Abstract 4198: Evaluation of a cancer immunotherapy with engineered arenavirus vectors and 4-1BB agonists in a preclinical tumor model

T cells play a central role in immune responses against cancer. Within the tumor, however, T cells are exposed to a plethora of inactivating factors causing various degrees of dysfunction, changes in metabolism and a generally reduced cellular fitness, eventually leading to tumor progression. To prevent or delay the onset of exhaustion and instead augment effector functions and persistence of functional T cells, costimulatory factors and cytokines are needed. Targeting 4-1BB (CD137), a member of the tumor necrosis factor receptor superfamily, has been shown to represent a promising strategy for inducing an activating signal in CD8+ T cells, resulting in increased pro-inflammatory cytokine secretion, cytotoxic function, and survival. Engineered arenavirus vectors based on lymphocytic choriomeningitis virus (LCMV) or Pichinde virus (PICV) have been shown previously to induce massive infiltration of tumor antigen specific CD8+ T cells into the tumor in several preclinical cancer models. To investigate whether enhanced co-stimulation via 4-1BB further improves T cell responses and/or tumor control, combination therapies with replicating LCMV based vectors (artLCMV) and 4-1BB agonists were explored. A single intravenous treatment of artLCMV encoding the tumor associated antigens (TAA) gp70 or Trp2 in B16.F10 tumor bearing mice induced TAA specific CD8+ T cells in both the periphery and the tumor, resulting in tumor growth delay and some complete responses. Combining artLCMV with agonistic anti-4-1BB significantly improved tumor control and increased the number of complete responders. Analysis of tumor infiltrating lymphocytes revealed higher absolute numbers of TAA specific CD8+ T cells in the combination group compared to the artLCMV alone group. Analyses of the TAA specific cells revealed that more cells expressed granzyme B, Ki67 and Bcl-XL when co-stimulated with anti-4-1BB compared to the group treated with artLCMV alone. Importantly, encoding 4-1BBL in addition to a TAA in artLCMV revealed similar outcomes as just summarized for the combination with agonistic antibodies. Overall, these experiments confirmed the strong antigenicity and T cell inducing capacity of the engineered arenavirus platform, leading to efficient tumor control in a stringent mouse model. Combination with 4-1BB agonists, either in form of antibodies or encoded within the vector genome, was shown to further augment TAA-specific T cell responses within the tumor, leading to better tumor growth control and a higher rate of complete responders. Citation Format: Judith Strauss, Marilies Scheinost, Theresa Kleissner, Diana Reckendorfer, Kimberly Pojar, Mohamed Habbeddine, Sarah Ahmadi-Erber, Daniela Deutschmann, Sarah Schmidt, Josipa Raguz, Igor Matushansky, Christoph Lampert, Klaus K. Orlinger, Henning Lauterbach. Evaluation of a cancer immunotherapy with engineered arenavirus vectors and 4-1BB agonists in a preclinical tumor model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 4198.