International Immunology, Vol 10, 1863-1872, Copyright © 1998 by Oxford University Press
RJ Connelly, MS Hayden, JK Scholler, TT Tsu, B Dupont, JA Ledbetter and SB Kanner
The combination of anti-CD2 mAb 9.6 and 9-1, specific for distinct
epitopes, induces proliferation of resting human T cells. The mitogenic
activity of this mAb mixture depends upon accessory cells and the 9-1 mAb
Fc domain. To further study the functional properties of these mAb, their
variable regions were cloned and expressed as monospecific single- chain Fv
(scFv) proteins fused to the human IgG1 Fc domain (scFvIg). A novel
bispecific scFvIg was constructed by cloning the two monospecific scFv
binding sites in tandem, with the 9.6 scFv placed N-terminal to the 9-1
scFvIg. Monospecific scFvIg binding to CD2 was comparable to that of the
corresponding parental mAb, while the bispecific scFvIg exhibited binding
activity similar to that of the 9-1 scFvIg. The combination of 9.6 scFvIg
and 9-1 mAb was mitogenic, whereas mixtures including the 9-1 scFvIg were
non-stimulatory, confirming the unique properties of the 9-1 IgG3 Fc.
Without the IgG3 tail, the bispecific 9.6/9-1 scFvIg was directly mitogenic
and was a more potent mitogen than the mAb mixture, but was accessory cell
dependent. Unlike the combination of mAb, the bispecific reagent did not
directly mobilize calcium in T cells. In comparison to the mAb mixture,
bispecific 9.6/9- 1 scFvIg-mediated stimulation of a mixed lymphocyte
reaction was significantly more resistant to inhibition of the CD28
co-stimulatory pathway by the inhibitor CTLA-4-Ig. These results show that
expression of the 9.6 and 9-1 binding sites together on a bispecific scFvIg
increased the mitogenic properties of the mAb and altered the degree of
accessory cell signals required for T cell activation.
ARTICLES
Mitogenic properties of a bispecific single-chain Fv-Ig fusion generated from CD2-specific mAb to distinct epitopes [In Process Citation]
Bristol-Myers Squibb Pharmaceutical Research Institute, Seattle, WA 98121, USA.
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