Antitumor efficacy and reduced toxicity using an anti-CD137 Probody therapeutic

Proc Natl Acad Sci U S A. 2021 Jun 29;118(26):e2025930118. doi: 10.1073/pnas.2025930118.


Costimulation via CD137 (4-1BB) enhances antitumor immunity mediated by cytotoxic T lymphocytes. Anti-CD137 agonist antibodies elicit mild liver inflammation in mice, and the maximum tolerated dose of Urelumab, an anti-human CD137 agonist monoclonal antibody, in the clinic was defined by liver inflammation-related side effects. A protease-activated prodrug form of the anti-mouse CD137 agonist antibody 1D8 (1D8 Probody therapeutic, Pb-Tx) was constructed and found to be selectively activated in the tumor microenvironment. This construct, which encompasses a protease-cleavable linker holding in place a peptide that masks the antigen binding site, exerted antitumor effects comparable to the unmodified antibody but did not result in liver inflammation. Moreover, it efficaciously synergized with both PD-1 blockade and adoptive T-cell therapy. Surprisingly, minimal active Pb-Tx reached tumor-draining lymph nodes, and regional lymphadenectomy did not abrogate antitumor efficacy. By contrast, S1P receptor-dependent recirculation of T cells was absolutely required for efficacy. The preferential cleavage of the anti-CD137 Pb-Tx by tumor proteases offers multiple therapeutic opportunities, including neoadjuvant therapy, as shown by experiments in which the Pb-Tx is given prior to surgery to avoid spontaneous metastases.

Keywords: 4-1BB; CD137; Probody; cancer immunotherapy.

MeSH terms

  • Animals
  • Antibodies, Monoclonal / pharmacology
  • Antineoplastic Agents / pharmacology
  • Antineoplastic Agents / therapeutic use*
  • Antineoplastic Agents / toxicity*
  • Cell Line, Tumor
  • Humans
  • Immunotherapy
  • Inflammation / pathology
  • Liver / pathology
  • Lung Neoplasms / secondary
  • Lymph Nodes / drug effects
  • Lymph Nodes / pathology
  • Mice
  • Neoadjuvant Therapy
  • Peptide Hydrolases / metabolism
  • Tumor Necrosis Factor Receptor Superfamily, Member 9 / metabolism*


  • Antibodies, Monoclonal
  • Antineoplastic Agents
  • Tumor Necrosis Factor Receptor Superfamily, Member 9
  • Peptide Hydrolases