A sustained response to low dose interferon-α in a case of refractory pure red cell aplasia

Acquired pure red cell aplasia (PRCA) may be the result of a cellular or humoral autoimmune process. One proposed mechanism is the destruction of erythroid progenitors by self-reactive, cytotoxic T cells or natural killer (NK) cells. These cells normally express MHC class I receptors (KIR) which inhibit cytotoxicity when the target cell expresses the HLA class I antigen(s) they bind. Therefore, loss of these antigens on maturing erythroid progenitors may render them susceptible to destruction by the pathogenic cells. Interferon-alpha (INF-alpha) increases HLA class I expression on hematopoietic precursor cells. Therefore, we initiated a trial of INF-alpha in a patient with refractory PRCA. Following treatment, he developed transfusion independence, and a sustained normal hematocrit. Analysis of bone marrow erythroid cells revealed an increase in expression of HLA class I molecules. INF-alpha should be used in a controlled trial in patients with PRCA to determine its activity and mechanism of action.