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Vaccines are critical tools to treat and prevent diseases. For an effective conjugate vaccine, the carrier is crucial, but few carriers are available for clinical applications. In addition, a drawback of current protein carriers is that high levels of antibodies against the carrier are induced by the conjugate vaccine, which are known to interfere with the immune responses against the target antigen. To overcome these challenges, we obtained the near atomic resolution crystal structure of an emerging protein carrier, i.e., the bacteriophage Qβ virus like particle. On the basis of the detailed structural information, novel mutants of bacteriophage Qβ (mQβ) have been designed, which upon conjugation with tumor associated carbohydrate antigens (TACAs), a class of important tumor antigens, elicited powerful anti-TACA IgG responses and yet produced lower levels of anticarrier antibodies as compared to those from the wild type Qβ-TACA conjugates. In a therapeutic model against an aggressive breast cancer in mice, 100% unimmunized mice succumbed to tumors in just 12 days even with chemotherapy. In contrast, 80% of mice immunized with the mQβ-TACA conjugate were completely free from tumors. Besides TACAs, to aid in the development of vaccines to protect against COVID-19, the mQβ based conjugate vaccine has been shown to induce high levels of IgG antibodies against peptide antigens from the SARS-CoV-2 virus, demonstrating its generality. Thus, mQβ is a promising next-generation carrier platform for conjugate vaccines, and structure-based rational design is a powerful strategy to develop new vaccine carriers.

More than two years into the global pandemic, SARS-CoV-2 remains a significant threat to public health. Immunities acquired from infection or current vaccines fail to provide long term protection against subsequent infections, mainly due to their fast-waning nature and the emergence of variants of concerns (VOCs) such as Omicron. To overcome these limitations, SARS-CoV-2 Spike protein receptor binding domain (RBD)-based epitopes were investigated as conjugates with a powerful carrier, the mutant bacteriophage Qβ (mQβ). The epitope design was critical to eliciting potent antibody responses with the full length RBD being superior to peptide and glycopeptide antigens. The full length RBD with orientation-controlled conjugation with mQβ activated both humoral and cellular immune systems in vivo, inducing broad spectrum, persistent and comprehensive immune responses effective against multiple VOCs including Delta and Omicron variants, rendering it a promising vaccine candidate.

As typical affinities of carbohydrates with their receptors are modest, polymers of carbohydrates (glycopolymers) are exciting tools to probe the multifaceted biological activities of glycans. In this review, the linear glycopolymers and the multivalency effects are first introduced. This is followed by discussions of methods to synthesize these polymers. Subsequently, the interactions of glycopolymers with plant lectins and viral/bacterial carbohydrate binding proteins are discussed. In addition, applications of the glycopolymers in facilitating glycan microarray studies, mimicking cell surface glycans, modulation of the immune system, cryoprotection of protein, and electron-beam lithography are presented to stimulate further development of this fascinating technology.

Ganglioside GD2 is an attractive tumor-associated carbohydrate antigen for anti-cancer vaccine development. However, its low immunogenicity and the significant side effects observed with anti-GD2 antibodies present significant obstacles for vaccines. To overcome these, a new GD2 derivative bearing an N-acetamide (NHAc) at its non-reducing end neuraminic acid (9NHAc-GD2) has been designed to mimic the 9-O-acetylated-GD2 (9OAc-GD2), a GD2 based antigen with a restricted expression on tumor cells. 9NHAc-GD2 was synthesized efficiently via a chemoenzymatic method and subsequently conjugated with a powerful carrier bacteriophage Qβ. Mouse immunization with the Qβ-9NHAc-GD2 conjugate elicited strong and long-lasting IgG antibodies, which were highly selective toward 9NHAc-GD2 with little cross-recognition of GD2. Immunization of canines with Qβ-9NHAc-GD2 showed the construct was immunogenic in canines with little adverse effects, paving the way for future clinical translation to humans.

The 60-year high Bordetella pertussis (B. pertussis) infection rate in the world suggests the urgent need for new anti-pertussis vaccines. Lipopolysaccharide (LPS) of B. pertussis is an attractive antigen for vaccine development. With the presence of multiple rare sugars and unusual glycosyl linkages, B. pertussis LPS is a highly challenging synthetic target. In this work, aided by molecular dynamics simulation and modeling, the pertussis LPS like pentasaccharide was chemically synthesized for the first time. The pentasaccharide was conjugated with a powerful carrier, bacteriophage Qβ as a vaccine candidate. Immunization of mice with the conjugate induced robust anti-glycan IgG responses with IgG titers reaching several million enzyme-linked immunosorbent assay (ELISA) units. The antibodies generated were long lasting and boostable, and could recognize multiple clinical strains of B. pertussis, highlighting the potential of Qβ-glycan as a new anti-pertussis vaccine.

Cytotoxic T lymphocytes (CTLs) are an important tool for anticancer immunotherapy. To elicit powerful CTL activities, ultra-pH-sensitive nanoparticles (NPs) based on methoxy poly(ethylene glycol)-b-[poly(diisopropylamino)ethyl methacrylate] have been synthesized as a vaccine delivery platform. A representative CTL epitope, ovalbumin (OVA) peptide antigen, was covalently conjugated to the polymer backbone through an acid responsive carboxy-dimethylmaleic amide linker (CDM) resulting in polymer P-CDM-OVA. Interestingly, while the P-CDM-OVA released OVA peptide slowly in a pH 6.4 buffer, the addition of bovine serum albumin (BSA) mimicking proteins encountered in a cellular and/or in vivo environment significantly accelerated the release process. Successful cell surface presentation of OVA was observed when P-CDM-OVA based ultra-pH-sensitive particles were incubated with antigen presenting cells. These P-CDM-OVA NPs greatly enhanced CTL responses in vivo compared to the free peptide or the previously reported acetalated dextran particles encapsulating OVA. The P-CDM was also investigated for adjuvant conjugation, and the coadministration of P-CDM-OVA and the P-CDM-adjuvant conjugate NPs further improved CTL responses in vivo and effectively reduced tumor growth in mice. Thus, the CDM linked polymer presents a promising platform for anticancer immunotherapy.

Adoptive transfer of immune cells is being actively pursued for cancer treatment. Natural killer (NK) cells, a class of cytotoxic immune cells, generally lack inherent selectivities toward cancer. To bestow tumor-targeting abilities and enhance anticancer efficacy, a new strategy is established to glycoengineer NK cells. Carbohydrate-based ligands for CD22, a marker for B cell lymphoma, are introduced onto NK cells through either metabolic engineering or glyco-polymer insertion. Such NK cells exhibited greatly enhanced cytotoxicities toward CD22+ lymphoma cells in a CD22-dependent manner. Importantly, both CD22+ lymphoma cell lines and primary lymphoma cells from human cancer patients can be effectively killed by the engineered NK cells. Furthermore, glycoengineered NK cells provided significant protection to tumor-bearing mice. Thus, NK cell glycoengineering is an exciting new approach for cancer treatment complementing the current immune cell genetic engineering strategy., Sweetening natural killer cells enhanced their tumor-killing abilities in vitro and reduced tumor growth in vivo.

Mucin-1 (MUC1) is a highly attractive antigenic target for anticancer vaccines. Naturally existing MUC1 can contain multiple types of O-linked glycans, including the Thomsen–Friedenreich (Tf) antigen and the Sialyl Thomsen-nouveau (STn) antigen. In order to target these antigens as potential anticancer vaccines, MUC1 glycopeptides SAPDT*RPAP (T* is the glycosylation site) bearing the Tf and the STn antigen, respectively, have been synthesized. The bacteriophage Qβ carrier is a powerful carrier for antigen delivery. The conjugates of MUC1-Tf and -STn glycopeptides with Qβ were utilized to immunize immune-tolerant human MUC1 transgenic (MUC1.Tg) mice, which elicited superior levels of anti-MUC1 IgG antibodies with titers reaching over 2 million units. The IgG antibodies recognized a wide range of MUC1 glycopeptides bearing diverse glycans. Antibodies induced by Qβ-MUC1-Tf showed strongest binding, with MUC1-expressing melanoma B16-MUC1 cells, and effectively killed these cells in vitro. Vaccination with Qβ-MUC1-Tf first followed by tumor challenge in a lung metastasis model showed significant reductions of the number of tumor foci in the lungs of immunized mice as compared to those in control mice. This was the first time that a MUC1-Tf-based vaccine has shown in vivo efficacy in a tumor model. As such, Qβ-MUC1 glycopeptide conjugates have great potential as anticancer vaccines.

Cytotoxic T lymphocyte (CTL) can have remarkable abilities to kill tumor cells. However, the establishment of successful CTL-based anticancer therapy has met with many challenges. Within tumor cells, there exist subpopulations with low or no expression of the targeted antigen (termed as antigen-loss variants). In addition, tumor cells can downregulate the levels of major histocompatibility complex class I (MHC-I) molecules on cell surface due to immune pressure. As a result, some tumor cells can escape the immune pressure bestowed by CTLs, resulting in treatment failure. To address these difficulties, a new approach is developed to deliver foreign high-affinity CTL epitopes to tumor tissues utilizing pH-responsive “smart” microparticles (MPs). These MPs could encapsulate CTL peptide epitope, release the peptide under acidic condition encountered in tumor tissues and enhance CTL activation. Mice bearing pre-established tumor as “antigen-loss variant” solid tumor models were administered intratumorally with MPs containing the CTL peptide, which showed 100% survival following the treatment. In contrast, all control mice died from tumor. Significant protection from tumor-induced death was also observed with systemic administration of CTL peptide-MPs. The therapeutic efficacy can be attributed to enhanced delivery of the epitope to tumor tissues, presentation of the epitope by tumor cells as well as tumor stromal cells and/or generation of epitope-specific CTLs by the peptide-containing MPs. These findings offer a promising new direction for treating established solid tumor using CTL therapy.

Many polycation-based gene delivery vehicles have limited in vivo transfection efficiency because of their excessive exterior positive charges and/or PEGylation, both of which could result in premature dissociation and poor cellular uptake and trafficking. Here, we reported novel hybrid PEGylated nanoparticles (HNPs) that are composed of (a) poly(ethylene glycol)-b-poly(aspartate)-adamantane (PEG-P(asp)-Ad) constituting the outer PEG layer to provide colloidal stability; (b) poly(ethylenimine)(10K) (PEI(10K)) forming complex coacervate with P(asp) as the cross-linked cage preventing premature dissociation; (c) cyclodextrin-decorated PEI(10K) (PEI(10K)-CD) forming the core with reporter plasmid DNA (pDNA). These HNPs exhibited an increased stability and higher in vitro transfection efficiency compared to traditional PEGylated nanoparticles (PEG-NP). Intratumoral injections further demonstrated that HNPs were able to successfully deliver pDNAs into tumors, while PEG-NP and PEI(25K) had only negligible delivery efficiencies. Moreover, HNPs’ in vivo stability and pDNA delivery capability post intravenous injection were also confirmed by live animal bioluminescence and fluorescence image analysis. It is likely that the coacervation integration at the interface of PEI(10K)-CD/pDNA core and the PEG shell attributed to the significantly improved in vivo transfection efficiency of HNPs over PEG-NP and PEI(25K). This study suggests that the HNP has the potential for in vivo gene delivery applications with significantly improved gene transfection efficiency.

Cytotoxic T lymphocytes (CTL) can have remarkable abilities to kill tumor cells. However, the establishment of successful CTL based anticancer therapy has met many challenges, which include 1) difficulties in generating highly functional CTLs targeting endogenous tumor associated CTL epitopes; 2) the existence of antigen-loss variant subpopulation within cancer cells, which fail to express the targeted antigen and can escape the immune pressure bestowed by the specific CTLs; and 3) the reduced expression of major histocompatibility complex class I (MHC-I) molecules on tumor cells due to immune editing. To address these difficulties, a new approach is developed to deliver foreign high affinity CTL epitopes to tumor tissues utilizing pH responsive “smart” microparticles (MPs). These MPs could encapsulate CTL peptide, release the peptide under acidic condition encountered in tumor tissues, and enhance CTL activation. Mice bearing existing solid tumor were administered intratumorally with MPs containing the CTL peptide, which showed 100% survival following the treatment. In contrast, all control mice died from tumor. Significant protection from tumor induced death was also observed with systemic administration of CTL peptide-MPs. The therapeutic efficacy can be attributed to enhanced delivery of the epitope to tumor tissues, presentation of the epitope by tumor cells as well as tumor stromal cells and/or generation of epitope specific CTLs by the peptide containing MPs. These findings offer a promising new direction for treating established solid tumor using CTL therapy. Citation Format: Xuefei Huang, Herbert Kavunja, Shuyao Lang, Suttipun Sungsuwan, Zhaojun Yin. Development of acid responsive microparticles for cytotoxic T-lymphocyte based antitumor immunotherapy [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr A030.