Abstract SY27-01: Synthetic vaccine for immunotherapy of high risk HPV infections.
Authors: Melief Cornelis J. M. 
Published: August 2014

Abstract
Therapeutic vaccination of persistent virus infections and associated diseases including (pre-)cancer so far has largely evaded success, mainly due to the fact that insufficiently consistent and robust effector T cell responses were induced by the commonly used vaccine constructs and formulations such as recombinant viruses and bacteria, recombinant proteins, DNA constructs, Dendritic Cell (DC) vaccines and exact HLA class I binding peptides (short peptides). Problems have been severe antigenic competition from vector sequences by recombinant viruses and bacteria, insufficiently powerful T cell generation by DNA constructs, insufficient homing to lymph nodes of injected DC and antigen presentation of short peptides by non-professional antigen presenting cells in vivo, causing tolerance instead of immunity. Much more robust and consistent T cell responses can be obtained by vaccination with long (28-35 amino acid long) synthetic peptides. Such immunogens are more efficiently processed and presented than intact proteins by DC and only DC can efficiently perform this task. Moreover, only concentrated antigen of choice is offered and antigenic competition therefore plays no role.
Phase I/II studies with an HPV16 SLP® vaccine, consisting of 13 long peptides covering the HPV16 E6 and E7 antigens, in patients with advanced HPV16-positive cervical cancer, revealed that this vaccine was safe and highly immunogenic. We then tested the clinical efficacy of this HPV16 SLP® vaccine in HPV16-induced high grade vulvar intraepithelial neoplasia (VIN3), a premalignant epithelial disorder, spontaneous regression of which occurs in less than 2% of patients and in which recurrence after standard treatment is high. In this phase 2 trial, 20 women with VIN3 were vaccinated three times sc in the limbs with a mix of the HPV16 E6 and E7 synthetic long peptides formulated in Montanide ISA-51. The endpoints were objective clinical responses, defined as reduction of at least 50% in lesion size (partial response) or complete regressions, and HPV16-specific T-cell responses. The vaccine was safe. At 3 months after the last vaccination, an objective response was observed in 12/20 (60%). Five patients showed a complete and durable regression of the lesions. The strength of the vaccine-induced HPV16-specific T-cell response was significantly higher in the group of patients with a complete regression of their lesions compared to non-responders. Patients with large lesions were less likely to experience a complete clinical response than patients with small lesions and we ascribe this to a larger proportion of vaccine induced HPV-specific regulatory cells in the patients with large lesions.
In a preclinical mouse model we have shown marked synergism in eradication of established HPV16 E6/E7+ tumors between platinum-based chemotherapy and HPV16 SLP vaccination, associated with a decrease in myeloid cells in the blood and in the tumor. In a pilot clinical study, end stage cervical cancer patients, treated with carbotaxol, showed no T cell immunodeficiency and showed robust T cell effector responses to a single dose of HPV16 SLP® vaccine. These findings set the stage for a randomized phase II study of chemo-immunotherapy in this category of patients, in which chemotherapy alone will be compared with chemo-immunotherapy.
In conclusion, treatment with the HPV16 SLP vaccine is effective in patients with established VIN disease. The SLP platform lends itself for development of therapeutic vaccines against many other chronic infections and non-viral cancers. In patients with cancer, it is attractive to combine this type of vaccination with chemotherapy and with immunomodulatory drugs such as type I interferon and checkpoint-control blocking monoclonal antibodies.
Citation Format: Cornelis J. M. Melief. Synthetic vaccine for immunotherapy of high risk HPV infections. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr SY27-01. doi:10.1158/1538-7445.AM2013-SY27-01