Identification of Transforming Growth Factor-P as a Contaminant in Factor VI11 Concentrates: A Possible Link With Immunosuppressive Effects in Hemophiliacs

In previous studies, we have shown that some, but not all IOW-, intermediate-, and high-purity factor Vlll concentrates inhibit interleukin-2 (IL-2) secretion from phytohemagglutinin (PHA)-stimulated T lymphocytes. We now present evidence that this inhibitory action of concentrates is, at least in part, due to contamination with transforming growth factor-/3 (TGF-P). Originally identified in platelets, TGF-/3 is a 25-kD homodimer that has been shown to be a natural and potent inhibitor of many immunologic responses. Using a specific bioassay, we have measured TGF-B in various factor Vlll concentrates. While some concentrates contained substantial amounts of the cytokine, there was a wide variation in concentrations of TGF-/3 in different products. These lev-