Enhancing Antitumor Immune Responses by Optimized Combinations of Cell-penetrating Peptide-based Vaccines and Adjuvants

Abstract

Cell penetrating peptides (CPPs) from the protein ZEBRA are promising candidates to exploit in therapeutic cancer vaccines, since they can transport antigenic cargos into dendritic cells and induce tumor-specific T cells. Employing CPPs for a given cancer indication will require engineering to include relevant tumor-associated epitopes, administration with an appropriate adjuvant, and testing for antitumor immunity. We assessed the importance of structural characteristics, efficiency of in vitro transduction of target cells, and choice of adjuvant in inducing the two key elements in antitumor immunity, CD4 and CD8 T cells, as well as control of tumor growth in vivo. Structural characteristics associated with CPP function varied according to CPP truncations and cargo epitope composition, and correlated with in vitro transduction efficiency. However, subsequent in vivo capacity to induce CD4 and CD8 T cells was not always predicted by in vitro results. We determined that the critical parameter for in vivo efficacy using aggressive mouse tumor models was the choice of adjuvant. Optimal pairing of a particular ZEBRA-CPP sequence and antigenic cargo together with adjuvant induced potent antitumor immunity. Our results highlight the irreplaceable role of in vivo testing of novel vaccine constructs together with adjuvants to select combinations for further development.

Mechanistic insights into the efficacy of cell penetrating peptide-based cancer vaccines

“…2). This was directly demonstrated using Zebra-derived CPPs, TAT, and penetratin [16, 22, 24, 46, 54, 55]. …”

Targeting self- and neoepitopes with a modular self-adjuvanting cancer vaccine

“…In addition, it was consistently shown, for various multiantigenic constructs, that CPP-mediated antigen uptake, not only with external adjuvant (10,11) but also within a self-adjuvanting protein, can promote CD8 and CD4 T cell immune responses. Furthermore, these immune responses were not limited to model antigens or neoantigens but were also induced for self-antigens both in mice (gp100 and gp70) and in NHPs (CEA, survivin, EPCAM, and MUC1).…”

“…We have previously demonstrated that this major drawback can be overcome by using cell-penetrating peptides (CPPs) as delivery vectors (10,11). These small peptides can cross the plasma membrane even when linked to large multiepitopic cargos, allowing antigens to be delivered into different processing compartments of DCs, so that they are presented on both MHC class I and class II, promoting CD8 and CD4 T cell activation, respectively (10).…”

“…Conjugating a vaccine to a TLR ligand was explored with various TLR ligands combined to a peptide or protein vaccine and resulted in improved antigen-specific CD8 T cell responses (12). Based on these findings, we optimized our CPP-based vaccine and recently demonstrated that part of the efficacy of CPP-based therapeutic cancer vaccines relies on their combination with the concomitant administration of the optimal adjuvant (11). A further enhancement of immune activation would be to conjugate the protein vaccine to an appropriate TLR ligand (13) as a state-of-the-art recombinant fusion protein vaccine construct, thereby benefitting from self-adjuvanticity.…”

Immunotherapy of Malignant Tumors in the Brain: How Different from Other Sites?

“…Given the critical importance of adjuvant choice for therapeutic cancer vaccination revealed in preclinical studies (119–121), this issue will eventually have to be addressed in a clinical context. Interestingly, subsequent to clinical and mice studies showing that preconditioning the tumor vaccine injection site by a recall response to tetanus/diphtheria improved lymph node homing of tumor antigen-bearing DCs and magnitude of immune responses (19), four studies (NCT02193347, NCT02709616, NCT02465268, NCT02366728) use a Td recall vaccine as adjuvant, some testing as part of their clinical trial efficiency of DC migration to lymph nodes (19).…”