Certification of a Standard Reference Material for Cytomegalovirus (CMV)

Summary

**Update**

As of September 1, 2015, SRM 2366a Cytomegalovirus DNA (TowneΔ147 BAC) for DNA Measurements was made available. The new material is a single component material at approximately 1.8 million copies per microliter.

Cytomegalovirus (CMV) is commonly carried by the general population (50% to 80%). After the initial infection the virus generally remains latent in the individual. However, in immune compromised individuals, such as organ transplant patients or patients with HIV, severe and possibly life threatening disease can result. Congenital infections in infants can be the most severe. The treatment for cytomegalovirus is toxic and available only by intravenous administration. It is important to quantify the viral load of a patient in order to determine the time and length of treatment. Quantitative PCR is the current favored approach to measurement of viral load but there is no FDA approved method nor are there any reference materials available to the clinical community. About 50% of the clinical testing laboratories use commercial reagents and the other 50% used laboratory developed tests. Not surprisingly, there are great interlaboratory differences in the results of proficiency testing schemes.

Description

The goal of this project is to provide a SI-traceable reference material for use by calibrant and reagent manufacturers in production of their own calibrants and standards. Clinical laboratories with in-house methods would be able to use the reference material for production of their own quality control materials which will be traceable to a NIST standard.  

It is non-trivial to produce a consistent Cytomegalovirus genome. Cytomegalovirus has a large genome and laboratory strains in culture in human fibroblasts have been shown to pack incomplete virus genomes in virus particles. An alternative is the use of a bacterial artificial chromosome (BAC) carrying the virus genome. NIST has acquired a BAC made from the Towne strain of Cytomegalovirus. The viral genome BAC was propagated in the bacteria, E. coli. The viral DNA will be certified for copy number and the sequence of selected regions will be released for informational value. Copy number will be determined using digital PCR. Regions to be sequenced include part or all of the following: UL34, UL54 (polymerase), UL55-56 (glycoprotein B), UL80, UL83 (phosphoprotein 65), UL97, UL122-126 (major immediate early and nearby sequence), UL132, and US17.

 

Major Accomplishments

• • Acquired the Towne strain BAC as an alternative to viral culture
  • Developed protocols for producing viral DNA from bacterial cell culture
  • Performed whole genome sequencing of the SRM using Illumina MiSeq and sequenced ~17 Kb using Sanger Sequencing
  • Completed homogeneity studies using droplet digital PCR
  • Completed stability studies using droplet digital and chamber digital PCR platforms
  • Performed in-house measurements of droplet volumes 
  • Tested multiple assays on both digital PCR platforms to determine CMV concentration in number of copies per microliter 

Additional Technical Details:

• • How to Use SRM 2366
  • Structure of CMV Genome

 

PCR Detection-Specific Information:

• • Sequence alignments
  • Primer and probe sequences with citations (pdf)
  • Location of primers and probes (full.pdf or cropped.pdf)