OFD1-Mediated T Cell Responses in MGUS Patients: Implications for Immunotherapy.

We have identified a panel of 11 novel antigens with induced antibody response in patients with Monoclonal Gammopathy of Undetermined Significance (MGUS) by screening a Multiple Myeloma (MM) cDNA library with patient serum using Serological Analysis of Recombinant Expression cloning (SEREX). Among these antigens, a specific antibody response against OFD1 protein was observed in 6/29 (20.6%) MGUS patients, while 0/12 newly diagnosed, 1/11 (8.3%) relapsed and 3/11 (27.2%) post-transplant MM patients in complete or partial remission showed an antibody response against this protein. Interestingly, in 1 of these patients the antibody response appeared only after autologous transplantation. No responses were observed in 25 healthy donors. OFD1 is widely expressed in embryonic stage with important role in organogenesis; however its expression decreases significantly in adult tissues. Moreover, OFD1 that is involved in the functional regulation of the Hedgehog-pathway, is dysregulated in solid tumors, suggesting a potential role in the tumorigenesis. We have observed the OFD1 expression at high levels in all 11 MM cell lines and 4 primary MM patient cells tested as compared with low or no expression in PBMC and normal bone marrow stromal cells. Specific sequences, derived from three clones corresponding to three different parts of OFD1 protein, were used to identify 15 peptides with potential binding to HLA-A*0201 and selected two peptides (3 and 8) on the basis of their high binding affinity. We observed presence of OFD1 specific CD8+ T cells, as measured by HLA-A2+ pentamers, on all 6 HLA2-A2+ MGUS patients tested. Presence of these cells was also observed in 5 MM patients. However, T cell proliferation following incubation with OFD1 peptides for 7days was observed only in MGUS (=6) while T cell proliferation was not observed in MM (n=5) patients indicating intact OFD1-specific responses in MGUS as compared with MM. These results highlight a possible role of OFD1 in the immune regulation in MGUS and provide the framework for further evaluation of OFD1 as a new potential target for immunotherapeutic approaches in both MGUS and MM.