Dear Editor,
SARS-CoV-2 infection is associated with marked lymphopenia that correlates with morbidity
and mortality [1, 2]. Here, we present the first report on serial immunophenotypic
and functional changes in 13 consecutively recruited patients infected with SARS-CoV-2
virus during their first week of ICU stay (Supplementary Table 1) with 10 healthy
donors used as controls.
Patients uniformly exhibited deep global and persisting T, NK and B cell lymphopenia
from ICU admission (D0) to day 7 (D7) (Fig. 1a to d). On D0, median absolute lymphocyte
count was dramatically reduced at 0.72 [0.65–0.88] G/L as were CD4 and CD8 T cell
counts at 0.29 [0.19–0.43] and 0.08 [0.05–0.1] G/L (Fig. 1a, e, f), such CD4 T cell
levels reflecting profound immunosuppression in HIV-infected patients. Few CD4 T cells
transiently expressed CTLA-4 during the first 3 days (Fig. 1g) while expression of
PD-1 was observed at D0 and increased until D7 (Fig. 1h). CD8 T cells significantly
and persistently expressed PD-1 from D0 to D7 while CTLA-4 expression remained unchanged
(Fig. 1i, j).
Fig. 1
Over time, ICU COVID-19 patients showed a profound and sustained lymphopenia correlated
with increased percentages of CD4 and CD8 expressing exhaustion marks and increased
frequency of immune suppressive cells. Box plot represent results for 10 healthy subjects
(controls) and for the following time point and number of COVID-19 ICU patients. The
number of patients is given below the horizontal axis of panel a. Boxes give the median
with the first and the third quartile. Whiskers represent min to max. Lines with bracket
and plain lines indicate a Mann–Whitney and ANOVA (Kruskall–Wallis test) comparison
with controls or during the ICU stay respectively. Test p values are represented by
*, ** and *** for p ≤ 0.05, p ≤ 0.01 and p ≤ 0.001 respectively. Upper panel a, b,
c, d, e, f: absolute lymphocytes count (ALC) (a), CD3 T-lymphocytes (b), Natural Killer
(NK) cells (c), B lymphocytes (d), CD4 (e) and CD8 T cells (f). Light blue boxes represent
controls and darker blue boxes represent patients. Middle panel g, h, i, j: percentages
of CD4 (g and h) and CD8 (i and j) T cells expressing CTLA-4 (g and i) and PD-1 (h
and j). Light green boxes represent controls and darker green boxes represent patients.
Lower panel k, l, m, n, o: percentages of CD4 +/CD25 +/CD127low regulatory T cells
(T-reg) [3] (k) expressing CTLA-4 (l) and PD-1 (m) and CD14 monocyte counts (n) with
quantification of the mHLA-DR at their surface membrane (o). Light orange boxes represent
controls and darker orange boxes represent patients
Being heterogeneous at D0 (Fig. 1k), percentages of regulatory T cells (Tregs) increased
during time. Few of them over-expressed CTLA-4 while PD-1 expression was strongly
and stably increased until D7 (Fig. 1l, m). Total granulocytes were moderately increased
with a transient egression of immature granulocytes in 4/10 patients at day 4–5 (Supplementary
Figure 1). Monocyte counts increased during the first week. Nevertheless, HLA-DR expression
was strongly down-regulated by a threefold factor at D0. Strikingly this decrease
persisted unabated until D7, possibly impairing antigen presentation, and was associated
with increased PD-L1 expression (Fig. 1n, o and Supplementary Figure 4d).
Being either an exhaustion or an activation marker, PD-1 is an inducer of CD8 T cell
apoptosis when activated. Therefore, functional evaluation of T-lymphocytes was performed
in three patients and controls for comparison. Meanwhile production of TNF-α and IL-2
was normal, CD4 T cell IFN-γ production was decreased (Supplementary Figure 2), indicating
a CD4 exhaustion process. In contrast, CD8 T cells could be involved in anti-viral
immune response since they produced higher levels of IFN-γ and TNF-α (Supplementary
Figure 3). Consistently, percentages of effector CD4 T cells were decreased while
those of effector memory and activated CD8 T cells were increased (Supplementary Figure 4a
to 4c). Circulating levels of IL-6 and IL-8 were moderately but significantly and
sustainly increased over time, reflecting the known SARS-CoV-2 related sub-acute inflammatory
response of innate immune cells [4] (Supplementary Figure 5).
Although our results warrant further confirmation in larger cohort, they strongly
suggest a multifaceted devastating effect of the virus to cause depletion of virtually
all classes of adaptive immune cells and to cause upregulation of potent T cell killing
and immunosuppressive mechanisms in critically-ill COVID-19 patients. Since T cells
are essential for definitive viral clearance, these results call into question therapies
(e.g., anti-IL-6, corticosteroids, JAK inhibitors) that aim to block the ability of
the patient to mount an effective immune response to the invading SARS-CoV-2. Knowing
that almost all anti-inflammatory therapies have also chronically failed in sepsis,
consideration to therapies that boost host immunity in selected severe ARDS ICU patients
(e.g., IL-7, IFN-γ or checkpoint inhibitors) may be appropriate [5, 6].
Electronic supplementary material
Below is the link to the electronic supplementary material.
Supplementary material 1 (PDF 229 kb)
Supplementary material 2 (PDF 551 kb)