Blocking CD13 in combination with a toll like receptor agonist increases the efficacy of cancer vaccine adjuvants

Abstract

Abstract Vaccines have been an extraordinary tool in the fight against human disease. Recent cancer research has revealed promising results leading to approved cervical and prostate cancer vaccines. Despite the success, a major downfall of these vaccines remains poor immunogenicity. MPLA (monophosphorylated lipid A) is a synthetic analog of LPS that binds to TLR4 leading to activation of the adaptive immune response without triggering deleterious inflammatory consequences. As such, MPLA has recently been FDA approved as an adjuvant of the prophylactic vaccine against HPV-driven (Human Papilloma Virus) cervical cancer. However, this vaccine is limited to non-preexisting HPV cases while protecting against only two out of the dozen HPV strains that can potentially lead to cervical cancer. Pertinent to this subject, we have found that the absence of CD13 in antigen presenting cells (APCs), leads to increased TLR4 endocytosis and bias toward the same endocytic-signaling pathway triggered by MPLA. CD13 is a large, multifunctional cell surface peptidase constitutively expressed on all lineages of myeloid cells. We have previously shown that lack of CD13 increases tumor antigen uptake and presentation, resulting in enhanced activation of tumor-specific cytotoxic T cells. The combination of these facts has led to the intriguing possibility that blocking CD13 may amplify the efficacy of MPL as an adjuvant and ameliorate the efficacy of prophylactic and therapeutic cancer vaccines. Therefore, we hypothesize that CD13-blocking agents will act as dual-action adjuvants by enhancing MPL-TLR4 endocytosis, and as a delivery system through increased endocytic antigen uptake and subsequent cytotoxic T cell activation.