Development of Novel ImmunoPET Tracers to Image Human PD-1 Checkpoint Expression on Tumor-Infiltrating Lymphocytes in a Humanized Mouse Model

• Published in: Molecular imaging and biology Vol. 19; no. 6; pp. 903 - 914
• Main Authors: Natarajan, Arutselvan, Mayer, Aaron T., Reeves, Robert E., Nagamine, Claude M., Gambhir, Sanjiv Sam
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.12.2017; Springer Nature B.V
• Subjects: Animal tissues; Animals; Antibodies, Monoclonal, Humanized - chemistry; Apoptosis; B7-H1 Antigen - metabolism; Cancer; Cell Line, Tumor; Chromatography, High Pressure Liquid; Computed tomography; Cytotoxicity; Disease Models, Animal; Exhaustion; Homing; Humans; Imaging; Immune checkpoint; Immune response; Immunoglobulin G; Immunotherapy; Interleukin 2 receptors; Leukocytes (mononuclear); Lymphocytes; Lymphocytes T; Lymphocytes, Tumor-Infiltrating - metabolism; Lymphocytes, Tumor-Infiltrating - pathology; Lymphoid tissue; Medical imaging; Medicine; Medicine & Public Health; Melanoma; Mice; Monoclonal antibodies; Organs; PD-1 protein; PD-L1 protein; Peripheral blood mononuclear cells; Positron emission; Positron emission tomography; Positron Emission Tomography Computed Tomography; Radiology; Radiopharmaceuticals; Research Article; Skin; Skin cancer; Spleen; Targeted cancer therapy; Tissue Distribution; Tomography; Tracers; Tumor-infiltrating lymphocytes; Tumors; Zirconium; 64-Cu; ImmunoPET; 89-Zr; Tumor-infiltrating lymphocytes; Keytruda; PD-1
• ISSN: 1536-1632; 1860-2002; 1860-2002
• DOI: 10.1007/s11307-017-1060-3

Purpose It is well known that cancers exploit immune checkpoints (programmed death 1 receptor (PD-1) and its ligand (PD-L1)) to evade anti-tumor immune responses. Although immune checkpoint (IC) blockade is a promising approach, not all patients respond. Hence, imaging of tumor-infiltrating lymphocytes (TILs) is of high specific interest, as they are known to express PD-1 during activation and subsequent exhaustion in the tumor microenvironment and are thought to be potentially predictive of therapeutic responses to IC blockade. Procedures We developed immune-tracers for positron emission tomography (PET) to image hPD-1 status of human peripheral blood mononuclear cells (hPBMCs) adoptively transferred to NOD- scid IL-2Rγ null (NSG) mice (hNSG) bearing A375 human skin melanoma tumors. The anti-PD-1 human antibody (IgG; keytruda) was labeled with either Zr-89 or Cu-64 radiometals to image PD-1-expressing human TILs in vivo . Results [ 89 Zr] Keytruda (groups = 2; NSG-ctl (control) and hNSG-nblk (non-blocking), n  = 3–5, 3.2 ± 0.4 MBq/15–16 μg/200 μl) and [ 64 Cu] Keytruda (groups = 3; NSG-ctl, NSG-blk (blocking), and hNSG-nblk; n  = 4, 7.4 ± 0.4 MBq /20-25 μg/200 μl) were administered in mice. PET-CT scans were performed over 1–144 h ([ 89 Zr] Keytruda) and 1–48 h ([ 64 Cu] Keytruda) on mice. hNSG mice exhibited a high tracer uptake in the spleen, lymphoid organs and tumors. At 24 h, human TILs homing into melanoma of hNSG-nblk mice exhibited high signal (mean %ID/g ± SD) of 3.8 ± 0.4 ([ 89 Zr] Keytruda), and 6.4 ± 0.7 ([ 64 Cu] Keytruda), which was 1.5- and 3-fold higher uptake compared to NSG-ctl mice ( p  = 0.01), respectively. Biodistribution measurements of hNSG-nblk mice performed at 144 h ([ 89 Zr] Keytruda) and 48 h ([ 64 Cu] Keytruda) p.i. revealed tumor to muscle ratios as high as 45- and 12-fold, respectively. Conclusions Our immunoPET study clearly demonstrates specific imaging of human PD-1-expressing TILs within the tumor and lymphoid tissues. This suggests these anti-human-PD-1 tracers could be clinically translatable to monitor cancer treatment response to IC blockade therapy.