We previously demonstrated that autologous dendritic cells that have endocytosed apoptotic bodies of chronic lymphocytic leukemia (CLL) cells (Apo-DC) can stimulate antileukemic T cell responses in vitro. In this phase I study, we vaccinated 15 asymptomatic CLL patients at five time points with Apo-DC administered intradermally either alone (cohort I), or in combination with subcutaneous granulocyte-macrophage-colony-stimulating-factor (GM-CSF) (cohort II) or with GM-CSF and intravenous low-dose cyclophosphamide (cohort III). Aim of the study was to evaluate the safety and immunogenicity of Apo-DC alone or in combination with GM-CSF and low-dose cyclophosphamide in CLL patients. All patients completed the vaccination schedule without dose-limiting toxicity. No objective clinical responses were seen. Vaccine-induced leukemia-specific immune responses were evaluated by IFN-γ ELISpot and proliferation assays over a 52 weeks observation period and immune response criteria were defined. According to these criteria, 10/15 patients were defined as immune responders. The frequency of immune-responding patients was higher in cohorts II (3/5) and III (5/5) than in cohort I (2/5). In order to further characterize the induced immune response, estimation of secreted cytokines and CD107-degranulation assay were performed. Clustering of T and CLL cells was observed in CD107-degranulation assay and visualized by confocal microscopy. Additionally, assessment of regulatory T cells (T(regs)) revealed their significantly lower frequencies in immune responders versus non-responders (P < 0.0001). Cyclophosphamide did not reduce T(regs) frequency. In conclusion, vaccination with Apo-DC + GM-CSF and cyclophosphamide was safe and elicited anti-CLL immune responses that correlated inversely with T(regs) levels. Lack of clinical responses highlights the necessity to develop more potent vaccine strategies in B cell malignancies.

Summary. Tumour-specific CD4þ T helper (Th) and CD8 þ T cytotoxic (Tc) cells may participate in the control and eradication of tumour cells. In the present study, idiotypespecific stimulation of CD4 þ and CD8 þ blood T cells from patients with monoclonal gammopathy of undetermined significance and patients with untreated multiple myeloma stage I was examined. Activation was measured in the CD4 þ and CD8 þ subsets enriched by magnetic microbeads as the incorporation of 3 H-thymidine and the secretion of interferon (IFN)-g, interleukin (IL)-2 and IL-4 by single cells using the enzyme-linked immunospot assay. Idiotype-specific T cells were found in four of seven patients. Stimulation was mainly confined to the CD4 þ subset in three of the four responding patients. This type of response was major histocompatibility complex (MHC) class II restricted as it could be inhibited by monoclonal antibodies against MHC class II (HLA-DR), but not against class I (HLA-ABC) molecules. Idiotype-specific CD8 þ T cells were also demonstrated in these patients although at a lower frequency. One patient showed a strong and dominating activation of CD8 þ T cells which could be blocked by antibodies against HLA-ABC but not against HLA-DR. Idiotype-specific CD4 þ or CD8 þ T cells were mainly of the type-1 subsets as judged by their secretion of IFN-g and IL-2. Thus, this study provides evidence for the presence of idiotype-specific and MHCrestricted CD4 þ and CD8 þ T cells of the type-1 subsets in patients with monoclonal gammopathies. Such T cells with the potential to control the growth of tumour B cells may be a suitable target for immunotherapeutic interventions in patients.

No abstract

No abstract