CD16, also called Fc.gamma. receptor-III (Fc.gamma.R-III), is a low affinity receptor for Immunoglobulin G (IgG). With other receptors of the immunoglobulin Fc portion (Fc.gamma.R-I, Fc.gamma.R-II, Fc.epsilon.R-I), CD16 plays an important role in mediating autoimmunity and inflamm atory responses.
Studies using monoclonal antibodies against CD16 have established this receptor's role in removing immune complexes from circulation and in mediating antibody-dependent cell mediated cellular cytotoxicity (ADCC) (see for example Van de Winkel et al., Immunol. Today, 14, 1993, pp.215-221). The binding of IgG with CD16 elicits NK/LGL cell activation and triggers ADCC. ADCC can be halted in the presence of high levels of soluble CD16.
It has been found (see Mathiot et al., J. Clin. Immunol., 13, (1), 1993, pp. 41-8) that the level of soluble CD16 was significantly decreased in patients with multiple myeloma compared with healthy volunteers. In addition a stage-dependent decrease of soluble CD16 was observed, with a highly significant difference between stage I and stages II+III myeloma patients. Therefore the measurement of soluble CD16 in serum is both a diagnostic and a prognostic marker of myeloma, which can be useful to define and guide novel immunomodulatory therapies of the disease.
It has further been found that CD16 is present in human serum and other body fluids and is elevated at sites of inflammation (see Fleit et al., Blood, 79, (10), 1992, pp. 2721-8).
From Ravetch et al. (J. Exp. Med., 170, 1989, pp. 481-97) it is clear that there are at least two isoforms of human CD16, type 1 and type 2, that can be designated as CD16-I and CD16-II, respectively. These two isoforms of CD16 are encoded by two separate but related genes, NA1 and NA2.
From Scallon et al. (PNAS USA, 86, pp.5079-83, July 1989) it is evident that CD16-I and CD16-II are distinct in both structure and cellular expression. CD16-I is expressed predominantly on the surface of neutrophils and monocytes, whereas CD16-II is expressed predominantly on the surface of macrophages, natural killer cells and large granular lymphocytes (NK/LGL). Furthermore, these two types of CD-16 are associated with the cell surface via two distinct mechanisms: CD16 type I is associated with the cell surface by glycosyl-phosphotidylinositol (GPI) linkage; whereas CD16 type II is anchored on the membrane with about 20 extra amino acids. Furthermore, the N-terminus of the mature CD16 has been investigated and the methionine residue at position 18 was identified as the N-terminal residue of the mature protein. Thus, the initial translation product contains a 17-amino acid signal peptide. The transmembrane region of CD16-II is shown to be from amino acid 209 to 229, whereas CD16-I is reported lacking transmembranal and cytoplasmic domains.
It has been determined that a single amino acid at position 203, Ser, found in isoform I versus Phe, found in type II, determines the membrane anchoring mechanism (see Lanier et al., Science, 246, 1989, pp. 1611-3).
For human CD16-I, a polymorphism has been reported previously, as is evident from FIG. 1, whereas only one alternative nucleic acid sequence encoding CD16-II has been published until now (Ravetch et al., J. Exp. Med., 170, 1989, pp. 481-97).
Recently, Huizinga et al. (see Blood, 76, pp. 1927-, 1990) published evidence that CD16-I deficiency is related to neonatal isoimmune neutropenia.
Bredius et al. (in Immunology, 83, pp. 624-, 1994) reported specifically that CD16-I-NA1 exhibited a 21-25% higher IgG1 mediated phagocytosis than CD16-I-NA2.
It has been reported that circulating levels of soluble CD16 are reduced in Multiple Myeloma, and an inhibitory effect of sCD16 on myeloma cells and pokeweed mitogen (PWM) -induced B-cell proliferation have been reported (see, respectively, Hoover et al., J. Cli. Inve., 95(1), pp.241-7, 1995) and Teillaud et al., Blood, 82(10), Nov. 15 1993).
European Patent Application EP 343 950 generally discloses soluble and membrane-bound human Fc.gamma.R-III polypeptides as well as nucleic acids capable of encoding the same. In particular, the sequence of a CD16-I variant and the sequence of CD16-II are shown in the Figures. This patent application further discloses various utilities for these polypeptides.
Citation of any document herein is not intended as an admission that such document is pertinent prior art, or considered material to the patentability of any claim of the present application. Any statement as to content or a date of any document is based on the information available to applicant at the time of filing and does not constitute an admission as to the correctness of such a statement.
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