AU2001241867A1 - Method for detecting the presence of target bacteria or a target component carbohydrate antigen thereof - Google Patents

Description

METHOD FOR DETECTING THE PRESENCE OF TARGET BACTERIA OR A TARGET COMPONENT CARBOHYDRATE ANTIGEN THEREOF

This application is a continuation-in-part of each of the following U.S. applications, all

of which were assigned to Binax, Inc., the corporation having the rights to receive assignment

in full of this application.

(1) Serial No. 09/139,720, filed August 25, 1998,

(2) Serial No. 09/156,486, filed September 16, 1998, now abandoned in favor of its

continuation-in-part application,

(3) ^• Serial No. 09/397,110, filed September 16, 1999,

(4) Serial No. 09/458,998, filed December 10, 1999, as a continuation-in-part of Serial No. 09/139,720.

INTRODUCTION TO THE PRESENT INVENTION

The present invention relates to achieving rapid and accurate diagnoses, of high sensi¬

tivity and specificity, of bacterial infections, caused by bacteria characterized by the possession

of carbohydrate antigens. In particular, the invention involves the initial purification of such

carbohydrate antigens to an essentially protein-free state, followed by utilization of each so-

purified carbohydrate antigen to affinity purify raw polyvalent antibodies to said antigen and

the utilization of the said so-purified antibodies in diagnostic tests of high accuracy, specificity

and sensitivity for detecting the presence of the original bacterium.

. The invention is applicable to bacteria possessing carbohydrate antigens, which bacteria

may be positive or negative to Gram's stain. The purified antibodies produced in accordance

with this invention are of at least the same order of specificity and sensitivity as commercially available monoclonal antibodies and are easier to produce and to work with than many such monoclonal antibodies. They offer wide opportunities for rapid diagnostic tests, e.g., via ICT

immunoassays, to identify bacteria that have heretofore been difficult to identify rapidly and

accurately, whereby diagnoses of bacterial diseases they caused were often arrived at slowly

and difficultly, using cumbersome methodology.

Each of the parent applications identified above is incorporated herein by reference

except for now-abandoned application Serial No. 09/156,486, the disclosure of which, in

essence, appears physically in its continuation-in-part application, U.S. Serial No. 09/397,110,

which is among the three applications incorporated herein by reference.

BACKGROUND OF THIS INVENTION

Gram-negative bacteria are known to have in common the possession of at least one

lipo-polysaccharide or other lipo-polycarbohydrate antigen, while Gram-positive bacteria are

known to possess the common characteristic of having at least one carbohydrate antigen that is a lipo-teichoic acid or teichoic acid or a derivative of either. Some of both the Gram-positive and Gram-negative bacteria also possess carbohydrate antigens that are capsular ~ i.e., these

antigens are each enclosed in a heavy capsular layer in their native state. This capsular layer

constitutes a slime-like substance that surrounds the bacterial cell wall of most bacteria.

U.S. Application Serial No. 09/139,720, which is fully incorporated herein by refer¬

ence, describes the purification to an essentially protein-free state of lipo-carbohydrate antigens

of bacteria of the Legionella species, all of which are Gram-positive. Emphasis is placed

therein on purifying carbohydrate antigens of Legionella pne mophila serotypes, including without limitation, the O-polysaccharide antigen of L. pneumophila serotype 1, the purification

of which to an essentially protein-free state, is described in detail.

The application shows that when the essentially protein-free O-carbohydrate antigen of

L. pneumophila serotype 1 (which serotype is known to be the causative organism for some 70

percent of the Legionella-c&used pneumonia-like illnesses that occur), is coupled (through a spacer molecule) to an affinity column as described and raw polyclonal antibodies to the un- purified antigen are passed over the column as described, the resulting purified antibodies are

highly antigen-specific and will readily identify the same antigen when it is present in bodily fluids taken from patients with disease caused by Legionella pneumophila serotype 1. Urine is

shown to be a preferred bodily fluid for this diagnostic purpose because:

(1) The L. pneumophila serotype 1 antigen appears in urine early in the disease state

and persists for some days even after appropriate therapeutic treatment is initiated;

(2) The collection of the test sample is non-invasive and simple, causing a minimum

of patient disruption as well as requiring no specially trained personnel or specially designed instrumentation; and

(3) Samples from, e.g. , sputum may give false negative or false positive results due

to difficulties in obtaining or culturing the sample, possible presence of colonies of bacteria in

the patient's nose or throat that are chronically present and were not causative of disease, and

other similar difficulties.

The L. pneumophila serotype 1 bacterium present in urine is dead and has at least in

part had its cell wall broken down as it is passed through the kidneys; hence the antigen is in a state readily accessible to the antigen-specific antibodies deposited in two areas on the ICT test

strip.

The efficacy of the antigen-specific antibodies described in U.S. Application Serial No.

09/139,720 in identifying whole, and to some extent, living bacteria in aqueous media consti¬

tuting environmental samples is further shown in the continuation-in-part Application Serial

No. 09/458,988, also incorporated herein by reference, wherein an enzyme immunoassay of

high specificity and sensitivity is described. This assay is based on use as the detecting agent

for the antigen, of antigen-specific antibodies obtained by purifying raw polyclonal antibodies

as described in detail in the parent application. The sensitivity and specificity of the so-

purified antibodies is in part illustrated by the short times within which the enzyme immuno¬

assay produced informative results, as well as by the small concentration (0.05 μg per test) of

antigen-specific antibodies that gave equally informative time results with a longer incubation time (1 hour).

U.S. Application Serial No. 09/397,110, also incorporated herein by reference, describes the purification to an essentially protein-free state of the C-polysaccharide cell wall

antigen present in the pneumococcal cell wall of all S. pneumoniae serotypes. This antigen is a

phosphocholine-containing polysaccharide derived from teichoic acid. The Streptococcus

pneumoniae strain of bacteria are all Gram-stain positive.

The essentially protein-free antigen (which contains less than about 10 percent by

weight thereof) is covalently coupled to a spacer molecule which is in turn fcovalently coupled

to an affinity column and the thus-prepared column is then used to purify raw polyclonal

antibodies to S. pneumoniae. The resulting antigen-specific purified antibodies showed high sensitivity and specificity in an ICT test for identifying S. pneumoniae in bodily fluids,

including urine in particular.

Numerous and varied efforts have been made in the past to use raw polyvalent

antibodies to carbohydrate antigens, or monoclonal antibodies to such antigens, of various

infectious Gram-negative or Gram-positive bacteria believed to be responsible for diseases of

the lower respiratory tract in diverse tests, including ELISA, counter-immunoelectrophoresis and/or latex agglutination tests for the presence of the .specific bacterium sought. While some

of the tests have been useful in some cases, none of them has so far gained sufficient clinical acceptance of reliability to be used independently of cell culture tests. The drawbacks of cell

culture tests and their tenuous reliability have been extensively documented in the art and are

discussed in parent applications 09/139,720 and 09/397,110.

To gain U.S. Food and Drug Administration ("FDA") approval of the L. pneumophila

serogroup 1 ICT test first described in parent Application Serial No.. 09/139,720 and the S.

pneumoniae ICT test that is the subject of parent Application Serial No. 09/397,110 and its

parent application, Serial No. 09/156,786, it was necessary for the assignee of these appli¬

cations, Binax, Inc., to conduct extensive clinical tests on each. Many of these clinical tests

are described in the two parent applications incorporated herein by reference. One of the important points about the clinical tests is that FDA regulations require extensive clinical

testing of diagnostic tests only in instances where the diagnostic test is recognized to represent

a substantial scientific and technical departure from tests that are already known and in

commercial use. The sensitivity and specificity of each of these two tests is believed to be much higher than the numbers shown in the parent applications indicate. The reason is that the numbers shown are based on comparison of these clinical test results with parallel results

obtained on the same clinical samples with other earlier available assay procedures or identi¬

fication techniques (such as cell culture tests), which prior available tests were known to be

tenuously reliable even when they were believed to be the best available identification methods

for detecting the involved bacteria or their antigenic components.

In short, this invention presents the opportunity for providing highly specific and sen-

sitive, rapid diagnostic tests for the wide spectrum of bacteria that possess carbohydrate antigens, which antigens manifest themselves in human bodily fluids of patients infected with the corresponding bacteria, especially urine.

BRIEF DESCRIPTION OF THE INVENTION

This invention involves novel specially purified, highly antigen-specific antibodies for

detecting the presence of bacterial carbohydrate antigens in fluids, especially human or other mammalian bodily fluids, and particularly urine.

These antibodies are prepared from raw polyvalent antibodies to the target carbohydrate

antigen by a method which comprises:

(a) purifying the raw target antigen to obtain an essentially protein-free antigen,

i.e., one containing not more than about 10 percent of protein,

(b) coupling the so-purified antigen to a spacer molecule by covalent binding,

(c) covalently coupling the free end of the spacer molecule to an affinity gel packed

into a chromatographic column, (d) passing the raw polyvalent antibodies to the raw antigen over the gel on the

column, and

(e) eluting the purified antibodies.

The purified antibodies eluted from the affinity gel are of high specificity, sensitivity

and accuracy and may be used in any of a variety of specifically developed immunoassay

procedures to detect the raw target antigen in fluid media, especially mammalian bodily fluids,

and particularly urine.

A preferred ICT procedure is described in parent application 09/139,720 for detecting the polycarbohydrate antigens of Legionella bacteria, and especially the O-polysaccharide antigen of L. pneumophila serogroup 1, while applications 09/156,486 and 09/397,110 describe an

analogous preferred ICT procedure for detecting the C-polysaccharide cell wall antigen present

in all serotypes of Streptococcus pneumoniae.

A similar ICT procedure for detecting the capsular polysaccharide antigen of H. influ- enzae type b is described herein in detail.

Heretofore it has not been recognized that the lipo-polycarbohydrate antigens typically

found in Gram-negative bacteria, the antigens comprising lipo-teichoic or teichoic acid or

derivatives thereof typically found in Gram-positive bacteria and the capsular polycarbohydrate

antigens frequently found in the heavy slime-like capsule surrounding the cell wall of many

bacteria of both Gram-positive and the Gram-negative types may all be detected by a rapid,

highly specific and sensitive immunoassay of the ICT type which employs antigen-specific

antibodies as the detecting agent, which antigen-specific antibodies are obtained according to

the schema for purifying raw polyclonal antibodies to carbohydrate antigens that is set forth in the second paragraph of this section. The fact that raw polyvalent antibodies to bacterial car¬

bohydrate antigens may be rendered highly antigen-specific and sensitive by subjecting them to

affinity purification with a purified target bacterial carbohydrate antigen that is essentially

protein-free likewise has not been appreciated heretofore. Likewise, the fact that carbohydrate

antigens from both Gram-negative and Gram-positive bacteria and/or from the capsular layer

surrounding both types of bacteria can all be purified and used to affinity purify antibodies to

such antigens to yield antigen-specific antibodies has not been heretofore recognized, nor has it

been appreciated that bacterial carbohydrate antigens can be detected rapidly with high accur¬

acy, sensitivity and specificity using such antigen-specific antibodies as a detecting agent.

BRIEF DESCRIPTION OF THE DRAWING

Figure 1 and its related Figures 1A, IB and 1C depict a typical ICT device of the type preferred in the performance of an assay for a bacterial carbohydrate antigen in accordance with this invention.

Figures 2, 3 and 4 are graphs showing, in Figure 2, the ability of antigen-specific puri¬

fied antibodies of this invention to detect other serotypes of H. influenzae type b than the one

to which the antibodies were raised. In Figures 3 and 4, the graphs reflect that the purified

antigen-specific antibodies of H. influenzae type b were not cross-reactive with antigens of H.

influenzae types a, c, d or f (Fig. 3) or with any of nontypical H. influenzae NT1, NT2, NT3

or NT4 or with H. para-influenzae. DETAILED DESCRIPTION OF THE INVENTION

The present invention represents an exceptional advance in methods for detecting bac¬

terial infection.

Because it is applicable to the detection in mammalian bodily fluids of bacterial carbo¬

hydrate antigens of all known types - i.e., the lipo-polycarbohydrate antigens including lipo-

polysaccharides, the antigenic lipo-teichoic acids and teichoic acids and their antigenic deriva¬

tives and the capsular polycarbohydrate antigens, including polysaccharides - and it represents a unified approach to the detection of bacterial infection not heretofore envisioned, this invention holds promise for permitting the rapid diagnosis of virtually any bacteria-caused disease

wherein the bacteria possess a carbohydrate antigen that manifests itself in the disease state in a

bodily fluid of the patient.

Of particular importance is the opportunity that this invention affords for rapid diag¬

nosis and rapid introduction of appropriate therapy in situations where a particular bacterially-

caused disease appears to be epidemic within a group — whether a small, confined group, e.g.,

in a school or geriatric center, or a widespread population as, e.g. , a town, a city or a larger

region.

Broadly speaking, the preferred immunochromatographic ("ICT") assay of this invention may be designed and configured to be run on any known disposable ICT device disclosed

in the art. Preferably it is designed to be conducted, and is conducted, using an ICT device of

the type disclosed in co-pending U.S. Patent Application Serial No. 07/706,639 of Howard

Chandler, or one of its continuation-in-part applications, all of which are assigned to Smith- Kline Diagnostics, Inc. but are exclusively licensed to Binax, Inc. (which is entitled to assign- ment of this application), in a wide area of use fields that includes diagnoses of human respira¬

tory system diseases.

The preferred device is suitably impregnated in one region thereof with affinity puri¬

fied, highly antigen specific antibodies to the target carbohydrate antigen of the bacterium

suspected of causing the disease. Labeled antigen-specific antibodies are applied to another

area of the device. The test sample suspected of containing the bacterium is contacted first

with the labeled antigen-specific antibodies, which then flow with the sample to the device area

containing unlabeled bound antigen-specific antibodies, whereupon if the target antigen indig¬

enous to the suspected bacterium is present in the sample, the labeled antibody:target carbohy¬

drate antigen conjugate already formed binds upon contact to the immobilized unlabeled antigen-specific antibodies, whereupon a visible color reaction is produced. The label may be

any substance known in the art to produce visible color upon the reaction of a labeled anti-

body:antigen complex with bound unlabeled antibodies. Such labels include various finely

divided metallics, various organic molecules, and various molecular combinations such as

enzyme combinations with another color-producing molecule. In this invention, colloidal gold

particles constitute the preferred label.

It is of major importance in designing the preferred test device, that the concentration

of antigen-specific antibody present at each of the two sites of the test device where reaction

occurs be sufficient to insure that antigen present in the test sample will be captured by the

labeled antigen-specific antibodies as the test sample contacts them and that labeled antigen-

specific antibody:antigen conjugate will be readily captured and held by the bound antibodies

at the sample capture line. Experimental work undertaken in connection with this invention has shown that active antigen-specific antibody to the target carbohydrate antigen must be

present at each site of a test device at which antige antibody reaction is to occur in a concen¬

tration of between 7.7 nanograms/sq. mm. of surface area and 385 nanograms/sq. mm. of

surface area. If antigen-specific antibody concentrations lower than 7.7 nanograms/sq. mm.

are present at a site where reaction is intended to occur, false negative results are likely to

occur.

As is known in the art, infectious bacteria frequently have multiple antigenic com¬

ponents. For example, S. pneumoniae is known to have a capsular antigen in addition to the polysaccharide cell wall antigen which is the target of the assay described in parent applica¬

tions Serial Nos. 09/156,486 and 09/397,110. The latter antigen was selected as the target antigen for the now-FDA-approved test which is described in these applications because that antigen is present in all known serotypes of S. pneumoniae and its relatively minor cross-

reactivity as described in the herein incorporated application Serial No. 09/397,110 is of a

nature that allows ready clinical differentiation of S. pneumoniae-caused infection from other

infections. It is noted that previous published attempts to detect S. pneumoniae in bodily fluids

have at best yielded systems having sensitivity and specificity in the 60-70 percent range with

both polyclonal and monoclonal antibodies - a range unacceptable for reliable diagnostic

purposes.

Among the mammalian fluids in which target carbohydrate antigens have been shown to

be successfully detected in ongoing clinical work with the respective described and FDA-

approved ICT tests for L. pneumophila serogroup 1 and S. pneumoniae are, in addition to the

preferred urine, sputum, nasb-pharyngeal exudates, middle ear fluid and cerebrospinal fluid. Other fluids in which these tests detect carbohydrate target antigens, when present, include

blood and bronchial fluid.

Selection of the target carbohydrate antigen for any particular bacterium is necessarily

based upon considerations of that antigen's cross-reactivity characteristics,, whether it is known

to be present in all or most serotypes of a bacterial strain, whether if peculiar to a particular

serotype of a strain, that serotype is known to be the most common source of disease caused by

the bacterium and like questions.

This invention offers unique capabilities in regard to ready diagnoses of bacterial infec¬

tions caused by any bacterium with one or more carbohydrate antigens of the types already

mentioned — i.e., lipo-polycarbohydrate antigens, antigens comprising lipo-teichoic or teichoic

acid and derivatives of either, and capsular carbohydrate antigens. Among the bacteria, carbohydrate target antigens of which are contemplated to be within the scope of this invention are Eaemophilus influenzae of various types, My coplasma pneumoniae, Chlamydia pneumo¬

niae, Klebsiella pneumoniae, Staphylococcus aureus, Mycobacterium tuberculosis, Pneudo-

monas aereiginosa, Acinetobacter, Moraxella catarrhalis, Neisseria Meningitis, group B

Streptococci, Escherichia coli, Listeria monocytogenes, the other species of Escherichia,

Klebsiella and Pseudomonas not specifically already named, Proteus mirabilis, Gardnerella

vaginalis, Serratia marcescens, the various other species of Proteus and Listeria not spe¬

cifically named, the various species of Enterobacter, Xanthomonas, Enterococcus, Bac-

teroides, Clostridium, Peptostreptococcus, Campylobacter, Salmonella and Alcaligenes and all

other bacterial species and strains not specifically named that have one or more carbohydrate

antigens of the types described. The polyclonal antibodies to be purified by the techniques of the present invention are

raised by conventional methods, by injecting an animal, e.g. , a rabbit or goat, with the crude

target antigen of the intended assay. Preferably the antigen preparation is subjected to heat

killing of cells before injecting the animal. After an appropriate lapse of time, the animal is

bled to obtain serum containing the desired antibodies, followed by purification of the latter. This serum may go through an intermediate purification step, e.g. , with ammonium sulfate or

an ion exchange resin to produce an IgG cut or may be purified directly.

For purposes of the affinity purification, the same crude carbohydrate target antigen

used to immunize the animal is grown in culture and then suitably purified to an essentially

protein-free state. As used herein the expression "essentially protein-free state" means a state

containing not more than ~ and preferably less than ~ about 10 percent (wt.Λvt.) of protein.

After the antigen is purified to the essentially protein-free state, it is coupled to a spacer

molecule by covalent binding. Examples of suitable spacer molecules include hydrazine,

bovine serum albumen ("BSA"), the conjugate of BSA and hydrazine and like molecules that

are capable of covalently bonding to purified carbohydrate antigens at one end while retaining

another reactive end that is capable of bonding covalently to an affinity gel.

The purified carbohydrate antigen: spacer molecule conjugate is next conjugated to an

affinity gel and the gel is used to purify the raw polyvalent antibodies in serum obtained by

bleeding the previously immunized animal, or an IgG cut thereof. The raw antibodies (or their IgG cut) are multiply applied to the affinity gel and are eluted from it as purified, highly antigen-specific antibodies. The following examples illustrate the preferred mode of affinity purification of anti¬

bodies to Haemophilus influenzae type b, including the preliminary separation and purification

of the capsular carbohydrate antigen used in that purification. Many methods for effecting _.

these separation and purification steps are known in the literature and may be substituted for

those herein described without departing from the scope of this invention, so long as the puri¬

fied antigen obtained is essentially protein-free as herein specified.

Example 1 — Culture Conditions for Culturing the Target Carbohydrate Antigen

Haemophilus influenzae type b (ATCC #10211) was grown in supplemented Mueller

Hinton broth at 37° C. with 5 percent CO₂ for 24 hours without agitation.

The broth composition, per liter, was:

Acid hydrolyzate of casein 17.5 g.

Beef heart extract 3.0 g .

Starch 1.5 g.

Supplements as follows were also present:

Hematin 15 mg./mL

NAD (nicotine adenine dinucleotide) 15 mg./mL

Yeast extract 5 mg./mL

The pH of this mixture was 7.3 ± 0.1 as measured at 25° C.

Example 2 — Purification of Carbohydrate Antigen

After 24 hours, 1.82 g. of cetyltrimethylammonium bromide CAS #57-09-0 was dis¬

solved in 30 mL of distilled water and the solution was added to 500 mL of broth supernatant

to yield a final concentration of 0.01 M cetyltrimethylammonium bromide. The mixture was incubated in an ice bath with stirring for one hour and left at 4° C. overnight. The mixture from Example 1 was centrifuged at 12,000 rpm and 4° C. for 20 minutes

to yield a pellet and a supernatant. Both were collected and treated, respectively, as follows:

(1) The pellet was resuspended in 0.5 M NaCl with sonication and was then drop-

wise precipitated at 4° C. in ten times the resuspension volume of ethanol., The resulting solu¬

tion was stored overnight at 4° C. to allow precipitation.

The solution was then centrifuged at 12,000 rpm for 20 minutes. The pellet was dis- solved in distilled water and then dialyzed against distilled water in dialysis tubing having a molecular weight cut-off of 3,500.

(2) The supernatant from the Example 1 mixture was stored at 40° overnight, and a

precipitate was then noted to have formed. The entirety of the contents of the container holding this was centrifuged at 12,000 rpm for 20 minutes. A pellet was recovered and was re-

suspended in 0.5 M NaCl with sonication. The resulting solution was dropwise precipitated in

ten times the resuspension volume of ethanol at 4° C. The solution was stored overnight at 4°

C. and a precipitate again formed. The solution and precipitate were centrifuged at 12,000

rpm for 20 minutes and a pellet was recovered. The pellet was dissolved in distilled water and

dialyzed against distilled water in dialysis tubing having a 3,500 molecular weight cut-off.

Thereafter the dialyzed solutions from (1) and (2) above were pooled and lyophilized.

Ninety mg. of Haemophilus influenzae type b polysaccharide antigen was obtained.

A solution of this antigen of 5.3 g/ml concentration was prepared and subjected to

Lowry assay for protein and found to contain 5 percent protein (wt/wt). The solution was also tested for carbohydrate by the phenol-sulfuric acid method and found to contain 36 percent (wt/wt). The solution was tested for activity by both the ELISA method and SDS-PAGE-

immunoblot and found to have requisite activity.

Example 3 - Preparation of Affinity Column

Five mg. of lyophilized Haemophilus influenzae type b polysacchaπde antigen was dis¬

solved in 4.52 mL of distilled water and the pH was adjusted to 5-6 with HC1; 15.64 mg. of

bovine serum albumen-hydrazine conjugate of pH 5-6 was then added, followed by mixing for

three minutes.

2.6 μg of l-ethyl-3- (3-dimethylaminopropyl) carbodiimide ("EDAC") was dissolved in

100 μL of distilled water. 50 μL of this solution was added to the antigen/BSA-hydrazine con¬

jugate solution, followed by three minutes of mixing. The balance of the EDAC solution was then added to this mixture followed by two hours of mixing at room temperature. The pH was then adjusted to 8 with NaOH and mixed for one hour at room temperature, followed by stor¬

age overnight at 4° C.

The next day the pH of the stored mixture was adjusted to 7 with HC1 and a portion was subjected to the ELISA test, confirming its activity.

2.12 mg. of the EDAC-treated antigen/BSA hydrazine conjugate was mixed with 2.4 g.

of washed Spherilose™ gel and the resulting mixture was incubated at room temperature for

two hours under top-to-bottom mixing conditions. 33.6 mg. of sodium cyanoborohydride was

then dissolved in 480 μl of dissolved water and one-half of this solution was added to the anti¬

gen/BSA hydrazine conjugate/Spherilose™ gel mixture. The resulting mixture was incubated

at room temperature for 3.5 hours under top-to-bottom mixing conditions. A coupled anti¬

gen/BSA hydrazine/Spherilose7^M gel was separated and washed with 20 volumes of distilled water, followed by resuspension in 4.8 mL of 0.2 M Tris-HCl blocking buffer of pH 7. The

remaining 240 μL of the above-described sodium cyanoborohydride solution was added to the

suspension and this mixture was incubated at room temperature for one hour and then over¬

night at 4° C. , under top-to-bottom mixing conditions throughout.

The coupled, blocked gel was separated and washed successively with 20 to 30 volumes

of distilled water, triple strength phosphate buffered-saline of pH 7.2, standard strength

phosphate-buffered saline of pH 9.2 and 3 M sodium thiocyanate in phosphate buffered saline

of pH 7.5 to simulate a mock antibody purification and was packed onto an affinity column.

Example 4 — Purification of H. influenzae type b Antibodies

To rabbit- - Haemophilus influenzae type b serum, NaCl was added to a final con¬

centration of 0.5 M NaCl and dissolved in the serum. The mixture was centrifuged at 5,000

XG for 20 minutes and filtered through cotton wool. Affinity gel from Example 3 was equili¬

brated with normal strength phosphate-buffered saline and the serum filtrate was applied to this gel four times. The gel was then washed with triple strength phosphate buffered saline, followed by normal strength phosphate buffered saline to remove unbound serum components.

Thereafter, the antibodies were eluted from the gel with 3 M sodium thiocyanate in

phosphate buffered saline (pH = 7.5) followed by 3 M sodium thiocyanate in distilled water

(pH 5 to 6). The recovered purified antibodies were dialyzed in normal strength phosphate

buffered saline of pH 7.2.

Example 5 — ICT Assay for Haemophilus Influenzae type b

A. Test Device Preparation A test device comprising a hinged cardboard housing equipped with a window to allow

the viewing of both the test results and control results was prepared as shown in Figure 1. The

device has a recess into which is placed a preformed plastic swab well on its right-hand side

(labeled 1 in the drawing) for receiving the sample-wetted swab. An overlabel show in Figure

1A is then placed over the entire right-hand side of the device. The overlabel has been equipped with two holes — a lower one (marked B on Figure 1A) into which the saturated swab

is to be inserted and an upper one (marked B on Figure 1A) toward which the swab will be

pushed after insertion thereof into the hole B. The arrangement of the overlabel with its holes

A and B, and the swab well cooperate to hold the swab in a proper position during the assay and to promote the expulsion of sorbed test sample liquid from the swab.

A preassembled test strip (marked B on Figure 1) described below, is inserted into the

recess on the left-hand side (labeled 2 on Figure 1) and held in place by an adhesive applied to

the bottom thereof. An overlabel shown in Figure IB is placed atop the left-hand side. It has

been equipped with a single hole (marked D in Figure IB) which mates to the right-hand side

hole A when the device is closed for performance of the assay.

The assembled device is stored in a sealed pouch with desiccant until it is used. Prior

to sealing the pouch and storing, a lightly adhesive tape is placed on the outer edge of the

right-hand half of the device.

B. Test Strip Preparation and Construction

As Figure 1C shows, the test strip for the assay is comprised of a pad of sorbent

material which has been impregnated with a conjugate of gold particles and affinity-purified

rabbit axiύ-Haemophilus influenzae B antibodies. In use, this conjugate is rendered flowable by contact with the liquid test sample. The conjugate pad contacts a nitrocellulose pad onto

which a capture line for sample that has reacted with the gold conjugate has been established

by imbedding affinity-purified rabbit an -Haemophilus influenzae B antibodies therein. The

nitrocellulose pad also includes a downstream control line established by striping the pad with

goat anti-rabbit immunoglobin (IgG). After passing the nitrocellulose pad, the sample residue

passes into an absorbent pad that serves as a reservoir for liquid.

The conjugate pad may be of non-woven polyester or extruded cellulose acetate. In

preparing the pad for use in this assay, gold particles of 45 run. diameter are conjugated,

according to the method of DeMay, "The Preparation and Use of Gold Probes" in Immuno- chemistry; Modern Methods and Application (J. M. Polak and S. Nan Νorden, eds., Wright, Bristol, England, 1986) or any of various other known methods, to affinity purified anti-

Haemophilus influenzae B antibodies. The affinity-purification is preferably achieved as

described above. See also P. Tyssen, "Affinity chromatography of Immunoglobulins or

Antibodies" contained in Practice and Theory of Enzyme Immunosassays (R.H. Burden and

P.H. Nan Knippedberg, eds., Elsevier, New York (1985). Any of various known methods of

affinity purification may be substituted for the preferred method without departing from the

present invention.

The gold conjugate particles are mixed with drying agent and embedded into a con¬

jugate pad. The drying agent used is aqueous 5mM sodium tetraborate, pH 8.0, containing 1.0

percent bovine serum albumin, 0.1 percent Triton X-100, 2.0 percent Tween 20, 8.0 percent sucrose, and 0.02 percent sodium azide. The pad is heated sufficiently to remove all the liquid

present and is stored in a low humidity environment pending assembly of the test device. These pads are especially chosen to hold the dry conjugate and to release it when wetted by

sample.

The nitrocellulose pad is first treated by individually embedding affinity purified anti-

Haemophilus influenzae b antibodies into a first portion of the pad. These_, antibodies act as the

capture lines. A control line is established by striping goat anti-rabbit IgG on the surface of

the pad. For those lines which are striped on the nitrocellulose pad, a solution consisting of

5mM sodium phosphate, pH 7.4, containing 5 percent methanol and 0.102 percent Intrawhite

dye is used as a carrier fluid for the antibodies. The nitrocellulose pad is then desiccated at a

temperature of 18-25° C. to promote permanent protein absorption thereto.

The absorbent pad used is of cellulosic material sold in commerce as Ahlstrom 243. It

requires no special treatment. All the pads are assembled in the order shown in Figure 1C on

an adhesive strip when the test device is put together for delivery to the customer.

C. Immunoassay Procedure

In the conduct of the assay according to the invention, finished test devices having the

swab well, the overlayers with holes and the test strip arranged as shown in the Figures are

utilized. A swab fashioned from fibrous Dacron is briefly immersed in the urine sample and is

then removed from the sample and immediately inserted, through the overlayer hole B on the

right-hand side of the device, into the sample well of the test device. Two or three drops of

"Reagent A", in this case a solution of 2.0 percent Tween 20, 0.05 percent sodium azide and

0.5 percent sodium dodecdyl sulfate in a 0.05 M sodium citrate-sodium phosphate buffer of pH

6.5 are added to the sample through the same hole. The adhesive strip on the edge of the

right-hand side is peeled away and the device is then closed. The sample immediately contacts the conjugate pad and flows through the immunochromatographic strip. After 15 minutes, the

test sample and control window are viewed and the results noted.

D. Results of Sample Testing

A number of urine specimens of two types were analyzed in test devices as described

above. The two types of urine samples evaluated were urine from patients without any pneumonia-type infection and urine containing Haemophilus influenzae b. All samples were

tested in duplicate. The following chart summarizes the results of testing:

The results above were consistent for both a non-woven polyester conjugate pad and an

extruded cellulose acetate conjugate pad. No differences were observed when either two or

three drops of "Reagent A" were added.

Example 6 - Cross-Reactivity/Compatibility of Antigen-Specific Antibodies to H. Influenzae Type b

A commercial preparation of synthetic H. influenzae type b sold under the label " ACT-

HIB" by Pasteur-Merieux-Connaught Laboratories as H. influenzae type b conjugate vaccine was injected into a rabbit and the rabbit was bled after the elapse of about 60 days.

The purified essentially protein-free capsular antigen as prepared in Example 2 was

covalently conjugated to a hydrazine-BSA conjugate as shown in Example 3 and the antigen:hydrazine-BSA conjugate was in turn covalently coupled to the same affinity gel

utilized in Example 3.

The rabbit serum containing raw polyclonal antibodies to H. influenzae type b was

purified against the purified antigen:BSA-hydrazine affinity gel in the manner described in

Example 4. The antigen-specific antibodies eluted from the gel were then utilized in compatibility and cross-reactivity tests, the results of which are graphed in Figures 2, 3 and 4 hereof.

A. Compatibility Tests

The compatibility tests were performed using a modified ELISA method as follows:

96- well polystyrene microtiter plates from Dynex Technologies, Inc. were coated with

100 mcl. aliquots of various strains of H. influenzae cell suspension (0.5 - 0.7 x 108 cells/ml.).

The plates were incubated at 37° C. for two hours and washed four times with PBS of pH 8.0

containing 0.02 percent Tween 20 ("PBST"). The microtiter wells were blocked with 200 mcl.

of PBS of pH 7.2 containing BSA in a concentration of 1 mg./ml. for one hour at room tem¬

perature. The plates were then again washed four times with PBST.

The purified antigen-specific antibodies obtained from the rabbit immunized with

commercial ACT-HIB as earlier described in this example were two-fold diluted through the

plates starting at a concentration of 0.5 mcg./ml. and ending at 0.008 mcg./ml.

The first horizontal row on the plates was used as a control. Instead of antibody

solution 100 mcl. of PBS was added to each well of this row. The plates were incubated for

one hour at room temperature and then washed four times with PBST. Thereafter 100 ml. of goat anti-rabbit IgG conjugated to horseradish peroxidase, diluted

1:6000 in PBST, was added to each well and the plates were incubated for 45 minutes at room

temperature. After again washing with PBST, 100 mcl. of TMB Peroxidase Substrate System

from KPL Laboratories, Gaithersburg, Maryland, was added to each well.,

The reaction in each well was stopped with 50 mcl. of IN H₂SO₄ after three to five

minutes of color development. The plates were counted at 450 nm wavelength in a spectro-

photometric ELISA reader.

The various H. influenzae type b strains tested were products available from American Type Culture Collection under accession numbers #10211 (this being the strain utilized in

Examples 1-5 hereof), #43335, #51654, and #43334. The results of the tests, which are

graphed in Figure 2 hereof, show that the antigen-specific antibodies obtained by injecting a

rabbit with ACT-HIB, bleeding the rabbit, and purifying the resultant antibody-containing

rabbit serum with purified capsular antigen from ATCC #10211 according to the procedures of

Examples 2 and 3 (designated as "[Hib-Ab]" in Figure 2), was most specific to and reactive

with ATCC #10211, but still highly specific to and reactive with the capsular antigen of each

of ATCC #43335, ATCC #51654 and #43334 at concentrations ranging from 0.063 mcg./ml.

to 0.5 mcg./ml., when compared to the control. Moreover, using instrumental detection of the

antigen-antibody reaction, the antigen-specific antibody of this invention produced discernible

reactivity with antigen relative to the control at lower concentrations as low as 0.008 mg./mcl.

B. Cross-Reactivity Tests

In these tests the antigen-specific purified H. influenzae type b antibodies of this exam¬

ple were tested against other species of H. influenzae, in two batches, following the test proto- col described for the compatibility tests of Figure 2, using the same controls described for

those tests.

For the first batch, Figure 3 is a graph comparing the reactivity of the antigen-specific

antibodies of this invention with the antigen from ATCC #10211 to which they are specific,

against antibodies of H. influenzae ("Hi" on the figure) types a, c, d and f. It demonstrates a

lack of cross-reactivity with all of types a, c, d and f, as compared to high reactivity with and

specificity for the type b H. influenzae antigen of ATCC #10211, at concentrations of 0.008

mcg./ml. to 0.063 mg./ml. A barely perceptible cross-reactivity with only H. influenzae type f

is observable at concentrations of antibody slightly above 0.063 mcg./ml. but even at the high¬

est concentrations of 0.5 mcg./ml. the reactivity with type f antigen is lower than that with

ATCC #10211 type a at the lowest concentration of antibody of 0.008 mcg./ml. The slight

cross-reactivity of type f with the antigen-specific antibody was adjudged too minor to be of

concern.

For the second batch, Figure 4 is a graph comparing the reactivity of the purified antigen-specific antibodies of this invention with each of four non-typable H. influenzae species

(NT1, NT2, NT3 and NT4) plus H. parainfluenzae as against the H. influenzae type b strain

ATCC #10211. Figure 4 demonstrates lack of cross reactivity of the antigen-specific anti¬

bodies of the invention with all of the H. influenzae non-typable species 1, 2, 3 and 4 and very

slight cross-reactivity with H. parainfluenzae at antibody concentrations of 0.125 mcg./ml. to

0.5 mcg./ml. This cross-reactivity, however, is of a lower order than the reactivity of the

antibodies at a concentration of 0.008 mcg./ml. with type b H. influenzae strains ATCC #10211 and it was adjudged of negligible importance. Figure 4 also confirms the strong specificity of the antibodies of this invention for H. influenzae type b capsular antigen.

Clearly, the purified antigen-specific antibodies of bacterial carbohydrate antigens can beneficially be utilized to detect the corresponding crude carbohydrate target antigen in any type of immunoassay and not just in those described herein. Equally clearly, substitution of

these purified antigen-specific antibodies for raw polyclonal antibodies in previously described

assays for the same target carbohydrate antigen will result in greater reliability, sensitivity and

specificity of each such assay. Furthermore, it is believed, albeit not yet demonstrated, that

substitution of these purified antigen-specific antibodies for monoclonal antibodies in assays

described in the prior art will give results at least as good as and, it is expected, in many

instances better and more reliable than those reported.

It is pointed out that the principles of this invention as herein disclosed lend themselves

readily to a plethora of adaptations of, permutations of and combinations with assay techniques

previously reported by others. Many of the steps disclosed herein can be accomplished using different reagents or conditions from those specifically disclosed. • Other methods of purifying

carbohydrate antigens to an essentially protein-free state can readily be devised. A vast array

of literature, both patent and non-patent, discusses the design and use of reliable, one-time-use, disposable immunoassay test devices that could be substituted for the preferred ICT device described and recommended herein. It is not intended that the present invention should be lim¬

ited with respect to substitutable assay devices, materials, ingredients or process steps except

insofar as the following claims may so limit it.

Claims (21)

1. A method for obtaining antigen-specific antibodies to a target bacterial carbo¬

hydrate antigen selected from among lipo-polycarbohydrate antigens, antigens comprising lipo-

teichoic acids or teichoic acid or derivatives of either, and capsular carbohydrate antigens, which comprises the steps of:

(a) purifying the target bacterial carbohydrate antigen to produce essentially protein-free antigen containing not more than about 10 percent of protein by weight,

(b) coupling said essentially protein-free antigen to a spacer molecule to produce a conjugate,

(c) coupling the conjugate from step (b) to an affinity gel to produce a further conjugate,

(d) passing raw polyclonal antibodies to the target bacterial antigen or an IgG cut thereof, over the further conjugate of step (c), and

(e) eluting from the further conjugate of step (c) purified antibodies specific to the crude target bacteria antigen.

2. Antigen-specific antibodies prepared by the method of Claim 1.

3. A method for assaying for the presence of target bacteria or a target carbohy¬

drate antigen component thereof in a test sample comprising a fluid suspected of containing the

target bacteria or their target carbohydrate antigen which method comprises contacting said test

sample with antigen-specific antibodies to said target antigen produced by purifying raw poly¬

clonal antibodies or an IgG cut thereof, according to the process of Claim 1.

4. The method of Claim 3 in which the test sample comprises a mammalian body

fluid obtained from a mammalian patient suspected of harboring a disease caused by said target bacteria.

5. The method of Claim 4 in which the test sample comprises human urine ob¬

tained from a patient suspected of having a disease caused by the target bacteria.

6. A method according to Claim 5 in which the target bacteria are Gram-negative

bacteria and their target antigen component is a lipo-polycarbohydrate.

7. A method according to claim 6 in which the lipo-carbohydrate is a lipo-

polysaccharide.

I¹

8. A method according to Claim 5 in which the target bacteria are Gram-positive

bacteria and their target antigen component is an antigen comprising a lipo-teichoic acid, a

teichoic acid or a derivative of either.

9. A method according to Claim 5 in which the target bacteria is Gram-positive or

Gram-negative and the target antigen is a capsular polycarbohydrate antigen.

10. A method according to Claim 9 in which the capsular polycarbohydrate antigen

is a capsular polysaccharide antigen.

11. An ICT assay for the detection of target bacteria or their target carbohydrate

antigen component, which comprises the steps of:

(a) contacting a sample of a fluid suspected of containing said target bacteria or their target carbohydrate antigen component with an ICT device comprising a strip of a bibulous material, which strip has

(i) a zone in which has been embedded a conjugate of:

(1) a labeling agent that displays a visible color change upon reaction of antibodies with their corresponding antigenic binding partner, and

(2) purified antigen-specific antibodies to the target carbohydrate antigen component, said antibodies having been purified by passage over a chromatographic affinity column to which is conjugated through a spacer molecule the essentially protein-free purified target carbohydrate antigen component.

(ii) a second zone having bound thereto the same purified antigen- specific antibodies in unconjugated form, which zone is equipped with a window for viewing color changes;

(b) allowing said sample to flow laterally along said test strip to said first zone;

(c) allowing said sample, together with said conjugate of affinity purified antibodies and label, to flow laterally along said test strip to said second zone; and

(d) within approximately 15 to 20 minutes from the commencement of step (a), observing through said window whether a line of color has appeared in said second zone, thereby indicating the presence in the sample of the target bacteria or their target carbohydrate antigen component, or both, or whether no line of color has so appeared indicating the absence of the target bacteria and their target carbohydrate antigen component.

12. A method for obtaining an essentially protein-free carbohydrate or antigen com¬

ponent from Gram-positive or Gram-negative bacteria, which comprises the steps of:

(a) culturing the bacteria for a time requisite to obtain a sample of desired size and harvesting the bacterial cells therefrom in the form of a wet cell pellet;

(b) suspending the wet cell pellet in an alkaline solution and mixing;

(c) adjusting the pH to an acid pH with a strong acid and centrifuging;

(d) separating the supernatant from step (c) and adjusting its pH to approximate neutrality;

(e) digesting this product with a broad spectrum protease enzyme preparation to destroy residual proteins;

(f) adjusting the pH to the alkaline side with a weakly alkaline aqueous solution;

(g) separating out the essentially protein free carbohydrate antigen on a size exclusion column equilibrated with a weakly alkaline solution; and (h) pooling material eluted in the first peak and adjusting its pH to approximate neutrality.

13. A method according to Claim 1 in which the target bacterial antigen is a capsular carbohydrate antigen of Haemophilus influenzae type b.

14. Antigen-specific antibodies according to Claim 2 which are^" specific to the

capsular carbohydrate antigen of Haemophilus influenzae type b.

15. A method according to Claim 3 wherein the target bacteria are Haemophilus.'

influenzae type b bacteria and their target carbohydrate antigen component is the capsular

carbohydrate antigen of those bacteria.

16. The method of Claim 15 wherein the target bacteria are Haemophilus influenzae

type b bacteria and their target carbohydrate antigen component is the capsular carbohydrate

antigen of those bacteria.

17. The method of Claim 15 wherein the test sample comprises human urine.

18. The method of Claim 11 in which the target bacteria are Haemophilus influenzae

type b bacteria, their target carbohydrate antigen components is a capsular carbohydrate anti¬

gen thereof, and the labeling agent is finely divided metallic gold.

19. A method according to Claim 12 in which the bacteria are Haemophilus influenzae type b bacteria and the essentially protein-free antigen component obtained is their essentially protein-free capsular carbohydrate antigen component.

20. A method according to Claim 3 in which the antigen-specific antibodies are present in a concentration of between 7.7 nanograms/sq. mm. of surface area and 385

nanograms/sq. mm. of surface area at each site of a test device at which antige antibody

reaction is to occur.

21. A method according to Claim 11 in which the antigen-specific antibodies are

present in a concentration of between 7.7 nanograms/sq. mm. of surface area and 385

nanograms/sq. mm. of surface area at each site of a test device at which antigen:antibody

reaction is to occur.