Abstract 4145: A novel form of 4-1BB agonist shows robust immune protection against various tumor types through CD4+memory-like T and NK cell axis

Background: Costimulation through 4-1BB (CD137) receptor has been targeted for cancer immunotherapy using agonistic antibodies, which have been shown to cause liver toxicity in preclinical and clinical settings. We hypothesized that this might not be a bona fide feature of 4-1BB signaling, but rather an antibody-mediated off-target effect. To test this hypothesis, we have generated a novel oligomeric form of the natural ligand, SA-4-1BBL, with robust costimulatory activity as a soluble protein. Pretreatment with SA-4-1BBL as a single agent protected mice against challenge with various tumor types, a feature that was not shared by an agonistic 4-1BB antibody. Study Design: C57BL/6 Mice were treated subcutaneously once or twice (two weeks apart) with various doses of SA-4-1BBL protein or an agonistic antibody (3H3) to 4-1BB, followed by challenge with various tumor cell lines subcutaneously into the left flank and monitored for tumor growth. For immunological studies, animals were treated with SA-4-1BBL twice, two weeks apart and then euthanized 7 days later to harvest various lymphoid tissues for immunophenotyping using flow cytometry. Antibodies against CD4 + T, CD8 + T, B, and NK cells were used in vivo to deplete individual cell types to assess their contribution towards the observed immune protection. Results: Pretreatment with SA-4-1BBL protected mice against 3 different tumor types, two lung cancer and one cervical cancer cell lines without detectable toxicity. The conferred protection against tumors was dose-dependent and evolved within two weeks of the first treatment. Importantly, the response was not tumor type-specific and lasted more than 8 weeks. In contrast to the protection conferred by SA-4-1BBL, pretreatment with the agonistic 4-1BB antibody had no impact on the tumor growth. Pretreatment with SA-4-1BBL expanded CD4 + CD44 + 4-1BB + T cells and NK cells producing IFN-γ. Our immune-cell depletion studies proved CD4 + T and NK cells to be indispensable for the observed anti-tumor effect. In marked contrast, depletion of CD8 + T cells or B cells had no significant impact on tumor growth. Also, in vivo blockade of IFN-γ negated SA-4-1BBL-conferred protection against tumor challenge. Conclusion: This study demonstrates unique and unexpected immunomodulatory features of SA-4-1BBL that bridge innate and adaptive immune responses with preventive efficacy against cancer. The tumor type-independent protection conferred by SA-4-1BBL is significant with important clinical implications for primary and secondary cancer prevention modalities. The safety profile of SA-4-1BBL and its cancer immunoprevention attributes are fundamental characteristics that are not shared by agonistic antibodies to the 4-1BB receptors. This highlights and emphasizes SA-4-1BBL’s potential for cancer immunoprevention and therapy. Funded in parts by NIH R41CA199956 award. Citation Format: Haval Shirwan, Hampartsoum B. Barsoumian, Lalit Batra, Pradeep Shrestha, William S. Bowen, Hong Zhao, Nejat K. Egilmez, Jorge G. Gomez-Gutierrez, Esma S. Yolcu. A novel form of 4-1BB agonist shows robust immune protection against various tumor types through CD4 + memory-like T and NK cell axis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4145.