Comparison of the Superagonist Complex, ALT-803, to IL15 as Cancer Immunotherapeutics in Animal Models

Abstract

Interleukin-15 (IL-15), a potent stimulant of CD8+ T and NK cells, is a promising cancer immunotherapeutic. ALT-803 is a complex of an IL-15 superagonist mutant and a dimeric IL-15 receptor αSu/Fc fusion protein that was found to exhibit enhanced biologic activity in vivo with a substantially longer serum half-life than recombinant IL-15. A single intravenous dose of ALT-803, but not IL-15, eliminated well-established tumors and prolonged survival of mice bearing multiple myeloma. In this study, we extended these findings to demonstrate the superior antitumor activity of ALT-803 over IL-15 in mice bearing subcutaneous B16F10 melanoma tumors and CT26 colon carcinoma metastases. Tissue biodistribution studies in mice also showed much greater retention of ALT-803 in the lymphoid organs compared to IL-15, consistent with its highly potent immunostimulatory and antitumor activities in vivo. Weekly dosing with 1 mg/kg ALT-803 in C57BL/6 mice was well-tolerated, yet capable of increasing peripheral blood lymphocyte, neutrophil and monocyte counts by >8-fold. ALT-803 dose-dependent stimulation of immune cell infiltration into the lymphoid organs was also observed. Similarly, cynomolgus monkeys treated weekly with ALT-803 showed dose-dependent increases of peripheral blood lymphocyte counts, including NK, CD4+, and CD8+ memory T cell subsets. In vitro studies demonstrated ALT-803-mediated stimulation of mouse and human immune cell proliferation and IFN-γ production without inducing a broad-based release of other proinflammatory cytokines (i.e., cytokine storm). Based on these results, a weekly dosing regimen of ALT-803 has been implemented in multiple clinical studies to evaluate the dose required for effective immune cell stimulation in humans.

A Novel Fusion of ALT-803 (Interleukin (IL)-15 Superagonist) with an Antibody Demonstrates Antigen-specific Antitumor Responses

“…5, A-C). The uptake of 64 Cu-NOTA-2B8T2M in the lymph nodes was comparable with what was observed previously with 64 Cu-NOTA-ALT-803 (12), which demonstrated the high IL-15 receptor-targeting efficiency for both of these fusion proteins. At 6 h post-injection (h.p.i.…”

“…In a comparative biodistribution study with native IL-15, ALT-803 was distributed to and retained better in lymphoid organs of mice (12). Similarly, 2B8T2M biodistribution data indicate uptake and retention in lymphoid tissues for at least 70 h. In the CD40 ϩ B cell depletion study in non-human primates, we found that lower dose levels of 2B8T2M were more efficacious than rituximab, particularly in the lymph nodes.…”

“…The N72D mutation increases the biological activity of IL-15 ϳ5-fold, and the IL-15N72D⅐IL-15R␣SuFc complex further enhances the activity of IL-15 ϳ25-fold compared with native IL-15 in vivo (3,4). Also, ALT-803 has greater binding activity with the IL-2R␤␥ C complex displayed on the surface of immune cells, a substantially longer serum half-life, and better biodistribution and retention in lymphoid tissues than native IL-15 (3,4,12). Exhibiting potent immunostimulatory and antitumor properties, ALT-803 is an effective agent against various tumors in animal models either as a single agent or in combination with other therapies (5,6).…”

“…Previous biodistribution studies of mice administered 64 Cu-labeled ALT-803 compared with 64 Cu-IL-15 showed distinct pharmacokinetic profiles demonstrating rapid clearance of 64 Cu-IL-15 through the renal pathway, whereas ALT-803 clearance occurred in the liver but was retained for at least 70 h in the lymphoid organs (12). In this study, 64 Cu-NOTA-2B8T2M was cleared from the mouse body through both the hepatobiliary and renal pathways, and kidney uptake was low (Fig.…”

Tumor-infiltrating lymphocytes are dynamically desensitized to antigen but are maintained by homeostatic cytokine

“…In mice, most studies investigating the activity of T cell enhancing drugs such as IL-15 have been performed with fast-growing ectopic or orthotopic tumor models (53,55,56). Despite their apparent advantages of speed and reliability, these tumor models lack the normal tumor development that allows for the establishment and maturation of a T cell pool prior to treatment.…”