MAbs to Mucin VNTR Peptides 369
369
30
Monoclonal Antibodies to Mucin VNTR Peptides
Pei Xiang Xing, Vasso Apostolopoulos, Jim Karkaloutsos,
and Ian F. C. McKenzie
1. Introduction
One of the interesting technical aspects of working with mucins is that it is rela-
tively easy to make antibodies to different mucin glycoproteins—mainly because the
repeat sequences in the variable numbers of tandem repeat (VNTR) region are highly
immunogenic. Indeed, all the mucin genes (MUC1–MUC8) (1,2) were originally
cloned using polyclonal antisera and Escherichia coli DNA expressions systems, in
which, because of the repeated sequences, the expressed cDNAs could be detected and
cloned. We found this of particular interest because we had tried very hard in the early
days of cloning to isolate lymphocyte surface antigens with monoclonal antibodies
(MAbs)—all these efforts failed. Because the VNTRs are so highly immunogenic,
immunization of mice with human tumors, mucin-containing materials such as the
human milk fat globule membrane (HMFGM) (isolated from human milk), cell mem-
branes or synthetic peptides, all lead to the production of MAbs. We have made
numerous MAbs to human mucin 1, 2, 3, and 4 VNTRs; to variants, and to mouse
muc1 (3–8). As will be described herein it is not difficult to make these antibodies,
and, for the most part, these can be easily characterized and the antibodies recognize
linear amino acids of peptides—whether the peptides are present in tissues or as native
molecules (immunohistological detection), or the examination of synthetic peptides,
whether they are bound to a solid support, in solution, on pins with one end tethered,
or conjugated to other proteins, e.g., keyhole limpet hemocyanin (KLH). In almost all
circumstances, the reactions obtained are clear-cut, which contrasts with many other
antipeptide antibodies that react with nonlinear structures (requiring appropriate sec-
ondary or tertiary folding for detection), which makes detection erratic. We describe
here the methods used to make the antibodies and the principles of their characteriza-
tion. In addition, we summarize the properties of MAbs to human MUC1 VNTR pep-
tide; to MUC1 variant peptides; to MUC2, MUC3, MUC4 VNTR peptides; and to
mouse muc1.
From:
Methods in Molecular Biology, Vol. 125: Glycoprotein Methods and Protocols: The Mucins
Edited by: A. Corfield © Humana Press Inc., Totowa, NJ
370 Xing et al.
2. Materials
1. Cell culture medium: Dulbecco’s modified Eagle’s medium (DMEM) containing 2 mM
glutamine, 100 µL/mL of penicillin, 100 µg/mL of streptomycin, and 10% fetal calf serum
(FCS).
2. Tissue culture flasks, canted neck (Falcon, Becton Dickinson Labware, NJ).
3. Microtest tissue culture plate, 96-well flat-bottomed with low-evaporation lid (Falcon,
Becton Dickinson Labware, NJ).
4. Applied Biosystems Model 430A automated peptide synthesizer (Foster City, CA).
5. Reagents for peptide synthesis were purchased from Applied Biosystems, except for the
amino acid derivatives, which were purchased from Auspep (South Melbourne, Australia).
6. Anhydrous trifluoromethanesulfonic acid (TFMSA).
7. Liquid chromatography reversal-phase high-performance liquid chromatography (HPLC)
(Waters, Milford, MA).
8. Brownlee C8-Aquapore RP-300 column (Applied Biosystems, Foster City, CA).
9. Polyethylene pins (Pepscan) (Cambridge Research Biochemicals, Cambridge, UK) (9,10).
10. Human milk was obtained from nursing mothers, and mouse milk from lactating mam-
mary glands of nursing mice (11).
11. Buffers for preparation of HMFGM (Subheading 3.3.)
a. Buffered saline solution: 0.15 M NaCl, 2 mM MgCl
2
, 10 mM Tris-HCl, pH 7.4.
b. Medium buffer: 75 mM MaCl, 1 mM MgCl
2
, 5 mM Tris-HCl.
c. Sucrose buffer: 0.3 M sucrose, 70 mM KCl, 2 mM MgCl
2
, 10 mM Tris-HCl, pH 7.4.
12. Glutathione, insolublized on cross linked beaded agarose (Sigma, St Louis, MO).
13. Thrombin, Thrombostat, 5000 U/5 mL (Parke Davis).
14. pGEX2T vector (Pharmacia, Uppsala, Sweden).
15. KLH, Slurry (Calibiochem, La Jolla, CA).
16. Phosphate-bufferd saline (PBS), pH 7.4.
17. Complete Freund’s adjuvant (Sigma).
18. Female BALB/c mice.
19. Female Lewis rats.
20. Mouse myeloma cell line NS1.
21. Coating buffer: 0.05 M carbonate-bicarbonate buffer, pH 9.6.
22. Polyvinyl chloride (PVC) U-bottomed microtiter plates (Costar, Cambridge, CA).
23. 50X HAT solution: containing 0.8 mM thymidine (Sigma), 5 mM hypoxanthine (6-
hydroxypurine, Sigma). 20 µM aminopterin (Sigma).
24. Sheep antimouse immunoglobulin (Ig) conjugated with horseradish peroxidase (HRP,
Amersham, Buckinghamshire, UK).
25. Sheep antirat Ig labeled with HRP (Amersham).
26. Rabbit antimouse Ig linked to HRP (Dakopatts, Copenhagen, Denmark).
27. Antimouse subclass antibodies (Serotec, Oxford, UK).
28. Substrate buffer for enzyme-linked immunosorbent assay (ELISA):
a. 0.03% 2, 2-azino-bis-(3-ehtylbenzathiazoline 6-sulfonate (ABTS), in 0.1 M citrate
buffer, pH 4.0, containing 0.02% H
2
O
2
.
b. 0.05% ABTS, in 0.1 M citrate buffer, pH 4.0, containing 0.12% H
2
O
2
.
29. ELISA plate reader (Kinetic Reader, Model EL312E, BIO-TEK Instruments, Inc.,
Winsooki, VT).
30. Buffers for ELISA to test peptide on pins:
a. Blocking buffer: of ELISA to test peptide on pins: 1% ovalbumin, 1% bovine serum
albumin (BSA), 0.1% Tween-20 in PBS, pH 7.2, and 0.05% sodium azide.
MAbs to Mucin VNTR Peptides 371
b. Disruption buffer: 1% sodium dodecyl sulfate (SDS), 0.1% 2-mercaptoethanol, 0.1 M
sodium dihydrogen othophosphate.
31. Sonicator (Unisonics, Sydney, Australia).
32. O.C.T. Compound (Tissue-Tek, Torrence, CA).
33. Aminoalkylsilane coated slides (12).
34. Microtome Cryostat HM 500 OM (Microm Laborgerate, Waldorf, Germany)
35. 3,3 Diaminobenzidine (DAB) (Sigma), 1.5 mg/mL in PBS containing 0.1% H
2
O
2
.
36. Electrophoresis power supply, EPS 500/100 (Phamacia, Uppsala, Sweden).
37. Flow cytometer (Becton Dickson).
38. 50% polyethyelene glycol 4000 (Merck, Darmstadt, Germany) in DMEM.
39. 37°C, 10% CO
2
in a humidified incubator.
40. BIAcore™ 2000 biosensor (Pharmacia) (13). CM5 sensor chip and the amine coupling kit (14).
3. Methods
3.1. Solid-Phase Peptide Synthesis
The peptides were produced using an Applied Biosystems Model 430A automated
peptide synthesizer, based on the standard Merrifield solid-phase synthesis method
(15,16). All reagents for synthesis were purchased from Applied Biosystems, except
for the amino acid derivatives, which were purchased from Auspep.
3.1.1. Peptide Synthesis
Solid-phase peptide synthesis (SPPS) was formulated by Merrifield (15). The con-
cept has undergone many improvements and is now a widely established technique.
1. Synthesis occurs from the carboxyl to the amino terminal of the peptide. The α-carboxyl
group of the C-terminal amino acid is covalently bonded to an insoluble polystyrene resin
bead via an organic linker.
2. The α-amino group of this amino acid and all subsequent amino acids used in the synthe-
sis are protected by an organic moiety. There are two fundamental organic moieties that
serve as protecting groups of the α-amino group: tertiary butyloxycarbonyl (tBOC), which
is acid labile; and fluorenylmethyloxycarbonyl chloride (Fmoc), which is base labile. In
our study, tBoc chemistry was employed to synthesize the MUC1, MUC2, MUC3, and
MUC4 peptides. There are three sites on an amino acid that are potentially reactive: the
α-amino group (NH
2
), the carboxyl group (COOH), and at certain side-chain functional
groups (R). The carboxyl group is not chemically protected because it is the site that
forms an amide bond with the α-amino group of the amino acid that was previously
coupled to the growing peptide chain.
3. The synthesis cycle consists of three chemical reactions repeated for each amino acid:
a. Deprotection: This is carried out by using trifluoroacetic acid (TFA) to effectively
remove (deprotect) the tBoc protecting group. This procedure allows the next amino
acid to react at that site to form an amide (peptide) bond.
b. Activation: This involves the formation of symmetric anhydrides that are very effec-
tive, activated carboxyl forms of amino acids. Dicyclohexylcarbodimide (DCC) was
used to generate symmetric anhydrides. There are three amino acids that do not form
stable symmetric anhydrides, and they can begin to degrade within 4 min of forma-
tion. The three amino acids asparagine, glutamine, and arginine are coupled as
1-hydroxybenzotriazole (HOBt) esters. When DCC/HOBt activation is utilized, sig-
nificantly improved coupling is achieved.
372 Xing et al.
c. Coupling: This occurs when the activated amino acid (symmetric anhydride) forms
an amide bond (CO-NH) with the growing peptide chain.
3.1.2. Postsynthesis: Cleavage
When a peptide has been synthesized, it is then “cleaved.” Cleavage is the process
that chemically “cuts” (cleaves) the peptide from the resin and any side chain protect-
ing groups that are present. The chemical linkers and protecting groups used in tBoc
peptide synthesis normally require very harsh conditions for effective removal. Pow-
erful acids, such as hydrofluoric acid (HF) or TFMSA are needed in conjunction with
scavengers. Scavengers are chemical moieties that have the ability to bind irreversibly
to amino acid protecting groups. These trapped cations are thus prevented from under-
going further reactions. There are numerous varieties of scavengers. Ethanedithiol
(EDT) has proved to be a most efficient scavenger for tertiary-butyl protecting groups
(a widely used protecting group). However, using a combination of scavengers is usu-
ally necessary. Thioanisole, water, phenol, p-cresol, phenol, and dimethylsulfide, to
name a few, have also been shown to be efficient scavengers in trapping protecting
groups and suppressing certain reactions from taking place (such as alkylation when
tryptophan or methionine are present in the peptide sequence) that would otherwise
proceed under normal cleavage conditions.
1. The cleavage mixture incorporated for the MUC1, MUC2, MUC3, and MUC4 peptides is
80% TFA, 8% TFMSA, 8% thioanisole, and 4% EDT. The mixture is allowed to react
with the peptide-resin for 30 min at room temperature.
2. After this time, the entire contents are filtered.
3. Thirty milliliters of chilled diethyl ether is used to precipitate the peptide, which is then
centrifuged and the supernatant discarded.
4. The pellet (crude peptide) is then dissolved with 6 M of guanidine hydrochloride, pH 7.5.
Care must be taken when selecting for appropriate scavengers, for instance, water is an
essential scavenger when using Fmoc synthesis. The combination of scavengers implemented
is determined by that protecting groups present on the peptide. The type of acid needed is
determined by the binding strength of the organic linker and side-chain protecting groups. As
an example, the organic linkers and protecting groups for Fmoc synthesis can be readily
cleaved with TFA. tBoc synthesis requires much stronger acids such as HF or TFMSA.
3.1.3. Purification
The method of choice for peptide purification is reversed-phase HPLC. This tech-
nique separates compounds based on the principles of hydrophobicity.
1. The peptides are purified using a Waters Model 441 HPLC, on a C8-Aquapore RP-300
column (Brownlee) using a gradient solvent system of 0.1% aqueous TFA 0.1% TFA,
39.9% H
2
O, and 60% CH
3
CN.
The purity of synthetic peptides was approx 90% as judged by HPLC and mass
spectometry.
3.1.4. The Peptides Synthesized
The peptides synthesized were derived from the MUC1, MUC2, MUC3, MUC4
peptides, which include (Table 1):
MAbs to Mucin VNTR Peptides 373
1. MUC1 VNTR peptide: the peptide Cp13-32, derived from MUC1 VNTR region (contain-
ing an N-terminal cysteine to form dimers); peptides from N- and C-terminal regions to
the VNTR, and cytoplasmic tail peptides of MUC1. The peptides were named by either
position number in the protein sequence (e.g., p344–364, Table 1) or in a two continuous
20-amino acid repeats (e.g., p1–40, Table 1), or by individual amino acid name com-
bined with the following peptide name, e.g., A-p1-15 (Table 1).
Table 1
Synthetic Peptides Used in Our Study
Peptide Amino acid sequence
a
MUC1
VNTR
p1-40 PDTRPAPGSTAPPAHGVTSA
PDTRPAPGSTAPPAHGVTSA
p1-24 PDTRPAPGSTAPPAHGVTSAPDTR
p5-20 PAPGSTAPPAHGVTSA
p13-32 PAHGVTSAPDTRPAPGSTAP
C-p13-32 (C)PAHGVTSAPDTRPAPGSTAP
p1-15 PDTRPAPGSTAPPAH
A-p1-15 APDTRPAPGSTAPPAH
N-terminal to VNTR
p31-55 TGSGHASSTPGGEKETSATQRSSVP
p51-70 RSSVPSSTEKNAVSMTSSVL
C-terminal to VNTR
p344-364 NSSLEDPSTDYYQELQRDISE
p408-423 TQFNQYKTEAASRYNL
Cytoplasmic tail of MUC1
p471-493 AVCQCRRKNYGQLDIFPARDTYH
p507-526 (C)YVPPSSTDRSPYEKVSAGNG
CT18 (C)SSLSYTNPAVVTTSANL
Variants of MUC1
SP11 (splicing peptide) (CY)TEKNAFNSS
sMUC1 (secreting peptide) VSIGLSFPMLP
MUC2
MI-29 (KY)PTTTPISTTTMVTPTPTPTGTQTPTTT
MUC3
SIB-35 (C)HSTPSFTSSITTTETTSHSTPSFTSSITTTETTS
MUC4
M4.22 (C)TSSASTGHATPLPVTDTSSAS
MUC5
M5 (C)HRPHPTPTTVGPTTVGSTTVGPTTVGSC
Mouse muc-1
MP26 (C)TSSPATRAPEDSTSTAVLSGTSSPA
Mouse CD4
T4NI KTLVLGKEQESAELPCECY
a
(C), (CY), (KY): These extra amino acids were added to the peptide.
374 Xing et al.
2. Two variant peptides of MUC1 (17,18):
a. Splicing peptide SP11, consisting of the amino acids 58–62 of the MUC1 (TEKNA)
and amino acids of 343–346 (FNSS), lacking VNTRs (C and Y are added to N-termi-
nus for conjugation and dimer formation).
b. Secreted form of MUC1, sMUC1, consisting of the 14 amino acids derived from a
secreted cDNA isoform; cytoplasmic tail peptide CT18, which is derived from the
last 17 amino acids of the MUC1 cytoplasmic tail region (15 of 17 amino acids are
identical with the mouse muc1 cytoplasmic tail) (Table 1).
3. MUC2, MUC3, and MUC4 VNTR peptides: peptides MI29 derived from the MUC2
VNTR gene, consisting of one repeat unit of 23 amino acids and part of the next repeat of
four amino acids PTTT (19); SIB35, derived from the MUC3 VNTR gene, containing
two repeat units of 17 amino acids (20), M4.22, derived from MUC4 VNTR gene (21),
corresponding to the thirty-first and thirty-eighth repeat (16 amino acids) and part of the
next repeat (5 amino acids, TSSAS).
4. Mouse muc1 peptide Mp26, derived from mouse tandem repeats (TRs), containing 20
amino acids of the seventh repeat and 5 amino acids of the eighth repeat (22). Cysteine
was added at the N-termini of the mucin VNTR peptides to aid disulfide bond dimer
formation as indicated in Table 1.
5. T4N1 representing the N-terminal of mouse CD4 was used as a negative control.
Hydrophilicity and antigenicity of the peptides were analyzed as described else-
where (23–25).
3.2. Peptide Synthesis Using Polyethylene Pins
1. Peptides are synthesized on polyethylene pins (Pepscan) (Cambridge Research Biochemicals,
Cambridge, UK) (9,10), and in our studies consisted of 20 overlapping 6-mer peptides of
MUC1 VNTR, e.g., PDTRPA, DTRPAP, TRPAPG,
APDTRP, that were made to map
the MUC1 epitopes reacting with MAbs (Table 2).
2. To map the epitopes of other mucin MAbs, overlapping peptides of MUC2, MUC3,
MUC4 and mouse muc1 are synthesized by the Pepscan method (4,5,7,8) (also commer-
cial available from Chiron, Australia).
3.3. Production of HMFGMS
(25,26)
1. Human milk (50 mL) is obtained from nursing mothers.
2. Dilute the milk with 50 mL buffered saline solution (see Subheading 2., item 11a).
3. Centrifuge the diluted milk at 2500g for 15 min.
4. Collect the floating cream and wash it three times with buffered saline.
5. Resuspend in cold medium buffer (see Subheading 2., item 11b) and homogenize it us-
ing a homogenizer (T8.01, IKA Labortechnik, Stauffen, Germany).
6. Centrifuge crude membranes at 10,000g for 1.5 h at 4°C. Resuspend the pellet in sucrose
buffer (see Subheading 2., item 11c) and store at –70°C.
3.4. Production of Human and Mouse MUC1 Glutathione-Fusion Protein
1. A human fusion protein (hFP) containing a glutathione-S-transferase (GST) and five
VNTR repeats of MUC1 is produced in E. coli using methods described elsewhere (6,27).
2. The 5 VNTR repeats are cleaved from FP using the site-specific protease thrombin.
3. Using the same method, a mouse fusion protein (mFP) containing 550 bp of TR region
(total 1065 bp, 16 repeats) is also produced (11,22). mFP consists of GST and 184 amino
acids of the mouse muc1 TR region (repeats 7–-16).
MAbs to Mucin VNTR Peptides 375
4. Both hFP and mFP are prepared from transformed E. coli DH5α, induced with 0.1 mM isopro-
pyl-β-
D
-thiogulactopyranoside, lysed by sonication and 1% Triton X-100 buffer, and purified
from the lysate using a GST-agarose column and eluted with 10 mM reduced glutathione (6,27).
5. GST is prepared using pGEX2T vector, without any insert, as a negative control.
3.5. Production of MAbs to Mucin VNTR Peptides
1. To produce antipeptide MAbs, two groups of antigens were used: peptide and fusion
proteins (hFP and mFP).
2. To prepare peptide as immunogen, mix 1 mL of peptide (2 mg/mL) and 1 mL of KLH (2
mg/mL) with 1 mL of 0.25% glutaraldehyde for 8 h at room temperature. Dialyze the
mixture in a dialysis tube against PBS, pH 7.4.
3. To immunize mice, emulsify conjugated peptides or fusion protein with equal volume of
complete Freund’s adjuvant, and inject 0.2 mL of the antigen-adjuvant mixture intraperi-
toneally into female Balb/c mice.
Table 2
MAbs to Mucin Peptides
Name Immunogen Host Ig Class Minimum epitope
a
MUC1
BCP7 C-P13-32 Mouse IgG2a VTSA
BCP8 C-P13-32 Mouse IgG2b DTR
VA1 hFP
b
Mouse IgG1 APG
VA2 hFP
b
Mouse IgG1 DTRPA
CT1.53 CT18 muc1 deficient mouse IgG1 NT
CT91 CT18 Rat IgG1 NT
a
SEC1 sMUC1 Mouse IgG2b NT
SEC2 sMUC1 Mouse IgG1 NT
SEC3 sMUC1 Mouse IgM NT
SP3.9 Sp11 Mouse IgG1 NT
MUC2
CCP31 MI29 Mouse IgA STTT
CCP37 MI29 Mouse IgG1 PTT
CCP58 MI29 Mouse IgG1 GTQTP
MUC3
M3.1 SIB35 Mouse IgG2a SITTIE
M3.2 SIB35 Mouse IgG2a NA
M3.3 SIB35 Mouse IgG1 PFSTSS
MUC4
M4.171 M4.22 Mouse IgG2a TPL
M4.275 M4.22 Mouse IgG1 PLPV
Mouse muc1
M30 Mp26 Rat IgM TSS
MFP25 mFP
c
Rat IgM LSGTSSP
MFP32 mFP
c
Rat IgM NA
a
NT, not tested; NA, not available.
b
Human mucin 1 fusion protein.
c
Mouse mucin 1 fusion protein.
376 Xing et al.
4. Inject the mice with 60–100 µg in 100–200 µL PBS after 4 and 6 wk of first injection.
5. Collect blood samples from immunized mice 1 wk after the third immunization.
6. Test the serum by ELISA using peptide-coated plates (see Subheading 3.6.1.).
7. Perform a fusion 3 d after the fourth injection of the conjugated peptides (4).
8. To produce B-cell hybridomas to human MUC1, fuse the mouse myeloma cell line NS1
(2 × 10
7
cells) with the spleen cells (10
8
) of immunized Balb/c mice as described else-
where (4).
9. To produce B-cell hybridomas to mouse muc1, immunize Lewis female rats with mouse
muc1 fusion protein or conjugated peptides (100 µg) as described under steps 2 and 3).
10. Screen the hybridoma supernatants on the immunizing peptide and a negative peptide by
ELISA, and tested further by immunoperoxidase staining on tissues, by flow cytometry,
or by any other method.
11. Determine the isotypes of MAbs by using antimouse or antirat subclass antibodies by 1%
agarose gel immunodiffusion.
3.6. ELISA Tests
3.6.1. Direct Binding
1. Coat PVC U-bottomed microtiter plates with 50 µL of 20 µg/mL of peptides in 0.05 M
carbonate-bicarbonate buffer, pH 9.6, at 37°C for 2 h or overnight at 4°C.
2. Wash plate twice with PBS-0.05% Tween-20.
3. Block nonspecific binding sites with 100 µL of 2% BSA for 1 h at room temperature.
4. Wash the plate with PBS-0.05% Tween-20, and add 50 µL of tissue culture supernatants of
hybridomas or purified antibody to the peptide-coated plate at room temperature for 1 h (3).
5. Thoroughly wash the plate 10 times with PBS-0.05% Tween-20, add 50 µL of sheep
antimouse Ig conjugated with HRP (Amersham) at 1:500 dilution in PBS, incubate 1 h at
room temperature.
6. Wash the plate 10 times with PBS-0.05% Tween-20, add the substrate, ABTS (see Sub-
heading 2., item 28a) and incubate the plate at room temperature for 10–30 min until the
positive well becoming the blue color.
7. Measure the absorbance at 405 nm using an ELISA plate reader.
3.6.2. Inhibition ELISA
1. Preincubate the MAb at a constant concentration (which was determined as 50% binding
in the direct binding ELISA) with peptides or relevant antigens (inhibitors) in a series
dilution for 2 h at room temperature.
2. Add the mixtures to the plates coated with antigens under Subheading 3.6.1., and further
incubated overnight at 4°C.
3. Detect the binding of residual MAb as described under Subheading 3.6.1.
4. Calculate the percentage of inhibition by comparing the binding of MAbs preincubated
with and without antigen (inhibitor): % of inhibition = [1 – (binding of MAb with inhibi-
tor/binding without inhibitor)] × 100%.
3.6.3. ELISA Tests of Peptides on Pins
Using small peptides (5–9-mer) on pins gives the ability to screen rapidly many
small peptides to find the reactive epitope (Pepscan). This procedure was first de-
scribed by Geysen et al. (9) and has been used as the standard method to define linear
epitopes.
MAbs to Mucin VNTR Peptides 377
1. Synthesize peptides on the pins following the standard method or purchase them from
Chiron.
2. Block the pins for 1 h in microtiter plates using blocking buffer (see Subheading 2., item
30a) at room temperature with agitation.
3. Add 150 µL of antibody to each well and incubate the antibody with the pins in the plate
overnight at 4°C.
4. Wash the pins four times for 10 min each in a tub containing 50 mL of PBS-0.05% Tween-
20 at room temperature with agitation.
5. Wash the microtiter plate four times 10 min each with PBS-0.05% Tween-20 at room
temperature with agitation.
6. Add 150 µL of sheep antimouse or antirat Ig labeled with HRP to each well in PBS-0.05%
Tween-20 (1:500), and incubate the pins with conjugate for 1 h at room temperature in
the microtiter plates.
7. Wash the pins with vigorous agitation (four times for 10 min each) in PBS-0.05% Tween-
20 and incubated at room temperature in the dark in microtiter plates containing 150 µL/
well of substrate 0.05% ABTS (see Subheading 2., item 28a), containing 0.04 mL H
2
O
2
/100 mL buffer. Stop the incubation when the plates appear to have sufficient color by
removing the pins, after which 50 µL from each well is transferred to another microtiter
plate and the absorbance read immediately at 405 nm using a plate reader.
8. The pins and their irreversibly bound peptides can be used many times if bound antibod-
ies are efficiently removed after each assay. To remove the bound antibodies, prewarm
the disruption buffer (see Subheading 2., item 30b) to 60°C. Place the pins in a sonica-
tion bath with sufficient disruption buffer to ensure that the pins are well covered. Soni-
cate the pins for 60 min.
9. Wash the pins four times with hot distilled water (60°C).
10. Wash the pins in boiling methanol for 2 min in a tub, and then air-dry. The pins may be
stored at room temperature in plastic bags containing silica gel.
3.7. Immunoperoxidase Staining
The reactivity and specificity of the MAbs can be determined by immunoperoxidase
staining on snap-frozen fresh human tissues or formalin-fixed tissues (4,28).
1. To prepare frozen sections, embed the tissues in OCT, snap-frozen in liquid nitrogen, and
stored at –20°C.
2. Cut the tissues at 6–8 µm using Microtom cryostat, attach the section to aminoalkylsilane-
coated slides (12), air-dry, and keep at –20°C until tested.
3. Fix slides with cold acetone for 10 min and air-dry.
4. Block endogenous peroxidase activity for 40 min at room temperature using 0.5% of
H
2
O
2
, and wash once with PBS.
5. Cover tissue sections with at least 100 µL of diluted tissue culture supernatant (1/5–1/10),
ascites (1/1000–1/10,000), or purified antibody (1–5 µg). Make dilutions with 0.5% BSA/
plain DMEM (without FCS).
6. Incubate slides with antibody in a humidified container for 40 min at room temperature.
7. Remove excess antibody by immersion of slides in PBS for 5 min, and repeat it three times.
8. Add 50–100 µL of rabbit antimouse Igs linked to HRP (1/50 in 0.5% BSA/DME) to cover
the sections in the slides for 40 min at room temperature.
9. Wash slides in PBS for 5 min, three times.
10. Cover the sections with 1.5 mg/mL of DAB (see Subheading 2., item 35) in PBS con-
taining 0.1% H
2
O
2
for 5 min or until brown color is visible on sections.
378 Xing et al.
11. Remove excess DAB by immersion of slides in running tap water.
12. Staining and mounting slides: Place slides in hemotoxylin for 2–10 min, wash with tap
water and Scotts water, and rinse in running tap water.
13. Pass tray of slides through 75, 95, and 100% alcohol and three times of shellex (1 min each).
14. Mount slide with cover-slip.
15. Grade the staining by microscope according to the following:
a. The percentage of cells stained: –, < 5%; +, 5–25%; 2+, 25–50%; 3+, 50–75%; 4+,
75–100%.
b. The density of staining: –, no staining; +, weak staining; 2+, moderate staining (dark
brown color); 3+, strong staining (dark brown color); 4+, very strong staining (con-
densed brown color).
16. For inhibition immunoperoxidase staining, preincubate MAbs with antigens (inhibitors)
as under Subheading 3.6.2.
3.8. Other Tests
Cells or cell lines can be tested by flow cytometry using standard methods. In addi-
tion, further characterization can be done as for any MAbs, e.g., Western blotting.
3.9. Affinity Measurements by Biosensor
Affinity of the MAbs can be routinely and easily performed–provided that there is
access to a biosensor machine. This adds a further level to selection at the screening
stage, at which MAbs of high or low affinity/avidity can be measured. In our studies,
we used MAbs at 100 µg/mL and a BIAcore 2000 biosensor (Pharmacia) (14).
1. The antigens peptide C-p13-32, FP, and 5 repeats of MUC1 VNTR peptide are immobi-
lized on a CM5 sensor chip using the amine coupling kit (14).
2. Sensor chips are regenerated with 10 mM glycine-HCl (pH 2.4).
3. K
a
(association kinetic constants) and k
d
(dissociation kinetic constants) are calculated
from sensorgram plots of MAb amount bound to immobilized antigens vs time. The affin-
ity of the MAbs (K
A
)are obtained by dividing K
a
by K
d.
The data is analysed to their
relative affinity and recorded: low, K
A
< 2.5 × 10
7
; medium, 1 × 10
8
> K
A
≥ 2.5 × 10
7
;
high, K
A
≥ 1 × 10
8
.
4. Notes
1. Generally, MAbs to mucins have been produced by immunizing with crude or purified
mucins—particularly HMFGM for MUC1, or whole tumors or their extracts. In this way,
many antibodies to MUC1 have been made which are reactive with breast cancer cells
and on further analysis these have clearly fallen into several groups, wherein the antibody
reacts with either predominantly carbohydrate, or peptide epitopes, or both carbohydrate
and peptide epitope (4,10,28). However it is sometimes difficult to make antibodies to
particular mucin sequences using crude antigens. With recent advances in both synthetic
peptide chemistry (see Chapters 11–12) and in the cloning of the cDNA encoding the
protein core of the mucins (see Chapters 24), comes the ability to make antimucin anti-
bodies by using synthetic moieties—as described herein. This represents a substantial
advance in being able to use clearly defined antigens rather than a mixture of materials
obtained by extracts from tissues or secretions. On the basis of mucin cDNA sequences,
and synthetic peptides, we and others have successfully made MAbs to synthetic peptides
MAbs to Mucin VNTR Peptides 379
derived from the cDNA sequences of VNTR regions of MUC1, MUC2, MUC3, and
MUC4 (4,5,7,8), and Reis et al. (30) have made MAb to MUC5AC mucins.
2. Our approach to produce the antibodies was to synthesize a peptide representing the whole
sequence of a VNTR, with an extension into the next VNTR so that all potential amino
acid epitopes were represented and to make a dimer peptide by adding a cysteine at the N-
terminal (cysteine can also be added to C- or both N- or C-terminals to form a dimer or a
ring form) in favor of forming a native construct (31).
3. It has been possible with some peptides—indeed, to some mucins—to predict the immu-
nogenic regions based on hydrophilicity analysis (23–25); for example, with MUC1, the
most hydrophilic region contains the amino acid APDTR, and indeed most antibodies
made to MUC1 native mucin react with this sequence. But this is not necessarily the case
when synthetic peptides are used for immunization, as some of the antibodies obtained
are to hydrophobic, and not to hydrophilic regions, indicating that with peptides there is
no absolute correlation between antigenicity and hydrophilicity. Similar results were also
reported by Geyson et al. (32). Nevertheless, selection of the hydrophilic region as a
peptide to synthesize is still the first choice to make MAbs for an interesting region, but it
should be noted that the hydrophobic region could also be immunogenic.
4. For immunization, the peptides should be conjugated to KLH or BSA, rabbit serum albumin
(RSA) using glutaraldehyde, since free peptides (<15 mer) are poorly immunogenic (13).
5. Producing FP is an alternative way to make a longer peptide, and it can satisfactorily be
used as an antigen to make MAbs.
6. The hybridoma supernatants should be screened on the immunizing peptide and a nega-
tive peptide by ELISA, and further tested by immunoperoxidase staining on tissues, by
flow cytometry or by any other method. It was of interest to us that screening on tissue
sections can be done at ~400 sections being rapidly read for a +/– reaction, or indeed any
specific staining patterns selected.
7. BSA- or RSA-conjugated peptide can also be used rather than unconjugated peptide in
ELISA; the concentration of coating antigen, such as a fusion protein or HMFGM can
vary from 0.1 to 20 µg/mL.
8. Snap-frozen tissues for immunoperoxidase staining should be used since most peptide
epitopes are damaged or masked by formalin fixation.
9. Inhibition tests in both ELISA and immunoperoxidase staining should be used to demon-
strate specific reactions.
10. The MAbs to peptide are useful reagents in the study of the mucin glycosylation and
recognition of T- and B-cells.
11. Producing FP is an alternative way to make a longer peptide and can be satisfactorily
used to make MAbs.
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