Abstract 4092: CD40L/4-1BBL virotherapy enhances efficacy of checkpoint blockade therapy in a resistant melanoma model
Authors: Wenthe Jessica , Naseri Sedigheh , Hellström Ann-Charlotte , Eriksson Emma , Loskog Angelica 
Published: August 2019

Abstract
Despite the impressive effects of checkpoint blockade antibody therapy seen across indications, many patients remain resistant to treatment. PD-1/PD-L1 blockade aims to restore the function of anergic tumor-infiltrating T cells, thereby inducing an efficient anti-tumor response. Thus, a prerequisite to benefit from checkpoint blockade is the presence of T cells in the tumor. One promising strategy to prime non-inflamed tumors for checkpoint blockade is the use of oncolytic viruses, which can additionally be engineered to express immunostimulatory molecules to further induce immune activation and T cell infiltration. In this study, we are investigating the use of the oncolytic adenovirus mLOAd703 expressing a murine trimerized membrane-bound (TMZ)-CD40L and 4-1BBL in the syngeneic murine B16 melanoma model. Adenoviruses cannot replicate in murine cells, but the immunostimulatory effect of the murine transgenes TMZ-CD40L and 4-1BBL can still be evaluated. LOAd703 (serotype 5/35) targets human CD46 for viral entry. Thus, a B16 cell line expressing human CD46 was used to allow infection.
Upon infection with mLOAd703, B16-hCD46 cells not only expressed the transgenes TMZ-CD40L and 4-1BBL, but also changed their phenotype to become more immunogenic by upregulating co-stimulatory molecules CD80 and CD86, as well as MHC molecules. Moreover, expression of the death receptor Fas was increased, altogether potentially making the tumor cells more susceptible to T cell-mediated killing. Strikingly, two markers (CD44 and beta-3 integrin) associated with metastasis were reduced upon virus infection. Previous in vivo studies in immunocompetent C57BL6 mice with a predecessor of mLOAd703, which only expresses murine TMZ-CD40L, led to an increase of CD8+ T cells and CD11b+MHCII+ antigen presenting cells in the tumors. However, these cells also upregulated PD-1 or PD-L1, respectively, which warrants a combination with P-D1/PD-L1 checkpoint blockade. To evaluate this combination, mice with established B16-hCD46 tumors were treated with mLOAd703 (intratumoral 6x, 1x10e9 IU/mouse/injection), checkpoint blockade antibody (anti-mouse PD-1 or PD-L1, i.p. 6x 5mg/kg/mouse/injection; BioXcell), or treated in combination with mLOAd703 plus anti-PD-1 or mLOAd703 plus anti-PD-L1. Monotherapy with checkpoint blockade antibodies did not reduce tumor growth in this model. However, mLOAd703 reduced tumor growth as a monotherapy, but this reduction was even further enhanced in combination with both anti-PD-1 and anti-PD-L1 therapy.
In conclusion, mLOAd703 could infect B16 cells expressing CD46, leading to TMZ-CD40L and 4-1BBL transgene expression. In addition, infected tumor cells became more immunogenic and reduced molecules involved in metastasis. In vivo studies revealed that mLOAd703 therapy sensitized PD-1/PD-L1-resistant mice to checkpoint blockade therapy.
Citation Format: Jessica Wenthe, Sedigheh Naseri, Ann-Charlotte Hellström, Emma Eriksson, Angelica Loskog. CD40L/4-1BBL virotherapy enhances efficacy of checkpoint blockade therapy in a resistant melanoma model [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 4092.