What is HLA Typing Test?
Human Leukocyte Antigens (HLA) typing is a next-generation sequencing-based test that helps find the best match for donor selection in allogeneic bone marrow and organ transplant. In bone marrow and organ transplantation, HLA of the donor identified as invaders by the recipient, cause rejection. Careful selection of the matched donor and recipient critically affects the outcome of transplantation.
Why do you need the test?
- During a bone marrow transplant, the donor’s bone marrow might be considered a foreign body and thereby be rejected by the recipient’s immune system
- More the mismatch, higher the chances of rejection
- HLA gene sequence determines the production of proteins that can lead to this rejection
- Hence it is important to match the immune signature of the potential donor(s) with that of the recipient
When do you need to get tested?
- Prior to a bone marrow transplant or an organ transplant, the treating clinician might want to check the compatibility of the donor tissue by opting for this test
- Post transplant, the clinician may check for compatibility using Chimerism test in order to decide the exact dose required of immunomodulators.
Who needs to get tested?
HLA typing test has to be performed on the samples from the recipient and donor(s).
- HLA testing is challenging due to its high polymorphic nature and high levels of sequence homology between the loci
- Using conventional typing methods, Serology, SSP, SSO, and SBT, are laborious and time-consuming which may not resolve ambiguities between homologous regions at allelic resolutions
- Besides, different HLA loci share nucleotide sequences which are difficult to map with conventional techniques
- NGS allows a single nucleotide-based sequencing to derive an accurate map of each HLA gene loci
- MedGenome uses next-generation sequencing for HLA Typing
- The comparison between various techniques is as follows:
|Serotyping||Non-sequencing based typing method where antibodies specific to HLA proteins are used to identify the proteins on the cell surface.||– Low Cost – Rapid – Tradition||– Crude method – Protein-based detection – Inaccurate typing – Protein binding to more than one serotype|
|Sequence-Specific Oligonucleotide Hybridization (SSO)||Typing method where specific oligos are first designed for genes of interest and then hybridized to patient or donor DNA to check for hybridization.||– Checking of specific target – Efficient||– Cannot account for unrecorded alleles – Hybridization errors – Need to know the target sequence – Cannot phase|
|Sanger Sequencing||Sanger sequencing or Sequencing by Termination (SBT) is a classical method used for sequencing specific regions of the MHC.||– Used to sequence regions of interest target – Fast – Base pair resolution – Coverage only 2X||– Different HLA alleles share similar sequences difficulty aligning – Cannot phase|
|Next-generation Sequencing||Performing long-range PCR to amplify HLA genes in the MHC region, fragmenting the amplified genes.||– Deep coverage (1000x) – Total MHC coverage – Rapid high throughput – Accurate and efficient – Phasing||– Data Analysis|
Salient features of the test
- High throughput high-resolution HLA testing in 4 fields
- Reporting HLA A*, HLA B*, HLA C*, HLA DRB1*, HLA DQB1*, DPB1*- 6 locus
- Less ambiguous positions, more accurate typing
- CAP & ASHI PT participation
- NMDP codes being provided
Data yield from the test
- Identification of novel allele
- Detection of null alleles
- Identification of mismatches
- Detection of sequence variations that regulate expression levels
- The customized coverage of MedGenome’s high-resolution allele HLA testing Panel provides the highest level of resolution, eliminating the need for follow-up testing to obtain a confident typing result
- The HLA locus is sequenced with high-quality, paired-end 2 × 150 bp reads, enabling the use of dense polymorphisms to assign phase accurately. This allows unambiguous HLA typing results to be derived directly from the sequencing data
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