Development and Clinical Validation of a Skin Test for In Vivo Assessment of SARS-CoV-2 Specific T-Cell Immunity

A novel skin test for in vivo assessment of SARS CoV 2 specific T cell immunity was developed using CoronaDerm PS, a multi epitope recombinant polypeptide encompassing MHC II–binding CD4+ T cell epitopes of the SARS CoV 2 structural proteins (S, E, M) and full length nucleocapsid (N). In silico epitope prediction and modeling guided antigen design, which was expressed in E. coli, purified (>95% purity), and formulated for intradermal administration. Preclinical evaluation in guinea pigs, mice, and rhesus macaques demonstrated a robust delayed type hypersensitivity (DTH) response at optimal doses (10–75 µg), with no acute or chronic toxicity, mutagenicity, or adverse effects on reproductive organs. An integrated clinical analysis included 374 volunteers stratified by vaccination status (EpiVacCorona, Gam COVID Vac, CoviVac), prior COVID 19 infection (Wuhan/Alpha, Delta, Omicron variants), and SARS CoV 2–naïve controls. Safety assessments across phase I–II trials recorded 477 adverse events, of which >88% were mild and self limiting; no severe or anaphylactic reactions occurred. DTH responses were measured at 24 h, 72 h, and 144 h post injection by papule and hyperemia measurements. Overall, 282/374 participants (75.4%) exhibited a positive skin test. Receiver operating characteristic analysis yielded an overall AUC of 0.825 (95% CI: 0.726–0.924), sensitivity 79.5% (95% CI: 75.1%–83.3%), and specificity 85.5% (95% CI: 81.8%–88.7%), with comparable diagnostic accuracy across vaccine and variant subgroups (AUC range 0.782–0.870). CoronaDerm PS–based skin testing offers a simple, reproducible, and low cost method for qualitative evaluation of T cell–mediated immunity to SARS CoV 2, independent of specialized laboratory equipment (Eurasian Patent No. 047119). Its high safety profile and consistent performance across diverse cohorts support its utility for mass screening and monitoring of cellular immune protection following infection or vaccination.