Identification of HLA Class I Alleles in Patients with Paroxysmal Nocturnal Hemoglobinuria with Different Clone Sizes

Introduction Paroxysmal nocturnal hemoglobinuria (PNH) is a hematological disease characterized by complement-mediated hemolysis, thrombosis, and bone marrow failure. Human leukocyte antigen (HLA) evolutionary divergence and mutations were widely analyzed in aplastic anemia (AA). However, there were few studies in PNH thus far.

Methods Patients with newly diagnosed PNH at Peking Union Medical College Hospital (PUMCH) were recruited from April 2019 to April 2021 according to International PNH Interest Group standards. They were analyzed the genotypes of classical HLA class I loci (A, B, C) using whole-exome sequencing (WES). Patients were further stratified into four groups according to the clone size (Group A: <10%; Group B: 10% ≤ to ≤50%; Group C: 50% < to ≤80%; Group D: >80%) to identify the association between HLA class I alleles and PNH clone size.

Result Samples from 40 patients were enrolled, including 20 classic PNH and 20 bone marrow failure (BMF)/PNH. There were 29 males and 11 females. The median age was 32 years (range, 16-70). The median PNH clone size measured by flaer-granulocyte ratio was 72% (range 1-99%). Among the 59 identified alleles in PNH, HLA-B genotypes, which were reported to be associated with severe AA, accounted for the highest percentage (46%). A*02:01, the most common one and found in all the four groups, was reported as one of the risk alleles overrepresents in AA. The alleles found in group A were significantly different from those in group B, C, and D ( P = 0.004, 0.006, and < 0.001, respectively). But there was no significant difference between B, C, and D groups ( P > 0.05). 47% of the alleles identified in group A were reported in AA, whereas only 26%, 23%, and 26% of the detected alleles in Group B, C, and D were reported in AA, respectively. The other alleles in B, C, D groups were mainly for the susceptibility of autoimmune diseases or drug-related adverse reactions. Among them, HLA-B*46:01, the most common and found in B, C and D groups, may indicate weak antigen presentation and immune ability. B*44, B*57:01, C*07:01 were unique in Group B, B*38:02 were identified in Group C and HLA-B*27 expressed most in Group D, which were mainly on cell survival, drug hypersensitivity, and complement activation.

Conclusion

Significantly different alleles were observed between PNH with smaller clone sizes (< 10%) and PNH with larger clone sizes (≥10%). Patients with smaller clone sizes had similar HLA class Ⅰ alleles to AA; whereas those with larger clone sizes had numerous unique alleles which may contribute to the pathogenesis of PNH.

Keywords: paroxysmal nocturnal hemoglobinuria, human leukocyte antigens, clone size, class I allele, pathogenesis