ABSTRACT
Purpose: Patients with end-stage kidney disease (ESKD) represent an extremely vulnerable group with many risk factors for adverse outcomes following SARSCoV- 2 infection. Key questions pertaining to ESKD patients awaiting transplantation include quantifying the rates of symptomatic & asymptomatic infection and determining if seroconverted patients have functional neutralising activity against SARS-CoV-2. The study of the immunological characteristics of COVID-19 in ESKD patients may help the design of an effective vaccination strategy against SARS-CoV-2 for potential transplant recipients. Methods: Serum samples were analysed by direct ELISA to detect anti-SARS-CoV-2 IgG antibodies using a recombinant Spike S11-530 subunit and Nucleocapsid protein (NP). Recombinant human anti-SARS-CoV-2 mAbs that bind to spike RBD and NP were used as positive controls. Neutralization potency against SARS-CoV-2 was measured using HIV-1 luciferase-based pseudotype assays. Titres of neutralising antibodies were calculated as 50% inhibitory dose (ID50), expressed as the highest dilution of plasma which resulted in 50% reduction of luciferase luminescence compared with controls. Results: 217 patients were on our wait-list as of May 2020 (115 receiving in-centre haemodialysis [ICHD], 41 on peritoneal dialysis and 61 pre-dialysis). 164 serum samples, of which 76% were obtained by June 2020 and coincided with the first peak of the pandemic in UK, were analysed. The observed seroprevalence of SARS-CoV-2 antibodies was 36% (95% CI 32-46). Seroconverted patients were more frail (median Clinical Frailty Scale score 3 [IQR: 3-4] vs 3 [IQR: 2-3];p=0.02), mostly from BAME background (76.3% vs 52.4%, p=0.04), had higher prevalence of diabetes (27.1% vs 12.4%;p=0.02), and received ICHD (84.7% vs 60%;p=0.006). Levels of anti-S1 and anti-NP SARS-CoV-2 IgG strongly correlated with ID50 (r=0.58, p<0.0001 and r=0.41, p=0.004, respectively). Peak CRP levels were correlated with ID50 (r=0.30;p=0.05). There were significant declines of S1 and NP antibody titres as well as neutralising activity by a median of 90 days. Conclusions: Analysis of SARS-CoV-2 antibodies and neutralising activity suggest robust functional responses are produced in infected ESKD patients, but titres wane significantly by 3 months. The level of functional immunity to SARS-CoV-2 in patients with ESKD may be used to risk stratify patients on national waiting-lists for renal transplantation and will help evaluate the efficacy of vaccination schedules in wait-listed patients once this becomes available.
ABSTRACT
Background: Understanding antibody immunity to SARS-CoV-2 and how the virus evades it is of critical importance in the fight against COVID-19. Our best hope of ending the pandemic is antibody-inducing vaccination, yet the precise targets and indeed protective capacity of antibodies remain incompletely defined. The coronaviral spike is the dominant viral antigen and the target of neutralizing antibodies. We discovered neutralizing epitopes located on the distal face of the SARS-CoV-2 spike N-terminal domain (NTD). Remarkably, instead of glycosylation, the virus uses a surface-exposed loop to restrict the access to this patch, and the gate is controlled through recruitment and dissociation of a metabolite. Methods: Using cryo-electron microscopy and X-ray crystallography we mapped a tetrapyrrole binding site to a deep cleft on the spike N-terminal domain (NTD, Fig. 1) and characterized structural features of a neutralizing epitope controlled by metabolite dissociation. Results: We show that SARS-CoV-2 spike binds biliverdin and bilirubin, the tetrapyrrole products of haem metabolism, with nanomolar affinity in a pH-sensitive manner. At physiological concentrations, biliverdin significantly dampened the reactivity of SARS-CoV-2 spike with immune sera and inhibited a subset of neutralizing antibodies. Access to the tetrapyrrole-sensitive epitope is gated by a flexible loop on the distal face of the NTD. Accompanied by profound conformational changes in the NTD, antibody binding requires relocation of the gating loop, which folds into the cleft vacated by the metabolite. Conclusion: It is well-established that viruses employ extensive glycosylation of their envelopes to shield antibody epitopes. Compared to glycosylation, epitope masking via metabolite recruitment has the advantage of reversibility. For instance, pH-dependence of the spike-tetrapyrrole interaction potentially allows dissociation within the late endosomal compartment. In summary, our results indicate that the virus co-opts the haem metabolite for the evasion of humoral immunity via allosteric shielding of a sensitive epitope and demonstrate the remarkable structural plasticity of the NTD.
ABSTRACT
Background: There is an urgent need to understand the nature of immune responses mounted against SARS-CoV-2, in order to better inform riskmitigation and vaccine strategies for people living with HIV (PLWH). Although not all PLWH are considered immunosuppressed, residual cellular immunodeficiency could influence COVID-19 disease severity and the evolution and durability of protective immunity. Information on the breadth, magnitude and longevity of SARS-CoV-2 specific responses in PLWH recovering from COVID-19 disease is currently lacking. In this study, we performed an integrated cross-sectional analysis of different branches of adaptive immunity to SARS-CoV-2 in PLWH and HIV negative donors in the convalescent phase of predominately mild COVID-19 disease. Methods: A total of n=47 HIV positive, controlled on ART, and n=35 HIV negative subjects were recruited at a median of 158 and 146 days post symptom onset respectively. SARS-CoV-2 antibodies against Spike (S1) and Nucleoprotein (N) were measured in serum by a Semiquantitative ELISA. A serum neutralisation assay with pseudotyped SARS-CoV-2 was performed to calculate the 50% inhibitory serum dilution (ID50). SARS-CoV-2 specific memory T cell responses were determined by IFN-γ ELISpot and intracellular cytokine production assays using peptide pools against SARS-CoV-2 structural and accessory proteins (Spike, Membrane, Nucleocapsid, Envelope, and ORF3a,6,7,8). Results: The majority of PLWH had detectable SARS-CoV-2 S-and N-specific antibodies with neutralizing activity at levels comparable to HIV negative subjects (p= 0.5753). Although, the overall magnitude of SARS-CoV-2 specific T cell responses measured by ELISpot was not significantly different between the groups (p=0.4642), this correlated with the size of the naïve CD4 T cell pool (r=0.5518, p=0.0143) and the CD4:CD8 ratio in PLWH (r= 0.3820, p=0.037). In both groups, SARS-CoV-2 specific CD4 T cells were more abundant compared to CD8 T cells (HIV-p= 0.002, HIV+ p=0.0019). Both humoral and cellular responses were detected between 5-7 months post infection, providing evidence of medium-term durability of responses irrespective of HIV serostatus. Conclusion: The majority of PLWH mount a functional adaptive immune response to SARS-CoV-2. Incomplete immune reconstitution on ART and persistent alterations in the T cell compartment could, however, impact the development of protective immunity to SARS-CoV-2. These findings have implications for the risk stratification and management of PLWH.