Persistent SARS-CoV-2 presence is companied with defects in adaptive immune system in non-severe COVID-19 patients

Bing Liu; Junyan Han; Xiaohuan Cheng; Long Yu; Li Zhang; Wei Wang; Lan Ni; Chaojie Wei; Yafei Huang; Zhenshun Cheng

Upon admission, PP patients received the same standard treatment in our hospital. After at least 7 days, 18 of them that were tested negative for SARS-CoV-2 in two consecutive examinations were retrospectively allocated to the PPN group, and 19 of them who remained positive at the same time point were designated as PPP patients. Of note, the PPP group have more males than the PPN group (86.4% [16 of 19] vs 50% [9 of 18]; p=0.02; Table 1 ). We did not find any differences in symptoms and laboratory findings for these two groups (supplementary Table 1 and 2). However, when lymphocyte subpopulations were examined, PPP patients were found to have significantly lower numbers of CD3 + T cells (p=0.001), CD4 + T cells (p=0.005), CD8 + T cells (p=0.003), and B cells (p=0.005), but higher proportion of NK cells (p=0.02) than PPN patients (Fig 1A and 1B) . Next, we determined the abnormalities for each parameters Lymphopenia was observed at illness onset in 72.8% of non-severe COVID-19 patients (the PA group) in our study, which is similar to those reported by Zhang et al [15] (75.4%), Mo et al [17] (73.5%), Wang et al [27] (70.3%), and Guan et al [2] (83.2%), suggesting the involvement of lymphocytes in the early phase of SARS-CoV-2 infection. Furthermore, lymphocyte count was reported to be correlated with disease severity. Significant higher numbers of lymphocytes were found in survivors versus non-survivors [4] , as well as critically ill versus severe [13, 14] , and severe versus non-severe cases [15, 16] . We focused on non-severe patients with persistent viral presence, and found that the PP group had markedly higher lymphocyte count (1.5 [1.3-1.8] vs 0.9 [0.7-1.3]; p<0.001) than the PA group, and were comparable to healthy subjects. This finding, together with alleviated symptoms and improvements of other laboratory findings, indicated that PP patients might be in the process of recovery, albeit their viral RNA were still tested positive. However, other parameters are required to determine if they were fully recovered. We therefore examined lymphocyte subsets and found that PPP patients had significantly lower numbers of CD3 + T cells (p=0.001), CD4 + T cells (p=0.005), CD8 + T cells (p=0.003), and B cells (p=0.005) than PPN patients (Fig 1A and 1B) . When compared with healthy subjects, PPP patients again exhibited much less CD3 + T cells (p=0.044), CD4 + T cells (p=0.034), and B cells (p=0.02) (Fig 2C and 2D ). Most strikingly, 10 PPN patients showed markedly increased CD3 + T cells (p=0.001), CD4 + T cells (p=0.002), CD8 + T cells (p=0.009), and B cells (p=0.008) after they turned negative for SARS-CoV-2. Together, these results suggest that measurement of these lymphocyte subpopulations could be used to distinguish non-severe patients with persistent viral presence from healthy subjects and those turned negative, and thus have clinical relevance for discharge management. Data are median (IQR) or n (%). P values were obtained from χ² tests , Fisher's exact tests, T tests or Mann-Whitney U tests, when appropriate. P < 0.05 was considered statistically significant (in bold).