Characterization of tumor-associated B-cell subsets in patients with colorectal cancer.

PURPOSE: A precise understanding of the mechanisms by which human immune cell subsets affect tumor biology will be critical for successful treatment of cancer using immunotherapeutic approaches. Recent evidence suggests that B cells can both promote and inhibit the development and progression of tumors. The aim of this study was to characterize the composition of the B-cell infiltrates in colorectal cancers (CRC) in order to gain further insight into the role of B cells in CRC. EXPERIMENTAL DESIGN: In this study we characterized B-cell subsets in primary tumors (n=38), metastases (n=6) and blood (n=46) of 51 patients with a diagnosis of CRC and blood of 10 healthy controls. B-cell subsets were analyzed by flow cytometry or immunohistochemistry. RESULTS: Peripheral blood of CRC patients contained a higher percentage of memory B cells than that of age-matched healthy controls. Furthermore, the percentage of B cells within tumors was higher than that in the peripheral blood of CRC patients while metastases were typically devoid of tumor-infiltrating B cells. Tumor-associated B cells were enriched for activated and terminally differentiated B cells. Relevant proportions of regulatory B cells could only be detected in advanced cancer and metastases. CONCLUSION: B cells constitute a significant proportion of the immune infiltrate in CRC. The B-cell infiltrate of primary CRC is characterized by an accumulation of terminally differentiated memory B cells or plasma cells suggestive of a specific immune response against the tumor. However advanced tumors and metastases are also infiltrated by a considerable number of regulatory B cells.

Using CD40-activated B cells to efficiently identify epitopes of tumor antigens.

The rapid development of genomics and proteomics has accelerated the discovery of antigens that play a role in host-tumor interaction and can be potentially targeted in tumor immunotherapy. Several independent approaches to characterize such antigens and identify the relevant epitopes have been developed. However, the detection, expansion, and characterization of antigen-specific T cells are essential steps common to all strategies. Efficient identification of epitopes, in particular in a preclinical setting, is often hampered by lack of significant numbers of antigen presenting cells at sufficient purity that readily expand low-frequency T-cell precursors. Using the cylins as a model family of self-tumor antigens, we show that CD40-activated primary human B cells can be used very efficiently to identify novel epitopes and characterize such tumor antigen-specific T cells.