Immunicy-1: Targeting BCMA with Cyad-211 to Establish Proof of Concept of an shRNA-Based Allogeneic CAR T Cell Therapy Platform

Off-the-shelf allogeneic CAR T cells derived from healthy donor cells have the potential to overcome many of the issues associated with the time-consuming manufacturing of autologous CAR T cells. However, adoptive transfer of allogeneic T cells carries the risk of graft-versus-host disease (GvHD). Most of the clinical experience with allogeneic CAR T cells is based on gene editing to eliminate T cell receptor (TCR) to mitigate the risk of GvHD. While clearly effective, the downsides of gene editing include multiple manufacturing steps requiring multiple clinical grade reagents, thus extending culture times, which can be associated with T cell exhaustion.

As an alternative, we have explored short hairpin RNA (shRNA) as a means to knockdown TCR expression at the mRNA level. This shRNA is co-expressed along with the CAR in a single clinical grade vector, therefore requiring just one step of genetic modification.

CYAD-211 is an allogeneic anti-BCMA CAR T that co-expresses a shRNA targeting CD3z which results in reduction of cell surface TCR expression. IMMUNICY-1 is an ongoing open-label Phase 1 trial (NCT04613557) designed to evaluate CYAD-211 in adult patients with refractory or relapsed multiple myeloma (MM) following at least two prior MM regimens. Patients receive non-myeloablative preconditioning (cyclophosphamide 300 mg/m²/day and fludarabine 30 mg/m²/day, for 3 days) followed by a single CYAD-211 infusion in a 3+3 dose escalation design evaluating three dose-levels (DL): 30x10 ⁶, 100x10 ⁶ and 300x10 ⁶ cells/infusion.

As of July 29, 2021, nine patients were enrolled across the 3 DLs. Patients had received a median of four prior lines of treatment. Seventy-eight percent of patients were previously exposed to all three major MM drug classes (proteasome inhibitors, immunomodulatory drugs, and anti-CD38 antibody therapy). Eight patients had prior autologous stem cell transplantation.

CYAD-211 was well tolerated. One patient developed grade 1 cytokine release syndrome. Two patients had Grade ≥ 3 hematologic toxicities possibly related to the experimental treatment. Two patients experienced infectious adverse events (1 grade 1 rhinitis and 1 grade 2 upper respiratory infection). There was no neurologic toxicity and no GvHD. There was no dose-limiting toxicity.

Eight patients were evaluated for activity per IMWG criteria. Two patients achieved partial response at dose-levels 1 and 2 while 5 patients had stable disease (SD). One patient with an ongoing SD (3 months +) showed evidence of reduction in size of plasmacytomas.

Analysis of peripheral blood samples by molecular methods confirmed the engraftment of CYAD-211. All patients had detectable CAR T cells. However, the engraftment was short lasting (3-4 weeks). There was a correlation between the depth of lymphodepletion and engraftment. There was also a dose-response in terms of CYAD-211 kinetics with a level neighboring 8,000 copies of CAR T per microgram of input DNA in patients at DL3.

These early data indicate that CYAD-211 is well tolerated with a good safety profile. While further study is required to fully understand the anti-BCMA potency of the CAR used in this trial, the lack of observed GvHD despite engraftment of CYAD-211 provides proof of concept of the safe administration of CAR T using a shRNA-allogeneic platform. The lack of sustained engraftment of CYAD-211 can be explained by rejection of the allogeneic cells by the recovering immune system of the recipient and calls for exploring the role of augmented lymphodepletion. Furthermore, given the ability to include multiple shRNA within the single CAR vector, future strategies will also examine knocking down other molecules that are important in driving immune rejection.