Perspective: Diagnostic laboratories should urgently develop T cell assays for SARS-CoV-2 infection.

Ameratunga, Rohan; Woon, See-Tarn; Jordan, Anthony; Longhurst, Hilary; Leung, Euphemia; Steele, Richard; Lehnert, Klaus; Snell, Russell; Brooks, Anna E S

INTRODUCTION Diagnostic tests play a critical role in the management of Sars-CoV-2, the virus responsible for COVID-19. There are two groups of tests, which are in widespread use to identify patients who have contracted the virus. The commonly used reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) test becomes negative once viral shedding ceases by approximately three weeks. Antibody tests directed to viral antigens become positive after the second week of infection. IgG antibody responses to the virus are muted in children, pregnant females and those with mild symptoms. IgA and IgM antibodies rapidly wane although IgG antibodies directed to the receptor-binding domain (RBD) of the spike (S) glycoprotein are more durable. Current data shows variability in the sensitivity of commercial and in-house antibody tests to SARS-CoV-2. AREAS COVERED The role of T cells in acute illness is uncertain but long-term protection against the virus may rely on memory T cell responses. Measuring memory T cell responses is important for retrospective confirmation of cases, who may have been infected early in the pandemic before reliable RT-qPCR tests were available and whose SARS-CoV-2 antibodies may have become undetectable. Relevant peer-reviewed published references from PubMed are included up to 15 March 2021. The reader is advised to seek up-to-date information on specific aspects of COVID-19 which are changing on a daily basis. EXPERT OPINION After surveying the literature, the authors present the case for urgent development of diagnostic T cell assays for SARS-CoV-2 by accredited laboratories.