Extensions of the mTPI and TEQR designs to include non-monotone efficacy in addition to toxicity for optimal dose determination for early phase immunotherapy oncology trials

Clinical Strategies for Enhancing the Efficacy of CAR T-Cell Therapy for Hematological Malignancies

Chimeric antigen receptor (CAR) T cells have been successfully used for hematological malignancies, especially for relapsed/refractory B-cell acute lymphoblastic leukemia and non-Hodgkin’s lymphoma. Patients who have undergone conventional chemo-immunotherapy and have relapsed can achieve complete remission for several months with the infusion of CAR T-cells. However, side effects and short duration of response are still major barriers to further CAR T-cell therapy. To improve the efficacy, multiple targets, the discovery of new target antigens, and CAR T-cell optimization have been extensively studied. Nevertheless, the fact that the determination of the efficacy of CAR T-cell therapy is inseparable from the discussion of clinical application strategies has rarely been discussed. In this review, we will discuss some clinical application strategies, including lymphodepletion regimens, dosing strategies, combination treatment, and side effect management, which are closely related to augmenting and maximizing the efficacy of CAR T-cell therapy.

Chimeric antigen receptor T-cell therapies: Optimising the dose

Lymphocytes such as T-cells can be genetically transduced to express a synthetic chimeric antigen receptor (CAR) that re-directs their cytotoxic activity against a tumour-expressed antigen of choice. Autologous (patient-derived) CAR T-cells have been licensed to treat certain relapsed and refractory B-cell malignancies, and numerous CAR T-cell products are in clinical development. As living gene-modified cells, CAR T-cells exhibit unique pharmacokinetics, typically proliferating within the recipient during the first 14 days after administration before contracting in number, and sometimes exhibiting long-term persistence. The relationship between CAR T-cell dose and exposure is highly variable, and may be influenced by CAR design, patient immune function at the time of T-cell harvest, phenotype of the CAR T-cell product, disease burden, lymphodepleting chemotherapy and subsequent immunomodulatory therapies. Recommended CAR T-cell doses are typically established for a specific product and indication, although for some products, stratification of dose based on disease burden may mitigate toxicity while maintaining efficacy. Re-evaluation of CAR T-cell dosing may be necessary following changes to the lymphodepleting regimen, for different disease indications, and following significant manufacturing changes, if product comparability cannot be demonstrated. Dose escalation trials have typically employed 3 + 3 designs, although this approach has limitations, and alternative phase I trial designs may facilitate the identification of CAR T-cell doses that strike an optimal balance of safety, efficacy and manufacturing feasibility.

2D (2 Dimensional) TEQR design for Determining the optimal Dose for safety and efficacy

Designs, such as the Eff-Tox, OBD (optimal biological dose), STEIN (simple efficacy toxicity interval), and TEPI (toxicity efficacy probability interval) designs, have been proposed to determine the optimal dose of a new oncology drug using both efficacy and toxicity. The goal of these designs is to select the optimal drug dose for further phase trials more accurately than dose finding designs that only consider toxicity, such as the 3 + 3, TEQR (toxicity equivalence range), mTPI (modified toxicity probability interval), and EWOC (escalation with overdose control) designs. We propose a new frequentist design for optimal dose selection, the 2D TEQR design, that is easier to understand and simpler to implement than the TEPI, Eff-Tox, STEIN and OBD designs, as it is based on the empirical or observed toxicity and efficacy rates and does not require specialized computations. We compare the performance of this new design with those of the TEPI, STEIN, Eff-Tox and OBD Isotonic designs. Although for the same sample size and cohort size, the frequentist 2D TEQR design is less accurate than the Bayesian TEPI design and also the STEIN design in selecting the optimal dose, the accuracy of optimal dose selection of the 2D TEQR design can be increased, in many cases, with a moderate increase in cohort size. The 2D TEQR design is as accurate as or more accurate than the Eff-Tox design in optimal dose selection, and better than the OBD Isotonic design, unless there is a clear peak in the true response rates, in which case the OBD Isotonic design performs better than the other designs.