LRPAP1 Is a Frequent B-Cell Receptor Antigen in Mantle Cell Lymphoma (MCL)

Introduction: Chronic antigenic stimulation may play an important role in the pathogenesis of malignant lymphomas. Although most MCL cases are believed to have an antigen-naive B cell as cell of origin, overrepresentation of certain VH genes has been reported. Therefore we screened BCRs from MCLs for possible antigens.

Methods: BCRs were expressed as recombinant Fabs based on corresponding pairs of functional variable region heavy and light chain genes, which had been amplified from isolated genomic DNA of snap-frozen MCL specimens and established MCL cell lines. The purified BCR-Fabs were checked for binding to proteins expressed on macroarrays of human cDNA expression libraries and on bacterial lysates. In addition, sera from patients with MCL were screened for antibodies against respective BCR antigens.

Results: The recombinant MCL-BCR derived Fabs from 9 patients and of four established MCL cell lines were tested on protein arrays. Recombinant lymphoma-BCR-derived Fabs from 4/9 patients and from 1/4 MCL cell lines reacted with human low density lipoprotein receptor-related protein associated protein 1 (LRPAP1). Specific secondary modifications of LRPAP1 explaining its autoimmunogenicity were not found. 8/30 patients with MCL had anti-LRPAP1-antibodies in their serum, which was the case in only 1/200 healthy controls. Finally, LRPAP1 specifically induced proliferation of Maver1 cells that express a BCR with specificity for LRPAP1.

Conclusions: LRPAP1 is the first molecularly defined antigenic target of MCL-BCRs. The high frequency of LRPAP1-reactive BCRs in MCL suggests a role of LRPAP1 in the pathogenesis of MCL, even in cases with unmutated VH genes. The prevalence of LRPAP1-antibodies in MCL patients and healthy controls identifies LRPAP1-antibody as the first serologic risk factor for MCL (odds ratio: 72.36)

Supported by Wilhelm-Sander-Stiftung