Purpose: UCART19 is an “off-the-shelf” genome-edited anti-CD19 CAR-T cell product, manufactured from unrelated healthy donor cells. Patients and Methods: UCART19 was administered to 25 adult patients with relapsed or refractory (R/R) B-cell acute lymphoblastic leukemia (B-ALL) in the CALM trial. All patients underwent lymphodepletion with fludarabine and cyclophosphamide ± alemtuzumab and received one of three ascending doses of UCART19. Given the allogeneic nature of UCART19, we analyzed the impact of lymphodepletion, HLA disparities and host immune system reconstitution on its kinetics, along with other factors known to affect autologous CAR-T cell clinical pharmacology. Results: Responder patients (12/25) had higher UCART19 expansion (Cmax) and exposure (AUCTlast) than non-responders (13/25), as measured by transgene levels in peripheral blood. The persistence of CAR+ T cells didn’t exceed 28 days in 10/25 patients and lasted beyond 42 days in 4/25. No significant correlation was found between UCART19 kinetics and administered cell dose, patient and product characteristics or HLA disparities. However, the number of prior lines of therapy and absence of alemtuzumab negatively impacted UCART19 expansion and persistence. Alemtuzumab exposure positively affected interleukin-7 and UCART19 kinetics, while negatively correlating with host T-lymphocyte AUC0-28. Conclusions: UCART19 expansion is a driver of response in adult R/R B-ALL patients. These results shed light on the factors associated with UCART19 kinetics, which remain highly affected by the impact of alemtuzumab on interleukin-7 and host-versus-graft rejection.

CAR-T cell therapies have shown tremendous results against various hematological cancers. Prior to cell infusion, a host preconditioning regimen is required to achieve lymphodepletion and improve CAR-T cell pharmacokinetic exposure, leading to greater chances of therapeutic success. To better understand and quantify the impact of the preconditioning regimen, we built a population-based mechanistic pharmacokinetic-pharmacodynamic model describing the complex interplay between lymphodepletion, host immune system, homeostatic cytokines, and pharmacokinetics of UCART19, an allogeneic product developed against CD19+ B cells. Data were collected from a phase I clinical trial in adult relapsed/refractory B-cell acute lymphoblastic leukemia and revealed three different UCART19 temporal patterns: 1) expansion and persistence, 2) transient expansion with subsequent rapid decline, and 3) absence of observed expansion. Based on translational assumptions, the final model was able to capture this variability through the incorporation of interleukin (IL)-7 kinetics, which are thought to be increased owing to lymphodepletion, and through an elimination of UCART19 by host T cells, which is specific to the allogeneic context. Simulations from the final model recapitulated UCART19 expansion rates in the clinical trial, confirmed the need for alemtuzumab to observe UCART19 expansion (along with fludarabine and cyclophosphamide), quantified the importance of allogeneic elimination, and suggested a high impact of multipotent memory T cell subpopulations on UCART19 expansion and persistence. In addition to supporting the role of host cytokines and lymphocytes in CAR-T cell therapy, such a model could help optimizing the preconditioning regimens in future clinical trials.