CD64-Directed Immunotoxin Inhibits Arthritis in a Novel CD64 Transgenic Rat Model

Abstract

Macrophages are known to play a key role during inflammation in rheumatoid arthritis (RA). Inflammatory macrophages have increased expression of CD64, the high-affinity receptor for IgG. Targeting this receptor through a CD64-directed immunotoxin, composed of an Ab against CD64 and Ricin A, results in effective killing of inflammatory macrophages. In this study, we show elevated levels of CD64 on synovial macrophages in both synovial lining and synovial fluid in RA patients. The CD64-directed immunotoxin efficiently eliminates activated synovial macrophages in vitro, while leaving quiescent, low CD64-expressing macrophages unaffected. To examine whether killing of CD64 macrophages results in therapeutic effects in vivo, we established an adjuvant arthritis (AA) model in newly generated human CD64 (hCD64) transgenic rats. We demonstrate that hCD64 regulation in this transgenic rat model is similar as in humans. After AA induction, treatment with CD64-directed immunotoxin results in significant inhibition of disease activity. There is a direct correlation between immunotoxin treatment and decreased macrophage numbers, followed by diminished inflammation and bone erosion in paws of these hCD64 transgenic rats. These data support synovial macrophages to play a crucial role in joint inflammation in AA in rats and in human RA. Selective elimination of inflammatory macrophages through a CD64-directed immunotoxin may provide a novel approach for treatment of RA.

Monomeric IgG1 Fc molecules displaying unique Fc receptor interactions that are exploitable to treat inflammation-mediated diseases

“…Indeed, a number of anti-FcgRI immunotoxins, composed of anti-FcgRI antibodies attached to various toxins, have recently been developed, and their efficacy has been demonstrated in vitro and in mouse models of different diseases, such as chronic cutaneous inflammation, rheumatoid arthritis, acute myeloid leukemia. 11,12,25,26,36,37 In this regard, the use of mFc to deliver therapeutic molecules could be particularly valuable because it provides extended circulating half-life and improved biodistribution by interacting with FcRn, 38,39 and it offers additional targeting to FcgRI-overexpressed cells, which in certain cases could lead to greater therapeutic benefit. For instance, one immediate application is to fuse mFc with anti-FcgRI immunotoxins.…”

Granzyme B-H22(scFv), a human immunotoxin targeting CD64 in acute myeloid leukemia of monocytic subtypes

“…H22 and its derivatives have been used in a variety of applications including as fusion proteins with antibodies (39 -41) and toxic components such as calicheamicin (42), Pseudomonas ETA ¶ (21) and Ricin A (19,20,22,37). Both Ricin A and ETA ¶ fusions to H22 have been used as therapeutic agents against AML cells (21,22).…”

“…Previous studies focusing on the targeting of dysregulated CD64 + cells in cutaneous inflammation and arthritis have shown that anti-CD64 immunotoxin treatment successfully eliminated CD64 + activated macrophages but left resting macrophages with low CD64 expression unaffected (19,20). The key element here is not the degree of CD64 expression but rather the actual state of activation of these cells.…”

Antibody-targeted vaccines

“…In addition to peripheral immune suppression, APC-targeting may also be able to induce central (thymus) T-cell tolerance to peptide antigens (Schjetne et al, 2005). Finally, recent disease model studies have explored the potential of using Fc receptor targeting to deliver immunomodulatory approaches for the treatment of rheumatoid arthritis (van Vuuren et al, 2006;Wenink et al, 2006).…”