Presence of HLA-DR15, a Minor PNH Clone, or an Aplastic Anemia - Associated Autoantibody Do Not Predict a Favorable Response to Immunosuppressive Therapy in Children with Aplastic Anemia.

The pathogenenesis of aplastic anemia (AA) is thought to involve an autoimmune process. 60% to 70% of patients respond to immunosuppressive therapy (IST) with antithymocyte globulin (ATG) and cyclosporine (CyA). The presence of HLA-DR15 and a minor paroxysmal nocturnal hemoglobinuria (PNH) clone have been shown to be closely associated with a good response to IST in adult patients with AA. Recently, several autoantibodies associated with AA have been found in sera from AA patient based on a peptide library derived from fetal liver or leukemic cell lines. Anti-PMS1 antibody was found in 10% of Japanese pediatric patients with AA. The relevance of the antibody to the pathophysiology of AA and its clinical significance is unclear.

We evaluated the response rate among patients who showed the presence of HLA-DR15, a minor PNH clone, and anti-PMS1 antibody to identify potential predictive markers for response to IST.

Patients and Methods

Plasma samples and peripheral red blood cells (RBCs) were obtained from 103 children with AA who were enrolled in the AA-97 study conducted by the Japan childhood AA study group. We used immunoblotting to detect anti-PMS1 autoantibodies. A minor PNH clone was defined as positive when CD55−/CD59− RBCs in peripheral blood increased more than 0.037%, as quantified by high-sensitivity flow-cytometry assay.

Patients with very severe (n=53) or severe AA (n=28) received ATG (lymphoglobulin 15mg/kg/d for 5 days) and CyA (6mg/kg/d), and patients with non-severe AA (n=22) were randomized to receive only ATG or ATG plus CyA. A complete response (CR) was defined as a neutrophil count >1.5x10*8~10*9/L, a platelet count >10x10*8~10*9/L, and a hemoglobin level >11.0g/dl. A partial response (PR) was defined as a neutrophil count >0.5x10*8~10*9/L, a platelet count >20x10*8~10*9/L, and a hemoglobin level >8.0g/dl. Overall response was defined as a CR and PR 6 months after IST. Subgroup analyses were conducted and differences in overall response were tested using the Mann-Whitney U-test.

Results

A total of 103 patients (66 boys and 37 girls) were enrolled. Results of HLA-DR15 typing were available in 85 children. Median age at diagnosis was 8 years (range, 1 to 15 years). Of the 103 patients, 82 (79.6%) had idiophatic AA, 18 (17.5%) had hepatitis-associated AA, and 3 (2.9%) had AA from other causes. Fifty-eight patients (56.3%) attained CR and PR 6 months after IST.

HLA-DR15 was present in 22 of 85 children (25.9%). Of the 22 patients who shared the HLA-DR15, 10 (45.5%) achieved a response. Of the 63 patients who did not share HLA-DR15, 34 (54.0%) responded (p=0.62).

Minor PNH clone was positive in 20 of 103 children (19.4%). Of the 20 patients who had minor PNH clone, 14 (70.0%) responded to IST, whereas 45 of 83 patients (54.2%) without minor PNH clone responded (p=0.31).

Anti-PMS1 antibody was detected in 15 of 103 children (14.6%). Of the 15 patients who had anti-PMS1 antibody, 6 (40%) responded. Of the 88 patients without anti-PMS1 antibody, 52 (59.1%) responded (p=0.26). No differences in patient demographics, including gender, age, causes, and the severity of AA were observed among subgroups.

Conclusion

In our study, these 3 markers failed to identify a subset of AA patients who respond to IST. This finding may suggest a difference in pathophysiology between children and adults with AA.