Haematopoietic regeneration by HLA-A*0206-deficient clones in severe aplastic anaemia without definitive immunosuppressive treatment.

We describe the case of a 74-year-old man with severe aplastic anaemia who experienced persistent remission attributed to proliferation of HLA allele-deficient clones. Despite an initial worsening of pancytopenia with eltrombopag and ciclosporin treatment, gradual trilineage haematopoietic recovery occurred, with blood counts normalizing over 3 years. Flow cytometry and deep nucleotide sequencing revealed that haematopoiesis was primarily supported by several clones with somatic mutations that inactivated antigen presentation via HLA-A*0206. This suggests that monitoring haematopoietic regeneration by immune escape clones could be an alternative approach for immune aplastic anaemia patients who possess HLA allele-deficient clones and cannot tolerate standard therapy.