Efficacy of Peptide (WT1) and Peptide(PRI) Vaccination for Patients With Low Risk Myeloid Malignancies

Leukemias and the related disorders myelodysplastic syndrome and myeloproliferative diseases represent a wide group of bone marrow stem cell malignancies. Some patients can be cured with chemotherapy or by allogeneic stem cell transplantation. However standard treatment approaches are not effective for patients who become refractory to chemotherapy, those who relapse after transplantation and those with progressive disease. The management of such patients remains unsatisfactory and requires new treatment approaches other than chemotherapy.

The immunological graft-versus-leukemia (GVL) effect seen after allogeneic stem cell transplantation suggests that stimulating the patient's own T cell responses to MDS and leukemia with a vaccine might also retard disease progression and even achieve disease remissions. Peptide (WT1) and peptide (PR1) were identified as target antigens because both antigens are highly expressed by cluster of differentiation 34 (CD34) plus stem cells of most patients with myeloid malignancies but not by normal marrow cells. An immunotherapeutic approach to vaccinate against PR1 and WT1 antigens could induce T cell response against MDS and leukemic cells while sparing normal cells and by using a combination of two antigens the risk of disease escape by antigen down regulation should be further diminished. Indeed in a safety study of one dose of a combination of peptide (PRl) and (WT1) vaccination, we demonstrated that immunological response against one or both vaccines could be induced in all subjects who were vaccinated. This immunological response was associated with a transient reduction in the leukemia burden. Furthermore the vaccine combination was well tolerated.

Therefore we propose this Phase II trial, the third in a series of planned peptide vaccine research protocols, which will evaluate the safety and efficacy associated with an immunotherapy approach using two peptide vaccines, namely PR 1 : 169- 177 and WT-1: 126-1 34 in Montanide adjuvant, administered concomitantly with GM-CSF (Sargramostim), every 2 weeks for 10 weeks (6 doses WT1 plus 6 doses PRl plus GM-CSF) in select patients diagnosed with MDS, AML or CML. Subjects with immunological response to one or both peptide vaccines will have the option of receiving an additional 6 boosters of the WT-1:126-135 and PR1:169-177 peptide vaccines at 3 monthly intervals.

The primary objective will be to evaluate the efficacy and toxicity associated with 6 doses of a combination of WT-1: 126-134 and PRl: 169-177 peptide vaccines in Montanide adjuvant administered concomitantly with GMCSF (Sargramostim) in selected patients with myeloid malignancies (MDS, AML, CML).

The primary endpoint will be immune response (studying changes in the frequencies of circulating PR1 and WT1 specific T cells) which will serves as a surrogate for evaluating for the efficacy of the study.