Validated Quantification of HHV-8 DNA Using Inter-Convertible Plasmid and Cell-Derived Calibrators: Optimization of a Whole-Blood qPCR Assay.

Human herpesvirus 8 (HHV-8) is the etiologic agent of Kaposi's sarcoma (KS), primary effusion lymphoma (PEL), multicentric Castleman disease (MCD), and KS-associated immune reconstitution inflammatory syndrome (IRIS-KS). Quantifying HHV-8 DNA in whole blood is clinically relevant, yet laboratory practices remain heterogeneous. Here, we developed and validated an in-house quantitative PCR (qPCR) assay targeting ORF26, optimized for whole blood. Assay calibration used plasmid, BCBL-1 cell-derived, and commercial HHV-8 DNA standards. Analytical validation was performed following the Clinical and Laboratory Standards Institute (CLSI) guidelines and the Minimum Information for Publication of Quantitative Real-Time PCR Experiments (MIQE) guidelines and showed a 95% limit of detection of 65.7 copies/reaction, efficiencies of 90-101% (R2 > 0.99), and intra/inter-assay coefficients of variation < 6.5%. Strong correlations were observed among the three calibrators (R2 > 0.97).Clinical validation against a composite reference yielded 100% sensitivity, specificity, PPV, and NPV. Viral loads (log10 copies/mL) varied by clinical condition: classic KS and transplant-associated KS showed the lowest medians (2.30-2.23), MCD HIV- and PEL intermediate values (2.83-3.72), and epidemic KS, MCD HIV+, and IRIS-KS the highest (4.12, 4.86, and 5.03, respectively). Viremia > 5 log10 copies/mL was associated with uncontrolled E-KS, MCD HIV+, and IRIS-KS. Longitudinal follow-up revealed viral load decline paralleled clinical improvement. This validated assay provides a robust, affordable tool for HHV-8 quantification in whole blood and supports its integration into diagnostic workflows and patient monitoring.