PD-1/PD-L1 Blocking Enhances CD33/CD3-Bispecific BiTE® Antibody (AMG 330) Mediated Lysis of Primary AML Cells

• Published in: Blood 2014-12, Vol.124 (21), p.3738-3738
• Main Authors: Krupka, Christina, Kufer, Peter, Kischel, Roman, Zugmaier, Gerhard, Köhnke, Thomas, Lichtenegger, Felix S, Schnorfeil, Frauke M, Altmann, Torben, Schneider, Stephanie, Fiegl, Michael, Spiekermann, Karsten, Sinclair, Angus M, Newhall, Kathryn J, Frankel, Stanley R, Baeuerle, Patrick, Hiddemann, Wolfgang, Riethmüller, Gert, Subklewe, Marion
• Format: Article
• Language: English
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood.V124.21.3738.3738

Antibody-based immunotherapy represents a promising strategy to target and eliminate chemoresistant leukemic cells in acute myeloid leukemia (AML). In our previous work, the potency of the CD33/CD3-bispecific BiTE® antibody AMG 330 to activate and redirect T-cells to AML cells was evaluated in a long-term culture system using unmanipulated peripheral blood (PB) or bone marrow (BM) samples from AML patients. We were able to show effective elimination of AML cells by AMG 330-activated and -expanded residual autologous T-cells (n=13, Krupka et. al, Blood 2014 123(3):356-65). The goal of the present study was to identify and manipulate factors that interfere with AMG 330-mediated lysis of primary AML cells. In our ex-vivo long-term culture system (n= 32 primary diagnosis, 3 relapse), we observed that successful elimination of primary AML cells was predominantly influenced by the initial effector:target (E:T) ratio. Reduced short-term lysis efficacy was observed for patient samples with low E:T ratios (median lysis: E:T ratio 1:10 99.3%) after 4 days of culture. However, after 12 days of culture this effect was less prominent as effector T-cell numbers increased and lysis was observed even in cultures with very low initial E:T ratios (up to an E:T ratio of 1:80). Considering the ubiquitous expression pattern of CD33 within the myeloid compartment, the number of AMG 330 treatment days will be limited due to expected hematotoxicity. Therefore, AMG 330 efficacy might benefit by increasing the E:T ratio within a short time period. Programmed cell death-1 (PD-1) and its primary ligand PD-L1 are immune checkpoints that limit T-cell responses and may contribute to slower lysis kinetics during AMG 330 treatment. Therefore, we assessed PD-1 expression on T-cells and PD-L1 expression on primary AML cells. No constitutive expression of PD-1/PD-L1 on T-cells and corresponding AML cells was found at primary diagnosis (PD-1: n=23; PD-L1: n=193). Upon the addition of AMG 330 to our primary ex-vivo AML cultures, we observed a strong upregulation of PD-1 on activated T-cells, which correlated with the extent of T-cell proliferation (10/10). This was most prominent within the subpopulation of CD4+/CD45RA-/CCR7- effector memory T-cells. Furthermore, in response to AMG 330-mediated T-cell activation, we observed an upregulation of PD-L1 on primary AML cells (16/19). Data obtained from AML cell lines confirmed an upregulation of PD-L1 after co-cultivation with T-cel