WO1988010272A1

WO1988010272A1 - Method of preserving a body fluid sample, prior to assay for hiv (aids) infection

Info

Publication number: WO1988010272A1
Application number: PCT/AU1988/000221
Authority: WO
Inventors: Garth Alexander Nicholson
Original assignee: Garth Alexander Nicholson
Priority date: 1987-06-26
Filing date: 1988-06-27
Publication date: 1988-12-29

Abstract

A method of detecting HIV infection in a patient, which comprises taking a sample of body fluid from a patient and drying said sample on an absorbent substrate. The sample may then be optionally eluated and the eluate or the dried sample tested for the presence of antibodies to HIV or to HIV antigens or RNA, by standard assays. The method of the invention permits anonymity by use of automated blood collection methods and coded absorbent substrates whereby the patient keeps a coded receipt or tear-off portion of the substrate and with that receipt or portion is able to obtain results of the test. The method of the invention enables antibody, antigen and RNA tests to be performed on the same sample, thus providing a means for a number of different tests to be carried out on a single stabilised, dried and inactivated sample.

Description

Method of preserving a body fluid sample, prior to assay for HIV (AIDS) infection

TECHNICAL FIELD The present invention relates to an improved method in the assay for the diagnosis of acquired immune deficiency syndrome or AIDS. By employing the method of the invention, there is less risk to persons handling samples, and, more importantly, patient anonymity can be preserved more reliably. The method of this invention permits antibody, viral RNA and antigen tests to be performed on the same sample.

BACKGROUND ART Acquired immune deficiency syndrome (AIDS) has been described as the first great pandemic of the second half of the twentieth century (Gallo, R. C, Scientific American, 256, 1, January 1987 p39).

The cause of AIDS has been conclusively shown to be a human retrovirus, Human Immunodeficiency Virus (HIV). The virus is known to be found in body fluids, particularly blood, saliva and semen. The initial screening test for persons exposed or thought to be exposed to HIV consists of an in vitro qualitative enzyme immunoassay (ELISA) for antibodies to the HIV in human serum or plasma. This is a semi-automated procedure and is the major screening test in blood banks and hospitals. This test is sensitive but false positive reactions occur. There are three other testing procedures:

Immunofluorescent assay, which is a non-automated procedure and thus is not well adapted to mass screening. It is used in confirmation of serum repeatedly positive to the ELISA screening test; Radioimmuno- precipitation assay; and Nestern immunoblot. The last two further tests which are more specific but less sensitive. In New South Wales, inter alia, testing for antibodies to HIV is performed in selected teaching hospitals and laboratories and thus most blood samples for HIV testing-require transport. Blood to blood contact is the high risk route of infection and cases are now coming to light where laboratory workers handling HIV positive blood have been infected such as by inadvertent needle-stick injury or by breaking of tubes containing infected blood and splashing of the blood to broken skin or to the mouth and eye areas. Clearly the risk of infection must be avoided or minimised at all costs as at present there is no known cure for AIDS and recent work is showing that there may be a large group of persons infected with the virus that do not snow symptoms. Consequently, transport of blood to the selected testing sites presents a serious problem and bl ood taken from patients for AIDS testing must be transported and handled extremely carefully as contact with blood carrying HIV is potentially very dangerous. Thus, transport of blood samples between the site of sampling and the site of testing requires strict precautions as does the handling of the blood sample for testing. Also, routinely most blood samples arekept at between about 0° and 4ºC for transport. Thus the cost of transportation in respect of blood products potentially carrying the virus is high and serious problems do exist with the transport thereof.

Furthermore an additional problem with conventional antibody testing for HIV infection is that antibodies to the virus do not appear in the blood for a time interval of at least three monthes after infection, which raises problems in the interpretation of a negative test in a patient who may fall within this initial "window" period. The ability to detect i nfecti on at an earl i er stage by testi ng for the presence of HIV RNA on a standard sample would obviously represent a considerable advantage over the prior art tests.

The present inventor has found that antibodies to HIV and HIV antigens and RNA can be stabilised during transport and handling whilst being in a relatively safe and manageable form by placing the sample of body fluid to be analysed on an absorbent substrate and drying the sample. A particularly preferred absorbent substrate is filter paper. The inventor has found that the HIV antibodies when eluated from the substrate retain their activity and the eluate can be assayed for antibodies to HIV to give reliable results.

DESCRIPTION OF THE INVENTION

Accordingly, in one form the invention provides a method of detecting HIV infection in a patient, which method comprises taking a sample of body fluid from said patient, applying said sample to an absorbent substrate, drying said sample, optionally eluating sai-d dried sample from said substrate and testing the dried sample or eluate for the presence of one or more of antibodies to or indicative of HIV or HIV antigens or RNA.

In another aspect the invention provides a method of stabilising antibodies to or indicative of HIV or HIV antigens or RNA in a body fluid, which method comprises applying a sample of said body fluid to an absorbent substrate and drying said sample on said substrate.

In a further aspect the invention provides a method of detecting HIV infection in a patient at an earlier stage than conventional antibody testing, in picking up patients in the "window" period, by the detection of HIV RNA, using the same stabilised and dried sample.

Preferably the absorbent substrate is filter paper or other absorbent cellulosic material such as nitrocellulose, or other absorbent material. Preferably the filter paper is of a high quality such as Schleicher and Schull No. SS2992, although gel or beads or other absorbent could be used to immobilise the body fluid in a form which is less prone to spillage or splashing. The body fluid may be blood or a fraction thereof, saliva or semen.

Immobilisation of the body fluid and antibodies to or indicative of HIV or HIV antigens or RNA therein on an absorbent substrate allows for treatment of the body fluid to reduce viral infectivity whilst maintaining activity of the antibodies to or indicative of HIV or HIV antigens or RNA insofar as their assay activity is concerned. This means that the body fluid can be more safely transported and handled.

Preferred treatments to reduce viral infectivity comprise heat treatment, treatment by UV light or other, e.g. gamma radiation, and treatment of the absorbent substrate with chemical additives that reduce viral infectivity. Heat treatment at about 60º for about 10 minutes to 6 days is suitable.

The absorbent substrate may be impregnated with a chemical to reduce HIV infectivity can be provided to medical practitioners or pathology laboratories where samples are taken for AIDS testing.

Piszkiewicz D. et al in Thromb. Res. 1986, Dec, 44(5), 701-77, report that heat treatment of blood products can be used to inactivate HIV. Therefore, in a preferred embodiment, the risk of contamination by the virus can be reduced by subsequent heat treatment of the body fluid on the absorbent substrate. Preferably heat treatment consists of heating at about 60°C for about 10 mins to about 6 days. Data as shown hereafter shows that heat treated samples still give a positive result and thus the antibodies to HIV are still active whilst the virus infectivity is substantially reduced.

Quinnan et al , in Transfusion, 26, 5, 1986, p481, describe methods for the inactivation of HIV. These methods include chemical treatment such as ethyl ether, β-propiolactone, formaldehyde or detergents, and such treatments are embraced by this form of the present invention. A particularly preferred means of treatment to reduce viral activity is to impregnate the absorbent substrate with a suitable chemical which will reduce viral infectivity such as 4-aminomethyltrioxsalen before or after placing the body fluid sample thereon and contacting the body fluid sample with UV light, before, during or after contact of sample with said substrate.

Testing can be performed by any known test method. Suitable immunological based assays include immuno-fluorescent assay, radioimmunoprecipitation assay, Western- immunoblot, and ELISA. When HIV RNA is determined, a polymerase chain reaction (PCR) assay is suitable.

The method of the invention permits anonymity by use of automated blood collection methods, coded paper sheets and automatic finger lancing or air jet machinery. The coded sheet can be sent to a central laboratory and the patient can keep a receipt or tear-off portion of the coded paper sheet.

BEST MODES OF CARRYING OUT THE INVENTION

In the practice of the invention, typically a sample of serum, whole blood or plasma is taken from the patient or is otherwise sampled. From the patient the sample may be removed using a syringe or by the "finger prick" method. The sample is then applied to the substrate, such as a filter paper strip. The preferred filter paper is Schleicher and Schull No. SS2992. Other high quality filter paper is also a further example of a preferred substrate. The sample is then air dried and a second application can then be applied if required. The sample may be then stored for a limited duration of days or weeks. If desired, the sample is treated in accordance with the above, to reduce viral infectivity.

When the body fluid is to be assayed, a portion or disc of filter paper impregnated with the body fluid is taken and the constituents of the body fluid are eluated from the substrate, such as with the assay diluent. Elution times may vary but times between 5 and 60 minutes are suitable preferably using a shaking apparatus. Small amounts of suitable detergent may be added to improve elution although this is not necessary. The eluated sample is then used in a typical HIV immunoassay such as that marketed by Abbott Laboratories as ABBOTT HTLV-III EIA No. 1037, which is the test kit used in New South Wales hospitals and laboratories.

In this test kit 10μl of blood is routinely used which is approximated by three punched out filter paper discs of about 6.5mm in diameter.

In general terms in the assay procedure using ABBOTT HTLV-III EIA No. 1037, 10μl of sample is diluted with 200μl of specimen diluent and mixed. Immobilised sample in accordance with the present invention is eluated from three 6.5mm discs using specimen diluent for about 10 minutes in a shaker and the eluate is made up to 210μl with specimen diluent. l0μl of the eluate or control is dispensed into appropriate wells of the reaction tray (2 negative and 3 positive controls are used) provided by the kit. 200μl of specimen diluent is added to each reaction well and a reaction bead (beads coated with HIV antigen and provided with kit) is added to each well and incubated at 40°C for one hour ± 5 minutes.

Each bead is then washed three times with 4-6μl distilled water. 200μl of conjugate (anti-human IgG (goat): horseradish peroxidase) is placed in wells with the bead and incubated at 40°C for 2 hours ± 10 minutes. Each bead is washed with 4-6ml of distilled water three times.

Beads are then transferred to assay tubes and 300μl of freshly prepared substrate consisting of o-phenylenediamine.2HCl (12.8mg/5ml) is then dispensed into assay tubes and incubated at room temperature for 30 ± 2 minutes. The reaction is stopped with 1ml of IN sulfuric acid.

Absorbence at 492nm is detected. Positive results are determined with respect to a reference range established for negative sera from non-exposed individuals. Full details of the assay accompanied kits and are readily available. It should be noted that any testing procedure for HIV antibodies is suitable for use in the present invention.

In a further form of the invention, the methodology of the invention is applicable to sera or other body fluids which are also infected by viral hepatitis. Viral hepatitis antibodies are quite commonly found in AIDS infected blood or blood thought to be AIDS infected. This virus also poses the significant risk to people handling the blood or other body fluid and in this further form of the invention there is provided a means of detecting viral hepatitis in a blood sample wherein a dried sample of a body fluid is eluated from an absorbent substrate and the eluate is tested for the presence of antibodies to or indicative of viral hepatitis. Generally the practice of the invention is also applicable to viral hepatitis.

The i nventi on i s further des cri bed wi th reference to the accompanying examples.

EXAMPLE 1 Two different samples of HIV antibody positive blood were placed on Schleicher and Schull No. SS2992 paper and air dried and left for 48 hours.

Two sets of three x 6.5mm discs were punched out from each sample and eluated in 210μl of sample diluent. These samples were then assayed using the assay procedure described generally above and more specifically accompanying the ABBOTT HTLV-III EIA No. 1037 kits. The results are as follows:

SAMPLE A₄₉₂

TEST 1 (+ve) > 2.0

TEST 2 (+ve) > 2.0

REFERENCE 1 (-ve) 0.215

REFERENCE 2 (-ve) 0.243

REFERENCE 3 (-ve) 0.365

PAPER WITHOUT SERUM 0.017 The above shows that sufficient HIV antibodies are stable on the filter paper for at least 24 hours so as to be detected in comparison to reference sera.

EXAMPLE 2 Two different samples of the same antibody positive blood and 3 reference sera as used in Example 1 were separately applied to Schleicher and Schull No. SS2992 filter paper in two applications and heat treated in an oven at 60°C for 24 hours. Two sets of 3 x 6.5mm discs were excised from each sample sheet and run through the ABBOTT assay. The results are as follows:

SAMPLE A₄₉₂

TEST 1 (+ve) 1.142

TEST 2 (+ve) 0.910

REFERENCE 1 (-ve) 0.084 REFERENCE 2 (-ve) 0.074 REFERENCE 3 (-ve) 0.069 PAPER BLANK 0.007

These resul ts show that the anti body is stabilised on the paper and thus can be heat treated and still be detectable in respect of the HIV assay. Antibody appears to be lost during heat treatment but this factor can be quantitated and additional excised paper or eluated sample can be added to the diluent to compensate for this factor. Additional application of the body fluid to the substrate can be used.

EXAMPLE 3 Two 10μl samples of antibody (-ve) and antibody (+ve) serum were added to filter paper. It was noted that the sera spread to different sized circles so multiple aliquots were prepared. The paper was then dried at room temperature for 24-48 hours.

Spots with a uniform diameter of 10mm only were used.

In Test A, two spots containing the full 10μl serum spot dried on paper were used.

In Test B, four 6.5mm spots punched out from the centre of 10mm serum spots dried on paper were used.

The spots were added to 800μl of Abbott diluent, shaken for ten minutes, 410μl of eluate were removed and tested according to Abbott recombinant HIV 1 EIA assay. The results are as follows:- RESULTS

Liquid serum test resu Its:

Negative controls average 0.054

Positive controls average 0.973

Cut off 0.200

Test A - dr i ed serum spots :

Abbot positive 0.947

Abbott negative 0.138

Patient #1 (known +ve) 2.000

Patient #2 (-ve) 0.113

Blank Paper 0.004

Test B - dried serum spots:

Abbot positive 0.494

Abbott negative 0.139

Patient #1 2.000

Patient #2 0.113

Blank Paper 0.004

Liquid Serum test:

Patient #1 2.000

Patient #2 0.171

The tests show that the eluated paper samples provide results which are equivalent to unmodiried serum samples of the same subjects, and equate well with tested unmodified negative and positive serum controls.

Where whole blood samples are to be used, either finger prick, capilliary blood or venesection samples at appropriate dilution factors are used and appropriate negative controls are established.

Claims

1. A method of detecting HIV infection in a patient, which method comprises taking a sample of body fluid from said patient, applying said sample to an absorbent substrate, drying said sample, optionally eluating said dried sample from said substrate and testing the dried sample or eluate for the presence of one or more of antibodies to or indicative of HIV or HIV antigens or RNA.

2. A method according to Claim 1, wherein the dried sample or eluate is tested for the presence of antibodies to or indicative of HIV, HIV antigens and RNA.

3. A method according to claim 1 or claim 2, wherein the body fluid is selected from the group consisting of blood, a blood fraction, saliva, or semen.

4. A method according to any one of claims 1 to 3, wherein said absorbent substrate is a coded sheet.

5. A method according to any one of claims 1 to 4, wherein said absorbent substrate is cellulosic material.

6. A method according to claim 5, wherein the cellulosic material is filter paper or nitrocellulose.

7. A method according to any one of claims 1 to 6, wherein the eluate is tested by means of an immunological reaction based assay.

8. A method according to claim 7, wherein the immunological reaction based assay is selected from the group consisting of immuno-fluorescent assay, radioimmunoprecipitation assay, Western immunoblot, or ELISA.

9. A method according to any one of claims 1 to 6, wherein HIV RNA is determined.

10. A method according to claim 9, wherein the HIV RNA is determined by polymerase chain reaction.

11. A method according to any one of claims 1 to 10, wherein said sample is treated to inactivate HIV before, during or after application to said absorbent substrate.

12. A method according to claim 11, wherein said treatment is selected from at least one of heat, irradiation, or chemical treatment.

13. A method according to claim 12, wherein said sample is heated at about 60°C for 10 min to 6 days.

14. A method according to claim 12, wherein said sample is irradiated with U.V. light or gamma radiation.

15. A method according to any one of claims 1 to 10, wherein said absorbent substrate is impregnated with a chemical agent.

16. A method according to claim 12 or claim 15, wherein said chemical agent is selected from the group consisting of ethyl ether, β-propiolactone, formaldehyde 4-aminomethyl trioxsalen or a detergent.

17. A method according to claim 16, wherein said chemical agent is 4-aminomethyltrioxsalen.

18. A method of detecting HIV infection in a patient, which method comprises taking a sample of body fluid from said patient by means of automatic finger lancing or air jet machinery, applying said sample to a coded paper sheet which incorporates a tear-off portion also bearing the identification code and which is retained by the patient, drying said sample on said coded paper sheet, optionally eluting said dried sample from said substrate, and testing the dried sample or eluate for the presence of one or more of antibodies to or indicative of HIV, or HIV antigens, or RNA.

19. A method of stabilising antibodies to or indicative of HIV or HIV antigens or RNA in a body fluid, which method comprises applying a sample of said body fluid to an absorbent substrate and drying said sample on said substrate.

20. A method according to Claim 19, wherein the body fluid is selected from the group consisting of blood, a blood fraction, saliva, or semen.

21. A method according to claim 19 or claim 20, wherein said absorbent substrate is cellulosic material.

22. A method according to claim 21, wherein the cellulosic material is filter paper or nitrocellulose.

23. A method according to any one of claims 19 to 22, wherein said sample is treated to inactivate HIV before, during or after application to said absorbent substrate.

24. A method according to claim 19, wherein said treatment is selected from at least one of heat, irradiation, or chemical treatment.

25. A method according to claim 24, wherein said sample is heated at about 60°C for 10 min to 6 days.

26. A method according to claim 24, wherein said sample is irradiated with U.V. light or gamma radiation.

27. A method according to claim 23 or 24, wherein said absorbent substrate is impregnated with a chemical agent.

28. A method according to claim 24 or claim 26, wherein said chemi ca l agent is selected from the group consisting of ethyl ether, β-propiolactone, formaldehyde 4-aminomethyltrioxsalen or a detergent.

29. A method according to claim 28, wherein said chemical agent is 4-aminomethyltrioxsalen.