Comparable antigen-specific T cell responses in vaccinees with diverse humoral immune responses after primary and booster BBIBP-CorV vaccination

BBIBP-CorV exerts efficient protection against SARS-CoV-2 infection. However, waning vaccine-induced humoral immune responses after two-dose vaccination has significantly undermined durable immuno-protection. In this study, we have demonstrated that although anti-spike (S) antibody responses in BBIBP-CorV vaccinees exhibited three serotypes after 6 months including de novo sero-negative, sero-positive and sero-decay features, S-specific interferon-γ release as well as Th1 cytokine production in CD4+ and CD8+ T cells were comparable, especially in vaccinees without detectable neutralizing antibodies. Notably, regardless of dramatic increases in humoral immunity after booster vaccination, T cell responses targeting S protein from either wild type or Omicron remained stable before and after booster vaccination in all three serotype vaccinees. Our results thus illustrate that unlike fluctuating humoral responses viral-specific T cell responses are extremely stable after booster vaccination. Sustained T cell responses might be dedicated to rapid restore of antibody responses after booster vaccination.BBIBP-CorV可有效抵御严重急性呼吸综合征冠状病毒2（SARS-CoV-2）感染。然而，两剂次接种后疫苗诱导的体液免疫应答发生衰减，已显著削弱了长期免疫保护效力。本研究证实，尽管接种BBIBP-CorV的受试者在接种6个月后，其抗刺突（S）抗体应答可呈现三种血清型表型，即新发血清阴性、血清阳性及血清衰减型，但CD4+和CD8+ T细胞的S特异性γ干扰素释放水平以及Th1型细胞因子产生量均无显著差异，尤其是在未检测到中和抗体的疫苗接种者中。值得注意的是，尽管加强接种后体液免疫水平大幅升高，但在三类血清型的疫苗接种者中，针对野生型或奥密克戎（Omicron）S蛋白的T细胞应答在加强接种前后均保持稳定。由此可见，与波动的体液免疫应答不同，加强接种后病毒特异性T细胞应答极为稳定。持续存在的T细胞应答或可助力加强接种后抗体应答的快速恢复。