Optimizing dendritic cell-based immunotherapy in multiple myeloma

Summary. Vaccination with idiotype protein-pulsed dendritic cells (DCs) has been explored in multiple myeloma and the results have been disappointing. These studies used immature DCs, which are less potent at activating T cells and could differentiate to macrophages once the cytokines were withdrawn. After intravenous administration, DCs accumulate in the lungs and liver for up to 48 h, thus reducing their potential to migrate to lymphoid organs and interact with T cells. To improve the efficacy of DC vaccination in myeloma, we investigated the use of idiotype-pulsed mature DCs administered subcutaneously. Five patients (three IgG and two IgA myeloma) with stable partial remission following high-dose chemotherapy were enrolled. DC vaccines were administered three times at 2-week intervals at least 4 months post transplantation. Idiotype-specific T-cell responses, detected using enzyme-linked immunospot (ELISPOT) (four patients) and proliferation (two patients) assays, were elicited in four and anti-idiotypic B-cell responses in all five patients. The cytokine-secretion profile of activated T cells demonstrated a type-1 response. A 50% reduction in serum M-component was observed in one immunologically responding patient that persisted for 6 months and stable disease (for 6 months) resulted in the other three patients. The remaining patient without an immune response to the vaccination relapsed. No major side-effects were noted. Thus, subcutaneous administration of idiotype-pulsed mature DCs induced idiotype-specific T- and B-cell responses. Current efforts are geared towards optimizing the conditions of DC generation and administration, and the development of in vitro assays to monitor the cytotoxicity of the T cells.