Marco Guadagnoli

Development and characterization of APRIL antagonistic monoclonal antibodies for treatment of B-cell lymphomas

APRIL (A proliferation-inducing ligand) is a TNF family member that binds two TNF receptor family members, TACI and BCMA. It shares these receptors with the closely related TNF family member, B-cell activating factor (BAFF). Contrary to BAFF, APRIL binds heparan sulfate proteoglycans (HSPGs), which regulates cross-linking of APRIL and efficient signaling. APRIL was originally identified as a growth promoter of solid tumors, and more recent evidence defines APRIL also as an important survival factor in several human B-cell malignancies, such as chronic lymphocytic leukemia (CLL). To target APRIL therapeutically, we developed two anti-human APRIL antibodies (hAPRIL.01A and hAPRIL.03A) that block APRIL binding to BCMA and TACI. Their antagonistic properties are unique when compared with a series of commercially available monoclonal anti-human APRIL antibodies as they prevent in vitro proliferation and IgA production of APRIL-reactive B cells. In addition, they effectively impair the CLL-like phenotype of aging APRIL transgenic mice and, more importantly, block APRIL binding to human B-cell lymphomas and prevent the survival effect induced by APRIL. We therefore conclude that these antibodies have potential for further development as therapeutics to target APRIL-dependent survival in B-cell malignancies.

Chronic lymphocytic leukemia disease progression is accelerated by APRIL-TACI interaction in the TCL1 transgenic mouse model

Although in vitro studies pointed to the tumor necrosis factor family member APRIL (a proliferation-inducing ligand) in mediating survival of chronic lymphocytic leukemia (CLL) cells, clear evidence for a role in leukemogenesis and progression in CLL is lacking. APRIL significantly prolonged in vitro survival of CD5(+)B220(dull) leukemic cells derived from the murine Eμ-TCL1-Tg (TCL1-Tg [transgenic]) model for CLL. APRIL-TCL1 double-Tg mice showed a significantly earlier onset of leukemia and disruption of splenic architecture, and survival was significantly reduced. Interestingly, clonal evolution of CD5(+)B220(dull) cells (judged by BCR clonality) did not seem to be accelerated by APRIL; both mouse strains were oligoclonal at 4 months. Although APRIL binds different receptors, APRIL-mediated leukemic cell survival depended on tumor necrosis factor receptor superfamily member 13B (TACI) ligation. These findings indicate that APRIL has an important role in CLL and that the APRIL-TACI interaction might be a selective novel therapeutic target for human CLL.

The Design and Characterization of Receptor-selective APRIL Variants

Background: APRIL binds two receptors, BCMA and TACI, so separating signaling outcomes is difficult. Results: We used an algorithm to design a variant of APRIL that specifically binds BCMA and two variants that selectively bind TACI. Conclusion: TACI and BCMA signals differ in the context of B cell stimulation. Significance: These variants will help decipher APRIL signaling in physiology and disease settings. A proliferation-inducing ligand (APRIL), a member of the TNF ligand superfamily with an important role in humoral immunity, is also implicated in several cancers as a prosurvival factor. APRIL binds two different TNF receptors, B cell maturation antigen (BCMA) and transmembrane activator and cylclophilin ligand interactor (TACI), and also interacts independently with heparan sulfate proteoglycans. Because APRIL shares binding of the TNF receptors with B cell activation factor, separating the precise signaling pathways activated by either ligand in a given context has proven quite difficult. In this study, we have used the protein design algorithm FoldX to successfully generate a BCMA-specific variant of APRIL, APRIL-R206E, and two TACI-selective variants, D132F and D132Y. These APRIL variants show selective activity toward their receptors in several in vitro assays. Moreover, we have used these ligands to show that BCMA and TACI have a distinct role in APRIL-induced B cell stimulation. We conclude that these ligands are useful tools for studying APRIL biology in the context of individual receptor activation.

A proliferation-inducing ligand (APRIL): the development of antagonistic agents as potential therapeutics and deciphering the role of heparan sulphate proteoglycans (HSPGs) in APRIL Signalling.

APRIL (a proliferation-inducing ligand or TALL-2 and TRDL-1) is a member of the tumour necrosis factor (TNF) superfamily and binds two TNF receptors: TACI (transmembrane activator and calcium modulator and cyclophilin ligand interactor) and BCMA (B-cell maturation antigen). APRIL is important for the maintenance of humoral immune responses, although was originally discovered due to its role in promoting tumourigenic responses. APRIL has since been shown to be involved in several autoimmune diseases and is also implicated as an important pro-survival factor in several B-cell malignancies. To target APRIL specifically for therapeutic purposes, we are developing novel APRIL antagonistic monoclonal antibodies. Here we describe the characterisation of these antibodies and the future direction of our studies. In addition we have performed experiments to further decipher the role of heparan sulphate proteoglycan (HSPG) interactions in APRIL signalling. We report that the HSPG interaction provides a platform for APRIL cross-linking and oligomerisation to signal effectively via BCMA and TACI, but does not appear to mediate direct signalling. The role of APRIL in solid tumours lacking the known APRIL receptors is also addressed.

Abstract 5480: Characterization of anti-human APRIL monoclonal antibodies capable of inhibiting APRIL-dependent B cell function and hyperproliferation.

A Proliferation Inducing Ligand (APRIL) is a TNF ligand that, via its receptors TACI and BCMA, is involved in both B cell physiology as well as in proliferation and survival of malignant B cells. To target APRIL-dependent stimulation of B cell cancers, we recently produced and characterized two monoclonal antagonistic anti-human APRIL antibodies called humanAPRIL.01A (hA.01A) and humanAPRIL.03A (hA.03A). In a first biochemical assay to validate their blocking activity, hA.01A was shown to fully prevent APRIL from binding to its receptors, whereas a substantial difference was detected for hA.03A, which inhibited APRIL binding to BCMA less efficiently than hA.01A. Epitope mapping subsequently revealed that hA.01A and hA.03A bind distinct sites on APRIL, which provided a structural rationale of their different blocking activities. Importantly, this differential inhibition profile can be used to functionally dissect BCMA and TACI-dependent signals and indicated that B cell survival and IgA production are regulated differently by these receptors. Primary CLL cultures were shown to be sensitive to APRIL neutralization using hA.01A. hA.01A also inhibited hyperplasia in a transgenic mouse model reminiscent of B-CLL. Altogether, these data indicate that hA.01A is a novel tool potentially useful for the targeted treatment of B cell-derived cancers such as B-CLL and Multiple Myeloma. Citation Format: Marco Guadagnoli, Katherine Cameron, Elise Veraar, Fiona Kimberley, Andrea van Elsas, Hans van Eenennaam, Jan Paul Medema. Characterization of anti-human APRIL monoclonal antibodies capable of inhibiting APRIL-dependent B cell function and hyperproliferation. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5480. doi:10.1158/1538-7445.AM2013-5480