Table 1.

Current methods for identifying genetically foreign microchimeric cells

Technique	Target	Advantages	Disadvantages
DNA amplification by polymerase chain reaction (PCR)	DNA encoding unique MHC haplotype alleles Y chromosome DNA (to identify microchimeric male cells in females) Other genetic polymorphisms such as insertion and deletions or minor alloantigens (for example, Rhesus factor or killer-cell immunoglobulin-like receptors)	High sensitivity High specificity Wide variety of potential targets for discriminating microchimeric cells	Precludes isolation of intact, live cells Pre-screening of individuals is required to identity unique DNA targets such as MHC haplotypes
Fluorescence in situ hybridization (FISH)	Y chromosome DNA-containing cells (to identify microchimeric male cells in females) Cells containing two X chromosomes (to identify microchimeric female cells in males)	When combined with fluorescence microscopy, FISH allows detection of rare cells within intact tissues with high sensitivity and specificity	Precludes isolation of intact, live cells Primarily allows identification of gender-discordant cells Limited analysis of other molecular parameters
Flow cytometry	Unique MHC haplotype alleles Discordant reporter constructs (such as green fluorescent protein or luciferase) Congenic cell surface antigens (such as CD45 alleles)	Analysis of cell associated molecular and phenotypical markers Purification of intact live cells to further investigate their function	Low specificity (high background) Requires antibodies against each molecular target