key: cord-0916611-068nqimz
authors: Rajamanickam, Anuradha; Pavan Kumar, Nathella; Pandiaraj, Arul Nancy; Selvaraj, Nandhini; Munisankar, Saravanan; Renji, Rachel Mariam; Venkataramani, Vijayalakshmi; Murhekar, Manoj; Thangaraj, Jeromie Wesley Vivian; Muthusamy, Santhosh Kumar; Chethrapilly Purushothaman, Girish Kumar; Bhatnagar, Tarun; Ponnaiah, Manickam; Ramasamy, Sabarinathan; Velusamy, Saravanakumar; Babu, Subash
title: Characterization of memory T cell subsets and common γ−chain cytokines in convalescent COVID‐19 individuals
date: 2022-03-08
journal: J Leukoc Biol
DOI: 10.1002/jlb.5cova0721-392rr
sha: 20dccf8e7dbd51aaf913af674d16747fdc86c93f
doc_id: 916611
cord_uid: 068nqimz

T cells are thought to be an important correlates of protection against SARS‐CoV2 infection. However, the composition of T cell subsets in convalescent individuals of SARS‐CoV2 infection has not been well studied. The authors determined the lymphocyte absolute counts, the frequency of memory T cell subsets, and the plasma levels of common γ−chain in 7 groups of COVID‐19 individuals, based on days since RT‐PCR confirmation of SARS‐CoV‐2 infection. The data show that both absolute counts and frequencies of lymphocytes as well as, the frequencies of CD4(+) central and effector memory cells increased, and the frequencies of CD4(+) naïve T cells, transitional memory, stem cell memory T cells, and regulatory cells decreased from Days 15–30 to Days 61–90 and plateaued thereafter. In addition, the frequencies of CD8(+) central memory, effector, and terminal effector memory T cells increased, and the frequencies of CD8(+) naïve cells, transitional memory, and stem cell memory T cells decreased from Days 15–30 to Days 61–90 and plateaued thereafter. The plasma levels of IL‐2, IL‐7, IL‐15, and IL‐21—common γc cytokines started decreasing from Days 15–30 till Days 151–180. Severe COVID‐19 patients exhibit decreased levels of lymphocyte counts and frequencies, higher frequencies of naïve cells, regulatory T cells, lower frequencies of central memory, effector memory, and stem cell memory, and elevated plasma levels of IL‐2, IL‐7, IL‐15, and IL‐21. Finally, there was a significant correlation between memory T cell subsets and common γc cytokines. Thus, the study provides evidence of alterations in lymphocyte counts, memory T cell subset frequencies, and common γ−chain cytokines in convalescent COVID‐19 individuals.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the cause for the Coronavirus disease 2019 (COVID-19) that affects individuals globally. For the most part COVID-19 infections are mild with recovery within 2-3 weeks. 1 However, a significant number of people progress to severe disease due to exaggerated immune response and pathology. 2, 3 The adaptive immune system, mainly, T cells play an important role in the clearance of viral infections. 4 Mild and severe incidents of COVID-19 are linked with a dramatically decreased total number of lymphocytes. 5 CD4 + T cell and CD8 + T cell responses might be crucial in SARS-CoV-2, for control and protection against primary SARS-CoV-2 infection. 6 Immune memory, after primary infection or immunization, is the basis of defensive immunity following a later infection. 7 The common-γ-chain cytokines plays a key role in health and disease. 8 Common cytokine receptor γ-chain family (γc cytokines) are linked with the development of memory T cell generation. 9, 10 Studies showed that, T cell development and maintenance and induction of T cell responses requires IL-2, IL-7, IL-15, and IL-21. 11 Lucas et al. exhibited that IL-2, IL-7, and IL-15 were enhanced in COVID-19 and associated with disease severity 12 and could stimulate IFN-γ secretion by an antigen-independent manner. 13 However, the impact of COVID-19 on common γc cytokines IL-2, IL-7, IL-15, and IL-21-levels have not been well studied in COVID-19.

Examining the intricacies of immune memory to SARS-CoV-2 is an important prerequisite to understand the duration of defensive immunity to COVID-19 formed by primary SARS-CoV-2 infection. Hence, we studied the ex-vivo phenotypic profile of CD4 + and CD8 + memory T cell subsets and the circulating levels of common γc cytokines in COVID-19 individuals more than 150 days after infection following RT PCR confirmation.

The study was approved by the Ethics Committees of ICMR-NIRT (NIRT-INo:2020047) and NIE (NIE/IHEC/202008-01). Informed written consent was obtained from all participants. All the methods were performed in accordance with the relevant institutional ethical committee guidelines.

Acute COVID-19 samples were obtained from individuals following between November 2020 and December 2020 after taking informed consent from the enrolled study individuals. 50 

Hematology was performed on all individuals using the Act-5 Diff hematology analyzer (Beckman Coulter). Demographic details and other clinical parameters are shown in Table 1 decsibed previously. 50 

Data analyses were performed using GraphPad PRISM.9 (GraphPad Software, Inc., San Diego, CA, USA). Cross-sectional analysis of frequency of memory cell subsets and hematology analysis was performed using polynomial model for best-fit curve (either first-order or second-order model). Geometric means (GM) were used for mea-surements of central tendency. Comparative analysis was done using 

The study population demographics and clinical characteristics are shown in Table 1 described previously. 50, 51 (There was no significant difference in age or sex between the study groups). 

To examine the relationship between lymphocyte counts and disease severity, we determined the absolute counts of lymphocytes in mild and severe COVID-19 individuals. The study population demographics and clinical characteristics are shown in Table 2 . As shown in Figure 4A 

Next, we wanted to determine the relationship between Memory T cell subsets and common γc cytokines levels in 7 groups of COVID-19 individuals. As shown in Figure 5A , CD4 + naïve T cells exhibited a significant positive correlation with regulatory T cells. In contrast, other memory subsets showed a significantly negative correlation with regulatory T cells. Further, we performed the correlation analysis between cytokines and memory subsets, CD4 + memory T cell subsets showed significant negative correlation with common γc cytokines levels ( Figure 5B ). Between CD8 + T cell subsets and common γc cytokines levels, mostly all the subsets with exception of T TEM showed a significant positive correlation with common γc cytokines levels ( Figure 5C ).

Finally, we performed correlation with clinical parameters and memory T cell subsets and common γc cytokines levels. There was no significant 

Multivariate logistic regression analysis was done to obtain the sta- (Table 3 ). week of infection and showed an increasing trend in lymphocytes. [23] [24] [25] [26] The existing data implies that peripheral T cell diminution is associated with disease severity and viral load and recovery of counts can happen swiftly either due by subsequent clinical or virological recovery. 27 In consistent with previous published studies, our study also indicates that the percentage and absolute counts were significantly decreased in severe cases in comparison with mild COVID-19 cases. months after post symptom onset. 36 Another recent study reported that circulating SARS-CoV-2 memory CD4 + and CD8 + T cells are present at ≥6 months post-symptom onset. 37 Mathew and Chen et al. reported that naïve T cells were decreased in convalescent COVID-19, but many effector and memory subsets are proportionally increased. [38] [39] [40] Very recent data indicated that the proportion of stem cell-like memory T (T SCM ) cells are increased, peaking at ≈120 days post-symptom onset. 32 Our data indicate that the frequencies of Our study has constraints that we did not examine the functional impact of these alterations in cellular subsets. We have also not explored the persistence of antigen -specific T cell responses in this study. Conversely, it does provide impetus to stimulate the study of the role of these T cell subsets in acute and convalescent COVID-19 and improve our understanding of memory T cell responses in COVID-19.

In addition, our study underlines the significance of these subsets and the role of common γc cytokines in COVID-19 infection. Our study has the advantage of a quite large sample size, provides the dynamics of memory T cell subsets and common γc cytokines from early infection to more than 6 months post COVID-19 infection. Our study also provides the detailed examination of common γc cytokines levels in plasma of IL-2, IL-7, IL-15, and IL-21 as well as their evolution over time. Our study thus implicates dynamic alterations in memory T cell subsets and common γc cytokines as one of the key events in COVID-19. The persistence of long-term SARS-CoV-2-memory T cells witnessed in our study is indicative of enduring defensive immunity in convalescent COVID-19 patients.

The 

The authors have declared that no conflict of interest.

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