Improved dendritic cell vaccination for combined melanoma immune therapy

Malignant melanoma is known for its fast progression and poor response to current treatments. Despite melanoma immunogenicity, tumor escape could be due to a profound immunosuppression in the melanoma microenvironment. Moreover, the development of melanoma-specific effector T cells may be hampered by insufficient tumor antigen delivery, processing and presentation of dendritic cells (DCs). Efficient MHC-peptide complex expression on the DC cell surface determines the degree and quality of the T cell response and the maximal amount of presented antigenic peptides is thus a key parameter in the design of DC-based cancer vaccines. We have recently established the production of constructs encoding the major histocompatibility complex (MHC) class I molecules that couples the peptide presentation and activation of DC. This modality was highly efficient in inhibiting tumor growth and improving survival, both in transplantable and spontaneous preclinical melanoma models. The goal of this study was to generate a novel and more potent DC vaccine for melanoma immunotherapy based on the recently developed bi-functional class of genetic mRNA cancer vaccines. To enhance the anti-tumor response, these modified DC present different chimeric MHC class I and MHC class II receptors, in order to become a multivalent DC vaccine allowing a simultaneous presentation of different melanoma associated antigens (MAA) of choice for induction of CD8+ CTL and CD4+ Th, respectively. Selected class I and class II restricted antigens derived from TRP-1 and Tyr were able to elicit a potent CD8+ CTL and CD4+ Th response. Furthermore, we studied selected TRP-1/Tyr- class I and class II receptors for their in vivo capacity to induce antitumor immune response in two different melanoma mouse models (ret transgenic and BRAF). Unexpectedly, co- electroporation of MHC-I and MHC-II chimeric constructs did not improve survival in melanoma bearing ret tg mice, probably due to increased activity of antigen-specific Tregs, which will be investigated in further studies. In contrast to these results, we also demonstrated that melanoma-bearing mice (ret-tg and BRAF) experienced tumor regression and significantly improved survival upon treatment with multivalent β2m-based-DC vaccine. Vaccination with chimeric TRP-1 and Tyr class I- β 2m DC vaccine and in particular the Mix-(TRP-1/Tyr)- β2m DC vaccine, mainly due to its multivalent properties, demonstrated increased frequency of IFNγ producing CD8+ T cells, complemented by increased, systemic CD 8+ T cell activity as well as an increase of CD8+ effector memory T cells. Importantly, these immune-stimulatory effects were found without any stimulatory effects on immunosuppressive Tregs and MDSC. Finally, we could detect signs of autoimmunity (vitiligo) in 3 ret-tg mice treated with TRP-1/Tyr class I-Mix DC vaccine, providing further evidence of increased immune stimulation. Our data suggest that immunotherapy with multivalent β2m-based-DC vaccine can significantly improve the survival of tumor bearing mice, especially by increasing the MAA-repertoire presented by the DCs. Notably, upon combination with ultra-low dose of paclitaxel T cell dependent immunity was even further enhanced by concomitant systemically reduction of immunosuppressive activity of MDSC and Treg, further providing rational for advantages in combined immunotherapy with our improved DC vaccine which will be investigated in more detail in future studies