Vaccination with DC/Multiple Myeloma Fusions in Conjunction with Stem Cell Transplantation.

Autologous transplantation results in the transient reversal of tumor mediated tolerance due to the reduction in disease bulk, the depletion of regulatory T cells, and in the increased presence of tumor reactive lymphocytes during the period of lymphopoietic reconstitution. As a result, cancer vaccines are being explored as a means of targeting residual myeloma cells following stem cell transplant. We have developed a cancer vaccine in which patient derived tumor cells are fused with autologous dendritic cells (DCs). In this way multiple tumor antigens are presented in the context of DC mediated costimulation. We are conducting a study in which patients with multiple myeloma (MM) undergo stem cell transplantation followed by vaccination with 3 doses of DC/MM fusions. DCs were generated from adherent mononuclear cells cultured with GM-CSF and IL-4 for 5–7 days and matured with TNFa. DCs strongly expressed costimulatory and maturation markers. Myeloma cells were isolated from bone marrow aspirates and were identified by their expression of CD38, CD138, and/or MUC1. DC and MM cells were fused with polyethylene glycol as previously described and fusion cells were quantified by determining the percentage of cells that coexpress unique DC and myeloma antigens. To date, 19 patients have been enrolled and 18 have completed vaccine generation. Mean yield of the DC and myeloma preparations was 1.84 × 10⁸ and 8.3 × 10⁷ cells, respectively. Mean fusion efficiency was 40% and the mean cell dose was 4.3 × 10⁶ fusion cells. As a measure of their potency as antigen presenting cells, fusion cells prominently stimulated allogeneic T cell proliferation in vitro. Mean stimulation indexes were 12, 57, and 31 for T cells stimulated by myeloma cells, DCs, and fusion cells, respectively. Adverse events judged to be potentially vaccine related included injection site reactions, pruritis, myalgias, fever, chills, and tachycardia. Six patients have completed the follow up period and 3 patients are currently undergoing vaccination. All patients achieved a partial response to transplant. Three patients demonstrated resolution of post-transplant paraprotein levels following vaccination. One patient with highly aggressive disease who experienced disease progression in the early post-transplant period, demonstrated initial response and then stabilization of disease with vaccination. We are examining the effect of transplant and vaccination on measures of cellular immunity, anti-tumor immunity and levels or activated as compared to regulatory T cells. T cell response to PHA mitogen was transiently depressed post-transplant. In contrast, a transient increase was noted post-transplant in mean T cell expression of IFNγ in response to autologous myeloma cell lysate. In preliminary studies, a relative increase in the ratio of activated (CD4/CD25^low) to regulatory (CD4/CD25^high) T cells was observed. To date, all evaluable patients demonstrated evidence of vaccine stimulated anti-tumor immunity as manifested by a rise in IFNγ expression by CD4 and/or CD8+ T cells following ex vivo exposure to autologous tumor lysate. In this ongoing study, fusion cell vaccination in conjunction with stem cell transplantation has been well tolerated, induced anti-tumor immunity and clinical responses in patients with multiple myeloma.