The sooner the better: Our laboratory experience with chorionic villus sampling (CVS) HLA typing prior to HSCT

Abstract

Aim Allogeneic Hematopoietic stem cell transplantation(HSCT) will prolong and improve the quality of life of babies born affected by inherited metabolic diseases. Genetic testing and preparation for a potential HSCT starts at 10 weeks of mother’s pregnancy. This study aims to describe our strategy to obtain an HLA typing from the minuscule tissue fragments submitted for HLA typing in preparation for an HSCT just after birth. Methods Mothers carrying babies that may be affected with Hurler or Krabbe A syndromes are the most frequent challenges at Duke Hospital. As needed, CVS is submitted to our laboratory and DNA is extracted using a micro method developed specifically for these samples to allow High Resolution HLA typing. Since maternal blood contamination of the CVS is a common finding, High Resolution HLA typing on the parents is also done to assist with the identification of all HLA alleles present on the CVS. Our laboratory sequencing strategy for HLA-A, B, C, DRB1 & DQB1 identifies most alleles in a hemizygous form and duplication of the same allele (potential homozygosis) is always resolved by both parents HLA typing. All positive SBT amplification reactions obtained for the CVS DNA are sequenced, and based on parents typing results we are able to identify, first the paternal haplotype present followed by the maternal one. The software SeqPilot®, used for high resolution data analysis, allows the analysis of all positive reactions chosen to be sequenced. Results The CVS samples we have tested (total of 20 cases) have provided the correct pool of alleles expected to be present and it facilitated cord blood searches for these unborn babies, providing an increased chance for successful treatment. Conclusions The HLA typing strategy we apply to CVS is only possible due to our level of expertise extracting DNA from small tissue fragments and the flexibility and data quality offered by the High Resolution HLA Typing methodology and software data analysis we use. The affected and genetic carrier unborn babies get a much higher chance at cure and survival when their diagnosis and treatment can be done earlier in their lives.