Engineering an APRIL-specific B Cell Maturation Antigen

Abstract

B cell maturation antigen (BCMA) is a tumor necrosis factor receptor family member whose physiological role remains unclear. BCMA has been implicated as a receptor for both a proliferation-inducing ligand (APRIL) and B cell-activating factor (BAFF), tumor necrosis factor ligands that bind to multiple tumor necrosis factor receptor and have been reported to play a role in autoimmune disease and cancer. The results presented herein provide a dual perspective analysis of BCMA binding to both APRIL and BAFF. First, we characterized the binding affinity of monomeric BCMA for its ligands; BAFF binding affinity (IC50 = 8 ± 5 μm) is about 1000-fold reduced compared with the high affinity interaction of APRIL (IC50 = 11 ± 3 nm). Second, shotgun alanine scanning of BCMA was used to map critical residues for either APRIL or BAFF binding. In addition to a previously described “DXL” motif (Gordon, N. C., Pan, B., Hymowitz, S. G., Yin, J., Kelley, R. F., Cochran, A. G., Yan, M., Dixit, V. M., Fairbrother, W. J., and Starovasnik, M. A. (2003) Biochemistry 42, 5977-5983), the alanine scanning results predicted four amino acid positions in BCMA (Tyr13, Ile22, Gln25, and Arg27) that could impart ligand specificity. Substitution of Tyr13 was tolerated for BAFF binding but not APRIL binding. Arg27 was required for high affinity binding to APRIL, whereas substitutions of this residue had minimal effect on affinity for BAFF. Further phage display experiments suggested the single mutations of I22K, Q25D, and R27Y as providing the greatest difference in APRIL versus BAFF binding affinity. Incorporation of the Q25D and R27Y substitutions into BCMA produced a dual specificity variant, since it has comparable binding affinity for both APRIL and BAFF, IC50 = 350 and 700 nm, respectively. Binding of the I22K mutant of monomeric BCMA to BAFF was undetectable (IC50 > 100 μm), but affinity for binding to APRIL was similar to wild-type BCMA. Based on these results, a BCMA-Fc fusion with the single I22K mutation was produced that binds APRIL, IC50 = 12 nm, and has no measurable affinity for BAFF. These results suggest that APRIL is the preferred ligand for BCMA and show that specificity can be further modified through amino acid substitutions. B cell maturation antigen (BCMA) is a tumor necrosis factor receptor family member whose physiological role remains unclear. BCMA has been implicated as a receptor for both a proliferation-inducing ligand (APRIL) and B cell-activating factor (BAFF), tumor necrosis factor ligands that bind to multiple tumor necrosis factor receptor and have been reported to play a role in autoimmune disease and cancer. The results presented herein provide a dual perspective analysis of BCMA binding to both APRIL and BAFF. First, we characterized the binding affinity of monomeric BCMA for its ligands; BAFF binding affinity (IC50 = 8 ± 5 μm) is about 1000-fold reduced compared with the high affinity interaction of APRIL (IC50 = 11 ± 3 nm). Second, shotgun alanine scanning of BCMA was used to map critical residues for either APRIL or BAFF binding. In addition to a previously described “DXL” motif (Gordon, N. C., Pan, B., Hymowitz, S. G., Yin, J., Kelley, R. F., Cochran, A. G., Yan, M., Dixit, V. M., Fairbrother, W. J., and Starovasnik, M. A. (2003) Biochemistry 42, 5977-5983), the alanine scanning results predicted four amino acid positions in BCMA (Tyr13, Ile22, Gln25, and Arg27) that could impart ligand specificity. Substitution of Tyr13 was tolerated for BAFF binding but not APRIL binding. Arg27 was required for high affinity binding to APRIL, whereas substitutions of this residue had minimal effect on affinity for BAFF. Further phage display experiments suggested the single mutations of I22K, Q25D, and R27Y as providing the greatest difference in APRIL versus BAFF binding affinity. Incorporation of the Q25D and R27Y substitutions into BCMA produced a dual specificity variant, since it has comparable binding affinity for both APRIL and BAFF, IC50 = 350 and 700 nm, respectively. Binding of the I22K mutant of monomeric BCMA to BAFF was undetectable (IC50 > 100 μm), but affinity for binding to APRIL was similar to wild-type BCMA. Based on these results, a BCMA-Fc fusion with the single I22K mutation was produced that binds APRIL, IC50 = 12 nm, and has no measurable affinity for BAFF. These results suggest that APRIL is the preferred ligand for BCMA and show that specificity can be further modified through amino acid substitutions. The tumor necrosis factor receptors (TNFRs) 1The abbreviations used are: TNFR, tumor necrosis factor receptor; CRD, cysteine-rich domain; TNF, tumor necrosis factor; BCMA, B cell maturation antigen; TACI, transmembrane activator and CAML interactor; BAFF, B cell-activating factor; BR3, BLyS (BAFF) receptor 3; ECD, extracellular domain; ELISA, enzyme-linked immunosorbent assay; PBS, phosphate-buffered saline; NNS, (A/C/GT) (A/C/G/T) (G/C) codon. 1The abbreviations used are: TNFR, tumor necrosis factor receptor; CRD, cysteine-rich domain; TNF, tumor necrosis factor; BCMA, B cell maturation antigen; TACI, transmembrane activator and CAML interactor; BAFF, B cell-activating factor; BR3, BLyS (BAFF) receptor 3; ECD, extracellular domain; ELISA, enzyme-linked immunosorbent assay; PBS, phosphate-buffered saline; NNS, (A/C/GT) (A/C/G/T) (G/C) codon. are a superfamily of transmembrane receptors involved in cell communication within the immune system. TNFR family members are structurally characterized by extracellular cysteine-rich domains (CRDs) that form ligand-binding motifs. Family members can be further classified based on intracellular domains that can either stimulate apoptosis through a death domain or cell proliferation through a TNF receptor-associated factor binding motif (1Bodmer J.L. Schneider P. Tschopp J. Trends Biochem. Sci. 2002; 27: 19-26Abstract Full Text Full Text PDF PubMed Scopus (691) Google Scholar, 2Locksley R.M. Killeen N. Lenardo M.J. Cell. 2001; 104: 487-501Abstract Full Text Full Text PDF PubMed Scopus (2936) Google Scholar). Downstream signaling for this subgroup of the TNFR superfamily activates the NF-κB intracellular pathway, often via TNF receptor-associated factors, ultimately resulting in cell proliferation (1Bodmer J.L. Schneider P. Tschopp J. Trends Biochem. Sci. 2002; 27: 19-26Abstract Full Text Full Text PDF PubMed Scopus (691) Google Scholar, 2Locksley R.M. Killeen N. Lenardo M.J. Cell. 2001; 104: 487-501Abstract Full Text Full Text PDF PubMed Scopus (2936) Google Scholar, 3Hatzoglou A. Roussel J. Bourgeade M.F. Rogier E. Madry C. Inoue J. Devergne O. Tsapis A. J. Immunol. 2000; 165: 1322-1330Crossref PubMed Scopus (192) Google Scholar). The corresponding TNF ligands share a common structural motif called the TNF homology domain, in the form of a β sheet jelly roll, through which the ligands trimerize for receptor activation. TNF family members are expressed in a membrane-bound form but can undergo proteolysis to produce an active soluble trimer. Generally, members of the TNFR superfamily found on B or T cells are type I transmembrane proteins that have several CRDs (1Bodmer J.L. Schneider P. Tschopp J. Trends Biochem. Sci. 2002; 27: 19-26Abstract Full Text Full Text PDF PubMed Scopus (691) Google Scholar). There are, however, receptors in a subgroup that are expressed by B cells, are type III transmembrane proteins, and contain a reduced number of CRDs: B cell maturation antigen (BCMA), transmembrane activator and CAML interactor (TACI), and BLyS (BAFF) receptor 3 (BR3, also called BAFF-R) (4Gross J.A. Johnston J. Mudri S. Enselman R. W. J. C. M. A. A. W. 2000; PubMed Scopus Google Scholar, M. R.M. A. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar, Sci. S. A. 2000; PubMed Scopus Google Scholar, C. Schneider P. C. M. Tschopp J. J.L. C. 2001; PubMed Scopus Google Scholar, J. N. M. M. S. M. J. M. Immunol. 2000; PubMed Scopus Google Scholar). The extracellular domain of the BCMA CRD, and the of a with the receptor for the BCMA and are the members of the TNFR TACI, BCMA, and an intracellular death domain, it is that these receptors are involved in cell in of BCMA presented for the BCMA intracellular with TNF receptor-associated factors, of and A. Roussel J. Bourgeade M.F. Rogier E. Madry C. Inoue J. Devergne O. Tsapis A. J. Immunol. 2000; 165: 1322-1330Crossref PubMed Scopus (192) Google Scholar). BCMA however, show no a or role for this receptor J.L. S. M. E. 2001; PubMed Scopus Google Scholar, S. Cell. 2001; PubMed Scopus Google Scholar). In in with its critical role in B cell and a of the a autoimmune disease P. M. Full Text Full Text PDF PubMed Scopus Google Scholar). a receptor extracellular and transmembrane domains but a intracellular domain, and for has a reduced number of B cells C. Schneider P. C. M. Tschopp J. J.L. C. 2001; PubMed Scopus Google Scholar). to be for B cell is for the B cell and the physiological role of BCMA is unclear. The TNF family member BAFF is the ligand for B cell proliferation to however, BAFF has also been reported to bind and BCMA Sci. S. A. 2000; PubMed Scopus Google Scholar, J. N. M. M. S. M. J. M. Immunol. 2000; PubMed Scopus Google Scholar, J.A. P. E. P. P. J. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar). APRIL, the TNF family member to BAFF, also binds and BCMA M. R.M. A. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar, C. Schneider P. C. M. Tschopp J. J.L. C. 2001; PubMed Scopus Google Scholar, J. N. M. M. S. M. J. M. Immunol. 2000; PubMed Scopus Google Scholar). with the of BAFF and APRIL are BAFF is expressed by cells, and cells, whereas APRIL is expressed by cells and by tumor cells M. M. M. J.L. Schneider P. N. Tschopp J. J. PubMed Scopus Google Scholar, O. A. P. M. R. O. J. V. J. S. W. J. PubMed Scopus Google Scholar, O. V. S. J.A. P. 2001; PubMed Scopus Google Scholar, P. C. J. PubMed Scopus Google Scholar, A. P. A. Immunol. 2002; PubMed Scopus Google Scholar, M. J. PubMed Scopus Google Scholar). of BAFF to be critical for B cell BAFF display in the and of and B cells, whereas a BAFF a autoimmune (4Gross J.A. Johnston J. Mudri S. Enselman R. W. J. C. M. A. A. W. 2000; PubMed Scopus Google Scholar, J.L. S. M. E. 2001; PubMed Scopus Google Scholar, Schneider P. P. J. Immunol. 2002; Scopus Google Scholar, S. N. M. J. Sci. S. A. 2000; PubMed Scopus Google Scholar). Based on in B these ligands and and corresponding receptors (BR3, BCMA, and provide for disease by N. M. W. J. 2002; Full Text Full Text PDF PubMed Scopus Google of autoimmune disease in with In of the receptor an receptor be a or a however, an receptor has not been that TNF ligands are and can bind of the corresponding be in affinity ligands binding to receptors in versus of binding suggest that has however, these used a fusion that could in that are by M. R.M. A. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar, Sci. S. A. 2000; PubMed Scopus Google Scholar, J. N. M. M. S. M. J. M. Immunol. 2000; PubMed Scopus Google Scholar). In this we characterized the APRIL and BAFF binding of the extracellular domains of monomeric BCMA, and in to the role that could play in ligand-binding affinity. we have an alanine J.A. J. 2000; PubMed Scopus Google Scholar, J.A. 2000; PubMed Google of the BCMA in to the residues specificity for binding to APRIL or BAFF. based on the alanine results, we produced a BCMA-Fc fusion with a single mutation in the BCMA ECD, I22K, that high affinity for APRIL but has no measurable binding to BAFF. the BAFF was expressed and as previously described J. M. PubMed Scopus Google Scholar). M. E. M. C. A. C. J. Full Text Full Text PDF PubMed Scopus Google was a APRIL and for amino of APRIL was into the of a modified with a and to an fusion The was into cells and in with to an of with was to a of for and of cell was in 100 of with 5 and on for by through a and for was a with of with and with of with fusion and by and of BCMA for residues of the BCMA was by and into the the and to an and a the BCMA BCMA was into the the and The was with into cells, and was and to 3 of of cells was the by on acid as described previously J. P. M. W. J. J. 2001; PubMed Scopus Google by on a BCMA the as a and used to the of the and the of both and in the respectively. BCMA-Fc and the of was to to form a fusion in the and expressed in cells as previously described M. R.M. A. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar). was used to the single mutant I22K in the fusion cells with the for of of the in cells produced BCMA-Fc The BCMA-Fc was the by affinity of for phage display of the BCMA extracellular domain was by of the residues into the J. Full Text Full Text PDF PubMed Scopus Google Scholar). The resulting residues the to a and an by the of the The was to the of BCMA with an residue the for the was by the was by PubMed Scopus Google to the for an the and residues of the was used to scanning as described previously A. A. Sci. S. A. 2000; PubMed Scopus Google Scholar). shotgun alanine for the wild-type or of substitutions in to a of these shotgun has shotgun positions and has shotgun positions and for of the and and of the described to of binding either BAFF, APRIL, or on 2001; PubMed Scopus Google Scholar). used to binding. in E. in the of phage used for the in the was or was was the of the phage the to the phage the and in a in of with and A. A. Sci. S. A. 2000; PubMed Scopus Google to of BCMA of binding BAFF, APRIL, or that found to be in as described previously 2001; PubMed Scopus Google Scholar). of and of binding to BAFF, and for and respectively. of binding to APRIL, and and respectively. the display binding to a of for the effect of mutation on ligand for amino acid a of ligand to display as described previously M.F. S. J. Full Text Full Text PDF PubMed Scopus Google Scholar). and was used to a as by J.A. 2000; PubMed Google of residues Ile22, Gln25, and The of the was as described for the shotgun alanine amino acid for has the of amino the are to by the of of to of of the amino acid a as suggested previously Sci. PubMed Scopus Google Scholar). The is the of to of for ligand by the of to of for display and of to a fusion of BCMA and the domain of A. E. C. M. PubMed Scopus Google was by to the and 3 of with the domain Sci. PubMed Scopus Google Scholar). was as described PubMed Scopus Google to mutations and by fusion proteins expressed by E. and by on as described previously PubMed Scopus Google Scholar). proteins further by on a had an the that of soluble factor and E. of with the of the amino acid was on a acid analysis was on the to the = for binding to either APRIL or BAFF in a of either APRIL or BAFF, was on The was with and for with of in In of of was to of ligand that in a and for the with 100 of was and for The was with and with 100 of a of for to through the the with by a in PBS, the was for 5 with 100 and The was with 100 of and the was In a of the ELISA, of receptors in with APRIL was the or residues BAFF was the was and as described previously J. M. PubMed Scopus Google Scholar). of was with a of in for 3 and with a of the with either APRIL or BAFF with 100 of receptor was and for The was with and with 100 of for The was and as described of Binding for to on a used to binding of receptors to APRIL and BAFF. The ligands to the a of the by the In cell was and used as the that receptor of the ligand could not be in to several binding the the was to by the cell with for for receptor in to in analysis was used to and binding by the BCMA on the interaction of BCMA with BAFF BCMA have a high affinity interaction with of about M. R.M. A. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar, J. N. M. M. S. M. J. M. Immunol. 2000; PubMed Scopus Google Scholar). with BCMA-Fc have a affinity for BAFF M. E. M. C. A. C. J. Full Text Full Text PDF PubMed Scopus Google Scholar). we have produced monomeric BCMA and for both BAFF and BCMA was as as E. as a fusion with the domain of A. a to and monomeric BCMA ECD, the domain fusion has the of high E. and through the was E. by a and the as a a not of Binding affinity for monomeric to APRIL and BAFF was by the described BCMA and BAFF used in these APRIL was since the is the in and APRIL share and the residues are APRIL was expressed and as a fusion and binding experiments with the fusion since of the by proteolysis in reduced APRIL in was to for binding to with APRIL with an IC50 of nm, whereas BAFF in for binding with BAFF with an IC50 of of APRIL binding affinity for and BCMA in a that the domain not the affinity binding the BCMA binding to be binding to APRIL and BAFF APRIL or J. M. PubMed Scopus Google BAFF that the affinity of binding to receptors are with the ligand IC50 of binding to APRIL (IC50 = 11 are about 1000-fold in affinity binding to BAFF (IC50 = 8 for previously reported binding of interaction have been reported to be in the M. R.M. A. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar, J. N. M. M. S. M. J. M. Immunol. 2000; PubMed Scopus Google Scholar, M. E. M. C. A. C. J. Full Text Full Text PDF PubMed Scopus Google a of receptor and ligands was to the of on receptor binding to APRIL and BAFF. binding of and to either BAFF or APRIL These that the binds to BAFF (IC50 = μm) with a 1000-fold reduced affinity compared with APRIL (IC50 = whereas a binds to both APRIL and BAFF with affinity (IC50 = 5 and nm, binds BAFF, its predicted physiological with IC50 = for and IC50 = for but have measurable affinity for The ligand binding affinity of BCMA was also by APRIL and BAFF for to of APRIL with the used in the I the for and to APRIL with a of nm, whereas binding to BAFF was not BAFF binding by BCMA produced via was also In BCMA-Fc to both BAFF = and APRIL = with high with the BCMA-Fc binding to APRIL a with a for the as for a to for receptor binding to in a of shotgun alanine A. A. Sci. S. A. 2000; PubMed Scopus Google of the single extracellular of BCMA was used to the of amino acid to the binding of either APRIL or BAFF. In to phage that by the phage the was into In these wild-type by amino acid positions in the BCMA and resulting in either the wild-type amino acid or alanine expressed the positions the wild-type residue is or the shotgun for amino acid substitutions. These for on the of to BAFF in the J. J. R. S. PubMed Scopus Google and of structural to residues found for in a shotgun of J. M. PubMed Scopus Google Scholar). The BCMA phage to of ligand or and display by binding to an that an on BCMA members M.F. S. J. Full Text Full Text PDF PubMed Scopus Google Scholar). is critical for and with to The for both BAFF and APRIL are in The of an amino acid the effect of on binding to display of whereas of to the of a effect are The Tyr13 in BCMA tolerated as as and for but was for The for a to BAFF binding but a effect on affinity for both BAFF and APRIL amino and are critical in that wild-type residues of to was for both APRIL and BAFF however, alanine was not this of was not tolerated for binding to BAFF but was with APRIL binding. The to to have on APRIL and BAFF but the difference in was In of Arg27 was preferred for binding to BAFF and for APRIL binding. in the of BCMA had no effect on ligand binding. results for residues Ile22, Gln25, and Arg27 suggest these positions as for providing ligand since had on BAFF and APRIL binding. Ile22, Gln25, and Arg27 for further phage by of these positions by for ligand binding. phage was to of either BAFF or APRIL and compared with the display for an amino acid a that that amino acid is a for binding to the in the substitutions that in the difference in J.A. 2000; PubMed Google Scholar, Sci. PubMed Scopus Google APRIL binding and BAFF binding are I22K, Q25D, and The I22K produced a for APRIL binding BAFF Q25D and R27Y in and for BAFF binding to APRIL BCMA positions and for binding to BAFF or in a In to the on ligand binding by the phage display results, produced as fusion proteins, and for BAFF and APRIL binding by These show that Tyr13 is critical for BCMA binding to APRIL, since or substitutions of this residue the IC50 by The of Tyr13 with or produced in affinity for BAFF. with the phage display results, the single amino acid of I22K in a in affinity for BAFF but about a for APRIL binding. The single of Q25D in not binding to BAFF to APRIL, whereas the single amino acid of R27Y reduced APRIL binding compared with The mutant produced a receptor that could bind both APRIL and BAFF with the affinity. These substitutions to since the effect for the mutant was the of for the single the Q25D in affinity for BAFF, but with R27Y it an of binding to APRIL or ± ± in a was used to the binding of the mutant proteins for APRIL with IC50 I22K, and Q25D APRIL in the R27Y binding to APRIL a 1000-fold in affinity. The affinity of this mutant results a in the on of which to to a binding and the The for binding to APRIL was not described by a binding that the and could not be binding to APRIL by in a of BCMA-Fc and I22K Binding to the single mutation I22K in a that high affinity for APRIL and no measurable binding to BAFF, this mutation was into BCMA-Fc to the affinity and specificity be in a The as described was used to binding of BCMA-Fc type and I22K fusion proteins to APRIL or BAFF for APRIL binding or J. M. PubMed Scopus Google for BAFF binding These that the single I22K, in BCMA in a that binds APRIL (IC50 = 12 with similar affinity to the type BCMA-Fc (IC50 = but has no measurable affinity to BAFF (IC50 > BCMA binds APRIL with high affinity. In the affinity of BCMA for BAFF is 1000-fold for the BCMA produced in E. binds APRIL with high affinity and is to produced by in cells, the affinity for BAFF be by a of also described the affinity of the interaction M. E. M. C. A. C. J. Full Text Full Text PDF PubMed Scopus Google however, is the of a high affinity interaction BCMA and with M. R.M. A. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar, J. N. M. M. S. M. J. M. Immunol. 2000; PubMed Scopus Google Scholar, M. E. M. C. A. C. J. Full Text Full Text PDF PubMed Scopus Google the binds BAFF with an high affinity. a receptor with a ligand binding can the affinity. it is that BAFF bind with high affinity to cells BCMA the receptors are on the cell it has been that and can form on the cell in the of ligand R.M. Lenardo M.J. 2000; PubMed Scopus Google BCMA to the domain for this physiological BCMA as a receptor for APRIL and not for BAFF. is with that the of BAFF on the of B cells are of BCMA J.L. S. M. E. 2001; PubMed Scopus Google Scholar). to BR3, a motif is presented the of a type I in BCMA N. M. W. J. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar, J. J. R. S. PubMed Scopus Google Scholar). alanine scanning of BCMA that the motif is critical for APRIL binding as as BAFF binding These results suggest that this of BCMA is in a on APRIL that is similar to the on BAFF for binding BCMA and N. J. Cell. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar, PubMed Scopus Google Scholar, C. O. R. E. 2002; PubMed Scopus Google Scholar). In the for the or the residue of the motif in BR3, in with BAFF residues and with the of the The residue of the motif in BR3, in a with BAFF residue and the of the be through a with BAFF residue for APRIL by or in with BCMA are not however, APRIL is to have a similar binding for the as in the residues are and or is in APRIL, of a with of the motif to the specificity of BCMA for APRIL and for BAFF. mutation of Tyr13 has effect on but the of Tyr13 for results in a in APRIL binding affinity. The J. J. R. S. PubMed Scopus Google that the of Tyr13 has the to form with and Arg27 on BCMA on BAFF results that of these are for BAFF binding. In the is for high affinity APRIL binding. the residue corresponding to in APRIL is a that the of Tyr13 results an within BCMA. the role of in the the of Tyr13 to APRIL binding be to an effect of the of in BAFF, a role could be by on the Arg27 of BCMA is also for APRIL versus mutation of this has effect on BAFF binding but APRIL binding III and In the Arg27 a with the R27Y mutant that this is not required for BAFF is with the of a high affinity since has a in the to APRIL has with it is Arg27 of BCMA is required for high affinity binding to Further of this effect of the In addition to the the specificity of for BAFF APRIL could be by the of a residue which a with for the residue to the mutation in affinity for APRIL J. J. R. S. PubMed Scopus Google and residues in are for BAFF binding J. M. PubMed Scopus Google Scholar). In addition to BCMA residues Tyr13 and results phage display experiments suggest that and are for ligand specificity. a with BAFF, and the I22K results in a affinity for BAFF. wild-type BCMA has and have a affinity for The residues for on BAFF, and are with and in the on APRIL residue it is that the I22K has no effect on affinity for The of is not in with BAFF, and the Q25D single mutation has no effect on APRIL or BAFF binding. Q25D affinity for BAFF with R27Y that a dual specificity BCMA was that Arg27 and in the of this effect is unclear. BAFF and APRIL have been implicated in autoimmune and APRIL has been to be in and M. M. M. J.L. Schneider P. N. Tschopp J. J. PubMed Scopus Google Scholar, P. Schneider P. J. S. N. C. J.L. C. Tschopp J. J. 2000; PubMed Scopus Google Scholar, E. 2000; Google Scholar). The N. M. W. J. 2002; Full Text Full Text PDF PubMed Scopus Google with on BAFF J.L. S. M. E. 2001; PubMed Scopus Google has been used to the role of BAFF in B cell The role of APRIL in B cell is since APRIL display B cell E. C. S. P. A. Cell. PubMed Scopus Google Scholar). BCMA-Fc has been used to suggest a role for APRIL in J. N. M. M. S. M. J. M. Immunol. 2000; PubMed Scopus Google and tumor P. Schneider P. J. S. N. C. J.L. C. Tschopp J. J. 2000; PubMed Scopus Google however, since BCMA binds BAFF with high the could be a of BAFF These in experiments could provide for an of APRIL BCMA was used as an the BCMA-Fc mutant I22K both high affinity and specificity for APRIL and be for the role of APRIL in and disease for the BCMA and for