The effect of sirolimus therapy on vaccine responses in transplant recipients

Immunosuppression and SARS-CoV-2 Infection in Kidney Transplant Recipients

Kidney transplant recipients (KTRs) infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) may have an increased risk of mortality compared with the general population and hemodialysis patients. As these patients are immunosuppressed, it might seem obvious to attribute this excess mortality to the impaired immunity induced by immunosuppression. In line with this reasoning is the low immune response, both cellular and humoral, that KTRs mount in response to the anti–SARS-CoV-2 vaccine; however, acute respiratory distress syndrome associated with coronavirus disease 2019 is triggered by a state of inflammation and cytokine release syndrome that lead to pulmonary damage and increased mortality. In that context, immunosuppressive treatment dampening the immune response could, in theory, be potentially beneficial.

This review aims at analyzing the current knowledge on the impact of immunosuppressive treatment on mortality in SARS-CoV-2–infected KTRs, the optimal management of immunosuppression in the coronavirus disease 2019 era, and the vaccine response and management in immunosuppressed KTRs.

The influence of selected factors on the immunogenicity of preventive vaccinations against hepatitis A, B and influenza in solid organ transplant recipients undergoing immunosuppressive therapy - a review

INTRODUCTION

Immunization is the most effective form of the primary prevention of infectious diseases. Knowledge on the efficacy and immunogenicity of vaccinations in the group of organ transplant patients taking chronic immunosuppressive treatment remains incomplete.

AREAS COVERED

The aim of this paper was to analyze factors influencing the post-vaccination response in patients undergoing chronic immunosuppressive therapy based on a literature review. Only publications that evaluated the immunogenicity of influenza, HAV and HBV vaccinations in patients on immunosuppressive therapy were reviewed.

EXPERT OPINION

The following methods are used to potentially increase the immunogenicity of vaccinations against HAV and HBV amongst post-transplantation patients: increasing the number of doses, increasing dose volumes, the method of administering as well as the addition of adjuvant. Immunogenicity is also impacted by the immunosuppression mechanism. Overall, vaccination has been concluded to be safe for post-transplantation patients and adverse events following immunization (AEFI) have typically been rated as mild or moderate. The instances of transplant rejections as observable in the long term have not been related to administered vaccinations. The data shows certain correlations of some factors with increased immunogenicity, however it is necessary to repeat the studies on a more representative group of patients.

Immunosuppression in Glomerular Diseases: Implications for SARS-CoV-2 Vaccines and COVID-19

BACKGROUND

Glomerular diseases (GD) are chronic conditions that often involve immune dysfunction and require immunosuppressive therapy (IST) to control underlying pathogenesis. Unfortunately, such diseases appear to heighten risks of severe outcomes in COVID-19 and predispose to other infections that may be life-threatening. Thus, averting preventable infections is imperative in GD patients.

SUMMARY

The advent of vaccines demonstrated to be safe and efficacious against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has favorably impacted the COVID-19 pandemic epidemiology. However, patients on ISTs were excluded from initial vaccine clinical trials. Thus, only limited and incomplete data are available currently regarding the potential impact of immunosuppression on immune response to or efficacy of the SARS-CoV-2 vaccines. However, new insights are emerging from SARS-CoV-2 vaccine studies, and impacts of ISTs on conventional vaccines are useful to consider. Mechanisms of immunosuppressive agents commonly used in the treatment of GD are reviewed with respect to implications for immune responses induced by SARS-CoV-2 vaccines. ISTs discussed include corticosteroids; alkylating agents; antimetabolites; calcineurin or mammalian target of rapamycin inhibitors; CD38+, CD20+, or CD19+ cell depletion; and complement protein C5 inhibition.

KEY MESSAGES

Many immunosuppressive therapies may potentially attenuate or impair protective immunity of the SARS-CoV-2 vaccines. However, as vaccines currently in use employ mRNA or nonreplicative viral vectors, they appear to be safe in patients on immunosuppression, further favoring vaccination. Moreover, predominant SARS-CoV-2 vaccines are likely to afford at least partial protective immunity through one or more immune mechanisms even in patients on IST. Guidelines and emerging strategies are also considered to optimize vaccine protection from COVID-19.

mTOR-Inhibition and COVID-19 in Kidney Transplant Recipients: Focus on Pulmonary Fibrosis

Kidney transplant recipients are at high risk of developing severe COVID-19 due to the coexistence of several transplant-related comorbidities (e.g., cardiovascular disease, diabetes) and chronic immunosuppression. As a consequence, a large part of SARS-CoV-2 infected patients have been managed with a reduction of immunosuppression. The mTOR-I, together with antimetabolites, have been often discontinued in order to minimize the risk of pulmonary toxicity and to antagonize pharmacological interaction with antiviral/anti-inflammatory drugs. However, at our opinion, this therapeutic strategy, although justified in kidney transplant recipients with severe COVID-19, should be carefully evaluated in asymptomatic/paucisymptomatic patients in order to avoid the onset of acute allograft rejections, to potentially exploit the mTOR-I antiviral properties, to reduce proliferation of conventional T lymphocytes (which could mitigate the cytokine storm) and to preserve Treg growth/activity which could reduce the risk of progression to severe disease. In this review, we discuss the current literature regarding the therapeutic potential of mTOR-Is in kidney transplant recipients with COVID-19 with a focus on pulmonary fibrosis.

A randomized, controlled trial comparing the immunogenicity and safety of a 23-valent pneumococcal polysaccharide vaccination to a repeated dose 13-valent pneumococcal conjugate vaccination in adult liver transplant recipients

BACKGROUND

Solid organ transplant (SOT) patients are at significant risk for invasive pneumococcal disease. The optimal pneumococcal vaccination strategy for SOT patients is not known.

METHODS

The potential adult liver transplant recipients were randomised into two arms: to receive a 23-valent pneumococcal polysaccharide vaccine (PPV23) before the transplantation or to receive a 13-valent pneumococcal conjugate vaccine (PCV13) before the transplantation and a second dose of PCV13 six months after the transplantation. Serotype-specific antibody concentrations and opsonophagocytic activity (OPA) were measured before and after the first vaccination (visits V1,V2) and six and seven months after the transplantation, e.g. before and after the second PCV13 (visits V3,V4).

RESULTS

Out of 47 patients, 19 (PCV13 arm) and 17 (PPV23 arm) received a liver transplant and all these patients completed the study (36/47, 76,6%). Each vaccine schedule elicited a good immune response. At V2, the geometric mean concentrations (GMĆs) of antibodies for serotypes 6A, 7F and 23F, and the geometric mean titers (GMT́s) of OPA for serotypes 4, 6A, 6B and 23F were significantly higher for PCV13, but the proportions of patients reaching OPA cut-off ≥ 8 or ELISA cut-off ≥ 1.0 µg/ml did not differ between the arms. At V3 the antibody concentrations and the OPA had declined to baseline in both arms. The second PCV13 vaccination elicited an immune response. There was no difference in adverse events. No vaccine-related allograft rejection was detected.

CONCLUSIONS

The immunogenicity of PPV23 and PCV13 was comparable in this patient material, but the seroresponses waned after transplantation. The second dose of PCV13 restored the immune responses and was well tolerated.

Sex-Specific Differences in HLA Antibodies after Pneumococcal Vaccination in Kidney Transplant Recipients

In transplant recipients vaccination against Streptococcus pneumoniae is recommended to reduce mortality from invasive pneumococcal disease. It is still debated if vaccination in transplant recipients triggers alloresponses. Therefore, it was our aim to define if vaccination with Prevenar 13^®, a 13-valent, conjugated pneumococcal vaccine (Pfizer, New York, NY, USA) that acts T cell dependently, induces human leukocyte antigen (HLA) antibodies in clinically stable kidney transplant recipients. Forty-seven patients were vaccinated once with Prevenar 13^® and HLA antibodies were determined prior to vaccination and at month 1 and 12 thereafter. In parallel, pneumococcal IgG antibodies were measured. Using Luminex™ Mixed Beads technology (One Lambda/Thermo Fisher, Canoga Park, CA, USA) we observed overall no change in HLA antibodies after vaccination. Pneumococcal antibodies increased significantly at month 1 (p < 0.0001) and remained elevated at month 12 (p < 0.005). A more detailed analysis of HLA antibodies showed that in 18 females HLA class I and II antibodies increased significantly at month 1 and 12 (p < 0.05); whereas in 29 males HLA class I and II antibodies tended to decrease. Using Luminex™ Single Antigen Beads assay, no de novo donor-specific HLA antibodies were detected after vaccination. In conclusion, the current data indicate that females may be more susceptible to the induction of (non-specific) HLA antibodies after vaccination.

Comparison of the immunogenicity of Dukoral® oral cholera vaccine between renal transplant recipients on either a calcineurin inhibitor or mycophenolate - A controlled trial

BACKGROUND

The evidence for recommendations regarding vaccination in solid organ transplant recipients is sparse. There is little data comparing vaccine responses between groups on different immunosuppressive drugs. This study was conducted to evaluate the antibody response to Dukoral® oral cholera vaccine in renal transplant recipients (RTR).

METHODS

In a single-center non-randomized controlled clinical trial, healthy volunteers (n = 21) and renal transplant recipients (n = 30) were vaccinated with the oral whole cell/recombinant B subunit cholera vaccine Dukoral® (Valneva Inc., Vienna, Austria). The RTR were stratified according to their maintenance immunosuppressive therapy: either prednisone and a calcineurin inhibitor (cyclosporine A or tacrolimus; P/CNI group; n = 15) or prednisone and mycophenolate (P/MMF group; n = 15). All volunteers ingested Dukoral® at baseline and at day 14. Serum samples were drawn at day 0 and day 21. The primary outcome was seroconversion, defined as either a 3-fold IgA serum titer increase in anti-cholera toxin B antibodies and/or a 4-fold rise in the serum vibriocidal titer.

RESULTS

Follow-up was complete. Seroconversion after vaccination was 57% (standard error, SE 9%) in RTR and 81% (SE 9%) in healthy controls (Relative Risk, RR 0.70; 95% CI 0.48-1.02). When stratified according to maintenance immunosuppression, the seroconversion rate was 67% (SE 12%) in the P/CNI group (RR compared with controls 0.82; 95% CI 0.55-1.25) and 47% (SE 13%) in the P/MMF group (RR compared with controls 0.58; 95% CI 0.32-1.03).

CONCLUSION

Adverse events were mild to moderate and transient. The response to Dukoral was weaker and the seroconversion rate was lower in renal transplant recipients than in healthy controls. In particular, those using mycophenolate had a poor response. Nevertheless, more than half of the transplant recipients seroconverted. Therefore oral vaccines should not be discarded as a potential tool for protection of solid organ transplant recipients. This trial is registered in clinicaltrials.gov under NCT01109914.

Vaccination Guidelines for Patients With Immune-Mediated Disorders on Immunosuppressive Therapies

BACKGROUND:

Patients with immune-mediated diseases on immunosuppressive therapies have more infectious episodes than healthy individuals, yet vaccination practices by physicians for this patient population remain suboptimal.

OBJECTIVES:

To evaluate the safety and efficacy of vaccines in individuals exposed to immunosuppressive therapies and provide evidence-based clinical practice recommendations.

METHODS:

A literature search for vaccination safety and efficacy in patients on immunosuppressive therapies (2009-2017) was conducted. Results were assessed using the Grading of Recommendation, Assessment, Development, and Evaluation system.

RESULTS:

Several immunosuppressive therapies attenuate vaccine response. Thus, vaccines should be administered before treatment whenever feasible. Inactivated vaccines can be administered without treatment discontinuation. Similarly, evidence suggests that the live zoster vaccine is safe and effective while on select immunosuppressive therapy, although use of the subunit vaccine is preferred. Caution regarding other live vaccines is warranted. Drug pharmacokinetics, duration of vaccine-induced viremia, and immune response kinetics should be considered to determine appropriate timing of vaccination and treatment (re)initiation. Infants exposed to immunosuppressive therapies through breastmilk can usually be immunized according to local guidelines. Intrauterine exposure to immunosuppressive agents is not a contraindication for inactivated vaccines. Live attenuated vaccines scheduled for infants and children ⩾12 months of age, including measles, mumps, rubella, and varicella, can be safely administered as sufficient time has elapsed for drug clearance.

CONCLUSIONS:

Immunosuppressive agents may attenuate vaccine responses, but protective benefit is generally maintained. While these recommendations are evidence based, they do not replace clinical judgment, and decisions regarding vaccination must carefully assess the risks, benefits, and circumstances of individual patients.

Pneumococcal vaccination in adult solid organ transplant recipients: A review of current evidence

This narrative review summarizes the current literature relating to pneumococcal vaccination in adult solid organ transplant (SOT) recipients, who are at risk of invasive pneumococcal disease (IPD) with its attendant high morbidity and mortality. The effect of the pneumococcal polysaccharide vaccine has been examined in several small cohort studies in SOT recipients, most of which were kidney transplant recipients. The outcomes for these studies have been laboratory seroresponses or functional antibody titers. Overall, in most of these studies the transplant recipients were capable of generating measurable serological responses to pneumococcal vaccination but these responses were less than those of healthy controls. A mathematical model estimated the effectiveness of polysaccharide vaccination in SOT recipients to be one third less than those of patients with HIV. The evidence for the efficacy of the pneumococcal conjugate vaccine in SOT is based on a small number of randomized controlled trials in liver and kidney transplant recipients. These trials demonstrated that SOT recipients mounted a serological response following vaccination however there was no benefit to the use of prime boosting (conjugate vaccine followed by polysaccharide vaccine). Currently there are no randomized studies investigating the clinical protection rate against IPD after pneumococcal vaccination by either vaccine type or linked to vaccine titers or other responses against pneumococcus. Concerns that vaccination may increase the risk of adverse alloresponses such as rejection and generation of donor specific antibodies are not supported by studies examining this aspect of vaccine safety. Pneumococcal vaccination is a potentially important strategy to reduce IPD in SOT recipients and is associated with excellent safety. Current international recommendations are based on expert opinion from conflicting data, hence there is a clear need for further high-quality studies in this high-risk population examining optimal vaccination regimens. Such studies should focus on strategies to optimize functional immune responses.

PI3Kδ hyper-activation promotes development of B cells that exacerbate Streptococcus pneumoniae infection in an antibody-independent manner

Streptococcus pneumoniae is a major cause of pneumonia and a leading cause of death world-wide. Antibody-mediated immune responses can confer protection against repeated exposure to S. pneumoniae, yet vaccines offer only partial protection. Patients with Activated PI3Kδ Syndrome (APDS) are highly susceptible to S. pneumoniae. We generated a conditional knock-in mouse model of this disease and identify a CD19+B220- B cell subset that is induced by PI3Kδ signaling, resides in the lungs, and is correlated with increased susceptibility to S. pneumoniae during early phases of infection via an antibody-independent mechanism. We show that an inhaled PI3Kδ inhibitor improves survival rates following S. pneumoniae infection in wild-type mice and in mice with activated PI3Kδ. These results suggest that a subset of B cells in the lung can promote the severity of S. pneumoniae infection, representing a potential therapeutic target.

A randomized control trial to establish the feasibility and safety of rapamycin treatment in an older human cohort: Immunological, physical performance, and cognitive effects

Inhibition of the mechanistic target of rapamycin (mTOR) pathway by rapamycin (RAPA), an FDA-approved immunosuppressive drug used as a clinical therapy to prevent solid organ allograft rejection, enhances longevity in mice. Importantly, RAPA was efficacious even when initiated in relatively old animals, suggesting that mTOR inhibition could potentially slow the progression of aging-associated pathologies in older humans (Harrison et al., 2009; Miller et al., 2011). However, the safety and tolerability of RAPA in older human subjects have not yet been demonstrated. Towards this end, we undertook a placebo-controlled pilot study in 25 generally healthy older adults (aged 70-95 years); subjects were randomized to receive either 1 mg RAPA or placebo daily. Although three subjects withdrew, 11 RAPA and 14 controls completed at least 8 weeks of treatment and were included in the analysis. We monitored for changes that would indicate detrimental effects of RAPA treatment on metabolism, including both standard clinical laboratory assays (CBC, CMP, HbA1c) and oral glucose tolerance tests (OGTTs). We also monitored parameters typically associated with aging that could potentially be modified by RAPA; these included cognitive function which was assessed by three different tools: Executive Interview-25 (EXIT25); Saint Louis University Mental Status Exam (SLUMS); and Texas Assessment of Processing Speed (TAPS). In addition, physical performance was measured by handgrip strength and 40-foot timed walks. Lastly, changes in general parameters of healthy immune aging, including serum pro-inflammatory cytokine levels and blood cell subsets, were assessed. Five subjects reported potential adverse side effects; in the RAPA group, these were limited to facial rash (1 subject), stomatitis (1 subject) and gastrointestinal issues (2 subjects) whereas placebo treated subjects only reported stomatitis (1 subject). Although no other adverse events were reported, statistically significant decrements in several erythrocyte parameters including hemoglobin (HgB) and hematocrit (Hct) as well as in red blood cell count (RBC), red blood cell distribution width (RDW), mean corpuscular volume (MCV), and mean corpuscular hemoglobin (MCH) were observed in the RAPA-treatment group. None of these changes manifested clinically significant effects during the short duration of this study. Similarly, no changes were noted in any other clinical laboratory, cognitive, physical performance, or self-perceived health status measure over the study period. Immune parameters were largely unchanged as well, possibly due to the advanced ages of the cohort (70-93 years; mean age 80.5). RAPA-associated increases in a myeloid cell subset and in T_REGS were detected, but changes in most other PBMC cell subsets were not statistically significant. Importantly, the OGTTs revealed no RAPA-induced change in blood glucose concentration, insulin secretion, and insulin sensitivity. Thus, based on the results of our pilot study, it appears that short-term RAPA treatment can be used safely in older persons who are otherwise healthy; a trial with a larger sample size and longer treatment duration is warranted.

Calcineurin inhibitor withdrawal or tapering for kidney transplant recipients

BACKGROUND

Calcineurin inhibitors (CNI) can reduce acute transplant rejection and immediate graft loss but are associated with significant adverse effects such as hypertension and nephrotoxicity which may contribute to chronic rejection. CNI toxicity has led to numerous studies investigating CNI withdrawal and tapering strategies. Despite this, uncertainty remains about minimisation or withdrawal of CNI.

OBJECTIVES

This review aimed to look at the benefits and harms of CNI tapering or withdrawal in terms of graft function and loss, incidence of acute rejection episodes, treatment-related side effects (hypertension, hyperlipidaemia) and death.

SEARCH METHODS

We searched the Cochrane Kidney and Transplant Specialised Register to 11 October 2016 through contact with the Information Specialist using search terms relevant to this review. Studies contained in the Specialised Register are identified through search strategies specifically designed for CENTRAL, MEDLINE, and EMBASE; handsearching conference proceedings; and searching the International Clinical Trials Register (ICTRP) Search Portal and ClinicalTrials.gov.

SELECTION CRITERIA

All randomised controlled trials (RCTs) where drug regimens containing CNI were compared to alternative drug regimens (CNI withdrawal, tapering or low dose) in the post-transplant period were included, without age or dosage restriction.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed studies for eligibility, risk of bias, and extracted data. Results were expressed as risk ratio (RR) or mean difference (MD) with 95% confidence intervals (CI).

MAIN RESULTS

We included 83 studies that involved 16,156 participants. Most were open-label studies; less than 30% of studies reported randomisation method and allocation concealment. Studies were analysed as intent-to-treat in 60% and all pre-specified outcomes were reported in 54 studies. The attrition and reporting bias were unclear in the remainder of the studies as factors used to judge bias were reported inconsistently. We also noted that 50% (47 studies) of studies were funded by the pharmaceutical industry.We classified studies into four groups: CNI withdrawal or avoidance with or without substitution with mammalian target of rapamycin inhibitors (mTOR-I); and low dose CNI with or without mTOR-I. The withdrawal groups were further stratified as avoidance and withdrawal subgroups for major outcomes.CNI withdrawal may lead to rejection (RR 2.54, 95% CI 1.56 to 4.12; moderate certainty evidence), may make little or no difference to death (RR 1.09, 95% CI 0.96 to 1.24; moderate certainty), and probably slightly reduces graft loss (RR 0.85, 95% CI 0.74 to 0.98; low quality evidence). Hypertension was probably reduced in the CNI withdrawal group (RR 0.82, 95% CI 0.71 to 0.95; low certainty), while CNI withdrawal may make little or no difference to malignancy (RR 1.10, 95% CI 0.93 to 1.30; low certainty), and probably makes little or no difference to cytomegalovirus (CMV) (RR 0.87, 95% CI 0.52 to 1.45; low certainty)CNI avoidance may result in increased acute rejection (RR 2.16, 95% CI 0.85 to 5.49; low certainty) but little or no difference in graft loss (RR 0.96, 95% CI 0.79 to 1.16; low certainty). Late CNI withdrawal increased acute rejection (RR 3.21, 95% CI 1.59 to 6.48; moderate certainty) but probably reduced graft loss (RR 0.84, 95% CI 0.72 to 0.97, low certainty).Results were similar when CNI avoidance or withdrawal was combined with the introduction of mTOR-I; acute rejection was probably increased (RR 1.43; 95% CI 1.15 to 1.78; moderate certainty) and there was probably little or no difference in death (RR 0.96; 95% CI 0.69 to 1.36, moderate certainty). mTOR-I substitution may make little or no difference to graft loss (RR 0.94, 95% CI 0.75 to 1.19; low certainty), probably makes little of no difference to hypertension (RR 0.86, 95% CI 0.64 to 1.15; moderate), and probably reduced the risk of cytomegalovirus (CMV) (RR 0.60, 95% CI 0.44 to 0.82; moderate certainty) and malignancy (RR 0.69, 95% CI 0.47 to 1.00; low certainty). Lymphoceles were increased with mTOR-I substitution (RR 1.45, 95% CI 0.95 to 2.21; low certainty).Low dose CNI combined with mTOR-I probably increased glomerular filtration rate (GFR) (MD 6.24 mL/min, 95% CI 3.28 to 9.119; moderate certainty), reduced graft loss (RR 0.75, 95% CI 0.55 to 1.02; moderate certainty), and made little or no difference to acute rejection (RR 1.13 ; 95% CI 0.91 to 1.40; moderate certainty). Hypertension was decreased (RR 0.98, 95% CI 0.80 to 1.20; low certainty) as was CMV (RR 0.41, 95% CI 0.16 to 1.06; low certainty). Low dose CNI plus mTOR-I makes probably makes little of no difference to malignancy (RR 1.22, 95% CI 0.42 to 3.53; low certainty) and may make little of no difference to death (RR 1.16, 95% CI 0.71 to 1.90; moderate certainty).

AUTHORS' CONCLUSIONS

CNI avoidance increased acute rejection and CNI withdrawal increases acute rejection but reduced graft loss at least over the short-term. Low dose CNI with induction regimens reduced acute rejection and graft loss with no major adverse events, also in the short-term. The use of mTOR-I reduced CMV infections but increased the risk of acute rejection. These conclusions must be tempered by the lack of long-term data in most of the studies, particularly with regards to chronic antibody-mediated rejection, and the suboptimal methodological quality of the included studies.

Serologic response after vaccination against influenza (A/H1N1)pdm09 in children with renal disease receiving oral immunosuppressive drugs

A limited number of reports are available regarding the effect of the influenza vaccine in pediatric patients receiving steroid and immunosuppressant therapy. The influenza A(H1N1)pdm09 vaccine was administered to 15 children with renal disease who were receiving steroid and immunosuppressant therapy (treatment group) and 23 children with who were not receiving these drugs (non-treatment group). Titer transition of the hemagglutination inhibition antibody was compared between the 2 groups immediately before vaccination and 4 weeks and 6 months after vaccination. Multivariate analysis showed a significant correlation between geometric mean titer, SCR, and SPR with age, while no correlation was observed between treatment with immunosuppressant therapy and efficacy. No serious adverse reactions occurred after vaccination. This strain is not present in existing influenza vaccines, and A(H1N1)pdm09HA vaccination was administered alone in 2009. The children in this study had not previously been exposed to this strain. Therefore, we evaluated the effect of the A(H1N1)pdm09HA vaccine without the effects of vaccination or past infection with A(H1N1)pdm09HA or A(H3N2) vaccination in the previous year.

Immunosuppressants in cancer prevention and therapy

Rapalogs such as rapamycin (sirolimus), everolimus, temserolimus, and deforolimus are indicated for the treatment of some malignancies. Rapamycin is the most effective cancer-preventive agent currently known, at least in mice, dramatically delaying carcinogenesis in both normal and cancer-prone murine strains. In addition, rapamycin and everolimus decrease the risk of cancer in patients receiving these drugs in the context of immunosuppressive regimens. In general, the main concern about the use of immunosuppressants in humans is an increased risk of cancer. Given that rapalogs are useful in cancer prevention and therapy, should they be viewed as immunosuppressants or immunostimulators? Or should we reconsider the role of immunity in cancer altogether? In addition to its anti-viral, anti-inflammatory, anti-angiogenic and anti-proliferative effects, rapamycin operates as a gerosuppressant, meaning that it inhibits the cellular conversion to a senescent state (the so-called geroconversion), a fundamental process involved in aging and age-related pathologies including cancer.

Vaccination against Streptococcus pneumoniae does not induce antibodies against HLA or MICA in clinically stable kidney transplant recipients

There are concerns in the community that immune activation after vaccination could lead to (subclinical) rejection. Our aim was to define if pneumococcal vaccination induced HLA antibodies using highly sensitive methods. Forty-nine kidney transplant recipients were immunized with Pneumovax 23. The median interval between transplantation and vaccination was 6.5 years, the median serum creatinine concentration 1.3, 1.3 and 1.4 mg/dL pre-vaccination, at month 1 and 15 post-vaccination, respectively. In none of the patients biopsy-proven acute rejection was diagnosed within three years post-vaccination. Pneumococcal, HLA class I and II and major histocompatibility class I-related chain A (MICA) antibodies were determined by Luminex™ technology (xMAP™ Pneumococcal Immunity Panel and LABScreen™ Mixed beads, respectively) and HLA antibodies also by ELISA (Lambda Antigen Tray™). While pneumococcal antibodies were significantly higher at month 1 and 15 post- vs. pre-vaccination (p<0.0001 each), HLA/MICA antibodies remained unchanged as determined by Luminex™ and ELISA. Positive Luminex™ reactions were present in 63%, 67% and 63% (HLA class I), 47%, 47% and 55% (HLA class II) and 29%, 29% and 29% (MICA) pre-vaccination, at month 1 and 15, respectively. In clinically stable kidney transplant recipients there is no evidence for an increase in HLA antibodies after pneumococcal vaccination.

B cell-specific deficiencies in mTOR limit humoral immune responses

Generation of high-affinity Abs in response to Ags/infectious agents is essential for developing long-lasting immune responses. B cell maturation and Ab responses to Ag stimulation require Ig somatic hypermutation (SHM) and class-switch recombination (CSR) for high-affinity responses. Upon immunization with either the model Ag 4-hydroxy-3-nitrophenylacetyl hapten (NP) conjugated to chicken γ globulin lysine (NP-CGG) or heat-killed Streptococcus pneumoniae capsular type 14 protein (Pn14), knock-in (KI) mice hypomorphic for mTOR function had a decreased ability to form germinal centers, develop high-affinity anti-NP-specific or anti-Pn14-specific Abs, and perform SHM/CSR. Hypomorphic mTOR mice also had a high mortality (40%) compared with wild-type (WT) (0%) littermates and had lower pneumococcal surface protein A-specific Ab titers when immunized and challenged with live S. pneumoniae infection. Mice with mTOR deleted in their B cell lineage (knockout [KO]) also produced fewer splenic germinal centers and decreased high-affinity Ab responses to NP-CGG than did their WT littermates. CSR rates were lower in mTOR KI and KO mice, and pharmacologic inhibition of mTOR in WT B cells resulted in decreased rates of ex vivo CSR. RNA and protein levels of activation-induced cytidine deaminase (AID), a protein essential for SHM and CSR, were lower in B cells from both KI and B cell-specific KO mice, concomitant with increases in phosphorylated AKT and FOXO1. Rescue experiments increasing AID expression in KI B cells restored CSR levels to those in WT B cells. Thus, mTOR plays an important immunoregulatory role in the germinal center, at least partially through AID signaling, in generating high-affinity Abs.

Incidence and risk of treatment-related mortality with mTOR inhibitors everolimus and temsirolimus in cancer patients: a meta-analysis

Background

Two novel mammalian targets of rapamycin (mTOR) inhibitors everolimus and temsirolimus are now approved by regulatory agencies and have been widely investigated among various types of solid tumors, but the risk of fatal adverse events (FAEs) with these drugs is not well defined.

Methods

We searched PubMed, EMBASE, and Cochrane library databases for relevant trials. Eligible studies included prospective phase II and III trials evaluating everolimus and temsirolimus in patients with all malignancies and data on FAEs were available. Statistical analyses were conducted to calculate the summary incidence, RRs and 95% confidence intervals (CIs) by using either random effects or fixed effect models according to the heterogeneity of the included studies.

Results

A total of 3322 patients with various advanced solid tumors from 12 trials were included. The overall incidence of mTOR inhibitors associated FAEs was 1.8% (95%CI: 1.3–2.5%), and the incidences of everolimus related FAEs were comparable to that of temsirolimus (1.7% versus 1.8%). Compared with the controls, the use of mTOR inhibitors was associated with an increased risk of FAEs, with a RR of 3.24 (95%CI: 1.21–8.67, p = 0.019). On subgroup analysis, a non-statistically significant increase in the risk of FAEs was found according to different mTOR inhibitors, tumor types or controlled therapy. No evidence of publication bias was observed.

Conclusion

With the present evidence, the use of mTOR inhibitors seems to increase the risk of FAEs in patients with advanced solid tumors. More high quality trials are still needed to investigate this association.

Serologic vaccination response after solid organ transplantation: a systematic review

BACKGROUND

Infectious diseases after solid organ transplantation (SOT) are one of the major complications in transplantation medicine. Vaccination-based prevention is desirable, but data on the response to active vaccination after SOT are conflicting.

METHODS

In this systematic review, we identify the serologic response rate of SOT recipients to post-transplantation vaccination against tetanus, diphtheria, polio, hepatitis A and B, influenza, Streptococcus pneumoniae, Haemophilus influenzae, Neisseria meningitides, tick-borne encephalitis, rabies, varicella, mumps, measles, and rubella.

RESULTS

Of the 2478 papers initially identified, 72 were included in the final review. The most important findings are that (1) most clinical trials conducted and published over more than 30 years have all been small and highly heterogeneous regarding trial design, patient cohorts selected, patient inclusion criteria, dosing and vaccination schemes, follow up periods and outcomes assessed, (2) the individual vaccines investigated have been studied predominately only in one group of SOT recipients, i.e. tetanus, diphtheria and polio in RTX recipients, hepatitis A exclusively in adult LTX recipients and mumps, measles and rubella in paediatric LTX recipients, (3) SOT recipients mount an immune response which is for most vaccines lower than in healthy controls. The degree to which this response is impaired varies with the type of vaccine, age and organ transplanted and (4) for some vaccines antibodies decline rapidly.

CONCLUSION

Vaccine-based prevention of infectious diseases is far from satisfactory in SOT recipients. Despite the large number of vaccination studies preformed over the past decades, knowledge on vaccination response is still limited. Even though the protection, which can be achieved in SOT recipients through vaccination, appears encouraging on the basis of available data, current vaccination guidelines and recommendations for post-SOT recipients remain poorly supported by evidence. There is an urgent need to conduct appropriately powered vaccination trials in well-defined SOT recipient cohorts.

Low seroconversion after one dose of AS03-adjuvanted H1N1 pandemic influenza vaccine in solid-organ transplant recipients

BACKGROUND

Immunocompromised individuals are more susceptible to complications produced by influenza infection. As a result, solid-organ transplant (SOT) recipients were targeted as a priority group to receive AS03-adjuvanted H1N1 influenza vaccine during 2009.

OBJECTIVE

To evaluate seroconversion after one dose of adjuvanted pandemic influenza H1N1 (pH1N1) vaccine in SOT recipients.

METHODS

Adult SOT recipients were enrolled to receive one 3.75 μg dose of adjuvanted pH1N1 vaccine. Serological status was tested using a hemagglutination inhibition assay before and two and four weeks postvaccination.

RESULTS

The five SOT recipients (one liver, two kidney and two lung transplants) had a median age of 50 years (range 36 to 53 years), and three were male, who were a median time of three years (range two months to 15 years) post-transplant. All patients were on a double or triple immunosuppressive regimen. The prevaccination pH1N1 titre was 1:10 in four patients and 1:40 in one patient. Seroprotection was observed only in one patient, with a rise in titre from 1:40 at baseline to 1:320 at both two and four weeks after vaccination. This lung transplant recipient had documented previous infection with pH1N1.

CONCLUSION

Results of the present small study call into question whether one dose of adjuvanted pH1N1 vaccine can provide seroprotection in SOT recipients.

Effects of sotrastaurin, mycophenolic acid and everolimus on human B-lymphocyte function and activation

Humoral rejection processes may lead to allograft injury and subsequent dysfunction. Today, only one B-cell-specific agent is in clinical use and the effects of standard and new immunosuppressant substances on B-cell activation and function are not fully clarified. The impact of sotrastaurin, mycophenolic acid and everolimus on human B-lymphocyte function was assessed by analysing proliferation, apoptosis, CD80/CD86 expression and immunoglobulin and IL-10 production in primary stimulated B cells. In addition, B-cell co-cultures with pre-activated T cells were performed to evaluate the effect of the different immunosuppressive agents on T-cell-dependent immunoglobulin production. Sotrastaurin did not inhibit B-cell proliferation, CD80/CD86 expression, and IgG production and had only minor effects on IgM levels at the highest concentration administered. In contrast, mycophenolic acid and everolimus had strong effects on all B-cell functions in a dose-dependent manner. All immunosuppressive agents caused decreased immunoglobulin levels in T-cell-dependent B-cell cultures. The data provided here suggest that mycophenolic acid and everolimus, but not sotrastaurin, are potent inhibitors of human B-lymphocyte function and activation.

Influenza vaccination for immunocompromised patients: systematic review and meta-analysis from a public health policy perspective

BACKGROUND

Immunocompromised patients are vulnerable to severe or complicated influenza infection. Vaccination is widely recommended for this group. This systematic review and meta-analysis assesses influenza vaccination for immunocompromised patients in terms of preventing influenza-like illness and laboratory confirmed influenza, serological response and adverse events.

METHODOLOGY/PRINCIPAL FINDINGS

Electronic databases and grey literature were searched and records were screened against eligibility criteria. Data extraction and risk of bias assessments were performed in duplicate. Results were synthesised narratively and meta-analyses were conducted where feasible. Heterogeneity was assessed using I(2) and publication bias was assessed using Begg's funnel plot and Egger's regression test. Many of the 209 eligible studies included an unclear or high risk of bias. Meta-analyses showed a significant effect of preventing influenza-like illness (odds ratio [OR]=0.23; 95% confidence interval [CI]=0.16-0.34; p<0.001) and laboratory confirmed influenza infection (OR=0.15; 95% CI=0.03-0.63; p=0.01) through vaccinating immunocompromised patie nts compared to placebo or unvaccinated controls. We found no difference in the odds of influenza-like illness compared to vaccinated immunocompetent controls. The pooled odds of seroconversion were lower in vaccinated patients compared to immunocompetent controls for seasonal influenza A(H1N1), A(H3N2) and B. A similar trend was identified for seroprotection. Meta-analyses of seroconversion showed higher odds in vaccinated patients compared to placebo or unvaccinated controls, although this reached significance for influenza B only. Publication bias was not detected and narrative synthesis supported our findings. No consistent evidence of safety concerns was identified.

CONCLUSIONS/SIGNIFICANCE

Infection prevention and control strategies should recommend vaccinating immunocompromised patients. Potential for bias and confounding and the presence of heterogeneity mean the evidence reviewed is generally weak, although the directions of effects are consistent. Areas for further research are identified.

Influenza vaccination in the organ transplant recipient: review and summary recommendations

Influenza virus causes a spectrum of illness in transplant recipients with a high rate of lower respiratory disease. Seasonal influenza vaccination is an important public health measure recommended for transplant recipients and their close contacts. Vaccine has been shown to be safe and generally well tolerated in both adult and pediatric transplant recipients. However, responses to vaccine are variable and are dependent on various factors including time from transplantation and specific immunosuppressive medication. Seasonal influenza vaccine has demonstrated safety and no conclusive evidence exists for a link between vaccination and allograft dysfunction. Annually updated trivalent inactivated influenza vaccines have been available and routinely used for several decades, although newer influenza vaccination formulations including high-dose vaccine, adjuvanted vaccine, quadrivalent inactivated vaccine and vaccine by intradermal delivery system are now available or will be available in the near future. Safety and immunogenicity data of these new formulations in transplant recipients requires investigation. In this document, we review the current state of knowledge on influenza vaccines in transplant recipients and make recommendations on the use of vaccine in both adult and pediatric organ transplant recipients.

Antibody response after a single dose of an AS03-adjuvanted split-virion influenza A (H1N1) vaccine in heart transplant recipients

BACKGROUND

Influenza A (H1N1) has emerged as a considerable threat for recipients of organ transplants. Vaccination against the novel influenza A (H1N1) virus has generally been advocated. There is limited experience with AS03-adjuvanted A/H1N1 pandemic influenza vaccines in immunosuppressed patients.

METHODS

We conducted an observational, nonrandomized single-center study to assess antibody response and vaccine-related adverse effects in 47 heart transplant recipients (44 men; age, 56±13 years). The AS03-adjuvanted, inactivated split-virion A/California/7/2009 H1N1v pandemic vaccine was administered. Antibody titers were measured using hemagglutination inhibition; immunoglobulin G (IgG) response was assessed using a new pandemic influenza A IgG enzyme-linked immunosorbent assay (ELISA) test kit and compared with hemagglutination-inhibition titers. Adverse effects of vaccination were assessed by a questionnaire.

RESULTS

Postvaccination antibody titers of greater than or equal to 1:40 were found in only 15 patients, corresponding to a seroprotection rate of 32% (95% confidence interval, 19%-47%). Sensitivity, specificity, positive predictive value, and negative predictive value of ELISA testing were 80.0%, 68.8%, 54.5%, and 88.0%, respectively. Age, time posttransplantation, and immunosuppressive regimen did not impact antibody response. Vaccination was well tolerated.

CONCLUSIONS

Single-dose administration of an AS03-adjuvanted vaccine against the novel influenza A (H1N1) virus did not elicit seroprotective antibody concentrations in a substantial proportion of heart transplant recipients; the new pandemic influenza A IgG ELISA test kit proved to be of limited clinical use.

Outcomes associated with influenza vaccination in the first year after kidney transplantation

BACKGROUND AND OBJECTIVES

Influenza vaccination is recommended in all renal transplant recipients. However, immunosuppression in the early period post-transplant may attenuate the immunologic response to the vaccine. Additionally, it has been theorized that vaccination can induce an immune response that could trigger rejection episodes.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In a retrospective cohort of 51,730 adult Medicare primary patients who were first transplanted from January 2000 to July 2006 and followed through October 2006, we assessed Medicare claims for influenza vaccination and influenza infections, respectively. Outcomes included allograft loss and death.

RESULTS

There were 9678 (18.7%) patients with claims for influenza vaccination in the first year post-transplant. Factors associated with vaccination included older age, diabetes, later year of transplant, and tacrolimus or mycophenolate at discharge. Vaccinations were less frequent among men, African Americans, highly sensitized patients, or those receiving induction immunosuppression or expanded criteria donor kidneys. Vaccination in the first year after transplant was associated with lower risk of subsequent allograft loss and death. Claims for influenza infection were reported in 310 (0.6%) patients and were not significantly associated with graft loss, although there was a trend toward death.

CONCLUSIONS

In the first year after renal transplantation, influenza vaccination was associated with a lower risk of subsequent allograft loss and death. Although this study cannot comment on formation of protective antibodies after vaccination, these data do not support withholding vaccination on the basis of concerns of adversely affecting allograft function.

Use of sirolimus in liver transplant recipients with renal insufficiency: a systematic review and meta-analysis

Sirolimus is used in patients with renal insufficiency after liver transplantation (LT) and especially in those with calcineurin inhibitor (CNI)-associated nephrotoxicity. We conducted a systematic review of all randomized controlled trials and observational studies to test the hypothesis that the use of sirolimus is associated with an improvement in renal function at 1 year in LT recipients with renal insufficiency [glomerular filtration rate (GFR) < 60 mL/minute or creatinine level ≥ 1.5 mg/dL]. We performed a search of all major databases, conference proceedings, and relevant journals through December 2009 and contacted content experts, corresponding authors, and the pharmaceutical manufacturer. A random effects model was used to determine the pooled estimate of the change in renal function and pooled risk estimates of adverse events that may be associated with sirolimus-based therapy at 1 year. Eleven studies (three randomized controlled trials and eight observational studies) met the final inclusion criteria. A nonsignificant improvement of 3.38 mL/minute [95% confidence interval (CI) = -2.93 to 9.69] was observed in methodologically sound observational studies and controlled trials reporting the primary outcome. In controlled trials, baseline GFR >50 mL/min sirolimus use was associated with an improvement of 10.35 mL/minute (95% CI = 3.98-16.77) in GFR or creatinine clearance. Sirolimus was not significantly associated with death [relative risk (RR) = 1.12, 95% CI = 0.66-1.88] or graft failure (RR = 0.80, 95% CI = 0.45-1.41), although reporting was incomplete. It was associated with a statistically significant risk of infection (RR = 2.47, 95% CI = 1.14-5.36), rash (RR = 7.57, 95% CI = 1.75-32.70), ulcers (RR = 7.44, 95% CI = 2.03-27.28), and discontinuation of therapy (RR = 3.61, 95% CI = 1.32-9.89).

CONCLUSION

Conversion to sirolimus from CNIs is associated with a nonsignificant improvement in renal function in LT recipients with renal insufficiency, although the results are limited by heterogeneity, a risk of bias, and a lack of standardized reporting.

Maintenance immunosuppressive therapy with everolimus preserves humoral immune responses

While the guidelines for vaccination in renal transplant recipients recommend the use of pneumococcal polysaccharide (PPS) and tetanus toxoid (TT), their efficacy in immunocompromised renal transplant recipients is not known. Here we tested the effect of everolimus on immune responses after vaccination by measuring the capacity of 36 stable renal transplant recipients to mount cellular and humoral responses after vaccination. Twelve patients in each treatment arm received immunosuppressive therapy consisting of prednisolone (P) plus cyclosporine (CsA), mycophenolate sodium (MPA), or everolimus. Patients were vaccinated with the T-cell-dependent antigens immunocyanin and TT, and the T-cell-independent PPS. Treatment with CsA partially inhibited and MPA completely abolished the capacity to mount a primary humoral response, whereas everolimus left this largely intact. Recall responses were inhibited by MPA only. All drug combinations inhibited cellular responses against TT. In patients treated with MPA, B-cell numbers were severely reduced. Thus, combined with P, treatment with MPA completely disturbed primary and secondary humoral responses. Everolimus or CsA allowed the boosting of T-cell-dependent and -independent secondary humoral responses. Treatment with everolimus allowed a primary response.

Inhibition of polyomavirus BK-specific T-Cell responses by immunosuppressive drugs

BACKGROUND

Reducing immunosuppression is the treatment of choice for polyomavirus-associated nephropathy in kidney transplant (KT) patients, but strategies and targets are uncertain.

METHODS

Using interferon-gamma ELISpot assays, we investigated immunosuppressive drug levels and polyomavirus BK (BKV) large T-antigen-specific T-cell responses in KT patients in vivo and in healthy donors after titrating immunosuppression in vitro.

RESULTS

In KT patients, BKV-specific T-cell responses were inversely correlated with tacrolimus trough levels (R=0.28, P<0.002), but not with mycophenolate levels, prednisone, or overall immunosuppressive dosing. In vitro tacrolimus concentrations above 6 ng/mL inhibited BKV- and cytomegalovirus-specific T-cells more than 50%, whereas less than 30% inhibition was observed below 3 ng/mL. Inhibition by cyclosporine A was more than 50% at concentrations of 1920 ng/mL and less than 30% below 960 ng/mL, corresponding to clinical C0 trough levels of 200 and 100 ng/mL, respectively. However, mycophenolate up to 8 microg/mL, leflunomide 50 microg/mL, or sirolimus concentrations 64 ng/mL did not inhibit BKV-specific interferon-gamma production, but antigen-dependent T-cell expansion.

CONCLUSIONS

Calcineurin-inhibitor concentrations are critical for BKV-specific T-cell activation. Reducing calcineurin inhibitors should be considered as first step, whereas conversion to mTOR inhibitors may be an attractive alternative or second step that should be validated in clinical BKV intervention trials.

Influenza virus vaccination in kidney transplant recipients: serum antibody response to different immunosuppressive drugs

INTRODUCTION

This study prospectively accessed the immune response to the inactivated influenza vaccine in renal transplant recipients receiving either azathioprine or mycophenolate mofetil (MMF). Side effects were investigated.

METHODS

Sixty-nine patients received one dose of inactivated trivalent influenza vaccine. Antihemagglutinin (HI) antibody response against each strain was measured before and one to six months after vaccination.

RESULTS

Geometric mean HI antibody titers for H1N1 and H3N2 strains increased from 2.57 and 2.44 to 13.45 (p = 0.001) and 7.20 (p < 0.001), respectively. Pre- and post-vaccination protection rates for H1N1 and H3N2 increased from 8.7% to 49.3% (p < 0.001); and 36.3% (p < 0.001) and seroconversion rates were 36% and 25.3%, respectively. There was no response to influenza B. The use of MMF reduced the H1N1 and H3N2 protection rates and the seroconversion rate for the H1N1 strain when compared with the use of azathioprine, and subjects transplanted less than 87 months also had inferior antibody response. Adverse events were mild and there were no change on renal function post-vaccination.

CONCLUSION

Renal transplant patients vaccinated against influenza responded with antibody production for influenza A virus strains, but not for influenza B. Use of MMF and shorter time from transplantation decreased the immune response to the vaccine.

Influenza in immunosuppressed populations: a review of infection frequency, morbidity, mortality, and vaccine responses

Patients that are immunosuppressed might be at risk of serious influenza-associated complications. As a result, multiple guidelines recommend influenza vaccination for patients infected with HIV, who have received solid-organ transplants, who have received haemopoietic stem-cell transplants, and patients on haemodialysis. However, immunosuppression might also limit vaccine responses. To better inform policy, we reviewed the published work relevant to incidence, outcomes, and prevention of influenza infection in these patients, and in patients being treated chemotherapy and with systemic corticosteroids. Available data suggest that most immunosuppressed populations are indeed at higher risk of influenza-associated complications, have a general trend toward impaired humoral vaccine responses (although these data are mixed), and can be safely vaccinated--although longitudinal data are largely lacking. Randomised clinical trial data were limited to one study of HIV-infected patients with high vaccine efficacy. Better trial data would inform vaccination recommendations on the basis of efficacy and cost in these at-risk populations.

Effects of immunosuppressive drugs on purified human B cells: evidence supporting the use of MMF and rapamycin

BACKGROUND

Humoral immunity is increasingly recognized as an important factor in the rejection of organ transplants. In general, humoral rejection is treated with standard immunosuppressive drugs. The direct effect of these immunosuppressive drugs on B cells is not well known.

METHODS

Purified human B cells devoid of T cells were stimulated with CD40L expressing L cells, or by anti-CD40 mAb with or without Toll-like receptor triggering, all in the presence of B-cell activating cytokines. These three protocols resulted in various degrees of B-cell stimulation. We added four commonly used immunosuppressive drugs (tacrolimus, cyclosporin, mycophenolic acid [MPA], and rapamycin) to these cultures and tested a variety of parameters of B-cell activity including proliferation, apoptosis induction, and both IgM and IgG production.

RESULTS

Tacrolimus and cyclosporin marginally inhibited B-cell proliferation and immunoglobulin production, and the extent of inhibition depended on the degree of the B-cell stimulation. In contrast, MPA and rapamycin profoundly inhibited both B-cell proliferation and immunoglobulin production, which was independent of the degree of B-cell stimulation. Both drugs induced B-cell apoptosis. Moreover, rapamycin caused a reduction in the number of B cells capable of producing immunoglobulins.

CONCLUSIONS

Our data show that MPA and rapamycin are capable of strongly inhibiting B cells responses. This provides a rationale for the use of both MPA and rapamycin to prevent or counteract humoral responses.

Influenza vaccination is efficacious and safe in renal transplant recipients

Whether influenza vaccination in solid-organ transplant recipients is efficacious remains a controversial issue. Furthermore, theoretical concerns have been raised regarding the safety of vaccination as it might trigger rejection of the allograft. The present prospective trial is aimed at investigating the antibody response and safety of influenza vaccination in renal transplant recipients (RTR). A total of 165 RTR and 41 healthy volunteers were vaccinated with a standard trivalent inactivated influenza vaccine. Hemagglutination-inhibiting (HI) antibodies were quantified before and 1 month after vaccination. Seroprotection (SP) and seroresponse (SR) were defined as a titer > or =40 and a 4-fold rise in HI titer, respectively. Similar SR rates were observed in both groups. Postvaccination SP rates in RTR amounted to 92.7%, 78.7% and 82.9% for A/H1N1, A/H3N2 and B, respectively. High baseline SP rates, most probably reflecting frequent preimmunizations, explain partly the high postvaccination SP rates. SR rate was independently and inversely associated with baseline SP rate. Mycophenolate mofetil (MMF) usage was associated with a 2.6-5-fold lower SR. Nonetheless, these patients showed good postvaccination SP rates. A booster dose did not enhance SP or SR rates. Influenza vaccination neither affected allograft function nor caused rejection episodes. In conclusion, influenza vaccination is efficacious and safe in renal transplantation.