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Transfecting with in vitro transcribed, protein-encoding mRNA is a simple yet effective method to express high levels of the desired RNA-encoded proteins in primary cells. Cells can be transfected with antigen-encoding mRNA, which is translated into protein and is processed by the cellular antigen-processing pathway to generate antigen-presenting cells. Another elegant and increasingly popular application is to transfect cells with mRNA that encodes immune modulating molecules (cytokines, chemokines, toll-like receptors (TLRs), immune receptor ligands, immune receptor targeting antibodies) which, when translated into protein, can program cell behavior and/or function. In this chapter we describe an efficient method to deliver mRNA into human dendritic cells (DCs) by electroporation. This is currently the method of choice to deliver mRNA into antigen-presenting cells for generating vaccines for cancer immunotherapy.

Interferon (IFN)-γ plays an important role in immunity and anti-tumor activity. It is produced by lymphocytes, but was recently shown to be also produced by human myeloid dendritic cells (DCs). We have shown that human mature t(9;22) acute lymphoblastic leukemia-derived (ALL) DCs induced autologous cytotoxic T cell responses and therefore asked whether t(9;22) ALL-DC secreted IFN-γ. IFN-γ varied among three cell line-derived ALL-DCs; median production from seven patient ALL-DCs was 3450 pg/ml (range 1450-8675). IFN-γ production was dependent on maturation of ALL-DCs. This is the first demonstration of IFN-γ production by t(9;22) ALL-DCs., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

Ex-vivo-activated B cells are an alternative source of antigen-presenting cells (APCs) and a potential replacement for dendritic cells (DCs) in immunotherapy. However, the ability of ex-vivo-activated B cells to function as potent APCs has been a concern, especially when compared to DCs. Our study investigated whether modification of activated B cells with immune stimulatory molecules could enhance the ability of activated B cells to stimulate T cells. We show that murine splenic B cells, activated with a combination of Toll-like receptor agonist and agonistic anti-CD40, stimulated antigen-specific CD8+ T cells more efficiently than cells activated with Toll-like receptor agonist or anti-CD40 alone, probably by down-regulation of the immune regulatory cytokine interleukin-10 (IL-10). However, the activated B cells were still poor T-cell stimulators compared to mature DCs. Therefore, we modified the activated B cells by simultaneous electroporation of multiple messenger RNAs encoding costimulatory molecules (OX40L and 4-1BBL), cytokines (IL-12p35 and IL-12p40) and antigen. We found that de novo expression or overexpression of OX40L, 4-1BBL and IL-12p70 on activated B cells synergistically enhanced proliferation as well as IL-2 and interferon-gamma production by CD8+ T cells. Furthermore, the RNA-modified activated B cells induced antigen-specific cytotoxic T lymphocyte responses as efficiently as mature DCs in vitro. Unexpectedly, modified activated B cells were inferior to mature DCs at in vivo induction of CD8+ T-cell responses. In summary, activated B cells modified to express immune stimulatory molecules are a potent alternative to DCs in immunotherapy.

Dendritic-like cells from t(9;22) acute lymphoblastic leukemia (ALL) blasts can activate T cells, while the original unmodified leukemic blasts cannot. To determine whether these functional differences were associated with differences in antigen-processing machinery (APM) component expression, we have measured the level of APM component expression in unmodified blasts and ALL-derived dendritic-like cells. Seven t(9;22) ALL patient samples and one cell line were studied for APM component expression utilizing a unique panel of recently developed monoclonal antibodies and a recently developed intracellular staining technique. In addition, the HLA class I antigen cell surface expression was measured. HLA class I antigens were similarly expressed on the unmodified blasts and on the autologous dendritic-like cells. Intracellular HLA class I antigen and tapasin expression (P=0.03 for both) were upregulated in all t(9;22) ALL-derived dendritic-like cells, in comparison to the unmodified blasts. These results provide a potential mechanism for the ability of t(9;22) ALL-derived dendritic-like cells to induce T-cell activation and, suggest that tapasin upregulation may serve as a marker to standardize and monitor the quality of the dendritic-like cells used in immunotherapy.

We asked herein whether functional dendritic-like cells could be generated from t(9;22) acute lymphoblastic leukemia (ALL) blasts. We first determined that the combination of interleukin (IL)-1beta, IL-3, IL-7, tumor necrosis factor-alpha, stem cell factor and CD40 ligand was optimal for generating dendritic-like cells from t(9;22) ALL cell lines. Following 6 days in culture, four of five cell lines demonstrated dendrite-like morphology, upregulation of CCR7, CD54, CD80 and CD86, uptake of extracellular proteins and activation of T cells, and similar results were obtained with blasts from three t(9;22) ALL patients. The dendritic-like cells appeared to be composed of populations resembling both immature and mature dendritic cells (DCs), distinguished by CD80 expression. CD80-CD86+ cells were classified as immature DCs, demonstrating high endocytic capability and inducing minimal allogeneic T cell proliferation, while CD80+CD86+ cells were classified as mature DCs, exhibiting negligible endocytic capability and inducing robust allogeneic T cell proliferation. These mature dendritic-like cells induced autologous cytotoxic T cell responses against the unmodified blasts in a patient who achieved prolonged remission. In summary, CD80+CD86+ cells generated from t(9;22) ALL blasts may be useful in adoptive immunotherapy for t(9;22) ALL.