Identification of Novel Antigens with Induced Immune Response in MGUS.

Monoclonal gammopathy of undetermined significance (MGUS) is an indolent condition that may be modulated by various factors including immunologic responses directed at the monoclonal cells. Several evidences have supported the idea that the immune system, in patients with MGUS, may play a role in controlling the progression to myeloma (MM) and the identification of antigenic targets could open the way for future immunotherapeutic approaches to delay or prevent such progression. We have screened a cDNA expression library from primary myeloma cells and used Serological Analysis of Recombinant cDNA Expression Library (SEREX) to identify antigens that are recognized by antibodies in MGUS patients and therefore may be targets of the immune system and possibly involved in the pathogenesis of this disease. We used high dilution (1:500) serum from 3 MGUS patients with stable disease for 1 to 4 years and identified a panel of 11 novel antigenic targets eliciting an immune response. Antibody response appeared to be directed against intracellular proteins involved in apoptosis (SON, Hip1), DNA and RNA binding proteins (KIAA0530, GPATC4), signal transduction regulators (AKAP11), developmental proteins (OFD1), transcriptional co-repressors (IRF2BP2), proteins of the ubiquitin-proteosome pathways (PSMC1). We have further analyzed frequency of antibody response against these antigens in additional 26 MGUS sera, 10 newly diagnosed and 10 MM patients in remission after auto-transplant and 25 normal donors. We have observed antibody response against OFD1 (20.6 %); KIAA0530 (10.3%); AKAP11 (10.3%); and GPATC4 (6.8%) in patients with MGUS. Interestingly, 1/10 patients with newly diagnosed MM (10%) and 3/10 (30%) patients in remission after auto-transplant had an antibody response against OFD1 with evidence of increase in antibody titer in one patient after transplant suggesting its importance as a target. No significant antibody responses were observed against any of these antigens in the sera of 25 health donors. We have further focused our studies on OFD1, a protein developmentally expressed in adult human organs that colocalizes with γ-tubulin in the centrosome and has LIS1 homology motifs suggesting its contribution in regulation of microtubule dynamics. We have confirmed, by western blot analysis and RT-PCR, the expression of OFD1 in MM cell lines and lack of its expression in normal cells including normal BMSC. In addition some myeloma cell lines express different spliced variant of this protein. Specific T cell responses directed at OFD1 and its role in cell signaling are under investigation. These data open the possibility to identify target antigens that are important in the disease process of MGUS and may allow us to design future vaccines and immunotherapeutic approaches targeting these antigens in MGUS as well as in MM.