Adenovector engineered interleukin-2 expressing autologous plasma cell vaccination after high-dose chemotherapy for multiple myeloma - A phase 1 study

Eight multiple myeloma patients participated in a phase 1 trial evaluating the feasibility and safety of subcutaneous vaccination with adenovirus engineered, autologous plasma cells after high-dose therapy. Plasma cells were concentrated from bone marrow harvests by negative selection and high gradient magnetic separation. The mean plasma cell yield was 2.61 × 10⁸. Transgene expression measured 48 h after plasma cell infection with an IL-2 expressing adenovirus averaged 2.95 ng/ml/10⁶ cells. Vaccine production was successful for 88% of patients. Two months after high-dose therapy, six patients received from one to five injections of 3.5-9.0 × 10⁷ cells/vaccine. Vaccines were well tolerated with only minor systemic symptoms reported. Injection with tumor cells induced a local inflammatory response consisting predominantly of CD8⁺ and/or TIA-1⁺ T-lymphocytes. Myeloma specific anti-tumor responses, assessed by interferon-γ (IFN-γ) release and cytotoxic T cell killing of autologous tumor cells, were not enhanced after vaccination in one evaluable patient. Clinical response, manifested as a decrease in serum paraprotein, was not observed in the one patient who had measurable disease at the time of vaccination. These results demonstrate that the generation of adenovector modified plasma cell vaccines is technically feasible and can be safely administered post-transplant. Further studies of immunlogic and clinical efficacy are required.