Bullous pemphigoid after SARS‐CoV‐2 vaccination: spike‐protein‐directed immunofluorescence confocal microscopy and T‐cell‐receptor studies

dear editor, Growing evidence suggests that SARS‐CoV‐2 vaccination is associated with a variety of cutaneous reactions. These include autoimmune‐mediated conditions such as autoimmune blistering diseases (AIBDs), one of which is bullous pemphigoid (BP). ¹ , ² We report new‐onset BP in two patients following their first SARS‐CoV‐2 vaccination.

The first patient was an 80‐year‐old man who noticed reddish itchy macules with small blisters on his lower legs 1 week after vaccination with BTN162b2. ² Two weeks later, after he had received his second shot, these erythematous/bullous lesions spread over his trunk (Figure 1a). The second patient was an 89‐year‐old man who noticed 2 days after the first BTN162b2 vaccination itchy erythematous/bullous lesions on his entire integument. Neither of the patients reported intake of any new medications or other newly diagnosed conditions prior to the AIBDs.

Figure 1.

(a) Clinical presentation of COVID‐19 vaccine‐induced bullous pemphigoid in the first patient. (b) On haematoxylin–eosin histology, both patients displayed slight spongiosis and subepidermal blisters with lymphocytic and eosinophilic infiltrates. (c, d) Representative immunofluorescence confocal microscopy images of normal skin of a control patient (c) and lesional skin of patient 1 (d) showing spike protein immunoreactivity. However, there was only a very likely unspecific immunoreactivity in the horny layer of the patient and control skin. (e) T‐cell receptor (TCR) analysis of patient 1. Classical TCR repertoire metrics: richness gives the number of unique TCR rearrangements within a sample; iChao1 is an estimator of the lower bound of the true richness of a sample; Simpsons’ diversity reflects the probability that two randomly picked sequences from a sample are the same; clonality reflects the abundance of clonally expanded T‐cell clonotypes within a sample. PBMC, peripheral blood mononuclear cell. (f) Frequency of the top six expanded T‐cell clonotypes within the whole TCR repertoire including blood and tissue of a patient. TCRMatch was used to infer the antigen specificity of the respective clonotype. (g) Clonotypes were annotated with the antigen specificity with the highest score according to TCRMatch. Depiction of the results from application of the GLIPH algorithm. Global similarities are marked in orange and local similarities in blue. Additional TCR sequences that recognize the SARS‐CoV‐2 spike protein (VDJdb) were subjoined to infer antigen specificity.

In both cases, subepidermal clefts were demonstrated on routine histology (Figure 1b). In both patients, direct immunofluorescence on frozen sections revealed linear deposits of IgG and C3 at the basement membrane zone. Indirect immunofluorescence showed bandlike IgG deposits on the epidermal side in both patients. In both cases, enzyme‐linked immunosorbent assay revealed highly elevated autoantibody levels against BP‐180 (365 U mL⁻¹ and 115 U mL⁻¹, normal range < 20) and BP‐230 (223 U mL⁻¹ and 41 U mL⁻¹, normal range < 20). Hence, both patients were diagnosed with BP. Both were successfully treated with a tapered systemic prednisolone regimen.

For immunofluorescence confocal laser scanning microscopy imaging, we used the antibody SARS‐CoV/SARS‐CoV‐2 Spike Protein S2 [mouse/IgG1, monoclonal antibody (clone 1A9), catalogue no. MA5‐35946 (Thermo Fisher Scientific, Waltham, MA, USA)]. We did not observe immunoreactivity for SARS‐CoV‐2 spike protein in the subepidermal compartment. There was only a very likely unspecific immunoreactivity in the horny layer of the patient and control skin specimens (Figure 1c, d). High‐throughput sequencing of the T‐cell receptor (TCR)Vβ CDR3 and TCR repertoire was investigated in lesional skin tissue and isolated peripheral blood mononuclear cells. Within the lesions of both patients, we observed a high clonality of T cells, with the top expanded T‐cell clone contributing almost 20% of all TCR transcripts (Figure 1e).

Using TCRMatch ³ to estimate the antigen specificity of the expanded T‐cell clonotype we found that several of the expanded T‐cell clones were indeed reactive to SARS‐CoV‐2 (Figure 1f). Using the GLIPH algorithm, ⁴ we identified several TCR clusters derived from T cells in both lesional tissue and peripheral blood that co‐clustered with the added spike‐protein‐reactive TCRs (Figure 1g). Importantly, by contrast, in control tissues obtained prior to the COVID‐19 pandemic or SARS‐CoV‐2 vaccinations, SARS‐CoV‐2 spike‐protein‐reactive T cells were not observed (data not shown).

The similarities with respect to both timing and the clinical and molecular features in the cases presented here point to a causal relationship between the vaccination and BP. There are several published cases of vaccine‐induced BP, the majority involving influenza but more recently also COVID‐19. ¹ , ⁵ , ⁶ For SARS‐CoV‐2 vaccines, the target antigen is the surface spike protein, which is used by the virus to bind and fuse with host cells. When speculating on autoimmune mechanisms following SARS‐CoV‐2 infection one may particularly consider molecular mimicry. ⁷ , ⁸ We hypothesized that molecular mimicry may exist between basement‐membrane‐specific proteins (e.g. BP‐180, BP‐230) and the SARS‐CoV‐2 spike protein. However, using an antibody against the spike protein we could not confirm this hypothesis.

With respect to the TCR repertoire in lesional skin, we observed a marked clonal expansion of T cells in both patients with BP, indicating an ongoing adaptive immune response. However, we cannot exclude that this T‐cell expansion was an epiphenomenon due to the vaccination per se. The two bioinformatic approaches further suggested that these T‐cell responses were reactive to SARS‐CoV‐2‐derived epitopes. ³ , ⁴ Our TCRMatch results suggested that some of the expanded T‐cell clones detected in the patients might be reactive to other SARS‐CoV‐2‐derived epitopes including nucleocapsid proteins. However, whether these T‐cell clones might hint at an undocumented previous infection with SARS‐CoV2 or some other mechanism, whereby a spike protein vaccine may induce such T cells, remains unclear at this point.

Author Contribution

Thilo Gambichler: Investigation (equal); Visualization (equal); Writing‐review & editing (equal). Nazha Hamdani: Formal analysis (equal); Investigation (equal); Methodology (equal); Supervision (equal); Writing‐review & editing (equal). Heidi Budde: Investigation (equal); Methodology (equal); Writing‐review & editing (equal). Marcel Sieme: Investigation (equal); Methodology (equal); Visualization (equal); Writing‐review & editing (equal). Marina Skrygan: Investigation (equal); Methodology (equal); Supervision (equal); Writing‐review & editing (equal). Lisa Scholl: Investigation (equal); Visualization (equal); Writing‐review & editing (equal). Heinrich Dickel: Data curation (equal); Supervision (equal); Writing‐review & editing (equal). Bertold Behle: Data curation (equal); Investigation (equal); Writing‐review & editing (equal). Nomun Ganjuur: Data curation (equal); Investigation (equal); Writing‐review & editing (equal). Christina Scheel: Validation (equal); Writing‐review & editing (equal). Nessr Abu Rached: Data curation (equal); Investigation (equal); Writing‐review & editing (equal). Lennart Ocker: Formal analysis (equal); Investigation (equal); Writing‐review & editing (equal). Rene Stranzenbach: Investigation (equal); Supervision (equal); Writing‐review & editing (equal). Martin Doerler: Investigation (equal); Writing‐review & editing (equal). Lukas Pfeiffer: Investigation (equal); Methodology (equal); Software (equal); Visualization (equal); Writing‐review & editing (equal). Juergen Becker: Conceptualization (equal); Formal analysis (equal); Investigation (equal); Methodology (equal); Validation (equal); Visualization (equal); Writing‐review & editing (equal).