Polyclonal expansion of TCR Vbeta 21.3+ CD4+ and CD8+ T cells is a hallmark of Multisystem Inflammatory Syndrome in Children.

Multiple Inflammatory Syndrome in Children (MIS-C) is a delayed and severe complication of SARS-CoV-2 infection that strikes previously healthy children. As MIS-C combines clinical features of Kawasaki disease and Toxic Shock Syndrome (TSS), we aimed to compare the immunological profile of pediatric patients with these different conditions. We analyzed blood cytokine expression, and the T cell repertoire and phenotype in 36 MIS-C cases, which were compared to 16 KD, 58 TSS, and 42 COVID-19 cases. We observed an increase of serum inflammatory cytokines (IL-6, IL-10, IL-18, TNF-α, IFNγ, CD25s, MCP1, IL-1RA) in MIS-C, TSS and KD, contrasting with low expression of HLA-DR in monocytes. We detected a specific expansion of activated T cells expressing the Vß21.3 T cell receptor ß chain variable region in both CD4 and CD8 subsets in 75% of MIS-C patients and not in any patient with TSS, KD, or acute COVID-19; this correlated with the cytokine storm detected. The T cell repertoire returned to baseline within weeks after MIS-C resolution. Vß21.3+ T cells from MIS-C patients expressed high levels of HLA-DR, CD38 and CX3CR1 but had weak responses to SARS-CoV-2 peptides in vitro. Consistently, the T cell expansion was not associated with specific classical HLA alleles. Thus, our data suggested that MIS-C is characterized by a polyclonal Vß21.3 T cell expansion not directed against SARS-CoV-2 antigenic peptides, which is not seen in KD, TSS and acute COVID-19.

Prior SARS-CoV-2 infection enhances and reshapes spike protein-specific memory induced by vaccination.

The diversity of vaccination modalities and infection history are both variables that have an impact on the immune memory of individuals vaccinated against SARS-CoV-2. To gain more accurate knowledge of how these parameters imprint on immune memory, we conducted a long-term follow-up of SARS-CoV-2 spike protein-specific immune memory in unvaccinated and vaccinated COVID-19 convalescent individuals as well as in infection-naïve vaccinated individuals. Here, we report that individuals from the convalescent vaccinated (hybrid immunity) group have the highest concentrations of spike protein-specific antibodies at 6 months after vaccination. As compared with infection-naïve vaccinated individuals, they also display increased frequencies of an atypical mucosa-targeted memory B cell subset. These individuals also exhibited enhanced TH1 polarization of their SARS-CoV-2 spike protein-specific follicular T helper cell pool. Together, our data suggest that prior SARS-CoV-2 infection increases the titers of SARS-CoV-2 spike protein-specific antibody responses elicited by subsequent vaccination and induces modifications in the composition of the spike protein-specific memory B cell pool that are compatible with enhanced functional protection at mucosal sites.

Hamster organotypic kidney culture model of early-stage SARS-CoV-2 infection highlights a two-step renal susceptibility.

Kidney pathology is frequently reported in patients hospitalized with COVID-19, the pandemic disease caused by the Severe acute respiratory coronavirus 2 (SARS-CoV-2). However, due to a lack of suitable study models, the events occurring in the kidney during the earliest stages of infection remain unknown. We have developed hamster organotypic kidney cultures (OKCs) to study the early stages of direct renal infection. OKCs maintained key renal structures in their native three-dimensional arrangement. SARS-CoV-2 productively replicated in hamster OKCs, initially targeting endothelial cells and later disseminating into proximal tubules. We observed a delayed interferon response, markers of necroptosis and pyroptosis, and an early repression of pro-inflammatory cytokines transcription followed by a strong later upregulation. While it remains an open question whether an active replication of SARS-CoV-2 takes place in the kidneys of COVID-19 patients with AKI, our model provides new insights into the kinetics of SARS-CoV-2 kidney infection and can serve as a powerful tool for studying kidney infection by other pathogens and testing the renal toxicity of drugs.

Association Between Maintenance Immunosuppressive Regimens and COVID-19 Mortality in Kidney Transplant Recipients.

BACKGROUND: Solid organ transplant recipients are at high risk for fatal forms of coronavirus disease 2019 (COVID-19). We conducted a cohort study among kidney transplant (KT) recipients from the French Solid Organ Transplant COVID-19 Registry to investigate the association between maintenance immunosuppressive drugs and 60-d mortality. METHODS: Data from all KT recipients with COVID-19 included in the French Solid Organ Transplant COVID-19 Registry between February 28, 2020, and December 30, 2020, were retrieved. We evaluated associations between immunosuppressive drugs and death within 60 d using logistic regression, with all baseline characteristics considered to influence outcome or immunosuppressive regimen. The Benjamini-Hochberg correction was used for controlling false positive rate; 40 multiple imputations were performed. Adjusted P value <0.05 was considered statistically significant. RESULTS: There were 1451 KT recipients included. Median age was 58 y, and 66.4% were men. Most frequent comorbidities were hypertension (81.9%), diabetes (34.5%), and cardiovascular disease (29.5%). Median time since transplant was 71 mo. Maintenance immunosuppression regimens included calcineurin inhibitors (1295, 89.2%), antimetabolites (1205, 83%), corticosteroids (1094, 75.4%), mammalian target of rapamycin inhibitors (144, 9.9%), and belatacept (58, 4.0%). Among 1451 transplant recipients, 201 (13.9%) died within 60 d. Older age and higher baseline serum creatinine were associated with mortality (odds ratios, 1.09 [1.07-1.11] and 1.01 [1.005-1.009], P < 0.001). Corticosteroid-free regimens were associated with a significantly lower risk of death (odds ratio, 0.48 [0.31-0.76]; P = 0.011). CONCLUSIONS: Corticosteroid-free regimens were associated with a lower risk of death in KT recipients with COVID-19. Long-term exposure to corticosteroids impairs immune functions and may predispose solid organ transplant recipients to severe forms of COVID-19.

Breakthrough COVID-19 cases despite prophylaxis with 150 mg of tixagevimab and 150 mg of cilgavimab in kidney transplant recipients.

The cilgavimab-tixagevimab combination retains a partial in vitro neutralizing activity against the current SARS-CoV-2 variants of concern (omicron BA.1, BA.1.1, and BA.2). Here, we examined whether preexposure prophylaxis with cilgavimab-tixagevimab can effectively protect kidney transplant recipients (KTRs) against the omicron variant. Of the 416 KTRs who received intramuscular prophylactic injections of 150 mg tixagevimab and 150 mg cilgavimab, 39 (9.4%) developed COVID-19. With the exception of one case, all patients were symptomatic. Hospitalization and admission to an intensive care unit were required for 14 (35.9%) and three patients (7.7%), respectively. Two KTRs died of COVID-19-related acute respiratory distress syndrome. SARS-CoV-2 sequencing was carried out in 15 cases (BA.1, n = 5; BA.1.1, n = 9; BA.2, n = 1). Viral neutralizing activity of the serum against the BA.1 variant was negative in the 12 tested patients, suggesting that this prophylactic strategy does not provide sufficient protection against this variant of concern. In summary, preexposure prophylaxis with cilgavimab-tixagevimab at the dose of 150 mg of each antibody does not adequately protect KTRs against omicron. Further clarification of the optimal dosing can assist in our understanding of how best to harness its protective potential.

Early Administration of Anti-SARS-CoV-2 Monoclonal Antibodies Prevents Severe COVID-19 in Kidney Transplant Patients.

Introduction: Kidney transplant recipients (KTRs) are prone to develop severe COVID-19 and are less well protected by vaccine than immunocompetent subjects. Thus, the use of neutralizing anti-SARS-CoV-2 monoclonal antibody (MoAb) to confer a passive immunity appears attractive in KTRs. Methods: We performed a French nationwide study to compare COVID-19-related hospitalization, 30-day admission to intensive care unit (ICU), and 30-day death between KTRs who received an early infusion of MoAb (MoAb group) and KTRs who did not (control group). Controls were identified from the COVID-SFT registry (NCT04360707) using a propensity score matching with the following covariates: age, sex, delay between transplantation and infection, induction and maintenance immunosuppressive therapy, initial symptoms, and comorbidities. Results: A total of 80 KTRs received MoAb between February 2021 and June 2021. They were matched to 155 controls. COVID-19-related hospitalization, 30-day admission to ICU, and 30-day death were less frequently observed in the MoAb group (35.0% vs. 49.7%, P = 0.032; 2.5% vs. 15.5%, P = 0.002; 1.25% vs. 11.6%, P = 0.005, respectively). No patient required mechanical ventilation in the MoAb group. The number of patients to treat to prevent 1 death was 9.7. Conclusion: The early use of MoAb in KTRs with a mild form of COVID-19 largely improved outcomes in KTRs.

Infection or a third dose of mRNA vaccine elicits neutralizing antibody responses against SARS-CoV-2 in kidney transplant recipients.

Transplant recipients, who receive therapeutic immunosuppression to prevent graft rejection, are characterized by high coronavirus disease 2019 (COVID-19)-related mortality and defective response to vaccines. We observed that previous infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), but not the standard two-dose regimen of vaccination, provided protection against symptomatic COVID-19 in kidney transplant recipients. We therefore compared the cellular and humoral immune responses of these two groups of patients. Neutralizing anti-receptor-binding domain (RBD) immunoglobulin G (IgG) antibodies were identified as the primary correlate of protection for transplant recipients. Analysis of virus-specific B and T cell responses suggested that the generation of neutralizing anti-RBD IgG may have depended on cognate T-B cell interactions that took place in germinal center, potentially acting as a limiting checkpoint. High-dose mycophenolate mofetil, an immunosuppressive drug, was associated with fewer antigen-specific B and T follicular helper (TFH) cells after vaccination; this was not observed in patients recently infected with SARS-CoV-2. Last, we observed that, in two independent prospective cohorts, administration of a third dose of SARS-CoV-2 mRNA vaccine restored neutralizing titers of anti-RBD IgG in about 40% of individuals who had not previously responded to two doses of vaccine. Together, these findings suggest that a third dose of SARS-CoV-2 mRNA vaccine improves the RBD-specific responses of transplant patients treated with immunosuppressive drugs.

Low T Cell Responsiveness in the Early Phase of COVID-19 Associates with Progression to Severe Pneumonia in Kidney Transplant Recipients.

Kidney transplant (KT) recipients are at increased risk of developing severe forms of COVID-19. Little is known about the immunological mechanisms underlying disease severity in these patients receiving T-cell targeting immunosuppressive drugs. We investigated the relationship between T cell responsiveness at the beginning of the infection and the risk of subsequent progression to respiratory failure. We performed a multicentric prospective study in KT recipients with a positive RT-PCR COVID-19 test and only mild symptoms at inclusion. Blood samples were collected at baseline in a cell culture system containing T cell stimuli. We assessed T cell responsiveness by computing the ratio between the levels of Th1, Th2, Th17 and Treg cytokines produced after polyclonal stimulation and the number of blood lymphocytes. We then used an unsupervised classification approach to stratify patients into low and high T cell responders and a penalized logistic regression to evaluate the association between T cell responsiveness and progression to severe pneumonia. Forty-five patients were included. All patients who progressed to severe pneumonia (24.4%, n = 11) were low T cell responders at baseline (p = 0.01). In multivariate analysis, low T cell responsiveness at baseline was the main risk factor for subsequent progression to severe pneumonia. This study provides novel insights into the mechanisms underlying COVID-19 severity in organ transplant recipients and data of interest to clinicians managing immunosuppressive drugs in these patients.

Predictive factors of a viral neutralizing humoral response after a third dose of COVID-19 mRNA vaccine.

Kidney transplant recipients (KTRs) have reduced ability to mount adequate antibody response after two doses of the COVID-19 mRNA vaccine. French health authorities have allowed a third booster dose (D3) for KTRs, but their response is heterogeneous and tools able to discriminate the responders are lacking. Anti-RBD IgG titers (chemiluminescence immunoassay), spike-specific cellular responses (IFN-γ-releasing assay, IGRA), and in vitro serum neutralization of the virus (the best available correlate of protection), were evaluated 7-14 days after the second dose (D2) of BNT162b2 vaccine in 93 KTRs. Among the 73 KTRs, whose serum did not neutralize SARS-CoV-2 in vitro after D2, 14 (19%) acquired this capacity after D3, and were considered as "responders." Exploratory univariate analysis identified short time from transplantation and high maintenance immunosuppression as detrimental factors for the response to D3. In addition, any of the presence of anti-RBD IgGs and/or positive IGRA after D2 was predictive of response to D3. By contrast, none of the KTRs with both a negative serology and IGRA responded to D3. In summary, routinely available bioassays performed after D2 allow identifying KTRs that will respond to a booster D3. These results pave the way for the personalization of vaccination strategy in KTRs.

A comprehensive assessment of long-term SARS-CoV-2-specific adaptive immune memory in convalescent COVID-19 Solid Organ Transplant recipients.

Long-term adaptive immune memory has been reported among immunocompetent individuals up to eight months following SARS-CoV-2 infection. However, limited data is available in convalescent patients with a solid organ transplant. To investigate this, we performed a thorough evaluation of adaptive immune memory at different compartments (serological, memory B cells and cytokine [IFN-γ, IL-2, IFN-γ/IL12 and IL-21] producing T cells) specific to SARS-CoV-2 by ELISA and FluoroSpot-based assays in 102 convalescent patients (53 with a solid organ transplants (38 kidney, 5 liver, 5 lung and 5 heart transplant) and 49 immunocompetent controls) with different clinical COVID-19 severity (severe, mild and asymptomatic) beyond six months after infection. While similar detectable memory responses at different immune compartments were detected between those with a solid organ transplant and immunocompetent individuals, these responses were predominantly driven by distinct COVID-19 clinical severities (97.6%, 80.5% and 42.1%, all significantly different, were seropositive; 84% vs 75% vs 35.7%, all significantly different, showed IgG-producing memory B cells and 82.5%, 86.9% and 31.6%, displayed IFN-γ producing T cells; in severe, mild and asymptomatic convalescent patients, respectively). Notably, patients with a solid organ transplant with longer time after transplantation did more likely show detectable long-lasting immune memory, regardless of COVID-19 severity. Thus, our study shows that patients with a solid organ transplant are capable of maintaining long-lasting peripheral immune memory after COVID-19 infection; mainly determined by the degree of infection severity.

A prospective observational study for justification, safety, and efficacy of a third dose of mRNA vaccine in patients receiving maintenance hemodialysis.

The level of protection achieved by the standard two doses of COVID-19 mRNA vaccines in patients receiving maintenance hemodialysis (MHD) remains unclear. To study this we used the French Renal Epidemiology and Information Network (REIN) Registry to compare the incidence and severity of 1474 cases of COVID-19 diagnosed in patients receiving MHD after none, one or two doses of vaccine. Vaccination significantly reduce COVID-19 incidence and severity, but 11% of patients infected after two doses still died. Lack of vaccinal protection in patients naïve for SARS-CoV-2 could be due to defective Tfh response [38% of patients with negative spike-specific CD4+ T-cell interferon gamma release assay] and failure to generate viral neutralizing titers of anti-spike receptor binding domain (RBD) IgGs (63% of patients with titer at or under 997 BAU/ml, defining low/no responders) after two doses of vaccine. To improve protection, a third dose of vaccine was administered to 75 patients [57 low/no responders, 18 high responders after two doses] from the ROMANOV cohort that prospectively enrolled patients receiving MHD vaccinated with BNT162b2 (Pfizer). Tolerance to the third dose was excellent. High responders to two doses did not generate more anti-RBD IgGs after three doses but had more side effects. Importantly, 31 (54%) of low/no responders to two doses reached neutralizing titers of anti-RBD IgGs after three doses. A positive interferon gamma release assay and/or suboptimal titer of anti-RBD IgGs after two doses were the only predictive variables for response to three doses in multivariate analysis. Thus, the standard scheme of vaccination insufficiently protects patients receiving MHD. Anti-RBD IgG and specific CD4+ T-cell response after two doses can guide personalized administration of the third dose, which improves the humoral response of SARS-CoV-2-naïve patients receiving MHD.

Missing Self-Induced Activation of NK Cells Combines with Non-Complement-Fixing Donor-Specific Antibodies to Accelerate Kidney Transplant Loss in Chronic Antibody-Mediated Rejection.

BACKGROUND: Binding of donor-specific antibodies (DSAs) to kidney allograft endothelial cells that does not activate the classic complement cascade can trigger the recruitment of innate immune effectors, including NK cells. Activated NK cells contribute to microvascular inflammation leading to chronic antibody-mediated rejection (AMR). Recipient NK cells can also trigger antibody-independent microvascular inflammation by sensing the absence of self HLA class I molecules ("missing self") on allograft endothelial cells. This translational study investigated whether the condition of missing self amplifies DSA-dependent NK cell activation to worsen chronic AMR. METHODS AND RESULTS: Among 1682 kidney transplant recipients who underwent an allograft biopsy at Lyon University Hospital between 2004 and 2017, 135 fulfilled the diagnostic criteria for AMR and were enrolled in the study. Patients with complement-fixing DSAs identified by a positive C3d binding assay (n=73, 54%) had a higher risk of transplant failure (P=0.002). Among the remaining patients with complement-independent chronic AMR (n=62, 46%), those in whom missing self was identified through donor and recipient genotyping exhibited worse allograft survival (P=0.02). In multivariable analysis, only proteinuria (HR: 7.24; P=0.01) and the presence of missing self (HR: 3.57; P=0.04) were independent predictors for transplant failure following diagnosis of chronic AMR. Cocultures of human NK cells and endothelial cells confirmed that addition of missing self to DSA-induced NK cell activation increased endothelial damage. CONCLUSIONS: The assessment of missing self at the time of diagnosis of chronic AMR identifies patients at higher risk for kidney transplant failure.

The ROMANOV study found impaired humoral and cellular immune responses to SARS-CoV-2 mRNA vaccine in virus-unexposed patients receiving maintenance hemodialysis.

Patients on maintenance hemodialysis (MHD), which are at high risk of infection by SARS-CoV-2 virus and death due to COVID-19, have been prioritized for vaccination. However, because they were excluded from pivotal studies and have weakened immune responses, it is not known whether these patients are protected after the "standard" two doses of mRNA vaccines. To answer this, anti-spike receptor binding domain (RBD) IgG and interferon gamma-producing CD4+ and CD8+ specific-T cells were measured in the circulation 10-14 days after the second injection of BNT162b2 vaccine in 106 patients receiving MHD (14 with history of COVID-19) and compared to 30 healthy volunteers (four with history of COVID-19). After vaccination, most (72/80, 90%) patients receiving MHD naïve for the virus generated at least one type of immune effector, but their response was weaker and less complete than that of healthy volunteers. In multivariate analysis, hemodialysis and immunosuppressive therapy were significantly associated with absence of both anti-RBD IgGs and anti-spike CD8+ T cells. In contrast, previous history of COVID-19 in patients receiving MHD correlated with the generation of both types of immune effectors anti-RBD IgG and anti-spike CD8+ T cells at levels similar to healthy volunteers. Patients receiving MHD naïve for SARS-Cov-2 generate mitigated immune responses after two doses of mRNA vaccine. Thus, the good response to vaccine of patients receiving MHD with a history of COVID-19 suggest that these patients may benefit from a third vaccine injection.

[Covid-19 in kidney transplantation: Lessons from the French Registry]. / Covid-19 en transplantation rénale, leçons du registre français.

The Covid-19 pandemic hits the French transplant population on March 3, 2020. Very quickly, a French registry was set up on behalf of the French Society of Transplantation allowing the collection of confirmed cases of Covid-19 occurring in kidney transplant recipients in almost all French centers. The analysis of this registry in conjunction with the data from the Agence de la Biomédecine (Cristal) has enabled us to obtain instructive results. We first showed that the incidence of severe forms among transplant patients hospitalized for Covid-19 was 46% and that their mortality was 22.8%. The risk factors for severe forms and mortality are described. Then we showed, by comparing transplant patients with immunocompetent patients matched for the main severity factors of the disease, that mortality among transplant patients was higher (17.9% vs 11.4%; P<0.001). In multivariate analysis, a creatinine level at admission above 115 µmol/L was associated with death, whereas being transplanted was not. Finally, comparing the transplant cohort with patients on the kidney transplant waiting list during the period from February to June 2020, we found that patients on the waiting list had a higher Covid-19-related excess mortality than transplant patients, mainly in areas of low viral circulation. In conclusion, the French Registry of transplant patients with Covid-19, which was rapidly set up at the beginning of the epidemic, has already enabled us to draw several lessons about this initially unknown infection, particularly in kidney transplant patients, a population which appeared to be particularly at risk.