Enhancing the immunogenicity of cancer vaccines by harnessing CLEC9A.

Dendritic cell (DC) vaccines are a safe and effective means of inducing tumor immune responses, however, a better understanding of DC biology is required in order to realize their full potential. Recent advances in DC biology have identified a crucial role for cDC1 in tumor immune responses, making this DC subset an attractive vaccine target. Human cDC1 exclusively express the C-type-lectin-like receptor, CLEC9A (DNGR-1) that plays an important role in cross-presentation, the process by which effective CD8+ T cell responses are generated. CLEC9A antibodies deliver antigen specifically to cDC1 for the induction of humoral, CD4+ and CD8+ T cell responses and are therefore promising candidates to develop as vaccines for infectious diseases and cancer. The development of human CLEC9A antibodies now facilitates their application as vaccines for cancer immunotherapy. Here we discuss the recent advances in CLEC9A targeting antibodies as vaccines for cancer and their translation to the clinic.

Potential therapeutic applications of recombinant, invasive E. coli.

An invasive Escherichia coli expressing the inv gene from Yersinia pseudotuberculosis was used as a vector for protein delivery to mammalian epithelial cells. Upon incubation with beta1-integrin-expressing mammalian cells, the bacteria are internalized, allowing bacteria-encoded proteins to function from within the mammalian cell. These bacteria are eventually processed in the host phagosome where they are destroyed. Expression of listeriolysin O from Listeria monocytogenes in the bacterium and its subsequent release into the phagosome triggers the breakdown of the membrane, allowing the release of the bacterial content into the cytosol of host cells. Using this vector, we demonstrate delivery of a gene and intact, functional proteins into mammalian cells in which beta1-integrin is expressed and accessible. At a ratio of bacteria/mammalian cells compatible with the survival of the mammalian cells, protein delivery can be observed in the entire cell population in vitro, while gene transfer is far less efficient. Protein delivery can also be achieved in vivo in mouse tumour models and can be detected at least 96 h after inoculation. Functional, natural E. coli proteins are delivered in the process and can provide therapeutic benefit in vivo, when associated with prodrugs. This therapeutic effect is associated with infiltration of neutrophils, eosinophils, macrophages and to a lesser extent dendritic cells in the tumour mass.

A recombinant E. coli vaccine to promote MHC class I-dependent antigen presentation: application to cancer immunotherapy.

We have examined the potential of recombinant Escherichia coli expressing listeriolysin O (LLO) to deliver tumour antigens to dendritic cells (DCs) for cancer immunotherapy. Using OVA as a model tumour antigen, we have shown in murine DCs that E. coli expressing cytoplasmic LLO and OVA proteins can deliver the OVA K(b)-restricted epitope SIINFEKL for MHC class I presentation. In contrast, when E. coli expressing OVA alone were used, MHC class II presentation of the OVA 323-339 I-A(b)-restricted peptide was predominant. When injected in vivo, DCs pulsed with E. coli expressing LLO and OVA induced production of cytotoxic T-lymphocytes capable of lysing an OVA-expressing melanoma cell line (B16-OVA) and resulted in suppression of tumour growth following challenge with B16-OVA. Immunisation of mice by direct injection of E. coli LLO/OVA provided a more potent anti-tumour response, resulting in complete protection in 75% of mice. Injection of live bacteria was not necessary as immunisation with paraformaldehyde-fixed E. coli LLO/OVA provided an even stronger anti-tumour response against B16-OVA. Altogether, our data highlight the potential of this system as a novel and efficient strategy for tumour immunotherapy.

Regulation of tumor cell motility and migration by CD63 in a human melanoma cell line.

CD63 belongs to the transmembrane 4 superfamily of membrane proteins and is expressed in several normal tissues as well as in melanoma cells. Previous reports have suggested that CD63 may play an important role in inhibiting melanoma progression, and this was supported by our studies showing that CD63 was associated with suppression of the growth of melanoma in nude mice. Recently, we and others have shown that CD63 may form noncovalent associations with beta1 integrins, which suggests that the function of CD63 may be related to that of integrins. To further explore the role of CD63 in melanoma, we transfected CD63 into a highly motile, CD63-negative melanoma cell line, KM3, which was shown to express alpha(v)beta5 as the predominant integrin with only trace amounts of beta1 integrins. Following transfection, CD63 was shown to associate with beta1 integrins, and beta1 expression appeared to be up-regulated. Cell motility in serum-containing media was markedly suppressed following transfection of CD63. This inhibition was potentiated by mAbs to CD63, and correlated with the level of CD63 expression. The CD63-transfected, but not the untransfected, melanoma cells showed increased adhesion and migration on the beta1 substrates, fibronectin, laminin, and collagen, whereas rates of migration were similar on the beta5 substrate, vitronectin. These results show that CD63 is involved in regulation of the motility of melanoma cells and their adhesion and migration on substrates associated with beta1 integrins. We suggest they provide further insights into the role of CD63 in tumor progression.

CD63 associates with transmembrane 4 superfamily members, CD9 and CD81, and with beta 1 integrins in human melanoma.

CD63 belongs to the Transmembrane 4 superfamily (TM4SF) of membrane proteins whose functions are largely unknown. Previous results have suggested that CD63 may play an important role in the regulation of melanoma progression. To explore the role of CD63 in melanoma we have examined its association with other molecules by immunoprecipitation of CD63 from detergent induced lysates of melanoma cells. These results are the first to demonstrate an association between CD63 and two other TM4SF members, CD9 and CD81 in 2 human melanoma cell lines. We are also able to identify an association between CD9 and CD63 with beta 1 integrins in melanoma. The results suggest that CD63 is capable of forming multicomponent complexes with TM4SF members and beta 1 integrins on the surface of melanoma. These findings provide further insights into the function of CD63.

Suppression of human melanoma cell growth and metastasis by the melanoma-associated antigen CD63 (ME491).

CD63 has been identified in human melanoma cells by a number of different monoclonal antibodies (MAbs). Studies with MAbs have shown that expression is most marked in naevi and early forms of cutaneous melanoma and reduced in vertical growth phase and metastatic lesions. To investigate further the role of CD63 in progression of melanoma, genomic CD63 was transfected into a CD63-negative human melanoma cell line using an episomal vector. The stable transfected melanoma cells had similar growth rates to control transfected melanoma cells in vitro but much lower growth rates when injected intradermally into athymic nude mice. The CD63-transfected cells also had a reduced number of metastases in the peritoneal cavity and subcutaneous sites when injected intravenously. MAb against CD63 did not influence the growth of CD63-transfected melanoma cells in vitro. Our results confirm previous studies using H-ras-transformed NIH3T3 fibroblasts and suggest that CD63 may have a role as a tumor suppressor gene in human melanoma that acts to limit invasion and progression of melanoma.