Multimodal vaccination targeting the receptor binding domains of Clostridioides difficile toxins A and B with an attenuated Salmonella Typhimurium vector (YS1646) protects mice from lethal challenge.

Developing a vaccine against Clostridioides difficile is a key strategy to protect the elderly. Two candidate vaccines using a traditional approach of intramuscular (IM) delivery of recombinant antigens targeting C. difficile toxins A (TcdA) and B (TcdB) failed to meet their primary endpoints in large phase 3 trials. To elicit a mucosal response against C. difficile, we repurposed an attenuated strain of Salmonella Typhimurium (YS1646) to deliver the receptor binding domains (rbd) of TcdA and TcdB to the gut-associated lymphoid tissues, to elicit a mucosal response against C. difficile. In this study, YS1646 candidates with either rbdA or rbdB expression cassettes integrated into the bacterial chromosome at the attTn7 site were generated and used in a short-course multimodal vaccination strategy that combined oral delivery of the YS1646 candidate(s) on days 0, 2, and 4 and IM delivery of recombinant antigen(s) on day 0. Five weeks after vaccination, mice had high serum IgG titers and increased intestinal antigen-specific IgA titers. Multimodal vaccination increased the IgG avidity compared to the IM-only control. In the mesenteric lymph nodes, we observed increased IL-5 secretion and increased IgA+ plasma cells. Oral vaccination skewed the IgG response toward IgG2c dominance (vs IgG1 dominance in the IM-only group). Both oral alone and multimodal vaccination against TcdA protected mice from lethal C. difficile challenge (100% survival vs 30% in controls). Given the established safety profile of YS1646, we hope to move this vaccine candidate forward into a phase I clinical trial.IMPORTANCEClostridioides difficile remains a major public health threat, and new approaches are needed to develop an effective vaccine. To date, the industry has focused on intramuscular vaccination targeting the C. difficile toxins. Multiple disappointing results in phase III trials have largely confirmed that this may not be the best strategy. As C. difficile is a pathogen that remains in the intestine, we believe that targeting mucosal immune responses in the gut will be a more successful strategy. We have repurposed a highly attenuated Salmonella Typhimurium (YS1646), originally pursued as a cancer therapeutic, as a vaccine vector. Using a multimodal vaccination strategy (both recombinant protein delivered intramuscularly and YS1646 expressing antigen delivered orally), we elicited both systemic and local immune responses. Oral vaccination alone completely protected mice from lethal challenge. Given the established safety profile of YS1646, we hope to move these vaccine candidates forward into a phase I clinical trial.

Population immunity to varicella in Canada: A Canadian Immunization Research Network (CIRN) study.

INTRODUCTION: The incidence of varicella in Canada has decreased by almost 99% since vaccination was introduced. However, variation in the timing and eligibility of vaccination programs across the country has resulted in some cohorts being under-vaccinated and therefore potentially susceptible to infection. METHODS: We used nationally representative specimens from the Biobank of Statistics Canada's Canadian Health Measures Survey (CHMS) as well as residual specimens from Ontario collected between 2009-2014 to estimate population immunity across age-groups and geography, and identify any groups at increased risk of varicella infection. RESULTS: The weighted proportion of specimens with antibody levels above the threshold of protection was 93.6% (95% CI: 92.4, 95.0). Protection was lowest among those aged 3-5 years (54.3%; 95% CI: 47.3, 61.4), but increased with age. Individuals born outside Canada had more than twice the odds of varicella susceptibility than those born in Canada (aOR: 2.7; 95% CI: 1.4, 5.0; p = 0.004). There were no differences by sex or geography within Canada, and there were no statistically significant differences when Ontario CHMS sera were compared to Ontario residual sera, apart from in participants aged 12-19 year age-group, for whom the CHMS estimate (91.2%; 95% CI: 86.7, 95.7) was significantly higher (p = 0.03) than that from residual specimens (85.9%, 95% CI: 81.1, 90.8). DISCUSSION: Varicella immunity in Canada is changing. Children appear to have low population immunity, placing them at greater risk of infection and at increased risk of severe disease as they age. Our results underscore the importance of performing periodic serosurveys to monitor further population immunity changes as the proportion of vaccine-eligible birth-cohorts increases, and to continually assess the risk of outbreaks.

AS03 adjuvant enhances the magnitude, persistence, and clonal breadth of memory B cell responses to a plant-based COVID-19 vaccine in humans.

Vaccine adjuvants increase the breadth of serum antibody responses, but whether this is due to the generation of antigen-specific B cell clones with distinct specificities or the maturation of memory B cell clones that produce broadly cross-reactive antibodies is unknown. Here, we longitudinally analyzed immune responses in healthy adults after two-dose vaccination with either a virus-like particle COVID-19 vaccine (CoVLP), CoVLP adjuvanted with AS03 (CoVLP+AS03), or a messenger RNA vaccination (mRNA-1273). CoVLP+AS03 enhanced the magnitude and durability of circulating antibodies and antigen-specific CD4+ T cell and memory B cell responses. Antigen-specific CD4+ T cells in the CoVLP+AS03 group at day 42 correlated with antigen-specific memory B cells at 6 months. CoVLP+AS03 induced memory B cell responses, which accumulated somatic hypermutations over 6 months, resulting in enhanced neutralization breadth of monoclonal antibodies. Furthermore, the fraction of broadly neutralizing antibodies encoded by memory B cells increased between day 42 and 6 months. These results indicate that AS03 enhances the antigenic breadth of B cell memory at the clonal level and induces progressive maturation of the B cell response.

Immunogenicity and safety of high-dose versus standard-dose inactivated influenza vaccine in rheumatoid arthritis patients: a randomised, double-blind, active-comparator trial.

BACKGROUND: Patients with rheumatoid arthritis have increased risk of seasonal influenza and influenza-related complications but have reduced vaccine immunogenicity. It is unknown whether patients with rheumatoid arthritis would benefit from more immunogenic vaccine formulations. This study investigated the immunogenicity and safety of a high-dose trivalent inactivated influenza vaccine (HD-TIV) in patients with rheumatoid arthritis compared to a standard-dose quadrivalent influenza vaccine (SD-QIV). METHODS: This study was a treatment-stratified, randomised, double-blind trial to compare the immunogenicity and safety of SD-QIV (15 µg of haemagglutinin [HA] per strain) versus HD-TIV (60 µg of HA per strain) in adults with rheumatoid arthritis who are positive for rheumatoid factor or anti-cyclic citrullinated peptide, or both, recruited during the 2016-17 and 2017-18 influenza seasons at three hospitals affiliated with McGill University (Montreal, QC, Canada). Participants had received treatment for rheumatoid arthritis with conventional or targeted synthetic disease-modifying antirheumatic drugs (DMARDs) or biological DMARDs, or combinations of them, were still on treatment at the time of enrolment, and their treatment had not been modified during the 3 months before enrolment. They were stratified into one of three groups according to treatment. Patients who, at enrolment, were taking conventional or targeted synthetic DMARDs (methotrexate, hydroxychloroquine, and sulfasalazine) as monotherapy or in combination were stratified to group 1; those who were taking a biological DMARD (anti-tumour necrosis factor or anti-interleukin 6), with or without methotrexate, hydroxychloroquine, or sulfasalazine (or a combination thereof) were stratified to group 2; and those who were taking abatacept, tofacitinib, or rituximab, with or without methotrexate, hydroxychloroquine, or sulfasalazine (or a combination thereof) were stratified to group 3. Participants were randomly allocated (1:1) to receive the SD-QIV or HD-TIV vaccine. Randomisation was based on a computer-generated allocation sequence, and participants, investigators, and research nurses responsible for safety assessments were masked to vaccine assignment. The primary outcome was the seroconversion rate (as measured by haemagglutination-inhibition assay) per strain at day 28. Analysis was done in the modified intention-to-treat population, which included all randomly assigned participants for whom seroconversion status was available. Safety was assessed throughout the surveillance period (day 0-186). This trial is registered at ClinicalTrials.gov, number NCT02936180. FINDINGS: Between Oct 24, 2016, and Dec 6, 2017, 696 patients with rheumatoid arthritis were invited to participate in the study and 279 were randomly assigned and vaccinated (140 [50%] received SD-QIV and 139 [50%] HD-TIV). 136 patients who received SD-QIV and 138 who received HD-TIV were included in the modified intention-to-treat anaysis. Patients who received HD-TIV were more likely to seroconvert than those who received SD-QIV: the odds ratio was 2·99 (95% CI 1·46-6·11) for seroconversion to strain A/H3N2, 1·95 (1·19-3·22) for seroconversion to strain B/Bris, 3·21 (1·57-6·56) for seroconversion to strain A/H1N1 (in 2016-2017), and 2·44 (1·18-5·06) for seroconversion to strain A/H1N1 (in 2017-2018). Similar results were observed in patients from groups 1 and 2; the number of individuals in group 3 was insufficient to draw conclusions. Local and systemic adverse events were similar in both vaccine groups, no serious adverse events were reported between days 0 and 28 in any group, and neither vaccine increased rheumatoid arthritis disease activity. INTERPRETATION: Our data suggest that in patients with seropositive rheumatoid arthritis, HD-TIV is safe and more immunogenic than SD-QIV. These results are the first evidence to support the use of the HD-TIV in these patients. FUNDING: The Arthritis Society-Canada.