Strategies to improve T-cell responses
Firstly, SARS-CoV-2 vaccines, such as mRNA-based vaccine encoding SARS-CoV-2 antigen (S protein) [89, 90], adenovirus type 5-vectored COVID-19 (Ad5-nCoV) vaccine [91] and whole-cell inactivated virus vaccines [92] can efficiently trigger virus-specific T cell and humoral immune responses. Secondly, SARS-CoV-2-specific T cells can be isolated from convalescent COVID-19 individuals and expanded in vitro for adoptive T‐cell therapy [93]. However, the safety and efficacy of adoptive T‐cell therapy for COVID-19 patients need to be validated in clinical trials. Thirdly, the recombinant IL-7 has been shown to induce the proliferation of naïve and memory T cells and might help to resolve lymphopenia and can be used for clinical treatment of COVID-19 [94, 95]. Administration of IFN-β1 and IFN-β2 could also help to improve antiviral T-cell responses.