Cross-reactive CD4+ T cells enhance SARS-CoV-2 immune responses upon infection and vaccination. - Loyal L; Braun J; Henze L; Kruse B; Dingeldey M; Reimer U; Kern F; Schwarz T; Mangold M; Unger C; Dörfler F; Kadler S; et al. (Science (New York, N.Y.), 2021)