AML-320: PD-1 Inhibition Facilitates the Anti-AML Response of Co-Targeting BCL-2 and Methyltransferases through Modulation of the Immune Microenvironment

Background Acute myeloid leukemia (AML) is a hematopoietic malignancy with an increased incidence among older patients. The long-term survival of older AML patients treated with established therapies remains poor. The BCL-2 inhibitor venetoclax with hypomethylating agent (HMA) improved response rates (CR/CRi> 65%) in newly diagnosed older AML patients, with median response duration of 11.3 months. Increased expression of program death-1 (PD-1) on T-cells is associated with AML immune-suppression, which contributes to chemoresistance. Venetoclax preserves T-cells immunity by sparing central memory T-cells and enhances anti-PD-1 efficacy in immune-competent mouse models in vivo. These findings prompted us to test the hypothesis that reactivation of immune function by PD-1 inhibition facilitates responses to venetoclax and decitabine. Results We examined serial peripheral blood (PB) samples from patients (n= 6) before and after decitabine and venetoclax (Dec_Ven, NCT03404193 ). The combination of Dec_Ven effectively reduced CD33+/CD34+ cells and increased CD3+ T-cells. The reduction of CD33+/CD34+ cells positively correlated with the depletion of circulating blasts (R = 0.64, p = 0.0001). Dec_Ven rapidly (Days 1–3) activated T-cells by upregulating CD69 and PD-1 in both CD4 and CD8 cells but led to T-cells exhaustion with persistently upregulated PD-1 and loss of CD69 on Days 3–8. Mass cytometry CyTOF immune profiling demonstrated that Dec_Ven reduced naive T-cells (CD45RA+CCR7+) but spared or increased frequencies of the central (CD45RA-CCR7+) and effector memory (CD45RA-CCR7-) CD4 or CD8 cells. In parallel, serum cytokine levels of IL2, IL-6, and INFg were increased with Dec_Ven therapy. To test if targeting PD-1 can amplify the anti-leukemia effect, PB cells from newly diagnosed AML patient pre- and post Dec_Ven were treated with anti-CD3 and anti-PD-1 in vitro. Blockade of PD-1 reduced CD33+/CD34+ cells in baseline sample (67% vs. 34%) and synergistically eliminated the residual leukemia cells in sample obtained on Day 3 following Dec_Ven therapy (4.5% post-Dec_Ven alone vs. 1.9% with anti-CD3/PD-1). Conclusions Our data indicate that combination Dec_Ven induces T-cells exhaustion but selectively preserves effector T-cells immune subsets. The “triple” combination therapy of HMA, venetoclax, and PD-1 antagonist may increase durability of responses by enhancing T-cell function and is being tested in clinical trial NCT02397720 . Funding This work is supported by R01CA235622.