Effect of SARS-CoV-2 mRNA-Vaccine on the Induction of Myocarditis in Different Murine Animal Models

Abstract

In the course of the SARS-CoV-2 pandemic, vaccination safety and risk factors of SARS-CoV-2 mRNA-vaccines were under consideration after case reports of vaccine-related side effects, such as myocarditis, which were mostly described in young men. However, there is almost no data on the risk and safety of vaccination, especially in patients who are already diagnosed with acute/chronic (autoimmune) myocarditis from other causes, such as viral infections, or as a side effect of medication and treatment. Thus, the risk and safety of these vaccines, in combination with other therapies that could induce myocarditis (e.g., immune checkpoint inhibitor (ICI) therapy), are still poorly assessable. Therefore, vaccine safety, with respect to worsening myocardial inflammation and myocardial function, was studied in an animal model of experimentally induced autoimmune myocarditis. Furthermore, it is known that ICI treatment (e.g., antibodies (abs) against PD-1, PD-L1, and CTLA-4, or a combination of those) plays an important role in the treatment of oncological patients. However, it is also known that treatment with ICIs can induce severe, life-threatening myocarditis in some patients. Genetically different A/J (most susceptible strain) and C57BL/6 (resistant strain) mice, with diverse susceptibilities for induction of experimental autoimmune myocarditis (EAM) at various age and gender, were vaccinated twice with SARS-CoV-2 mRNA-vaccine. In an additional A/J group, an autoimmune myocarditis was induced. In regard to ICIs, we tested the safety of SARS-CoV-2 vaccination in PD-1^-/- mice alone, and in combination with CTLA-4 abs. Our results showed no adverse effects related to inflammation and heart function after mRNA-vaccination, independent of age, gender, and in different mouse strains susceptible for induction of experimental myocarditis. Moreover, there was no worsening effect on inflammation and cardiac function when EAM in susceptible mice was induced. However, in the experiments with vaccination and ICI treatment, we observed, in some mice, low elevation of cardiac troponins in sera, and low scores of myocardial inflammation. In sum, mRNA-vaccines are safe in a model of experimentally induced autoimmune myocarditis, but patients undergoing ICI therapy should be closely monitored when vaccinated.

Keywords: SARS-CoV-2; mRNA vaccine; myocardial function; myocarditis; side effects.

Figure 1

Effect of 0.2 µg mRNA-vaccine on 5–7 weeks old female (n = 15) and male (n = 13), and on 23-weeks old female (n = 9) and male (n = 11) A/J wt mice. Data is presented as a mean ± SEM. (a) Calculated heart weight to body weight ratio on day 42. Statistical significance was determined by one-way ANOVA: * p = 0.0358, *** p = 0.0007. (b) Evaluation of hsTnT-levels in mouse serum collected on day 42. (c) Histopathological examination of inflammation score in grades in HE stained heart sections on day 42, evaluated by two independent investigators. (d) Echocardiographic examination of ejection fraction using M-mode on day 0 and day 42.

Figure 2

Effect of 2.5 µg mRNA-vaccine on 5-weeks old female (n = 11) and male (n = 5) A/J wt mice. Data is presented as a mean ± SEM. (a) Calculated heart weight to body weight ratio on day 42. (b) Determination of hsTnT-values in mouse serum collected on day 42. (c) Histopathological examination of inflammation score in grades in HE stained heart sections on day 42, evaluated by two independent investigators. (d) Determination of produced antibodies against pooled spike protein peptide sequences in mouse serum on day 42 by ELISA.

Figure 3

Comparison of 0.2 µg and 2.5 µg mRNA-vaccine on 5-weeks old A/J wt mice with untreated females (n = 4) and males (n = 6). Data is presented as a mean ± SEM. (a) Evaluation of heart weight to body weight ratio on day 42. (b) Comparison of hsTnT-values in mouse serum collected on day 42. (c) Histopathological examination of inflammation score in grades in HE stained heart sections on day 42, evaluated by two independent investigators. (d) Echocardiographic examination of ejection fraction using M-mode on day 0 and day 42.

Figure 4

Strain specific differences (BL/6 vs. A/J) of 2.5 µg mRNA-vaccination. Data is presented as a mean ± SEM (vaccine n = 6, untreated n = 5). (a) Comparison of heart weight to body weight ratio on day 42. (b) Measured hsTnT-levels in mouse sera collected on day 42. (c) Histopathological examination of inflammation score in grades in HE stained heart sections on day 42, evaluated by two independent investigators. (d) Echocardiographic assessment of ejection fraction using M-mode on day 0 and day 42.

Figure 5

Effect of 2.5 µg mRNA-vaccine on the induction of an experimental autoimmune myocarditis with 150 µg TnI peptide in A/J mice (n = 8). Data is presented as a mean ± SEM. (a) Calculated heart weight to body weight ratio on day 42. (b) Determination of hsTnT-levels in mouse serum collected on day 42. Statistical significance was determined by Mann–Whitney: * p = 0.0373. (c) Histopathological examination of inflammation score in grades in HE stained heart sections on day 42, evaluated by two independent investigators. (d) Echocardiographic assessment of ejection fraction using M-mode on day 0 and day 42 after TnI immunization.

Figure 6

Impact of 2.5 µg mRNA-vaccine on BL/6 PD−1^+/+ and BL/6 PD-1^−/− in combination with immune inhibition. Data is presented as a mean ± SEM (PD−1^+/+ untreated n = 5, vaccine n = 6, vaccine + aCTLA-4 n = 6; PD-1^−/− untreated n = 5, vaccine female n = 7, male n = 5, vaccine + aCTLA-4 n = 6). (a) Heart weight to body weight ratio on day 42. Statistical significance was determined by t-test, * p = 0.0029. (b) Determination hsTnT-levels of mouse serum collected on day 42. (c) Histopathological examination of inflammation score in grades in HE stained heart sections on day 42, evaluated by two independent investigators. (d) Inflamed heart section of a BL/6 PD-1^−/− mouse after vaccination and anti-CTLA-4 co-treatment.