Methodological optimisation of thymocyte isolation and cryopreservation of human thymus samples

Premature lymphocytes develop into non-autoreactive, mature naïve CD4⁺ or CD8⁺ T cells in the thymus before entering the circulation. However, in-depth characterization of human thymocyte development remains challenging due to limited availability of human thymus samples and the fragile nature of thymocyte populations. Thymocytes often do not survive cryopreservation and thawing procedures, especially the fragile CD4⁺CD8⁺ double positive population. It is generally recommended to use fresh human thymus tissue on the day of excision to avoid any biases in thymocyte composition. This hampers the possibility to perform multiple experiments on the same thymus sample. To establish how the thymocyte viability and composition can be maintained, we compared two thymocyte isolation methods used for human and/or mice thymi, three cryopreservation methods in combination with our most gentle thawing technique. Based on our findings we established that fresh human thymi remain viable in cold storage for up to two days post-surgery without compromising thymocyte composition. Thymocytes can be cryopreserved if required, although the CD4⁺CD8⁺ double positive populations may be reduced. Our study provides thoroughly optimized methods to study human thymocyte development over a considerable time-frame post-surgery.