Several live attenuated influenza virus

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Neutralizing antibodies specific for respiratory syncytial virus (RSV) represent a major protective mechanism against RSV infection, as demonstrated by the efficacy of the immune-prophylactic monoclonal antibody palivizumab in preventing RSV-associated lower respiratory tract infections in premature infants. Accordingly, the RSV neutralization assay has become a key functional method to assess the neutralizing activity of serum antibodies in preclinical animal models, epidemiology studies, and clinical trials. In this study, we qualified a 24-h, fluorescent focus-based microneutralization (RSVA FFA-MN) method that requires no medium exchange or pre- or postinfection processing to detect green fluorescent protein-expressing RSV strain A2 (RSVA-GFP)-infected cells, using a high-content imaging system for automated image acquisition and focus enumeration. The RSVA FFA-MN method was shown to be sensitive, with a limit of detection (LOD) and limit of quantitation (LOQ) of 1:10, or 3.32 log2; linear over a range of 4.27 to 9.65 log2 50% inhibitory concentration (IC50); and precise, with intra- and interassay coefficients of variation of <21%. This precision allowed the choice of a statistically justified 3-fold-rise seroresponse cutoff criterion. The repeatability and robustness of this method were demonstrated by including a pooled human serum sample in every assay as a positive control (PC). Over 3 years of testing between two laboratories, this PC generated data falling within 2.5 standard deviations of the mean 98.7% of the time (n = 1,720). This high-throughput and reliable RSV microneutralization assay has proven useful for testing sera from preclinical vaccine candidate evaluation studies, epidemiology studies, and both pediatric and adult vaccine clinical trials.

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.Varicella-zoster virus (VZV; human herpesvirus 3) is a member of the Alphaherpesvirinae family. It is the etiological cause of two distinct and common diseases in humans: chickenpox and zoster. Exposure of immunologically naïve individuals to VZV results in chickenpox, a condition typically occurring during the first two decades of life. Chickenpox is usually a mild disease, although severe complications have been reported, especially in immune-compromised individuals or patients suffering from hematopoietic malignancies (29, 31). Resolution of the primary infection does not result in complete elimination of the virus, which subsists in a latent stage in sensory neural ganglia, despite sustained cellular and humoral immunity (1). This latent stage can be maintained for the remainder of the individual's life span. VZV reactivation from latency causes the symptoms of zoster which can be associated with severe and debilitating pain. A significant fraction of patients (up to 20%) will eventually suffer from long-term chronic neuralgia (postherpetic neuralgia) due to permanent nerve damage. The causes of reactivation are not fully understood, but a combination of fatigue, stress, and a declining level of cell-mediated immunity seems to be implicated. Indeed, there is a strong link between the rate of clinical reactivation and the increase in age of the affected patients (8).Several pediatric live attenuated vaccine formulations, which have proven very efficac...