Description of four new HLA alleles in the Finnish population: A*03:283N, A*68:167, C*03:327, C*03:361.

New HLA alleles found in the Finnish population: A*03:283N, A*68:167, C*03:327 and C*03:361.

Platelet donor selection for HLA-immunised patients; the impact of donor-specific HLA antibody levels.

BACKGROUND: Approximately 20% of patients with a recurrently poor platelet transfusion increment show human leukocyte antigen (HLA) alloantibodies. The aim of this study was to analyse the impact of mean fluorescence intensity (MFI) levels of donor-specific HLA antibodies and the feasibility of the HLAMatchmaker algorithm in donor selection. STUDY DESIGN AND METHODS: A total of 270 HLA-typed platelet transfusion responses of 40 patients were included in the study. The patients' immunisation status was determined with Luminex-based methods, and HLA alloantibody strengths were defined as the MFI. For the Matchmaker eplet matching, the HLA-ABC Eplet Matching Version 2.1 was used. RESULTS: In 62% of the 270 transfusions, HLA antibodies against the transfused platelets were present, with a median cumulative MFI level of 2026 (range: 299-29 203). In multivariate analysis, a cumulative MFI level higher than 1000 emerged as an independent risk factor for a poor platelet transfusion increment, along with infection and the age of the product. CONCLUSION: The HLAMatchmaker algorithm alone is not a sufficient tool for donor selection. Donor selection based primarily on the levels of donor-specific HLA antibodies is a preferable practice.

Conflicting HLA assignment by three different typing methods due to the apparent loss of heterozygosity in the MHC region.

Loss of heterozygosity (LOH) has been reported to cause false human leukocyte antigen (HLA) homozygous typing results in pre-transplant patients suffering from haematological malignancies, who in fact are HLA heterozygous. This poses a challenge for histocompatibility testing, as a stem cell graft from a genuinely HLA homozygous donor to a mistyped patient may lead to acute life-threatening graft-vs-host disease. LOH in the HLA region on chromosome 6 is known to be quite common in solid tumours, helping malignant cells to escape T-cell surveillance, but the incidence in haematological malignancies is less well known and the estimates vary. Here we report LOH in the HLA region of five patients with haematological malignancy. We found considerable differences in sensitivity between the three different HLA typing methods used in our laboratory: SSP was clearly the most sensitive method for detecting the lost haplotype, followed by rSSO, while SBT was the least sensitive technique. A subsequent, retrospective genotyping of 65 HLA homozygous haematological patients by SSP method showed no mistyped LOH cases in our laboratory in the past 10 years. The frequency of HLA homozygosity was found to be similar between haematological patients and control groups. It is important for an HLA laboratory to be aware of the differences in various HLA typing techniques' sensitivity for detecting an under-represented haplotype between HLA typing techniques when genotyping patients with haematological diseases. It is advisable for HLA laboratories to have at least two different methods with different sensitivities in their repertoire to be able to retype samples when a false homozygous result is suspected.

HLA antigen, allele and haplotype frequencies and their use in virtual panel reactive antigen calculations in the Finnish population.

The human leukocyte antigen (HLA) antigen, allele and haplotype frequencies of the Finnish population are quite unique because of a rather restricted and homogeneous gene pool. This has a strong influence on finding suitable donors for transplant patients; hence knowledge about the HLA frequencies of the patient population is essential. Here we report the HLA antigen frequencies for a large population sample and show high resolution HLA allele frequencies for 11 loci, including the rarely typed DPA1 and DQA1 loci. Furthermore, the most common Finnish high resolution haplotypes are presented for five HLA loci. The study shows that there are fewer HLA haplotypes in the Finnish population compared with mixed populations, and the common Finnish HLA haplotypes are more frequent. Using HLA antibody identification and panel reactive antibody calculations we show that a virtual population-specific panel, combined with single antigen testing, gives a more accurate and reliable estimate of the reactivity of the recipient serum against potential solid organ donors within the Finnish population. The results can be directly used to improve donor search for patients waiting for stem cell transplantation and to allocate highly immunised patients accurately to acceptable mismatch programs.