Figure 1. RNA- and protein-based biomarkers for biologic therapy selection and diagnosis.
Various methods exist for collecting biomarkers from the skin, including shave or punch biopsy or minimally invasive approaches such as tape stripping, superficial epidermal curettage, or microneedle patches. In addition, systemic biomarkers from the blood can be measured. RNA analysis techniques include RT-PCR, microarray, sequencing approaches, or in situ analysis using hybridization probes. Proteins can be analyzed by IHC/IF, immunoassay, MS-based methods, proximity extension, or aptamer-based methods for high-throughput proteomics. Each method of analysis is labeled with compatible collection methods on the basis of references in this review. The RNA or protein levels of different immunologic molecules or other molecular correlates could be used for rational selection of biologic therapy and to aid in the diagnosis of CIRs. CIR, clinically/histopathologically indeterminate rash; IF, immunofluorescence; IHC, immunohistochemistry; RISH, RNA in situ hybridization; scRNA-seq, single-cell RNA sequencing; MS, mass spectrometry.