Detection of nucleic acids in cells and tissues by in situ polymerase chain reaction

The solution-based polymerase chain reaction (PCR) method for amplification of defined gene sequences has proved a valuable tool not only for basic researchers but also for clinical scientists. Using even a minute amount of DNA or RNA and choosing a thermostable enzyme from a large variety of sources, one can enlarge the amount of the gene of interest, which can be analyzed and sequenced. Therefore, genes, or segments of gene sequences present only in a small sample of cells or small fraction of mixed cellular populations can be examined. One of the major drawbacks of the solution-based PCR technique is that the procedure does not allow for the association of amplified signals of a specific gene segment with the histological cell type(s) (1-2). For example, it would be advantageous to determine what types of cells in the peripheral blood circulation or in pathological specimens carry HIV-1 gene sequences, a vector used for gene therapy, an aberrant gene in a leukemia patient, or to determine the percentage of leukemia cells present following antitumor therapy.