Development of a compact bidirectional promoter-driven dual chimeric antigen receptor (CAR) construct targeting CD19 and CD20 in the Sleeping Beauty (SB) transposon system.

Background: A bidirectional promoter-driven chimeric antigen receptor (CAR) cassette provides the simultaneous expression of two CARs, which significantly enhances dual antigen-targeted CAR T-cell therapy.

Methods: We developed a second-generation CAR directing CD19 and CD20 antigens, incorporating them in a head-to-head orientation from a bidirectional promoter using a single Sleeping Beauty transposon system. The efficacy of bidirectional promoter-driven dual CD19 and CD20 CAR T cells was determined in vitro against cell lines expressing either, or both, CD19 and CD20 antigens. In vivo antitumor activity was tested in Raji lymphoma-bearing immunodeficient NOD-scid IL2Rgamma (NSG) mice.

Results: Of all tested promoters, the bidirectional EF-1 promoter optimally expressed transcripts from both sense (CD19-CAR) and antisense (GFP.CD20-CAR) directions. Superior cytotoxicity, cytokine production and antigen-specific activation were observed in vitro in the bidirectional EF-1 promoter-driven CD19/CD20 CAR T cells. In contrast, a unidirectional construct driven by the EF-1 promoter, but using self-cleaving peptide-linked CD19 and CD20 CARs, showed inferior expression and in vitro function. Treatment of mice bearing advanced Raji lymphomas with bidirectional EF-1 promoter-driven CD19/CD20 CAR T cells effectively controlled tumor growth and extended the survival of mice compared with group treated with single antigen targeted CAR T cells.

Conclusion: The use of bidirectional promoters in a single vector offers advantages of size and robust CAR expression with the potential to expand use in other forms of gene therapies like CAR T cells.