Enhancement of human T cell responses to allogeneic stimuli by factor VIII concentrates

The effect of factor VIII concentrate, from commercial and National Health Services manufacturers, on in vitro lymphocyte proliferative response to allogeneic stimulator cells was investigated. Factor VIII preparations 'purified' by ion exchange or by monoclonal antibody affinity had no effect in this assay but lymphocyte proliferation in response to allogeneic cells was markedly and consistently enhanced by some intermediate purity factor VIII concentrates and, to a lesser extent, by a factor IX preparation. These preparations did not stimulate lymphocyte proliferation in the absence of other mitogens. The co-mitogenic factor(s) present in intermediate purity factor VIII was not identified. However, enhanced proliferation was not due to factor VIII itself, nor to albumin or fibronectin. The clinical relevance of the immunomodulatory activity of intermediate purity factor VIII concentrates in vitro is discussed.