Impact of Kidney Transplantation on Humoral Immunity Against SARS-CoV-2: A Case Series From Belgium

Anti–severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines have shown good efficacy in kidney transplant candidates¹, contrasting with disappointing results in kidney transplant recipients (KTRs).² However, the impact of starting immunosuppressive treatments for KTRs on anti-SARS-CoV-2 humoral immunity has been poorly investigated to date.

We report the evolution of anti-SARS-CoV-2 antibody (Ab) titers in 14 KTRs, transplanted in our center between January 2021 and June 2021, who received at least 1 vaccine dose before KT. We assessed the anti–receptor-binding domain (RBD) Ab titers (Elecsys anti-SARS-CoV-2, Roche Diagnostics GmbH, Mannheim, Germany; positive threshold ≥0.8 U/mL) on the day of transplantation (day 0) and 28 d after (d 28). This work received an institutional review board approval.

Ten patients had received their second dose of either the BNT162b2 (Pfizer-BioNTech, n = 8) or ChAdOx1 nCoV-19 vaccine (AstraZeneca, n = 2) with a mean time of 57 d (range, 25–78) before KT. Four patients had received a single dose of vaccine (Pfizer n = 2, AstraZeneca n = 2) with a mean time of 29 d (range, 15–30) before KT. The mean age was 58 y (range, 32–77) and 57% were male individuals. Twelve patients were on dialysis before transplantation with a mean duration of 54 mo (range, 20–122). One patient had a prior history of COVID-19.

After KT, all patients were treated with an association of tacrolimus (trough levels, 10–13 ng/mL), mycophenolate (500 mg BID), and steroids. Sensitized patients (n = 3) and KTRs who received a graft from a living donor (n = 2) were additionally inducted with thymoglobulin and basiliximab, respectively. None of the patients developed COVID-19 after KT.

On day 0, the mean anti-RBD Ab titer was high (mean ± SEM: 1124 ± 441 U/mL). However, KTRs who had received a single dose of vaccine (n = 4) showed low mean Ab titer (0.83 ± 0.43 U/mL). On day 28, we observed a significant decrease of anti-RBD Ab titers (Figure 1). However, Ab titers remained high (514 ± 205 U/mL) compared with those reached in vaccinated KTRs that we previously published.² Not surprisingly, the 4 patients who had received a single dose of vaccine had low Ab titer on day 28 (2.85 ± 1.84 U/mL). Interestingly, on day 28, anti-RBD Ab titers in patients inducted with thymoglobulin (n = 3) or basiliximab (n = 2) were high (107, 332, 787 and 577, 1132 U/mL, respectively).

FIGURE 1.

Evolution of anti-RBD antibody titers. Mean ± SEM antibody titer on d 0 and d 28: 1124 ± 441 U/mL and 514 ± 205

U/mL (P = 0.003, Wilcoxon test). RBD, receptor-binding domain.

Our results are in line with those recently published.^3,4 Yi et al³ showed persistent immunogenicity 25 d after KT of the mRNA vaccine in 8 KTRs (including 5 who received a T-cell depleting induction). Mohamadou et al⁴ also demonstrated that despite a 55% drop, anti-SARS-CoV-2 Ab titers remained high 15 d after KT in 7 patients (6 inducted with antithymocyte globulins and 1 with basiliximab) who had received 2 mRNA vaccine doses before transplantation.

These results suggest that fully vaccinated patients maintain high Ab titers against SARS-CoV-2 in the first month post-KT, even in KTRs receiving induction therapy. It highlights the benefit to vaccinate all candidates before KT.⁵ Other studies are required to assess the long-term evolution and the impact of other therapies used in KT (ie, rituximab) on anti-SARS-CoV-2 Ab acquired before KT.