In situ polymerase chain reaction detection of viral DNA, single-copy genes, and gene rearrangements in cell suspensions and cytospins.

The study of low-copy viral or genomic DNA sequences by in situ hybridization (ISH) is often limited by sensitivity. Using the polymerase chain reaction (PCR) for the amplification of target DNA sequences in fixed cells [in situ PCR] (ISPCR) before ISH, we have been able to greatly improve the sensitivity of ISH. Viral DNA present in low copy number, single-copy genes, as well as immunoglobulin gene rearrangements (VH3 family genes), were successfully amplified in cells in suspension or on glass slides (cytospins). Single primer pairs were used in the in situ amplification step and 35S- or digoxigenin-11-dUTP-labeled region specific oligonucleotide probes were used for detection of amplificants by ISH. Artifacts, presumably resulting from leakage of in situ amplificants out of cells, may be a significant problem in selected instances. By optimal fixation and permeabilization of cells, limiting PCR cycle number, amplification of long DNA sequences, and/or incorporation of biotinylated dNTPs to produce bulkier amplificants together with washing of cells after ISPCR, diffusion artifacts were significantly reduced. Probe hybridization to single-stranded long PCR fragments or messenger RNA were excluded as a source for false-positive ISPCR results. The techniques reported dramatically increase the sensitivity of ISH in the detection of low-copy viral infection as well as in the study of gene rearrangements, and provide unique opportunities to study chromosomal translocations and point mutations at the cellular level.