Edited by: Andrew R. Gennery, Newcastle University, United Kingdom
Reviewed by: Esther De Vries, Tilburg University, Netherlands; Matthew S. Buckland, Great Ormond Street Hospital, United Kingdom
This article was submitted to Primary Immunodeficiencies, a section of the journal Frontiers in Immunology
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The inability to produce an adequate and protective immune response to polysaccharides antigens present on the surface of pathogens renders individuals susceptible to recurrent and severe sinopulmonary infections due to encapsulated bacteria. In patients with suspected primary immunodeficiencies (PID), an early and accurate diagnosis of antibody production deficiency will provide the individual with prompt and more appropriate treatment (
The current gold-standard test to evaluate the response to the polysaccharide vaccine is based on the measurement and interpretation of the antibody response to the 23-valent pneumococcal polysaccharide vaccine (PPV) (
A meta-analysis of anti-pneumococcal antibody responses on an individual serotype basis in healthy individuals showed that the ratios of pre- and post-vaccination titters varied widely and depended on the particular antibody serotype and baseline levels [4]. There is not a clear consensus from laboratories between the measurement and importance of each individual serotype response and the total value of the pneumococcal polysaccharide IgG vaccine (
Borgers et al. (
On the other hand, it is assumed that a healthy immune response to polysaccharide vaccine normally develops by 2 years of age, but this is extremely variable and may take longer in some children (
Therefore, the interpretation of this vaccine response comes with some challenges and can be complex (
TV is a capsular polysaccharide vaccine, administrated to populations at risk of developing typhoid fever or to individuals traveling to endemic areas, licensed in 1988 for assessment of adaptive immunity in adults and children > 18 months of age (
At present, there is very little evidence supporting TV vaccination for the assessment of adaptive immunity in a pediatric population (
The main purpose of the current study was to explore the potential value of TV vs. PPV as a diagnostic tool to analyze the response to a pure polysaccharide vaccine in a pediatric population that has received both pneumococcal conjugated vaccine and 23-valent pneumococcal vaccine.
This was a single-institution, observational study, conducted at the Hospital Clínico San Carlos, Madrid, Spain.
Sixty-one children with recurrent upper and/or lower respiratory tract infection (
After a median interval of 35 days, post vaccinations, blood was drawn from all 28 subjects. Pre- and post-immunization serum samples were separated by centrifugation and then stored in aliquots at −40°C for analysis. Twenty-three out of 28 patients had received pneumococcal conjugate vaccine as part of their childhood vaccination schedule. Therefore the PPV pre-vaccination concentration represents the maintenance response to pneumococcal conjugate vaccine. None of the patients had previously received intravenous immunoglobulin therapy or immunosuppressive treatment. As this is an observational study, describing only the results of a routine intervention at our center to measure antibody production, no informed consent was required. The study was approved by the center's ethics committee.
Specific antibodies raised against TV and PPV were measured using commercial ELISA kits; VaccZyme™ human anti-
The following cut-offs were used: pre TV vaccination IgG 28 U/mL (upper normal limit for pre-vaccination TV IgG concentration) (
Data were analyzed by Chi-squared, Fisher's exact, Pearson, and Spearman correlation coefficient and Mann Whitney
We measured pre-vaccination concentrations for PPV and TV Vi IgG antibodies in the 61 subjects. The median age was 4 years (range, 2–17), with an M:F ratio of 0.6. The median baseline antibody concentrations were 9.8 mg/L for PPV IgG (range 0.33–27.0 mg/L) and <7.4 U/mL for TV IgG (range 7.4–32.7 U/mL), respectively. There was no influence of age on pre-vaccination titers.
A significantly higher percentage of individuals (70%, 43/61) showed pre-vaccination PPV IgG titers above 27 mg/L compared to 8% (5/61) that showed pre-vaccination TV IgG titers above 28 U/mL (
Pre-TV titers were below 7.4 U/mL in 69% (42/61) of subjects and the remaining 31% (19/61) presented titers below 28 U/mL. Thus, 92% (56/61) of individuals showed no serological evidence of previous exposure to the antigen, meaning that the Typhim Vi antigen might be considered as a neoantigen, as is the case in the vast majority of the adult population in Spain.
In 28 of the 61 children, response to antibody production confirmed the clinical suspicion of immunodeficiency. They were therefore immunized with PPV and TV. Post-vaccination TV IgG titers was 55 U/mL (range 7.4–465.0 U/mL). Seventy-five percent (21/28) achieved a 3-fold increase for TV IgG post-vaccination. The patients were categorized into two groups based on their response to TV, pediatric responders (R,
Post-vaccination PPV IgG titers were 27 mg/L (range 0.86–27.0 mg/L), although it must be taken into account that the highest total measurement for this antibody are 27 mg/L, meaning that FI would be significantly lower in patients with high pre-vaccination titers (described below).
The trend in PPV response between pre- and post-vaccination in the same 28 patients was not the same as that obtained with TV (
Antibody concentrations Pre- Post TV IgG and PPV IgG in children referred for immunological investigation.
Median post-TV IgG concentrations were significantly higher in R (184 U/mL, range 21.4–465.1 U/mL) compared to NR (7.4 U/mL, range 7.4–16.2U/mL,
We sought to determine the clinical significance of obtaining a TV response in the pediatric population by comparing the clinical characteristics in the R vs. NR when considered the well-known warning signs of PID proposed by the Jeffrey Modell Foundation (
Comparison of the TV R and NR clinical characteristics with the Jeffery Modell Warning Criteria for pediatric PIDs.
>4 ear infections in 1 year | 4 (19%) | 3 (42.8%) | 0.31 |
>2 severe sinus infections in 1 year | 0 (0%) | 0 (0%) | – |
>2 months treatment with antibiotic giving Little effect | 0 (0%) | 0 (0%) | – |
>2 pneumonias per year | 4 (19%) | 4 (57%) | 0.02 |
Insufficient weight gain or growth delay | NA | NA | – |
Recurrent deep skin or organ abscesses (including liver and lungs) | 0 (0%) | 0 (0%) | – |
Persistent thrush in mouth or fungal infections on the skin | 0 (0%) | 0 (0%) | – |
Need for intravenous antibiotics to clear infections | 3 (3%) | 6 (85%) | 0.01 |
>2 Deep seated infections (including septicemia and meningitis) | 1 (5%) | 2 (28.5%) | 0.14 |
Family history of a PID | NA | NA | - |
Only 4 of 28 children showed isolated lacked response to PPV (FI ≤ 1). Of these 4 patients, only 1 required hospitalization because of severe pneumococcal pneumonia despite being vaccinated with PPV and normal basic analysis and immunological tests. The remaining 3 patients presented with mild symptoms, such as self-limited viral infections. These 4 patients were between 2 and 3 years of age and all of them had previously received the pneumococcal conjugate vaccine as part of their vaccination schedule. Remarkably, all 4 patients showed an adequate response (FI > 3) to TV.
Three out of 7 TV NR while adequately responded to PPV. However, these 3 patients suffered from recurrent low-tract respiratory infections (i.e., pneumonia and bronchiectasis) and associated concurrent immunological alteration (i.e., IgM deficiency, IgA deficiency, and Familial Cold Autoinflammatory syndrome). The remaining 4 patients lacked responses to both PPV and TV, presented recurrent respiratory and gastrointestinal manifestations and intracranial hypertension and were diagnosed with Behçet's disease, partial IgA deficiency, primary antibody deficiency, and common variable immunodeficiency (CVID) (details of the 7 TV NR are shown in
Clinical and serological profiles of TV NR.
Gender | F | F | F | F | M | M | M |
Age | 3 | 16 | 6 | 4 | 10 | 9 | 14 |
Diagnosis/follow up | IgM deficiency | Bechet's disease | Primary antibody deficiency | Partial IgA deficiency | Common Variable Immunodeficieny | Selective IgA deficiency | Familial Cold Autoinflamamatory síndrome. |
Notable clinical features | Recurrent pneumonias CT scan: atelectasis and bronchiectasis | Neutropenia, recurrent respiratory and urinary tract infection, vaginal candidiasis infection | Recurrent bronchitis, bronchiectasis, laryngomalacia, bronchomalacia. | Recurrent respiratory infections, atopic dermatitis and moderate bronchial asthma | Chronic diarrhea, recurrent ear infections. Intracranial hypertension. | Recurrent higher and lower respiratory tract infections (Sinusitis, ear infections, and pneumonia). Bronchiectasis. | Recurrent episodes of fever and systemic inflammation cold-related, higher, and lower respiratory tract infections (Sinusitis, pharyngitis, ear infections, and pneumonia), recurrent bronchiolitis. Bronchiectasis. |
TV FI | 1 | 1 | 0.3 | 1 | 1 | 2.1 | 1.7 |
PPV FI | 14 | 0.9 | 1.2 | 0.4 | 2.6 | 8.4 | 7 |
IgG |
6.66 | 10.8227 | 10.18 | 11.44 | 3.10 | 16.20 | 7.87 |
IgG1 |
4.76 | 4.34 | 6.53 | 7.43 | 0.34 | 7.75 | 4.65 |
IgG2 |
0.96 | 4.74 | 1.59 | 2.49 | 0.03 | 5.63 | 2.27 |
IgA |
0.54 | 2.12 | 0.93 | 0.009 | <0.002 | <0.002 | 1.06 |
IgM |
0.004 | 1.84 | 1.23 | 1.72 | <0.09 | 0.07 | 1.1 |
No significant differences were found when stratifying patients according to their ages, 2 patients between 2 and 5 years of age, 3 between 5 and 10 and 2 over 10.
High circulating concentrations of pneumococcal antibodies can be a complicating factor when interpreting the PPV response (
Cautions joint interpretation of baseline antibody titers together with fold-increase is essential to adequately discriminate humoral defects and this interpretation show clinical implications. In our study, we observed that baseline levels of PPV were high at pre-vaccination in up to one-third of patients tested, which could be a reflection of the antibodies generated in previous vaccination against pneumococcal conjugate vaccine. When pre-vaccination titers are already high, immune capacity may be normal despite low “fold-increase” (
The Spanish childhood vaccination schedule since 2006 recommends the compulsory vaccination of children with a protein-conjugated polysaccharide vaccine as part of a four-stage program (2, 4, 6, and 12–15 months). Measurement of IgG PPV in antibody response may be complicated by prior vaccination with this vaccine (
The main conclusion of our preliminary investigation is that TV seems to be a more reliable indicator of PID/SID. However, in our series of children from the 4 isolated non-responders to PPV that appear to have the worst clinical course, 3 had a self-limiting viral infection and just one confirmed exposure to pneumococcal pneumonia, with no other alterations in the immunological profile. As a result, we hypothesize that this finding could be related to a specific alterations in the T-dependent potentiated functional response associated with immunological immaturity, relying on the fact that the polysaccharide response to TV was adequate. This may be due to the fact that all 4 were 2–3 years-old and previously vaccinated with conjugate pneumococcal vaccine. However, we consider that a medical follow-up of these cases would be recommended, as well as another test to determine the production of antibodies against total and specific PPV for each serotype.
Five out of 28 patients had not received pneumococcal conjugate vaccine as part of their childhood vaccination, since they were born before 2006 or between 2012 and 2015 when this vaccine was not mandatory in the Spanish vaccination calendar. However, when determining the production of antibodies against PPV, this was adequate.
For patients who presented a deficit of production of TV antibodies, a relationship between them was established with other immunological failures, as well as more severe clinical manifestations, showing more consistency for PID diagnosis.
Several studies have reported a variable TV response in healthy volunteers. The FI concentration in healthy children (range, 5–15 years) was between 3- and 8-fold, which may vary according to previous vaccination (
In our study, we report the measurement of TV IgG as a marker of adaptive immunity in children and illustrate the advantage of measuring the TV response associated with the gold standard compared to measuring and interpreting the isolated PPV response. We confirm that baseline concentrations of TV IgG were low in children compatible with data in adults (
This investigation emphasizes the clinical value of measuring TV IgG as a diagnostic tool for assessing adaptive immunity and aiding the patients' therapeutic decision process.
One limitation in this study is its inability to distinguish between high responses of 23-valent pneumococcal polysaccharide vaccine to a few individual serotypes and a good overall response. Consistently, the impossibility of having healthy control of children, since TV is outside the vaccination schedule, is another limitation and therefore our ethics committee would not have approved it. However, children with benign infections with normal TV response from our cohort may be considered as a control group. Vaccination of healthy children against TV is not required as part of the routine immunization schedule, which led us to extrapolate reference ranges from healthy pediatric populations from previous reports (
Moreover, based on published studies, assessment of the TV response could be considered as the additional gold-standard test for assessing polysaccharide production (
In our cohort, baseline TV antibodies were undetectable in the vast majority of patients and the range of response was wide, reinforcing their utility in clinical practice (
We hypothesize that measurement of polysaccharide antibody response using PPV may be influenced by prior exposure of the pneumococcal conjugate vaccine, generating an enhanced T-dependent response. Our current study supports the concept that TV is a useful diagnostic tool for assessing polysaccharide antibodies responses, when the isolated determination of serotypes against pneumococcus is unfeasible, since TV response is not influenced by previous exposure due to the low prevalence of the disease, showing clearer behavior. It supports previous reports detailing the low prevalence of
To conclude, we propose that interpretation of the IgG response to TV may be superior to that found for total PPV alone, aimed at evaluating the response to the polysaccharide vaccine in the pediatric population previously vaccinated with the conjugate pneumococcal vaccine.
The datasets generated for this study are available on request to the corresponding author.
KG-H, SS-R, CG, JR, and MF-A contributed conception and design of the study. RP, SG-G, and MR have contributed to the immunological study of PID. CO and AR organized the database. IG performed the statistical analysis. KG-H wrote the first draft of the manuscript. SS-R, ER, JO-G, AP, and LW wrote sections of the manuscript. All authors contributed to manuscript revision, read and approved the submitted version.
AP and LW are employed by The Binding Site Group Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
We would like to thank the reviewers for their thoughtful comments and efforts toward improving our manuscript.