IL-6 combined with CD8+ T cell count early predict in-hospital mortality for patients with COVID-19

METHODS. A total of 1,018 patients confirmed COVID-19 were enrolled in our retrospective study from two centers. The data of clinical features, laboratory tests, immunological tests, radiological findings, and outcomes were collected. Univariate and multivariable logistic regression analysis were performed to evaluate factors associated with in-hospital mortality. Receiver operator characteristic (ROC) curves and survival curves were plotted to evaluate the clinical usefulness.


survival patients with COVID-19
3 Socio-demographic and clinical characteristics of COVID-19 patients in this cohort are 4 shown in Table 1. We detected T lymphocyte subsets and plasma cytokine levels in 5 enrolled patients. The counts of all T lymphocyte subgroups were markedly lower in the 6 non-survivor group than in the survivor group (P<0.001), especially in CD8 + T cells with 7 less than half the count (96.89 vs. 203.98 cells/μL, P<0.001) ( Table 2). The serum levels 8 of all tested cytokines on admission, including IL-2R, IL-6, IL-8, IL-10, and TNF-α, were 9 significantly higher in the non-survivor group (P<0.001). Among them, IL-6 was elevated 10 most significantly, with an upward trend of more than ten times (56. 16 vs. 5.36 pg/mL, 11 P<0.001). As shown in Figure 1A, the area under curve (AUC) derived from CD8 + T cells 12 was much larger than that derived from CD3 + cells or CD4 + cells (AUC CD8 + =0.832[0.804- 14 As shown in Figure 1B, the AUC of IL-6 (0.899[0.878-0.920]) was larger than that of other 15 cytokines tested (P<0.001), such as ), ]), 16 IL-10(0.748[0.704-0.791]), and ). Therefore, we assumed that 17 CD8 + T cell counts and IL-6 are the two most important indicators associated with in- 18 hospital mortality among all the tested immunologic parameters, including T cell subsets 19 and cytokines. Additionally, we also investigated the correlation between CD8 + T cell 20 counts and inflammatory status. Our results showed that plasma IL-6 levels in patients with 21 COVID-19 were positively correlated with plasma C-reactive protein (CRP); (R 2 = 0.424, 22 P < 0.001); (Figure 2A). A significant negative correlation was found between CD8 + T 23 cell counts and IL-6 levels (R 2 = 0.255, P <0 .001); ( Figure 2B). The plasma CRP levels 1 in patients with COVID-19 were negatively correlated with CD8 + T cell counts (R 2 = 0.294, 2 P < 0.001); ( Figure 2C). These findings showed that CD8 + T cell counts were negatively 3 correlated with the inflammatory indicators of CRP and IL-6. Univariate logistic regression analysis was performed to investigate the risk factors 8 associated with in-hospital mortality in patients with COVID-19. On the basis of the ROC 9 curve for CD8 + T cells, the cutoff value was defined from Youden's index as 165 cells/µL. 10 The count of CD8 + T cells below 165 cells/μL was regarded as low. We defined a high 11 concentration of IL-6 to be more than 20 pg/mL, according to a previous study (6). Then, 12 by multivariable logistic regression analysis, two indicators were identified to be 13 independent risk factors associated with in-hospital mortality, including IL-6 >20 pg/mL 14 (OR=9.781; 95% CI, 6.304-15.174; P<0.001) and CD8 + T cell counts <165 cells/μL 15 (OR=5.930; 95% CI, 3.677-9.562; P<0.001), after adjusting for confounding factors 16 including age, sex, and underlying diseases (hypertension, coronary heart disease, diabetes 17 mellitus, and underlying pulmonary diseases) ( Table 3).

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In groups I to IV, the proportion of patients with shock was 6 (1.2%), 20 (20.4%), 21 14 (10.3%), and 116 (50.4%), respectively. The number of deaths among the four groups were 15 6 (1.2%), 22 (22.4%), 29 (14.3%), and 144 (62.6%) in sequence. However, we observed 16 that the hospitalization time of group IV was not extended more significantly than that of 17 group II or III as the majority of individuals in group IV were non-survivors with shorter 18 survival times.

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In addition, in group IV, the white blood cell and neutrophil counts as well as the levels of  Early in-hospital mortality prediction of IL-6 combined with CD8 + T cell count in 5 patients with COVID-19 6 Kaplan-Meier survival curves indicated that groups I to IV had different survival times 7 (Figure 3). Compared to group I, the patients from the other three groups had worse 8 survival times (P<0.001). More importantly, the patients from group IV had a much shorter 9 survival time than those from groups II or III (P<0.001). There was no statistical difference 10 between groups II and III (P=0.205) (Figure 3). Moreover, the ROC curve of the model  (1, [7][8][9] However, studies on the association between immunologic indexes and 3 outcomes of COVID-19 are lacking. This study is the first investigation to discover the role 4 of these two indicators, IL-6 elevation and CD8+ T cell count reduction, in contributing to 5 the outcome of COVID-19. We also attempted to stratify patients into more accurate 6 prognostic groups. It is very important for clinicians to better understand immunologic 7 dysregulations in fatal cases and provide potential target interventions. 8 Flow cytometry analysis indicated that CD3 + , CD4 + , and CD8 + T cell counts were 9 significantly lower in non-survivors than in survivors. The absolute count of CD8 + T cells 10 was below 100 cells/µL in non-survivors, which is less than half of the total number of 11 surviving cells. Furthermore, an interesting finding in our study is that the AUC of the 12 CD8 + T cell subset was larger than that of the CD3 + or CD4 + T cell subset. These findings 13 indicated a more obvious change in CD8 + T cells in non-survivors with COVID-19. 14 Multivariable analysis indicated that lower CD8 + T cell counts were an independent 15 mortality related risk factor in COVID-19 patients after adjusting for confounding factors 16 including age, sex, and underlying diseases (hypertension, coronary heart disease, diabetes 17 mellitus, and underlying pulmonary diseases). Therefore, it is reasonable to consider that 18 CD8 + T cell counts is a more important risk factor for predicting mortality than CD4 + T 19 cells or total CD3 + T cells in patients with COVID-19. These results also support the need 20 for lymphocyte classification tests and suggest that CD8 + T cells are more vulnerable to 21 the effects of SARS-CoV-2 infectious patients. Similarly, the reduction of CD8 + T cell 22 counts in our cohort was in agreement with other studies that have examined these markers. 23 Chen et al. described the immunologic features in severe and moderate COVID-19, and 1 found that SARS-CoV-2 infection might affect CD4 + T and CD8 + T cell numbers as well 2 as IFN-γ production (2). A study also indicated that both helper T cells and suppressor T 3 cell numbers were significantly decreased in severe COVID-19 patients, while the 4 percentage of naïve helper T cells was increased (10). Previous studies have found  CoV-specific CD8 + T cell responses in most infectious individuals, and the level of T cell 6 response in patients with MERS was related to disease severity (11,12). In addition, 7 another team discovered a similar phenomenon where depletion of CD8 + T cells facilitated 8 hosts at risk of MERS-CoV-induced infection (13) Our results may provide a potential 9 strategy for later therapy targeting CD8 + T cell activation in COVID-19 patients. trend also occurred in TNF-α, IL-8, and IL-10 in our study. This result was documented in 23 another study, which showed that severe COVID-19 cases had higher levels of IL-2R, IL-1 6, IL-10, and TNF-α than moderate cases (2, 3). Although both IL-8 and IL-10 showed a 2 significant increase, the values did not exceed the upper limit, suggesting their limited 3 value. Our results showed that the AUC of IL-6 was larger than that of IL-2R, 4 or TNF-α. Furthermore, multivariate analysis indicated that increased levels of IL-6 were 5 an independent risk factor that contributed to mortality in patients. Therefore, IL-6 was  In this cohort, individuals were divided into four groups according to the level of IL-22 6 and CD8 + T cell counts. Median age in different sections, comorbidities (hypertension 23 and diabetes mellitus, and vital signs (T, HR, and RR) were significantly different among 1 the four groups. The patients from group IV had higher white blood cell, neutrophil, d-2 dimer, LDH, and SOFA scores as well as lower lymphocytes and platelets. These indicators 3 were confirmed to be associated with the death of patients with COVID-19 in recent studies 4 (9,21). The proportion of patients who had ventilation (NPPV and IMV), ICU admission, 5 shock, and death in group IV was significantly higher than those in any other group. The 6 time of hospital stay or time of onset to discharge or death in group IV was not shown to 7 be longer than that of any other group. More importantly, the patients from group IV had 8 much worse survival than those in the other groups. Based on the evidence above, IL-6 9 elevation combined with CD8 + T cell count reduction was found to be associated with poor 10 outcomes in patients with COVID-19. Through univariate and multivariate logistic 11 regression analysis of mortality related risks in patients with COVID-19, we confirmed 12 that IL-6 (>20 pg/mL) and CD8+T cell counts (<165 cells/μL) were two vital mortality-13 related risk factors. Therefore, we further incorporated them to build a model in order to 14 predict death risk. By ROC analysis, we found that our new model had a better ability to 15 predict in-hospital mortality earlier in comparison to the commonly used CURB-65 score 16 (age 65 years, respiratory rate, confusion, urea, blood pressure)(22). Therefore, we  research has limited generalizability as all the patients enrolled in our study were Chinese.

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The clinical features of patients might be different in other countries or areas. Additionally, 1 there may be some inherent biases by using this study format. Our results should be further 2 validated by a multiple-center, prospective study.

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In conclusion, via this two-center retrospective study of patients diagnosed with 4 COVID-19 in Wuhan, we first identified two reliable prognostic indicators, IL-6 (>20 5 pg/mL) and CD8+T cell counts (<165 cells/μL), which can accurately stratify patients into 6 risk categories and effectively predict mortality of patients with COVID-19. These two 7 indicators may serve as a guide to clinicians to evaluate patient prognoses, make 8 appropriate decisions, and optimize medical resources. imaging that showed obvious lesion progression within 24-48 hours >50%, critical: in 23 addition to the above symptoms, meets one of the following conditions: 1) respiratory 1 failure and required mechanical ventilation; 2) cases with shock; 3) cases with other organ 2 failure and required ICU monitoring treatment.
3 Data Collection 4 The data were collected from the hospital's electronic medical record system, which 5 included socio demographic information, comorbidities, clinical symptoms, routine  Disturbance of consciousness, 2. BUN> 7 mmol / L, 3. Respiratory rate≥ 30 times/min, 4.