DotScan helps join the dots in identifying heart disease

University of Sydney researchers claim to have achieved almost perfect discrimination between two major forms of heart disease from patients' blood samples, using Sydney firm Medsaic's proprietary DotScan technology.

Prof Cris dos Remedios told the 2006 Lorne Conference on Protein Structure and Function that his research group, in the university's Institute of Biomedical Research, had neatly differentiated a group of patients with ischaemic heart disease from another group with idiopathic dilated cardiomyopathy, and also accurately identified healthy controls.

Dos Remedios, the co-inventor of DotScan , told the conference that the technology employed protein microarrays to profile expression patterns of some 80 different CD antigens on lymphocytes,

The Sydney team has previously shown that the protein microarray technology can accurately distinguish between different forms of leukaemia and lymphoma, infectious diseases and autoimmune diseases such as psoriasis, using fresh, 5ml blood samples from patients.

The heart disease array consists of a nitrocellulose-coated microscope slide dotted with an array of about 80 monoclonal antibodies, each recognising a specific leucocyte surface antigen.

After treatment to remove red blood cells, the serum sample is incubated with the microarray for 30 minutes, and the antibodies reacting with their complementary antigens, capturing those cells displaying the antigens. Unbound cells are washed off.

The resulting microarray pattern is scanned, converted to a digital image, and recorded in a database. The expression patterns for each patient are then grouped according to similarities in antigen expression patterns and levels.

Special algorithms then perform pair-wise matching to identify those individuals whose leucocyte antigen expression patterns are most similar. Comparisons with healthy controls filter out antigens that are shared by healthy subjects and those with heart disease.

Dos Remedios showed the conference a dendrogram derived from all the heart disease patients. Each individual's antigen-expression profile is unique, but the software assigns them to groups on the basis of overall similarities and differences.

"The patients who had been diagnosed by conventional techniques as having ischaemic heart disease grouped in one cluster, and those with idiopathic cardiomyopathy in the other," dos Remedios said. "We showed the clinicians the results, and they were amazed. There was one patient who had been diagnosed with IHD who grouped with the ICM group, but the clinicians said they wouldn't have believed the result if the separation had been 100 per cent accurate. "

"About 99 per cent of lymphocytes are actually circulating within tissues, rather than in the bloodstream, and they send signals back to the immune system about inflammatory trouble spots," he said.

In their patterns of surface antigens, lymphocytes effectively represent a dynamic record and archive of disease states within the body. Dos Remedios said the lymphocytes 'remember' a bout of leukaemia -- long after a patient has been cured, their lymphocytes still carry an antigenic record of the cancer.

Dos Remedios predicts that eventually, when comprehensive arrays of monoclonal antibodies are available to 'read' all surface antigens, it should be possible to perform a complete diagnostic and prognostic health check on a patient from a single, 5ml blood sample. It will not only reveal current and past disease states, but whether a cancer patient is likely to relapse.

He said the technology also had the power to greatly refine diagnosis -- DotScan will create a positive feedback loop between microarray data and conventional clinical diagnostic techniques, leading to automated diagnoses.