Activated B lymphocytes and tumor cell lysate as an effective cellular cancer vaccine.

Cancer vaccines that utilize patient antigen-presenting cells to fight their own tumors have shown exciting promise in many preclinical studies, but have proven quite challenging to translate to clinical feasibility. Dendritic cells have typically been the cell of choice for such vaccine platforms, due to their ability to endocytose antigens nonspecifically, and their expression of multiple surface molecules that enhance antigen presentation. However, dendritic cells are present in low numbers in human peripheral blood and must be matured in culture before use in vaccines. Mature B lymphocytes, in contrast, are relatively abundant in peripheral blood, and can be quickly activated and expanded in overnight cultures. We devised an optimal stimulation cocktail that engages the B cell antigen receptor, CD40, TLR4 and TLR7, to activate B cells to present antigens from lysates of the recipient's tumor cells, precluding the need for known tumor antigens. This B cell vaccine (Bvac) improved overall survival from B16F1 melanoma challenge, as well as reduced tumor size and increased time to tumor appearance. Bvac upregulated B cell antigen presentation molecules, stimulated activation of both CD4+ and CD8+ T cells, and induced T cell migration. Bvac provides an alternative cellular vaccine strategy that has considerable practical advantages for translation to clinical settings.

Nuclear TRAF3 is a negative regulator of CREB in B cells.

The adaptor protein TNF receptor-associated factor 3 (TRAF3) regulates signaling through B-lymphocyte receptors, including CD40, BAFF receptor, and Toll-like receptors, and also plays a critical role inhibiting B-cell homoeostatic survival. Consistent with these findings, loss-of-function human TRAF3 mutations are common in B-cell cancers, particularly multiple myeloma and B-cell lymphoma. B cells of B-cell-specific TRAF3(-/-) mice (B-Traf3(-/-)) display remarkably enhanced survival compared with littermate control (WT) B cells. The mechanism for this abnormal homeostatic survival is poorly understood, a key knowledge gap in selecting optimal treatments for human B-cell cancers with TRAF3 deficiency. We show here for the first time to our knowledge that TRAF3 is a resident nuclear protein that associates with the transcriptional regulator cAMP response element binding protein (CREB) in both mouse and human B cells. The TRAF-C domain of TRAF3 was necessary and sufficient to localize TRAF3 to the nucleus via a functional nuclear localization signal. CREB protein was elevated in TRAF3(-/-) B cells, without change in mRNA, but with a decrease in CREB ubiquitination. CREB-mediated transcriptional activity was increased in TRAF3-deficient B cells. Consistent with these findings, Mcl-1, an antiapoptotic target of CREB-mediated transcription, was increased in the absence of TRAF3 and enhanced Mcl-1 was suppressed with CREB inhibition. TRAF3-deficient B cells were also preferentially sensitive to survival inhibition with pharmacologic CREB inhibitor. Our results identify a new mechanism by which nuclear TRAF3 regulates B-cell survival via inhibition of CREB stability, information highly relevant to the role of TRAF3 in B-cell malignancies.

PTEN redundancy: overexpressing lpten, a homolog of Dictyostelium discoideum ptenA, the ortholog of human PTEN, rescues all behavioral defects of the mutant ptenA-.

Mutations in the tumor suppressor gene PTEN are associated with a significant proportion of human cancers. Because the human genome also contains several homologs of PTEN, we considered the hypothesis that if a homolog, functionally redundant with PTEN, can be overexpressed, it may rescue the defects of a PTEN mutant. We have performed an initial test of this hypothesis in the model system Dictyostelium discoideum, which contains an ortholog of human PTEN, ptenA. Deletion of ptenA results in defects in motility, chemotaxis, aggregation and multicellular morphogenesis. D. discoideum also contains lpten, a newly discovered homolog of ptenA. Overexpressing lpten completely rescues all developmental and behavioral defects of the D. discoideum mutant ptenA-. This hypothesis must now be tested in human cells.