Session: 703. Adoptive Immunotherapy: Poster III
Hematology Disease Topics & Pathways:
Diseases, AML, Biological, Therapies, checkpoint inhibitors, Biological Processes, immunotherapy, Clinically relevant, Myeloid Malignancies, immune mechanism
Using a standard calcein AM in vitro cytotoxicity assay, we co-cultured AML targets, including U937 HLA-A2+ (U937-A2) AML cell line and primary patient AML, with CG1-CTL and PR1-CTL. AML cells were loaded with calcein AM and then incubated with CTL at increasing effector to target ratios. Pembrolizumab or isotype antibody was added to the cultures. After 4 hours, calcein AM was measured to determine cell viability. Our results demonstrated that U937-A2 cells and patient primary AML samples can be effectively lysed by CG1/PR1 CTL. In vitro lysis of AML by CTL was enhanced after the addition of pembrolizumab in comparison with the AML cells that were co-cultured only with CTL. Killing was dose-dependent and decreased at the lower effector:target ratios. We then tested whether anti-leukemia activity can be enhanced in vivo. For these experiments, NOD/SCID gamma (NSG) mice were engrafted with U937-A2 cells or patient AML intravenously (IV) via tail vein at a dose of 1 x 106 to 1 x 107 cells. After confirming engraftment (1-5% PB HLA-A2+/human (h) CD45+ cells), CG1-CTL and PR1-CTL (0.5 x 106) were administered to mice IV via tail vein and pembrolizumab or isotype antibody [100ug/mouse] was given intraperitoneally 4 times over 2 weeks. Mice were monitored for clinical graft versus host disease (GVHD) and AML 3 times/week. Mice were sacrificed at approximately 2 weeks following treatment and bone marrow (BM) was processed and analyzed for residual AML (Human[h] CD45+/mouse[m] CD45- cells) by flow cytometry. Our data demonstrate a decrease in U937-A2 (Figure) and primary AML after treatment with CG1/PR1-CTL. This decrease was enhanced when pembrolizumab was administered to the CTL-treated mice in comparison with mice treated with pembrolizumab only, CTL only, or CTL+ isotype. Furthermore, there was no increased toxicity or GVHD after the addition of pembrolizumab. Together these data highlight the potential for combination immune checkpoint blockade and antigen specific CTL to eradicate AML in vitro and in vivo.
Disclosures: Daver: Sunesis: Consultancy; Novartis: Research Funding; Kiromic: Research Funding; Daiichi-Sankyo: Consultancy, Research Funding; Incyte: Consultancy, Research Funding; Karyopharm: Consultancy, Research Funding; Alexion: Consultancy; Pfizer: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; BMS: Consultancy, Research Funding; Otsuka: Consultancy; Incyte: Consultancy, Research Funding; ImmunoGen: Consultancy, Research Funding; ARIAD: Research Funding; Pfizer: Research Funding.