Antigen binding of human IgG Fabs mediate ERK-associated proliferation of human breast cancer cells.

Serum-circulating antibody can be linked to poor outcomes in some cancer patients. To investigate the role of human antibodies in regulating tumor cell growth, we constructed a recombinant cDNA expression library of human IgG Fab from a patient with breast cancer. Clones were screened from the library with breast tumor cell lysate. Sequence analysis of the clones showed somatic hypermutations when compared to their closest VH/VL germ-line genes. Initial characterizations focused on five clones. All tested clones displayed stronger binding to antigen derived from primary breast cancers and established breast cancer cell lines than to normal breast tissues. In vitro functional studies showed that four out of five tested clones could stimulate the growth of MDA-MB-231 breast cancer cell lines, and one out of five was able to promote MCF-7 cell growth as well. Involvement of ERK2 pathway was observed. By 1H-NMR spectra and Western blot analysis, it was evident that two tested antibody Fabs are capable of interacting with sialic acid. Our study suggests a possible role for human antibody in promoting tumor cell growth by direct binding of IgG Fab to breast tumor antigen. Such studies prompt speculation regarding the role of serum antibodies in mediating tumor growth as well as their contribution to disease progression.

Tumor lysate-specific cytotoxic T lymphocytes in multiple myeloma: promising effector cells for immunotherapy.

The idiotype protein, secreted by myeloma plasma cells, is a tumor-specific but weak antigen. Idiotype-based immunotherapy has been explored in myeloma patients with disappointing results. It is conceivable that myeloma cells contain a multitude of tumor antigens that can more effectively stimulate antitumor T cells. To explore the possibility of using whole myeloma cells as a source of tumor antigens for immunotherapy, the current study was undertaken to generate and examine the function of myeloma-specific cytotoxic T lymphocytes (CTLs) by using dendritic cells (DCs) pulsed with myeloma cell lysates as stimulating cells. After repeated stimulation, specific CTL lines, containing CD4(+) and CD8(+) T cells, were generated from myeloma patients. Our results show that these T cells not only recognized and lysed autologous myeloma protein-pulsed DCs, they also killed autologous primary myeloma cells. Occasionally, CTLs responded to autologous idiotype-pulsed DCs and to allogeneic primary myeloma cells. No cytolytic activity, however, was detected against autologous lymphocytes including B cells, suggesting that the T cells acted specifically against myeloma cells. Cytotoxicity against target cells was major histocompatibility complex class 1 and, to a lesser extent, class 2 restricted and was dependent mainly on the perforin-mediated pathway. CTLs secreted predominantly interferon-gamma and tumor necrosis factor-alpha on antigenic stimulation, indicating a type 1 T-cell subset. These findings represent the first demonstration that tumor cell lysate-primed CTLs kill only myeloma cells, not autologous lymphocytes. This provides a rationale for myeloma cell-based immunotherapy in multiple myeloma.

Malignancy: Idiotypic Immune Targeting of Multiple Myeloma.

Immunotherapy of malignant diseases remains a major therapeutic challenge. In multiple myeloma, interests have been focussed primarily on the targeting of the idiotypic protein since it represents one of the few tumor specific antigens. Various vaccination strategies have been employed, including the use of naked protein, protein conjugated to Keyhole Limpet Hemocyanin and, most recently, vaccine delivered via dendritic cells. Studies so far indicate the feasibility of inducing potentially beneficial idiotype-specific immune responses in the autologous hosts. However, the antitumor responses produced by the vaccines have been generally modest and sup-optimal. Further work is therefore ongoing to optimize the antitumor responses by including cytokines in the vaccination schedule. In addition, the development of a polyvalent vaccine is also being explored. The next few years should prove interesting and crucial in bringing effective and reliable immunotherapeutic strategies to the clinics.