ORIGINAL RESEARCH published: 23 June 2022 doi: 10.3389/fmed.2022.924267 Individuals With Higher CD4/CD8 Ratio Exhibit Increased Risk of Acute Respiratory Distress Syndrome and In-Hospital Mortality During Acute SARS-CoV-2 Infection Ana Pascual-Dapena 1,2 , Juan José Chillaron 3 , Gemma Llauradó 3 , Isabel Arnau-Barres 4 , Juana Flores 3 , Inmaculada Lopez-Montesinos 5 , Luisa Sorlí 5 , Juan Luis Martínez-Pérez 1,2 , Silvia Gómez-Zorrilla 5 , Juan Du 5 , Natalia García-Giralt 5 and Robert Güerri-Fernández 1,5,6* 1 Medicine and Life Sciences Department, Pompeu Fabra University, Barcelona, Spain, 2 Departament de Medicina, Universitat Autonoma de Barcelona, Barcelona, Spain, 3 Endocrinology Department, Hospital del Mar Institute of Medical Edited by: Research, Barcelona, Spain, 4 Geriatrics Department, Hospital del Mar Institute of Medical Research, Barcelona, Spain, Sara Manti, 5 Infectious Diseases Department, Hospital del Mar Institute of Medical Research, Barcelona, Spain, 6 Centro University of Catania, Italy de Investigación Biomédica en Red en Enfermedades Infecciosas, Ciberinfecc, Instituto de Salud Carlos III, Madrid, Spain Reviewed by: Jose Alberto Choreño-Parra, Instituto Nacional de Enfermedades Background: CD4/CD8 ratio has been used as a quantitative prognostic risk factor Respiratorias-México (INER), Mexico in patients with viral infections. This study aims to assess the association between in- Alejandro Vallejo, hospital mortality and at admission CD4/CD8 ratio among individuals with acute SARS- Ramón y Cajal Institute for Health Research, Spain CoV-2 infection. *Correspondence: Methods: This is a longitudinal cohort study with data of all consecutive patients Robert Güerri-Fernández rguerri@imim.es admitted to the COVID-19 unit at Hospital del Mar, Barcelona, Spain for ≥48 h between March to May 2020. The CD4+ CD8+ T-cell subset differentiation was assessed by Specialty section: flow cytometry at admission as well as a complete blood test. Patients were classified This article was submitted to Infectious Diseases – Surveillance, according to CD4/CD8 ratio tertiles. The primary outcome was in-hospital mortality and Prevention and Treatment, the secondary outcome was acute respiratory distress (ARDS). a section of the journal Frontiers in Medicine Results: A total of 338 patients were included in the cohort. A high CD4/CD8 ratio Received: 20 April 2022 (third tertile) was associated with a higher in-hospital mortality [adjusted Cox model Accepted: 06 June 2022 hazard ratio (HR) 4.68 (95%CI 1.56–14.04, p = 0.006), reference: second tertile HR Published: 23 June 2022 1]. Similarly, a high CD4/CD8 ratio (third tertile) was associated with a higher incidence Citation: Pascual-Dapena A, Chillaron JJ, of ARDS [adjusted logistic regression model OR 1.97 (95%CI 1.11–3.55, p = 0.022) Llauradó G, Arnau-Barres I, Flores J, reference: second tertile HR 1]. There was a trend of higher in-hospital mortality and Lopez-Montesinos I, Sorlí L, Luis Martínez-Pérez J, incidence of ARDS in patients within the first tertile of CD4/CD8 ratio compared with Gómez-Zorrilla S, Du J, the second one, but the difference was not significant. No associations were found with García-Giralt N and total lymphocyte count or inflammatory parameters, including D-dimer. Güerri-Fernández R (2022) Individuals With Higher CD4/CD8 Ratio Exhibit Conclusion: CD4/CD8 ratio is a prognostic factor for the severity of COVID-19, Increased Risk of Acute Respiratory Distress Syndrome and In-Hospital reflecting the negative impact on prognosis of those individuals whose immune response Mortality During Acute SARS-CoV-2 has abnormal CD8+ T-cell expansion during the early response to the infection. Infection. Front. Med. 9:924267. doi: 10.3389/fmed.2022.924267 Keywords: SARS-CoV-2, prognose, mortality, CD4/CD8 ratio, ARDS Frontiers in Medicine | www.frontiersin.org 1 June 2022 | Volume 9 | Article 924267 Pascual-Dapena et al. SARS-CoV-2 Mortality and High CD4/CD8 INTRODUCTION secondary outcome was acute respiratory distress syndrome (ARDS) defined as a PaO2 -to-FiO2 ratio < 200 and compatible SARS-CoV-2 has caused a world-wide pandemic, with more than alveolar X-Ray infiltrates. 400 million confirmed cases and over 5.8 million deaths until March 2022 (1). Ethics Considerations Since its first detection in December of 2019, several prognosis The Institutional Ethics Committee of Hospital del Mar of factors have been described. Some of them are directly associated Barcelona approved the study and due to the nature of the with uncontrolled immune response to the virus leading to retrospective data review and the emergent situation derived a hyperinflammatory status, and some other ones such as from the SARS-coV-2 pandemic, waived the need for informed hypoalbuminemia or myocardial injury, depend on the host consent from individual patients (CEIm 2020/9352). clinical response (2, 3). The impact of the virus in the immune system can be summarized as lymphopenia, which has been Statistical Analysis widely reported as a notable aspect of SARS-CoV-2 infection. Continuous variables are expressed as mean and standard This is common to other respiratory viral infections, including deviation or the median and interquartile range (IQR). influenza A H3N2 virus or human rhinovirus (4, 5). However, Qualitative variables are presented as frequencies (percentages). lymphopenia associated with SARS-CoV-2 infection is more Normality for baseline characteristics was evaluated by Shapiro– intense, it lasts longer (5, 6) and it seems to be more selective Wilk normality test. Quantitative data was analyzed by Kruskal– in T cell lineages, with a higher impact on CD8+ T cells (7, 8). Wallis test and Dunn’s test or Wilcoxon rank-sum (Mann– Notwithstanding, a larger wide-spread lymphopenia involving Whitney) test, and qualitative data was analyzed by chi-square CD4+ T cells, CD8+ T cells, B cells and natural killer cells has test or Fisher exact test, as required. Appropriate coefficient tests also been reported (9, 10). were used for correlation among various continuous variables. The CD4/CD8 ratio has shown relevance in chronic viral The association between the CD4/CD8 ratio and its tertiles infections such as HIV infection, in which the CD4/CD8 ratio and the primary outcome (in-hospital mortality) was assessed has been reported as a quantitative outcome reflecting the critical with unadjusted/adjusted Cox proportional hazards models. The role of both T-cells subsets in the HIV pathogenesis or disease reference group was the second tertile of CD4/CD8 ratio, for progression. Examination of CD4/CD8 ratio as a quantitative representing the most physiological range of values. Results are trait can be important to patient care as it might be used as a expressed as hazard ratio (HR) [95% confidence interval (CI)]. prognostic risk factor (11–13). The same model was explored with tertiles of CD4+ T-cells and This study aims to assess the association between in-hospital CD8+ T-cells. The association between the secondary end points mortality and at admission CD4/CD8 ratio in individuals with and the CD4/CD8 ratio and its tertiles was assessed by logistic acute SARS-CoV-2 infection, to elucidate if a T-cell subset regression. The area under curve (AUC)-receiver operating disbalance might be behind an abnormal response of the host characteristics (ROC) curve was obtained for the CD4/CD8 ratio against the virus. analyzed as a continuous variable. The level of significance in this study was set at a p ≤ 0.05 and CI of 95%. All statistical analyses were performed MATERIALS AND METHODS using STATA/MP V.14. Study Design and Patient Selection A longitudinal cohort study where data of all consecutive patients RESULTS admitted to the COVID-19 unit at Hospital del Mar, Barcelona, Spain for ≥48 h between March to May 2020 were collected. A total of 388 individuals admitted to COVID-19 unit were The study procedures have previously been described (3, 14). As included in the eligibility review, 210 (54%) males and 178 per protocol, the differentiation of CD4+ CD8+ T-cell subset was (46%) females. Median age was 63 years (IQR 52–75). Patients assessed in all admitted patients by flow cytometry at admission were divided into three groups according to the CD4/CD8 (day 1 of hospitalization), as well as a complete blood test. ratio tertile. Baseline characteristics of each group are shown in The single-cell suspensions were stained with Aqua-viability Table 1. Tertile 2 which encompasses the more physiological dye and PacBlue-anti-CD3 and ECD-anti-CD4 from Beckman- range of values (1.49–2.41; 15) was considered as reference Coulter (Brea, CA, United States); and APC-H7-anti-CD8 from for comparisons. This group showed the lowest rate of in- Becton-Dickinson (San Jose, CA, United States) according to hospital mortality, the lowest intensive care unit admissions manufacturers’ recommendations. Fluorescence-activated cell and the lowest acute respiratory distress syndrome (ARDS) sorter analysis was performed on a custom Becton-Dickinson incidence (Table 1). LSR II flow cytometer used for data acquisition and analyzed with Total lymphocyte count was not different between the three FlowJo (TreeStar, Ashland, OR, United States). A representative tertiles (p = 0.679), with a median in the lower limit of reference example of the gating strategy for the lymphocyte subsets is values of a normal hemogram (median 1.03 106 lymphocytes/ml, shown in Supplementary Figure 1. IQR 0.75–1.39), showing a common tendency to lymphopenia Patients were classified according to CD4/CD8 ratio tertiles. in all groups. The first tertile showed the lowest CD4+ T-cell The primary outcome was in-hospital mortality and the count and the third tertile showed the lowest CD8+ T-cell Frontiers in Medicine | www.frontiersin.org 2 June 2022 | Volume 9 | Article 924267 Pascual-Dapena et al. SARS-CoV-2 Mortality and High CD4/CD8 TABLE 1 | Baseline characteristics and the comparison according to the three different CD4/CD8 T-cell ratio tertiles. Overall CD4/CD8 T-cell ratio First tertile second tertile Third tertile p-value (≤1.494) (1.495–2.413) (≥2.414) n 388 130 129 129 Age, median (IQR) 63 (52–75) 65 (53–77) 62 (50–74) 64 (53–73) 0.409 Male, n (%) 210 (54%) 80 (62%) 66 (51%) 64 (49%) 0.082 Current smoker, n (%) 28 (7%) 10 (7%) 6 (4.6%) 12 (9.3%) 0.347 Days of symptoms, median (IQR) 7 (4–9) 7 (5–9) 7 (4–9) 7 (5–9) 0.732 In-hospital stay, days, median (IQR) 9 (6–16) 9 (6–15) 9 (5–16) 9 (6.5–17) 0.843 Comorbidities, n (%) Hypertension 215 (55%) 69 (53%) 66 (51%) 80 (62%) 0.173 Diabetes mellitus 95 (24%) 32 (24%) 36 (28%) 27 (21%) 0.427 Cardiovascular disease 45 (11.6%) 12 (9.2%) 13 (10%) 20 (15.5%) 0.261 Chronic respiratory disease 34 (8.7%) 11 (8.4%) 13 (10%) 10 (7.7%) 0.812 Chronic kidney disease 120 (30%) 50 (38%) 38 (29.5%) 32 (24.5%) 0.052 Chronic liver disease 30 (7.7%) 15 (11.5%) 6 (4.6%) 9 (7%) 0.134 Immune condition 16 (4%) 4 (3%) 5 (4%) 7 (5%) 0.411 Charlson comorbidity index No comorbidity 171 (44%) 58 (44%) 54 (42%) 59 (45%) 0.933 Medium-low (1–2) 125 (32%) 35 (27%) 51 (39.5%) 39 (30%) 0.083 High (≥3) 92 (24%) 37 (28.5%) 23 (18%) 32 (25%) 0.118 Clinical markers at onset, median (IQR) C-Reactive protein mg/dl 7 (3.1–15.6) 6.8 (3.7–13.4) 6.1 (2.7–14.5) 7.8 (2.8–19.2) 0.772 IL-6 pg/ml 40 46.6 33.8 39.3 0.928 (13–83) (19.9–75.7) (13.2–83.8) (10–92) D-Dimer UI/l 765 870 650 825 0.018 (460–1,330) (520–1,550) (390–1,020)* (460–1,520) ‡ Creatinin mg/dl 0.93 0.94 0.9 0.93 0.329 (0.73–1.12) (0.74–1.14) (0.73–1.07) (0.73–1.14) Hemogram, median (IQR) Lymphocyte 106 count/ml 1.03 1.04 1.09 0.98 0.679 (0.75–1.39) (0.73–1.45) (0.74–1.41) (0.77–1.31) CD4+ T-cell (106 cells/ml) 0.380 0.285 0.417 0.492 <0.001 (0.250–0.609) (0.179–0.416) (0.280–0.609)* (0.331–0.743) † ‡ CD8+ T-cell (106 cells/ml) 0.199 0.295 0.211 0.127 <0.001 (0.123–0.345) (0.181–0.435) (0.150–0.339)* (0.079–0.191) † ‡ Severity parameters, median (IQR) MEWS 2 (1–3) 2 (1–3) 2 (1–3) 2 (2–3) 0.401 PaO2 -to-FiO2 ratio, 208 210 265 171 0.249 (112–310) (132–317) (92–316) (108–278) CURB-65 1 (0–2) 1 (0–2) 1 (0–2) 1 (0–2) 0.157 Outcomes, n (%) In-hospital Mortality 33 (8.5%) 12 (9%) 5 (4%) 16 (12%)‡ 0.050 ARDS 99 (25%) 35 (27%) 24 (19%) 40 (31%) 0.078 ICU-Admission 85 (21%) 29 (22%) 25 (19%) 31 (24%) 0.674 Data are given as median (IQR) or n (%) unless otherwise indicated. CURB-65, confusion, urea >7 mmol/L, respiratory rate $30/min, low blood pressure #90/60 mm Hg, and age 65 years; FiO2 , fraction of inspired oxygen; MEWS, Modified Early Warning Score; PaO2 , arterial partial pressure of oxygen. *P < 0.05 for second tertile compared with first tertile. † P < 0.05 for third tertile compared with first tertile. ‡ P < 0.05 for third tertile compared with second tertile. count, suggesting that the abnormal CD4/CD8 ratio was due to reference second tertile. However, these differences were not depletion of CD4+ T-cells or lack of expansion of CD8+ T-cells, sustained after multivariate adjustment. respectively, and not because of an anomalous expansion of Additionally, no significant differences were observed among one of the cell-types. No significant differences in inflammatory tertile groups in the severity scores at admission, nor in the markers were found among groups, except for D-dimer levels main comorbidities. In spite of not being different across all which were higher in first and third tertiles (p = 0.018), showing tertiles, chronic kidney disease was significantly more prevalent an increased underlying infection activity compared to the in patients with lower ratios (first tertile) when compared to the Frontiers in Medicine | www.frontiersin.org 3 June 2022 | Volume 9 | Article 924267 Pascual-Dapena et al. SARS-CoV-2 Mortality and High CD4/CD8 TABLE 2 | Adjusted models for in-hospital mortality and ARDS risk according to increase in mortality. Thus, higher CD4/CD8 ratios (third tertile) the CD4/CD8 T-cell ratio tertiles. was significantly associated with increased risk of in-hospital In-hospital mortality Hazard ratio CI (95%) p-value mortality [HR 4.42 (95% CI: 1.36–12.55); p = 0.005] respect to second tertile (Table 2). We also found this trend in lower ratios First tertile (Ref: 1, second tertile) 2.16 0.71 6.58 0.175 (first tertile), but without statistical significance as compared to Third tertile (Ref: 1, second tertile) 4.68 1.56 14.04 0.006 the reference [HR 2.69 (95% CI: 0.94–7.69); p = 0.064]. This ARDS Odds ratio CI (95%) p-value association presents a comprehensive Kaplan–Meier log rank of 8.75 (p = 0.012). After adjusting by age, sex, comorbidity, and First tertile (Ref: 1, second tertile) 1.58 0.87 2.87 0.131 severity of the episode, the third tertile remained significantly Third tertile (Ref: 1, second tertile) 1.97 1.11 3.55 0.022 associated with in-hospital mortality [HR 4.68 (1.56–14.04); ARDS: Acute respiratory distress syndrome. p = 0.006] (Table 2). No association was found with mortality and Adjusted models. For In-hospital mortality we used a Cox Proportional Hazards total lymphocyte count or inflammatory parameters, including model, adjusted for age, sex, comorbidity, and severity of the episode. For ARDS we applied a logistic regression model adjusted for age, sex, D-dimer. No global differences between CD4/CD8 ratio and the comorbidity, and severity. incidence of ARDS were found (p = 0.078). However, when analyzing across tertiles, the third tertile with higher CD4/CD8 ratio showed an increased incidence of ARDS after adjusting by highest ratios (third tertile; p = 0.018), but showed no differences age, sex and comorbidity [OR 1.97 (95% CI: 1.11–3.55); p = 0.022] when compared to the reference tertile. than the reference group. There was no association between We found a significant association between CD4/CD8 ratio ARDS and lower ratios (p = 0.131). and in-hospital mortality [HR1.08 (95%CI: 1.03–1.41); p = 0.002]. Several sensitivity analyses were performed, creating models Each unit increase in the ratio was associated with an 8% that controlled for specific comorbidities like chronic kidney FIGURE 1 | (A) Unadjusted Hazard ratio for In-hospital mortality (Cox Proportional Hazards model) for CD4/CD8 ratio tertiles, CD4 tertiles, and CD8 tertiles. (B) Adjusted Hazard ratio by age, sex, comorbidity, and severity for in-hospital mortality (Cox Proportional Hazards model) for CD4/CD8 ratio tertiles, CD4 tertiles, and CD8 tertiles. Frontiers in Medicine | www.frontiersin.org 4 June 2022 | Volume 9 | Article 924267 Pascual-Dapena et al. SARS-CoV-2 Mortality and High CD4/CD8 disease, inflammatory markers, as well as creating an alternative A division of groups (considering standard measures of CD4/CD8 ratio: <1.0, 1.0–2.5, >2.5, instead of tertiles). All analyzes yielded similar findings that are in favor of those already presented (data not shown). In an alternative exploratory model with the same adjustment but considering CD4 and CD8 tertiles, no association was found with in-hospital mortality (Figure 1). Receiver Operating Characteristics curves and AUCs were used to assess the discriminative accuracy of the CD4/CD8 ratio on mortality (Figure 2A) and ARDS (Figure 2B). In this case, the CD4/CD8 ratio was analyzed as a continuous variable. The AUC (95% CI) for discriminating mortality was 0.56 (0.44–0.68), standard error = 0.061. Using the best cut-off point of 2.027 in the CD4/CD8 ratio, the sensitivity was 57.6% with a specificity of 58.03%. The AUC (95% CI) for discriminating ARDS was 0.50 (0.43–0.57), standard error = 0.036, hence the model using lineal values of the CD4/CD8 ratio has no discrimination capacity to distinguish between patients with or without ARDS. B DISCUSSION We report an association between the CD4/CD8 ratio and in-hospital mortality due to acute SARS-CoV-2 infection, regardeless of total lymphocyte count. Higher ratios (third tertile), which demonstrated lack of CD8+ T cell expansion, were significantly associated with mortality, but also lower ratios (first tertile) showed a trend to worse prognosis. An abnormal CD4/CD8 ratio is often viewed as clinically relevant (16–18), it rarely measures below 1.0 or above 2.5 (15) and its disbalance by excess or defect always offers insights about immune malfunction. There is evidence that the CD4/CD8 ratio is genetically controlled in healthy humans (15, 19) and in the case of sarcoidosis, for example, a higher CD4+/CD8+ ratio is FIGURE 2 | ROC curve for the CD4/CD8 ratio: (A) The best cutoff for found in patients who carry HLA-DRB1∗ 03 (19). mortality discrimination is ≥ 2.027 Sensitivity: 57.58% Specificity: 58.03%; (B) Indeed, the CD4/CD8 ratio has been used clinically in the best cutoff for ARDS discrimination is ≥ 1.945 Sensitivity: 48.48% Specificity: 53.98%. different scenarios: For example in the diagnosis of sarcoidosis and in chronic granulomatours diseases where a depletion in CD8+ T-cells leading to a higher CD4/CD8 ratio seems to be protective to worse disease presentations (19). Conversely, in during the acute infection. There is also a trend in the case of HIV infection, the CD4/CD8 ratio is abnormally low (20). This the lower tertile of the CD4/CD8 ratio which could be taken shows on the one hand, the damage that the infection induces into consideration. in the CD4+ T-cell compartment, and on the other hand, the In our cohort, individuals with higher CD4/CD8 ratio levels restoration of the immune system after starting antiretroviral had lower CD8+ T-cell levels, showing an inadequate expansion treatment, which sometimes restores CD4+ T-cells correctly but of CD8+ cytotoxic T-cells, while those with lower CD4/CD8 ratio favors an over-expansion of CD8+ T-cell compartment (12, 21, levels had lower CD4+ T-cell levels (not an abnormal expansion 22). Thus, a CD4/CD8 ratio below 1 in individuals with HIV of CD8+ T-cells). under antiretroviral therapy shows an incomplete and abnormal Therefore, the absence of an adequate expansion of CD8+ reconstitution of the immune system (12, 23, 24). These low T-cells, leading to higher CD4/CD8 ratios, has a deleterious ratios have been associated with worse outcomes like increased impact on the prognosis of the infection in terms of in-hospital cardiovascular events, long-term complications, and all-cause mortality but also in ARDS incidence (13, 25). mortality (18). Hence, there are clinical scenarios in which a This highlights the determining role of cytotoxic cellular depletion in CD8+ T-cells can be beneficial, and others where an immunity in the response in the acute phase of infection, setting expansion can be detrimental. its importance as keystone for a first line defense against SARS- A particular scenario occurs in SARS-CoV-2 infection where, CoV-2 infection. Although this fact has been reported by some as we report, the highest tertile of CD4/CD8 ratio (with authors, the evidence remained inconclusive (26, 27) or was based values > 2.4) is associated with a higher risk in-hospital death in small populations (28). Frontiers in Medicine | www.frontiersin.org 5 June 2022 | Volume 9 | Article 924267 Pascual-Dapena et al. SARS-CoV-2 Mortality and High CD4/CD8 We can infer that an impaired CD8+ T-cell response with whose immune response is disbalanced with an abnormal CD8+ low cell clonal expansion, may lead to a poorer infection control T-cell depletion during the early response to the infection. This and consequently worse prognosis, as opposed to a high and is different to other viral infections such as HIV, for which robust clonal expansion of this subset of T-cell that may be persistently low CD4/CD8 ratio is associated with worse outcome associated with milder forms of the disease (29, 30). In fact, an and increased risk of non-AIDS (18), or systemic diseases early development of a cytotoxic CD8+ T cell response, typically like sarcoidosis, for which lack of expansion and high ratios observed within 7 days of symptoms and peaking at 14 days, is is advantageous. correlated with effective viral clearance (7) and mild disease (31). In this line, Zuani et al. studied the T-cell subset composition in the peripheral blood of COVID-19 survivors and non-survivors DATA AVAILABILITY STATEMENT (11). Analyzing CD8+ T-cell subpopulations, they observed lower counts in memory cells and effector memory cells re-expressing Some or all datasets generated during and/or analyzed during CD45RA (temra) among non-survivors with a lower absolute the current study are not publicly available but could be available CD8+ T-cell count (11). from the corresponding author on reasonable request. Notably, our patients with lower CD8 levels leading to a higher CD4/CD8 ratio did not present a more severe acute presentation of infection nor more inflammation at admission to the hospital ETHICS STATEMENT when comparing to the other groups. It reflects the important role of the CD8+ T-cell subset in controlling the infection in its early The studies involving human participants were reviewed and stages, before an hyperinflammatory state has been established. approved by Ethics Committee PsMar CEIm 2020/9352. Written However, we also found a trend to a worse prognosis among informed consent for participation was not required for this the individuals in the lowest tertile of CD4/CD8 ratio. Similarly study in accordance with the national legislation and the to what happens in HIV infection inadequate and persistent institutional requirements. expansion of CD8+ T-cells can lead to an excessive uncontrolled immune response that can also affect the prognosis of the SARS- CoV-2 infection. AUTHOR CONTRIBUTIONS In fact, individuals with the lowest or highest CD4/CD8 ratio have worse prognosis than individuals within the second tertile. RG-F, AP-D, and JC conceptualized and conducted the study. This could be related to the fact that patients within the lowest AP-D, RG-F, JC, and NG-G revised methodology and did data tertile also have a trend increased mortality. Hence, the risk analysis. IA-B, IL-M, JL, SG-Z, GL, and JD contributed with of a poorer prognosis is determined by the fact of having an recruitment and data curation. All authors have revised and unbalanced CD4/CD8 out of the normal range. edited the final manuscript. This study has some limitations that must be stated. Firstly, it is a single-center study, with the consequent limited population. Also, the retrospective nature of the study does not allow FUNDING us to establish causality between the CD4/CD8 ratio and the outcome. In addition, only CD4+ or CD8 T-cells global count This work received support and funding from Centro de were analyzed. Further studies to evaluate how naïve, effector Investigación Biomédica en Red de Fragilidad y Envejecimiento memory cells and other subpopulations are associated with Saludable (CIBERFES; grant number CB16/10/00245), FEDER worse prognosis, pinpointing the underlaying mechanisms for funds, and the FIS Project from Instituto de Salud Carlos III, the depletion of CD8+ Tcells and broadening our findings. Ministerio de Ciencia e Innovación (grant number PI16/01860 This study also presents some strengths. Importantly, samples and PI19/00019). “PI19/00019” and “PI16/01860”, funded by are consistently collected at admission for all patients, therefore Instituto de Salud Carlos III (ISCIII) and co-funded by the not generating bias and being a good representation of patients European Union. who need hospitalization due to COVID-19. Likewise, the healthcare was provided under the same guidelines by the same group of healthcare providers, eliminating variability that could SUPPLEMENTARY MATERIAL lead to difference in outcomes. In conclusion, CD4/CD8 ratio is a prognostic factor for The Supplementary Material for this article can be found acute SARS-CoV-2 infection independent of CD4 or CD8 alone, online at: https://www.frontiersin.org/articles/10.3389/fmed. reflecting the negative impact on prognosis of those individuals 2022.924267/full#supplementary-material REFERENCES 2. Arnau-Barrés I, Pascual-Dapena A, López-Montesinos I, Gómez-Zorrilla S, Sorlí L, Herrero M, et al. Prevalence and prognostic value of myocardial injury 1. World Health Organization [WHO]. COVID-19 Weekly Epidemiological in the initial presentation of SARS-Cov-2 infection among older adults. J Clin Update. Geneva: World Health Organization (2022). Med. 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Zaman MM, Recco RA, Raguthu L, Likki S, Reddy S. Characteristics of and do not necessarily represent those of their affiliated organizations, or those of HIV-1-infected patients with CD4/CD8 lymphocyte ratio normalization on the publisher, the editors and the reviewers. Any product that may be evaluated in antiretroviral therapy. AIDS Patient Care STDS. (2000) 14:647–9. doi: 10.1089/ this article, or claim that may be made by its manufacturer, is not guaranteed or 10872910050206568 endorsed by the publisher. 17. Pahwa S, Read JS, Yin W, Matthews Y, Shearer W, Diaz C, et al. CD4 +/CD8 +T cell ratio for diagnosis of HIV-1 infection in infants: women and Copyright © 2022 Pascual-Dapena, Chillaron, Llauradó, Arnau-Barres, Flores, infants transmission study. Pediatrics. (2008) 122:331–9. doi: 10.1542/peds. Lopez-Montesinos, Sorlí, Luis Martínez-Pérez, Gómez-Zorrilla, Du, García-Giralt 2007-2308 and Güerri-Fernández. This is an open-access article distributed under the terms 18. Serrano-Villar S, Sainz T, Lee SA, Hunt PW, Sinclair E, Shacklett BL, et al. HIV- of the Creative Commons Attribution License (CC BY). The use, distribution or infected individuals with low CD4/CD8 ratio despite effective antiretroviral reproduction in other forums is permitted, provided the original author(s) and the therapy exhibit altered T cell subsets, heightened CD8+ T Cell activation, copyright owner(s) are credited and that the original publication in this journal and increased risk of non-AIDS morbidity and mortality. PLoS Pathog. (2014) is cited, in accordance with accepted academic practice. No use, distribution or 10:e1004078. doi: 10.1371/journal.ppat.1004078 reproduction is permitted which does not comply with these terms. Frontiers in Medicine | www.frontiersin.org 7 June 2022 | Volume 9 | Article 924267