Preclinical evaluation of anti-ROR1 CAR T cells employing a ROR1 binding SCFV derived from the clinical stage mab cirmtuzumab.

Abstract

41 Background: Chimeric antigen receptor (CAR)-modified T cells (CAR-T) were generated targeting cells expressing ROR1, which is present on many malignant cancers and has been associated with cancer stemness and chemo-resistance. The ROR1 CAR utilizes the humanized single-chain fragment variable (scFv) binding domain of UC-961 (cirmtuzumab), which exhibits high affinity and specificity for human ROR1 and has demonstrated an excellent safety profile in Phase 1 studies. Methods: CAR constructs with varying spacer regions and intracellular co-stimulatory domains, using the scFV of cirmtuzumab, were constructed and used to generate CAR-T cells from healthy donors. These ROR1 CAR-T cells were tested for cytotoxicity against lymphoid cancer cells in vitro and in vivo studies that employed immune-deficient mice engrafted with labeled human leukemia cells MEC1 or MEC1-ROR1, which had been transfected to stably express ROR1. Results: The 2nd generation and 3rd generation CAR-T-cells with analogous spacer regions were comparably potent and selectively cytotoxic for cells bearing the ROR1 target antigen. But the 2nd generation CARs demonstrated greater potency in vitro even at low effector to target ratios. For the in vivo studies, mice received a single injection of ROR1 CAR-T cells or activated T cells from the same donor as a control. The ROR1 CAR-T cells rapidly cleared the leukemic cells from the animals, whereas animals receiving control T cells or no therapy quickly succumbed to progressive disease within 3 weeks. The administered CAR-T products remained highly active following administration and could be detected for ≥ 3 months without evidence for T cell exhaustion. Conclusions: The generated CAR-T cells utilizing constructs with the Fv of cirmtuzumab, a humanized mAb highly specific for ROR1, onco-embryonic surface antigen, effectively and selectively killed neoplastic cells bearing ROR1 both in vitro and in vivo. As ROR1 expression and signaling has been associated with cancer stemness and chemo-resistance utilizing ROR1 CAR-T therapy to target cancer cells might mitigate tumor escape. These data strongly support the rationale for continued development of our ROR1 CAR-T.

Advancing CAR T-cell therapy for chronic lymphocytic leukemia: exploring resistance mechanisms and the innovative strategies to overcome them

“…Hudecek et al reported the first ROR1-targeted CAR-T cell with cytotoxicity in CLL and MCL cells [ 96 ] . More recently, Prussak et al reported on a ROR1-specific CAR T-cell that effectively and selectively killed ROR1-containing lymphoid cancer cells in mice [ 98 ] .…”

“…While ROR1 is highly expressed in undifferentiated embryonic stem cells, it is not found in other adult tissue types except for a low expression in adipose tissue [96] . Additionally, higher levels of ROR1 on CLL cells are associated with more aggressive disease, and its expression remains stable across progression and treatment [97] . Therefore, it presents an attractive prospect for achieving highly targeted effects, thereby mitigating adverse events and reducing immunosuppression.…”

Recent Advances in CAR T-Cell Therapy for Patients with Chronic Lymphocytic Leukemia

“…Thus, it is an attractive target for CAR T cell therapy, as it has the potential to improve specificity, efficacy, and reduce side effects of such a B-cell depletion and hypogammaglobulinemia related to treatment. In preclinical models of CLL, ROR1 CAR T-cells demonstrated selective toxicity for ROR1 expressing leukemia cells, with rapid clearance of leukemia cells in vivo [ 58 ]. A phase 1 clinical trial (NCT02706392) of ROR1 CAR T-cells for patients with both hematologic and solid tumors is currently underway.…”