Screening for Immunodeficiencies in Children With Invasive Pneumococcal Disease: Six-year Experience From a UK Children's Hospital.

BACKGROUND: A previous study showed that investigation of children with invasive pneumococcal disease (IPD) revealed an immunodeficiency in up to 10% of cases. Following this report, we implemented a protocol to investigate children with IPD, to assess the proportion with an immunodeficiency in our setting. METHODS: We retrospectively identified patients who presented with IPD from January 2015 to November 2020 and collected data from medical records. Immunological investigations included complement C3 and C4 levels, classical and alternative pathway complement function, IgG, IgA and IgM levels, specific IgG levels (H. influenza B, tetanus and pneumococcal serotypes), peripheral blood film, lymphocyte subsets, and CD62L-shedding upon activation with Toll-like receptor-agonists in selected cases. RESULTS: We identified a total of 68 children with IPD, with a mortality of 6%. Immunological investigations were performed in 51 children. Four children (8%) had abnormal findings that were deemed of clinical significance. Two children had complement deficiencies (Factor I and C2 deficiency), one child had specific antibody deficiency, and another child had low IgM, low NK-cells and poor persistence of serotype-specific anti-pneumococcal IgG concentrations. Of the 17 children with IPD who were not tested for immunodeficiencies, 4 died and four had possible explanations for the infection. CONCLUSIONS: We identified clinically relevant abnormal immunological findings in 4/51 (8%) of children with IPD. Our results support the recommendation to perform immunological investigations in children with IPD, since this might reveal underlying immunodeficiencies, allowing for necessary preventive measures and close follow-up.

Establishment of a healthy human range for the whole blood "OX40" assay for the detection of antigen-specific CD4+ T cells by flow cytometry.

BACKGROUND: Clinical investigation of antigen-specific T cells in potentially immunodeficient patients is an important and often challenging aspect of patient diagnostic work up. Methods for detection of microbial exposure to the T-cell compartment exist but are laborious and time consuming. Recently, a whole blood technique involving flow cytometry and detection of CD25 and OX40 (CD134) expression on the surface of activated CD4+ T cells was shown to be accurate and concordant when compared with more traditional methods of antigen-specific T-cell detection. METHODS: Whole heparinized blood was collected from healthy donors and set up using the "OX40" assay to detect antigen-specific CD4+ T-cell responses to Varicella Zoster Virus, Epstein-Barr Virus (EBV), Cytomegalovirus, Candida albicans, and Streptococcus pneumoniae. RESULTS: The "OX40" assay technique was clinically validated for routine use in an NHS clinical immunology laboratory by analysis of incubation length (40-50 h), sample transport time (up to 24 h at room temperature), concordance with serology testing, proliferation and interferon-gamma production. In addition, 63 healthy controls (age range 21-78) were tested for responses to generate a healthy control reference range. CONCLUSIONS: The OX40 assay, as presented in this report, represents an economical, rapid, robust whole blood technique to detect antigen-specific T cells, which is suitable for clinical immunology diagnostic laboratory use.

The zwitterionic type I Streptococcus pneumoniae polysaccharide does not induce memory B cell formation in humans.

In contrast to other pneumococcal serotypes, which are thought to be T-independent antigens, type 1 Streptococcus pneumoniae polysaccharide (Sp1) is a zwitterionic polysaccharide (ZPS). It has previously been shown to be processed and presented by antigen-presenting cells utilizing the MHC-II pathway, which leads to Sp1-induced T cell proliferation, a hallmark of thymus-dependent immune responses. We used peripheral blood mononuclear cells obtained from adults enrolled in a randomised clinical trial to investigate memory B cell responses following immunisation with the 23-valent pneumococcal plain polysaccharide vaccine. Administration of this serotype 1 containing vaccine resulted in the depletion of serotype 1 antigen-specific pre-existing memory B cells compared to baseline. This finding indicates that this ZPS is not processed by a classical TD mechanism within the MHC-II pathway.

Pneumococcal conjugate and plain polysaccharide vaccines have divergent effects on antigen-specific B cells.

BACKGROUND: A 23-valent unconjugated pneumococcal polysaccharide vaccine (23vP), routinely administered at the age of 65, has limited effectiveness, and revaccination induces attenuated antibody responses. It is not known whether pneumococcal polysaccharide-protein conjugated vaccines (PCV), although highly effective in infants, offer any immunological advantages over 23vP in adults. METHODS: We immunized adults with schedules combining both PCV and 23vP and investigated B-cell responses to establish whether PCV7 (a 7-valent PCV) induced T-dependent responses in adults, to assess the role of memory B cells in 23vP-induced antibody hyporesponsiveness, and to identify the B-cell subtypes involved. RESULTS: A single dose of PCV7 induced significant increases in serotype-specific memory B-cell populations in peripheral blood indicating a T-dependent response. Conversely, immunization with 23vP resulted in a decrease in memory B-cell frequency. Furthermore, memory B-cell responses to subsequent immunization with PCV7, when given after 23vP, were attenuated. Notably, B1b cells, a subset important in protecting mice against pneumococci, were also depleted following immunization with 23vP in humans. CONCLUSIONS: This study indicates that PCV7 may have an immunological advantage over 23vP in adults and that 23vP-induced depletion of memory and B1b-cell subsets may provide a basis for antibody hyporesponsiveness and the limited effectiveness of 23vP. Clinical Trials Registration. ISRCTN: 78768849.