Dendritic cells are the most potent antigen-presenting cells known; owing to

Dendritic cells are the most potent antigen-presenting cells known; owing to their ability to stimulate antigen-specific cytolytic and memory T-cell responses their use as malignancy vaccines is rapidly increasing. the phenotype and function of the DCs after infusion are rarely known and so the surrogate readout of vaccine efficacy is usually post-vaccine T-cell activity (enzyme-linked immunospot [ELISPOT] delayed-type hypersensitivity response and cytotoxicity among others) and clinical responses. The persistence of DCs in a mature state after infusion cannot be assumed since in the absence of maturation stimuli at the injection site DCs may dedifferentiate and/or pass away and if robustly stimulated they may rapidly become worn out [55]. Analysis of the location and quantity of viable DCs at numerous time points following vaccination would aid the design of more effective vaccines but as yet good imaging strategies for DC migration in humans are lacking. CTEP Genetic modification to improve dendritic cell vaccines While T-cell responses to DC vaccines have been reported in approximately half of the published clinical trials objective tumor response rates remain low. Increased efficacy has come with increased understanding of the complexities associated with the balance between immunity and tolerance and the characteristics required by effective DCs. However the development of strategies to ensure these characteristics are retained after Rabbit polyclonal to ZNF280A. infusion remains challenging. Studies in mice have demonstrated that even after antigen loading and maturation auto logous wild-type DCs are ineffective at inducing a T-cell response strong enough to completely eliminate established tumors [56]. To combat these issues investigators have genetically altered DCs in multiple ways to enhance their function and efficacy (Physique 1). These strategies fall broadly into two groups: overexpression of positive regulators and inhibition of unfavorable regulators. Physique 1 Genetic modification of dendritic cells can lead to the enhancement of immunogenicity migration longevity cytokine secretion or a combination of these thus yielding a more effective vaccine. Overexpression of surface stimulatory molecules Multiple signaling pathways are crucial to the CTEP induction of a mature stimulatory DC and an optimal T-cell response. Membrane-bound costimulatory molecules are some of the most important products of mature DCs and have been overexpressed using a variety of viral and nonviral vectors in both preclinical and clinical trials [24 39 For example DCs expressing the tumor antigen carcinoembryonic antigen (CEA) together with the three costimulatory molecules CD80 CD54 and CD58 from a fowlpox vector were used to vaccinate 14 malignancy patients leading to increased CEA-specific T cells in ten patients and one partial remission [24]. Ligation of CD40 on DCs with CD40L on antigen-specific Th cells is known to enhance DC expression of costimulatory molecules cytokines and chemokines. To mimic this conversation DCs have been altered by CTEP adenoviral transduction [40] or mRNA electro poration [57] to express CD40L. In order to better control the CD40 pathway Spencer and colleagues engineered a CD40 construct CTEP whose activity is usually induced upon addition of chemical inducer of dimerization (CID) AP1903 [58]. Inducible CD40-expressing DCs activated with TLR4 ligands effectively primed antigen-specific Th1 antitumor responses and after addition of the CID exhibited enhanced migration both and [58]. This strategy is currently in clinical trials using prostate-specific antigen as an antigen in patients with prostate malignancy. Other costimulatory molecules that have interested experts include GITR-L 4 CTEP CD70 and OX40L [57 59 Vaccination with a combination of DCs expressing tumor antigen RNA and secreting anti-GITR-mAbs enhanced tumor-specific T-cell immunity and resulted CTEP in sustained long-term memory T-cell responses in mice [59]. Transgenic expression of CD70 on murine DCs was enough to break CD8+ tolerance and establish protective immunity to tumor challenge or virus infection [60 61 Electroporation with mRNAs encoding a combination of CD70 CD40L and a constitutively active TLR4 generated mature cytokine and.