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4289 ADGRG1/GPR56 As a Marker of CD8+ Tumor-Reactive T Cells in Acute Myeloid Leukemia

Program: Oral and Poster Abstracts
Session: 618. Acute Myeloid Leukemias: Biomarkers and Molecular Markers in Diagnosis and Prognosis: Poster III
Hematology Disease Topics & Pathways:
Research, Fundamental Science, Acute Myeloid Malignancies, AML, Bioinformatics, Diseases, Myeloid Malignancies, Profiling
Monday, December 9, 2024, 6:00 PM-8:00 PM

Yihan Mei1*, Yu Liu1*, Wenbing Liu1*, Manling Chen1*, Qing Rao1*, Min Wang1*, Shaowei Qiu, MD1*, Runxia Gu, MD1* and Jianxiang Wang, MD2

1State Key Laboratory of Experimental Hematology, National Clinical Research Center for Blood Diseases, Institute of Hematology & Blood Diseases Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Tianjin, China
2State Key Laboratory of Experimental Hematology, National Clinical Research Center for Blood Diseases, Institute of Hematology and Blood Diseases Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Tianjin, China

Key words: AML; tumor-reactive T cell; ADGRG1

Objective: Given the promising clinical efficacy of T cell-based immunotherapy in solid tumors, there is a growing interest in harnessing T cells for treating acute myeloid leukemia (AML). However, the characteristics of tumor-reactive T cells and their unique molecular markers remain unclear. In this study, we aim to explore the specific marker of AML tumor-reactive T cells.

Methods: Bone marrow (BM) T cells from newly diagnosed AML patients were collected for scRNA-seq and scTCR-seq. These data were integrated with publicly available healthy donors' single-cell data. Using the STARTRAC-like algorithm, tumor-reactive T cells were identified based on the tumor enrichment index, clonal expansion index, proliferation index, and activation of TCR signaling pathways. Further validation was conducted on experimental approaches like CD33 CAR-T and target cell co-culture models and IFN-γ release assays. RNA-seq data from 42 AML patients were used for further validation by deconvolution.

Results:

By integrating single-cell data from healthy donors and AML patients, T cells were clustered with specific markers and we focused on CD8+ T cells for further analysis. Using the STARTRAC-like algorithm, these subgroups were categorized into tumor-reactive T cells and bystander T cells. Unlike solid tumors, tumor-reactive T cells in AML were predominantly terminally differentiated effector T cells and did not show significant upregulation of exhaustion markers like PD-1. Instead, they exhibited a senescent-like cytotoxic profile (CD27-CD28-KLRG1+) with upregulation of NK cell-associated molecules. Notably, ADGRG1 was significantly elevated and almost specifically expressed in tumor-reactive T cells compared to bystander T cells. In a conditional knock-in leukemia mouse model, high expression of ADGRG1 was also observed in CD8+ tumor-reactive T cells at the single-cell level. This suggested that ADGRG1 may serve as a unique AML CD8+ tumor-reactive T cell marker.

To further validate this hypothesis, anti-CD33 CAR-T and Molm13 were applied as an artificial effector-target cell model. When stimulated by CD3/CD28 Dynabeads or cocultured with K562 (CD33-), neither CAR-T nor vector T cells showed significant ADGRG1 expression. However, cocultured with Molm13 (CD33+), the ADGRG1 was significantly upregulated on anti-CD33 CAR-T cells (p = 0.016), suggesting the TCR-antigen interaction induces the evident ADGRG1 upregulation. Then ADGRG1+/-CD8+ T cells were isolated from the BM samples of newly diagnosed AML patients from various subtypes and co-cultured with the matched patient's BM CD34+ leukemia blast cell. It was observed that ADGRG1+CD8+ T cells secreted significantly higher levels of IFN-γ upon co-culture 48h with blasts, demonstrating the tumor reactivity of ADGRG1+CD8+ T cells. The characteristic of ADGRG1 as a marker for tumor-reactive T cells might be a common feature of tumor-reactive T cells in AML.

We also conducted a preliminary exploration into the clinical significance of the ADGRG1+CD8+ T cell subset. By deconvolution based on the single-cell landscape of AML patients, relapsed/refractory patients had lower levels of ADGRG1+CD8+ T cells in their BM (p = 0.004), suggesting that a lower proportion of these cells at the initial diagnosis might indicate a poor prognosis.

Conclusions: By drawing on experiences from solid tumor research, we identified tumor-reactive T cells with unique phenotypes in AML and detected ADGRG1 as their marker. Our findings provide a simpler, more feasible approach for future tumor-reactive TCR screening.

Disclosures: Wang: AbbVie: Membership on an entity's Board of Directors or advisory committees.

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