxicity and host-versus-graft rejection limiting efficacy. PBCAR0191, an anti-CD19 allogeneic CAR T cell, was designed to limit the risk of GvHD by specifically inserting a CD19 specific CAR into the TRAC (T cell receptor alpha constant) locus in cells harvested from healthy donors. Those cells are then expanded, a CD3 elimination step is performed, followed by another expansion, and then PBCAR0191 is vialed and frozen for shipment then thawing, dilution, and infusion at the treatment site. To reduce the risk of PBCAR0191 rejection and increase the chances of cell expansion, lymphodepletion prior to dosing is required. This phase 1 3+3 dose escalation study is designed to identify an optimal dose of PBCAR0191 for efficacy evaluation.

Methods:

In each of 3 dose levels (3 x 10⁵, 1 x 10⁶, and 3 x 10⁶ CAR-T+ cells/kg), up to 6 patients may be enrolled in each of 2 cohorts (Non-Hodgkin Lymphoma (NHL) and Acute Lymphoblastic Leukemia (ALL)). Eligibility requirements include adequate organ function, confirmed diagnosis to fit one of the cohorts, evaluable disease, at least 2 prior standard treatment regimens, no immunodeficiencies, no CNS disease, no active infections or other major medical issues requiring intervention, and no active GvHD. Eligible patients may have received allogeneic stem cell transplant or another CAR-T therapy. Lymphodepletion was administered on day -5 to day -3 using fludarabine 30mg/m2/day and cyclophosphamide 500mg/m2/day. Cells were administered on day 0. Correlative serum and PBMC samples were taken, while patients remained on study, on days 0, 1, 3, 7, 10, 14, 28, 42, 60 and every 30 days until 180 and then every 90 days until day 360. Assessment of response compared to baseline was performed on day 14 (optional for NHL only), and days 28, 60, 90, 180, 270, and 360, until progression.

Results:

Three patients with advanced NHL were enrolled and treated in DL1 between April 25, 2019 and May 24, 2019. Two males (one MCL, one DLBCL) and 1 female (DLBCL) ages 34 - 64 (median 64) years were treated. Two screen failures occurred, both patients with ALL, due to non-compliance (1) and loss of CD19 surface expression (1). One patient enrolled post disease progression after treatment with Axicabtagene ciloleucel. No significant toxicity was observed, including no serious adverse events and no dose-limiting toxicities with all patients having a minimum follow-up of 28 days (median 60 days). Two of the three patients experienced objective tumor response by Lugano criteria, at day 14 and day 28, respectively. Both patients progressed due to new lesions (on day 28 and day 60, respectively). The third patient has not met the definition of response, but has had evidence of central necrosis, decreased tumor size, and decreased PET-avidity at day 28, in the context of post-infusion tumor site pain and mild CRS symptoms. Peripheral blood analysis for CAR-T expansion has identified preliminary evidence of cell expansion with a low absolute numbers quantified, likely due to the low dose level at which treatment was initiated. Peripheral blood serum analysis for IFN-gamma, IL-6, and IL-15 indicate preliminary evidence of cell expansion, though not definitive.

Conclusions:

Further enrollment of patients into DL2 is ongoing. Data from DL2 entered by early October will be included in a presentation in the meeting. Findings to date indicate preliminary evidence of short-lived cell-mediated anti-tumor effect and preliminary evidence of cell expansion in vivo, which will be evaluated more fully at DL2 and DL3.