Quantitative measurement of varicella-zoster virus infection by semiautomated flow cytometry.

Varicella-zoster virus (VZV; human herpesvirus 3) is the etiological cause of chickenpox and, upon reactivation from latency, zoster. Currently, vaccines are available to prevent both diseases effectively. A critical requirement for the manufacturing of safe and potent vaccines is the measurement of the biological activity to ensure proper dosing and efficacy, while minimizing potentially harmful secondary effects induced by immunization. In the case of live virus-containing vaccines, such as VZV-containing vaccines, biological activity is determined using an infectivity assay in a susceptible cellular host in vitro. Infectivity measurements generally rely on the enumeration of plaques by visual inspection of an infected cell monolayer. These plaque assays are generally very tedious and labor intensive and have modest throughput and high associated variability. In this study, we have developed a flow cytometry assay to measure the infectivity of the attenuated vaccine strain (vOka/Merck) of VZV in MRC-5 cells with improved throughput. The assay is performed in 96-well tissue culture microtiter plates and is based on the detection and quantification of infected cells expressing VZV glycoproteins on their surfaces. Multiple assay parameters have been investigated, including specificity, limit of detection, limit of quantification, range of linear response, signal-to-noise ratio, and precision. This novel assay appears to be in good concordance with the classical plaque assay results and therefore provides a viable, higher-throughput alternative to the plaque assay.

Development and utilization of activated STAT3 detection assays for screening a library of secreted proteins.

Interleukin-6 (IL-6) family of cytokines are multifunctional proteins that play an important role in host defenses, acute phase reactions, immune responses, hematopoiesis, and tumorigenesis. The cytokines are produced by various lymphoid and nonlymphoid cells and mediate their biological activity through initial low-affinity binding to cell surface receptors, which are specific for their respective ligands. Ligand-specific receptor binding results in the receptor heterodimerization with ubiquitously expressed signal-transducing transmembrane component gp130 followed by activation of the gp130-associated Janus kinase, which, in turn, phosphorylates signal transducer and activator of transcription 3 (STAT3). Phosphorylated STAT3 (pSTAT3) dimerizes and translocates to the nucleus, where it activates gene transcription. Activation of STAT3 is essential to IL-6 family-associated physiological effects. Therefore, the ability to assess STAT3 phosphorylation is important for drug discovery efforts targeting IL-6 family cytokines. Various reagents and technologies are available to detect the effect of IL-6 type cytokines in treated cells. The present study describes the development of two pSTAT3 detection assays: the high-throughput screening assay based on Meso-Scale Discovery technology, which utilizes electrochemoluminescent signal measurements for the detection of pSTAT3 in treated cell extracts, and the secondary characterization assay based on fluorescent imaging analysis, which monitors pSTAT3 nuclear translocation in cells after activation. We have successfully utilized these assays to screen a small library of secreted proteins and identified inducers of STAT3 phosphorylation. The results obtained in this study demonstrate that both assays are robust, reliable, and amenable to high-throughput screening applications.

Rapid automation of a cell-based assay using a modular approach: case study of a flow-based Varicella Zoster Virus infectivity assay.

Vaccine manufacturing requires constant analytical monitoring to ensure reliable quality and a consistent safety profile of the final product. Concentration and bioactivity of active components of the vaccine are key attributes routinely evaluated throughout the manufacturing cycle and for product release and dosage. In the case of live attenuated virus vaccines, bioactivity is traditionally measured in vitro by infection of susceptible cells with the vaccine followed by quantification of virus replication, cytopathology or expression of viral markers. These assays are typically multi-day procedures that require trained technicians and constant attention. Considering the need for high volumes of testing, automation and streamlining of these assays is highly desirable. In this study, the automation and streamlining of a complex infectivity assay for Varicella Zoster Virus (VZV) containing test articles is presented. The automation procedure was completed using existing liquid handling infrastructure in a modular fashion, limiting custom-designed elements to a minimum to facilitate transposition. In addition, cellular senescence data provided an optimal population doubling range for long term, reliable assay operation at high throughput. The results presented in this study demonstrate a successful automation paradigm resulting in an eightfold increase in throughput while maintaining assay performance characteristics comparable to the original assay.