New: Bioscientia performs corona antibody test

Tuesday 07 April 2020, 17:00

The Bioscientia laboratories now offer a test for the detection of IgA and IgG antibodies against SARS-CoV-2. The test is performed from serum, heparin or EDTA plasma. The Robert Koch Institue (RKI) does not yet have a case definition that could serve as a decision criterion for an indication for testing. Therefore, we recommend the request of antibody detection to confirm a fresh SARS-CoV-2 infection.

All test manufacturers we are in contact with report high production capacities. They expect sufficient supply capacity to meet the upcoming demand in German laboratories from April 20. Samples that you send us by then will be carefully archived and examined as soon as they are ready for testing. Alternatively, you can send us fresh sera from the week after Easter. 

Unless there are pandemic-related bottlenecks in the supply of test components, samples will be processed on the same day. 

Notes on the interpretation of the results:

As expected, first studies with sera from patients with proven SARS-CoV-2 infection and various test systems have shown that detectable antibodies develop in the course of an infection after 1-4 weeks.

The antibody tests primarily serve to diagnose a SARS-CoV-2 infection and support the direct detection of the pathogen.

For the frequently desired use, namely the confirmation of an immunity against SARS-CoV-2, there are currently not yet sufficient data available.

Cross-reactivities are described for the systems tested by us against other beta-corona viruses such as OC-43 and SARS-CoV-1. The test manufacturer states the specificity for IgG detection at 98.5%, for IgA detection at 92.5%. Furthermore, the IgA test showed 12.7% positive results in a blood donor collective collected before the pandemic.

For these reasons, we are initially concentrating our test capacities on the detection of antibodies in confirmed PCR-positive cases. This can, for example, support the production of immunotherapeutic drugs (plasma donations).

An antibody test detects antibodies that are produced by a patient's immune system against parts of e.g. pathogens (antigens). These are protein, sugar or fat molecules that are located on the outside of the envelope of viruses or bacteria. Among them there are those that occur in several related pathogens and others that are found exclusively on the surface of the sought-after germ, i.e. are highly specific.

Antibodies (immunoglobulins) are basically formed against all foreign substances that our immune cells encounter. In order to obtain the most accurate, specific results possible from an antibody test, we concentrate on the highly specific antibodies that are directed against the pathogen-typical proteins.

During the immune response to a pathogen, early antibodies are initially formed (e.g. immunoglobulin A, abbreviated IgA, usually also immunoglobulin M, abbreviated IgM) and later more mature antibodies (IgG). The antibodies can sometimes be measured just a few days after the pathogen has entered the body, sometimes weeks later, sometimes not until the pathogen has already left the body.

The IgG antibodies usually remain detectable in the blood for a very long time, often for life, and then ensure a rapid immune reaction if the same pathogen should enter the body again. We call this state of readiness immunity.

The presence of IgA and IgG in blood serum and the ratio of IgA and IgG concentrations to each other indicates the phase of infection. For example, if only IgA is measured and no IgG, this indicates a recent infection. The opposite case - IgA negative, IgG high - is typical for a more recent infection.

In our case, we want to detect IgG and IgA antibodies against SARS-CoV-2 in order to find out whether and when the person under investigation has immunologically dealt with the Covid-19 pathogen. We want to find out whether and when the patient has been immunologically tested with SARS-CoV-2, and not with SARS-CoV-1, MERS or another coronavirus, of which there are a number of harmless types that also provoke immune responses. That's what we call "cross-reaction". For example, antibodies against the corona virus OC-43 are common.

We are essentially interested in two questions:

  1. Does the test find all patients who have actually experienced an infection with SARS-CoV-2 (sensitivity)?
  2. Are the antibodies found also specifically produced only against SARS-CoV-2 and not against related pathogens (specificity)?

Our claim as Bioscientia is to substantiate this selectivity of the test with our own data. For this purpose, we have been taking blood samples from suitable patients since the beginning of March, from whom we also know the result of the corona PCR, for example, and we examine the antibodies formed in various test systems.

The first results are encouraging and allow cautious statements about unknown patient samples:

  • The test is suitable for the confirmation of a healed infection after positive PCR
  • The test also clarifies whether patients are suitable as "antibody donors". At some universities and blood donation centres, studies are underway to enable such antibody donations to be administered to seriously ill patients (passive vaccination).
  • The test is only suitable to a very limited extent for "free screening" of persons who have had neither clinical symptoms nor a positive PCR result.

In the current phase of the pandemic, the public is hoping for statements based on antibody detection, as we are familiar with from other viral diseases such as mumps and measles.

Concrete examples: 

Is a geriatric nurse with positive antibody detection allowed to have contact with senior citizens in need of care? 
Can an IgG-positive at-risk patient resume his or her normal life without special protective measures? 
Does an IgG-positive nurse really not pose a risk of infection for patients with pre-existing conditions or the residents of nursing homes with the known increased risk?
Are grandchildren with positive antibody detection allowed to visit their grandparents again without concern?
These questions cannot yet be conclusively answered with the available test systems and are the subject of studies that Bioscientia, among others, is conducting. It will probably take several months before the database is sufficiently robust to provide serious answers. Oxford professor John Bell, for example, has plausibly presented this assessment.

The exact molecular structure of SARS-CoV-2 has been known since about the beginning of January 2020; since then, its components can be used to produce antibody tests. However, practical experience in the use of the first commercially available antibody tests is still scarce; the pandemic will not last long enough for this to happen. These three questions have not yet been conclusively clarified:

  1. When exactly during the infection does the production of IgA antibodies begin and when does the production of IgG antibodies begin?
  2. In what way does the test measure cross-reacting antibodies against other corona viruses? So how reliably does a positive result indicate antibodies against exactly SARS-CoV-2?
  3. For many viruses the following applies: a correspondingly high content of IgG antibodies in the patient's blood protects against recurrence of the disease; these antibodies demonstrate immunity. Is it the same here?

We have been offering the first antibody detection since the beginning of April, with reference to the currently still limited informative value. Other laboratories in other countries have also started testing. The number of manufacturers of CE-certified and sufficiently validated test kits is limited worldwide. As with pathogen detection by PCR, delivery bottlenecks are therefore already expected, which can only be eliminated slowly by increasing capacities.

They are not suitable for providing reliable answers to the above questions. This is because there are not sufficient study data available to prove sensitivity and specificity.

Concrete:

  • A positive rapid test does not unequivocally prove a past infection with SARS-CoV-2, or even immunity. The person tested could therefore become infected and pass on the virus.
  • A negative rapid test does not reliably rule out a past infection with SARS-CoV-2. The tested person could therefore remain isolated for no reason.
  • Because of the obligation to notify, positive rapid test results must be examined in a specialist laboratory anyway, because rapid test results are not accepted by the notification authorities. 

And the same applies to antibody rapid tests as to antibody laboratory tests: they are not suitable for detecting an acute infection with SARS-CoV-2 because antibodies are not formed until weeks after the start of the infection.

Anyone for whom there is a medical indication.

We measure the antibodies with the so-called ELISA method, which is easy to automate and allows the same-day processing of large sample quantities. This is how the test works:

  1. A plastic plate with 96 wells is coated with antigen. The walls of the wells then contain an extract of virus components of SARS-CoV-2.
  2. A patient sample is pipetted into each well. If there are antibodies against the virus components on the wall of the sample, they will bind to it - just like in the body. After 20 minutes, everything that has not bound is removed from the well.
  3. Now a second antibody is pipetted in, which shows two special features: 

    a) one end binds specifically to a certain antibody type (here IgA or IgG). As a result, all patient antibodies that have coupled to the antigen in step 2. are now bound in turn.

    b)the other end of the second antibody carries a labelling molecule, which reacts in the next step and provides the measurement signal. 

    The patient antibody sought is now - if present in the sample - packed between "its" antigen and the labelled second antibody. This is why this test method is also called the sandwich method.
  4. Everything that has not reacted is rinsed out of the wells again. A solution is now pipetted to the remaining "sandwich packages" which reacts with the labelling molecules from step 3.b). The result is a coloration, the intensity of which is measured. The stronger the colour, the more antibodies were in the patient serum.