Detection of rearranged immunoglobulin DNA in plasma

Abstract

17518 Background: Tumor DNA is increasingly recognized as a marker in plasma or serum. B cells are characterized by immunoglobulin heavy chain rearrangements (IgH-R)and B cell malignancies by clonal IgH-R. We hypothesized that detection of clonal IgH-R DNA (a DNA spike) might reflect the presence of malignancy. Methods: We used a PCR and capillary electrophoresis. DNA from plasma of 6 healthy donors, 5 patients treated with rituximab, 5 persons with AIDS (PWA) but not lymphoma, 5 patients with AIDS-related lymphoma (ARL) and 5 patients with Hodgkin’s lymphoma (HL) was studied. In some cases matched peripheral blood mononuclear cells (PBMC) and followup specimens were available. Results: In plasma from healthy donors there was a normal (bell-shaped) distribution of IgH-R. In patients treated with rituximab (including a patient with an autoimmune disorder but no malignancy), IgH-R in plasma decreased by at least 100-fold. In PWA, there was a normal distribution of IgH-R. In pretreatment plasma from 2 of 5 patients with ARL, a DNA spike was detected superimposed on the background of IgH-R. The DNA spike was not detected in PBMC. In both ARL patients the spikes disappeared with therapy. However, in 1 it reappeared, and shortly thereafter the patient relapsed. Clinical relapse was associated with an increase in spike amplitude. The spike disappeared again with salvage chemotherapy. Identity of the pretreatment and relapse spikes was confirmed by sequencing. In 1 of 5 patients with HL a pretreatment DNA spike was detected in plasma. It decreased in serial specimens during the first month of combination chemotherapy. Conclusions: A normal distribution of rearranged Ig DNA is readily detected in plasma from healthy donors and patients. This normally distributed rearranged Ig DNA consistently disappears with rituximab therapy. A DNA spike can be detected in the plasma of some patients with B lineage lymphoma even when that spike is not evident in PBMC consistent with the possibility that this DNA is not derived from circulating tumor cells. The reappearance of a DNA spike may presage relapse. Further investigation will be required to determine the sensitivity and specificity of detection of such Ig DNA spikes and to confirm a tumor origin. No significant financial relationships to disclose.