Monitoring Immune Responses Following Vaccination with Autologous Dendritic like Leukaemia Cells.

It has been demonstrated that in a proportion of patients with Acute Myeloid Leukaemia (AML) their leukaemic blasts can be induced to differentiate into Dendritic Like Leukaemic Cells (DLLC) in vitro under the influence of GMCSF, IL-4 and TNF alpha. DLLC hold promise as cellular vaccines aimed at eradicating Minimal Residual Disease following successful induction of remission by chemotherapy. In A Phase I/II Multi-Centre Study we assessed leukaemic blasts of 21 patients with AML for their cytokine driven potential to differentiate into DLLC in vitro. 7 out of 21 (33%) patients showed DLLC conversion of their AML blasts based on morphological appearances and immunophenotype. 5 patients have completed chemotherapy and were then eligible to receive 4 escalating doses of subcutaneous DLLC vaccine. Immune responses to the administration of the vaccine are monitored by a combination of methods. The emergence of leukaemia specific T-cells following vaccination is demonstrated using Elispot assaying of Interferon gamma release in an in vitro re-stimulation assay. In WT1 expressing patients HLA-Tetramers allow to determine the frequency of WT1 specific T-cells. Regulatory T-cells (CD4/CD25 positive) are monitored by flow-cytometry. Monitoring of Minimal Residual Disease (MRD) is undertaken by means of real-time quantitative RT-PCR for leukaemia specific fusion transcripts or WT1 gene expression.

4 patients have so far completed the DLLC vaccination course. Vaccination was well tolerated with minimal side effects. A more than two-fold increase of leukaemia specific cytotoxicity was demonstrated following DLLC vaccination in one patient, while reduction of MRD was seen in several patients during the vaccination. The increase in CD4 /CD25 positive regulatory T-cells observed in several patients post vaccination may serve to dampen the induced anti-leukaemic immunity.