Medullary carcinoma of the breast (MCB) is a morphologically and biologically distinct subtype of human breast cancer that, despite cytologically anaplastic features, has a more favorable prognosis than other types of breast cancer at similar stages of differentiation. It has been proposed that the improved clinical outcome is due, at least in part, to the presence of a prominent lymphoplasmacytic cell infiltrate in the tumor stroma. We studied the B lymphoplasmacytic cell infiltrates in MCB to determine the role of the antibody response produced by the local infiltrating cells. Oligoclonal predominance among tumor-infiltrating B cells in a panel of MCB patients was observed, suggesting that certain B cell clones were expanded, possibly in response to specific tumor-associated stimuli. IgG antibody phagedisplay libraries were generated from MCB-infiltrating lymphoplasmacytic cells of two patients, and MCB-reactive monoclonal antibodies were retrieved by selection on fresh-frozen MCB tissue sections. Analysis by mass spectrometry revealed that the antigen targeted by the dominant clones in the oligoclonal B lymphoplasmacytic response in both patients was not a cancer-specific antigen but the cytoskeletal protein ␤-actin. MCB exhibits an increased rate of apoptosis, and apoptotic MCB cells were shown to expose actin on the cell surface, permitting its recognition by the humoral immune system. Further, actin fragments, similar to those observed after cleavage with the apoptotic protease granzyme B, were observed in MCB tissue. Our results indicate that the major antibody response produced by tumorinfiltrating B lymphoplasmacytic cells are autoimmune in nature and a consequence of the perturbed state of increased MCB apoptosis caused by granzyme B-induced T cell cytotoxicity and͞or intrinsic cellular factors of MCB cells. medullary carcinoma of the breast ͉ oligoclonality ͉ antibody phage display libraries ͉ apoptosis ͉ human monoclonal antibodies T he immune response, upon manipulation, has been shown to be effective in combating cancer, but the role of the spontaneous immune response in controlling tumor growth and spread remains controversial. For most cancers, the immune system seems to have a limited effect, partially because of low immunogenicity and distortion of various effector functions of the infiltrating immune cells. Interestingly, however, some cancers possess prominent lymphoplasmacytic infiltrates associated with a favorable prognosis, suggesting that effective anti-cancer responses may develop spontaneously. Medullary carcinoma of the breast (MCB), a subtype constituting Ϸ3-7% of all breast cancers, is an example of such a tumor. MCB is characterized by a set of morphologic criteria originally defined by Ridolfi et al. (1), including well circumscribed borders, syncytial growth pattern with absence of glandular pattern, and lymphoplasmacytic cell infiltrates in the tumor stroma. Additionally, MCB cells have large pleomorphic nucleoli, increased mitotic rate, sparse necrosis, and no tubular component...

Tumor-infiltrating lymphoplasmacytic cells are a key feature of medullary carcinoma of the breast (MCB), a distinct subtype of human breast cancer that, despite cytologically anaplastic characteristics, has a more favorable prognosis than other types of breast cancer. Since it has been proposed that the improved clinical outcome is due at least in part to the presence of a prominent lymphoplasmacytic cell infiltrate in the tumor stroma, we recently examined the tumor-infiltrating B cell response in MCB and showed that it is oligoclonal and directed against an intracellular protein translocated to the cell surface upon MCB cell apoptosis. Human Abs cloned from MCB lymphoplasmacytic infiltrate-derived phage display libraries and reflecting the dominant part of the response were used to identify the target Ag as actin. Here, we have characterized in detail the cloned human IgG Abs and the translocation process of actin to the cell surface of apoptotic MCB cells. Our analysis shows that the cloned Abs bind specifically and with high affinity to actin, as determined by ELISA and surface plasmon resonance. Sequence analysis revealed that the Abs are highly somatically mutated, with high replacement to silent ratios, indicative of an Ag-driven, affinity-matured response. Interestingly, the tumor-infiltrating B cells in half the MCB patients mainly exhibited an IgG2 response, while IgG1 dominated in the others. To gain insight to the molecular events that may elicit such an Ab response, we examined the translocation of actin to the cell surface of apoptotic MCB cells using flow cytometry and laser scanning cytometry. Our results show that actin becomes exposed on the cell surface of a large proportion of apoptotic MCB cells as an early apoptotic event. We propose that the Ab response against actin produced by tumor-infiltrating B lymphoplasmacytic cells is Ag-driven, affinity-matured, and elicited due to the increased rate of apoptosis occurring within the MCB tumor that facilitates the translocation and proteolytic fragmentation of intracellular proteins.

An increasing number of studies suggest the importance of antibodies in the pathogenesis of most systemic and organ-specific autoimmune diseases, although there is considerable controversy over the precise role of the autoantibodies involved. In humans, a major obstacle to progress is the identification and cloning of the relevant autoantibodies and autoantigens. Here, an approach based on the sequential use of antibody phage display and antigen expression libraries is developed and applied to a donor suffering from rheumatoid arthritis (RA), splenomegaly, and peripheral destruction of neutrophils leading to neutropenia (Felty's syndrome). An antibody phage display library was constructed from bone marrow from the donor and a high-affinity human mAb, ANA15, selected by panning against fresh neutrophils and independently by panning against a fixed cell line. The antibody showed strong staining of neutrophils and a number of cell lines. Probing of a gt11 expression library from an induced myelomonocytic cell line with the mAb ANA15 identified the eukaryotic elongation factor 1A-1 (eEF1A-1) as a novel autoantigen. The specificity of ANA15 was confirmed by reactivity with both purified and recombinant eEF1A-1. Screening of a large panel of sera revealed that 66% of patients with Felty's syndrome had elevated levels of anti-eEF1A-1 antibodies. The cloning of this antibodyantigen pair should permit rational evaluation of any pathogenicity resulting from the interaction and its significance in neutropenia.antibody phage display ͉ cDNA expression libraries ͉ autoimmune neutropenia ͉ human mAb ͉ elongation factor 1A

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