Immune profiling of COVID-19 vaccine responses in people with multiple sclerosis on B cell-depleting therapy (preprint)

Background and ObjectivePeople with multiple sclerosis (pwMS) receiving B cell-depleting therapies have impaired antibody responses to vaccination. In a proportion of individuals, repeat vaccination against COVID-19 leads to seroconversion. We sought to describe the immune phenotype of pwMS on ocrelizumab, and identify clinical and immunological determinants of an effective vaccine response. MethodsThis was a single-centre, prospective cohort study. Peripheral blood samples were collected from pwMS receiving ocrelizumab (n = 38) pre and post administration of a third dose of mRNA COVID-19 vaccine. Immunogenicity was measured by T cell IFN{gamma} ELISpot, antibody titres, and live virus neutralisation. Humoral immunity was benchmarked against pwMS receiving natalizumab (n = 15), and against a correlate of real-world protection (50% reduction in incidence of infection) from SARS-CoV-2 ancestral and omicron BA.5 variants. The peripheral immune phenotype was comprehensively assessed by flow cytometry, and potential clinical and phenotypic determinants of response to vaccination identified. ResultsImmune cell populations relevant to disease and vaccine response were altered in pwMS receiving ocrelizumab versus natalizumab treatment, including depleted CD20-expressing B cell, T cell and NK cell populations, and elevated CD27+CD38+ T cell and NK8 cell frequencies. Following a third vaccine dose, 51% of pwMS on ocrelizumab were seropositive for SARS-CoV-2 receptor-binding-domain IgG, and 25% and 14% met the threshold for effective neutralisation of live SARS-CoV-2 ancestral and omicron BA.5 virus, respectively. B cell frequency at the time of vaccination, but not time since ocrelizumab infusion, was positively correlated with antibody response, while a strong negative correlation was observed between CD56bright NK cell frequency and antibody response in the ocrelizumab group. In this exploratory cohort, CD3-CD20+ B cells (% of lymphocytes; OR=3.92) and CD56bright NK cells (% of NK cells; OR=0.94) were predictive of an effective neutralising antibody response in second dose non-responders (AUC: 0.98). DiscussionOcrelizumab treatment was associated with an altered immune phenotype, including recently described T cell and NK populations with potential roles in disease pathogenesis. However, seroconversion was severely impaired by ocrelizumab, and less than half of those who seroconverted following a third vaccine dose demonstrated effective immunity against SARS-CoV-2 ancestral or omicron BA.5. B cell frequency was associated with an effective antibody response, while immunomodulatory CD56bright NK cells were identified as a potential negative determinant of response in those with inadequate B cell numbers. Immune phenotype rather than time since ocrelizumab infusion may help to stratify individuals for prophylaxis.

mTOR inhibition improves the formation of functional T cell memory following COVID-19 vaccination of kidney transplant recipients (preprint)

Inadequate immune response to vaccination is a long-standing problem faced by immunosuppressed kidney transplant recipients (KTRs), requiring novel strategies to improve vaccine efficacy. In this study, the potential of mechanistic target of rapamycin inhibitors (mTORi) to improve T cell responses to COVID-19 vaccination was investigated. Following primary vaccination with adenoviral (ChAdOx1) or mRNA (BNT162b2) COVID-19 vaccines, KTRs receiving rapamycin demonstrated T cell responses greater than those of healthy individuals, characterized by increased frequencies of vaccine-specific central memory, effector memory and TEMRA T cells, in both the CD4+ and CD8+ compartments. Relative to standard-of-care triple therapy, mTORi-based therapy was associated with a 12-fold greater functional T cell response to primary vaccination of KTRs. The use of rapamycin to augment T cell responses to COVID-19 booster (third dose) vaccination was next investigated in a randomized, controlled trial. Immunosuppression modification with rapamycin was feasible and well-tolerated, but did not improve vaccine-specific T cell responses in this cohort. To understand the parameters for effective use of rapamycin as a vaccine adjuvant, mice were treated with rapamycin before primary or booster vaccination with ancestral and/or Omicron COVID-19 vaccines. Supporting the findings from KTRs, significant enhancement of functional and stem-like memory T cell responses was observed when rapamycin was administered from the time of primary, rather than booster, vaccination. Collectively, a positive effect of mTOR inhibitors on vaccine-induced T cell immunity against COVID-19 in humans was demonstrated.

COVID-19 convalescents exhibit deficient humoral and T cell responses to variant of concern Spike antigens at 12 month post-infection (preprint)

Background The duration and magnitude of SARS-CoV-2 immunity after infection, especially with regard to the emergence of new variants of concern (VoC), remains unclear. Here, immune memory to primary infection and immunity to VoC was assessed in mild-COVID-19 convalescents one year after infection and in the absence of viral re-exposure or COVID-19 vaccination. Methods Serum and PBMC were collected from mild-COVID-19 convalescents at ∼6 and 12 months after a COVID-19 positive PCR (n=43) and from healthy SARS-CoV-2-seronegative controls (n=15-40). Serum titers of RBD and Spike-specific Ig were quantified by ELISA. Virus neutralisation was assessed against homologous, pseudotyped virus and homologous and VoC live viruses. Frequencies of Spike and RBD-specific memory B cells were quantified by flow cytometry. Magnitude of memory T cell responses was quantified and phenotyped by activation-induced marker assay, while T cell functionality was assessed by intracellular cytokine staining using peptides specific to homologous Spike virus antigen and four VoC Spike antigens. Findings At 12 months after mild-COVID-19, >90% of convalescents remained seropositive for RBD-IgG and 88.9% had circulating RBD-specific memory B cells. Despite this, only 51.2% convalescents had serum neutralising activity against homologous live-SARS-CoV-2 virus, which decreased to 44.2% when tested against live B.1.1.7, 4.6% against B.1.351, 11.6% against P.1 and 16.2%, against B.1.617.2 VoC. Spike and non-Spike-specific T cells were detected in >50% of convalescents with frequency values higher for Spike antigen (95% CI, 0.29-0.68% in CD4 + and 0.11-0.35% in CD8 + T cells), compared to non-Spike antigens. Despite the high prevalence and maintenance of Spike-specific T cells in Spike ‘high-responder’ convalescents at 12 months, T cell functionality, measured by cytokine expression after stimulation with Spike epitopes corresponding to VoC was severely affected. Interpretations SARS-CoV-2 immunity is retained in a significant proportion of mild COVID-19 convalescents 12 months post-infection in the absence of re-exposure to the virus. Despite this, changes in the amino acid sequence of the Spike antigen that are present in current VoC result in virus evasion of neutralising antibodies, as well as evasion of functional T cell responses. Funding This work was funded by project grants from The Hospital Research Foundation and Women’s and Children’s Hospital Foundation, Adelaide, Australia. MGM is THRF Early Career Fellow. BGB is THRF Mid-Career Fellow. This project has been supported partly with Federal funds from the National Institute of Allergy and Infectious Diseases, National Institutes of Health, Department of Health and Human Services, under Contract No. 75N93021C00016 to A.S. and Contract No. 75N9301900065 to A.S, D.W. Evidence before this study We regularly searched on PubMed and Google Scholar in June-October 2021 using individual or combinations of the terms “long-term immunity”, “SARS-CoV-2”, “antigenic breadth”, “variant of concern” and “COVID-19”. We found studies that had assessed immune correlates at multipe time points after COVID-19 disease onset in convalescents, but not the antigenic breadth of T cells and antibodies and not in relation to VoC. Other immune studies in virus naive vaccinees, or vaccinated convalescents evaluated VoC-specific immunity, but not in convalescents that have not been vaccinated. In summary, we could not find long-term studies providing and in-depth evaluation of functionality of humoral and cell-mediated immunity, combined with addressing the adaptability of these immune players to VoC. Added value of this study The window of opportunity to conduct studies in COVID-19 convalescents (i.e. natural immunity to SARS-CoV-2) is closing due to mass vaccination programs. Here, in a cohort of unvaccinated mild-COVID-19 convalescents, we conducted a comprehensive, longitudinal, long-term immune study, which included functional assays to assess immune fitness against antigenically different VoC. Importantly, the cohort resided in a SARS-CoV-2-free community for the duration of the study with no subsequent re-exposure or infection. Our findings reveal a deeply weakened humoral response and functional vulnerability of T cell responses to VoC Spike antigens. Implications of all the available evidence This study provides a valuable snapshot of the quality of SARS-CoV-2 natural immunity and its durability in the context of a pandemic in which new variants continuously emerge and challenge pre-existing immune responses in convalescents and vacinees. Our results serve as a warning that delays in vaccination programs could lead to an increase in re-infection rates of COVID-19 convalescents, caused by virus variants that escape humoral and cell-mediated immune responses. Furthermore, they reinforce the potential benefit of booster vaccination that is tuned to the active variants.

Long-term perturbation of the peripheral immune system months after SARS-CoV-2 infection (preprint)

Increasing evidence suggests immune dysregulation in individuals recovering from SARS-CoV-2 infection. We have undertaken an integrated analysis of immune responses at a transcriptional, cellular, and serological level at 12, 16, and 24 weeks post-infection (wpi) in 69 individuals recovering from mild, moderate, severe, or critical COVID-19. Anti-Spike and anti-RBD IgG responses were largely stable up to 24wpi and correlated with disease severity. Deep immunophenotyping revealed significant differences in multiple innate (NK cells, LD neutrophils, CXCR3+ monocytes) and adaptive immune populations (T helper, T follicular helper and regulatory T cells) in COVID-19 convalescents compared to healthy controls, which were most strongly evident at 12 and 16wpi. RNA sequencing suggested ongoing immune and metabolic dysregulation in convalescents months after infection. Variation in the rate of recovery from infection at a cellular and transcriptional level may explain the persistence of symptoms associated with long COVID in some individuals.