Functional Fv fragment of an antibody specific for CD28: Fv-mediated co-stimulation of T cells

The most predominant co-stimulation pathway, which is critical for T cell a ctivation and proliferation, is the CD28-B7 pathway, The anti-CD28 monoclon al antibody (mAb) also provides a co-stimulatory signal to T cells. In orde r to construct a functional Fv fragment (complex of VH and VL domains) of a nti-CD28 antibody using a bacterial expression system, cDNA encoding the va riable regions of immunoglobulin from 15E8 hybridoma cells was cloned and e xpressed in Escherichia coli, The Fv fragment was obtained as a soluble pro tein from the periplasmic fraction and showed a binding pattern similar to parental IgG, The Fv fragment induced proliferation of peripheral blood mon onuclear cells in the presence of anti-CD3 or anti-CD2 mAb and enhanced ant i-tumor activity of antiMUC1 X anti-CD3 bispecific antibody when tested wit h lymphokine-activated killer cells with T cell phenotype. Thus, the anti-C D28 Fv fragment will be promising not only for the study of costimulation, but also for cancer immunotherapy. (C) 2000 Federation of European Biochemi cal Societies. Published by Elsevier Science B.V. All rights reserved.