Induction of complete and molecular remissions in acute myeloid leukemia by Wilms' tumor 1 antigen-targeted dendritic cell vaccination

Abstract

Active immunization using tumor antigen-loaded dendritic cells holds promise for the adjuvant treatment of cancer to eradicate or control residual disease, but so far, most dendritic cell trials have been performed in end-stage cancer patients with high tumor loads. Here, in a phase I/II trial, we investigated the effect of autologous dendritic cell vaccination in 10 patients with acute myeloid leukemia (AML). The Wilms' tumor 1 protein (WT1), a nearly universal tumor antigen, was chosen as an immunotherapeutic target because of its established role in leukemogenesis and superior immunogenic characteristics. Two patients in partial remission after chemotherapy were brought into complete remission after intradermal administration of full-length WT1 mRNA-electroporated dendritic cells. In these two patients and three other patients who were in complete remission, the AML-associated tumor marker returned to normal after dendritic cell vaccination, compatible with the induction of molecular remission. Clinical responses were correlated with vaccine-associated increases in WT1-specific CD8+ T cell frequencies, as detected by peptide/HLA-A*0201 tetramer staining, and elevated levels of activated natural killer cells postvaccination. Furthermore, vaccinated patients showed increased levels of WT1-specific IFN-gamma-producing CD8+ T cells and features of general immune activation. These data support the further development of vaccination with WT1 mRNA-loaded dendritic cells as a postremission treatment to prevent full relapse in AML patients.

Conflict of interest statement

Conflict of interest statement: V.F.V.T. and Z.N.B. received patent (US7547551) support from Argos Therapeutics.

Figures

Fig. 1.

Induction of complete remission by DC vaccination in patients UPN08 (A) and UPN16 (B). The gray-striped bars indicate the periods of chemotherapy (CTx) administration with subsequent hematological recovery from bone-marrow aplasia (I, induction chemotherapy; C, consolidation chemotherapy; C1, first cycle; C2, second cycle). A detailed description of the administered chemotherapeutic regimens is provided in Table S1. The brown arrowheads indicate the time points of DC immunization; the first cycle consisted of four biweekly (biw) injections (4 × biw) followed by DTH immunomonitoring testing. Both patients achieved a complete remission after four biweekly DC vaccinations, as evidenced by normalization of the myeloblast percentage in the bone marrow (inserts) and WT1 mRNA expression levels (blue line). The horizontal dashed line represents the upper normal limit of WT1 mRNA expression in peripheral blood. In patient UPN16, DC therapy was accompanied by a transient thrombocytopenia (dotted green line). Note the refractoriness to chemotherapy with abnormally increased bone-marrow blast cell percentage and WT1 expression after the last chemotherapy course before DC vaccination. Patient UPN16 eventually relapsed in the bone marrow, and this relapse was preceded by molecular relapse as indicated by the loss of control of WT1 expression levels.

Fig. 2.

Longitudinal control of AML minimal residual disease with repetitive DC vaccinations in patient UPN06. The gray-striped bar indicates the time period for induction and consolidation chemotherapy (CTx; details in Table S1) and subsequent recovery from bone-marrow aplasia. The brown arrowheads indicate the time points of DC vaccination; the first cycle consisted of four biweekly injections (4 × biw) followed by DTH immunomonitoring. The kinetics of WT1 mRNA expression levels in peripheral blood are represented by the blue line, showing a normalization below the background threshold (horizontal dashed line) after chemotherapy and a first molecular relapse that was reversed with five successive DC vaccinations. Increases in WT1 mRNA expression were observed on several occasions and were consistently controlled by maintenance DC vaccine administrations on a bimonthly basis. This graph is also representative of similar observations in patient UPN01, with the difference that patient UPN01 relapsed molecularly (i.e., loss of control of WT1 mRNA expression levels) and subsequently, morphologically in the bone marrow.

Fig. 3.

Increase in WT1-specific IFN-γ–producing CD8+ T cells postvaccination. PBMC were restimulated using WT1 mRNA-electroporated mature DC for 1 wk. After 7 d, cultured PBMC were rechallenged using a WT1 peptide pool and assayed for intracellular IFN-γ production. Rechallenge with medium served as the negative control in all cases. Intracellular cytokine staining showed significantly higher percentages of IFN-γ–producing CD8+ T cells postvaccination compared with antigen stimulation of PBMC obtained prevaccination (P = 0.007) and compared with a medium control (P = 0.02; n = 9; insufficient cell numbers were available from patient UPN05 for culture and subsequent analysis).