Previous Article | Next Article 
Infection and Immunity, August 2005, p. 5229-5232, Vol. 73, No. 8
0019-9567/05/$08.00+0 doi:10.1128/IAI.73.8.5229-5232.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Characterization of a Humanized Monoclonal Antibody Recognizing Clumping Factor A Expressed by Staphylococcus aureus
Paul J. Domanski,1
Pratiksha R. Patel,1
Arnold S. Bayer,2
Li Zhang,1
Andrea E. Hall,1
Peter J. Syribeys,1
Elena L. Gorovits,1
Dawn Bryant,1
John H. Vernachio,1
Jeff T. Hutchins,1 and
Joseph M. Patti1*
Inhibitex, Inc., Alpharetta, Georgia,1
LA Biomedical Research, Torrance, California2
Received 4 October 2004/
Returned for modification 1 December 2004/
Accepted 14 March 2005

ABSTRACT
We report the humanization and characterization of monoclonal
antibody (MAb) T1-2 or tefibazumab, a monoclonal antibody that
recognizes clumping factor A expressed on the surface of
Staphylococcus aureus. We demonstrate that the binding kinetics of MAb T1-2
is indistinguishable compared to that of its murine parent.
Furthermore, MAb T1-2 is shown to enhance the opsonophagocytic
uptake of ClfA-coated latex beads, protect against an intravenous
challenge in a prophylactic model of rabbit infective endocarditis,
and enhance the efficacy of vancomycin therapy in a therapeutic
model of established infective endocarditis.

TEXT
Staphylococcus aureus is a major pathogen in a significant number
of serious nosocomial and community-acquired infections. It
has been estimated that approximately 56% of all
S. aureus strains
causing infections in the intensive care unit are methicillin
resistant (
17). More recently, reports documenting an increase
in community-associated infections caused by methicillin-resistant
Staphylococcus aureus (MRSA) (
13) and vancomycin-resistant
S. aureus strains in patients from Michigan (
3), Pennsylvania (
1),
and New York (
2) have served to further highlight the increasing
dilemma clinicians face in treating serious
S. aureus infections.
With a limited number of approved therapeutic options available
to address such infections, the development of novel therapies
is clearly warranted.
Over the past decade, a family of S. aureus cell surface adhesins, known as MSCRAMMs (for microbial surface components recognizing adhesive matrix molecules), have been shown to interact with high affinity and specificity to host tissues or implanted biomaterials (5, 15), and this step is considered to be the first in the infection process. Clumping factor A (ClfA) is a fibrinogen-binding adhesin thought to be a primary factor contributing to the colonization of implanted biomaterials or damaged endothelial surfaces at the site of endovascular infections (18). The biological role of ClfA in vivo in such infections has been demonstrated in numerous studies (12, 16, 19) and suggests that ClfA is a major virulence factor of S. aureus. The clfA gene has been shown to be expressed in vivo and is present in nearly all clinical S. aureus strains examined to date (4, 21). Furthermore, the biological impact of targeting ClfA was demonstrated by Josefsson and colleagues, who found that active immunization with recombinant ClfA protein and passive immunization with human polyclonal anti-ClfA antibodies protected mice against S. aureus septic arthritis and sepsis-induced death (7).
We recently described the generation of a murine monoclonal antibody (MAb 12-9) that is specific for ClfA, binds with high affinity, inhibits the adherence of S. aureus to immobilized fibrinogen, and protects mice against sepsis-induced death by MRSA (6). We now report the production and characterization of a MAb, T1-2, or tefibazumab, a humanized version of murine MAb 12-9.
Humanization and selection of the NSO T1-2 cell line.
12-9 variable region mRNA was isolated from hybridoma cells using standard molecular biology techniques and sequenced. Humanization was carried out using a process described by Padlan (14). Using this technique, targeted residues were mutated to mimic the most homologous human germ line subgroup using mutagenic oligonucleotides via PCR (PCR Reagent System; Life Technologies, Gaithersburg, Maryland). In the VL sequence, only 7 amino acids (6.25% of total) were changed: VL 1 (N
D), 3 (M
V), 9 (S
D), 15 (A
L), 18 (K
R), 22 (S
N), and 63 (T
S). In the VH region, a total of 9 amino acids (7.4% of total) were changed: VH 13 (A
K), 17 (S
T), 23 (A
T), 76 (S
N), 83 (Q
T), 84 (Y
A), 85 (D
A), 89 (M
V), and 113 (A
S). Appropriate humanized V-regions, human constant regions (immunoglobulin G1 [IgG1]), and mammalian leader sequences were subcloned into glutamine synthetase (GS) selection vectors licensed from Lonza Biologics (Berkshire, United Kingdom).
The NS0 (GS) cell line (Lonza Biologics, Berkshire, United Kingdom) was transfected (FuGene 6; Roche Diagnostics, Indianapolis, IN) with the linearized plasmid containing DNA encoding the humanized 12-9 variable heavy and light chains as directed by Lonza protocols (Lonza Biologics, Berkshire, United Kingdom). Immunoglobulin present in the supernatant from growth positive clones was assayed for reactivity to ClfA by surface plasmon resonance (SPR) by a two-step method as previously described (6), i.e., a goat anti-human-F(ab')2 antibody (GAH-F(ab')2; Jackson ImmunoResearch, West Grove, PA)-labeled CM5 chip to facilitate antibody capture (step 1) and passing recombinant ClfA protein over the captured MAb (step 2). ClfA-positive clones were expanded, and the most stable clone with the highest production, MAb T1-2, was chosen as the lead candidate for characterization and production.
In vitro analysis of MAb T1-2.
MAb T1-2 bound to both recombinant and native ClfA, and provided the same level of inhibition of ClfA/fibrinogen binding in vitro as its murine predecessor (data not shown). SPR analysis revealed that the binding kinetics of MAb12-9 and MAb T1-2 were indistinguishable (MAb 12-9, equilibrium dissociation constant [KD] = 2.10 x 1010; T1-2, KD = 2.54 x 1010), indicating that the site-specific mutations made did not alter the critical antigen-binding regions of the MAb.
Conversion of the murine Fc region to human IgG1 was designed to increase the opsonic potential of MAb T1-2. This functional activity was evaluated by using a latex bead-based flow cytometric assay with human polymorphonuclear cells (PMNs), thus eliminating the interference of protein A on the surface of intact S. aureus cells. The phagocytic product (PP = mean beads per cell x percent fluorescent PMN) was calculated for each reaction as described in detail previously (9-11). The data in Fig. 1 clearly show that MAb T1-2 facilitates enhanced PMN uptake of the ClfA-coated beads (P values versus MAb T1-2: beads only, <0.001; complement alone, <0.001; and human IgG1, <0.001). Complement alone and nonspecific human IgG1 resulted in minimal levels of phagocytosis by the human PMNs (Fig. 1).
In vivo efficacy of MAb T1-2.
To assess the in vivo therapeutic potential of MAb T1-2 against
invasive MRSA infections, a rabbit infective endocarditis (IE)
model was utilized. Female outbred New Zealand White rabbits
(Irish Farms, Corona, CA) weighing approximately 2.5 kg underwent
carotid artery-to-left ventricle catheterization as previously
described (
8). All rabbits were maintained according to National
Institutes of Health animal husbandry standards. For prophylactic
studies, approximately 18 h after catheterization animals received
a single dose of MAb T1-2 intravenously (i.v.) (10 mg/kg or
30 mg/kg) or normal human i.v. Ig (IVIG; 300 mg/kg) (Panglobulin;
ZLB, Bern, Switzerland). Twenty-four hours later, the passively
immunized rabbits were challenged i.v. with 2.7
x 10
6 CFU of
MRSA strain 67-0 (courtesy of Henry Chambers, University of
CaliforniaSan Francisco and San Francisco General Hospital,
San Francisco). Limited pharmacokinetic analysis revealed specific
anti-ClfA titers increased following MAb administration and
then dissipated gradually over the 72-h postinfection period
(Fig.
2A). None of the animals receiving MAb T1-2 were blood
culture positive at sacrifice. In contrast, 4/6 animals (60%)
given human IVIG were bacteremic (Fig.
2B). Moreover, only one
animal receiving the lower MAb T1-2 (10 mg/kg) dose and none
of the animals receiving 30 mg/kg of MAb T1-2 experienced seeding
of vegetations or kidneys. All of the animals that were treated
with normal IVIG developed bacterial seeding in both the vegetation
and kidney (Fig.
2C and
2D). The levels of bacteria recovered
from the target organs of rabbits receiving MAb T1-2, compared
with the normal IVIG-treated animals, were significantly lower
(Fig.
2B, C, and D;
P < 0.02).
In the therapeutic IE model, MAb T1-2 was used as adjunctive
therapy with vancomycin and was administered 24 h after infection
with MRSA 67-0. We used both a single-dose or two-dose regimen
(successive doses administered 72 h apart). Blood levels of
MAb T1-2 indicated that anti-ClfA antibody titers diminished
over time in the single-dose group, and in the two-dose group
MAb T1-2 levels rose after the second dose to levels similar
to that achieved after the primary dose (Fig.
3A). Within 24
h of administration, in the cohort MAb T1-2 plus vancomycin
treatment, nearly all blood cultures were rendered culture negative
(8/9) (data not shown), and all but one animal remained blood
culture negative for the next 24 h. At 96 h posttherapy, two
additional animals in this group developed recrudescent bacteremia
(data not shown). These cases of recrudescent bacteremia supported
the rationale for a treatment group that received a second dose
of MAb T1-2 at 72 h following the initiation of therapy (Fig.
3; 2
x MAb T1-2). Of note, all animals in the two-dose antibody
group remained blood culture negative during the entire postinfection
period (data not shown), while all control animals remained
blood culture positive. Vancomycin alone exerted a slow impact
on bacteremia clearance over the treatment period, with 33%,
67%, and 67% of blood cultures being culture negative at 24,
48, and 72 h posttherapy, respectively (data not shown). In
the aortic vegetations, vancomycin alone reduced MRSA densities
compared to untreated controls, although these differences did
not reach statistical significance (Fig.
3B). Coadministration
of one or two doses of MAb T1-2 with vancomycin significantly
reduced vegetation MRSA densities (Fig.
3B) as compared to untreated
controls. In the kidneys (Fig.
3C) and spleen (Fig.
3D), vancomycin
alone reduced MRSA densities as compared to those of untreated
controls, although this did not reach statistical significance.
Similar to the vegetation data above, single-dose and two-dose
MAb T1-2 administrations significantly reduced MRSA densities
in kidneys (Fig.
3C) and spleen (Fig.
3D) as compared to untreated
controls.
Previous data from our laboratories have indicated that polyclonal
antibodies to recombinant ClfA are effective in preventing bacteremia
(
20). In this report we show that a single prophylactic administration
of the MAb T1-2 is extremely effective in reducing target organ
seeding and/or an increase in clearance, indicating that MAb
T1-2, by itself, is capable of reducing the severity of IE MRSA
infection. We also demonstrate the benefit of combining antibody
therapy with conventional antibiotic treatment, as therapeutic
administration of the MAb T1-2 with vancomycin significantly
enhanced the clearance and/or reduced seeding of MRSA to target
tissues compared to vancomycin alone. This is an important observation,
given that in the clinical setting, MAb T1-2 would most likely
be coadministered with an antibiotic, representing the current
standard of care. Currently, the exact mechanism by which T1-2
reduces the level of bacteremia, vegetation, and organ screening
is not precisely defined; however, the observed biological activities
are consistent with an affinity for ClfA, inhibition of adherence
of
S. aureus to fibrinogen, and opsonophagocytosis. In conclusion,
these findings strongly support further evaluation of such humanized
MAbs directed against key adhesins in well-designed clinical
trials to either prevent or mitigate serious
S. aureus infections.

ACKNOWLEDGMENTS
We thank Jin Wang, Jeffery Robbins, and Laurie Donald for their
expert technical assistance and Yin Lee for assistance with
the animal model.

FOOTNOTES
* Corresponding author. Mailing address: Inhibitex, Inc., 9005 Westside Parkway, Suite 400, Alpharetta, GA 30004. Phone: (678) 746-1144. Fax: (678) 746-0624. E-mail:
jpatti{at}inhibitex.com.

Editor: F. C. Fang

REFERENCES
1 - Anonymous. 2002. Staphylococcus aureus resistant to vancomycinUnited States, 2002. Morb. Mortal. Wkly. Rep. 51:565-567.[Medline]
2 - Anonymous. 2004. Vancomycin-resistant Staphylococcus aureusNew York, 2004. Morb. Mortal. Wkly. Rep. 53:322-323.[Medline]
3 - Chang, S., D. M. Sievert, J. C. Hageman, M. L. Boulton, F. C. Tenover, F. P. Downes, S. Shah, J. T. Rudrik, G. R. Pupp, W. J. Brown, D. Cardo, and S. K. Fridkin. 2003. Infection with vancomycin-resistant Staphylococcus aureus containing the vanA resistance gene. N. Engl. J. Med. 348:1342-1347.[Free Full Text]
4 - Colque-Navarro, P., M. Palma, B. Söderquist, J.-I. Flock, and R. Möllby. 2000. Antibody responses in patients with staphylococcal septicemia against two Staphylococcus aureus fibrinogen binding proteins: clumping factor and an extracellular fibrinogen binding protein. Clin. Diagn Lab. Immunol. 7:14-20.[Abstract/Free Full Text]
5 - Foster, T. J., and M. Hook. 1998. Surface protein adhesins of Staphylococcus aureus. Trends Microbiol. 6:484-488.[CrossRef][Medline]
6 - Hall, A. E., P. J. Domanski, P. R. Patel, J. H. Vernachio, P. J. Syribeys, E. L. Gorovits, M. A. Johnson, J. M. Ross, J. T. Hutchins, and J. M. Patti. 2003. Characterization of a protective monoclonal antibody recognizing Staphylococcus aureus MSCRAMM protein clumping factor A. Infect. Immun. 71:6864-6870.[Abstract/Free Full Text]
7 - Josefsson, E., O. Hartford, L. O'Brien, J. M. Patti, and T. Foster. 2001. Protection against experimental Staphylococcus aureus arthritis by vaccination with clumping factor A, a novel virulence determinant. J. Infect. Dis. 184:1572-1580.[CrossRef][Medline]
8 - Kupferwasser, L. I., M. R. Yeaman, S. M. Shapiro, C. C. Nast, P. M. Sullam, S. G. Filler, and A. S. Bayer. 1999. Acetylsalicylic acid reduces vegetation bacterial density, hematogenous bacterial dissemination, and frequency of embolic events in experimental Staphylococcus aureus endocarditis through antiplatelet and antibacterial effects. Circulation 99:2791-2797.[Abstract/Free Full Text]
9 - Lehmann, A. K., A. Halstensen, I. S. Aaberge, J. Holst, T. E. Michaelsen, S. Sornes, L. M. Wetzler, and H.-K. Guttormsen. 1999. Human opsonins induced during meningococcal disease recognize outer membrane proteins PorA and PorB. Infect. Immun. 67:2552-2560.[Abstract/Free Full Text]
10 - Lehmann, A. K., A. Halstensen, and C. F. Bassoe. 1998. Flow cytometric quantitation of human opsonin-dependent phagocytosis and oxidative burst responses to meningococcal antigens. Cytometry 33:406-413.[CrossRef][Medline]
11 - Lehmann, A. K., A. Halstensen, J. Holst, and C. F. Bassoe. 1997. Functional assays for evaluation of serogroup B meningococcal structures as mediators of human opsonophagocytosis. J. Immunol. Methods 200:55-68.[CrossRef][Medline]
12 - Moreillon, P., J. M. Entenza, P. Francioli, D. McDevitt, T. J. Foster, P. Francois, and P. Vaudaux. 1995. Role of Staphylococcus aureus coagulase and clumping factor in pathogenesis of experimental endocarditis. Infect. Immun. 63:4738-4743.[Abstract]
13 - Morin, C. A., and J. L. Hadler. 2001. Population-based incidence and characteristics of community-onset Staphylococcus aureus infections with bacteremia in 4 metropolitan Connecticut areas, 1998. J. Infect. Dis. 184:1029-1034.[CrossRef][Medline]
14 - Padlan, E. A. 1991. A possible procedure for reducing the immunogenicity of antibody variable domains while preserving their ligand-binding properties. Mol. Immunol. 28:489-498.[CrossRef][Medline]
15 - Patti, J. M., B. L. Allen, M. J. Mcgavin, and M. Hook. 1994. MSCRAMM-mediated adherence of microorganisms to host tissues. Annu. Rev. Microbiol. 48:585-617.[Medline]
16 - Que, Y.-A., J.-A. Haefliger, P. Francioli, and P. Moreillon. 2000. Expression of Staphylococcus aureus clumping factor A in Lactococcus lactis subsp. cremoris using a new shuttle vector. Infect. Immun. 68:3516-3522.[Abstract/Free Full Text]
17 - Richards, M. J., J. R. Edwards, D. H. Culver, and R. P. Gaynes et al. 1999. Nosocomial infections in medical intensive care units in the United States. Crit. Care Med. 27:887-892.[CrossRef][Medline]
18 - Siboo, I. R., A. L. Cheung, A. S. Bayer, and P. M. Sullam. 2001. Clumping factor A mediates binding of Staphylococcus aureus to human platelets. Infect. Immun. 69:3120-3127.[Abstract/Free Full Text]
19 - Stutzmann Meier, P., J. M. Entenza, P. Vaudaux, P. Francioli, M. P. Glauser, and P. Moreillon. 2001. Study of Staphylococcus aureus pathogenic genes by transfer and expression in the less virulent organism Streptococcus gordonii. Infect. Immun. 69:657-664.[Abstract/Free Full Text]
20 - Vernachio, J., A. S. Bayer, T. Le, Y.-L. Chai, B. Prater, A. Schneider, B. Ames, P. Syribeys, J. Robbins, and J. M. Patti. 2003. Anti-clumping factor A immunoglobulin reduces the duration of methicillin-resistant Staphylococcus aureus bacteremia in an experimental model of infective endocarditis. Antimicrob. Agents Chemother. 47:3400-3406.[Abstract/Free Full Text]
21 - Wolz, C., C. Goerke, R. Landmann, W. Zimmerli, and U. Fluckiger. 2002. Transcription of clumping factor A in attached and unattached Staphylococcus aureus in vitro and during device-related infection. Infect. Immun. 70:2758-2762.[Abstract/Free Full Text]
Infection and Immunity, August 2005, p. 5229-5232, Vol. 73, No. 8
0019-9567/05/$08.00+0 doi:10.1128/IAI.73.8.5229-5232.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
This article has been cited by other articles:
-
Baer, M., Sawa, T., Flynn, P., Luehrsen, K., Martinez, D., Wiener-Kronish, J. P., Yarranton, G., Bebbington, C.
(2009). An Engineered Human Antibody Fab Fragment Specific for Pseudomonas aeruginosa PcrV Antigen Has Potent Antibacterial Activity. Infect. Immun.
77: 1083-1090
[Abstract]
[Full Text]
-
Tuchscherr, L. P. N., Buzzola, F. R., Alvarez, L. P., Lee, J. C., Sordelli, D. O.
(2008). Antibodies to Capsular Polysaccharide and Clumping Factor A Prevent Mastitis and the Emergence of Unencapsulated and Small-Colony Variants of Staphylococcus aureus in Mice. Infect. Immun.
76: 5738-5744
[Abstract]
[Full Text]
-
Bekeredjian-Ding, I., Inamura, S., Giese, T., Moll, H., Endres, S., Sing, A., Zahringer, U., Hartmann, G.
(2007). Staphylococcus aureus Protein A Triggers T Cell-Independent B Cell Proliferation by Sensitizing B Cells for TLR2 Ligands. J. Immunol.
178: 2803-2812
[Abstract]
[Full Text]
-
Hetherington, S., Texter, M., Wenzel, E., Patti, J. M., Reynolds, L., Shamp, T., Swan, S.
(2006). Phase I dose escalation study to evaluate the safety and pharmacokinetic profile of tefibazumab in subjects with end-stage renal disease requiring hemodialysis.. Antimicrob. Agents Chemother.
50: 3499-3500
[Abstract]
[Full Text]
-
Weems, J. J. Jr., Steinberg, J. P., Filler, S., Baddley, J. W., Corey, G. R., Sampathkumar, P., Winston, L., John, J. F., Kubin, C. J., Talwani, R., Moore, T., Patti, J. M., Hetherington, S., Texter, M., Wenzel, E., Kelley, V. A., Fowler, V. G. Jr.
(2006). Phase II, Randomized, Double-Blind, Multicenter Study Comparing the Safety and Pharmacokinetics of Tefibazumab to Placebo for Treatment of Staphylococcus aureus Bacteremia.. Antimicrob. Agents Chemother.
50: 2751-2755
[Abstract]
[Full Text]
-
Pourmand, M. R., Clarke, S. R., Schuman, R. F., Mond, J. J., Foster, S. J.
(2006). Identification of Antigenic Components of Staphylococcus epidermidis Expressed during Human Infection.. Infect. Immun.
74: 4644-4654
[Abstract]
[Full Text]
-
Kelly-Quintos, C., Cavacini, L. A., Posner, M. R., Goldmann, D., Pier, G. B.
(2006). Characterization of the Opsonic and Protective Activity against Staphylococcus aureus of Fully Human Monoclonal Antibodies Specific for the Bacterial Surface Polysaccharide Poly-N-Acetylglucosamine.. Infect. Immun.
74: 2742-2750
[Abstract]
[Full Text]