Immune Response Characterization after Controlled Infection with Lyophilized Shigella sonnei 53G

Abstract

Shigella is a major cause of moderate to severe diarrhea largely affecting children (<5 years old) living in low- and middle-income countries. Several vaccine candidates are in development, and controlled human infection models (CHIMs) can be useful tools to provide an early assessment of vaccine efficacy and potentially support licensure. A lyophilized strain of S. sonnei 53G was manufactured and evaluated to establish a dose that safely and reproducibly induced a ≥60% attack rate. Samples were collected pre- and postchallenge to assess intestinal inflammatory responses, antigen-specific serum and mucosal antibody responses, functional antibody responses, and memory B cell responses. Infection with S. sonnei 53G induced a robust intestinal inflammatory response as well as antigen-specific antibodies in serum and mucosal secretions and antigen-specific IgA- and IgG-secreting B cells positive for the α4β7 gut-homing marker. There was no association between clinical disease outcomes and systemic or functional antibody responses postchallenge; however, higher lipopolysaccharide (LPS)-specific serum IgA- and IgA-secreting memory B cell responses were associated with a reduced risk of disease postchallenge. This study provides unique insights into the immune responses pre- and postinfection with S. sonnei 53G in a CHIM, which could help guide the rational design of future vaccines to induce protective immune responses more analogous to those triggered by infection. IMPORTANCE Correlate(s) of immunity have yet to be defined for shigellosis. As previous disease protects against subsequent infection in a serotype-specific manner, investigating immune response profiles pre- and postinfection provides an opportunity to identify immune markers potentially associated with the development of protective immunity and/or with a reduced risk of developing shigellosis postchallenge. This study is the first to report such an extensive characterization of the immune response after challenge with S. sonnei 53G. Results demonstrate an association of progression to shigellosis with robust intestinal inflammatory and mucosal gut-homing responses. An important finding in this study was the association of elevated Shigella LPS-specific serum IgA and memory B cell IgA responses at baseline with reduced risk of disease. The increased baseline IgA responses may contribute to the lack of dose response observed in the study and suggests that IgA responses should be further investigated as potential correlates of immunity.

Immune response characterization in a human challenge study with a Shigella flexneri 2a bioconjugate vaccine

“…When considering overall magnitude of the response, the IgG subclass titres observed in this study confirm previously documented differences across IgG1 and IgG2 responses based on Shigella serotype, with S. flexneri 2a and S. sonnei inducing either an IgG2 or IgG1 dominated response, respectively [ 22 , 27 , 28 ]. However, in the current study, when the focus in placed on the association of each IgG subclass with protection from shigellosis rather than overall magnitude of response, a potentially important role for Shigella -specific serum IgG1 in protection from shigellosis post-parenteral immunization is suggested.…”

“…Frozen PBMCs from baseline (day 0), 7 days post-first immunization (day 7), as well as 3 and 7 days post-challenge (days 59 and 63) were thawed, washed and separated into α4β7 positive and negative PBMC populations as previously described using Miltenyi OctoMACS™ columns [22] . The anti-α4β7 monoclonal antibody used for separation (Act-1; NIH AIDS Reagent Program) was conjugated to Alexa Fluor 647, allowing the purity of α4β7 populations to be assessed by flow cytometry.…”

“…Frozen PBMCs from baseline (day 0), 28 days post-second immunization (day 56) and 28 days post-challenge (day 84) were thawed, washed and expanded as previously described [22] . After expansion, the cells were washed twice with mitogen-free complete RPMI medium, adjusted to 5 × 10 6 cells/ml and cultured as described above to collect ALS from memory B cells.…”

“…After expansion, the cells were washed twice with mitogen-free complete RPMI medium, adjusted to 5 × 10 6 cells/ml and cultured as described above to collect ALS from memory B cells. Successful expansion of memory B cell populations was assessed using flow cytometry as previously described [22] . Briefly, criteria for a successful expansion was defined as a post-expansion increase in cells positive for the CD19 B cell marker, as well as a ≥ 20% increase in B cells positive for the CD27 memory marker.…”

Establishment of a Controlled Human Infection Model with a Lyophilized Strain of Shigella sonnei 53G

“…It also is possible that a correlation between the disease outcome and immune responses to other Shigella antigens, such as the Ipa proteins, or other immunological responses (such as memory B cells, antibody-secreting cells [ASCs], and antibodies in lymphocyte supernatant [ALS]), may be observed. These immunological analyses are described in the companion article (13).…”