A vaccine that boosts the immune response could improve the effect of conventional treatment with imatinib or interferon alfa for patients with chronic myeloid leukemia, according to an article in the February 19th issue of The Lancet.

Chronic myeloid leukemia develops when there is a breakage and swapping of DNA between chromosomes 9 and 22, resulting in a shortened chromosome called the Philadelphia chromosome. Cells with the abnormal chromosome make a protein that encourages aberrant growth and division. Patients are generally treated with imatinib or interferon alfa. Treatment with imatinib can lead to complete cytogenetic remission, where no Philadelphia chromosomes are detected during cell division. However, a complete molecular response, where there is no evidence of the protein produced by the Philadelphia chromosomes, is rare.

Monica Bocchia and her Italian colleagues tested whether a vaccine that targets a protein derived from the Philadelphia chromosome could help to eradicate the disease. The investigators enrolled 16 individuals (10 patients on imatinib and 6 on interferon) with stable, but detectable disease. Patients were given one dose (six injections) of the protein vaccine every two weeks while they continued their conventional treatment. Patients were assessed before vaccination and after three and six doses for evidence of the disease.

A total of 9 of 10 patients on imatinib showed progressive reduction of residual disease after three and six doses of the vaccine with 5 patients reaching complete cytogenetic remission. Furthermore, 3 of the 5 patients also obtained undetectable disease at a molecular level. Of the 6 patients on interferon alfa, 5 showed a reduction of stable disease during vaccinations, with 2 reaching complete cytogenetic remission.

Dr Bocchia commented, “Our preliminary data suggest that the addition of this vaccine to patients treated with conventional treatment might favor further reduction of the residual disease and increase the number of patients who reach a molecular response, the best surrogate of cure for those with chronic myeloid leukemia. Studies that focused on improving the assessment of residual disease after vaccination, including larger numbers of patients as well as longer follow-up are under way to assess definitively the role of this vaccine against leukemia.”

In an accompanying commentary Saswati Chatterjee and Dr K.K. Wong (and colleagues commented that although almost identical to other previous studies on this vaccine, Bocchia’s research is the first to show a clinical response.

Dr Chatterjee concluded, “Given the ease of administration, lack of toxicity, and early promise of efficacy, vaccine development against the fusion protein or other chronic myeloid leukemia-specific antigens appears to be a reasonable avenue for further investigation. In the meantime, we will eagerly await the results of disease free-survival in the vaccinated group and confirmatory studies by other investigators in the field.”