We followed 35 individuals with confirmed history of COVID-19 who were willing to donate blood regularly and had neutralizing antibody titers over 160 at the first blood collection. Demographic data, onset duration before blood donation, symptoms and severity of individuals were showed in Table 1.
Table 1
Demographic data, onset duration before blood donation, symptoms and severity of 35 donors with confirmed history of COVID-19 who had neutralizing antibody titers to SARS-CoC-2 over 160 at the first blood collection.
No.
|
Donor ID
|
NT titer
|
Sex
|
Age
|
Onset duration before blood donation (day)
|
Symptom (1=Yes, 0=No)
|
Pneumonia
|
ICU
|
Treatment
|
Fever
|
Cough
|
Sore throat
|
Running nose
|
Hard breathing
|
Others
|
1
|
LAB63V00020
|
1280
|
M
|
55
|
58
|
1
|
1
|
0
|
0
|
0
|
0
|
No
|
No
|
Receive medication according to symptoms
|
2
|
LAB63V00022
|
160
|
M
|
26
|
56
|
1
|
1
|
1
|
1
|
1
|
0
|
No
|
No
|
Receive medication according to symptoms
|
3
|
LAB63V00026
|
2560
|
M
|
38
|
58
|
1
|
1
|
0
|
0
|
0
|
0
|
No
|
No
|
Receive medication according to symptoms
|
4
|
LAB63V00029
|
2560
|
M
|
43
|
56
|
1
|
1
|
0
|
0
|
0
|
0
|
Yes
|
No
|
Receive antiviral drug
|
5
|
CCP63000001
|
640
|
M
|
30
|
41
|
0
|
0
|
0
|
0
|
0
|
0
|
No
|
No
|
Receive medication according to symptoms
|
6
|
CCP63000003
|
1280
|
M
|
42
|
22
|
0
|
0
|
0
|
1
|
0
|
0
|
No
|
No
|
Receive medication according to symptoms
|
7
|
CCP63000005
|
160
|
M
|
42
|
54
|
1
|
1
|
0
|
0
|
0
|
0
|
No
|
No
|
Receive medication according to symptoms
|
8
|
CCP63000026
|
640
|
M
|
46
|
62
|
1
|
0
|
1
|
0
|
0
|
0
|
No
|
No
|
Receive antiviral drug
|
9
|
CCP63000027
|
640
|
M
|
51
|
61
|
0
|
0
|
0
|
0
|
0
|
0
|
No
|
No
|
Receive medication according to symptoms
|
10
|
CCP63000038
|
160
|
M
|
26
|
49
|
1
|
1
|
0
|
1
|
0
|
0
|
No
|
No
|
Receive antiviral drug
|
11
|
CCP63000046
|
640
|
F
|
38
|
53
|
0
|
0
|
0
|
0
|
0
|
0
|
No
|
No
|
Receive antiviral drug
|
12
|
CCP63000049
|
320
|
M
|
37
|
60
|
1
|
1
|
0
|
0
|
0
|
0
|
Yes
|
No
|
Receive medication according to symptoms
|
13
|
CCP63000050
|
640
|
M
|
38
|
53
|
1
|
1
|
0
|
0
|
1
|
Muscle pain
|
Yes
|
Yes
|
Receive oxygenation therapy
|
14
|
CCP63000053
|
160
|
M
|
29
|
67
|
1
|
1
|
0
|
0
|
0
|
0
|
No
|
No
|
Receive medication according to symptoms
|
15
|
CCP63000055
|
640
|
M
|
46
|
60
|
0
|
0
|
0
|
0
|
1
|
0
|
No
|
No
|
Receive medication according to symptoms
|
16
|
CCP63000056
|
1280
|
M
|
48
|
60
|
1
|
0
|
0
|
0
|
0
|
0
|
No
|
Yes
|
Receive antiviral drug
|
17
|
CCP63000057
|
320
|
M
|
50
|
60
|
0
|
0
|
0
|
0
|
0
|
0
|
No
|
Yes
|
Receive antiviral drug
|
18
|
CCP63000061
|
640
|
M
|
33
|
55
|
0
|
1
|
0
|
0
|
0
|
0
|
No
|
No
|
Receive medication according to symptoms
|
19
|
CCP63000064
|
1280
|
M
|
48
|
49
|
1
|
0
|
0
|
0
|
0
|
0
|
No
|
No
|
Receive antiviral drug
|
20
|
CCP63000070
|
1280
|
F
|
39
|
58
|
1
|
1
|
0
|
0
|
1
|
0
|
No
|
No
|
Receive medication according to symptoms
|
21
|
CCP63000073
|
1280
|
M
|
37
|
65
|
1
|
1
|
1
|
1
|
0
|
Allergic rash
|
No
|
No
|
Does not receive medication
|
22
|
CCP63000077
|
320
|
M
|
34
|
53
|
1
|
0
|
0
|
0
|
1
|
0
|
No
|
Yes
|
Receive antiviral drug
|
23
|
CCP63000095
|
160
|
M
|
27
|
52
|
1
|
1
|
0
|
0
|
0
|
0
|
No
|
No
|
Receive medication according to symptoms
|
24
|
CCP63000096
|
160
|
M
|
58
|
47
|
1
|
0
|
0
|
0
|
0
|
0
|
No
|
No
|
Receive medication according to symptoms
|
25
|
CCP63000100
|
160
|
F
|
38
|
71
|
1
|
0
|
0
|
0
|
0
|
0
|
No
|
No
|
Receive medication according to symptoms
|
26
|
CCP63000113
|
160
|
M
|
39
|
72
|
1
|
1
|
1
|
0
|
0
|
Anorexia
|
No
|
Yes
|
Receive medication according to symptoms
|
27
|
CCP63000114
|
160
|
M
|
37
|
64
|
1
|
0
|
0
|
0
|
0
|
Diarrhea
|
No
|
No
|
Receive medication according to symptoms
|
28
|
CCP63000118
|
640
|
M
|
48
|
70
|
0
|
1
|
1
|
0
|
1
|
Diarrhea
|
No
|
No
|
Receive medication according to symptoms
|
29
|
CCP63000138
|
640
|
F
|
33
|
75
|
1
|
1
|
1
|
0
|
1
|
0
|
Yes
|
No
|
Receive medication according to symptoms
|
30
|
CCP63000153
|
320
|
M
|
34
|
67
|
1
|
1
|
0
|
0
|
1
|
0
|
No
|
Yes
|
Receive medication according to symptoms
|
31
|
CCP63000158
|
160
|
M
|
29
|
34
|
1
|
1
|
0
|
0
|
1
|
0
|
Yes
|
No
|
Receive medication according to symptoms
|
32
|
CCP63000166
|
320
|
M
|
29
|
29
|
1
|
0
|
0
|
0
|
0
|
0
|
No
|
Yes
|
Receive medication according to symptoms
|
33
|
CCP63000189
|
2560
|
M
|
24
|
85
|
1
|
1
|
1
|
0
|
1
|
Diarrhea
|
No
|
Yes
|
Receive medication according to symptoms
|
34
|
CCP63000194
|
640
|
F
|
53
|
68
|
1
|
1
|
0
|
0
|
0
|
0
|
No
|
No
|
Receive medication according to symptoms
|
35
|
CCP63000209
|
320
|
F
|
35
|
69
|
1
|
0
|
1
|
0
|
0
|
0
|
Yes
|
Yes
|
Receive oxygenation therapy
|
Blood samples were collected every 2-3 weeks and tested for neutralizing antibody titers, and the sequential blood collection was terminated once the neutralizing antibody titer declined to lower than 160. Figures 1 showed patterns of neutralizing antibody titers and binding antibody levels of RBD, NTD, S2 and NP of the individuals. Sera from donors in figure 1a exhibited similar trend between neutralizing titer and binding level of RBD, NTD, S2 and NP which mostly decreased over time. The neutralizing antibody titers decreased to lower than 160 within 3 months after the first blood collection in 9 donors. Another 3 donors ID CCP63000038, CCP63000114 and LAB63V00029 had neutralizing antibody titers below 160 after 13, 33 and 23 weeks, respectively. The neutralizing activities of sera from these donors probably belonged to all of these epitopes at the periods of collection.
There were 10 donors with high neutralizing antibody titers in figure 1b but they were lost to follow-up after 2 months leaving 13 donors with sequential antibody titer data over 3-12 months. These 13 donors showed persistently high neutralizing titer over than 3 months. Interestingly, donor ID. CCP63000073 and CCP63000189 still had high neutralizing titer at 640 and 1280, respectively, at 1 year after the first collection. As RBD is generally a major target of SARS-CoV-2-neutralizing antibodies, similar trend between neutralizing titers and binding levels of RBD were observed in donor ID LAB63V00020, LAB63V00022, CCP63000005, CCP63000026, CCP63000046, CCP63000077, CCP63000095, CCP63000118, CCP63000194 and CCP63000209. However, donor ID CCP63000050, CCP63000055, CCP63000073, CCP63000096, CCP63000113, CCP63000138, CCP63000166 and CCP63000189 had persistently high neutralizing titer (≥320), but their binding levels to RBD rapidly decreased. This decline of the RBD binding antibody levels in these subjects was faster than the decline of antibody to the other domains. As time passed, the dramatically decreasing of binding antibody to RBD continued while neutralizing titers were still maintained. This suggested that other epitopes were also crucial.
Binding antibody level of NTD mostly decreased over time except sera of donor ID CCP63000077, CCP63000113, CCP63000118, CCP63000138 and CCP63000194 which corresponded to the persistently high neutralizing titer. However, donor ID CCP63000027 and LAB63V00020 always had low binding level of NTD since the first collection. Their neutralizing antibodies may target NTD much lesser than other epitopes. Although binding antibody level of NP usually dropped over time, donor ID CCP63000114, CCP63000189 and CCP63000194 demonstrated similar trends between to NP and S2, which also corresponded to their neutralizing titers.
Surprisingly, binding antibody specific to S2 was always stable or slowly decreased in most of donors in this study. Donor ID CCP63000055, CCP63000077 and CCP63000189 clearly demonstrated long lasting and high neutralizing titer ≥640 with the high and constant level of binding antibody to S2 for 35, 43 and 47 weeks, respectively. We also tested these sera for neutralizing titers against a delta variant isolate and found that these sera with high neutralizing titers and high S2-binding antibody did not show significantly higher cross neutralization to the delta variant than sera with lower S2-binding antibody (Table2). This suggested that the persistent neutralizing activity mainly targeted variable S1 epitopes despite the low binding antibody to the NTD and RBD domains.
Overall, the antibody response to each epitope can be differently maintained over time after infection. The persistent neutralizing titer despite the low level of binding antibody to RBD was probably from the specific binding antibodies to non-RBD epitopes such as S2, NP and even quaternary epitopes. For natural infection, RBD seems to be mainly responsible in earlier periods and other epitopes may play roles for neutralizing activities in later periods.
Table 2
NT titer and binding antibody level of RBD, S2, NP and NTD epitope
Donor ID
|
Collection time
of serum (week)
|
NT titer
|
Optical density of ELISA binding
|
Wuhan
|
Delta
|
RBD
|
S2
|
NP
|
NTD
|
Donors with persistently high NT and S2-binding antibodies but declining RBD-binding antibody.
|
CCP63000055
|
1
|
640
|
80
|
1.474
|
2.068
|
1.491
|
1.863
|
CCP63000441
|
31
|
320
|
40
|
0.463
|
1.995
|
0.461
|
0.770
|
CCP63000138
|
1
|
640
|
20
|
1.526
|
2.414
|
1.732
|
1.421
|
CCP63000395
|
17
|
320
|
20
|
0.638
|
2.180
|
1.115
|
1.123
|
CCP63000166
|
1
|
320
|
<10
|
1.985
|
1.676
|
1.639
|
1.293
|
CCP63000446
|
30
|
320
|
<10
|
0.424
|
1.871
|
0.981
|
0.797
|
Donors with persistently high NT and RBD-binding antibodies.
|
CCP63000142
|
3
|
640
|
80
|
1.910
|
1.241
|
1.305
|
1.195
|
CCP63000404
|
20
|
320
|
<10
|
1.162
|
1.201
|
1.213
|
0.659
|
CCP63000018
|
2
|
640
|
320
|
2.219
|
1.455
|
1.565
|
1.593
|
CCP63000276
|
10
|
640
|
80
|
1.989
|
1.216
|
1.296
|
1.042
|
LAB63V00026
|
1
|
2560
|
80
|
2.009
|
1.170
|
1.809
|
2.017
|
CCP63000330
|
12
|
640
|
20
|
1.428
|
1.363
|
0.829
|
1.249
|
Donors with rapidly decreasing NT and RBD-binding antibodies.
|
CCP63000009
|
2
|
640
|
20
|
2.012
|
1.195
|
1.944
|
0.975
|
CCP63000027
|
1
|
640
|
80
|
0.995
|
0.840
|
1.308
|
0.259
|
LAB63V00029
|
1
|
2560
|
80
|
2.339
|
1.101
|
2.031
|
1.403
|