Recently, an increasing number of laboratoriesnhave begun to use molecular techniques for HLA typing. Most such techniques are based on the polymerase chain reaction (PCR) of DNA isolated from peripheral blood cells, although other tissue sources can also be used. PCR is a method of producing large quantities of a specific gene using a DNA polymerase and synthetic oligonucleotide primers that hybridize with unique DNA strands of that gene.
Two general DNA typing methods with commercial reagen kits are available to the clinical HLA laboratory.
The sequence-specific oligonucleotide probe method utilizes HLA locus-specific primers for PCR amplification, and the subsequent amplification products are probed with a number of specific oligonucleotide sequences that can define the different alleles of an HLA gene.
The other method, sequence-specific primer typing, utilizes allele-specific primers for PCR amplifications. The amplified DNA fragments have different molecular weight, which can be detected with gel electrophoresis. Molecular HLA typing is more precise than serologic HLA typing, and the molecular typing reagens are much more readily available.
Other molecular methods permit DNA sequencing of entire HLA genes, but they are being used by few clinical laboratories.