Recent cancer immunotherapy breakthroughs have fundamentally changed oncology and revived the fading hope for a cancer cure. The immune checkpoint inhibitors (ICI) became an indispensable tool for the treatment of many malignant tumors. Alongside ICI, the application of oncolytic viruses in clinical trials is demonstrating encouraging outcomes. Dozens of combinations of oncolytic viruses with conventional radiotherapy and chemotherapy are widely used or studied, but it seems quite complicated to highlight the most effective combinations. Our review summarizes the results of clinical trials evaluating oncolytic viruses with or without genetic alterations in combination with immune checkpoint blockade, cytokines, antigens and other oncolytic viruses as well. This review is focused on the efficacy and safety of virotherapy and the most promising combinations based on the published clinical data, rather than presenting all oncolytic virus variations, which are discussed in comprehensive literature reviews. We briefly revise the research landscape of oncolytic viruses and discuss future perspectives in virus immunotherapy, in order to provide an insight for novel strategies of cancer treatment.

One of the well-known X-linked genetic disorders is hemophilia, which could be hemophilia A as a result of a mutation in the F8 (factor VIII) gene or hemophilia B as a result of a mutation in the F9 (factor IX) gene, leading to insufficient levels of the proteins essential for blood coagulation cascade. In patients with severe hemophilia, factor VIII or factor IX activities in the blood plasma are considerably low, estimated to be less than 1%. This is responsible for spontaneous or post-traumatic bleeding episodes, or both, leading to disease complications and death. Current treatment of hemophilia relies on the prevention of bleeding, which consists of expensive lifelong replacement infusion therapy of blood plasma clotting factors, their recombinant versions, or therapy with recombinant monoclonal antibodies. Recently emerged gene therapy approaches may be a potential game changer that could reshape the therapeutic outcomes of hemophilia A or B using a one-off vector in vivo delivery and aim to achieve long-term endogenous expression of factor VIII or IX. This review examines both traditional approaches to the treatment of hemophilia and modern methods, primarily focusing on gene therapy, to update knowledge in this area. Recent technological advances and gene therapeutics in the pipeline are critically reviewed and summarized. We consider gene therapy to be the most promising method as it may overcome the problems associated with more traditional treatments, such as the need for constant and expensive infusions and the presence of an immune response to the antibody drugs used to treat hemophilia.

Throughout the years, several hundred million people with rare genetic disorders have been receiving only symptom management therapy. However, research and development efforts worldwide have led to the development of long-lasting, highly efficient, and safe gene therapy for a wide range of hereditary diseases. Improved viral vectors are now able to evade the preexisting immunity and more efficiently target and transduce therapeutically relevant cells, ensuring genome maintenance and expression of transgenes at the relevant levels. Hematological, ophthalmological, neurodegenerative, and metabolic therapeutic areas have witnessed successful treatment of hemophilia and muscular dystrophy, restoration of immune system in children with immunodeficiencies, and restoration of vision. This review focuses on three leading vector platforms of the past two decades: adeno-associated viruses (AAVs), adenoviruses (AdVs), and lentiviruses (LVs). Special attention is given to successful preclinical and clinical studies that have led to the approval of gene therapies: six AAV-based (Glybera® for lipoprotein lipase deficiency, Luxturna® for retinal dystrophy, Zolgensma® for spinal muscular atrophy, Upstaza® for AADC, Roctavian® for hemophilia A, and Hemgenix® for hemophilia B) and three LV-based (Libmeldy® for infantile metachromatic leukodystrophy, Zynteglo® for β-thalassemia, and Skysona® for ALD). The review also discusses the problems that arise in the development of gene therapy treatments, which, nevertheless, do not overshadow the successes of already developed gene therapies and the hope these treatments give to long-suffering patients and their families.

In vitro disease modeling can be used both for understanding the development of pathology and for screening various therapies, such as gene therapies. This approach decreases costs, shortens research timelines, reduces animal testing, and may be more accurate in replicating the disease phenotype compared to animal models. This review focuses on the two types of stem cells: induced pluripotent stem cells (iPSCs) and mesenchymal stem cells (MSCs), which can be used for this purpose. Special attention is given to the impact of the isolation source and the variable expression of certain phenotypic markers on the differentiation capacity of these cells. Both similarities and critical differences between iPSCs and MSCs, as well as the outcomes of past and ongoing clinical trials, are discussed in order to gain insight and understanding as to which of these two cell types can be more suitable for the particular biomedical application.

Anti-cancer therapy based on oncolytic viruses (OVs) is a targeted approach that takes advantage of OVs’ ability to selectively infect and replicate in tumor cells, activate the host immune response, and destroy malignant cells over healthy ones. Vesicular stomatitis virus (VSV) is known for its wide range of advantages: a lack of pre-existing immunity, a genome that is easily amenable to manipulation, and rapid growth to high titers in a broad range of cell lines, to name a few. VSV-induced tumor immunity can be enhanced by the delivery of immunostimulatory cytokines. The targeted cytokine delivery to tumors avoids the significant toxicity associated with systemic delivery while also boosting the immune response. To demonstrate this enhanced effect on both tumor growth and survival, a novel recombinant VSV (rVSV)-mIL12-mGMCSF, co-expressing mouse IL-12 (interleukin-12) and GM-CSF (granulocyte-macrophage colony-stimulating factor), was tested alongside rVSV-dM51-GFP (rVSV-GFP) that was injected intratumorally in a syngeneic in vivo C57BL/6 mouse model infused subcutaneously with B16-F10 melanoma cells. The pilot study tested the effect of two viral injections 4 days apart and demonstrated that treatment with the two rVSVs resulted in partial inhibition of tumor growth (TGII of around 40%) and an increased survival rate in animals from the treatment groups. The effect of the two VSVs on immune cell populations will be investigated in future in vivo studies with an optimized experimental design with multiple higher viral doses, as a lack of this information presents a limitation of this study.

The level of transduction efficiency of the target retinal cells affects the choice of AAV serotype and the outcome of gene replacement therapy for inherited retinal diseases. This study focused on the tropism and transduction efficiency of AAV2.7m8-, AAV5-, AAV8-, and AAV9-GFP in ARPE-19 and HEK293 cells. Fluorescence intensity was assessed bi-hourly by means of IncuCyte S3 live imaging microscopy. Within 12 h, AAV2.7m8 demonstrated the highest transduction efficiency at four viral concentrations of 1-, 3-, 6-, and 8 × 10⁴ VG/cell in a dose-dependent manner, followed by AAV5 in ARPE-19 and AAV9 in HEK293 cells. The transduction efficiency of AAV2.7m8 at a dose of 6 × 10⁴ VG/cell was 21, 202, and 323 times higher in ARPE-19 cells and 324, 100, and 52 times higher in HEK293 cells compared to AAV5, AAV8, and AAV9, respectively. This trend remained for 4 days at all viral concentrations, as additionally shown by flow cytometry. At a dose of 6 × 10⁴ VG/cell, AAV2.7m8 (97% GFP-positive cells, GFP +) was nearly two and 10 times as efficient as AAV5 (52% GFP+) and AAV9 or AAV8 (both 9%), respectively, in ARPE-19 cells. In HEK293 cells, 95% of AAV2.7m8-, 26% of AAV9-, 17% of AAV8-, and 12% of AAV5-transduced cells were GFP-positive.