Comparative analysis of cancer vaccine settings for the selection of an effective protocol in mice.

Background: Cancer vaccines are considered a promising therapeutic approach. However, their clinical results are
not yet satisfactory. This may be due to the the difficulty of selection of an efficient tumor associated antigen (TAA)
and immunization protocol. Indeed, the weak antigenicity of many TAA impairs the design of robust procedures,
therefore a systematic analysis to identify the most efficient TAA is mandatory. Here, we performed a study to
compare different gp100 vaccination strategies to identify the best strategy to provide a 100% protection against
experimental melanoma in a reproducible manner.
Methods: C57BL/6J mice were challenged subcutaneously with B16F10 melanoma cells, after vaccination with: a)
mouse or human gp10025-33 peptide plus CpG adjuvant; b) mouse or human gp100 gene; c) mouse or human
gp10025-33 peptide-pulsed dendritic cells (DC). Alternatively, a neutralizing anti-IL-10 monoclonal antibody (mAb)
was subcutaneously administered at the site of tumor challenge to counteract regulatory cells. Finally,
combinatorial treatment was performed associating human gp10025-33 peptide-pulsed DC vaccination with
administration of the anti-IL-10 mAb.
Results: Vaccination with human gp10025-33 peptide-pulsed DC was the most effective immunization protocol,
although not achieving a full protection. Administration of the anti-IL-10 mAb showed also a remarkable protective
effect, replicated in mice challenged with a different tumor, Anaplastic Large Cell Lymphoma. When immunization with
gp10025-33 peptide-pulsed DC was associated with IL-10 counteraction, a 100% protective effect was consistently
achieved. The analysis on the T-cell tumor infiltrates showed an increase of CD4+granzyme+ T-cells and a decreased
number of CD4+CD25+Foxp3+ Treg elements from mice treated with either gp10025-33 peptide-pulsed DC vaccination
or anti-IL-10 mAb administration. These data suggest that processes of intratumoral re-balance between effector and
regulatory T cell subpopulations may play a critical protective role in immunotherapy protocols.
Conclusions: Here we demonstrate that, in the setting of a cancer vaccine strategy, a comparative analysis of different
personalized approaches may favour the unveiling of the most effective protocol. Moreover, our findings suggest that
counteraction of IL-10 activity may be critical to revert the intratumoral environment promoting Treg polarization, thus
increasing the effects of a vaccination against selected TAA.