HLA Typing
HLA typing is a genetic test used to match patients and donors for bone marrow or cord blood transplants. HLA stands for human leukocyte antigen, which is a protein or marker found on most cells in the human body. The immune system uses these markers to recognize which cells belong to itself and which do not. HLA genes encode the human major histocompatibility complex (MHC) proteins, which are divided into MHC class I and MHC class II. HLA genes are located on chromosome 6p21 and are one of the most polymorphic gene families in the human genome, with more than 10,000 different HLA alleles identified so far. The polymorphism of HLA genes leads to differences in tissue compatibility and immune response ability among individuals. HLA genes are associated with transplant rejection, autoimmune diseases, vaccine pharmacogenomics, cancer, infectious diseases, and mate selection. The purpose of HLA typing is to determine the individual's HLA class I and class II gene polymorphisms, which provide the basis for transplant matching and disease association research.
Fig.1 Gaps in HLA typing technologies. (Liu C, 2021)
The Basic Principle, Main Method and Operation Process of HLA Typing
HLA typing is a genetic test used to determine an individual's HLA allele types, which provide the basis for transplant matching and disease association research. HLA typing can reflect the individual's tissue compatibility, that is, the degree of matching between HLA alleles of the transplant donor and recipient, as well as the individual's susceptibility and responsiveness to certain diseases and drugs.
The main methods of HLA typing are three: the serological method, the molecular biology method, and the chip-based method. The serological method is a method of determining HLA type by using specific antibodies to bind with HLA antigens and produce cytotoxic reactions, but it cannot distinguish between HLA and non-HLA antibodies. The molecular biology method is a method of amplifying HLA genes by using polymerase chain reaction (PCR) and other techniques and analyzing HLA gene sequences by using sequence-specific primers (SSP), sequence-specific oligonucleotide probes (SSO), restriction fragment length polymorphism (RFLP), or sequencing techniques, which can achieve high resolution. The chip-based method is a method of using a microarray chip with multiple fixed HLA-specific probes to hybridize with amplified HLA genes and determining HLA type by signal intensity, which can detect multiple HLA genes at the same time.
Table 1. Comparison of different HLA Typing methods
| HLA Typing method | Advantages | Disadvantages |
|---|---|---|
| Serological method | Simple, fast, cheap | Low resolution, cannot distinguish between HLA and non-HLA antibodies, limited by blood supply |
| Molecular biology method | High resolution, can detect newly discovered HLA alleles, not limited by blood supply | Complex, time-consuming, expensive, require specialized equipment and personnel |
| Chip-based method | High throughput, can detect multiple HLA genes simultaneously, not limited by blood supply | Medium resolution, cannot detect unknown HLA alleles, require specialized equipment and personnel |
The operation process of HLA typing generally includes five steps: sample collection, DNA extraction, HLA gene amplification, HLA allele typing, and result analysis. Sample collection is the collection of samples containing nucleated cells from patients or donors, such as peripheral blood, oral mucosal cells, or tissue sections. DNA extraction is used to extract high-quality DNA from samples for subsequent HLA gene amplification and typing. HLA gene amplification involves using PCR and other techniques to exponentially copy the target HLA gene region for subsequent detection and analysis. HLA allele typing is to use SSP, SSO, RFLP, sequencing, or chip techniques to analyze the sequence of amplified HLA genes and determine the individual's HLA allele type. Result analysis is to interpret and annotate the typing results according to the naming rules and databases established by the International Histocompatibility Working Group (WHO Nomenclature Committee for Factors of the HLA System).
Applications of HLA Typing
HLA Typing is a method of detecting an individual's HLA allele types that has a wide range of applications in transplant medicine and disease diagnosis and treatment. HLA Typing can help match transplant donors and recipients, improve transplant success rates, and reduce the risk of rejection and graft-versus-host disease. HLA Typing can also help discover HLA-related genetic diseases and immune diseases and provide the basis for diagnosis and treatment.
The applications of HLA Typing can be divided into three aspects: organ transplantation, hematopoietic stem cell transplantation, and disease diagnosis and treatment. Organ transplantation is a treatment method that transplants the donor's organ (such as a kidney, liver, heart, etc.) into the recipient's body to replace the recipient's organ with impaired function. Hematopoietic stem cell transplantation is a treatment method that transplants the donor's hematopoietic stem cells (such as bone marrow, peripheral blood, or cord blood hematopoietic stem cells) into the recipient's body to restore the recipient's normal hematopoietic function and immune function. Disease diagnosis and treatment are based on using HLA Typing to discover HLA-related genetic diseases and immune diseases, such as bare lymphocyte syndrome (BLS), macrophage activation syndrome (MAS), rheumatoid arthritis (RA), diabetes mellitus (DM), Behcet's disease (BD), etc., and provide the basis for diagnosis and treatment.
HLA Typing has a common goal in these three aspects: to improve the individual's quality of life and survival period. HLA Typing can help select the most suitable donors and recipients, thereby reducing the occurrence and severity of immune rejection and graft-versus-host disease and improving the transplant success rate and long-term survival rate. HLA Typing can also help evaluate the individual's susceptibility and responsiveness to certain diseases and drugs and provide guidance for personalized treatment.
References
- Baxter-Lowe LA. The changing landscape of HLA typing: Understanding how and when HLA typing data can be used with confidence from bench to bedside. Hum Immunol. 2021;82(7):466-477.
- Liu C. A long road/read to rapid high-resolution HLA typing: the nanopore perspective. Hum Immunol. 2021;82(7):488-495.
- CD Genomics. HLA Typing: Introduction, Methods, and Applications. https://www.cd-genomics.com/hla-typing-introduction-methods-and-applications.html
- Duke JL, et al. Determining performance characteristics of an NGS‐based HLA typing method for clinical applications. Hla. 2016;87(3):141-152.
- Carapito R, et al. Next-generation sequencing of the HLA locus: methods and impacts on HLA typing, population genetics and disease association studies. Hum Immunol. 2016;77(12):1016-1023.
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- Marsh SG, et al. Nomenclature for factors of the HLA system, 2010. Tissue Antigens. 2010;75(4):291-455.
- Wang L, et al. Development and application of a PCR-RFLP method for rapid identification of Fusarium oxysporum f.sp cubense race 4 based on the SNPs in the IGS region of rDNA. J Phytopathol. 2019;167(11-12):667-674.
