In vitro and in vivo model of a novel immunotherapy approach for chronic lymphocytic leukemia by anti-CD23 chimeric antigen receptor

Chronic lymphocytic leukemia (CLL) is characterized by an accumulation of mature CD19⁺CD5⁺CD20^dim B lymphocytes that typically express the B-cell activation marker CD23. In the present study, we cloned and expressed in T lymphocytes a novel chimeric antigen receptor (CAR) targeting the CD23 antigen (CD23.CAR). CD23.CAR⁺ T cells showed specific cytotoxic activity against CD23⁺ tumor cell lines (average lysis 42%) and primary CD23⁺ CLL cells (average lysis 58%). This effect was obtained without significant toxicity against normal B lymphocytes, in contrast to CARs targeting CD19 or CD20 antigens, which are also expressed physiologically by normal B lymphocytes. Moreover, CLL-derived CD23.CAR ⁺ T cells released inflammatory cytokines (1445-fold more TNF-β, 20-fold more TNF-α, and 4-fold more IFN-γ). IL-2 was also produced (average release 2681 pg/mL) and sustained the antigen-dependent proliferation of CD23.CAR⁺ T cells. Redirected T cells were also effective in vivo in a CLL Rag2^-/-γ_c^-/- xenograft mouse model. Compared with mice treated with control T cells, the infusion of CD23.CAR⁺ T cells resulted in a significant delay in the growth of the MEC-1 CLL cell line. These data suggest that CD23.CAR⁺ T cells represent a selective immunotherapy for the elimination of CD23⁺ leukemic cells in patients with CLL.