Abstract
CAR T cells targeting the B lymphocyte antigen CD19 have led to remarkable clinical results in B cell leukemia and lymphoma but eliminate all B lineage cells, leading to increased susceptibility to severe infections. As malignant B cells will express either immunoglobulin (Ig) light chain κ or λ, we designed a second-generation CAR targeting Igκ, IGK CAR. This construct demonstrated high target specificity but displayed reduced efficacy in the presence of serum IgG. Since CD19 CAR is insensitive to serum IgG, we designed various combinatorial CAR constructs in order to maintain the CD19 CAR T cell efficacy, but with IGK CAR target selectivity. The Kz-19BB design, combining CD19 CAR containing a 4-1BB costimulatory domain with an IGK CAR containing a CD3zeta stimulatory domain, maintained the target specificity of IgK CAR and was resistant to the presence of soluble IgG. Our results demonstrate that a combinatorial CAR approach can improve target selectivity and efficacy.
Highlights
As a ubiquitous marker of B cells, CD19 was an ideal antigen to limit on-target off-tumor toxicity but resulted in complete B cell aplasia [7,8,9]
The B cell receptor (BCR) consists of two identical immunoglobulin (Ig) heavy and light chains, and owing to allelic exclusion of immunoglobulin (Ig) genes, malignant B cells from an individual tumor are clonal for their BCR and express either Ig kappa (κ) or Ig lambda (λ) light chains [12, 13]
To investigate the activity and specificity of the immunoglobulin kappa (IGK) chimeric antigen receptor (CAR), we tested it against B cell lymphoma cell lines with variable Igκ expression levels (REC-1, SU-DHL-4, BL-41, DAUDI, and U2932) and included three Igλ+ cell lines (Mino, Granta-519, MAVER-1), one cell line that lacked Ig light chains (SC-1) and two non–B cell controls (Jurkat and K562) (Fig. 1A and Fig. S1A)
Summary
As a ubiquitous marker of B cells, CD19 was an ideal antigen to limit on-target off-tumor toxicity but resulted in complete B cell aplasia [7,8,9]. IGK CAR T cells kill Igκ+ target cells but are inhibited in the presence of human serum and soluble IgG To overcome the reduced efficacy of IGK CAR T cells in the presence of HS while maintaining Igκ target restriction, we designed different "AND"-type constructs of CD19 or Igκ scFv using a single costimulatory domain, either 4-1BB domain (KBB and 19BB) or CD3ζ domain (Kz and 19z) (Fig. 2A).
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