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A vast range of immunotherapeutic strategies are being considered for the treatment of cancer, only some of which are discussed above. Immunotherapy is unlikely to become a stand-alone treatment for cancer; it is far more likely that it will be used as a method to treat minimal residual disease or recurrence following more conventional treatment, such as surgical removal of primary tumour masses. This is emphasized by the fact that the effectiveness of treatment in animal models is more striking in the preventative, rather than the therapeutic, setting. The ultimate measure for the success of these approaches is clinical efficacy, but practical considerations must also be taken into account. For example, assuming equivalent efficacy and toxicity, relatively simple procedures such as cytokine administration will be preferable to manipulated autologous cell therapies. The immune status of patients is also a critical consideration when designing clinical trials and assessing results; many cancer patients are immunosuppressed either as a result of the cancer or of previous treatments.Assessment of the relative efficacy of the different approaches is currently very difficult because relative potency in animal models is rarely tested and, even if it were, would probably not be predictive of the potency in patients. However, over the next few years, as the results of ongoing, or imminent, clinical trials become available, a clearer picture of the potential of immunotherapy for the treatment of cancer will hopefully emerge, and, specifically, there might be indications as to which approaches show the most potency, with least toxicity, in patients. Thus, we hope to gain insights into the most promising approaches to help the immune system win this battle.

We recently published the construction and evaluation of a beta-catenin-dependent, highly active promoter, CTP1, and its possible application for the treatment of colorectal cancer using gene-directed enzyme prodrug therapy with adenoviral (Ad) vectors. Alternative Ad-based approaches such as tumor-specific, replication-competent vectors and/or exploiting therapeutic gene products with intrinsic toxic activity, such as gibbon ape leukemia virus fusogenic membrane glycoprotein, diphtheria toxin A (DTA), and ricin, would demand a very tightly regulated promoter to avoid breakthrough replication and toxicity in nontumor tissue and Ad producer cell lines. In this study we optimized the activity/specificity profile of the synthetic beta-catenin-dependent promoter by varying its basal promoter, the number of Tcf binding sites, and the distance between these and the basal promoter. The optimal promoter, CTP4, showed virtually undetectable expression in cells with normal beta-catenin regulation but high level expression in cells deregulated for beta-catenin. Using CTP4 we were able to generate, for the first time to our knowledge, an Ad vector expressing fully active wild-type DTA without the need for time-consuming and cumbersome production systems. CTP4 should be the promoter of choice for Ad-based gene therapies of tumors deregulated for beta-catenin. We provide preliminary evidence that these may include prostate and ovarian as well as colorectal cancer.

Condensing peptide-DNA complexes have great potential as nonviral agents for gene delivery. To date, however, such complexes have given transfection activities greatly inferior to adenovirus and somewhat inferior to cationic lipid-DNA complexes, even for cell lines and primary cells in vitro. We report here the identification of a novel condensing peptide, CL22, which forms DNA complexes that efficiently transfect many cell lines, as well as primary dendritic and endothelial cells. We report studies with sequence and structure variants that define some properties of the peptide that contribute to efficient transfection. We demonstrate that the superior transfection activity of CL22 compared with other DNA condensing peptides is conferred at a step after uptake of the complexes into cells. We show that CL22-DNA complexes have transfection activity that is at least equivalent to the best available nonviral agents.