Low-Dose Rapamycin-Regulated SC-DARIC33: Advancing CD33-Targeted CAR T Cell Therapy for Acute Myeloid Leukemia

The research focuses on a CD33-targeted immunotherapy for acute myeloid leukemia (AML) using CAR T cells. The therapy involves a DARIC33 complex that activates T cells in response to the tumor antigen when exposed to rapamycin (RAPA). The study utilized human AML xenograft NSG mouse models and GMP-compliant methods for T cell production. It was found that low concentrations of RAPA are necessary for DARIC33's in vivo activity and its anti-AML effects.

The CAR T cells were produced at a clinical scale, using a method that involves stimulation, transduction, and expansion in a serum-free medium with specific cytokines. The cells' activation and anti-AML capabilities were tested in vitro by monitoring cytokine production and target cell lysis in the presence or absence of RAPA. Mice were treated with DARIC33 and RAP A, and RAPA levels in their blood were measured.

Results showed that DARIC33 and control CAR T cells had similar characteristics for engraftment and anti-tumor effects. The presence of RAPA was required for DARIC33 to produce cytokines effectively. The optimal RAPA concentration to activate DARIC33 was determined through blood sample incubations, indicating an EC50 of 2.6nM.

In vivo studies demonstrated DARIC33's ability to control tumor growth in mice, with a comparison made to pediatric RAPA pharmacokinetic models. The study suggested that oral daily dosing of RAPA at 0.5 mg/m^2 would achieve effective whole blood concentrations in most patients.

The study concludes that low doses of RAPA are adequate for regulating DARIC33. A phase 1 clinical trial is planned to evaluate the safety of DARIC33 in pediatric AML patients, involving escalating cell doses and low-dose RAPA administration. Monitoring of peripheral blood samples will assess myeloid cell recovery post-RAPA dosing, aiming to confirm the safety and feasibility of modulating DARIC33 CAR T cells with intermittent low-dose RAPA.