Effect of intermediate-purity factor VIII (FVIII) concentrate on lymphocyte proliferation and apoptosis: transforming growth factor-beta is a significant immunomodulatory component of FVIII

Factor concentrates have been shown to have a variety of immunomodulatory e ffects in vitro. The presence of plasma-derived factor VIII (pdFVIII) has b een shown to diminish lymphocyte proliferative response to mitogens. Recent ly, we have shown the presence of transforming growth factor-beta (TGF-beta ) as an immunomodulatory component present in plasma-derived FVIII concentr ate. However, the addition of neutralizing antibody to TGF-beta did not abr ogate the inhibitory effect of pdFVIII on monocyte cytokine production, sug gesting the presence of other, as yet undetermined, immunomodulatory agent/ s in pdFVIII. To further characterize the immunomodulatory effects of pdFVI II, the in vitro effect of pdFVIII concentrate on proliferation and apoptos is of mitogen-stimulated T cells was studied using whole blood and purified T cells. The presence of pdFVIII increased the apoptosis of phytohaemagglu tinn (PHA) -stimulated CD4 and CD8 T-cell subsets as determined by Annexin V binding and DNA fragmentation. T-cell subsets showed a pdFVIII dose-depen dent inhibition of entry into S-phase and G(1) arrest. Addition of neutrali zing anti-TGF-beta reduced some of these changes. To determine the physiolo gical relevance of these findings, blood samples from five patients receivi ng FVIII prophylaxis were similarly studied ex vivo and showed significantl y increased apoptosis of T-cell subsets as determined by Annexin V staining . TGF-beta has been reported to be a potent inhibitor of T-cell proliferati on, arresting the cell cycle in G(1) phase and causing apoptosis. Together, these findings suggest that TGF-beta is a significant immunomodulatory com ponent of pdFVIII concentrates.