Environmental Factor, November 2009, National Institute of Environmental Health Sciences
Experts Review Revisions to Local Lymph Node Assay Method
By Debbie McCarley
On October 20-22, scientists from NIEHS, the Environmental Protection Agency, the Food and Drug Administration (FDA), and the Consumer Product Safety Commission (CPSC) participated in an international expert consultation to evaluate modifications of the murine local lymph node assay (LLNA) - a test method for detecting potential skin-sensitizing substances.
This expert consultation meeting, which also included experts from industry and other stakeholder organizations, was convened by the Organisation for Economic Co-operation and Development (OECD) and co-hosted by CPSC at its headquarters in Bethesda, Md. Also hosting the meeting were the NTP Interagency Center for the Evaluation of Alternative Toxicological Methods (NICEATM) (https://www.niehs.nih.gov/news/newsletter/2009/november/science-experts.cfm ) and the Interagency Coordinating Committee on the Validation of Alternative Methods (ICCVAM)(https://ntp.niehs.nih.gov/pubhealth/evalatm/iccvam/index.html).
The group of 20 scientists from five countries reviewed proposed revisions to OECD Test Guideline (TG) for the LLNA, TG 429. The proposed revisions provide multiple mechanisms for reducing the number of animals in each test by up to 40 percent. They also provide a standardized approach and improved guidance for establishing the highest test dose, as well as performance standards that can be used to expedite the validation of modified versions of the LLNA. All of the proposed revisions are based on the recommendations recently forwarded to U.S. federal agencies by ICCVAM, an interagency committee administered by NICEATM.
The expert group also reviewed drafts of two new proposed test guidelines for nonradioisotopic versions of the LLNA. These test methods - the LLNA: DA, which measures adenosine triphosphate (ATP) content, and LLNA: BrdU-ELISA, which measures bromodeoxyuridine (BrdU) incorporation - do not require radioisotopes to measure lymphocyte proliferation, which is a requirement in the traditional LLNA. The availability of OECD test guidelines for these test methods will allow more widespread use of the LLNA by enabling it to be used where use of radioisotopes is not permitted. The draft test guidelines are also based on an ICCVAM evaluation of LLNA: DA and LLNA: BrdU-ELISA. Final ICCVAM recommendations on the usefulness and limitations of these test methods in the U.S. are currently being finalized and will likely be forwarded to U.S. federal agencies by the end of the year.
The expert group will meet again later this year to consider revised versions of the test guidelines based on discussions and recommendations at the October meeting. The revised draft TGs will then be sent out for review and comment by OECD member countries.
U.S. federal agencies originally accepted the LLNA in 1999 for safety testing, based on ICCVAM recommendations that the LLNA was a valid substitute for the traditional guinea pig test methods used to identify potential sensitizers. The LLNA has many advantages, including using fewer animals, eliminating the potential discomfort that can occur with positive results in the guinea pig methods, and providing dose-response information. The LLNA also reduces the amount of time needed for testing of potential sensitizers, as it can be completed in one week, as compared to four weeks for the guinea pig test.
(Debbie McCarley is the Special Assistant to Rear Admiral William Stokes, D.V.M., D.A.C.L.A.M., director of the NTP Interagency Center for the Evaluation of Alternative Toxicological Methods.)
About the OECD Test Guidelines Programme
OECD is an international organization that provides a setting where governments compare policy experiences, seek answers to common problems, identify good practices, and coordinate domestic and international policies. The 30 OECD member countries work together to support sustainable economic growth, raise living standards, assist other countries' economic development and contribute to growth in world trade.
A validated test method for establishing the safety or hazards of a chemical or product can achieve acceptance on the international level when it is included in a test guideline developed by the OECD. OECD Test Guidelines are based on the most relevant internationally agreed testing methods used by government, industry and independent laboratories. The Working Group of National Coordinators (WNT) oversees the work of the Test Guidelines Programme. The governments of OECD member and participating countries nominate national coordinators. The test guideline development process allows for input by a variety of stakeholders. NICEATM and ICCVAM actively participate in the development of OECD guidelines for the testing of chemicals.
The first version of a test guideline is sent to the WNT, who prepare national positions on the test guideline and also collect comments from national experts and other stakeholders. In most cases, an expert group is established after the first commenting round to address comments received from the WNT. The expert group may meet once or several times, as appropriate. Usually, two or three commenting rounds are necessary before the submission of a draft Test Guideline to the WNT for approval. Comments may be technical comments, such as ones related to the validation or to performance criteria, or policy comments, such as those related to animal welfare concerns.
Formal adoption of a method as a test guideline issued by OECD allows it to be used in all OECD member countries, which include Japan, Canada and most countries in the European Union.