Human Leucocyte Antigen System and Selection of Unrelated Hematopoietic Stem Cell Donors: Impact of Patient-Donor (Mis)matching and New Challenges with the Current Technologies

HLA-DPB1 and DPA1 ~ DPB1 linkage mismatch affects the survival of recipients receiving HLA-14/14 matched unrelated donor HSCT

To analyse the effect of HLA-DPA1 and HLA-DPB1 allelic mismatches on the outcomes of unrelated donor haematopoietic stem cell transplantation (URD-HSCT), we collected 258 recipients with haematological disease who underwent HLA-10/10 matched URD-HSCT. HLA-A, -B, -C, -DRB1, -DQB1, -DRB3/4/5, -DQA1, -DPA1 and -DPB1 typing was performed for the donors and recipients using next-generation sequencing (NGS) technology. After excluding 8 cases with DQA1 or DRB3/4/5 mismatches, we included 250 cases with HLA-14/14 matching for further analysis. Our results showed that the proportion of matched DPA1 and DPB1 alleles was only 10.4% (26/250). The remaining 89.6% of donors and recipients demonstrated DPA1 or DPB1 mismatch. In the DPA1 matched and DPB1 mismatched group, accounting for 18.8% (47/250) of the cohort, DPB1*02:01/DPB1*03:01 allelic mismatches were associated with decreased 2-year OS and increased NRM. DPB1*02:02/DPB1*05:01 and DPB1*02:01/DPB1*05:01 mismatches showed no impact on outcomes. Moreover, the specific allelic mismatches observed were consistent with the DPB1 T-cell epitope (TCE) classification as permissive and non-permissive. We innovatively established an analysis method for DPA1 ~ DPB1 linkage mismatch for cases with both DPA1 and DPB1 mismatched, accounting for 70% (175/250) of the total. DPA1*02:02 ~ DPB1*05:01/DPA1*02:01 ~ DPB1*17:01 linkage mismatches were associated with lower 2-year OS, especially among AML/MDS recipients. DPA1*02:02 ~ DPB1*05:01/DPA1*01:03 ~ DPB1*02:01 linkage mismatches showed no impact on outcomes. In conclusion, applying the DPA1 ~ DPB1 linkage mismatch analysis approach can identify different types of mismatches affecting transplant outcomes and provide valuable insight for selecting optimal donors for AML/MDS and ALL recipients.

Detection of novel HLA alleles by Next-Generation Sequencing in the Croatian population

The introduction of Next-Generation Sequencing (NGS) methodology in the histocompatibility testing for both allo-HSCT and solid organ transplantation enables the sequencing of all HLA genes, which in turn leads to the discovery of many new HLA alleles. Over the last 3 years, we have identified 28 novel alleles (HLA-A*02:1079, A*03:01:01:112, A*11:01:01:83, A*11:01:01:87, A*24:595, A*68:01:01:15, B*07:02:01:107, B*08:01:01:67, B*08:01:01:69, B*13:02:01:25, B*15:01:82, B*15:18:08, B*18:01:01:76, B*27:02:06, B*27:05:02:34, B*40:06:01:17, B*40:517, C*04:01:01:173, C*04:477, C*05:276, C*07:01:01:130, C*12:03:80, C*12:03:01:62, DQA1*05:01:01:10, DPB1*13:01:07, DPB1*1146:01, DPB1*1456:01 and DPB1*1514:01) using the NGS method. The presented data emphasises the benefits gained by the utilisation of the NGS-based techniques in HLA genotyping but also provides new insight on the HLA polymorphism in the Croatian population.

A novel HLA-C*04 variant, HLA-C*04:01:01:174, identified in a healthy individual from Greece

HLA-C*04:01:01:174 differs from the HLA-C*04:01:01:06 allele by one nucleotide substitution in the intron 5.

An intermediate-sized donor registry experience: HLA barriers in matching procedures

The data enabling the estimation of the possibility of finding a matched unrelated donor (MUD) within a relatively short time is important for the success of hematopoietic stem cell transplantation (HSCT). In the present study, 738 unrelated Croatian patients in the program of unrelated HSCT were retrospectively analyzed for gender matching, donor origin (national or international), the distribution of HLA alleles and haplotypes, as well as for the probability of finding a 9-10/10 MUD. Almost 70% of the patients in our study group had a 10/10 MUD, while among the patients with a 9/10 MUD, a 1st field resolution level mismatched donor was selected for 55.0% of patients. The majority of pairs were HLA-A mismatched (33.8%). A comparison of HLA allele frequencies between two subgroups of patients revealed significant differences for 13 alleles. However, after p value correction, the difference in frequency remained significant only for four alleles; three HLA alleles (B*08:01, C*07:01, and DRB1*03:01) demonstrated a significantly higher frequency among patients with a 10/10 MUD (Pcorr < 0.0001, Pcorr = 0.0096, and Pcorr < 0.0001, respectively), while the B*35:08 allele was significantly more present among patients with a 9/10 MUD (Pcorr = 0.0328). The comparison of the distribution of HLA haplotypes between patients with a 10/10 MUD and patients with a 9/10 MUD showed significant differences for a number of two-locus and three-locus haplotypes, as well as for one five-locus haplotype (HLA-A*01:01~B*08:01~C*07:01~DRB1*03:01~DQB1*02:01), which was significantly more present in the group of patients with a 10/10 MUD. At least one HLA haplotype from the group of non-frequent HLA haplotypes (positions >1000) was carried by patients with a 9/10 MUD. The data obtained by the present study will contribute to a better estimation of the probability of finding a suitable 9-10/10 MUD for Croatian patients in need of HSCT.