Abstract

   Nucleic acid vaccines have shown promising potency and efficacy for
   cancer treatment with robust and specific T-cell responses. Improving
   the immunogenicity of delivered antigens helps to extend therapeutic
   efficacy and reduce dose-dependent toxicity. Here, we systematically
   evaluated chemokine-fused HPV16 E6/E7 antigen to improve the cellular
   and humoral immune responses induced by nucleotide vaccines in vivo. We
   found that fusion with different chemokines shifted the nature of the
   immune response against the antigens. Although a number of chemokines
   were able to amplify specific CD8 + T-cell or humoral response alone or
   simultaneously. CCL11 was identified as the most potent chemokine in
   improving immunogenicity, promoting specific CD8 + T-cell stemness and
   generating tumor rejection. Fusing CCL11 with E6/E7 antigen as a
   therapeutic DNA vaccine significantly improved treatment effectiveness
   and caused eradication of established large tumors in 92% tumor-bearing
   mice (n = 25). Fusion antigens with CCL11 expanded the TCR diversity of
   specific T cells and induced the infiltration of activated specific T
   cells, neutrophils, macrophages and dendritic cells (DCs) into the
   tumor, which created a comprehensive immune microenvironment lethal to
   tumor. Combination of the DNA vaccine with anti-CTLA4 treatment further
   enhanced the therapeutic effect. In addition, CCL11 could also be used
   for mRNA vaccine design. To summarize, CCL11 might be a potent T cell
   enhancer against cancer.

Supplementary Information

   The online version contains supplementary material available at
   10.1186/s12943-024-01958-4.

   Keywords: CCL11, Chemokines, Molecular adjuvant, Nucleic acid vaccines
   and CCR3 + cells

Background

   Comprising mRNA or DNA antigen precursors, nucleotide vaccines are
   taken up by host cells, where their nucleotide sequences are translated
   into antigens intracellularly. Then, the antigens could be degraded by
   the proteasome in the cytoplasm to generate epitope peptides for MHC-I
   molecules and to activate cytotoxic responses. The extracellularly
   secreted antigens are phagocytized by antigen-presenting cells (APCs)
   to trigger T helper cell or humoral immunity simultaneously. The
   characteristics of nucleotide vaccines endowed them with the ability
   not only in prophylactic but also in therapeutic settings to treat
   diseases such as cancer. Many clinical trials of tumor nucleic acid
   vaccines are in progress, of which a therapeutic DNA vaccine for the
   treatment of cervical intraepithelial neoplasia (CIN), targeting the E6
   and E7 antigens of the HPV 16 and 18 strains, has shown a positive
   effect in patients in a phase 2b trial [[43]1]. Besides, an
   individualized RNA mutanome vaccine successfully immunized melanoma
   patients, resulting in a good T-cell response and prolonging
   progression-free survival [[44]2]. The immunogenicity of nucleic acid
   vaccines is the key to success. Therefore, further improvement is
   highly desirable.

   Improvement of immunogenicity can be achieved by nucleotide sequence
   optimization to increase mRNA stability and the expression of antigens
   [[45]3]. Epitope optimization could promote cross-recognition of
   wild-type antigens and break immune tolerance to wild-type antigens
   [[46]4]. Introducing MHC class I trafficking signals (MITD) or
   lysosomal / endosomal localization signals to assist the process of MHC
   class I or class II epitope presentation by dendritic cells (DCs) has
   also been applied to increase cellular immune responses [[47]5, [48]6].
   Gene fusion to combine tetanus toxoid fragments with antigens has been
   widely used in both DNA and mRNA vaccine design, aiming at
   strengthening the immune response [[49]7, [50]8]. However, this
   approach may lead to a more potent tetanus toxoid fragment response
   since antigen dominance hierarchies shape CD8 T-cell phenotypes
   [[51]9]. As antigen expression of the nucleic acid vaccine is extremely
   low, selective targeting of antigens to APCs is the key to increase
   effective biological distribution and immunogenicity. APCs have
   specific receptors that could be targeted by receptor-specific
   monoclonal antibodies (mAbs) or natural ligands [[52]10]. Delivering
   antigens together with the interaction between natural ligands such as
   chemokines and specific receptors on the surface of APCs could realize
   APC activation, with the advantage of no or weak induction of immune
   responses of the chemokines themselves and potential adjuvant effects.

   Chemokines and chemokine receptors contribute to leukocyte trafficking
   and recruitment to sites of inflammation. Indeed, XCL1, CCL3 (MIP1α),
   CCL5 (RANTES), CCL7, CCL20, CCL21, CCL22, CCL25, CCL27, CCL28, CXCL10
   and CXCL13 have been demonstrated to significantly promote cellular and
   humoral responses when fused or co-delivered with antigens from viruses
   or tumors [[53]11–[54]17]. However, systematic evaluation of the immune
   response of chemokines after fusing with antigens has not been
   reported. It remains unclear whether chemokines have different
   preferences for inducing cellular and humoral immunity. Thus,