Abstract
Introduction
Kidney transplant patients (KT) are at high risk for severe COVID‐19 and presented attenuated antibody responses to vaccination when compared to immunocompetent individuals. Torquetenovirus (TTV) has recently gained attention as a potential surrogate marker of the net state of immunosuppression. We evaluated the association between pre‐vaccination TTV viral load and anti‐spike total antibody response to SARS‐CoV‐2 vaccination in KT.
Material and Methods
The 114 adult KT recipients enrolled in this prospective single‐center cohort study received two doses of SARS‐CoV‐2 mRNA BNT162b2 vaccine. Serum samples were collected immediately before vaccination at the days when patients received both the first (T0) and the second dose (T1) and 16–45 days after the second dose (T2). Primary endpoint was the development of anti‐spike total antibodies after vaccination. Demographic, clinical, and laboratorial parameters were compared between patients with and without detectable SARS‐CoV‐2 antibodies at T2.
Results
Ninety‐nine patients (86.8%) were naïve for SARS‐CoV‐2 before vaccination. Fifty‐six (56.6%) patients developed anti‐spike total antibodies at T2. The use of mTOR inhibitors was associated with a favorable response (p = .005); conversely, mycophenolic acid (MPA) was associated with a negative response (p = .006). In a multivariable model, the presence of TTV at T0 ≥ 3.36 log10 cp/ml was associated with unfavorable vaccine response (OR: 5.40; 95% CI: 1.47–19.80; p = .011), after adjusting for age and eGFR at T0.
Conclusions
Higher TTV viral loads before vaccination are associated with reduced anti‐spike total antibody response in SARS‐CoV‐2 mRNA BNT162b2 vaccinated KT patients. The association between TTV viral load and vaccine response may be an added‐value in the optimization of vaccination regimens in KT.
Keywords: kidney transplantation, SARS‐CoV‐2, torquetenovirus, vaccine
1. INTRODUCTION
In December 2019, severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) emerged as the etiologic agent of Coronavirus disease 2019 (COVID‐19). 1 Kidney transplant patients (KT) have been considered high risk patients for severe COVID‐19 2 ; vaccination emerged as a crucial strategy, readily recommend by international guidelines. SARS‐CoV‐2 messenger‐ribonucleic acid (mRNA) vaccines appear to be safe in KT recipients, 3 but attenuated antibody responses were observed when compared to immunocompetent individuals. Seroconversion rates range from 0% to 17% following one COVID‐19 vaccine dose and 3%–59% after two COVID‐19 vaccine doses. 4 Therefore, a third and even four dose of mRNA COVID‐19 vaccine have been recommended. 5 Evaluation of humoral response to SARS‐CoV‐2 vaccine is the best readily available tool to measure its efficacy. Different immunosuppressive protocols may influence the efficacy of SARS‐CoV‐2 vaccine. Mammalian target of rapamycin (mTOR) inhibitors were associated with a better immune response 6 and the opposite effect was described with mycophenolic acid (MPA). 7
No ideal marker reliably defines the immune function of KT patients. Torquetenovirus (TTV) has recently gained attention as a potential surrogate marker of the net state of immunosuppression. 8 TTV can be detected in up to 90% of healthy individuals without association with any specific disease. Peripheral blood viral loads of TTV reflect the overall strength of innate and specific immunity in solid‐organ transplant patients, 8 as low TTV levels are associated with graft rejection and high TTV levels associate with a higher risk of infection. 8 We recently reported a patient diagnosed with COVID‐19 3 months after KT, whose TTV DNA load increased with COVID‐19 onset and reduced after its resolution 9 In addition, a Dutch group, demonstrated a better humoral response to SARS‐CoV‐2 vaccination in lung transplant patients with lower TTV loads before vaccination. 10
Thus, we evaluated if TTV load before vaccination is associated with anti‐spike (anti‐S) total antibody response in response to SARS‐CoV‐2 mRNA BNT162b2 vaccine in KT patients.
2. MATERIAL AND METHODS
2.1. Study design and population
A total of 114 adult KT recipients (at least 6 months post‐KT and without rejection episodes in the previous 3 months) were enrolled in this prospective single‐center cohort study. All KT patients received two doses of SARS‐CoV‐2 mRNA BNT162b2 vaccine with an interval of 21 days between doses in May and June 2021 at our Kidney Transplant Center.
All participants provided informed consent.
Serum samples were collected immediately before vaccination at the days when patients received both the first (T0) and the second dose (T1) and 16–45 days after the second dose (T2).
The cohort included KT patients previously infected with SARS‐CoV‐2 and virus‐naïve subjects. Prior infection with SARS‐CoV‐2 was defined either by known infection diagnosed more than 6 months pre‐vaccination or the presence of positive anti‐S and/or anti‐nucleocapsid (anti‐N) SARS‐CoV‐2 total antibodies at T0.
Patients were then stratified considering anti‐N or anti‐S SARS‐CoV‐2 total antibodies positivity at T0 (positive patients—Group A; negative patients—Group B). Group B was thereafter stratified into two groups: patients with positive TTV DNA viral load at T0 (Group C) and patients with negative TTV DNA viral load at T0.
Since it was impossible to define if patients with negative TTV DNA had latent infection, with undetectable viral loads at T0, we excluded this subgroup of patients from subsequent analysis. Group A patients were excluded from the SARS‐CoV‐2 vaccine response analysis since all of them had previously formed anti‐S antibodies.
Estimated glomerular filtration rate (eGFR) was computed using the Chronic Kidney Disease Epidemiology Collaboration (CKD‐EPI) equation. 11
All patients received triple immunosuppression, mainly with tacrolimus, MPA, and prednisolone or with tacrolimus, mTOR inhibitor, and prednisolone. No patient changed immunosuppression regimen during follow‐up. Tacrolimus was administered orally at .15 mg/kg/day divided into two doses and adjusted to maintain a target trough concentration between 4 and 10 ng/ml, depending on the time elapsed after KT. Prednisolone was prescribed since the fifth day after KT (.6 mg/kg) and was tapered to 5 mg/day during the first 3 months after KT. MPA (mycophenolate mofetil 1000 mg orally twice daily) was started after KT and was reduced if adverse events appeared; it was reduced to 1000–1500 mg daily dose after the first 3–6 months. Everolimus was started at 2.0 mg/day with dose adjusted to achieve target trough concentrations of 3–8 ng/ml throughout.
Anti‐S and anti‐N antibodies, TTV DNA viral load, Immunoglobulins G, A, and M and eGFR rate were determined at T0, T1, and T2.
The primary endpoint was the development of anti‐S total antibodies after vaccination (favorable vs. unfavorable response). Demographic characteristics, type of donor, time since transplantation, maintenance immunosuppression, and length of follow‐up collected at baseline, were compared between the groups with and without detectable anti‐S antibodies at T2.
The study is in compliance with the Declaration of Helsinki, follows national and international guidelines for health data protection and was approved by the Ethics Committee of the “Centro Hospitalar Lisboa Ocidental” (approbation code 2134).
2.2. Anti‐SARS‐CoV‐2 total antibodies detection
Electro‐chemiluminescence immunoassay (ECLIA) was used to detect anti‐N and quantify anti‐S(RBD) (ElecsysAnti‐SARS‐CoV‐2 S and Anti‐SARS‐CoV‐2 N, Roche), on a Cobas e602 analyzer, with a positivity threshold of 1.0 (index) for anti‐N and .8 U/ml for Anti‐S(RBD), following manufacturer's instructions. These thresholds were validated in recent studies. 12 , 13
2.3. Quantitative TTV DNA viral load
DNA extraction from serum samples, and amplification of DNA was performed as previously described. 14 , 15 In brief, DNA extraction was carried out using the eMAG System (BioMerieux, Marcy, France). For DNA amplification and quantification, the Argene R‐Gene TTV quantification kit (BioMerieux) was used on an Applied Biosystems 7500 (Thermofisher, Waltham, MA, USA) according to the manufacturer's instructions. The R gene assay is designed to detect the majority of TTV genotypes. 1 , 6 , 7 , 8 , 10 , 12 , 15 , 16 , 19 , 27 , 28 The threshold defining positivity was 100 copies/ml. Results are expressed in log10 copies/ml.
2.4. Statistical analysis
An exploratory analysis was carried out for all variables. Categorical data were presented as frequencies and percentages, and continuous variables as mean (standard deviation) or median and inter‐quartile range (25th percentile;75th percentile), as appropriate. Nonparametric tests (Chi‐square, Fisher's Exact, Mann‐Whitney U) were used to compare patients who responded to the vaccine and those who did not. Additionally, generalized additive regression models for the response to SARS‐CoV‐2 vaccination were also used. Model performance was assessed with Hosmer‐Lemeshow goodness of fit test and with the area under the ROC curve (receiver operating characteristic). For TTV in T0 (TTV‐T0), the best cut‐point that discriminates patients regarding response to SARS‐CoV‐2 vaccination was obtained through the minimum p‐value approach, and corresponding sensitivity and specificity estimated.
The level of significance α = .05 was considered. All data were analyzed using SPSS 22.0 (IBM Corp. Released 2013. IBM SPSS Statistics for Windows. Armonk, NY, USA: IBM Corp) and R software (R: A Language and Environment for Statistical Computing, R Core Team, R Foundation for Statistical Computing, Vienna, Austria, 2014).
3. RESULTS
3.1. Patients’ characteristics
One hundred fourteen KT patients (52 men; 62 women) were included in the study, with 46.54 ± 12.02 years and a median follow up after KT of 104.73 months (P25 = 53.52; P75 = 170.33). Only five patients (4.4%) received a kidney allograft within 1 year before vaccine administration. Sixty‐eight patients (59.6%) received T‐cell depleting as induction therapy. Two patients (1.8%) had one episode of acute rejection in the past year; none of them developed anti‐S antibodies.
No patient developed anti‐N antibodies between T0 and T2 or had symptoms compatible with COVID‐19 during follow up.
The number of patients in each study group is presented in the flow chart of Figure 1.
FIGURE 1.
Study design flow chart
3.2. Vaccine response in positive SARS‐CoV‐2 patients before vaccination (Group A)
Fifteen patients (13.2%) had prior infection with SARS‐CoV‐2 before vaccination.
All these patients presented Anti‐S at T0 despite immunosuppression regimen. Anti‐S levels at T2 were significantly higher in patients with previously solved COVID‐19, comparing with SARS‐CoV‐2 naïve patients: 23 253.0 (13 010.0–43 840.0) U/ml versus 57.3 (9.025–370.500) U/ml (p < .001). Moreover, 56.6% of SARS‐CoV‐2 naïve individuals had a positive response to vaccination against 100% of the patients with COVID‐19 (p = .001).
3.3. Vaccine response and associated factors (Group B)
Table 1 depicts demographic and laboratorial characteristics of SARS‐CoV‐2 naïve patients (n = 99). Fifty‐six (56.6%) patients developed anti‐S total antibodies at T2 with a median titer of 57.3 (P25 = 9.03; P75 = 370.50) U/ml.
TABLE 1.
Demographic and laboratorial characteristics of SARS‐CoV‐2 naïve patients (Group B)
| Characteristics | Total (n = 99) | Anti‐spike + Ab at T2 (n = 56) | Anti‐spike − Ab at T2 (n = 43) | p value |
|---|---|---|---|---|
| Age in years – mean (SD) | 46.1 (11.6) | 44.3 (9.48) | 48.3 (13.61) | .105 a |
| Gender – n (%) | 1.000 b | |||
| Male | 44 (44.4) | 25/56 (44.6) | 19/43 (44.2) | |
| Female | 55 (55.6) | 31/56 (55.4) | 24/43 (55.8) | |
| Type of donor‐ (n/%) | .143 | |||
| Deceased | 64 (64.6) | 39/64 (60.9) | 25/64 (39.1) | |
| Living | 35 (35.4) | 17/35 (48.6) | 18/35 (51.4) | |
| Time after KT, months | 100.9 (54.0–169.9) | 94.1 (51.4–159.2) | 120 (64.3–178.9) | .280 |
| eGFR ml/min, T0 | 59.0 (44.0–82.0) | 71.5 (51.3–86.5) | 49 (41–71) | .003 |
| Calcineurinic inhibitors – n (%) | 92 (92.9) | 51/92 (55.4) | 41/92 (44.6) | .696 b |
| mTOR inhibitors – n (%) | 20 (20.2) | 17/20 (85.0) | 3/20 (15.0) | .005 b |
| MPA – n (%) | 86 (86.9) | 44/86 (51.2) | 42/86 (48.8) | .006 b |
| Last available tacrolimus level ng/ml, mean (SD) n = 86 | 6.1 (1.5) | 6.2 (1.6) | 5.8 (1.4) | .252 a |
| Hemoglobin (IQR), g/dl, T0 | 13.3 (12.0–14.3) | 13.7 (12.6–14.7) | 12.8 (11.3–13.6) | .002 |
| Immunoglobulin G, T0 (mg/dl) | 958.0 (843.8–1175.0) | 1030.0 (880.0–1220.0) | 914.0 (786.0–1070.0) | .035 |
| Immunoglobulin A, T0 (mg/dl) | 202.5 (152.5–258.3) | 199.0 (163.0–270.0) | 212.0 (137.0–244.0) | .427 |
| Immunoglobulin M, T0 (mg/dl) | 96.6 (62.5–135.8) | 96.2 (64.7–144.0) | 97.0 (48.9–128.0) | .567 |
Abbreviations: eGFR, estimated glomerular filtration ratio; IQR, interquartile range; KT, kidney transplantation; MPA, mycophenolic acid; mTOR, mechanistic target of rapamycin; SD, standard deviation.
p‐value obtained by Student's t test.
p‐value obtained by Fisher exact test; other p‐values were obtained by Mann‐Whitney test.
A serological response to the vaccine was more likely to occur with the use of mTOR inhibitors (p = .005). Seventeen of the 20 patients (85%) treated with mTOR developed positive anti‐S antibodies at T2. Conversely, serological response to the vaccine was associated with immunosuppression schemes not containing MPA (p = .006). In fact, from 13 patients not treated with MPA, 12 (92.3%) responded to vaccination; only one patient (7.7%) not receiving MPA failed to develop anti‐S antibodies. No patient received azathioprine.
Higher hemoglobin levels (p = .002), higher Immunoglobulin G levels (p = .035) and higher eGFR (p = .003), at T0, were also associated with an appropriate serological response (Table 1).
3.4. Vaccine response and associated factors (Group C)
Table 2 depicts demographic and laboratorial characteristics of SARS‐CoV‐2 naïve patients with positive TTV‐T0 (n = 75).
TABLE 2.
Demographic and laboratorial characteristics of SARS‐CoV‐2 naïve patients with positive TTV DNA viral load at T0 (Group C)
| Characteristics | Total (n = 75) | Anti‐spike + Ab at T2 (n = 44) | Anti‐spike − Ab at T2 (n = 31) | p value |
|---|---|---|---|---|
| Age in years – mean (SD) | 46.2 (11.1) | 44.1 (8.8) | 49.1 (13.4) | .072 a |
| Gender – n (%) | 1.000 b | |||
| Male | 40 (53.3) | 23/44 (52.3) | 17/31 (54.8) | |
| Female | 35 (46.7) | 21/44 (47.7) | 14/31 (45.2) | |
| Type of donor‐ (n/%) | .440 b | |||
| Deceased | 53 (70.7) | 33/53 (62.3) | 20 /53 (37.7) | |
| Living | 22 (29.3) | 11/22 (50.0) | 11/22 (50.0) | |
| Time after KT, months | 86.7 (51.7–154.0) | 86.5 (44.6–154.6) | 93.2 (56.5–151.3) | .675 |
| eGFR T0, ml/min | 60.0 (43.0–83.0) | 71.5 (52.8–85.0) | 48.0 (41.0–70.0) | .005 |
| Calcineurinic inhibitors – n (%) | 71 (94.7) | 40/71 (56.3) | 31/71 (43.7) | .084 c |
| mTOR inhibitors – n (%) | 14 (18.7) | 14/14 (100) | 0/14 (0) | <.001 b |
| MPA– n (%) | 65 (86.7) | 34/65 (52.3) | 31/65 (47.7) | .004 b |
| TTV viral load T0, log copies/ml | 4.05 (3.24–4.94) | 3.71 (3.02–4.62) | 4.46 (3.60–5.08) | .021 |
| TTV viral load T1, log copies/ml | 3.60 (2.71–4.78) | 3.30 (2.71–4.49) | 4.19 (3.01–4.78) | .088 |
| TTV viral load T2, log copies/ml (n = 73) | 4.29 (3.24–5.00) | 4.0 (3.13–4.49) | 4.57 (4.00–6.01) | .005 |
| Last available tacrolimus level, ng/ml, mean (SD) n = 68 | 6.1 (1.6) | 6.4 (1.7) (n = 39) | 5.8 (1.4) (n = 29) | .121 a |
| Hemoglobin T0, g/dl | 13.5 (12.30–14.60) | 13.95 (13.10–14.78) | 13.0 (11.90–13.90) | .008 |
| Immunoglobulin G, T0, (mg/dl) | 986.0 (878.0–1190.0) | 1025.0 (890.5–1212.5) | 957.0 (839.0–1120.0) | .237 |
| Immunoglobulin A, T0, (mg/dl) | 199.0 (159.0–263.0) | 195.5 (163.3–274.5) | 218.0 (125.0–248.0) | .767 |
| Immunoglobulin M, T0, (mg/dl) | 84.9 (49.8–124.0) | 92.5 (68.3–140.8) | 82.1 (47.1–104.0) | .199 |
Abbreviations: eGFR, estimated glomerular filtration ratio; IQR, interquartile range; KT, kidney transplantation; MPA, mycophenolic acid; mTOR, mechanistic target of rapamycin; SD, standard deviation; TTV, torquetenovirus.
p‐value obtained by Student's t test.
p‐value obtained by Fisher exact test.
p‐value obtained by Pearson's chi‐squared test; other p‐values were obtained by Mann‐Whitney test.
TTV DNA viral load was measured in serum at T0, T1 and T2, and the median TTV viral load was significantly different between T1 and T0 (p = .005) and between T1 and T2 (p < .001), with lower viral loads at T1 (Figure 2).
FIGURE 2.
Evolution of TTV load at study time points
Immunosuppressive regimen was associated with antibody response. All 14 patients treated with mTOR inhibitors developed serological response at T2 (p < .001). A lower proportion for antibody response was associated with MPA therapy (n = 34;52.3%) and all 10 patients without MPA developed anti‐S antibodies at T2 (p = .004). Time after KT was not associated with vaccination response (p = .675).
3.5. TTV DNA viral load association with antibody response (Group C)
Table 3 displays the results of univariable logistic regression for Spike antibody response at T2.
TABLE 3.
Univariable logistic regression analysis for Spike antibody response at T2 (Group C)
| Variables | Odds ratio estimate | 95% CI | ||
|---|---|---|---|---|
| Lower limit | Upper limit | p‐value | ||
| Actual age | 1.04 | .99 | 1.09 | .057 |
| Hemoglobin T0 (g/dl) | .65 | .47 | .91 | .011 |
| eGFR T0 (ml/min) | .98 | .96 | 1.00 | .025 |
| Creatinine (mg/dl) | 1.58 | .82 | 3.05 | .177 |
| Immunoglobulin G T0, (mg/dl) | .999 | .997 | 1.001 | .247 |
| Immunoglobulin M T0, (mg/dl) | .992 | .982 | 1.002 | .123 |
| TTV T0 (log10 cp/ml) | 1.68 | 1.09 | 2.60 | .020 |
| TTV T0 > cutoff point 3.36 (log10 cp/ml) | 4.67 | 1.39 | 15.67 | .013 |
| Last available tacrolimus level (ng/ml) | .78 | .56 | 1.07 | .124 |
Dependent variable: Anti spike antibodies response at T2 (unfavorable vs. favorable vaccine response).
Abbreviations: eGFR, estimated glomerular filtration ratio; TTV, torquetenovirus.
We evaluated the association between TTV‐T0 viral load and anti‐S antibodies formation after SARS‐CoV‐2 vaccination. For each increase of 1 log TTV‐T0 the chance of having an unfavorable vaccine response increases 1.68 times (p = .020). A TTV‐T0 cut‐off value of 3.36 log10 cp/ml was determined considering anti‐S antibodies detection (p = .013), with a sensitivity of 87.1% and a specificity of 40.9% for discriminating antibody response.
In the multivariable model, the presence of TTV‐T0 ≥3.36 log10 cp/ml was associated with unfavorable vaccine response (OR: 5.40; 95% CI: 1.47–19.80; p = .011), after adjusting for age and eGFR at T0 (Table 4). Model's good calibration and discrimination abilities were obtained (Hosmer‐Lemeshow test p = .562 and AUC = .76; 95%CI:.648–.865; p < .001), respectively.
TABLE 4.
Multivariable logistic regression analysis for antibody response at T2 (Group C)
| Variables | Odds ratio estimate | 95% CI | ||
|---|---|---|---|---|
| Lower limit | Upper limit | p‐value | ||
| TTVt0 ≥ 3.36 (log10 cp/ml) a | 5.40 | 1.47 | 19.80 | .011 |
| Actual age (years) | 1.05 | 1.00 | 1.10 | .067 |
| eGFR T0 (ml/min) | .98 | .95 | .99 | .025 |
Dependent variable: Anti spike antibodies response at T2 (unfavorable vs. favorable vaccine response).
Abbreviation: eGFR, estimated glomerular filtration rate.
Reference category TTVt0 < 3.36 (log10 cp/ml).
4. DISCUSSION
The association between TTV viral load at baseline and anti‐S total antibody response after SARS‐CoV‐2 mRNA BNT162b2 vaccination at T2 was analyzed in a cohort of KT patients.
At baseline, 99 patients were naïve for SARS‐CoV‐2; only 56.6% developed anti‐S antibodies after two vaccine doses, after a median of 30 days post second dose (T2). Affeldt et al. 16 studied 86 SARS‐CoV‐2‐naïve KT recipients using BNT162b2 with a median of 30 days after their second vaccination reporting a seroconversion rate of 39.5% and Nazaruk et al. 17 found anti‐S antibodies in 57.1% of KT patients, 4–8 weeks after second dose. Antibody response to mRNA vaccines in KT patients is inferior to the general population, ranging between 37.5% and 54% after two doses of vaccine. 18 , 19 , 20
Regarding immunosuppression, 92.3% of patients not treated with MPA responded to vaccine with antibody response. Our study is consistent with previous published studies where seroconversion rate was significantly lower in KT recipients on immunosuppressive regimens containing MPA. 17 , 21 , 22 It inhibits inosine‐5′‐monophosphate dehydrogenase, suppressing antibody formation and proliferation and cell mediated immune responses. 23 Conversely, the presence of mTOR was associated with a better immune response to COVID‐19 vaccine, since 87% of patients treated with mTOR inhibitors, developed anti‐S antibodies at T2 and in consistent with findings by Netti et al. 6 A possible mechanism for the enhanced immune response to the mRNA COVID‐19 vaccine in KT treated with mTOR is its immunomodulatory effects in memory CD8+ and CD4+ T cells by promoting the enhancement of memory precursor effector cells that could differentiate into long‐lived memory cells. 24
Patients with higher hemoglobin levels and a greater eGFR were more likely to develop an antibody response. Lower hemoglobin levels and lower eGFR are associated with allograft dysfunction, which could decrease humoral response. 25 , 26
Long period between transplantation and vaccination has been associated with positive humoral SARS‐CoV‐2 response. 23 In our study, time since transplantation was not associated with vaccine response as almost 90% of patients received the allograft at least 2 years before the study, with minimized doses of immunosuppression before vaccination.
Until now, no reliable marker has been identified to quantify the net state of immunosuppression in transplant patients. Kinetics of TTV DNA load is a potential marker of immune function 8 and has also been investigated in the prediction of severe nosocomial infections and mortality in critically ill COVID 19‐patients. 27
The interaction between TTV and viral antigens has already been described. In healthy individuals, TTV load slightly increases after immunologic stimulation with influenza and hepatitis B vaccination. We found a lower median TTV DNA viral load at T1, returning to baseline levels at T2. We postulated that vaccine stimulation of specific immunity could lead to a transient immune reconstitution, which would be associated with a lower TTV load.
In our study, 75.8% of patients had detectable TTV DNA, with a median viral load at baseline of 4.05 log10 cp/ml. TTV load is associated with rejection and infection in solid organ transplant recipients and cutoff values for risk stratification of such events have been proposed for KT patients, but only along the first year after transplantation. 8
We found that the development of anti‐S antibodies after two doses of BNT162b2 vaccine was more frequent in KT recipients with lower TTV loads at baseline. The optimal cut‐off value of TTV viral load, which best discriminates patients with positive from negative response, was 3.36 log10 cp/ml. A TTV viral load higher than 3.36 log10 cp/ml has a five‐fold increase in the odds of non‐development of antibodies. We reached a high sensitivity of 87.1%, so we expect that this cut‐off is effective in identifying vaccine responders. This information may become useful to identify the optimal time for an efficient boosting. 28
Our data was corroborated by a recent study 10 of 103 lung transplant patients vaccinated with two doses of mRNA‐123 SARS‐CoV‐2 vaccine. Authors showed that lower TTV loads at baseline correlated with higher S‐specific antibodies 28 days after the second vaccination.
At baseline, 13.2% of patients had COVID‐19 prior to vaccination. All of them developed anti‐S pre‐vaccination and anti‐S antibodies levels post‐vaccination were significantly higher, independent of immunosuppressive regimen. In convalescent COVID‐19 patients, antibody levels decline slightly after 6–8 months, whereas vaccine‐induced immunity appears to decrease more rapidly. 29 Benning et al. 30 revealed that 18 convalescent KT recipients showed significantly higher anti‐S antibody levels compared with 2‐dose BNT162b2 vaccinated KT recipients. Consequently, additional boosting or a higher dose stimulus might need to be applied in non‐responders. 31 After the conclusion of this study, all solid organ recipients received a third dose of mRNA vaccine and are eligible for a fourth one.
This study has some limitations. First, we did not evaluate cellular responses to SARS‐CoV‐2. Assessment of humoral response alone may underestimate vaccine effect, since some studies demonstrated a significant T‐cell immunity in cases of humoral non‐response. 32 Second, the analysis of anti‐S titers might not reflect the global immunologic status, since the extent to which anti‐S titer correlates with protection against infection and severe COVID‐19 is still not understood. In addition, follow‐up on waning antibody titers is unavailable.
In conclusion, this study established an association between higher TTV viral loads pre‐vaccination and reduced anti‐S response in SARS‐CoV‐2 mRNA BNT162b2 vaccinated KT patients. A TTV viral load higher than 3.36 log10 cp/ml has a five‐fold increase in the odds of absence of antibody response. In addition, TTV kinetics varies along SARS‐CoV‐2 vaccination, with lower DNA viral loads after the first vaccine inoculation.
The association between TTV viral load and vaccine response should be investigated in other cohorts of KT patients as a potential added‐value strategy in the optimization of the COVID‐19 vaccination regimens.
AUTHOR CONTRIBUTIONS
S. Querido: Concept/design, data collection, data analysis, drafting article. T. Adragão: statistics, critical revision of article. C. Ormonde: data analysis, data collection. I. Pinto/ AL Papoila: statistics, critical revision of article. MA Pessanha/ P. Gomes/ JM Figueira/ C. Cardoso/ JF Viana: data analysis/interpretation. A. Weigert: critical revision of article/ approval of article.
CONFLICT OF INTEREST
None.
ACKNOWLEDGMENTS
Diogo Francisco, Carla Rocha, Ana Casqueiro, Regina Oliveira, Ana Albuquerque, Lília Oliveira, Ana Margarida Casaca, Inês Sousa, and the remaining participating Nursing and Clinical Pathology teams of Hospital Santa Cruz for sample collection. Inês Costa from LBM for TTV viral load testing. Celia Pereira for invaluable secretarial assistance. Isabel Pereira, for statistical support and critical revision of the article.
Querido S, Adragão T, Pinto I, et al. Torquetenovirus viral load is associated with anti‐spike antibody response in SARS‐CoV‐2 mRNA BNT162b2 vaccinated kidney transplant patients. Clin Transplant. 2022;36:e14825. 10.1111/ctr.14825
DATA AVAILABILITY STATEMENT
The data that support the findings of this study are available from the corresponding author upon reasonable request.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
The data that support the findings of this study are available from the corresponding author upon reasonable request.