Dynamics of antibodies to SARS-CoV-2 in convalescent plasma donors

OBJECTIVES

Characterisation of the human antibody response to SARS-CoV-2 infection is vital for serosurveillance purposes and for treatment options such as transfusion with convalescent plasma or immunoglobulin products derived from convalescent plasma. In this study, we longitudinally and quantitatively analysed antibody responses in RT-PCR-positive SARS-CoV-2 convalescent adults during the first 250 days after onset of symptoms.

METHODS

We measured antibody responses to the receptor-binding domain (RBD) of the SARS-CoV-2 spike protein and the nucleocapsid protein in 844 longitudinal samples from 151 RT-PCR-positive SARS-CoV-2 convalescent adults. With a median of 5 (range 2-18) samples per individual, this allowed quantitative analysis of individual longitudinal antibody profiles. Kinetic profiles were analysed by mixed-effects modelling.

RESULTS

All donors were seropositive at the first sampling moment, and only one donor seroreverted during follow-up analysis. Anti-RBD IgG and anti-nucleocapsid IgG levels declined with median half-lives of 62 and 59 days, respectively, 2-5 months after symptom onset, and several-fold variation in half-lives of individuals was observed. The rate of decline of antibody levels diminished during extended follow-up, which points towards long-term immunological memory. The magnitude of the anti-RBD IgG response correlated well with neutralisation capacity measured in a classic plaque reduction assay and in an in-house developed competitive assay.

CONCLUSION

The result of this study gives valuable insight into the long-term longitudinal response of antibodies to SARS-CoV-2.

The effect of methotrexate on tumour necrosis factor concentrations in etanercept-treated rheumatoid arthritis patients

OBJECTIVES

Recently, we demonstrated that early low concentrations of circulating, adalimumab-bound TNF in RA patients treated with adalimumab was associated with future anti-drug antibody formation. Furthermore, low TNF was associated with less frequent baseline MTX use. This is remarkable, because of the anti-inflammatory effects of MTX and a potential inhibiting effect on cytokine production. We hypothesized an indirect effect of non-MTX use on low TNF concentrations via immunogenicity. To investigate the effect of MTX on TNF concentrations independent of anti-drug antibody formation, we measured TNF in RA patients treated with etanercept, a drug with low immunogenicity.

METHODS

TNF was quantified in 186 consecutive etanercept-treated RA patients at baseline and at weeks 4, 16 and 28. The dynamics of TNF during etanercept treatment were compared with dynamics recently published for adalimumab.

RESULTS

We demonstrated that TNF concentrations at week 4 did not associate with baseline MTX or remission after 28 weeks. Furthermore, median (interquartile range) TNF increased from <112 (<112-<112) pg/ml at baseline to 548 (344-688) pg/ml at week 4 and remained stable at week 16 and 28 [598 (442-756) and 568 (444-755) pg/ml, respectively].

CONCLUSION

Circulating TNF did not associate with MTX usage in etanercept-treated patients. This implies that MTX does not have a direct effect on TNF concentrations in circulation and that the association between early low TNF and non-use of MTX for adalimumab is thus most likely due to anti-drug antibody formation.

Dynamics of circulating TNF during adalimumab treatment using a drug-tolerant TNF assay

Patients with rheumatoid arthritis (RA) can be successfully treated with tumor necrosis factor (TNF) inhibitors, including the monoclonal antibody adalimumab. Once in remission, a proportion of patients can successfully discontinue treatment, indicating that blocking TNF is no longer required for disease control. To explore the dynamics of circulating TNF during adalimumab treatment, we developed a competition enzyme-linked immunosorbent assay that can quantify TNF in the presence of large amounts of TNF inhibitor, i.e., a "drug-tolerant" assay. In 193 consecutive adalimumab-treated patients with RA, we demonstrated that circulating TNF increased in average of >50-fold upon treatment and reached a stable concentration in time for most patients. A similar increase in TNF was found in 30 healthy volunteers after one dose of adalimumab. This implies that TNF in circulation during anti-TNF treatment is not primarily associated with disease activity. During treatment, TNF was in complex with adalimumab and could be recovered as inactive 3:1 adalimumab-TNF complexes. No quantitative association was found between TNF and adalimumab concentrations. Low TNF concentrations at week 4 were associated with a higher frequency of antidrug antibodies (ADAs) at subsequent time points, less frequent methotrexate use at baseline, and less frequent remission after 52 weeks. Also in healthy volunteers, early low TNF concentrations are associated with ADAs. In conclusion, longitudinal TNF concentrations are mostly stable during adalimumab treatment and may therefore not predict successful treatment discontinuation. However, early low TNF is strongly associated with ADA formation and may be used as timely predictor of nonresponse toward adalimumab treatment.

Effect of the oral thrombin inhibitor dabigatran on allergic lung inflammation induced by repeated house dust mite administration in mice

Asthma is a chronic disease of the airways; asthma patients are hampered by recurrent symptoms of dyspnoea and wheezing caused by bronchial obstruction. Most asthma patients suffer from chronic allergic lung inflammation triggered by allergens such as house dust mite (HDM). Coagulation activation in the pulmonary compartment is currently recognized as a feature of allergic lung inflammation, and data suggest that coagulation proteases further drive inflammatory mechanisms. Here, we tested whether treatment with the oral thrombin inhibitor dabigatran attenuates allergic lung inflammation in a recently developed HDM-based murine asthma model. Mice were fed dabigatran (10 mg/g) or placebo chow during a 3-wk HDM airway exposure model. Dabigatran treatment caused systemic thrombin inhibitory activity corresponding with dabigatran levels reported in human trials. Surprisingly, dabigatran did not lead to inhibition of HDM-evoked coagulation activation in the lung as measured by levels of thrombin-antithrombin complexes and D-dimer. Repeated HDM administration caused an influx of eosinophils and neutrophils into the lungs, mucus production in the airways, and a T helper 2 response, as reflected by a rise in bronchoalveolar IL-4 and IL-5 levels and a systemic rise in IgE and HDM-IgG1. Dabigatran modestly improved HDM-induced lung pathology (P < 0.05) and decreased IL-4 levels (P < 0.01), without influencing other HDM-induced responses. Considering the limited effects of dabigatran in spite of adequate plasma levels, these results argue against clinical evaluation of dabigatran in patients with asthma.