CTLA4Fcε, a novel soluble fusion protein that binds B7 molecules and the IgE receptors, and reduces human in vitro soluble CD23 production and lymphocyte proliferation

Abstract

SummaryImmunoglobulin E-mediated allergy and certain autoimmune diseases are characterized by the presence of a T helper type 2 (Th2) immune response and allergen-specific or self-reactive IgE. Soluble CD23 (sCD23) is a B-cell factor that fosters IgE class-switching and synthesis, suggesting that sCD23 may be a therapeutic target for these pathologies. We produced a recombinant protein, CTLA4Fce, by fusing the ectodomain of the immunoregulatory molecule cytotoxic T-lymphocyte antigen 4 (CTLA-4) with a fragment of the IgE H-chain constant region. In SDS-PAGE/inmunoblot analyses, CTLA4Fce appeared as a 70 000 MW polypeptide that forms homodimers. Flow cytometry showed that CTLA4Fce binds to IgE receptors FceRI and FceRII/CD23, as well as to CTLA-4 counter-receptors CD80 and CD86. Binding of CTLA4Fce to FceRII/CD23 appeared stronger than that of IgE. Since the cells used to study CD23 binding express CD80 and CD86, simultaneous binding of CTLA4Fce to CD23 and CD80/CD86 seems to occur and would explain this difference. As measured by a human CD23-specific ELISA, CTLA4Fce -but not IgE -induced a concentration-dependent reduction of sCD23 in culture supernatants of RPMI-8866 cells. Our results suggest that the simultaneous binding of CTLA4Fcɛ to CD23-CD80/CD86 may cause the formation of multi-molecular complexes that are either internalized or pose a steric hindrance to enzymatic proteolysis, so blocking sCD23 generation. CTLA4Fce caused a concentration-dependent reduction of lymphocyte proliferation in human peripheral blood mononuclear cell samples stimulated in vitro with concanavalin A. The ability to bind IgE receptors on effector cells, to regulate the production of sCD23 and to inhibit lymphocyte proliferation suggests that CTLA4Fcɛ has immunomodulatory properties on human Th2 responses.

Tracing IgE-Producing Cells in Allergic Patients

“…The latter is a quinone methide triterpene derived from Tripterygium wilfordii and capable of potentiating TNF-induced apoptosis [172]. CTLA4Fcε, a Th2 modulatory component, has so far only been tested in vitro [22]. CTLA4Fcε is a recombinant fusion protein of the ectodomain of the immunoregulatory molecules cytotoxic T lymphocyte antigen 4 (CTLA-4) with a fragment of IgE heavy chain constant region and thus binds to IgE receptors as well as CD80 and CD86.…”

“…So far, only the anti-IgE antibody omalizumab has been marketed and successfully reduces the burden of severe and otherwise uncontrollable asthma [17,18,19]. Several new approaches such as depleting IgE through extracorporal IgE immunoabsorption [13,20] as well as specifically targeting effector [21,22] or IgE+ B cells [23] are being explored and will be discussed in this review.…”

Anti-IgE therapy for IgE-mediated allergic diseases: from neutralizing IgE antibodies to eliminating IgE+ B cells

“…Researchers have constructed a fusion protein containing the CD80/CD86-binding domain of CTLA-4 and the Fcε receptor-binding domain of the IgE H chain [ 51 ]. This recombinant protein binds both FcεRI/FcεRII and CTLA-4 receptors (i.e., CD80 and CD86), thereby suppressing Th2 responses.…”

“…CTLA4 Fcɛ and CD23-CD80/CD86 combine to form a multi-molecule polymer, which acts as a spacer to influence production of soluble CD23. In an experiment involving human peripheral blood mononuclear cell samples stimulated in vitro, CTLA4 Fcɛ reduced the rate of lymphocyte proliferation in the presence of the lectin concanavalin A; in the same experiment, CTLA4 Fcɛ was also shown to bind IgE receptors on effector cells, thereby influencing soluble CD23 biosynthesis and inhibiting lymphocyte proliferation [ 51 ]. Given its demonstrated ability to affect IgE levels and the generation of IgE-secreting cells, the recombinant fusion protein CTLA4Fcɛ may be an effective medicine for controlling IgE-mediated immunodeficiency and other related diseases [ 51 ].…”

Biomarker Dynamics in B-cell Lymphoma: A Longitudinal Prospective Study of Plasma Samples Up to 25 Years before Diagnosis

“…While sTNF-R1 mediates TNFa effects (13), both sCD27 and sCD30 have a crucial role in regulating cellular activity in subsets of T-, B-, and natural killer cells (14,15). The soluble form of CD23, which is a Fc receptor for IgE, is released from activated B cells and is itself a stimulator of B-cell proliferation, inducing antibody class switching (16). CXCL13, the ligand of CXCR5, is a homeostatic chemokine that partly regulates B-cell trafficking (17).…”