A Significant Contribution of the Classical Pathway of Complement in SARS-CoV-2 Neutralization of Convalescent and Vaccinee Sera.

Although high titers of neutralizing Abs in human serum are associated with protection from reinfection by SARS-CoV-2, there is considerable heterogeneity in human serum-neutralizing Abs against SARS-CoV-2 during convalescence between individuals. Standard human serum live virus neutralization assays require inactivation of serum/plasma prior to testing. In this study, we report that the SARS-CoV-2 neutralization titers of human convalescent sera were relatively consistent across all disease states except for severe COVID-19, which yielded significantly higher neutralization titers. Furthermore, we show that heat inactivation of human serum significantly lowered neutralization activity in a live virus SARS-CoV-2 neutralization assay. Heat inactivation of human convalescent serum was shown to inactivate complement proteins, and the contribution of complement in SARS-CoV-2 neutralization was often >50% of the neutralizing activity of human sera without heat inactivation and could account for neutralizing activity when standard titers were zero after heat inactivation. This effect was also observed in COVID-19 vaccinees and could be abolished in individuals who were undergoing treatment with therapeutic anti-complement Abs. Complement activity was mainly dependent on the classical pathway with little contributions from mannose-binding lectin and alternative pathways. Our study demonstrates the importance of the complement pathway in significantly increasing viral neutralization activity against SARS-CoV-2 in spike seropositive individuals.

Longitudinal Assessment of SARS-CoV-2-Specific T Cell Cytokine-Producing Responses for 1 Year Reveals Persistence of Multicytokine Proliferative Responses, with Greater Immunity Associated with Disease Severity.

Cell-mediated immunity is critical for long-term protection against most viral infections, including coronaviruses. We studied 23 severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-infected survivors over a 1-year post-symptom onset (PSO) interval by ex vivo cytokine enzyme-linked immunosorbent spot assay (ELISpot) assay. All subjects demonstrated SARS-CoV-2-specific gamma interferon (IFN-γ), interleukin 2 (IL-2), and granzyme B (GzmB) T cell responses at presentation, with greater frequencies in severe disease. Cytokines, mainly produced by CD4+ T cells, targeted all structural proteins (nucleocapsid, membrane, and spike) except envelope, with GzmB and IL-2 greater than IFN-γ. Mathematical modeling predicted that (i) cytokine responses peaked at 6 days for IFN-γ, 36 days for IL-2, and 7 days for GzmB, (ii) severe illness was associated with reduced IFN-γ and GzmB but increased IL-2 production rates, and (iii) males displayed greater production of IFN-γ, whereas females produced more GzmB. Ex vivo responses declined over time, with persistence of IL-2 in 86% and of IFN-γ and GzmB in 70% of subjects at a median of 336 days PSO. The average half-life of SARS-CoV-2-specific cytokine-producing cells was modeled to be 139 days (~4.6 months). Potent T cell proliferative responses persisted throughout observation, were CD4 dominant, and were capable of producing all 3 cytokines. Several immunodominant CD4 and CD8 epitopes identified in this study were shared by seasonal coronaviruses or SARS-CoV-1 in the nucleocapsid and membrane regions. Both SARS-CoV-2-specific CD4+ and CD8+ T cell clones were able to kill target cells, though CD8 tended to be more potent. IMPORTANCE Our findings highlight the relative importance of SARS-CoV-2-specific GzmB-producing T cell responses in SARS-CoV-2 control and shared CD4 and CD8 immunodominant epitopes in seasonal coronaviruses or SARS-CoV-1, and they indicate robust persistence of T cell memory at least 1 year after infection. Our findings should inform future strategies to induce T cell vaccines against SARS-CoV-2 and other coronaviruses.

Management of immune thrombotic thrombocytopenic purpura with caplacizumab: a Canadian, single-centre, real-world experience.

When combined with therapeutic plasma exchange (TPE) and immunosuppression, upfront universal administration of caplacizumab was shown to be effective in the management of immune thrombotic thrombocytopenic purpura (iTTP). However, access to this drug remains challenging in many jurisdictions. We retrospectively review results of a single-institution experience with caplacizumab over a 3-year period. During the study period, we treated 48 patients with iTTP, of which 11 (23%) received caplacizumab. Eight of these 11 patients (73%) were female; the median age was 45 years (IQR 37.0-58.5). All received TPE within 24 h of admission (median 9 exchanges, IQR 7.0-12.5), and high-dose steroids. Caplacizumab was initiated for a median of 6 days after admission (IQR 2.5-8.0) and continued for a median of 26 days (IQR 14.0-33.0). Five patients (45%) had refractory disease at caplacizumab initiation. Ten patients (91%) survived, reaching clinical remission. Platelet normalization was reached with a median of 4 days following caplacizumab initiation (IQR 1.5-4.0). Complications included minor bleeding (n = 1) and local allergic reaction (n = 1). No patients experienced TTP exacerbation; relapse occurred in two patients (18%) over 1-5 years of follow-up. Caplacizumab appeared to be effective and safe, despite delayed initiation and in the setting of refractory disease.

Immune thrombotic thrombocytopenic purpura (TTP) is a rare, life-threatening blood condition characterized by low platelets, anemia, and formation of blood clots in the small blood vessels. The condition results from a patient's immune system attacking a blood protein called ADAMTS13. The standard treatment for iTTP is plasma exchange (which replaces ADAMTS13) and medications, which suppress the immune system. Recently, a new medication, caplacizumab, has been shown to improve outcomes in iTTP, if combined with a standard treatment. However, this drug is expensive, and not readily available in all parts of the world, including Canada. In this article, we present the first Canadian experience with caplacizumab. Due to its limited access, the drug is frequently used in patients who are refractory to standard treatment or presented with severe organ damage. This contrasts with previously published studies, where it has been used upfront and in all patients with TTP. We find that caplacizumab may be safe and effective in this setting, demonstrating a low mortality rate and rapid recovery in most patients. While upfront and universal use of caplacizumab in the treatment of iTTP is optimal, our approach could be used in settings, where access to this medication is restricted.

Nurses best practices for the management of thrombotic thrombocytopenic purpura.

A group of Canadian apheresis nurses developed best practice for in the management of thrombotic thrombocytopenic purpura (TTP). The recommendations address issues related to infusion protocols, preventing and managing adverse events, comprehensive patient assessments, treatment procedures, as well as pre- and post- treatment care. The Canadian group encourages institutes to include nurses on committees that examine recommendations for TTP management.