Arenavirus Therapy in Combination with Checkpoint Blockade as an Effective Way for Better Tumour Clearance.

Viruses have been widely used to treat cancer for many years and they achieved tremendous success in clinical trials with outstanding results, which has led to the foundation of companies that develop recombinant viruses for a better tumor treatment. Even though there has been a great progress in the field of viral tumor immunotherapy, until now only one virus, the oncolytic virus talimogene laherparepvec (TVEC), a genetically modified herpes simplex virus type 1 (T-VEC), has been approved by the FDA for cancer treatment. Although oncolytic viruses showed progress in certain cancer types and patient populations but they have yet shown limited efficacy when it comes to solid tumors. Only recently it was demonstrated that the immune stimulatory aspect of oncolytic viruses can strongly contribute to their anti-tumoral activity. One specific example in this context are arenaviruses, which have been shown to be non-cytopathic in nature lead to the massive immune activation within the tumor resulting in strong anti-tumoral activity. This strong immune activation might be also linked to their noncytopathic features, as their immune stimulatory potential is not self-limiting as is the case for oncolytic viruses due to their fast eradication by anti-viral immune effects. Because of this strong immune activation, arenaviruses appear superior to oncolytic viruses when it comes to potent and long-lasting anti-tumor effects in a broad variety of tumor types. Currently one of the most promising therapeutics which has turned to be very much beneficial for the treatment of different cancer types is represented by antibodies targeting checkpoint inhibitors such as PD-1/PD-L-1. In this review, we will summarize anti-tumoral effects of arenaviruses, and will discuss their potential to be combined with checkpoint inhibitors for a more efficient tumor treatment, which further emphasizes that arenavirus therapy as a viroimmunotherapy can be an efficient tool for the better clearance of tumors.