Targeted and untargeted CD137L fusion proteins for the immunotherapy of experimental solid tumors.
BACKGROUND
CD137L is a member of the tumor necrosis factor superfamily that provides a costimulatory signal to T cells. In this study, two novel CD137L fusion proteins were produced and compared with the CD137 agonist antibody 2A.


METHODS
Murine CD137L was linked to the COOH terminus of either the Fc fragment of immunoglobulin (untargeted version) or TNT-3 (targeted version), an antibody that binds to necrotic regions of tumors. Groups of mice bearing established Colon 26 tumors were then treated daily x 5 with each fusion protein or 2A to determine their immunotherapeutic potential.


RESULTS
Both fusion proteins retained CD137L activity in vitro and TNT-3/CD137L showed tumor-binding activity by biodistribution analysis in tumor-bearing mice. The fusion proteins also produced similar responses in vivo at the 1 nmol per dose range and showed a 60% (TNT-3/CD137L) or 40% (Fc/CD137L) survival of treated mice at 150 days after tumor implantation, similar to the effects of 2A. Morphologic and immunohistochemical analyses showed massive central necrosis and infiltration of granzyme B-positive cells in necrotic areas and viable peripheral regions of treated tumors. Finally, cell depletion studies showed that CD137L-mediated tumor regression was CD8(+) T cell dependent.


CONCLUSIONS
From these studies, it was determined that both targeted and untargeted CD137L fusion proteins showed effective antitumor activity, but that the targeted version was more potent. Therefore, the use of the natural CD137 ligand is a promising approach to the treatment of solid tumors by virtue of its ability to produce physiologic costimulation within the tumor, limiting side effects often seen with agonist antibody therapies.
Zhang
Nan
N
Department of Pathology, Keck School of Medicine, University of Southern California, Los Angeles, California 90033, USA.
Sadun
Rebecca E
RE
Arias
Robyn S
RS
Flanagan
Meg L
ML
Sachsman
Suzanne M
SM
Nien
Yu-Chih
YC
Khawli
Leslie A
LA
Hu
Peisheng
P
Epstein
Alan L
AL
D053330:4-1BB Ligand / Q000096:biosynthesis / Q000235:genetics / Q000627:therapeutic use*; D000818:Animals; D015496:CD4-Positive T-Lymphocytes / Q000187:drug effects; D018414:CD8-Positive T-Lymphocytes / Q000187:drug effects; D003110:Colonic Neoplasms / Q000737:chemistry / Q000473:pathology / Q000628:therapy*; D005260:Female; D053804:Granzymes; D007141:Immunoglobulin Fc Fragments / Q000096:biosynthesis / Q000235:genetics / Q000627:therapeutic use*; D007167:Immunotherapy; D008212:Lymphocyte Depletion; D051379:Mice; D008807:Mice, Inbred BALB C; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000235:genetics / Q000627:therapeutic use*
D053330:4-1BB Ligand; D007141:Immunoglobulin Fc Fragments; D011993:Recombinant Fusion Proteins; C505975:Tnfsf9 protein, mouse; D053804:Granzymes