A Phase I Study of Immunization of Indolent Non Hodgkin’s Lymphoma Patients with Autologous Monocyte-Derived Dendritic Cells Loaded with Heat Shocked and Killed Autologous Tumor Cells.

B-cell malignancies represent a potential target for anti-cancer vaccination programs due to the expression of tumor-specific antigens. Although immunization with tumor-derived idiotype protein is a frequently used procedure, vaccination with DCs loaded with killed tumor cells may activate response to a much wider range of antigens, without requiring prior molecular identification of such determinants. Furthermore, such DC-based vaccines could be available to all patients, irrespective of the HLA type. To evaluate the safety and tolerability of this approach, 18 patients with measurable relapse/refractory follicular (FCL; n= 12) and lymphoplasmocytoid (n= 6) lymphoma have been enrolled in a phase I study. Median prior number of treatment regimens was 2 (range 1–5) comprising 4 patients treated with high-dose chemotherapy supported by autologous stem cell transplantation. The vaccination was started after at least 6-months from the last chemotherapy treatment. All patients were evaluable for toxicity and 16/18 patients for efficacy with a median follow-up of 12.5 months (range 3–29 months). Each patient received 4 intradermal/subcutaneous injections at 2-weekly intervals of 50x10e6 tumor-loaded DCs. Immature DCs were generated by 5-days culture of autologous monocytes in the presence of IL-4 and GM-CSF. After selection by immunomagnetic technique, autologous CD19+ tumor cells, harvested from lymph nodes (n= 12) and/or peripheral blood (n= 6), were heat shocked and then irradiated by UVC. DCs were loaded for 48 hrs with killed tumor cells and then, to induce their maturation, were cultured for 12 hrs in the presence of TNF-alfa. Overall, vaccinations were well tolerated and no autoimmune reactions were observed. Mild erythema in the site of injection developed in the majority of patients (12/18), but only in 2 cases induration and extended erythema was observed. Six of 16 (37.5%) evaluable patients had objective responses. Two patients had partial responses (PR). One is still in PR and the other had a PR lasting 7 months. Four patients had complete remission (CR). Two patients are still in CR and the other 2 patients had a mean CR duration of 14.5 months. The remaining 10 patients had stable disease (n=5) or progressive disease (n=5). The overall monitoring of immune responses is ongoing. However, in one patient in PR, we evaluated the frequency of anti autologous tumor-specific T cells, by ELISPOT assay for IFN-gamma, on pathologic lymph nodes harvested before and after 2 months from the last vaccination. A significant increase of specific T-cell frequency was observed in the post-vaccination lymph node, compared to the tissue sample taken before vaccination. Moreover, evaluation of CD8+ T cell maturation markers, by analysis for CCR7 and CD45RA expression, indicated a shift of tumor-infiltrating T cells towards memory and effector stages in the lymph-node isolated after vaccination. In conclusion, injection of DCs loaded with killed tumor cells is a well-tolerated procedure achieving clinical and immunological responses also in the presence of significant tumor burden. However, further strategies, following DC-vaccination, are needed to ensure durable immune and clinical responses.