Preventive Vaccination with Mesenchymal Stem Cells Protects Mice from Lethal Infection Caused by Herpes Simplex Virus 1

Abstract

Herpes simplex viruses 1 and 2 (HSV-1 and HSV-2) infect almost all organs and tissues, cause genital herpes-the most common sexually transmitted disease-disorders of the central nervous system (CNS), and lead to severe complications in children. Despite the available drugs, the incidence of HSV-1/2 continues to rise. None of the prophylactic vaccine candidates have shown a protective effect in trials nor approval for use in clinical practice. We have investigated the protective properties of mesenchymal stem cells (MSC) isolated from the bone marrow of mice. A comparative analysis of the protective response to the introduction of primary and modified MSCs (mMSC) was carried out using the plasmid containing gene of the HSV and an inactivated virus in a model of lethal HSV-1 infection in mice. mMSCs were obtained by transfection of the Us6 gene encoding glycoprotein D (gD) of the HSV, the plasmid contained the same gene. After twofold immunization with primary MSCs, the formation of antibodies interacting with the viral antigen (according to enzyme immunoassay data) and neutralizing the infectious activity of HSV-1 in the reaction of biological neutralization was observed in the peripheral blood of mice. In addition, the introduction of primary MSCs induced the production of interferon gamma (INF-γ) which is detected in the peripheral blood of mice. After infection with HSV-1, the immunized mice showed significantly increased titers of virus-specific antibodies, an increased level of IFNγ, and were completely protected from lethal HSV-1 infection. The protective effect of the other three immunogens was lower and did not exceed 50-65%. Considering the wide availability of MSCs, the proven safety of intravenous administration, and the results obtained in this work on the ability to induce innate, adaptive and protective immunity to HSV-1, MSCs can be considered a promising basis for the development of new cellular vaccines for the prevention of herpesvirus and other viral infections.

Keywords: DNA immunization; genetically modified mesenchymal stem cells; herpes simplex virus 1; mesenchymal stem cells; protective activity; recombinant DNA; transfection.

Fig. 1.

Immunocytochemical detection of the gD protein of HSV in a genetically modified MSC transfected with the DNAgD plasmid. (a) Primary culture of MSC; (b) modified MSCs. The arrows indicate the accumulation of the gD protein in the cytoplasm of the transfected cells (brown staining). The nuclei are stained with hematoxylin (blue staining). Magnification 400×.

Fig. 2.

Levels of the cytokines IL-2 (a), IL-6 (b), and IFNγ (c) secreted by primary and genetically modified MSCs in vitro. Results are presented as mean ± SD calculated from three replicates. *p < 0.05 compared to MSC (t-test).

Fig. 3.

Humoral immune response to immunization before and after infection of mice with lethal doses of HSV-1. (a) Titers of antiviral antibodies (ELISA); (b) relative levels of HSV-1-specific antibodies of IgG subclasses in immunized animals: group 1 (MSC), group 2 (MSCgD), group 3 (DNAgD), group 4 (iHSV), and group 5 (control). The results of ELISA are presented as absorbance values ​​at 450 nm (OD₄₅₀). §Ratio IgG2a/IgG1. (c) Titers of neutralizing antibodies ( virus neutralization assay); *p < 0.05, between groups (t-test); #p <0.05, compared to all groups (t-test).

Fig. 4.

Index of stimulation of splenocyte proliferation before and post infection of mice with lethal doses of HSV-1. The results are presented as mean ± SD, calculated for three replicates in immunized animals: group 1 (MSC), group 2 (MSCgD), group 3 (DNAgD), group 4 (iHPV), and group 5 (control); n/e—not examined. *p < 0.05, between groups (t-test); #p < 0.05, compared to all groups (t-test).

Fig. 5.

Protective response during experimental systemic HSV-1 infection in mice immunized with MSCs (group 1), mMSCs (group 2), DNAgD (group 3), or iHSV (group 4), and in the control group (group 5). * p < 0.05, # p < 0.05, survival in control compared with immunized groups (Kaplan–Meier estimator).