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From the Human Immunology and Cancer Program, Department of Medicine, University of Tennessee Graduate School of Medicine, Knoxville, Tennessee
| Abstract |
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| Introduction |
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Amyloid deposition, thus, is not necessarily an irreversible process.20-22 In the case of AL, the existence of endogenous mechanisms that can effect amyloid removal has been evidenced by the finding that proteins extracted from pathological deposits most often consist of fragments formed from the degradation of the carboxyl-terminal portion of their precursor light chain molecules, presumably by neutrophil-derived proteases.1 That AL fibrils are not eliminated totally may result from their nonforeign nature and the bodys consequent failure to mount an effective immune response to this material. Additionally, the presence of other molecules co-deposited with amyloid, eg, P component23 and certain glycosaminoglycans,24,25 has been alleged to interfere with amyloidolysis.26-28
To investigate factors that could promote amyloid resolution, we have developed an in vivo experimental model involving mice in which amyloidomas were produced by the subcutaneous injection of human AL extracts. We now report the results of studies in which it was shown that this material was in fact removed by an immune mechanism associated with the formation of anti-amyloid antibodies and a resultant neutrophil cellular reaction. Based on these observations, we have generated a murine monoclonal antibody (mAb) that recognizes an epitope present on AL amyloid fibrils, as evidenced by enzyme-linked immunosorbent assay (ELISA), immunoblotting, and immunohistochemistry. This reagent, when administered to mice bearing human AL amyloidomas, bound to the fibrils and elicited a neutrophil response. Notably, this process resulted in rapid and complete elimination of the amyloid tumors, as compared to untreated animals. The demonstration that this anti-amyloid antibody can effect amyloidolysis in vivo provides a potentially novel means of therapy for patients with primary amyloidosis.
| Materials and Methods |
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The method used to prepare water-soluble amyloid extracts was
essentially that described by Pras et al.29
Briefly, 30 to
40 g of fresh-frozen (-80°C) or 10 g of lyophilized spleen
or liver obtained postmortem from patients with AL amyloidosis were
homogenized in
300 ml of cold saline with a Virtis-Tempest apparatus
(Virtis, Gardiner, NY). The homogenates were centrifuged at 6°C for
30 minutes at 17,000 rpm and residual saline-soluble material was
removed by repeated homogenization and washing until the resultant
supernatant had an OD of <0.10 at A280. The
pellet was then repeatedly homogenized, washed with cold deionized
water, centrifuged, and the amyloid-containing supernatants
lyophilized. The amount of protein recovered represented approximately
one-third to one-fifth the weight of the starting material.
The light chain composition and VL subgroup of the amyloid was determined by amino acid sequencing (Procise Protein Sequencing System; Applied Biosystems, Foster City, CA) and ionizing mass spectroscopy (PE SCIEX API 150 EX; Perkin Elmer, Norwalk, CT) of high-performance liquid chromatography-separated peptides obtained by trypsin digestion of reduced and pyridylethylated protein30 extracted from the water-soluble material with 6 mol/L guanidine HCl. The presence of the proteoglycan heparan sulfate was established using an Azure A assay.31
Monoclonal Antibody
A lyophilized sample of a V
fragment
derived from endopeptidase cleavage of a
4 Bence Jones
protein32
was dissolved in a 1 mol/L sodium acetate
buffer, pH 4.9, to a final concentration of 1 mg/ml, precipitated from
solution by heat treatment at 56°C for 15 minutes, and resuspended in
phosphate-buffered saline (PBS) before injection into BALB/c mice. The
techniques used to generate and characterize the murine mAb 11-1F4 were
as previously described,33,34
as were those to
fluorescein-label, obtain through pepsin digestion an
F(ab')2 fragment, and biotinylate the
antibody.35
Immunochemical Assays
For solid-phase ELISA,33 96-well flat-bottomed microwell plates (Corning CoStar, Corning, NY) were filled with 50 µl of a 10 µg/ml solution of human light chain containing fibrils extracted from amyloidotic livers and spleens or with recombinant VL fibrils36,37 and allowed to dry overnight by incubation at 37°C. After blocking and washing, appropriately diluted samples of mouse serum, culture fluid supernatant, or purified mAb were added to each well. Detection of bound antibody was accomplished using a peroxidase-labeled goat anti-mouse IgG antiserum (BioRad, Richmond, CA) and a 2,2'-amino-bis [3-ethylbenzthinzoline-6 sulfuric acid] substrate solution (Kirkegaard and Perry Laboratories, Gaithersburg, MD). Color development was terminated after 15 minutes by the addition of 2% oxalic acid and measured at an OD of 415 nm using an ELISA plate reader (Bio-Tek Instruments, Winoski, VT).
For Western blotting, amyloid extracts were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions using the NuPAGE electrophoresis system (Novex, San Diego, CA). The proteins were electrotransferred to 0.45-µm Immobilon membranes (Millipore, Bedford, MA) and, after blocking, were exposed to mouse sera, purified murine anti-light chain mAbs,34 or an anti-P component reagent (Calbiochem, La Jolla, CA). The blots were washed and treated with an alkaline phosphatase-labeled horse anti-mouse IgG antiserum (ABC kit, Vector Laboratories, Burlingame, CA). Bound protein was detected with the Western Blue Stabilized Substrate (Promega, Madison, WI). Immunohistochemical analyses were performed using the ABC technique as specified by the manufacturer (Vector) on 4-µm-thick deparaffinized tissue sections mounted on poly-L-lysine-coated slides. The primary and secondary antibodies and substrate used were 11-1F4, an affinity-purified goat anti-mouse IgG horseradish-peroxidase conjugate (Bio-Rad), and diaminobenzidine (Vector), respectively.
Microscopy
Four- to 6-µm-thick tissue sections were cut for light
microscopy. Stains for leukocyte esterases were performed using napthol
AS-D chloroesterase and
-naphthyl acetate solutions (Sigma
Diagnostics, St. Louis, MO), according to the manufacturers
directions. To detect amyloid, the sections were treated with a freshly
prepared alkaline Congo red solution and viewed under polarized light
using a filter polarizer (Leitz, Rockleigh, NJ) with a gypsum plate and
a filter analyzer. For electron microscopy, precipitates were applied
to formvar carbon-coated copper grids, air-dried, stained with 1%
phosphotungstic acid, and viewed with a Hitachi H-600 electron
microscope (Hitachi Science Systems, Ltd., Ibaraki, Japan).
Amyloidoma Formation
Lyophilized water-soluble amyloid extracts were suspended in 25 ml of sterile saline and homogenized with a PCU-2 Polytron apparatus (Brinkman, Luzerne, Switzerland). The fibrils were sedimented by centrifugation at 6°C for 30 minutes at 17,000 rpm; the resultant pellet was resuspended in 1 ml of sterile saline and rehomogenized. This solution was injected subcutaneously between the scapulae of mice using an 18-gauge needle attached to a 6-ml syringe. The size of the resultant amyloidoma was measured by daily palpation and confirmed at necroscopy. High-resolution X-ray-computed tomography images were acquired using a microCat apparatus (Oak Ridge National Laboratory, Oak Ridge, TN).
Mice
BALB/c, CD-18 null, and C.B-17 SCID mice were purchased from Charles River Laboratories (Wilmington, MA), Jackson Laboratories (Bar Harbor, ME), and Taconic (Germantown, NY), respectively. All mice were treated in accordance with National Institutes of Health regulations under the aegis of a protocol approved by the University of Tennessees Animal Care and Use Committee.
| Results |
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or
light chain-related molecules that, in most cases, consisted
primarily of the variable region (VL) plus the
first
50 residues of the constant region (CL)
and, in others, VL fragments or intact molecules.
Additionally, these extracts contained the expected amyloid-associated
P- component,23
as well as the proteoglycan heparan
sulfate.24
The injected material formed a readily visible,
palpable mass on the backs of animals, the size of which depended on
the amount of material injected (eg, 0.2 to 2.5 cm in maximum
diameter). The amyloidoma remained localized and unchanged for
10 to
24 days, as evidenced by high-resolution X-ray-computed tomography;
after that point, the tumors began to regress and eventually
disappeared throughout an
4-day period (Figure 1)
or
nature or the VL subgroup of the
amyloid extract; however, in studies involving five different
and
seven
amyloidomas, AL
extracts typically resolved more slowly
than did AL
(AL
, 18 ± 6 days versus AL
,
13 ± 3 days). Sufficient material was available to repeat
experiments at least four times in eight of the 12 cases where it was
found that this effect was reproducible in healthy, young animals
regardless of the tissue source of the amyloid. However, dissolution of
the induced amyloidomas was consistently delayed beyond 3 months in
aged (>18 months) and immunodeficient (SCID) mice.
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-naphthyl acetate-negative, polymorphonuclear cells, ie, neutrophils
(Figure 2)
3 months). Further, amyloidolysis was delayed in animals
rendered profoundly neutropenic by co-administration of 250 µg of the
anti-neutrophil mAb Gr-139
given at the time of amyloidoma
induction and again on day 3.
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or AL
extracts (Figure 3)
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4 Bence Jones
protein32
that, on thermal denaturation under acidic
conditions, formed material that possessed the characteristic features
of amyloid,1
namely, after Congo red staining, it
exhibited green birefringence when viewed by polarizing microscopy and,
by electron microscopy, appeared fibrillar. Spleen cells harvested from
the immunized animals were fused with SP2/0 cells and culture fluid
supernatants from the resultant hybridomas were screened for reactivity
in a solid-phase ELISA33
using as capture proteins
and
amyloid fibrils. Selected hybridoma colonies were injected
intraperitoneally into pristane-primed BALB/c mice and the resultant
mAbs purified from ascitic fluid by gel filtration. Among those tested,
one, an IgG1 antibody (designated 11-1F4), exhibited the greatest
degree of reactivity with both types of molecules. Notably, the binding
of mAb 11-1F4 was unrelated to the VL or
CL isotypic properties of the amyloid proteins
tested, ie, there was no correlation between the
V
/V
subgroup or
C
/C
nature of the
light chain constituent and the interaction with this antibody.
Alternatively, when tested in a liquid-phase ELISA33
against a panel of Bence Jones proteins representative of the four
major V
and five V
subgroups, this reagent was specific only for
4 light chains.
The anti-amyloid reactivity of 11-1F4 also was evidenced
immunohistochemically. As shown in Figure 4
, both AL
and AL
deposits were
recognized by this antibody. Most importantly, we found that mAb 11-1F4
bound to AL amyloid in vivo. In one such experiment, a mouse
injected with an AL
1 amyloid extract was inoculated concomitantly in
the thigh with 100 µg of fluores-cein-labeled antibody. The animal
was sacrificed 36 hours later and the excised amyloidoma examined by
fluorescence microscopy (Figure 5)
. The
labeled antibody localized only to the amyloidoma and not to any mouse
tissue. Similarly, this reagent did not react with normal human tissue.
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, studies
involving two different extracts (HIG and GRA) revealed that
even a single injection of the antibody resulted in rapid and complete
disappearance of the amyloid tumor, as compared to untreated animals
(Table 1)
1 amyloidoma
was reduced >90% within 4 days after antibody injection, as compared
to control animals. However, to achieve a similar response in certain
AL
-type amyloidomas, multiple doses of the reagent were required.
These were given as a series of 100-µg injections beginning at the
time when the amyloidoma was induced (day 0) and then again on days 2,
4, and 6 (Figure 6
amyloidomas were tested in the
mouse model (JON, SHE, FIE, BUE, and BAL), it was found that treatment
with mAb 11-1F4 decreased by as much as fourfold the time in which the
amyloid tumors were eliminated. Notably, although single or repeated
doses of two other anti-light chain mAbs34
that recognized
AL fibrils (eg, 31-8C7) expedited amyloidolysis, the 11-1F4 reagent was
unique in that it accelerated removal of both AL
and AL
amyloid.
In contrast, three anti-light chain mAbs that lacked such reactivity
were ineffective.
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| Discussion |
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and AL
amyloid fibrils.
Pre-incubation of the amyloid extracts with immune serum resulted in
more rapid resolution of the induced amyloidomas in normal and SCID
mice.
These observations led us to immunize mice with human
VL fibrils and to generate an antibody that
recognized an amyloid-related epitope, as demonstrated
immunochemically. Based on the pattern of reactivity, we established
that this determinant was not necessarily related to the
or
nature of the AL fibrils or to the VL subgroup of
the immunogen used to prepare the antibody. Thus, we posited that this
anti-amyloid reagent recognized a ß-pleated structure common to AL
fibrils; that such material contains antigenic sites not exposed on the
soluble light chain precursor protein has been shown by other
investigators.40,41
We also found that mAb 11-1F4
recognized other forms of amyloid, as evidenced in immunohistochemical
analyses of AA-, ATTR-, ALyS-, AApoA1-, and Aß-containing tissues. In
each case, similar patterns of reactivity were obtained with 11-1F4 and
antibodies specific for these five different types of amyloid proteins
(Wall J, Macy S, Weiss DT, Solomon A, unpublished studies).
The therapeutic potential of mAb 11-1F4 was demonstrated in our
in vivo experimental model where its administration into
normal or SCID mice in which human AL amyloidomas had been induced
resulted in marked acceleration of amyloidolysis, as compared to
untreated animals. This antibody was shown to localize within the
amyloid tumors and, further, rapid resolution of this material occurred
before the mice could mount a detectable humoral immune response to the
human proteins contained within the AL extracts. Although a single
100-µg injection of antibody 11-1F4 resulted in rapid amyloidolysis
in mice bearing the two AL
amyloidomas, for three of five AL
amyloid tumors studied, several doses were required to achieve complete
resolution. The apparent resistance of AL
versus AL
fibrillar deposits to immune-mediated lysis also was noted in
nonantibody-treated mice. Although it has been postulated that the
presence of the amyloid-associated P component or
glycosaminoglycans may protect fibrils from degradation by
cellular or humoral processes,26-28
amyloidolysis
occurred in both treated and control animals despite the presence of
these components in the amyloid extracts used for injection.
Antibody-mediated amyloid resolution in our experimental AL mouse model was associated with an infiltration of neutrophils within the amyloid. The essentiality of these cells in effecting AL amyloid dissolution was demonstrated in studies involving neutropenic, as well as CD-18 knockout mice in which a component of the neutrophil ß-integrin cell-surface adhesion molecule is lacking and, thus, extravascular diapedesis of neutrophils is prevented.38
Based on our experimental data, we posit that amyloidolysis resulted
from a three-step process that included: 1) the binding or opsonization
of fibrils by the anti-amyloid mAb; 2) attraction and activation of
neutrophils via an interaction between their Fc
receptors and the
Fc
portion of the antibody molecule; and 3) enzymatic and/or
chemical proteolysis42-44
of the amyloid by
neutrophil-derived endopeptidases or free radicals, respectively.
Although subcutaneous amyloidomas occur in patients with AL amyloidosis, most often, pathological fibrillar deposits are found in organs throughout the body.2 Because of the lack of a suitable animal model of this disease process, it remains to be determined if administration of an anti-amyloid antibody would expedite lysis of systemically deposited material. However, because mAb 11-1F4 also recognizes other types of amyloid proteins, eg, AA, we have tested it in our transgenic AA amyloidotic mice45 that develop extensive hepatic fibrillar deposits and found that there was a rapid and marked diminution of this material in the livers of animals given this reagent (Wall J, Schell M, Wooliver C, Wolfenbarger DA, Weiss DT, Solomon A, unpublished studies). Indeed, that humoral immunity may effect amyloidolysis has been inferred from the report by Schenk et al46 who demonstrated using a transgenic mouse model of Alzheimers disease that older animals immunized with a synthetic Aß peptide had considerable reduction in cerebral Aß amyloid plaques.
The use of anti-amyloid antibodies to effect removal of pathological fibrillar deposits would provide a novel means to treat patients with primary (AL) amyloidosis. Currently, efforts are underway to prepare a chimerized or humanized version of the murine 11-1F4 mAb that eventually can be tested clinically. Although conventional or high-dose anti-plasma cell chemotherapy still would be required to eliminate the synthesis of the AL precursor light chain, the previous administration of such a reagent would serve to reduce the total body amyloid burden and possibly improve organ function. The development of therapeutic strategies designed to eliminate pathological fibrillar deposits by passive or active46 immunotherapy would represent a major advance for patients with primary amyloidosis, as well as those with other acquired or inherited amyloid-associated disorders.
| Acknowledgements |
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| Footnotes |
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Supported in part by United States Public Health Service Research Grant CA 10056 from the National Cancer Institute. R. H. is the recipient of a Brian D. Novis Award from the International Myeloma Foundation; A. S. is an American Cancer Society Clinical Research Professor.
A preliminary report of this work was presented in abstract form.47
Accepted for publication June 13, 2000.
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