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The advancements in immunotherapy have significantly transformed traditional cancer treatment to strategies harnessing the immune system to eliminate cancer cells. Recent studies have emphasized the potential of virotherapy modalities as a promising immunotherapy approach.

In this thesis, I evaluated the therapeutic potential of LOAd703, in both preclinical (paper I-III) and clinical (paper IV) settings. LOAd703 is an adenovirus 5/35 chimera encoding two strong immunostimulatory genes: trimerized, membrane-bound CD40L and 4-1BBL. LOAd703 can infect all cell types in the tumor microenvironment (TME) and induce expression of the transgenes but replicates selectively in tumor cells and induce oncolysis.

In paper I, we evaluated how CD40 stimulation influences LOAd703-induced tumor immunogenicity in solid tumors. This study demonstrated that LOAd703 can induce immunogenic cell death, marked by cell-surface exposure of calreticulin, upregulation of death receptors (TRAIL-R1/R2 and Fas), alongside a rise in caspase 3/7 activity. We noticed that the obtained effects were potentiated in CD40-positive cancer cells, indicating additional impact of CD40 signaling. In paper II, the feasibility and potential synergistic effects of LOAd703 combined with chemotherapy in ovarian cancer was evaluated. LOAd703 alone and in combination increased the expression of TRAIL-R2, Fas, and MHC-I. Moreover, LOAd703 controlled tumor-growth and prolonged survival with and without chemotherapy in a xenograft mouse model. In paper III, LOAd703 was evaluated in multiple myeloma (MM). The results demonstrated that infection with the virus downregulates markers associated with MM progression (e.g. CD70, ICAM-1, CXCL10). Immune cell co-cultures with LOAd703 MM cells induced release of IFN-γ and expression of CD69 and CD107a on CD4+ and CD8+ T cells. In paper IV, we evaluated clinical samples from three phase I/II trials to assess the profile of LOAd703 leakage into bloodstream, shedding, anti-adenoviral immune responses and their potential correlation to adverse events and overall survival (OS). LOAd703 DNA was detected in blood early post intratumoral injections but was decreased already after 24-hours. Presence of neutralizing antibodies was confirmed at baseline, which increased post treatment initiation. Additionally, we observed some dose-dependent correlation between ADA and immune-related adverse events or OS.

Taken together, this thesis highlights the significant potential of TME-gene engineering by LOAd703.