Abstracts of 4th Annual UKMF Scientific Meeting on 07-Feb-2003
Clinical and immunological results of MAGE vaccination
Pierre van der Bruggen1,2, Yi Zhang1,2, Pierre G. Coulie1, Aline van Pel1,2, Christophe Lurquin1,2, Didier Coleau1,2 and Thierry Boon1,2.
1Unit of Cellular Genetics, University of Louvain, Brussels,
Belgium, B-1200
2Ludwig Institute for Cancer Research, Brussels Branch, Belgium,
B-1200.
Shared tumour-specific antigens such as those encoded by gene MAGE-3 were used for small-scale therapeutic vaccination trials of melanoma patients with detectable disease. The vaccines consisted of an antigenic peptide, a protein, a pox family recombinant virus (ALVAC) carrying a MAGE-3 sequence, or dendritic cells pulsed with an antigenic peptide.
The results of a number of MAGE-3 peptide, protein, and recombinant virus trials can be briefly summarized as follows. No significant toxicity was observed. Complete or partial clinical responses were observed in about 10% of the patients, and an additional 10% showed tumour regressions of lesser clinical significance. Tumour regressions occurred more frequently with regionally than with distantly metastatic melanoma. They often became noticeable only after several months of vaccination and, when they became complete, this often took several additional months. Responses were often mixed, with some metastases progressing at a time where others were clearly regressing.
The 20% rate of tumour regressions that was observed appears to be well above the rates of spontaneous regressions that have been reported, and we are therefore inclined to conclude that the regressions are caused by the content of the vaccine. But 80% of the vaccinated patients fail to display any detectable regression. This failure could be due to two major causes that are not mutually exclusive: a failure of the vaccine to induce a significant T cell response or a resistance of the tumour to immune attack. To establish which of the two is the major cause of failure, it is essential to establish whether there is a correlation between the observation of a T cell response against the vaccine antigen and the observation of tumoural regression. If only those patients who show tumour regression show CTL responses, this will suggest that the induction of CTL responses is limiting.
To detect anti-MAGE-3.A1 T cell responses, we resorted to an in vitro restimulation with the antigenic peptide in the presence of IL-2, IL-4 and IL-7, before labelling with tetramers. In order to evaluate precursor frequencies, these "mixed lymphocyte-peptide cultures" (MLPC) were carried out in limiting dilution condition.
Tetramer-positive cells were sorted and cloned. The specificity of the CTL clones was verified, and their TCR sequenced. Using this approach we found weak CTL responses in some of the patients who showed tumour regression after vaccination with peptide or recombinant ALVAC. The CTLp frequencies in the blood vary from 3 x 10-5 to 6 x 10-7 of the CD8 cells. These responses were usually monoclonal, and clonotypic PCR performed directly on PBMC confirmed the low CTLp frequencies. We have observed anti-MAGE-3.A1 CTL responses in 5/10 regressor patients and only in 1/14 progressors, leaving open the possibility that a correlation will be found between clinical and immunological responses. Such a correlation has not yet been demonstrated. If this correlation is established, it will indicate that, under our conditions of vaccination, the induction of an anti-MAGE T cell response is the main limiting factor for clinical success. It will then be important to find modalities of vaccination that induce better T cell responses. CTL responses by patients vaccinated with dendritic cells incubated with peptide MAGE-3.A1 have been reported, and preliminary results suggest that these responses are polyclonal, with higher CTL frequencies than in patients vaccinated with peptides. If this is confirmed, it will be crucial to examine whether such vaccinations with dendritic cells induce better clinical responses. HLA-DP4 multimers containing a MAGE-3 peptide have recently been obtained and used to analyse patients injected with this HLA-class II restricted peptide.