Specificity of ex vivo–expanded CST. Following 10 to 12 days of culture, specificity of CD4 and CD8 T-cell populations for membrane, spike, and nucleocapsid proteins was assessed by intracellular cytokine staining for IFN-γ and TNF-α. (A) Subject 2 demonstrates a CD4-predominant response targeting structural proteins. (B-C) Summary data of the response of expanded CD4⁺ T cells (B) and CD8⁺ T cells (C) in response to membrane, spike, and nucleocapsid proteins by intracellular cytokine staining was analyzed in convalescent donors (n = 11), and the percentage of T cells was compared with actin-stimulated controls via 2-tailed Student t test. *P < .05, **P < .01.