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.