I-15: Therapeutic Vaccination Strategies in Malignancies with Focus on B-CLL (Pages: 14-14)

Kokhaei P *,


A therapeutic strategy that may potentially delay progression or prevent relapse of B-cell chronic lymphocytic leukemia (B-CLL), is antileukemic vaccine therapy. This study focuses on comparing different strategies for loading antigen on dendritic cells (DC) with the aim of delineating the most effective antigen presentation platform for stimulating anti-leukemic T cells. We have studied different methods of loading DC with tumour preparations i.e. DC-tumour cell fusion, apoptotic tumour cells (Apo-DC), tumor cell lysate (DC-lysate) and total tumour RNA (DC-RNA). We examined autologous T cell activation by DC that had endocytosed leukemic B cell apoptotic bodies (Apo- DC) and compared it to the T-cell stimulatory capacity of DC that were fused with tumour cells. A T cell proliferative response was observed in four out of five CLL patients when using Apo-DC whereas fusion hybrids lacked the ability to elicit a proliferative response. Both preparations were able to induce an IFN-γ response. In the second phase of study the T cell stimulation capability of Apo-DC was compared with that of DC-RNA and DC-lysate. In all six CLL patients tested, Apo-DC induced greater HLA-restricted T-cell responses than DC pulsed with tumour lysate or RNA. ELISpot assay revealed high IFN-γ secretion by T-cells when Apo-DC was used to stimulate autologous T cells. Real-time PCR confirmed higher expression of IFN-γ and IL-2 mRNA in T-cells stimulated with Apo-DC. Our data suggest that cellular vaccines based on DC loaded with apoptotic bodies may be suitable for vaccination trial in patients with B-CLL. In the third study we investigated the feasibility of largescale generation of monocyte-derived DC from B-CLL patients as well as the effects of freezing and thawing on the function of DC loaded with autologous tumour cell preparations. Based on the results obtained from eight B-CLL patients, it appeared that the total yield of monocytic precursors, as well as the purity, was higher with immunomagnetic separation compared to counterflow elutriation. DC pulsed with autologous apoptotic tumour cells before cryopreservation retained their morphology, surface phenotype, as well as ability to stimulate T cell proliferation and cytokine production (IFN-γ). Our results demonstrate that monocyte precursors can be successfully isolated and that an adequate number of DC required for clinical therapy can be generated from blood. Finally we studied safety, immune and clinical effects of patients in phase I and Phase II clinical trial, Using a combination of leukapheresis and affinity based technologies (CliniMACS) for monocyte. enrichment. 16 patients were accrued in three different cohorts receiving Apo- DC alone, Apo-Dc + GM-CSF or Apo- Dc + GM-CSF +low dose CTX. Vaccination were well tolerated and increased leukemia specific immune response in 10/15 patients were observed. CD4+ CD25high FOXP+ regulatory T cells measured in one year follow up period were significantly lower in immune responder vs non-responders (p<000.1). Some patients were immunized for a long period of time and achieved a complete response in blood and a partial response in bone marrow.