What is HLA Typing?
HLA stands for “Human Leucocyte Antigen,” which determines a person’s tissue type. Tissue typing is different from blood type.
Until recently, Preimplantation Genetic Testing (PGT) procedures were primarily used as a diagnostic method to identify genetic issues present in embryos. However, this method can now be used for therapeutic purposes as well. HLA typing on embryos is the most common application of PGT for therapeutic purposes.
In particular, in childhood diseases that can be treated with bone marrow or cord blood stem cell transplantation, when a suitable donor cannot be found within the family or close relatives, the combination of IVF and PGT allows for HLA typing on embryos to be performed.
How is HLA Typing Performed?
Embryos obtained through in vitro fertilization (IVF) in the context of assisted reproductive technology can be selected for transfer to the uterus based on their potential to be free from genetic diseases and their compatibility (HLA matching) with a sibling who requires stem cell transplantation.
After pregnancy and childbirth, stem cells are extracted from umbilical cord blood or bone marrow. These stem cells are then transplanted to the affected sibling, allowing them to regain their health. This approach is known as HLA typing on embryos. With HLA typing, families can have a healthy child even if they carry a genetic disease, while also ensuring the recovery of a sibling in need of treatment.
HLA typing on embryos is increasingly being preferred as a treatment approach, particularly for diseases where stem cell transplantation is possible, such as Thalassemia, Leukemia, Fanconi Anemia, and Wiscott Aldrich Syndrome. Finding a suitable donor in such cases can be extremely challenging, so giving birth to a “savior sibling” can save the life of the affected sibling.
How to Check for HLA?
In order to perform HLA typing on embryos, cell samples need to be obtained from the embryos during the pre-pregnancy period, which requires obtaining embryos through the process of in vitro fertilization (IVF).
In naturally conceived pregnancies, it is not possible to monitor the development of embryos before pregnancy. Therefore, HLA typing can only be done in the early stages of an established pregnancy.
Processes of HLA Typing
An HLA typing for embryos is not a standalone procedure; it is a process that needs to be planned in conjunction with IVF treatment. The stages of the process can be summarized as follows:
- Initial setup: Blood or tissue samples are collected from the couple and affected child to prepare for the genetic procedure at the embryo level.
- After the preparation phase, the couple is included in the IVF treatment program.
- With a controlled ovarian stimulation protocol, eggs are retrieved and fertilized with sperm obtained from the partner to create embryos.
- The obtained embryos are then analyzed for HLA compatibility with the affected sibling in terms of the specific genetic disease.
- The suitable embryos are transferred to the uterus to achieve pregnancy.
- The overall process typically takes around 2-4 weeks for genetic preparation, and around 3 weeks for IVF, embryo retrieval, genetic analysis, and embryo transfer.
The success rate of the treatment depends on the number and quality of eggs and embryos obtained during the IVF stage, as well as the presence of suitable embryos for genetic analysis.
Theoretically, it can be expected that around 25% of the analyzed embryos would be HLA compatible with the affected sibling. However, in the case of a single-gene disorder, this percentage may decrease to around 18%. These are general percentages, and the actual rates of finding suitable embryos and achieving pregnancy can vary significantly between couples.
During the process, if pregnancy is achieved and a healthy birth occurs, the cord blood stem cells or bone marrow stem cells can be collected from the newborn for the treatment of the affected sibling.
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