A2B530 Harnesses Unique Mechanism of Action to Integrate CAR T in Solid Tumors

Diane M. Simeone, MD

Looking to replicate the impressive findings with chimeric antigen receptor (CAR) T-cell therapies observed in patients with hematologic malignancies, investigators have initiated the BASECAMP-1 trial (NCT04981119) with the hope of identifying patients with advanced solid tumors who will be suitable candidates for treatment in the phase 1/2 EVEREST trial (NCT05736731) evaluating the agent A2B530.^1,2

There are currently no FDA-approved CAR T-cell agents for the treatment of solid tumor malignancies. Multiple other phase 1 clinical trials are in progress evaluating the safety and efficacy of CAR T-cell agents, both as monotherapies and part of combination regimens, in solid tumor malignancies such as glioblastoma as well as gastrointestinal, renal, prostate, ovarian, and thoracic cancers.²

One obstacle to the development of CAR T-cell agents for patients with solid tumors, outside of the complexity of the tumor microenvironment, is the lack of specificity of the agents to affect the target antigen. Fatal adverse effects (AEs) have been reported due to CAR T-cell agents damaging healthy tissues that also expressed the target antigen. Additionally, the heterogeneity of tumor antigens in solid tumors compared with that of hematologic malignancies, leads to inconsistent and incomplete malignant cell death.²

For example, carcinoembryonic antigen (CEA) has been identified as a therapeutic target of interest for the application of CAR T-cell agents in patients with solid tumors because it is expressed in most pancreatic and lung cancers, among other cancer types. However, it is also expressed in regular epithelial cells of the gut, often leading to on-target, off-tumor toxicity with several other CEA-directed therapies.³

“There have been unique challenges in [applying CAR T-cell therapies to] solid tumors, [including] understanding of the tumor microenvironment,” Diane M. Simeone, MD, the director of the Pancreatic Cancer Center and the associate director of translational research at the Perlmutter Cancer Center in New York, New York, said in an interview with OncologyLive. “However, with increasing analysis of human tumors, in particular with the burgeoning field of single-cell sequencing, we’re getting a much more detailed look into the tumor microenvironment of solid tumors. That is going to help us drive new technologies in immunotherapy. With CAR T, there are advances in the technologic aspects of T-cell preparation, the targeting strategies, and the strategies to mitigate off-target effects. The combination of these things coming together are hopefully poising us to move CAR T-cell therapy into effectiveness for solid tumors.”

To address these hurdles in solid tumors, A2B530 was designed using the novel, logic-gated T-cell therapy platform Tmod. Tmod agents contain an activating receptor, either a CAR or a T-cell receptor, thatrecognizes an antigen on the surface of tumor cells, specifically CEA in the case of A2B530, and an inhibitory receptor, or blocker, based on the LIR-1 protein designed to enhance the tumor specificity of the agent. The blocker portion of A2B530 leverages loss of heterozygosity of the antigen HLA-A*02, one of the most common alleles seen in tumor cells in a US population, to prevent the CAR from affecting healthy tissues.^3,5

Previous findings have suggested that the LIR-1 “blocker” may be tuned to recognize molecules that share properties of the HLA-I family. Additionally, the blocking mechanism is self-activated and specifically mitigates cross-reactivity when active. This blocker effect results in high specificity for Tmod agents in terms of killing tumor cells compared with normal cells. Tmod cell activation has also been shown to be reversible.⁵

“This novel Tmod platform leverages loss of genes in tumors to protect normal cells while killing tumor cells,” Kedar Kirtane, MD, the physician director for engagement of special populations for clinical trials and an assistant member in the Department of Head and Neck-Endocrine Oncology at Moffitt Cancer Center in Tampa, Florida, said in an interview with OncologyLive. “This CAR T has an activator and a blocker; the activator binds antigens that are uniquely expressed on tumor and then the blocker binds antigens only expressed on normal cells. If one of these Tmod T cells encounters a normal cell, the blocker will block and the activator won’t activate. But if it encounters a cancer cell, the blocker won’t be engaged in the activator can destroy that tumor cell. So it surveys both normal and abnormal cells and it can differentiate between the 2, which is really the unique characteristic that will hopefully improve safety and efficacy of the cell therapies.”

A2B530 is therefore classified as a Tmod CAR T-cell therapy that targets tumors that express CEA and are also without HLA-A*02.⁵

Preclinical findings evaluating the efficacy A2B530 in targeting colorectal, pancreatic, and lung cancer cells were presented at the Society for Immunotherapy of Cancer’s 37th Annual Meeting in Boston, Massachusetts, in November 2022. T cells from HLA-A*02–positive donors were transducedwith a single lentivirus to express the CAR, the blocker, and an shRNA-targeting β2M. NOD scid gamma mice subcutaneously implanted with normal (CEA-positive, HLA-A*02-postive) and tumor (CEA-positive, HLA-A*02-negative) cells were used to examine the in vivo activity of A2B530. The mice were subsequently treated with A2B530 or control T cells intravenously.³

Data from the preclinical study showed that the control CEA CAR T cells killed CEA-positive target cell lines regardless of HLA-A*02 expression and the CEA Tmod cells selectively killed tumor cells. Notably, in mixed cell cultures, CEA Tmod cells killed only the HLA-A*02-negative target cells and the control CAR killed both the HLA-A*02-negative and HLA-A*02-postive cell lines. The Tmod cells also displayed bidirectional control between the activated and blocked states.³

EVEREST-1 Set to Examine A2B530 in Solid Tumors

To be eligible for the EVEREST-1 trial, patients must first be appropriately enrolled in the BASECAMP-1 study (NCT04981119). BASECAMP-1 is a non-interventional, observational study that is designed to compile information on how a solid tumor might lose HLA via next-generation sequencing. Patients enrolled in the trial will undergo apheresis and have their T cells stored for future use to produce A2B530 as part of EVEREST-1.⁵

When disease progression occurs, eligible patients in BASECAMP-1 will be screened for EVEREST-1 and the patient’s T cells will be used to manufacture A2B530. There is no time requirement between the studies, allowing patients to go directly from BASECAMP-1 to EVEREST-1 based on their own disease course.^1,2

“It’s a very unique design for a cell therapy trial,” Kirtane said. “We’re getting a lot of the prescreening out of the way and figuring out who could potentially benefit from the therapy very early on.”

EVEREST-1 is aiming to enroll approximately 160 adult patients with recurrent unresectable, locally advanced, or metastatic solid tumors that express CEA and do not express HLA-A*02. Tumor types that will make up the trial include pancreatic, colorectal, and NSCLC.²

Patients must have a life expectancy of at least 3 months, have an ECOG performance status of 1 or less, have received previous therapy for their solid tumor, and have adequate organ function to be eligible for the study. Those who have undergone priorallogeneic stem cell or solid organ transplant, a cancer therapy within 3 weeks or 3 half-lives of A2B530 infusion, or radiotherapy within 28 days of A2B530 infusion will not be included.²

The coprimary end points of the phase 1 portion of the study are the rate of adverse events and dose-limiting toxicities as well as determining the recommended phase 2 dose. In phase 2, the primary end point is overall response rate. Secondary end points include persistence of A2B530 and cytokine analysis. The trial is not yet recruiting patients and is estimated to be completed in December 2028.²

“With this trial and some others that are coming on board, we’re in a unique position to really evaluate for the first time pretty compelling approaches in testing CAR T-cell therapy in solid tumors,” Simeone said. “I’m very excited for the opportunity to offer this therapy for our patients. I am looking forward to seeing how this approach can be best deployed and to broaden the portfolio of patients that will be eligible for this treatment by increasing the activator portfolio along with the HLA subtypes that are eligible for the trial.”

References

1. A study to evaluate the safety and efficacy of A2B530, a Logic-gated CAR T, in subjects with solid tumors that express CEA and have lost HLA-A*02 expression (EVEREST-1). ClinicalTrials.gov. Updated February 21, 2023. Accessed April 4, 2023. https://www.clinicaltrials.gov/ct2/show/NCT05736731
2. Patel U, Abernathy J, Savani BN, Oluwole O, Sengsayadeth S, Dholaria B. CAR T cell therapy in solid tumors: a review of current clinical trials. EJHaem. 2021;3(suppl 1):24-31. doi:10.1002/jha2.356
3. Hecht RJ, Sandberg M, Wang X, et al. A2B530, an autologous CEA-directed Tmod T-cell therapy with an inhibitory receptor gated by HLA-A*02 to target colorectal, pancreatic, and lung cancer.
   J Immunother Cancer. 2022;10:229 doi:10.1136/jitc-2022-SITC2022.0229
4. DiAndreth B, Hamburger AE, Xu H, Kamb A. The Tmod cellular logic gate as a solution for tumor-selective immunotherapy. Clin Immunol. 2022;241:109030. doi:10.1016/j.clim.2022.109030
5. Pipeline. A2 Biotherapeutics. Accessed April 4, 2023. bit.ly/3KvPMoD
6. Solid tumor analysis for HLA loss of heterozygosity (LOH) and apheresis for CAR T- cell manufacturing (BASECAMP-1). ClinicalTrials.gov. Updated March 22, 2023. Accessed April 4, 2023. https://clinicaltrials.gov/ct2/show/NCT04981119