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3416 CD64 CAR-T Therapy Targets Venetoclax-Resistant Monocytic Acute Myeloid Leukemia

Program: Oral and Poster Abstracts
Session: 702. CAR-T Cell Therapies: Basic and Translational: Poster II
Hematology Disease Topics & Pathways:
Research, Acute Myeloid Malignancies, AML, Translational Research, Drug development, Diseases, Treatment Considerations, Myeloid Malignancies, Biological Processes, Technology and Procedures, Study Population, Animal model
Sunday, December 8, 2024, 6:00 PM-8:00 PM

Haley M. Simpson, MD, PhD1, Amanda Novak, BS2*, Catherine Danis, PhD3, Michael Yarnell, BSc4*, Phoebe Duong5*, Brett M Stevens, PhD, BS6*, Craig T Jordan, PhD6 and M. Eric Kohler, MD, Ph.D7

1Division of Hematology, University of Colorado, Aurora, CO
2Department of Pediatrics, University of Colorado Anschutz Medical Campus, Aurora, CO
3University of Colorado, Anschutz Medical Campus, Aurora, CO
4University of Colorado Anschutz Medical Campus, Aurora, CO
5University of Colorado, Aurora
6Division of Hematology, University of Colorado Anschutz Medical Campus, Aurora, CO
7Division of Hematology/Oncology/Bone Marrow Transplant and Center for Cancer and Blood Disorders, Ch, Aurora, CO

Introduction:

Acute Myeloid Leukemia (AML) continues to have a poor prognosis despite therapeutic advances. Venetoclax-based therapy induces remissions in approximately 70% of patients, but duration of response is limited and relapses are common. We have previously shown a higher propensity for venetoclax resistance in AML with a monocytic (FAB M5) phenotype and correspondingly inferior overall survival after venetoclax/azacitidine (Ven/Aza) treatment relative to patients with non-M5 AML (Pei, et. al. Cancer Discovery, 2020). We further demonstrated that while leukemia stem cells (LSCs) with an undifferentiated phenotype are sensitive to Ven/Aza, a unique monocytic LSC (m-LSC) population, which uniformly expresses CD64, can drive monocytic AML relapses in patients treated with Ven/Aza (Pei, et. al., Cancer Discovery, 2023). As venetoclax is integral in many AML treatment regimens, we developed a novel CD64-directed chimeric antigen receptor (CAR) to target the Ven/Aza-resistant m-LSC population. We have previously shown CD64 CAR T cells are effective against CD64+ AML cell lines in vitro and in vivo. To further optimize this CAR T cell product for clinical translation, we have evaluated the efficacy of AML patient-derived CD64 CAR T cells, characterized their in vivo persistence, tested their synergy with venetoclax against patient-derived AML with mixed undifferentiated and monocytic populations, and validated a new humanized scFv. Collectively, these pre-clinical data support the development of our CD64 CAR T cells for a planned phase I/II clinical trial for patients with post-Ven/Aza relapsed AML.

Methods:

Second-generation CD64 CAR constructs incorporating different scFv’s and costimulatory molecules were transduced into T cells from healthy donors or AML patients. Phenotype, in vitro function, in vivo efficacy and persistence were evaluated for CD64 CAR T cells both alone and in combination with Ven/Aza.

Results:

We previously demonstrated that CD64 CAR T cells effectively clear monocytic AML cell lines in xenograft models, however the optimal design to maintain efficacy and enhance persistence is unknown. We found the 4-1BB costimulatory domain drove a final CAR T cell product that was predominantly CD4 cells with either a T stem cell memory (TSCM) or T central memory (TCM) phenotype. In contrast, the CD28 costimulatory domain generated a CD64 CAR T cell product that was balanced between CD4 and CD8 cells, which surprisingly were heavily skewed towards a TSCM phenotype. Despite these differences, we found ~10-fold greater persistence of CD64BBz CAR T cells, relative to CD6428z, in vivo after leukemia clearance (p<0.05). Persisting CAR T cells predominantly displayed a T effector memory phenotype and showed limited expression of the inhibitory receptors PD1 and TIM3. In patients the immunogenicity of the CAR molecule can impact persistence, so we next tested a novel humanized CD64 scFv. Using low doses, humanized CD64BBz(hu) CAR T cells were able to completely clear established THP1 leukemia, whereas CD64BBz CAR T cells with the murine scFv (CD64BBz(mu)) only cleared 66.7% of mice and CD64-28z(mu) was only effective in 11.1% of engrafted mice.

Given the intention to use CD64 CAR T cells for patients relapsed after Ven/Aza, we tested the ability to generate CAR T cells from AML patient-derived T cells. We successfully manufactured patient-derived CD64 CAR T cells, which were functional against AML cell lines and could eliminate autologous CD64+ AML. Furthermore, we found differential susceptibility to Ven/Aza and our CAR T cells in patient-derived AML samples consisting of a mixture of primitive/undifferentiated and monocytic populations. Treatment with Ven/Aza specifically reduced the CD34+/CD64- (primitive) AML subpopulation, whereas our CAR T cells eliminated the monocytic CD64+ subpopulation.

Conclusions:

Through these pre-clinical studies, we have identified the optimal scFv and costimulatory domain of our CD64-directed CAR to maximize efficacy and persistence as well as defined the ability of our CD64 CAR T cells to target Ven/Aza resistant, monocytic AML. These data suggest that CD64 CAR T cells can target venetoclax-resistant m-LSCs and support the development of a phase I/II clinical trial to test the safety of this potential salvage regimen for patients who relapse after Ven/Aza therapy.

Disclosures: No relevant conflicts of interest to declare.

*signifies non-member of ASH