The local lymph node assay (LLNA) is an in vivo test for identification of skin‐sensitising substances by measuring radioactive thymidine incorporation into the lymph node (OECD TG 429). Several non-animal methods and their combinations as defined approaches have been adopted as OECD Test Guidelines. However, there may be cases where the substance to be tested falls outside the applicability domain of non-animal-based methods, necessitating the use of the LLNA Test Guideline. The current project proposes to add an alternative, non-radioactive proliferation measurement as a refinement of the existing OECD TG 429.
Draft Test Guideline No. 429 on the local lymph node assay
- Submission period
- 29 October - 10 December 2025
Background public consultation
Project description
A project led by Germany was included in the Test Guideline Programme workplan in 2025 for the inclusion of the LLNA cell count method (LNCC) as an alternative read-out for OECD TG 429. The LNCC is identical to the adopted test method in all aspects besides the approach to assess lymph node proliferation, i.e. lymph node cell suspensions are subjected to a cell counting procedure (instead of scintillation counting after tail vein injection of radiolabelled e.g. thymidine). Using cell counts instead of incorporation of radiolabelled thymidine presents an animal welfare advantage, reduces variability (no tail vein injection) and omits the use of radiochemicals saving resources for the conduct and training of the assay.
How to contribute
The draft updated TG 429 is currently under a commenting round by the Working Party of the National Coordinators of the Test Guidelines Programmes and open for comments from the public at the same time. Interested parties are invited to contact their National Coordinators at least a week before 10 December 2025.
Document for public comments
