Pneumococcal Antibody Function for Immunologic Evaluation: Normal Results in Older Adults, and a Novel Analytical Model for Vaccine Response

Distinct baseline immune characteristics associated with responses to conjugated and unconjugated pneumococcal polysaccharide vaccines in older adults

Pneumococcal infections cause serious illness and death among older adults. The capsular polysaccharide vaccine PPSV23 and conjugated alternative PCV13 can prevent these infections; yet, underlying immunological responses and baseline predictors remain unknown. We vaccinated 39 older adults (>60 years) with PPSV23 or PCV13 and observed comparable antibody responses (day 28) and plasmablast transcriptional responses (day 10); however, the baseline predictors were distinct. Analyses of baseline flow cytometry and bulk and single-cell RNA-sequencing data revealed a baseline phenotype specifically associated with weaker PCV13 responses, which was characterized by increased expression of cytotoxicity-associated genes, increased frequencies of CD16+ natural killer cells and interleukin-17-producing helper T cells and a decreased frequency of type 1 helper T cells. Men displayed this phenotype more robustly and mounted weaker PCV13 responses than women. Baseline expression levels of a distinct gene set predicted PPSV23 responses. This pneumococcal precision vaccinology study in older adults uncovered distinct baseline predictors that might transform vaccination strategies and initiate novel interventions.

Reduced quantity and function of pneumococcal antibodies are associated with exacerbations of COPD in SPIROMICS

While hypogammaglobulinemia is associated with COPD exacerbations, it is unknown whether frequent exacerbators have specific defects in antibody production/function. We hypothesized that reduced quantity/function of serum pneumococcal antibodies correlate with exacerbation risk in the SPIROMICS cohort. We measured total pneumococcal IgG in n = 764 previously vaccinated participants with COPD. In a propensity-matched subset of n = 200 with vaccination within five years (n = 50 without exacerbations in the previous year; n = 75 with one, n = 75 with ≥2), we measured pneumococcal IgG for 23 individual serotypes, and pneumococcal antibody function for 4 serotypes. Higher total pneumococcal IgG, serotype-specific IgG (17/23 serotypes), and antibody function (3/4 serotypes) were independently associated with fewer prior exacerbations. Higher pneumococcal IgG (5/23 serotypes) predicted lower exacerbation risk in the following year. Pneumococcal antibodies are inversely associated with exacerbations, supporting the presence of immune defects in frequent exacerbators. With further study, pneumococcal antibodies may be useful biomarkers for immune dysfunction in COPD.

Navigating diagnostic options for inborn errors of immunity in children: a case-based illustration

PURPOSE OF REVIEW

In recent years, there has been a dramatic increase in the number of recognized inborn errors of immunity (IEI), many of which present in childhood. This review discusses diagnostic approaches for some of the more common presentations of IEI in childhood.

RECENT FINDINGS

Implementation of newborn screening (NBS) using the T cell receptor excision circle (TREC) assay has led to the timely identification of patients with severe combined immunodeficiency (SCID) as well as both syndromic and nonsyndromic forms of T cell lymphopenia, including DiGeorge syndrome. Improvements in the availability of immunophenotyping assays, genetic testing and advanced diagnostic techniques such as the artificial thymic organoid system can improve diagnostic clarity and impact management plans. Diagnostic improvements in humoral immunodeficiency include development of novel assays to quantify and functionally evaluate polysaccharide vaccine response.

SUMMARY

IEI represent a rapidly growing field, particularly in paediatrics. Use of state-of-the-art diagnostic testing can facilitate rapid identification of IEI, hopefully allowing for initiation of prompt treatment and improved patient outcomes.

Specific antibody deficiency: Pearls and pitfalls for diagnosis

OBJECTIVE

Specific antibody deficiency is an immune deficiency defined by the presence of normal quantitative levels of immunoglobulins but impaired antibody responses to polysaccharide antigens in patients presenting with frequent otosinopulmonary infections with pyogenic bacteria. This review summarizes the pitfalls associated with defining exactly what constitutes an "impaired" antibody response to polysaccharide antigens and the importance of documenting actual pyogenic infections before making a diagnosis of an immune deficiency.

DATA SOURCES

PubMed review using the following words: specific antibody deficiency, pneumococcal vaccination, salmonella vaccination, infectious sinusitis Study Selection: This review focused on key studies that have been utilized to define what constitutes a "normal" humoral immune response to pneumococcal and salmonella vaccination in healthy subjects as well as published papers defining current expert opinion.

RESULTS

Published studies demonstrate wide variability in response to pneumococcal vaccination in healthy individuals making it daunting to define what constitutes an abnormal response. These challenges are exacerbated by striking laboratory variability in reporting results.

CONCLUSION

Clinical evaluations in individuals with self-reported recurrent acute sinusitis or lower respiratory infections need to document an infectious etiology with pyogenic bacteria and must rule out an underlying primary airway inflammatory disorder before consideration is made regarding the presence of an immune deficiency. In addition, decision making regarding diagnosis and treatment of patients being evaluated for humoral immunodeficiency should not hinge solely on the strict application of defined cutoffs for "normal" response to a single polysaccharide vaccine, but rather a global assessment of humoral immune function in the context of the clinical presentation.

Pneumococcal IgG Antibody Responses to 23vPPV in Healthy Controls Using an Automated ELISA

Measurement of pre- and post-pneumococcal antibody levels after immunization with the 23-valent capsular polysaccharide pneumococcal vaccine (23vPPV) is indicative of a T-independent antibody response. The World Health Organisation ELISA is considered gold standard yet is labor-intensive and technically difficult to perform. Interpretation criteria defining an adequate response to 23vPPV remain controversial. The diagnostic Immunology Laboratory at The Royal Children's Hospital, Melbourne (RCH), performs an in-house multi-serotype automated ELISA. The primary objective of this study was to verify RCH interpretation criteria for the laboratory's automated ELISA. Forty pneumococcal conjugate vaccine (PCV)-naïve healthy adults aged 18 to 25 years and 22 PCV-primed healthy children aged 2 to 5 years were immunized with 23vPPV. A serum sample was collected immediately prior and 28 to 42 (± 7) days post immunization. Samples were analyzed on the Tecan Freedom Evo 200 ELISA with adequate response defined as post-immunization antibody level of 1.3 µg/mL or fourfold rise from baseline in ≥ 10/15 serotypes in adult participants and ≥ 4/8 serotypes in pediatric participants. Thirty-nine (97.5%) adults and 22 (100%) children achieved an adequate response to 23vPPV. In PCV-naïve adults, serotypes contained within the conjugate vaccines were less immunogenic, with 12 (30%) adults not achieving an adequate antibody response when only PCV serotypes were used for interpretation. Our diagnostic laboratory has verified the interpretation criteria used for an automated multi-serotype pneumococcal ELISA method. Clinical Trial Registration: ANZCTR registration number ACTRN12618000822280.