Long-peptide vaccination with driver gene mutations in p53 and Kras induces cancer mutation-specific effector as well as regulatory T cell responses

Abstract

Mutated proteins arising from somatic mutations in tumors are promising targets for cancer immunotherapy. They represent true tumor-specific antigens (TSAs) as they are exclusively expressed in tumors, reduce the risk of autoimmunity and are more likely to overcome tolerance compared to wild-type (wt) sequences. Hence, we designed a panel of long peptides (LPs, 28–35 aa) comprising driver gene mutations in TP35 and KRAS frequently found in gastrointestinal tumors to test their combined immunotherapeutic potential. We found increased numbers of T cells responsive against respective mutated and wt peptides in colorectal cancer patients that carry the tested mutations in their tumors than patients with other mutations. Further, active immunization of HLA(-A2/DR1)-humanized mice with mixes of the same mutated LPs yielded simultaneous, polyvalent CD8+/CD4+ T cell responses against the majority of peptides. Peptide-specific T cells possessed a multifunctional cytokine profile with CD4+ T cells showing a TH1-like phenotype. Two mutated peptides (Kras[G12V], p53[R248W]) induced significantly higher T cell responses than corresponding wt sequences and comprised HLA-A2/DR1-restricted mutated epitopes. However, vaccination with the same highly immunogenic LPs strongly increased systemic regulatory T cells (Treg) numbers in a syngeneic sarcoma model over-expressing these mutated protein variants and resulted in accelerated tumor outgrowth. In contrast, tumor outgrowth was delayed when vaccination was directed against tumor-intrinsic Kras/Tp53 mutations of lower immunogenicity. Conclusively, we show that LP vaccination targeting multiple mutated TSAs elicits polyvalent, multifunctional, and mutation-specific effector T cells capable of targeting tumors. However, the success of this therapeutic approach can be hampered by vaccination-induced, TSA-specific Tregs.

Long-term survival of patients with stage III colon cancer treated with VRP-CEA(6D), an alphavirus vector that increases the CD8+ effector memory T cell to Treg ratio

“…10 Two potential explanations are the use of vaccines in heavily pretreated advanced cancer patients and immunization platforms that simultaneously activate immunosuppressive regulatory T cells along with the desired effector T cell response. 11 Vaccine platforms for targeting CEA have included peptides, proteins, modified tumor cells, DNA, mRNA, viral vectors, and dendritic cells (DC). 10 We previously reported on the use of virus-like replicon particle (VRP)-CEA (AVX701), an alpha-VRP, based on attenuated Venezuelan equine encephalitis virus encoding the modified epitope CEA(6D) which we designate as VRP-CEA, to activate CEA-specific immune responses.…”

Generation of multiepitope cancer vaccines based on large combinatorial libraries of survivin‐derived mutant epitopes

“…37 All of these observations may explain, in part, why immunization with highly immunogenic neoantigens is not sufficient to achieve anti-tumor effects, as was shown in a recent study, where vaccination with mutated p53 and KRAS peptides resulted in a strong increase in regulatory T cells and accelerated tumor growth in a syngeneic sarcoma model. 38 In our study, the differential changes in the amount of CD11b + Ly6C int/low Ly6G + suppressor G-MDSCs in the lungs and tumors of vaccinated mice may explain the stronger inhibition of lung metastasis by VEL-NT compared with VEL-CT ( Fig. 1).…”

CUE-101, a Novel E7-pHLA-IL2-Fc Fusion Protein, Enhances Tumor Antigen-Specific T-Cell Activation for the Treatment of HPV16-Driven Malignancies

“…Recombinant IL2 (aldesleukin) therapy also enhances antitumor immunity (34), but toxicities associated with aldesleukin curbs its use in the clinic and expansion of Tregs may limit its effectiveness (35,36). Vaccination approaches can have similar limitations, where long peptides have generated both effector and Treg responses (37). In contrast, CUE-101 is a single molecule with the minimal essential signals for direct activation of antigen-specific CD8 þ T cells, functioning as an off-the-shelf therapeutic to enhance antigen-specific Tcell responses without requiring ex vivo manipulation.…”