Single-dose Effectiveness of Mpox Vaccine in Quebec, Canada: Test-negative Design With and Without Adjustment for Self-reported Exposure Risk

INTRODUCTION

During the 2022 mpox outbreak, the province of Quebec, Canada, prioritized first doses for pre-exposure vaccination of people at high mpox risk, delaying second doses due to limited supply. We estimated single-dose mpox vaccine effectiveness (VE) adjusting for virus exposure risk based only on surrogate indicators available within administrative databases (eg, clinical record of sexually transmitted infections) or supplemented by self-reported risk factor information (eg, sexual contacts).

METHODS

We conducted a test-negative case-control study between 19 June and 24 September 2022. Information from administrative databases was supplemented by questionnaire collection of self-reported risk factors specific to the 3-week period before testing. Two study populations were assessed: all within the administrative databases (All-Admin) and the subset completing the questionnaire (Sub-Quest). Logistic regression models adjusted for age, calendar-time and exposure-risk, the latter based on administrative indicators only (All-Admin and Sub-Quest) or with questionnaire supplementation (Sub-Quest).

RESULTS

There were 532 All-Admin participants, of which 199 (37%) belonged to Sub-Quest. With exposure-risk adjustment based only on administrative indicators, single-dose VE estimates were similar among All-Admin and Sub-Quest populations at 35% (95% confidence interval [CI]:-2 to 59) and 30% (95% CI:-38 to 64), respectively. With adjustment supplemented by questionnaire information, the Sub-Quest VE estimate increased to 65% (95% CI:1-87), with overlapping confidence intervals.

CONCLUSIONS

Using only administrative data, we estimate one vaccine dose reduced the mpox risk by about one-third; whereas, additionally adjusting for self-reported risk factor information revealed greater vaccine benefit, with one dose instead estimated to reduce the mpox risk by about two-thirds. Inadequate exposure-risk adjustment may substantially under-estimate mpox VE.

SARS-CoV-2 infection among healthcare workers: the role of occupational and household exposures during the first three pandemic waves in Quebec, Canada

Objective

We described the evolution of SARS-CoV-2 source of infection in a cohort of healthcare workers (HCWs) of Quebec, Canada, during the first three pandemic waves. We also estimated their household secondary attack rate (SAR) and its risk factors.

Design

Cross-sectional surveys.

Participants

HCWs with a SARS-CoV-2 infection confirmed by polymerasa chain reaction and diagnosed between March 2020 and May 2021.

Methods

We collected demographic, clinical, vaccination, and employment information, self-reported perceived source of infection, and transmission to household members during the first three pandemic waves. SAR was calculated for households with ≥2 members where the HCW was the index case. A Poisson regression model estimated the association between risk factors and SAR.

Results

Among the 11,670 HCWs completing the survey, 91%, perceived their workplace as the source of infection during the first wave (March-July 2020), 71% during the second wave (July 2020-March 2021), and 40% during the third wave (March-May 2021). Conversely, HCWs reported an increasing proportion of household-acquired infections with each wave from 4% to 14% and 33%, respectively. The overall household SAR of 7,990 HCWs living with ≥1 person was 30% (95%CI: 29-30). SAR increased with the presence of symptoms, older age, and during Alpha-variant predominant period.

Conclusions

HCWs and their household members were largely affected during the first pandemic waves of COVID-19, but the relative importance of occupational exposure changed overtime. Pandemic preparedness in healthcare settings is essential to protect HCWs from emerging biological hazard exposures.

New insights into immune mechanisms of antiperlecan/LG3 antibody production: Importance of T cells and innate B1 cells

Autoantibodies against perlecan/LG3 (anti-LG3) have been associated with increased risks of delayed graft function, acute rejection, and reduced long-term survival. High titers of anti-LG3 antibodies have been found in de novo renal transplants recipients in the absence of allosensitizing or autoimmune conditions. Here, we seek to understand the pathways controlling anti-LG3 production prior to transplantation. Mice immunized with recombinant LG3 produce concomitantly IgM and IgG anti-LG3 antibodies suggesting a memory response. ELISpot confirmed the presence of LG3-specific memory B cells in nonimmunized mice. Purification of B1 and B2 subtypes identified peritoneal B1 cells as the major source of memory B cells reactive to LG3. Although nonimmunized CD4-deficient mice were found to express LG3-specific memory B cells, depletion of CD4⁺ T cells in wild type mice during immunization significantly decreased anti-LG3 production. These results demonstrate that B cell memory to LG3 is T cell independent but that production of anti-LG3 antibodies requires T cell help. Further supporting an important role for T cells in controlling anti-LG3 levels, we found that human renal transplant recipients show a significant decrease in anti-LG3 titers upon the initiation of CNI-based immunosuppression. Collectively, these results identify T cell targeting interventions as a means of reducing anti-LG3 levels in renal transplant patients.

Use of IVIg to identify potential miRNA targets for allograft rejection and GvHD therapy

Allograft rejection (AR) and graft-versus-host disease (GvHD) are serious complications following transplantation. Micro-RNAs (miRNAs) have recently been identified as key players in the regulation of these disorders. Because intravenous immunoglobulin (IVIg) has shown therapeutic potential for the prophylaxis and post-transplant reduction of AR and GvHD, we hypothesized that the effect of IVIg could result from the modulation of specific miRNA expression. To identify such miRNA, we performed mixed lymphocyte reactions (MLRs) as an in vitro model of AR and GvHD, with or without IVIg. We herein show that IVIg strongly inhibits the MLRs. This inhibition is associated with a modulation in the expression of miRNAs implicated in the regulation of pro-inflammatory cytokine (IL-2, IL-6, IFN-γ) and costimulatory molecule (CD80) expression. We propose that these identified miRNAs could represent potential therapeutic targets for the prevention and therapy of AR and GvHD.

Induction of PD-L1 on monocytes: a new mechanism by which IVIg inhibits mixed lymphocyte reactions

Allograft rejection and graft-versus-host disease (GvHD) are frequent complications following solid organ or stem cell transplantation in which T cell activation plays a central role. Despite the development of new immunosuppressive drugs that improve the success rate of transplantation, allograft survival continues to be a challenge. Recently, intravenous immunoglobulin (IVIg) has been proposed as prophylaxis and post-transplant treatment to reduce acute rejection episodes. IVIg is a therapeutic agent that is known to down-modulate T cell functions in patients with autoimmune disorders. To test the hypothesis that this immunomodulatory effect could be beneficial in the context of transplantation, we used mixed lymphocyte reactions (MLR) as an in vitro model of allograft rejection and GvHD. Our results show that IVIg strongly inhibits the MLR as evaluated by IL-2 secretion, a well-known marker of T cell activation. IVIg also modulates the secretion of other pro-(IL-6, IFN-γ) and anti-inflammatory (IL-1RA) cytokines. More importantly, we show that IVIg induces monocytes with a CD80(low) PD-L1(high) phenotype and that blockade of PD-L1 partially abrogates the inhibitory effect of IVIg. We have thus identified a new mechanism by which IVIg inhibits T cell functions in the context of transplantation, supporting the potential usefulness of IVIg in the prevention or treatment of graft rejection and GvHD.

IVIg-induced anti-inflammatory monocytes (CD14 low, HLA-DR high) with a low CD80 and high PDL1 expression inhibits T cell activation in allogeneic mixed lymphocytes reactions (P2194)

Intravenous immunoglobulin (IVIg) is a therapeutic preparation of human IgG isolated from plasma donations and has been proposed as a therapy to improve the rate of graft survival in patients with a high risk for antibody-mediated-rejection. Blocking of anti-HLA antibodies by anti-idiotypic IgG present in IVIg was proposed to explain the rapid effect of IVIg. However, a long-term reduction of anti-HLA alloreactivity in IVIg-treated patients suggests that IVIg modulates the functions of immune cells. In the present study, we showed using the allogeneic mixed lymphocyte reaction (MLR) as an in vitro model of allograft rejection and GvHD that IVIg strongly inhibits IL-2 secretion (T cell activation) and modulates the level of other pro- and anti-inflammatory cytokines secretion. To determine the mechanisms underlying the inhibition of T cell activation in MLR, we studied the effect of IVIg on the phenotype of the cells involved in MLR. Our results revealed that MLR inhibition by IVIg correlates with the induction of anti-inflammatory monocytes (CD14 low, HLA-DR high) with a low CD80 and high PDL1 expression. To evaluate the importance of PDL1 on the MLR inhibition, anti-PDL1 was added during the MLR. Blocking of PDL1 restored the MLR, as evaluated by IL-2 secretion. We thus propose that PDL1 plays a central role in the inhibition of MLR. Our results help to better understand how IVIg induces long-term peripheral tolerance and improves graft survival in transplanted patients.

IVIg prevents the in vitro activation of T cells by neutralizing the T cell activators

Clinical observations in patients treated with IVIg revealed significant modulations in T cell populations and functions. However, it is unclear whether IVIg acts directly on activated T cells to suppress their functions. To clarify the exact mechanism of IVIg action, we studied its effect on T cells activated using anti-CD3/CD28 microbeads to mimic stimulatory signals provided by accessory cells. We report here that IVIg reduces T cell proliferation and cytokine secretion by interfering with the ability of anti-CD3/CD28 microbeads to deliver activating signals to T cells. We further show that the interference occurs between IVIg and anti-CD3/CD28 microbeads and does not involve T cells. In conclusion, our work suggests that T cells are not a direct target of IVIg and that the modulation of T cell populations and functions observed in treated patients is the indirect consequence of a direct effect of IVIg on accessory cells.

ROLE OF ACCESSORY CELLS IN THE IVIG-MEDIATED INHIBITION OF T CELL ACTIVATION (48.5)

Intravenous immunoglobulin (IVIg) is a therapeutic preparation of human IgG isolated from thousands of plasma and is currently used for the treatment of an increasing number of immune disorders. A decreased T cell activation was reported in some patients treated with IVIg. To understand the mechanisms responsible for this anti-inflammatory effect, several groups of investigators have performed in vitro assays in which PBMC were activated with immobilized anti-CD3. The main conclusion derived from these works is that IVIg inhibited the functions of activated T cell. However, direct effect of IVIg on activated T cells has been questioned recently. In the present study, we re-examined the mechanisms by which IVIg interferes with the functions of T cells activated with immobilized anti-CD3. First, the level of T cell activation after anti-CD3 stimulation of PBMC, purified T cells or PBMC depleted from monocytes was measured. Our results showed that in the absence of monocytes, T cells did not proliferate in response to anti-CD3 stimulation, suggesting that monocytes are essential to lead to full T cell activation. Second, we evaluated the effect of IVIg on T cell activation after anti-CD3 stimulation of PBMC. Our results showed that T cells were not activated in the presence of IVIg suggesting that not only T cells but also monocytes could be the target of IVIg. Work is underway to better define the role of monocytes in the effects of IVIg on T cell activation.

Neutralization of mitogenic lectins by intravenous immunoglobulin (IVIg) prevents T cell activation: does IVIg really have a direct effect on T cells?

Intravenous immunoglobulin (IVIg) is used for the treatment of an increasing number of autoimmune diseases. Clinical observations on IVIg-treated patients have revealed a modulation of T cell populations and functions in these patients. In vitro studies aimed at understanding the mechanisms underlying the effects of IVIg on T cells led to the conclusion that IVIg directly affected lectin-activated T cell functions. However, more recent studies have suggested the absence of a direct effect of IVIg on T cells. In the present work, we revisited the effect of IVIg on T cells using lectin-stimulated human T cells and showed that IVIg inhibited T cell functions only when added simultaneously with the activating lectin. Further, we showed that IVIg depleted from lectin-reactive IgG was no longer inhibitory, suggesting that the effect of IVIg on T cells was the consequence of lectin neutralization, possibly by interaction with glycans present in F(ab')(2) portion of IgG molecules. Our results challenge the previously widely accepted notion that IVIg exerts its anti-inflammatory effects by acting directly on T cells and suggest that effects of IVIg observed in treated patients are rather a consequence of the recently reported inhibitory effect of IVIg on antigen presentation.

Modulation of MHC II and costimulatory molecules expression on monocytes by intravenous immunoglobulins (147.17)

Intravenous immunoglobulins (IVIg) are therapeutic preparations of human IgG isolated from thousands of plasma donations and are known to have anti-inflammatory effects in many autoimmune diseases. IVIg are also used as prophylactic agent to reduce episodes of allograft rejection but the mechanisms responsible for this effect remain to be determined. In the present work, we showed by using a mixed lymphocyte reaction as an in vitro model of allograft rejection and GvHD, that IVIg strongly inhibited T cell activation. To explain this inhibition, we postulated that IVIg modulated the expression of MHC II and costimulatory molecules expressed on APC and involved in antigen presentation and regulation of T cell activation. To study this hypothesis, PBMC were cultured with or without 10 mg/ml IVIg for 24 hours, followed by flow cytometry analysis of cell surface expression of 8 different molecules. Among these, the expression of 5 was significantly modulated on monocytes. IVIg decreased the expression of MHC II (50%), CD80 (80%), CD86 (52%) and L-ICOS (50%). Interestingly, preliminary results showed a 5-fold increase in the expression of PD-L1, a negative regulator of T cell activation. These results suggest that IVIg impair the presentation of allopeptides to T cells as well as induce negative signalling in these cells, leading to their reduced activation. Altogether these findings could help explain the induction of peripheral tolerance and improvement of graft survival by IVIg.

Dose-dependent inhibition of BrdU detection in the cell proliferation ELISA by culture medium proteins

Determination of the proliferation rate of cultured mammalian cells is widely done using incorporation of 5-bromo-2-deoxyuridine into replicating DNA followed by quantitative detection in ELISA using a specific monoclonal antibody. However, we noted that the BrdU ELISA results did not correlate with viable cell counts when increasing concentrations of proteins were added to test their effects on proliferating cells. This observation suggested that proteins could interfere with BrdU incorporation or detection in the commercial BrdU ELISA used. We show here that the presence of exogenous proteins during cell fixation and DNA denaturation significantly inhibited BrdU detection presumably by coating the extracted DNA by a concentration-dependent protein film. A simple modification to the manufacturer's protocol (cell washing) permitted to avoid this interference and resulted in a significant increase of the assay sensitivity.