Discussion
In this study, we report the clinical occurrence of MDR with high
eosinophilia in severely ill COVID-19 patients and address whether MDR
in severe COVID-19 patients has a cellular and molecular signature that
differs from DRESS and MDR unrelated to COVID-19. IMC revealed that
CD8+ but T cells made up the majority of the T cell
infiltrate in COVID-MDR. Clustering analyses identified four
CD8+ T lymphocyte subpopulations, with the most
cytotoxic, proliferative subset being predominant in COVID-MDR. Also,
Mo/Mac in COVID-MDR had a highly activated phenotype. Spatial analysis
revealed that overall interactions patterns appeared similar among all
indications. Mediators of cytolysis pathways and eosinophil chemotaxis
were upregulated on an mRNA level in COVID-MDR skin. Proteomic immune
signatures in the blood widely differed between COVID-MDR, MDR and
DRESS, especially with respect to expression of eosinophil chemotaxis-,
type 2 inflammation-, Innate immunity-, and immunosuppression-related
proteins.
One striking finding of this COVID-MDR case series is that all patients
had particularly severe COVID-19 disease and all patients developed MDR
about 1 month after their initial COVID-19 diagnosis, a time point when
SARS-CoV2 is no longer detectable in nasopharyngeal swabs. SARS-CoV-2
had been previously detected in lesional skin of COVID-19 patients18 and we hypothesized
that the virus might directly impact MDR development. Since SARS-CoV-2
RNA was undetectable in lesional COVID-MDR skin, we now favor an
indirect impact of SARS-CoV-2 on COVID-MDR pathogenesis, possibly from
peripheral immune activation. Severe COVID-19 has been associated with
cytokine storm features, hemodynamic instability and multi-organ
failure30-36. In line
with these
studies30,37-39,
levels of cytokine storm-associated cytokines and chemokines were highly
increased in COVID-MDR. Moreover, several ‘cytotoxicity’ and
‘eosinophilic inflammation’ mediators were upregulated both in serum
(protein level) and lesional skin (mRNA level) of COVID-MDR patients.
These findings suggest that severe COVID-19 might impact the drug
reaction through activation of cytotoxic CD8+ T cells,
Mo/Mac and eosinophils.
By IMC, prominent CD8+ T cell infiltrates and highly
activated Mo/Mac clusters were characteristic of COVID-MDR.
Interestingly, a recent paper has identified dysfunctional
HLA-DRlowCD163high and
HLA-DRlowS100AhighCD14+ Mo in the blood of severely affected COVID-19
patients40. This
resembles the Mo/Mac phenotype that we identified in COVID-MDR.
Additional features that were unique to Mo/Mac in COVID-MDR was the very
high expression of CD16, CD206, and CD11c. The role of these Mo/Mac in
the pathogenesis of MDR in COVID-19 patients remains to be elucidated.
Specifically, whether they promote DDH by functioning as
antigen-presenting cells, or whether they are effector mediators of
inflammation or even trained immunity remains to be determined.
One limitation of our study is that small sample size impacts our
ability to determine the significance of the characteristic cell-cell
interactions observed between diagnostic groups. Nevertheless, this
study represents the first IMC neighborhood analysis in human skin. We
anticipate that IMC application in other allergic and inflammatory skin
conditions will shed new insights into cutaneous immune cell
interactions.
Apart from contributing to the understanding of COVID-MDR, our study
also provides new insights into DRESS and MDR unrelated to COVID-19.
Viral reactivation, especially human herpes virus 6 or Epstein-Barr
virus reactivation, are seen in about 75% of DRESS
cases41. In these
patients, activated peripheral CD8+ T lymphocytes
secrete large amounts of TNF and IFN-γ41. Our data show that
DRESS is characterized by a similar systemic inflammatory response as
COVID-MDR, although to a lesser extent. There is relatively little
existing data about the effector immune response in DRESS, but the few
studies that do exist, hint towards an aberrant T cell response, as
evidenced by increased serum granzyme
B42 and atypical T
cells 43. Our skin IMC
data did however not show prominent CD8+ T cell
infiltrates in DRESS supports a previous finding, that
CD16+ monocytes are depleted in DRESS lesional
skin44. Our results
also show that in comparison to HC, DRESS Mo/Macs have upregulation of
CD206 and CD163, and in comparison to MDR and COVID-MDR, there is an
upregulation of HLA-DR and CD370.
Taken together, MDR in severely ill COVID-19 patients is likely the
result of a hyperinflammatory immune response that culminates in
activation of Mo/Mac and highly cytotoxic CD8+ T
cells. These cutaneous findings are possibly initiated by or exacerbated
by a robust systemic COVID-19-induced immune response. Although our
characterization of the COVID-MDR was comprehensive, future studies with
larger patient cohorts are needed to verify these findings.