Abstract 1924: The paraproteins of patients with familial MGUS / multiple myeloma (MM) target family-specific antigens: Experience with paratarg-7 and paratarg-8

Background: Antigenic targets of paraproteins in monoclonal gammopathy of undetermined significance (MGUS) and multiple Myeloma (MM) might play a role in the pathogenesis of these neoplasms by chronic antigenic stimulation. However, very few antigens have been identified, of which most were specific for one individual paraprotein only. In contrast, we recently described paratarg-7 (P-7), a protein of unknown function which is expressed in all human tissues as the target of 15% of IgA and IgG paraproteins in MGUS and MM (Grass et al. Lancet Oncology 2009; 10: 950-956). MGUS/MM patients with P-7 specific paraproteins all carry a hyperphosphorylated variant of P-7 (pP-7), which is inherited in a dominant fashion, explaining pP7-posistive cases of familial MGUS/MM. pP-7 is the first molecularly defined autosomal-dominant risk factor for MGUS/MM and is associated with the highest odds ratio (7.9) of all risk factors for MGUS/MM known to date. Since not all cases of familial MGUS/MM have a P-7 specific paraprotein, we set out to identify the antigenic targets of paraproteins in cases of familial MGUS/MM that are not carriers of pP-7. Methods: The sera of 28 members of a family with familial MGUS/MM (Lynch et al. N Engl J Med 2008;359:152-157) were tested for antibody reactivity against antigens represented in a fetal brain derived protein macroarray using a modified SEREX approach (Preuss et al. International J. Cancer 2009;125, 656-661). Results: Sera from 28 family members were analyzed. The sera of all 6 family members affected by MGUS (n=3) and MM (n=3) reacted with paratarg-8, which is encoded by the ATG13 gene, a member of the “autophagy regulatory complex” family of genes. The titers ranged from 1:107 to 1:108. No antibody reactivity was detected in the sera of non-affected family members nor in the paraproteins from >300 other patients tested. Conclusions: The paraproteins of members affected by familial MGUS/MM are directed against family-specific antigenic targets, suggesting that the genetic background shared by these patients entertains a chronic auto-immune response. Paratarg-7 and paratarg-8 are the first family-specific antigens that have been molecularly defined to date. Whether the antigen/paraprotein interaction is an epiphenomeon or invovled in the pathogenesis of familial cases of MGUS/MM can now be addressed using specific molecular tools. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was u