Development of Novel Approaches to Optimize CAR T-cell Therapies for B-cell Malignancies

Division Of Basic Sciences - Nci

Investigators

Linked publications & trials

Abstract

CD19-targeted immunotherapy, including CAR T-cells and T-cell engaging bispecific antibodies, has transformed the treatment of relapsed or chemotherapy refractory B-cell malignancies. Despite high remission induction rates and the potential for durable remissions, growing experience, particularly in B-ALL suggests that 50% or more may relapse within the first year, with a substantial fraction emerging with CD19 loss as a mechanism of immune escape. For those with relapse retaining CD19 expression, second CD19 CAR T-cell infusions are frequently unsuccessful, further limiting options for salvage therapy in these highly refractory patients. Indeed, outcomes for patients with post CAR T-cell relapse is remarkably poor. Accordingly, the overarching goal of Project 1 is to implement novel strategies to extend durable remission following CAR T-cells in children and young adults with B-ALL, thereby improving overall survival. This goal is addressed through the following three specific aims, as delineated below. Specific Aim 1: Evaluate the ability of combinatorial targeted strategies to prevent antigen negative relapse. Background: With the hypothesis that dual-antigen targeting may overcome mechanisms of immune escape through antigen loss which occur following single antigen targeting, advancing combinatorial approaches represents one potential way to improve durable remissions following CAR T-cells. With over a decade of direct experience in leading efforts testing novel CAR T-cell based strategies in children and young adults with B-ALL in the POB, my team was perfectly situated to advance novel approaches in combinatorial targeting. Building upon on the prior experience with effective CD19 CAR T-cell targeting and CD22 CAR T-cell targeting, the latter for which I authored a successful application to the FDA for "Breakthrough Therapy Designation" in 2019, testing a combinatorial treatment approach targeting both CD19 and CD22 simultaneously was a natural next step. Accomplishments: Based on a construct developed by the Fry Lab (former POB) where dual antigen targeting was achieved based on two scFvs configured in tandem,I developed a clinical trial testing a novel bivalent CD19/CD22 CAR T-cell construct (CD19.22.BB CART) in children and young adults with B-ALL (NCT03448393). The trial began enrollment in 2018 and we published our initial experience in Blood in 2022 based on the experience of the first 20 children and young adults with B-ALL who were infused. We found that this construct was highly effective in inducing remissions, including in those patients who had received prior CAR T-cell therapy. Additionally, the toxicity profile was relatively well-tolerated with minimal rates of high-grade CRS or severe neurotoxicity. Persistence, however, was limited despite the incorporation of a 4-1BB costimulatory domain prompting both further investigation and the utilization of this construct as a bridge to HSCT. Additionally, through further laboratory-based experiments, we also found that CD22 targeting for this construct was suboptimal-limiting the ability to effectively dually-target CD19 and CD22 simultaneously. The trial has now complete enrollment with 30 patients at the recommended phase 2 dose. The overall experience led to a promising efficacy signal and use of this construct as a bridge to HSCT. Through efforts led by the Taylor Lab, we explored these clinical observations through a reverse-translation approach and were able to: 1) compare differences in promoters used in CAR T-cell constructs and 2) explore the features of the bivalent CD19.22.BB CART to several novel bicistronic CD19/CD22 CAR T-cell constructs that effectively expressed both CD19 and CD22 scFv independently on the cell surface. Based on these efforts, a construct utilizing an EF1-alpha promoter with the CD19.28/CD22.BB-built directly upon our prior experiences with the single antigen CAR T-cell targeted strategies that were previously explored in the POB, was chosen to move forward into the clinic based on both improved CD22 targeting and cytokine production. We have successfully translated this effort to the clinic and enrolled our first patient to our CD19/CD22 bicistronic CAR T-cell trial for children and young adults with B-ALL in January 2023 (NCT05442515). 10 patients have been treated since that time with the initial experience suggesting higher potency, improved CD22 targeting and enhanced persistence. The initial data was presented at the 2024 American Society of Hematology Meetings in December 2024 and a full manuscript is in active development, while we explore the biologic correlatives of this construct. Current Research: Early experiences on the CD19.28/CD22.BB have already shown clear differences between this construct and its bivalent predecessor, prompting dose de-escalation to 3e5 transduced CAR T-cells/kg based on severe ICANS seen in 2 of 4 patients treated at 1e6 transduced CAR T-cells/kg. This is in stark comparison to the maximum tolerated and effective dose used with our bivalent CAR T-cell construct which was at 3e6 transduced CAR T-cells/kg. Notably, however, all 10 of 10 patients treated to date have achieved a minimal residual disease (MRD) negative CR and 2 of 4 patients who did not pursue a consolidative HSCT post CAR T-cell infusion remain in an ongoing remission at approximately 2 years post CAR T-cells - certainly the long-term efficacy of this construct warrants further exploration. Enrollment is ongoing. Efforts in advancing CD22 single-antigen targeting remain in active development. Specific Aim 2: Test novel CAR T-cell constructs targeting non-CD19 antigens in B-ALL. Background: A high-risk subgroup of B-ALL, termed "Philadelphia-like, or Ph-like" has been associated with high rates of chemotherapy resistance and relapse. Approximately half of these childhood and adult Ph-like ALL cases harbor a rearrangement in cytokine receptor like factor-2 (CRLF2), which encodes one subunit of the thymic stromal lymphopoietin receptor (TSLPR) and heterodimerizes with the IL7Ra subunit. Given the high frequency of CRLF2-R in B-ALL across the age spectrum with detectable TSLPR overexpression by flow cytometry, an anti-CRLF2-TSLPR (TSLPR CART) CAR T-cell construct was created in the Fry Lab (former POB). Earlier this year, we received the "ok to proceed" from the FDA and are planning to open a first in human, phase 1 study evaluating TSLPR-CART cells in young adults with Ph-like ALL and provide a much-needed treatment option for this ethnically diverse patient subgroup. Regarding the trial design, dose-escalation will be conducted using a 3+3 design. Eligible participants for this trial will initially be young adult participants aged >18 years to <39 years of age with relapsed or refractory CRLF2-R (TSLPR expressing) B-ALL. Specific Aim 3: Develop a risk-stratified approach to improve long-term durable remission Background: While novel constructs to improve upon the current limitations of single antigen targeting are in development, optimizing the utilization of CAR T-cell constructs that are currently available and being used for children and adults in real-time is of the utmost importance. In this regard, I have embarked on a series of studies (both retrospective and prospective) that will help to establish standards of care in risk-stratification in the peri-CAR T-cell timeline to improve outcomes for patients receiving CD19 CAR T-cells. Key efforts have focused on understanding the impact of sequential antigen targeting, identification of risk factors associated with relapse, and development of a prospective study that will serve to establish a post-CAR T-cell biomarker-based monitoring approach to optimally risk-stratify patients post-infusion. The CAR-CURE trial is actively enrolling.