Oncolytic virotherapy is gaining interest in the clinic as a new weapon against cancer. In vivo administration of oncolytic viruses showed important limitations that decrease their effectiveness very significantly: the antiviral immune response causes the elimination of the therapeutic effect, and the poor natural ability of oncolytic viruses to infect micrometastatic lesions significantly minimizes the effective dose of virus. This review will focus on updating the technical and scientific foundations of one of the strategies developed to overcome these limitations, ie, using cells as vehicles for oncolytic viruses. Among many candidates, a special type of adult stem cell, mesenchymal stem cells (MSCs), have already been used in the clinic as cell vehicles for oncolytic viruses, partly due to the fact that these cells are actively being evaluated for other indications. MSC carrier cells are used as Trojan horses loaded with oncoviruses, are administered systemically, and release their cargos at the right places. MSCs are equipped with an array of molecules involved in cell arrest in the capillaries (integrins and selectins), migration toward specific parenchymal locations within tissues (chemokine receptors), and invasion and degradation of the extracellular matrix (proteases). In addition to anatomical targeting capacity, MSCs have a well-recognized role in modulating immune responses by affecting cells of the innate (antigen-presenting cells, natural killer cells) and adaptive immune system (effector and regulatory lymphocytes). Therefore, carrier MSCs may also modulate the immune responses taking place after therapy, ie, the antiviral and the antitumor immune responses.
Celyvir (autologous mesenchymal cells-MSCs-that carry an oncolytic adenovirus) is a new therapeutic strategy for metastatic tumors developed by our research group over the last decade. There are limitations for studying the immune effects of human oncolytic adenoviruses in murine models since these viruses do not replicate naturally in these animals. The use of xenografts in immunodeficient mice prevent assessing important clinical aspects of this therapy such as the antiadenoviral immune response or the possible intratumoral immune changes, both of tumor infiltrating leukocytes and of the microenvironment. In our strategy, the presence of MSCs in the medicinal product adds an extra level of complexity. We present here a murine model that overcomes many of these limitations. We found that carrier cells outcompeted intravenous administration of naked particles in delivering the oncolytic virus into the tumor masses. The protection that MSCs could provide to the oncolytic adenovirus did not preclude the development of an antiadenoviral immune response. However, the presence of circulating antiadenoviral antibodies did not prevent changes detected at the tumor masses: increased infiltration and changes in the quality of immune cells per unit of tumor volume, and a less protumoral and more inflammatory profile of the tumor microenvironment. We believe that the model described here will enable the study of crucial events related to the immune responses affecting both the medicinal product and the tumor.
Little is known about the effect of oncolytic adenovirotherapy on pediatric tumors. Here we present the clinical case of a refractory neuroblastoma that responded positively to Celyvir (ICOVIR-5 oncolytic adenovirus delivered by autologous mesenchymal stem cells) for several months. We analyzed samples during tumor evolution in order to identify molecular and mutational features that could explain the interactions between treatment and tumor and how the balance between both of them evolved. We identified a higher adaptive immune infiltration during stabilized disease compared to progression, and also a higher mutational rate and T-cell receptor (TCR) diversity during disease progression. Our results indicate an initial active role of the immune system controlling tumor growth during Celyvir therapy. The tumor eventually escaped from the control exerted by virotherapy through acquisition of resistance by the tumor microenvironment that exhausted the initial T cell response.
e15217 Background: We used oncolytic virotherapy carried by autologous marrow-derived mesenchymal cells to treat children with metastatic/refractory tumors (NCT01844661; 10.1016/j.ymthe.2020.01.019 and 10.1016/j.canlet.2015.11.036). Most patients did not show clinical response while a small group did. Methods: We have carried out a comprehensive study of the transcriptome of this new advanced therapy medicine (ATM) to find determinants that might be associated with clinical outcome. Results: The study of the ATM's transcriptome from a first cohort of patients identified signatures associated to biological processes in the infected carrier cells that distinguished responders from non-responders (viral infection and nucleic acid metabolism; immune regulatory routes; cell-cell adhesion; mitosis; cell metabolism; response to stress; and bone marrow fibrosis). Next, we used an approach based on systems biology and neural networks to identify candidates responsible for the differences found in gene expression signatures. We then validated the identified candidates using samples obtained from a second independent cohort of patients, by quantitative PCR and ELISA. Mesenchymal cells of the responding patients expressed significantly lower levels of the MAVS and NDRG1 genes compared with those of the non-responders after oncolytic adenoviral infection. Both genes are related to cellular antiviral responses and cellular metabolism. Accordingly, mesenchymal cells of responders produced significantly lower amounts of IL-6 and CCL-2 than non-responders’ cells. Conclusions: These results point to possible pretreatment biomarkers and the possibility of optimizing a universal version of the carrier cells for the oncolytic virus in this new ATM.
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