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Transfer factor (TF) is a heterogeneous mix of low-molecular weight molecules obtained from dialyzed leukocyte extract that is capable of transferring cell-mediated immunity. As an immunostimulatory drug TF is used to improve treatment of infectious diseases, allergies, cancer and immune deficiencies. The main benefit of TF preparations as immunotherapeutic agents is the induction of a rapid immune response and the potential of TF as an adjuvant in combination with other drugs might lead to development of novel approaches to combat various diseases in the future. The process of TF preparation is rather simple. However, with respect to fact that TF is composed by several multifunction molecules, it is likely that during the activity measurement based only on one single parameter, other TF biological activities might be overlooked. In addition, separated TF components might display synergetic activity effect. According to recent European Pharmacopoeia there is no general protocol for immuno-stimulatory drugs (including TF) activity measurement available. Nevertheless, for the process of TF preparation, control of input material and for final pharmaceutical product batches it is inevitable to guaranty proper quality control including appropriate in vivo or in vitro test(s) for TF biological activity assay. The animal-origin materials and in vivo assays convey a considerable logistic, ethic and economic problem, meanwhile the available in vitro assays have been reported with limited reproducibility and sometimes contradictory results. The currently used method for testing biological activity of TF is the in vitro MTT cells proliferation assay that is recognized by control authorities in Slovak Republic. Keywords: immune system; transfer factor; dialysable leukocyte extract; diseases; MTT cells proliferation assay.

Some biological and physico-chemical properties were tested in 50 lots of transfer factor (TF). Each lot contained the extracts of a pool of 20 buffy coats, each originating from a 400 ml blood donation of a healthy individual. The optical densities at 260 and 280 nm were within a narrow range in all TF lots. The ratio 260/280 was 2.56-3.02. One unit TF (defined as the extract of two buffy coats (corresponding to 1-2 X 10(9) leucocytes) contained 36.58 +/- 3.77 mg of peptides as measured by the Lowry method and 123.6 +/- 4.5 mg ribose as estimated by the orcinol method. Cytotoxicity of TF lots was tested by measurement of chromium release of PHA-stimulated lymphocytes. Cytotoxicity was above 10% in 20 of 27 TF lots tested, most of which were produced by an Amicon ultrafiltration cell. Pyrogenicity was present in 8 of 42 TF lots produced by Amicon filters, but only in 1 of 8 lots produced by Sartorius filters. Sephadex G-10 chromatograms of TF gave characteristic patterns yielding 8 peaks. Sephadex G-25 chromatograms reproducibly showed 5 peaks. The distribution of osmotic activity, peptides and ribose in respect of the chromatographic fractions is given.