Dendritic cell (DC) vaccination with low dose temozolomide phase I/II trial in melanoma patients: Preliminary data on peripheral blood regulatory t-cells (Treg) and DC-TEM8 expression modulations.

Abstract

e13029 Background: Cytolytic T lymphocytes (CTL) able to kill tumor cells are efficiently induced by Dendritic Cells (DC); however, immunosuppressive factors, as CD4+CD25+FoxP3+ T lymphocytes (T-reg) and TEM8 expression by DC, hamper efficient activation. After our experience of a vaccination trial using autologous mature DC (mDC) pulsed with autologous tumor lysate (ATL) and Keyhole Limpet Hemocyanin (KLH), in 2007 we started a phase I/II study with low-doses temozolomide (ldTMZ, given by Schering Plough Italy) before the vaccine in metastatic melanoma patients. Methods: TMZ 75mg/m2/day (maximum total dose 100mg/day) for 14 days (-14 to -1), DC Vaccination (day 0), and IL-2 3MUI/day s.c (days 2-5) q every 2 weeks for the first 4 vaccine and then monthly. Clinical and radiological evaluation as well as Delayed-type hypersensitivity (DTH) test for in vivo immunomonitoring were performed at basal and every 4 vaccinations. Circulating T-reg were evaluated at day -14, 0 and after IL-2. TEM8 expression in mDC (TEM8 mRNA ratio mDC vs immature DC) was investigated in 5 non progressing patients (NP) and in 7 progressing patients (PD) by QRT-PCR. Results: Up to September 2010, 17 patients were treated (5 females and 12 males, median age 57 years). Out of 15 evaluable patients 1 showed partial response (PR) of 6 months, 6 stable disease (SD) of 4,4,4,9,9,10 months and 8 progressed (PD), without major toxicities. All responders had positive DTH test, although weak in 1 patient with SD and in 3 patients with PD. TEM8 mRNA levels increased after iDC maturation, but no significant difference was found in mDC TEM8 expression mean fluorescence intensity between NP and PD. The absolute number of Treg (evaluated in 12 patients) decreased after TMZ treatment in 4 of the 6 PD patients and in all NP patients; however, after IL-2 administration, all patients except 4 of the 7 NP showed a rebound peak of Treg. Conclusions: These preliminary data suggest that ldTMZ may down-modulate T-reg population. Further investigations are needed to understand the role of T-reg and their relatively low growth after IL-2 administrations in NP patients.