Sophie Cayeux

Expression of B7.1 (CD80) in a renal cell carcinoma line allows expansion of tumor-associated cytotoxic T lymphocytes in the presence of an alloresponse

We have selected a well-characterized human renal cell carcinoma (RCC) line as the basis for development of a genetically engineered tumor cell vaccine to be applied in an allogeneic setting. This cell line was genetically modified by retroviral transduction to express B7.1 costimulatory molecules. The unmodified tumor cells and B7.1-expressing tumor cells were compared for their ability to induce tumor-associated responses in allogeneic peripheral blood mononuclear cells (PBMC) of two normal control donors having single MHC class I allele matches with the tumor cells. PBMC primed using B7.1-modified tumor cells showed a preponderance of CD3+CD8+ cytotoxic T lymphocytes (CTL) that proliferated over extended periods of time in mixed lymphocyte tumor cell (MLTC) cultures. Strong cytolytic activity developed in the primed populations and included allospecific CTL with specificity for mismatched HLA-A, -B and -C molecules. Nevertheless, it was possible to isolate CTL clones that were able to lyse tumor cells but not lymphoblastoid cells that expressed all the corresponding allospecificities. Thus, induction of complex allospecific responses did not hinder the development of tumor-associated CTL in vitro. These results support the use of this genetically modified allogeneic tumor cell line for vaccination of partial-MHC matched RCC patients.

Genetic approaches to cancer immunotherapy

A new era of immunotherapy of cancer has begun, often referred to as gene therapy. The general concepts have not changed, but the available methods and reagents and the understanding of how immune responses are induced and regulated. Of importance are the following: (a) a number of gene transfer techniques, (b) the discovery of an array of cloned and functionally characterised cytokines, (c) the knowledge of how (tumor) cells can present peptides of potentially any cellular protein to T cells by MHC molecules, (d) the basic principles of activation of T cells which are believed to play a central role in immunotherapy and (e) molecular mechanisms of malignant transformation. A multitude of experimental strategies for cancer immunotherapy are employed which are based on solid ground as was never before the case. Most experimental work has been done in order to construct tumor cell vaccines by genetic engineering with cytokines and/or other immunostimulatory proteins such as B7. In mouse tumor models it has been shown that gene modified tumor cell vaccines can be more effective than traditional tumor vaccines which they are going to replace in the clinic. However, it should not be withholded that experimental tumor models have revealed some chronic problems in tumor immunology, that is the individuality of each tumor which makes general conclusion difficult and the rapid modulation of the hosts immune system by the tumor. If the flood of new and important information during the last 5 years is considered, one can optimistically assume that these problems can be resolved, but the clue to successful cancer immunotherapy in most cases has to come from well-defined experimental models.

Decreased generation of anti-tumor immunity after intrasplenic immunization.

The localization of antigen and the nature of the host antigen‐presenting cells (APC) that present it to T cells are two major determinants of antigen immunogenicity. While lymph nodes appear to be the major site for T cell priming, recently the spleen was shown to provide an optimal microenvironment for direct CD8+ cytotoxic T cell (CTL) priming by tumor cells even in the absence of known costimulatory molecules on tumor cells. We analyzed whether the splenic microenvironment would support T cell priming also when host APC are involved (cross‐priming) which is probably the major pathway during the generation of anti‐tumor immunity. We performed immunization / challenge experiments using different tumor cells (B7.1+, B7.1– and / or β‐gal+, β‐gal–) known to induce CTL to a variable extent either exclusively by cross‐priming (B7–) or at least partially by direct priming (B7+). Our results demonstrate that tumor take in the spleen required much less cells than at a subcutaneous injection site. Additionally, intrasplenic immunization was invariably ineffective compared to subcutaneous immunization. We further showed that B cells were not responsible for the inefficient intrasplenic immunization. Therefore delivering the tumor cell antigens inside the spleen by intrasplenic immunization did not improve but rather decreased the efficacy of tumor cell vaccines.

Retroviral B7.1 Gene Transfer in Cancer Cells Protects Cytotoxic T Cells from Deletion by “Veto” Apoptosis

It is generally accepted that T cell activation requires two distinct signals. The first signal is dependent on the ligation of the T cell receptor (TCR)/CD3 complex and the CD4 and CD8 co-receptors [1]. The second signal can be provided by cell surface molecules which mediate essential co-stimulatory signals, thereby complementing the TCR/CD3-mediated events [2, 3]. CD28 is a potent co-stimulatory molecule, and ligation of CD28 with agonistic antibodies or its natural ligands (B7.1 (CD80) and B7.2 (CD86)) synergizes with TCR-mediated signaling to initiate and maintain T cell responses [3, 4]. Recently, ligation of CD28 by agonistic antibodies was shown to prevent activation-induced cell death (AICD) by apoptosis during activation of resting T cells [5]. This was related to the upregulation of bcl-xL, a potent apoptosis-preventing member of the bcl-2 gene family. Overexpression of bcl-xL in Jurkat T cells inhibits both CD3 and CD95 (Fas/APO-1)-mediated apoptosis [5].