Sequential Shifting in T-helper and T-cytotoxic Subset Cell Population in Mild and Severe COVID-19 Patients Infected With Variant B.1.61

Aim: Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) modulates antiviral immunity via T cells, but whether these cells are active or abundant in coronavirus disease 2019 (COVID-19) patients is unknown. The present study aimed to investigate the temporal shifting in the T-cell population and their subsets, T-Helper (Th) cell (CD4) and T-Cytotoxic (Tc) cell (CD8) in COVID-19 patients. Method: Thirty confirmed COVID-19 patients (nasal swab reverse transcription-polymerase chain reaction (RT-PCR) confirmed) were enrolled. On the basis of oxygen saturation (SpO2) levels, patients were stratified into two categories: (i) mild (n=11) having fever and SpO2 level >95%, and (ii) severe (n=19) on the ventilator, and in the intensive care unit (ICU) as per the Indian Council of Medical Research (ICMR) guidelines. Thirty age-sex-matched controls without infectious diseases unrelated to COVID-19 were also enrolled in the study. Patients with inflammatory diseases and severe comorbidities that compromise immunity were excluded from the study. Immunophenotyping flow cytometry assay was used to evaluate T-cell viability, Th, and Tc cells population in mild and severe COVID-19 patients on day 1 (at admission) and day 4 (decreasing the infection load) in the second COVID-19 wave (variant: B.1.61). Categorical variables were expressed as frequency and percentage and p-values were calculated by Chi-square test. All the variables were represented in median and Q1 (25 percentile) and Q3 (75 percentile). The Mann-Whitney test was used to compare the study groups. The Δ mean differences were calculated by using the Paired samples t-test. The statistically significant level was taken as p<0.05. Results: Hemoglobin, total leukocyte count (TLC), lymphocytes, monocytes, and eosinophils were significantly reduced in patients (p<0.05). A significant decrease of CD4 and CD8 cells in severe COVID-19 patients vs. controls (CD4, median 49; CD8, 40.12; p>0.05) was seen. Th-EM (effector memory)-Tim-3 (T-cell immunoglobulin domain and mucin domain 3)+ was significantly higher (p=0.002) however, Tc-EMRA (effector memory cells re-expressing)-Tim-3+, Tc-Naive-Tim-3+, Tc-EM-PD1+ and Tc-CM (central memory)-Tim-3+ significantly reduced (p<0.05) in mild COVID-19 patients than controls. Similarly, in severe COVID-19 patients, Th-EMRA-Tim-3+, Th-Naive-PD1+, Th-EM-PD1+, Th-EM-Tim 3+ and Th-CM-Tim-3+ showed a significant reduction (p<0.05) and Tc-EMRA-Tim-3+, Tc-Naive-Tim-3+, Tc-EM-PD1+, and Tc-CM-Tim-3+ showed similar results. In mild vs. severe group, decreased T-cells (p=0.001), Th-EMRA-Tim-3+ (p=0.024), and Th-Navie-Tim-3+ (p=0.005), and significantly increased (p<0.05) Tc-Naive-Tim3+ (p=0.001), Tc-EM-Tim-3+ (p=0.031), and Tc-CM-Tim-3+ (p=0.08) were observed. Severe COVID-19 patients showed a significant increase in Th-Naive-Tim3+ (day 4-day 1; δ43, p=0.019), Th-EM-Tim3+ (δ 16.24, p=0.033), and Th-CM-Tim3+ (δ 13.57, p=0.041). Conclusion: T-cell populations and CD8 subset help to differentiate the mild and severe COVID-19 patients. Monitoring T cells, especially CD8 subset changes, has important implications for diagnosing and treating mild and severe patients being critically ill.