Circulating Spike Protein Detected in Post-COVID-19 mRNA Vaccine Myocarditis

Abstract

Background: Cases of adolescents and young adults developing myocarditis after vaccination with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-targeted mRNA vaccines have been reported globally, but the underlying immunoprofiles of these individuals have not been described in detail.

Methods: From January 2021 through February 2022, we prospectively collected blood from 16 patients who were hospitalized at Massachusetts General for Children or Boston Children's Hospital for myocarditis, presenting with chest pain with elevated cardiac troponin T after SARS-CoV-2 vaccination. We performed extensive antibody profiling, including tests for SARS-CoV-2-specific humoral responses and assessment for autoantibodies or antibodies against the human-relevant virome, SARS-CoV-2-specific T-cell analysis, and cytokine and SARS-CoV-2 antigen profiling. Results were compared with those from 45 healthy, asymptomatic, age-matched vaccinated control subjects.

Results: Extensive antibody profiling and T-cell responses in the individuals who developed postvaccine myocarditis were essentially indistinguishable from those of vaccinated control subjects, despite a modest increase in cytokine production. A notable finding was that markedly elevated levels of full-length spike protein (33.9±22.4 pg/mL), unbound by antibodies, were detected in the plasma of individuals with postvaccine myocarditis, whereas no free spike was detected in asymptomatic vaccinated control subjects (unpaired t test; P<0.0001).

Conclusions: Immunoprofiling of vaccinated adolescents and young adults revealed that the mRNA vaccine-induced immune responses did not differ between individuals who developed myocarditis and individuals who did not. However, free spike antigen was detected in the blood of adolescents and young adults who developed post-mRNA vaccine myocarditis, advancing insight into its potential underlying cause.

Keywords: COVID-19; SARS-CoV-2; mRNA; myocarditis; vaccine.

Figure 1.

Study overview. After they received a coronavirus disease 2019 (COVID-19) mRNA vaccination, blood samples were collected from adolescents and young adults who developed myocarditis or who had no vaccine-related complications. The concentrations of anti–severe respiratory syndrome coronavirus disease 2 (SARS-CoV-2) antibodies, SARS-CoV-2 antigens, and cytokines were measured, and hematology and T-cell profiling was performed with the collected blood samples.

Figure 2.

Humoral responses. Humoral responses of adolescents and young adults with postvaccine myocarditis (n=10) compared with age-matched postvaccine control subjects (n=17). A and B, Immunoglobulin (Ig) M/G/A to spike and RBD (receptor binding protein); (C) Fc receptors to Spike; (D) antibody-dependent complement deposition (ADCD), neutrophil phagocytosis (ADNP), and cellular phagocytosis (ADCP); (E) correlation heat map; (F) phage immunoprecipitation sequencing; and (G) heat map of VirScan. A through E include only samples that were collected within 11 days after the second vaccination dose to allow time-equivalent comparison of severe respiratory syndrome coronavirus disease 2 (SARS-CoV-2)–specific responses. F and G include 5 individuals with postvaccine myocarditis and 7 healthy vaccinated control subjects. Analysis by Mann-Whitney U map. *P<0.5. **P<0.01. ***P<0.001. ****P<0.0001.

Figure 3.

Cytokine profiles. The concentration of cytokines detected in the plasma of adolescents with postvaccine myocarditis (n=16) compared with age-matched postvaccine control subjects (n=44). Plots are shown in order of decreasing significance between the mean values of each group for the following cytokines: (A) interleukin (IL)-6; (B) IL-8; (C) tumor necrosis factor (TNF)-α; (D) IL-10; (E) interferon (IFN)-γ; (F) IL-1β; (G) IL-4; (H) IL-5; (I) IL-22; and (J) IL-12p70. All data represent mean values for duplicate measurements. Significance was calculated with the Mann-Whitney U test. *P<0.05. **P<0.01. ***P<0.001. ****P< 0.0001.

Figure 4.

Circulating SARS-CoV-2 antigen. Free and total S1 and spike levels (A) measured in the plasma of the vaccinated control (n=44) and myocarditis (n=16) cohorts. Antigen data corresponding to all individuals who received the BNT162b2 vaccine (● ; n=59) and those who received the Moderna vaccine (○; n=2). Free antigen is measured by directly diluting patient plasma, whereas total antigen is measured after treating the plasma with dithiothreitol (DTT) to denature any antigen-bound antibodies. Free and total antigen levels vs days after vaccination (B). Longitudinal measurements associated with the same myocarditis patient are connected with lines. All data points represent mean values for duplicate measurements. Dashed gray lines indicate the limit of detection for each assay. SARS-CoV-2 indicates severe acute respiratory syndrome coronavirus 2.

Figure 5.

MIS-C vs postvaccine myocarditis. S1 (A), spike (B), cardiac troponin T (C), and C-reactive protein (CRP; D) levels detected in the blood samples of individuals with multisystem inflammatory syndrome in children (MIS-C; n=9) vs those with postvaccine myocarditis (n=17). All data points represent mean values for duplicate measurements. Significance was calculated with the Mann-Whitney U test. **P<0.01. ****P<0.0001.