Inter-laboratory validation of a harmonized PNH flow cytometry assay.

BACKGROUND: A network comprising 11 laboratories aimed to consolidate PNH testing by developing and validating an assay guided by previous guidelines and studies. Network analyses of >20 native samples yielded key findings that were used to create and reshape the final protocol. METHODS: Twenty-seven native samples were distributed to all participating laboratories for blind testing, local analysis, and subsequent re-analysis by a central laboratory. Inter-laboratory clone size precision (coefficient of variation [CV]) was monitored for each sample, and the findings used to refine the test protocol. Linearity and precision tests were performed, assay limits of blank and detection were calculated, and limits of quantification were determined. RESULTS: When using the final protocol, enumeration of cells with a PNH phenotype by all participating laboratories was comparable, with no clinically significant discrepancies or false-positive or false-negative results reported. Of note, the biological characteristics of the sample affected precision. For example, CVs were higher when PNH and normal cells showed contiguous expression of GPI-linked antigens. A red cell gating strategy that eliminated non-specific type II PNH phenotypic events was devised, enabling reliable reporting of events in the type II red cell gate. The final protocol provided an assay with a Limit of Quantification of 0.01% for neutrophils and red cells, and 0.1% for monocytes. CONCLUSIONS: We describe a robust network-validated PNH assay that may aid other laboratories to set up and validate high resolution PNH analysis. © 2018 International Clinical Cytometry Society.

Immunodominant Francisella tularensis antigens identified using proteome microarray.

Stimulation of protective immune responses against intracellular pathogens is difficult to achieve using non-replicating vaccines. BALB/c mice immunized by intramuscular injection with killed Francisella tularensis (live vaccine strain) adjuvanted with preformed immune stimulating complexes admixed with CpG, were protected when systemically challenged with a highly virulent strain of F. tularensis (Schu S4). Serum from immunized mice was used to probe a whole proteome microarray in order to identify immunodominant antigens. Eleven out of the top 12 immunodominant antigens have been previously described as immunoreactive in F. tularensis. However, 31 previously unreported immunoreactive antigens were revealed using this approach. Twenty four (50%) of the ORFs on the immunodominant hit list belonged to the category of surface or membrane associated proteins compared to only 22% of the entire proteome. There were eight hypothetical protein hits and eight hits from proteins associated with different aspects of metabolism. The chip also allowed us to readily determine the IgG subclass bias, towards individual or multiple antigens, in protected and unprotected animals. These data give insight into the protective immune response and have potentially important implications for the rational design of non-living vaccines for tularemia and other intracellular pathogens.