A collaborative study to establish the 2nd international standard for tissue plasminogen activator (t-PA)

An international collaborative study involving ten laboratories located in eight different countries was undertaken in order to replace the current International Standard (I.S.) for tissue plasminogen activator (t-PA). Two lyophilised candidate preparations of high purity were assessed in comparison with the current I.S. for t-PA using only a clot lysis assay. One preparation (coded 86/670) was purified from a cultured melanoma cell supernatant and was about 98% single chain t-PA while the other preparation (coded 86/624) was derived from Chinese hamster ovary (CHO) cells following DNA recombinant procedures and was 75% single chain t-PA. Both candidate preparations of t-PA compared in quite a satisfactory manner with the current I.S. from the viewpoint of the biometrics of parallel line bioassays and both preparations were quite stable for long periods at low temperatures and stable from up to 1 month at temperatures of 20 degrees and 38 degrees C. Both fulfil the criteria to serve as a satisfactory 2nd International Standard for t-PA. The Fibrinolysis Subcommittee of the International Committee for Thrombosis and Haemostasis recommended the melanoma source t-PA (86/670) as the next I.S. in order to maintain continuity with the 1st I.S. which was also a melanoma-type preparation. The data from the ten laboratories indicated that each ampoule of the new proposed standard contains 850 international units of t-PA activity by the clot lysis assay. It is planned to present the results of this study to the Expert Committee on Biological Standardization of the World Health Organization at its next meeting and to request that the preparation to t-PA, coded 86/670, be established as the 2nd International Standard for t-PA.