Comparison of CTL reactivity in the spleen and draining lymph nodes after immunization with peptides pulsed on dendritic cells or mixed with Freund's incomplete adjuvant

CTLA-4 blockade during dendritic cell based booster vaccination influences dendritic cell survival and CTL expansion

Dendritic cells (DCs) are potent antigen-presenting cells and critical for the priming of CD8+ T cells. Therefore the use of these cells as adjuvant cells has been tested in a large number of experimental and clinical vaccination studies, in particular cancer vaccine studies. A number of protocols are emerging that combine vaccination with CTL expanding strategies, such as e.g. blockade of CTLA-4 signalling. On the other hand, the lifespan and in vivo survival of therapeutic DCs have only been addressed in a few studies, although this is of importance for the kinetics of CTL induction during vaccination. We have previously reported that DCs loaded with specific antigens are eliminated by antigen specific CTLs in vivo and that this elimination affects the potential for in vivo CTL generation. We now show that CTLA-4 blockade increases the number of DC vaccine induced LCMV gp33 specific CTLs and the lysis of relevant in vivo targets. However, the CTLA-4 blockage dependent expansion of CTLs also affect DC survival during booster DC injections and our data suggest that during a booster DC vaccine, the largest increase in CTL levels is already obtained during the first vaccination.

Identification of an HLA-A*0201 restricted Bcl2-derived epitope expressed on tumors

A large number of human tumor-associated antigen-derived peptides have been identified that are recognized by CTLs in a MHC-I restricted fashion. The apoptosis inhibitory protein Bcl2 is overexpressed in many human cancers as part of their neoplastic phenotype. Since inhibition or loss of Bcl2 expression might impair tumor growth and survival, this protein may serve as a rational target for vaccine-induced CTL responses. By Western blot technique, we screened a panel of established human tumor cell lines for proteins involved in the apoptotic process. Two of eight tumor cell lines, a B lymphoma (Loukes) and a colon carcinoma (CCL220) cell line showed increased Bcl2 protein expression whereas the majority of tumor cell lines expressed proapoptotic proteins. Neither fibroblasts nor peripheral blood mononuclear cells showed Bcl2 expression. An HLA-A*0201 restricted CTL epitope was deduced in silica from the amino acid sequence of the Bcl2 protein and its binding affinity for HLA-A*0201 was confirmed using a biochemical binding assay. We here demonstrate that the 9-mer peptide Bcl2(85-93) induces specific CTL reactivity in immunized C57-A2K(b) or -A2D(b) tg mice. These Bcl2(85-93) specific CTLs react with and lyse Bcl2-expressing human colon carcinoma CCL220 cells which have been transfected with a chimeric HLA-A*0201/H2-K(b) DNA construct similar to that expressed in the transgenic mice. Based on these observations, we suggest that Bcl2(85-93) may be a target for immune therapy.

Intranasal vaccination with SfbI or M protein-derived peptides conjugated to diphtheria toxoid confers protective immunity against a lethal challenge with Streptococcus pyogenes

We investigated whether intranasal immunisation with diphtheria toxoid (DT) conjugated polypeptides encompassing T and B cell epitopes of the SfbI protein (FNBR) or a conformational-constrained B cell epitope of the M1 protein (J8) was able to confer protection against lethal mucosal challenge with a heterologous Streptococcus pyogenes strain. To this end, BALB/c mice were immunised with the conjugates. Strong antigen-specific antibody responses were observed in both serum and mucosal secretions. Vaccinated mice were challenged 10 days after the last boost by the intranasal route. Animals receiving FNBR-DT co-administered with either the cholera toxin B subunit (CTB) or the TLR 2/6 agonist MALP-2 were efficiently protected against the virulent S. pyogenes strain (90% and 70% survival, respectively), whereas those immunised with J8-DT plus either CTB or MALP-2 showed intermediate levels of protection (60% and 40%, respectively). The obtained results indicate that in our experimental animal model peptide-based conjugate vaccines represent a valid alternative to protect against streptococcal infection.

The effect of a therapeutic dendritic cell-based cancer vaccination depends on the blockage of CTLA-4 signaling

Dendritic cells (DCs) were pulsed with the H-2K(b) binding OVA(257-264)-peptide (SIINFEKL), and used as one single-injection vaccine in combination with anti-CTLA-4 monoclonal antibody (mAb) to treat mice inoculated 3 days previously with 3x10(5) E.G7-OVA lymphoma cells. Neither DC vaccination nor CTLA-4 blockage alone prevented tumor growth in tumor challenged mice. In contrast, the combination of one vaccination and injection of anti-CTLA-4 mAb lead to rejection or retarded tumor growth in more than 60% of the mice. The OVA-transgene or the SIINFEKL-epitope was not lost in the progressing tumors of vaccinated mice, however, the highest degree of anti-SIINFEKL reactivity of host CTLs in an IFN-gamma ELISPOT assay was found only in mice showing complete tumor rejection. Vaccinated mice having rejected E.G7-OVA tumors were capable of rejecting subsequent challenges with 1x10(6) E.G7-OVA tumor cells, and later on these mice even rejected wild-type EL-4 tumor cells indicating that tumor epitope spreading takes place during the process of vaccination-induced E.G7-OVA rejection. In agreement with these observations, mice having rejected E.G7-OVA tumors showed long lasting CTL memory in spleen and bone marrow towards both the SIINFEKL-peptide and other EL-4-derived tumor rejecting epitopes.