Understanding the T cell immune response in SARS coronavirus infection

Janice Oh, Hsueh-Ling; Ken-En Gan, Samuel; Bertoletti, Antonio; Tan, Yee-Joo

The SARS-CoV genome encodes four structural proteins: spike (S), envelope (E), membrane (M) and nucleocaspid (N). In addition, a set of unique accessory proteins (namely ORF 3a, 3b, 6, 7a, 7b, 8a, 8b and 9b) is also found. Functionally, the N protein packs the RNA into a helical nucleocapsid; while the S protein forms the characteristic projections on the virion surface for the attachment and entry into the host cells; and together, N, M and E control the assembly of the virion. At present, no significant homology has been found for the accessory proteins to the viral proteins of other coronaviruses; in fact, they were found to be dispensable for virus replication in cell culture despite contributing to viral pathogenesis. 14, 15 Neutralizing antibodies against SARS-CoV found in patients and animals infected with SARS-CoV block viral entry by binding to the S glycoprotein. 16 Besides the humoral response, the role of T cells in viral infections has been known to be just as important. Whilst neutralizing antibodies can prevent viral entry, the body also requires SARS-CoV specific CD4 1 T helper cells for the development of these specific antibodies. Similarly, CD8 1 cytotoxic T cells are important for the recognition and killing of infected cells, particularly in the lungs of infected individuals. Despite the increasing number of reports that investigated memory CD4 1 and CD8 1 T cell responses in recovered SARS patients, there is a lack of data that describes the kinetics of the T cell response during a SARS-CoV infection. This review will focus on the memory T cell studies and its possible implications on treatment and vaccine development. For easy reference, all the T cell epitopes identified are summarized in Table 1 .