Stereotyped immunoglobulin (IG) light chain rearrangements using the IGLV3-21 gene with G110R mutation define a subset of chronic lymphocytic leukemia (CLL) patients with aggressive clinical course, poor prognosis and limited therapeutic options. This G110R mutation is a highly specific driver in CLL and has the unique ability to confer autonomous B cell receptor (BCR) signaling via mediating homotypic BCR self-interactions. To advance treatment of these patients, we aimed to develop a chimeric antigen receptor (CAR) T cell product to selectively target the CLL-specific IGLV3-21-G110R neoepitope.

We translated the IG heavy and light chains of a murine IGLV3-21-G110R-targeting antibody into the single-chain variable fragment (scFv) format and generated murine and humanized second generation CAR constructs. Constructs were transduced into T cells from healthy donors and CLL patients. We performed in vitro co-culture assays using different cell models engineered to express BCRs with IGLV3-21-G110R light chain as well as primary healthy human B and CLL cells to assess killing and specificity via live cell imaging and IFN- secretion. We further tested epitope selectivity and safety in xenografts as well as two humanized mouse models after injection of healthy or CLL patient peripheral mononuclear cells (PBMCs) and CAR T cells.

The generated scFv exhibited binding affinities identical to the original antibody. IGLV3-21-G110R targeting CAR T cells generated from healthy donors and CLL patients eradicated IGLV3-21-G110R expressing cell lines and primary CLL cells, but not polyclonal healthy B cells in in vitro co-culture assays as determined in live cell killing assays and IFN- secretion. We did not observe differences in efficacy between the murine or humanized CAR backbones. In vivo experiments showed substantially reduced outgrowth of transplanted cell lines or primary CLL patient PBMCs in xenograft models accompanied by prolonged survival and even disease eradication in 17% of mice. Treatment of humanized mouse models with G110R-specific CAR T cells did not reduce B counts after 7-17 days post-injection of PBMCs from healthy individuals.

We designed and demonstrated activity as well as selectivity and safety of the – to our knowledge - first truly tumor-specific, biomarker-driven cellular targeting approach for a hematological malignancy.