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High-dose Mycophenolate Use at Vaccination Is Independently Associated With Breakthrough COVID-19 Among Lung Transplant Patients

Joerns, John MD1; Bollineni, Srinivas MD1; Mahan, Luke D. MSN, APRN, FCCP1; Mohanka, Manish R. MD1; Lawrence, Adrian MD1; Timofte, Irina MD1; Torres, Fernando MD1; La Hoz, Ricardo M. MD2; Zhang, Song PhD3; Kershaw, Corey D. MD1; Kaza, Vaidehi MD1; Terada, Lance S. MD1; Banga, Amit MD1

Author Information
doi: 10.1097/TP.0000000000004089

Vaccine effectiveness in solid organ transplant patients is impaired compared with the general community after 2 doses of mRNA vaccines.1,2 The presence of comorbidities and use of immunosuppressive (IS) agents may contribute to this, with antimetabolites notably associated with an inadequate humoral response to vaccines,3 although it is not known if there are differences between antimetabolites or impact of doses especially among vulnerable lung transplant (LT) patients.

We sought to assess the baseline characteristics and IS regimen among a cohort of vaccinated LT patients who developed breakthrough infections and contrast them to a control group of vaccinated LT patients without coronavirus disease 2019 (COVID-19). Using a single-center retrospective chart review study approved by the University of Texas Southwestern Medical Center Institutional Review Board with a waiver of informed consent (STU-2020-1400) we reviewed all single or bilateral LT patients who tested positive for severe acute respiratory syndrome coronavirus 2 on a nasopharyngeal swab between March 1, 2020 and September 24, 2021. Vaccination has been undertaken by 398 of 444 (89.6% at the time of this report). Fourteen of the COVID-19–positive patients had been fully vaccinated, all of whom were symptomatic and included as cases in the current analysis. We randomly selected 40 vaccinated LT patients who did not develop COVID-19 during the 6 mo following their vaccination to serve as the control group. Figure S1 (SDC, shows the selection of the two study groups.

The usual IS regimen and management consisted of the following:

  1. Oral prednisone: started at 1 mg/kg in divided doses, slow taper to a baseline of 15 mg at the end of 3 mo and 0.01 mg/kg by the end of the first year and beyond.
  2. Calcineurin inhibitor: tacrolimus is the preferred agent with trough levels maintained between 10 and 15 ng/mL during the first year followed by 5 to10 ng/mL thereafter.
  3. Antimetabolite: azathioprine maintained at 2 to 3 mg/kg being the preferred agent with mycophenolate mofetil (MMF) as the alternative for patients with liver or marrow dysfunction on azathioprine, presence of donor-specific antibodies (DSAs), or unexplained progressive allograft dysfunction. MMF is typically initiated at 1500 mg/d in 2 divided doses and titrated up to 3000 mg/d. Patients with significant and intolerable gastrointestinal side effects on MMF are maintained on lower doses or switched back to azathioprine.
  4. Cylex Immuknow assay (Cylex, Inc., Columbia, MD) and absolute lymphocyte counts (ALCs) are used to titrate the antimetabolite dose.
  5. Depending on the extent of allograft injury and treatment responsiveness, patients with DSAs are managed with a combination of intravenous immunoglobulin, plasmapheresis, rituximab, and bortezomib.

All patients were encouraged to get vaccination against COVID-19 as soon as the vaccines received US Food and Drug Administration emergency use authorization. Vaccination was delayed for 3 mo after undergoing LT or after treatment with antithymocyte globulin and for 1 mo after pulse dose corticosteroid. Patients were not routinely tested for a serological response to vaccination.

We reviewed and compared patient demographics (age, gender, and race), body mass index, transplant indication, relevant comorbidities, namely diabetes comorbid renal dysfunction (estimated glomerular filtration rate [eGFR] <60 mL/min/1.73 m2) and chronic lung allograft dysfunction, time since the LT, the type and timing of the vaccine (duration of follow-up from 2 wk after the last vaccine dose), the IS regimen at the time of vaccination, as well as the mean of the last 2 values on the Cylex assay and ALC during the 6 months before the vaccination.4

The categorical variables were reported as proportions, whereas quantitative variables were presented as median with inter-quartile range as appropriate. Univariate comparisons were done using Mann-Whitney U test and Fisher exact test as appropriate. The markers of the extent of immune suppression (Cylex assay and ALC) and the eGFR at the time of vaccination were analyzed both as quantitative and categorical variables using predefined cutoffs.

The association of IS variables at the time of vaccination and breakthrough infections was evaluated using propensity matching with the propensity scores (PSs) calculated from age, time since LT, and diabetes. With the usual caliber PS matching, only 7 patients from each group could be matched so we developed a multivariate logistic regression (MLR) model using the complete study group (n = 54). For variable selection, we identified those significant at a P value of <0.1 on univariate analysis, age, race, and vaccine type to determine the independent association between the predictor variables and breakthrough infections.

Since late February 2021, breakthrough symptomatic infection among vaccinated patients has been 3.5%. Most breakthrough infections among the vaccinated cohort coincided with the increase in the community prevalence during the summer months (July and August 2021). Patients had been vaccinated with 2 doses of either BNT162b2 (Pfizer) (n = 9) or mRNA-1273 (Moderna) (n = 4) with 1 patient receiving Ad26.COV2.S vaccine. The median time from vaccination to breakthrough infection was 138 d (range, 42–179 d). All patients were maintained on standard triple IS per protocol at the time of vaccination. The IS regimen was not modified for any of the patients around the time of vaccination and none of the patients had any change to their regimen between the time of vaccination and the breakthrough infection. One patient had received 1 dose of rituximab (375 mg/m2) 6 wk before the first vaccine dose and monthly intravenous immunoglobulin infusions.

Vaccinated patients with breakthrough COVID-19 were compared with the control group as shown in Table 1. The groups were similar with regard to the demographics, significant comorbidities, time since vaccination, and time since LT, and both the groups had similar median Cylex and ALC levels. However, patients with breakthrough infection seemed more likely to be on MMF as the antimetabolite (P = 0.15), and a higher proportion of patients with breakthrough infection were on daily MMF dose of >1000 mg (P = 0.03). When compared with azathioprine or MMF dose of ≤1000 mg/d, the risk of breakthrough infection was significantly higher among patients on a daily MMF dose of >1000 mg (P = 0.006).

TABLE 1. - Comparative analysis of characteristics among vaccinated lung transplant patients with and without breakthrough COVID-19
Variable Breakthrough infection after COVID-19 vaccination (median with IQR or proportions) Odds ratio (95% CI) P Adjusted odds ratio (95% CI) P
Yes (n = 14) No (n = 40)
Age (y) 51 (39–58) 60 (46–63) 0.05 0.97 (0.91-1.04) 0.421
BMI at diagnosis (kg/m2) 29 (25.2–30.2) 27.3 (22.8–31.9) 0.88
Male gender 64.3% 50% 1.8 (0.51-6.3) 0.5
Race 0.31 0.86 (0.41-1.8)a 0.69
 Caucasian 64.3% 70%
 African American 21.4% 12.5%
 Hispanic 14.3% 5%
 Others 12.5%
Transplant indication (%)
 Restrictive 28.6% 55% 0.4
 Obstructive 21.4% 17.5%
 Suppurative 35.7% 22.5%
 Vascular 14.3% 5%
Type of transplant
 Single None 17.5% 0.25
 Bilateral 85.7% 80%
 Dual organ 14.3% 2.5%
Time since transplant (mo) 41 (30–81) 51 (32–63) 0.6
Time since vaccination at the time of study reportb 199 (161–240) 205 (32–263) 0.34
Diabetes 42.9% 40% 1.13 (0.33-3.9) 1.0
Comorbid renal dysfunctionc 28.6% 40% 0.6 (0.16-2.25) 0.53
Established preinfection CLAD 14.3% 22.5% 0.57 (0.1-3.1) 0.7
Cylex assay (ng/mL)d 440 (100–872) 387 (125–870) 0.38 1.0 (0.99-1.01) 0.36
Cylex levels <250 ng/mLd 21.4% 30.6% (n = 36) 0.62 (0.1-2.7) 0.73
Absolute lymphocyte counts (×103/µL)d 1.4 (0.3-2.5) 1.43 (0.35-2.9) 0.62 0.21 (0.03-1.26) 0.09
Absolute lymphocyte counts (×103/µL) <1000d 35.7% 30% 1.3 (0.4-4.7) 0.75
Prednisone dose (mg) 6.25 (5–10) 7.5 (5–10) 0.17
Calcineurin inhibitor use 100% 87.5% 0.31
Antimetabolite agent
 Azathioprine 7.1% 27.5% 4.9 (0.6-42.3) 0.15
 Mycophenolate mofetil 92.9% 72.5%
Azathioprine or MMF <1000 mg
 Yes 14.3% 57.5% 8.1 (1.6-41.1) 0.006 10.8 (1.63-71.46) 0.014
 No 85.7% 42.5%
MMF dose (n = 42) (n = 13) (n = 29)
 ≤1000 mg 7.7% 44.8% 9.75 (1.12-85.2) 0.03
 >1000 mg 92.3% 55.2%
Use of anti–B-cell antibody during 3 mo before vaccination 7.1% None 0.26
Type of COVID-19 vaccine
 BNT162b2 (Pfizer) 64.3% 60% 0.4 0.48 (0.08-2.86)e 0.72
 RNA-1273 (Moderna) 28.6% 35%
 Ad26.COV2.S (J&J) 7.1% 5%
The immunosuppressive agents and their doses were recorded at the time of vaccine initiation. However, none of the patients had any changes to their immunosuppressive regimen during the course of vaccination.
aCaucasians were the reference group.
bVaccines were considered effective 2 wk after the last dose.
cRenal dysfunction was indicated by the estimated glomerular filtration rate of <60 mL/min/1.73 m2 on 2 separate laboratory values at least 1 mo apart around the time of vaccination.
dMean of the last 2 values during the 6 mo preceding the vaccination; Cylex assay was unavailable for 4 patients in the control group.
ePfizer vaccine was the reference group.
BMI, body mass index; CI, confidence interval; CLAD, chronic lung allograft dysfunction; COVID-19, coronavirus disease 2019; MMF, mycophenolate mofetil.

In the PS matched group, a higher proportion of patients with breakthrough infections were on high-dose MMF (odds ratio [OR], 8.0; 95% confidence interval [CI], 0.6-107) although it did not achieve statistical significance. On MLR analysis, the association of MMF dose of >1000 mg/d with breakthrough infections was independent of age, race, type of vaccine, as well as the level of Cylex and ALC at the time of vaccination (adjusted OR, 10.8; 95% CI, 1.6-71.5; P = 0.014; Table 1). All but 1 of the vaccinated LT patients with breakthrough COVID-19 were on MMF-based IS, and a significantly higher proportion of patients were on a daily MMF dose of >1000 mg.

Although azathioprine is the first-choice antimetabolite in our program, patients transition to MMF progressively with time. The time since transplant was statistically similar among the 2 groups, although it was numerically higher for the controls, which is reassuring regarding the robustness of the analysis. As a sensitivity analysis, we added the time since transplant to the MLR model, and no significant change in the association between daily MMF dose of >1000 mg and breakthrough infection was seen (adjusted OR, 11.9; 95% CI, 1.7-85.9; P = 0.013). Apart from the development of DSAs with or without allograft dysfunction that may be managed with additional B cell–directed therapies (such as rituximab), other indications for switching to MMF are unlikely to create a bias, where in patients on MMF would have been at an increased risk of breakthrough infections. Only 1 patient with breakthrough infection had received rituximab (prevaccination), and none of the other patients had received any additional B cell–directed therapies during the 3 mo before the vaccination.

Irrespective of the type of IS, we compared the level of immunosuppression among the 2 groups using 2 laboratory variables, ALC and Cylex assay. We also compared the eGFR at the time of vaccination5 and found no difference between the groups using these 3 variables (Table 1).

High-dose MMF use has been shown to be associated with lower vaccine-induced seroconversion rates in some transplant populations, including those after COVID-19 vaccines,6,7 although the association of MMF and COVID-19 breakthrough infection has not previously been reported. In a prospective study among kidney transplant patients receiving the influenza vaccine, postvaccination protective titers were significantly lower among patients on MMF compared with azathioprine.8 The impact of antimetabolites on vaccine responsiveness seems to be dose-related, with a significant impairment in the immunogenicity at doses of >2000 mg/d.6 Our results demonstrate the clinical significance in terms of the higher risk of breakthrough infections among LT patients who are typically maintained on higher doses of MMF.

These findings have significant implications for LT patients who suffer high morbidity and mortality from COVID-19.9 Additional vaccine doses have been found to facilitate a more robust immunological response,10 but there are limited data assessing the clinical implications of such a response. Larger studies with concurrent assessment of immunogenicity with the third dose of vaccines among patients on different IS regimens, including a dose reduction in MMF (<1000 mg) or a temporary switch to azathioprine for the period of vaccination, need to be trialed.

In conclusion, we report a cohort of LT patients with breakthrough COVID-19 in whom high-dose MMF at the time of vaccination seemed to be independently associated with an increased risk of breakthrough infections.


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