The ability of donor lymphocyte infusions (DLI) to induce complete responses (CR) in patients with relapsed multiple myeloma (MM) following allogeneic bone marrow transplantation provides clear evidence of graft-versus-myeloma (GVM) immunity. To identify GVM associated target antigens, we previously screened an MM cDNA expression library with post DLI serum from 5 MM patients who achieved CR after DLI. One of the antigens identified in the screening was dihydrolipoamide acetyltranferase the E2 component of the pyruvate dehydrogenase complex (PDC-E2). Using a phage plate assay, antibody reactivity against PDC-E2 was found in 2 of 9 MM and 1 of 5 chronic myeloid leukemia (CML) patients who achieved a CR after DLI. No antibodies were found before DLI, in 20 normal donors, 10 patients who underwent T-cell depleted allogeneic BMT, 6 MM DLI non-responders and 20 patients with chronic GVHD. Primary biliary cirrhosis (PBC) is an autoimmune liver disease in which more than 80% of patients have autoantibodies against PDC-E2. In patients with PBC the major immunogenic epitope of PDC-E2 has been mapped to the region associated with the inner lipoyl domain. To better characterize the antibody response in MM patients who had a CR after DLI a GST-PDC-E2 fusion protein was purified and used to quantify the antibody response by ELISA. Using this sensitive assay we found 1 additional MM DLI responder who had antibody reactivity against PDC-E2. Analysis performed at serial time points after DLI showed that reactivity persisted for 1.5 and 3 years after DLI in two MM patients and 3 years after DLI in the CML DLI responder. To map the antibody response after DLI and compare this to antibody reactivity in patients with PBC, we synthesized a series of 85 overlapping peptides covering the entire length of PDC-E2 and analyzed the specificity of the antibody response by ELISA. Using this assay, post-DLI serum was found to be reactive against 4 peptides located in the E2 catalytic domain of PDC-E2 but no reactivity was detected against peptides located in the inner lipoyl domain of the protein, the region commonly recognized by auto-antibodies in PBC. Analysis of serial samples showed that the antibody response persisted against these peptides up to 2–3 years after DLI but no reactivity was found pre-DLI and in normal serum. In conclusion we show that PDC-E2, a common auto-antigen in the autoimmune disease PBC, is also the target of an antibody response in patients with MM and CML who achieve a CR after DLI. The antibody response found after DLI is directed against a different region of the protein. Further studies characterizing T cell epitopes in these patients are underway and they will help to better characterize the immune response against PDC-E2 in patients after DLI.

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