CpG ODN are being actively investigated as cancer vaccine adjuvants because they mature plasmacytoid dendritic cells (pDC) into potent antigen-presenting cells. In addition, TLR ligands induce a broad range of other immunologic effects in pDC including the secretion of interferon α (IFNa) and chemokines which alter lymphocyte migration. Whether these CpG-ODN driven TLR ligand signals enhance antigen specific Immunity and/or trafficking In humans Is presently unknown. We evaluated the efficacy of the CpG-ODN, 1018-ISS, as a vaccine adjuvant given with GM-CSF to induce T cell immunity in humans to the tumor antigen hTERT. Seventeen patients with advanced solid tumors were treated with 6 cycles of GM-CSF (x 3d), CpG-ODN (escalating from 3mg - 100mg × 1d) followed by a peptide vaccine (a CD8 epitope from hTERT), in a Phase I dose escalation study. Surprisingly, only one of seventeen patients showed a detectable hTERT-specific tetramer T cell response. However, the majority of patients developed marked peripheral blood (PB) lymphopenia after CpG-ODN. Time-course flow cytometry analysis of PB revealed that CD8, CD4, NK and B cell counts were all depressed immediately after CpG-ODN. The effect was transient, with normal counts returning after a week, suggesting that CpG-ODN induced alteration in cell migration rather than cell death. To find further evidence for altered migration we examined vaccine sites. Clinically, vaccine sites showed significant swelling/induration within hours of CpG-ODN administration, though none was dose-limiting. Immunohistochemistry of vaccine biopsies showed significant, perivascular accumulation of CD4 and CD8 T cells clustered around CD123+ pDC. Biopsies after CpG-ODN, but not after GM-CSF, showed a marked increase in expression of MxA, an interferon-inducible gene suggesting that the local activation of pDC with resultant IFNa secretion. qRT-PCR confirmed significant increases in a panel of IFNa-inducible genes in the PB after CpG-ODN, indicating a systemic effect of IFNa secretion. Lastly, we showed directly that CpG-ODN markedly increased the ability of purified pDC to induce T cell migration in an in vitro transwell assay, demonstrating that CpG-ODN stimulation of human pDC not only induces IFNa, but also other chemokines that are sufficient to chemoattract T cells. Our results show that

  1. CpG-ODN with GM-CSF may not be an effective adjuvant strategy for peptide tumor vaccines; but

  2. sequenced GM-CSF/CpG-ODN causes a chemokine response that effects T cell migration to the peripheral tissues.

These findings suggest a role for CpG beyond that of a vaccine adjuvant as a mediator of lymphocyte migration, targeting immune responses to specific peripheral tissues. Therapeutic intratumoral GM-CSF/CpG-ODN injection could profoundly alter the local immunologic milieu, recruiting activated pDC and T cells to the tumor site, and tipping the balance towards an effective tumor-specific immune response.

Author notes

Disclosure:Employment: Drs. Kanzler and Coffman are employees of Dynavax technologies. Ownership Interests: Drs. Kanzler and Coffman own stock in Dynavax technologies.