Indoleamine 2,3-dioxygenase 1 (IDO1), IDO2 and tryptophan 2,3-dioxygenase (TDO) represent some of the key immune regulators. Their increased activity has been demonstrated in a number of human malignancies but not yet in chronic myeloid leukemia (CML). In the present study, the activity of these enzymes was tested in 29 CML patients and 28 healthy subjects by monitoring the kynurenine (KYN)/tryptophan ratio. Serum samples taken prior to the therapy displayed a highly significant difference in KYN levels between the patient and control groups. However, increased KYN levels were detected in only 13 (44.8%) of these CML patients. The KYN levels in pretreatment sera of the patients correlated with the tumor burden. There was also a strong correlation between KYN levels and uric acid levels (UA). This suggests but does not prove the possible involvement of UA in activating IDO family of enzymes. Whenever tested, the increased KYN levels normalized in the course of the therapy. Patients with normal KYN levels in their pretreatment sera and subsequently treated with interferon-α, showed a transitory increase in their KYN levels. The present data indicate that CML should be added to the malignancies with an increased activity of the IDO family of enzymes and suggest that IDO inhibitors may be used in the treatment of CML patients.

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As cancer stem cells (CSCs) are resistant to chemotherapy, radiotherapy and targeted molecular therapy, immunotherapy of tumors could be aimed at their elimination. Markers specific for CSCs have not been identified to date, but microarray analyses have shown that CSCs and embryonic stem cells use similar transcriptional programs, thus suggesting the production of shared transcription factors. In this study, we developed an experimental DNA vaccine against the transcription factor Sox2 that is important for self-renewal of stem cells and is overexpressed in numerous human cancers. The Sox2 gene was codon optimized for the expression in human cells, its sequences encoding two nuclear localization signals (NLSs) were mutagenized, and the sequence coding for the PADRE helper epitope was fused with its 5' terminus. While codon optimization did not increase Sox2 production and mutagenesis in NLSs only partially reduced nuclear localization of Sox2, the addition of the PADRE epitope was crucial for the enhancement of Sox2 immunogenicity. The antitumor effect was shown after immunization against mouse oncogenic TC-1/B7 cells derived from the lung cancer cell line TC-1 and characterized by high Sox2 production. Sox2-specific reactivity in an ELISPOT assay was further augmented by the depletion of regulatory T (Treg) cells, but this depletion did not enhance the antitumor effect. These data demonstrated the induction of immune responses against the Sox2 self-antigen, but did not confirm the usefulness of Treg depletion when combined with antitumor vaccination.

Abstract. Therapeutic DNA vaccines against oncogenic infection with human papillomavirus type 16 (HPV16) are mostly targeted against viral oncoproteins E7 and E6. To adapt the E7 oncoprotein for DNA immunization, we have previously reduced its oncogenicity by modification of the Rb-binding site and enhanced immunogenicity of the modified E7GGG gene by the fusion with the 5'-terminus of the gene encoding E. coli ß-glucuronidase (GUS). In this study, we attempted to improve immunogenicity of the GUS-based anti-E7 vaccines by increasing the steady-state level of fusion proteins. We fused deletion mutants of E7GGG and codon-optimized E7GGG with the 5'-terminus of GUS and unaltered E7GGG with the 3'-terminus of GUS. Furthermore, we mutated the initiation codon of the GUS gene in the E7GGG.GUS construct, as GUS alone was produced from this fusion gene. We found that only the fusion of E7GGG with the 3'-terminus of GUS (GUS.E7GGG) and deletion mutants of E7GGG with the 5'-terminus of GUS increased the steady-state level of fusion proteins in transfected human 293T cells. Analysis of immune reactions induced in mice by vaccination via a gene gun showed that the increased steady-state level of fusion proteins resulted in augmented production of E7-specific antibodies, but did not enhance cellmediated anti-tumor immunity. Finally, we joined the signal sequence of the adenoviral E3 protein with GUS.E7GGG. This modification led to the predominant localization of the fusion protein in the endoplasmic reticulum and enhancement of CD8 + T-cell response, while antibody production was reduced. In conclusion, we found modifications of the E7GGG.GUS fusion gene that augmented either humoral or cell-mediated immune responses.

In DNA vaccination, CD4(+) T-cell help can be enhanced by fusion of a gene encoding an immunization protein with a foreign gene or its part providing T(h) epitopes. To study the effect of helper epitope localization in a protein molecule, the influence of the vicinity of the helper epitope, and the impact of chimeric protein cellular localization, we fused the helper epitope p30 from tetanus toxin (TT, aa 947-967) with the N- or C-terminus of the mutated E7 oncoprotein (E7GGG) of human papillomavirus type 16, enlarged the p30 epitope with the flanking residues containing potential protease-sensitive sites and altered the cellular localization of the fusion constructs by signal sequences. The p30 epitope enhanced the E7-specific response, but only in constructs without added signal sequences. After localization of the fusion proteins into the endoplasmic reticulum and endo/lysosomal compartment, the TT-specific T(h)2 response was increased. The synthetic Pan DR epitope (PADRE) induced a stronger E7-specific response than the p30 epitope and its stimulatory effect was not limited to nuclear/cytoplasmic localization of the E7 antigen. These results suggest that in the optimization of immune responses by adding helper epitopes to DNA vaccines delivered by the gene gun, the cellular localization of the antigen needs to be taken into account.