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.