Model-Based Translational Rapamycin Dose Selection to Promote Engraftment and Expansion of the Engineered Regulatory T cell (EngTreg) product GNTI-122 in Human
Benjamin Guiastrennec (1)*, Darius Schweinoch (1)*, Marko Repic (2), Gene I Uenishi (2), Priya Saikumar-Lakshmi (2), Karen Mueller (2). *Authors contributed equally to this work.
(1) IntiQuan GmbH, Basel, Switzerland; (2) GentiBio Inc., Cambridge MA, USA.
Objectives: Functional and/or absolute interleukin-2 (IL-2) scarcity is implicated in many autoimmune diseases and significantly impairs regulatory T cells (Tregs) persistence and potency. IL-2 signaling defects of Tregs are hallmarks of Type 1 diabetes mellitus (T1D), a chronic autoimmune disease [1]. This leads to impaired immune tolerance and destruction of pancreatic insulin-producing beta cells by T effectors [2]. T1D progresses toward insulin deficiency and uncontrolled symptomatic hyperglycemia. Tregs have potential to preserve long-term immune tolerance in recently diagnosed T1D patients. Autologous Tregs are considered safe with variable efficacy in clinical T1D trials [3]. GNTI-122, an engineered Treg product, expresses T cell receptor (TCR) targeting pancreatic islet antigens (pharmacologic activity) and a chemically induced signaling complex (CISC) that selectively activates the IL-2 pathway after rapamycin dosing to stimulate engraftment. Herein, in vitro and in vivo data were utilized to select a rapamycin dose to support GNTI-122 engraftment and persistence in children (≥3 to <13 years of age), adolescents (≥13 to <18 years of age), and adults (≥18 years of age) for future clinical trials.
Methods: This model-based translational analysis was conducted in 5 sequential steps. First, relationships between rapamycin concentrations, TCR stimulation, and GNTI-122 expansion and viability were characterized by a NLME model developed on in vitro cell count and viability data collected over 10 days. Second, in vitro CISC receptor activation caused by rapamycin stimulation was evaluated via exposure-response (ER) models. Both the fraction of cells with active signal transducer and activator of transcription 5 (STAT5) signaling (downstream target of CISC) and the magnitude of phosphorylated STAT5 activation (via mean fluorescence intensity, MFI) in cell culture were characterized. Third, the relation between observed in vivo engraftment in mice blood and predicted rapamycin trough concentration (Ctrough) was characterized on Day 19 post GNTI-122 injection in an ER analysis. Fourth, published rapamycin pharmacokinetic (PK) profiles in human were digitized and augmented into a database, which in turn was used to select and qualify published PK rapamycin models in human. Fifth, a target rapamycin Ctrough was defined based in vitro and in vivo responses predicted by the models. The selected PK rapamycin models were then used to define typical dosing required in human to achieve the target Ctrough.
Results: The in vitro cell count and viability model featured 2 GNTI-122 cell subpopulations (viable and non-viable cells). Viable cells can expand in a rapamycin-dependent manner in presence of TCR stimulation after an initial delay of 2.0 days up to 8.8 days post-GNTI-122 injection. Rapamycin was further predicted to reduce the rate of GNTI-122 cells that transition to a non-viable state independently of TCR stimulation. The in vitro fraction of cells with active STAT5 signaling and the phosphorylated STAT5 MFI, were both described by sigmoidal Emax models with a baseline for which the rapamycin concentration to achieve half-maximum effect were 0.80 ng/mL and 1.25 ng/mL, respectively. In vivo, GNTI-122 engraftment on Day 19 in blood was modeled with a sigmoidal Emax for which the half-maximum effect parameter was estimated for rapamycin Ctrough at 5.5 ng/mL. Two published rapamycin PK models were qualified and selected for adult [4] and children and adolescents [5]. A target rapamycin Ctrough range of 3-4 ng/mL was selected, at this level the fractions of the maximal effects predicted in vitro were 60% for Day 10 cell count, 71% for Day 10 viability, 85% for the fraction of cells with active STAT5 signaling, and 79% for the phosphorylated STAT5 MFI. Based on simulations, a 14 day regimen of 2 mg daily in adolescents and adults and 1.5 mg/m2 body surface area daily in children could achieved this target.
Conclusions: GNTI-122 enables delivery of an IL-2 like signal to Tregs through CISC. Using a novel modeling approach, we have characterized this mechanism and identified a safe and effective dose of rapamycin to support the engraftment and persistence of GNTI-122 cells in patients with recently diagnosed T1D. Beyond T1D, this approach overcomes a key technical hurdle for leveraging Tregs as therapeutics. Last, this analysis also serves as a use case for model informed drug development (MIDD) in new cell therapies.
References:
[1] Tang Q, Bluestone JA. The Foxp3+ regulatory T cell: a jack of all trades, master of regulation. NatImmunol. 9(3):239-44. 2008.
[2] Norris JM, Johnson RK, Stene LC. Type 1 diabetes-early life origins and changing epidemiology. Lancet Diabetes Endocrinol., 8(3):226-238. 2020.
[3] Bluestone JA, Buckner JH, Fitch M, Gitelman SE, Gupta S, Hellerstein MK, et al. Type 1 diabetes immunotherapy using polyclonal regulatory T cells. Sci. Transl. Med., 7(315):315ra189. 2015.
[4] Dansirikul C, Morris RG, Tett SE, Duffull SB. A Bayesian approach for population pharmacokinetic modelling of sirolimus. Br J Clin Pharmacol, 62(4):420–434. 2006.
[5] Sabo AN, Jannier S, Becker G, Lessinger JM, Entz-Werlé N, Kemmel V. Sirolimus Pharmacokinetics Variability Points to the Relevance of Therapeutic Drug Monitoring in Pediatric Oncology. Pharmaceutics 13:470. 2021.