CT Antigen-Specific Immune Response From DAC/DC Vaccine Correlates With Clinical Outcome In Patients With Relapsed Neuroblastoma

Neuroblastoma is the most common solid tumor in children in the first year of life. Despite high-dose chemotherapy, irradiation and autologous stem cell transplantation, nearly half of these patients relapse, a group for whom there are limited treatment options. The cancer-testis (CT) antigens MAGE-A1, MAGE-A3 and NY-ESO-1 are expressed on neuroblastoma cells in low levels and we have previously shown that the demethylating chemotherapy drug decitabine (DAC) can upregulate the expression of CT antigens in neuroblastoma. We developed a clinical study combining DAC to upregulate CT antigens followed by a dendritic cell (DC) vaccine targeting CT antigens MAGE-A1, MAGE-A3 and NY-ESO-1. Here we report the effects of DAC/DC vaccine in generating antigen-specific immune response and evaluate if there exists a correlation between development of antigen-specific immune responses and clinical responses. The treatment regimen includes 4 cycles of therapy, each consisting of DAC 10mg/m²/day for 5 days, followed by 2 weekly vaccinations consisting of autologous DC pulsed with overlapping peptide mixes derived from full length MAGE-A1, MAGE-A3 and NY-ESO-1. The number of DC administered in the vaccine was based on patient weight, and ranged from 3 to 10 x10⁶ cells. The topical TLR agonist imiquimod was used at the site of vaccination to facilitate immune responses to the vaccine. Peripheral blood was collected weekly to assess antigen-specific immune response. Peripheral blood mononuclear cells were archived at various time points, stimulated for 24 h with MAGE-A1, MAGE-A3 and NY-ESO-1 peptide mixes and studied for the presence of CD137⁺ antigen-specific cells by flow cytometry. The regimen was well tolerated and highly feasible. We were able to culture DC for 10/10 neuroblastoma patients enrolled on the study. Development of an antibody or a T cell response to the vaccine was defined as either new onset or a two fold increase in the level of antibodies or number of MAGE-A1, MAGE-A3 and NY-ESO-1 specific, CD137⁺ T cells over baseline levels. The clinical and immunological outcomes of seven neuroblastoma patients treated so far with the DAC/CT antigen vaccine is summarized in table 1. Two patients are in complete remission, one of whom is two years from completing therapy, and another patient is 9 months from therapy. Both these patients demonstrated an increase in the number of circulating CD3⁺CD8⁺CD137⁺ and CD3⁺CD4⁺CD137⁺ T cells against one of the CT antigens in the vaccine. Of the five patients who had disease progression, one had a partial response to his chemotherapy and radiation resistant tumor 2 months post-vaccine. This patient had an antibody response to these antigens post-vaccination but no CD8⁺ or CD4⁺ T cell response. Another patient who had no evidence of disease for 8 months following the last vaccine prior to disease recurrence had an antigen-specific CD8⁺ T cell response against MAGE-A1, MAGE-A3 and NY-ESO-1 antigens but no CD4⁺ T cell response. These data indicate that DAC/DC vaccine targeting MAGE-A1, MAGE-A3 and NY-ESO-1 are efficient in generating an antigen-specific immune response in four of seven patients studied and there exist a correlation between the presence of immune response and positive clinical outcome.

No relevant conflicts of interest to declare.