The Fc‐alpha receptor is a new target antigen for immunotherapy of myeloid leukemia

Abstract

Antibody-based immunotherapy of leukemia requires the targeting of specific antigens on the surface of blasts. The Fc gamma receptor (CD64) has been investigated in detail, and CD64-targeting immunotherapy has shown promising efficacy in the targeted ablation of acute myeloid leukemia (AML), acute myelomonocytic leukemia (AMML) and chronic myeloid leukemia cells (CML). Here we investigate for the first time the potential of FcaRI (CD89) as a new target antigen expressed by different myeloid leukemic cell populations. For specific targeting and killing, we generated a recombinant fusion protein comprising an anti-human CD89 single-chain Fragment variable and the well-characterized truncated version of the potent Pseudomonas aeruginosa exotoxin A (ETA'). Our novel therapeutic approach achieved in vitro EC 50 values in range 0.2-3 nM depending on the applied stimuli, that is, interferon gamma or tumor necrosis factor alpha. We also observed a dose-dependent apoptosis-mediated cytotoxicity, which resulted in the elimination of up to 90% of the target cells within 72 hr. These findings were also confirmed ex vivo using leukemic primary cells from peripheral blood samples of three previously untreated patients. We conclude that CD89-specific targeting of leukemia cell lines can be achieved in vitro and that the efficient elimination of leukemic primary cells supports the potential of CD89-ETA' as a potent, novel immunotherapeutic agent.Under normal physiological conditions, the Fc-alpha receptor (FcaR, CD89) is present on monocytes, macrophages, neutrophils and eosinophils. Its biological function is to interact with IgA-opsonized targets, triggering several immunological defense processes, e.g. phagocytosis, antibody-dependent cellmediated cytotoxicity and the stimulation of inflammatory mediators. 1 In many human tissues, most of the CD89 1 cells are neutrophils and monocytes/macrophages. Furthermore, although monocytes in the blood express relatively high levels of CD89, most tissue macrophages (particularly those located in the gut lamina propria) tend not to express CD89 on the surface, with a parallel downregulation of CD14. 2 This suggests that the abundance of CD89 depends on the differentiation stage of myeloid cells. The biological relevance of CD89 downregulation during the maturation of myeloid precursor cells is unknown.On the other hand, the presence of anomalous numbers of myeloid cells in the blood is indicative of several myelogenous hematological malignancies, with AML and CML being the most common. 3 The different forms of myeloid leukemia have been categorized using the French-American-British (FAB) system divided into eight subtypes (M0-M7). The World Health Organisation (WHO) uses expanded criteria. 4 A standard panel of markers is used for detailed diagnosis and classification, including Fc gamma receptor (FcgRI) (CD64) which is present on AML subtypes M0-M5 in varying degrees. 5 Thus far, there is no evidence that other Fc receptors can be used as diagnostic antigens or therapeutic targets in A...

Immunoglobulin A: magic bullet or Trojan horse?

“…Of note, as FcaRI is upregulated in leukaemic tumour cells, FcaRI might be a target antigen itself in this case [65]. In conclusion, IgA autoantibodies can be considered Trojan horses as they contribute to disease via the recruitment of neutrophils.…”

CD64-directed microtubule associated protein tau kills leukemic blastsex vivo

“…We have shown in previous studies that 200 nM is a sufficient dose of hCFP or IT to achieve the receptor-specific induction of apoptosis within 12 h [7, 8, 14, 15]. We therefore used the same dose for the constructs tested in this study.…”

Elimination of different leukaemia subtypes using novel CD89‐specific human cytolytic fusion proteins

“…Furthermore, the cytotoxic effect was antigen‐specific, as shown by the absence of any effect against CD89 − Jurkat (Fig ) cells and proven in a competition assay (Figure S3). In previous studies, αCD89(scFv)‐ETA’ induced apoptosis in 35–70% of γ‐interferon(IFNγ)‐stimulated cells (Mladenov et al , ). Here, αCD89(scFv)‐ETA’ induced apoptosis in 80% of stimulated HL‐60 cells but had only a small effect on MonoMac‐1 and U937 cells (Fig ).…”

“…It is involved in IgA binding, phagocytosis, cytokine release and antibody‐dependent cell‐mediated cytotoxicity (Valerius et al , ; Bakema & van Egmond, ). Due to the natural expression of CD89 on myeloid cells and the involvement of these cells in different subtypes of acute myeloid leukaemia (AML) and chronic myeloid leukaemia (CML), CD89 might also be a promising receptor for targeted immunotherapy of haematopoietic malignancies (Mladenov et al , ).…”

“…We used a mutant form of angiogenin (Ang GGRR ), which is less sensitive to its natural inhibitors because the site of interaction has been modified (Cremer et al , ). Here we describe the development of two novel hCFPs, αCD89(scFv)‐MapTau and αCD89(scFv)‐Ang GGRR , that are analogous to αCD89(scFv)‐ETA’, which comprises the truncated version of the Pseudomonas aeruginosa exotoxin A (ETA’) and a CD89‐specific scFv (Mladenov et al , ).…”