Enhanced immunogenicity and antitumour effects with heterologous prime-boost regime using vaccines based on MG7-Ag mimotope of gastric cancer

A T-cell-dependent antibody response (TDAR) method in BALB/c mice based on a cytometric bead array

Most current methods to assess T-cell-dependent antibody responses (TDAR) are semi-quantitative and based on measures of antibody titer generated against a standard antigen like keyhole limpet hemocyanin (KLH). The precision, sensitivity, and convenience of TDAR assays might be improved by applying rapid, sensitive, specific cytometric bead assays (CBA). In the study here, KLH antigen was covalently coupled onto the surface of cytometric beads using immune microsphere technology, and IgM antibody capture spheres were prepared for use in pretreatment processing of samples. The working parameters associated with this novel TDAR-CBA system were optimized in orthogonal experiments. The optimal concentration of the KLH coating solution in this system was 160 μg/ml, that of the anti-KLH IgG capture spheres 6.0 × 10⁵/ml, and the optimal dilution of fluorescein isothiocyanate (FITC)-conjugated Affini-Pure Goat Anti-Mouse IgG (H + L) was 60 μg/ml. Repeated tests indicated that this approach yielded good linearity (r² = 0.9937) method, with a within-run precision of 3.1-4.9%, and a between-run precision of 4.4-4.9%. This new approach had a limit of detection of 113.43 ng/ml (linear range = 390.63-50 000), and an interference rate of just 0.04-3.51%. Based on these findings, it seems that a new mouse TDAR assay based on CBA can be developed that would appear to be more sensitive, accurate, and precise than the current TDAR assay approaches based on traditional ELISA.

Prime-boost vaccination targeting prostatic acid phosphatase (PAP) in patients with metastatic castration-resistant prostate cancer (mCRPC) using Sipuleucel-T and a DNA vaccine

Background

Prostatic acid phosphatase (PAP) is a prostate tumor antigen, and the target of the only FDA-approved anti-tumor vaccine, sipuleucel-T. We have previously reported in two clinical trials that a DNA vaccine encoding PAP (pTVG-HP) could elicit PAP-specific, Th1-biased T cells in patients with PSA-recurrent prostate cancer. In the current pilot trial we sought to evaluate whether this vaccine could augment PAP-specific immunity when used as a booster to immunization with sipuleucel-T in patients with metastatic, castration-resistant prostate cancer (mCRPC).

Methods

Eigthteen patients with mCRPC were randomized to receive sipuleucel-T alone or followed by intradermal immunization with pTVG-HP DNA vaccine. Patients were followed for time to progression, and immune monitoring was conducted at defined intervals.

Results

Overall, patients were followed for a median of 24 months. 11/18 patients completed treatments as per protocol. No treatment-associated events > grade 2 were observed. Th1-biased PAP-specific T-cell responses were detected in 11/18 individuals, and were not statistically different between study arms. Higher titer antibody responses to PAP were detectable in patients who received pTVG-HP booster immunizations. Median time to progression was less than 6 months and not statistically different between study arms. The median overall survival for all patients was 28 months.

Conclusions

These findings suggest that prime-boost vaccination can augment and diversify the type of immunity elicited with anti-tumor vaccination in terms of T-cell and humoral immunity. Future studies will explore DNA as priming immunization rather than a booster immunization.

Trial registration

NCT01706458.

Conjugation of toll-like receptor-7 agonist to gastric cancer antigen MG7-Ag exerts antitumor effects

AIM: To investigate the effects of our tumor vaccines on reversing immune tolerance and generating therapeutic response.

METHODS: Vaccines were synthesized by solid phase using an Fmoc strategy, where a small molecule toll-like receptor-7 agonist (T7) was conjugated to a monoclonal gastric cancer 7 antigen mono-epitope (T7-MG1) or tri-epitope (T7-MG3). Cytokines were measured in both mouse bone marrow dendritic cells and mouse spleen lymphocytes after exposed to the vaccines. BALB/c mice were intraperitoneally immunized with the vaccines every 2 wk for a total of three times, and then subcutaneously challenged with Ehrlich ascites carcinoma (EAC) cells. Three weeks later, the mice were killed, and the tumors were surgically removed and weighed. Serum samples were collected from the mice, and antibody titers were determined by ELISA using an alkaline phosphate-conjugated detection antibody for total IgG. Antibody-dependent cell-mediated cytotoxicity was detected by the lactate dehydrogenase method using natural killer cells as effectors and antibody-labeled EAC cells as targets. Cytotoxic T lymphocyte activities were also detected by the lactate dehydrogenase method using lymphocytes as effectors and EAC cells as targets.

RESULTS: Vaccines were successfully synthesized and validated by analytical high performance liquid chromatography and electrospray mass spectrometry, including T7, T7-MG1, and T7-MG3. Rapid inductions of tumor necrosis factor-α and interleukin-12 in bone marrow dendritic cells and interferon γ and interleukin-12 in lymphocytes occurred in vitro after T7, T7-MG1, and T7-MG3 treatment. Immunization with T7-MG3 reduced the EAC tumor burden in BALB/c mice to 62.64% ± 5.55% compared with PBS control (P < 0.01). Six or nine weeks after the first immunization, the monoclonal gastric cancer 7 antigen antibody increased significantly in the T7-MG3 group compared with the PBS control (P < 0.01). As for antibody-dependent cell-mediated cytotoxicity, antisera obtained by immunization with T7-MG3 were able to markedly enhance cell lysis compared to PBS control (31.58% ± 2.94% vs 18.02% ± 2.26%; P < 0.01). As for cytotoxic T lymphocytes, T7-MG3 exhibited obviously greater cytotoxicity compared with PBS control (40.92% ± 4.38% vs 16.29% ± 1.90%; P < 0.01).

CONCLUSION: A successful method is confirmed for the design of gastric cancer vaccines by chemical conjugation of T7 and multi-repeat-epitope of monoclonal gastric cancer 7 antigen.

An optimized peptide vaccine strategy capable of inducing multivalent CD8+ T cell responses with potent antitumor effects

Therapeutic cancer vaccines are an attractive alternative to conventional therapies for treating malignant tumors, and successful tumor eradication depends primarily on obtaining high numbers of long-lasting tumor-reactive CD8⁺ T cells. Dendritic cell (DC)-based vaccines constitute a promising approach for treating cancer, but in most instances low immune responses and suboptimal therapeutic effects are achieved indicating that further optimization is required. We describe here a novel vaccination strategy with peptide-loaded DCs followed by a mixture of synthetic peptides, polyinosine-polycytidylic acid (poly-IC) and anti-CD40 antibodies (TriVax) for improving the immunogenicity and therapeutic efficacy of DC-based vaccines in a melanoma mouse model. TriVax immunization 7–12 d after priming with antigen-loaded DCs generated large numbers of long-lasting multiple antigen-specific CD8⁺ T cells capable of recognizing tumor cells. These responses were far superior to those generated by homologous immunizations with either TriVax or DCs. CD8⁺ T cells but not CD4⁺ T cells or NK cells mediated the therapeutic efficacy of this heterologous prime-boost strategy. Moreover, combinations of this vaccination regimen with programmed cell death-1 (PD-1) blockade or IL2 anti-IL2 antibody complexes led to complete disease eradication and survival enhancement in melanoma-bearing mice. The overall results suggest that similar strategies would be applicable for the design of effective therapeutic vaccination for treating viral diseases and various cancers, which may circumvent current limitations of cell-based cancer vaccines.

Cancer vaccines inducing antibody production: more pros than cons

To date, passive immunotherapy with monoclonal antibodies is a well-established option in clinical oncology. By contrast, anticancer vaccines are less advanced, with the exception of successfully applied prophylactic vaccines against oncogenic virus infections. The creation of therapeutic vaccines is still a great challenge mostly due to the self-nature of tumor antigens. Therapeutic vaccines may be based on patient-specific material including pulsed effector cells, or tumor-associated antigens and derivatives thereof, such as peptides, mimotopes and nucleic acids. The latter represents a more universal approach, which would set an ideal economic framework resulting in broad patient access. In this article we focus on cancer vaccines for antibody production, in particular mimotope vaccines. The collected evidence suggests that they will open up new treatment options in minimal residual disease and early stage disease.

Screening and Identification of Recombinant Anti-Idiotype Antibodies against Gastric Cancer and Colon Cancer Monoclonal Antibodies by a Phage-Displayed Single-Chain Variable Fragment Library

Several monoclonal antibodies (McAbs) have been developed that show high sensitivity and specificity to gastric cancer and colorectal cancer. However, few of the antigens recognized by these antibodies have been identified. The authors now report the selection of anti-idiotype (anti-id) antibodies of MGb1 McAb against gastric cancer and MC5 McAb against colorectal cancer using phage-displayed single-chain variable fragment (ScFv) libraries. After purification, the anti-id antibodies were approximately 30 kd and could be recognized by MGb1/MC5 McAb. Anti-id antibodies significantly blocked the binding of MGb1 and MC5 to gastric cancer/colorectal cancer cells, respectively, suggesting that the antibodies were specific to MGb1 and MC5. Antibodies against gastric and colorectal cancer could be detected in mice at 6 weeks after immunization with the anti-id antibodies. At week 8, antibody titers reached 1:400. The anti-id antibodies may be useful as novel reagents for developing vaccines against gastric cancer and colorectal cancer.

Viral vectors in malaria vaccine development

Traditional vaccine technologies have resulted in an impressive array of efficacious vaccines against a variety of infectious agents. However, several potentially deadly pathogens, including retroviruses and parasites, have proven less amenable to the application of traditional vaccine platforms, indicating the need for new approaches. Viral vectors represent an attractive way to deliver and present vaccine antigens that may offer advantages over traditional platforms. Due to their ability to induce strong cell-mediated immunity (CMI) in addition to antibodies, viral vectors may be suitable for infectious agents, such as malaria parasites, where potent CMI is required for protection. Poxvirus-vectored malaria vaccines have been the most extensively studied in the clinic, achieving significant reductions in liver-stage parasite burden. More recently, adenovirus-vectored malaria vaccines have entered clinical testing. The most promising approach - heterologous prime-boost regimens, in which different viral vectors are sequentially paired with each other or with DNA or recombinant protein vaccines - is now being explored, and could provide high-grade protection, if findings in animal models are translatable to humans. Significant barriers remain, however, such as pre-existing immunity to the vector particle and an unexplained safety signal observed in one trial suggesting an increased risk of HIV acquisition in volunteers with pre-existing immunity to the vector.

Expression and prognostic value of MG7-Ag in patients with surgically resectable esophageal squamous cell carcinoma

PURPOSE

MG7-Ag is a human gastric-carcinoma-associated antigen. The expression of MG7-Ag was found to increase gradually with the development and progression of gastric cancer. Moreover, a poorer prognosis was found in MG7-Ag positive gastric-carcinoma patients than in MG7-Ag negative patients. However, neither MG7-Ag expression nor its clinical significance has been previously examined in squamous cell carcinoma (SCC) of the esophagus. In this study, we examined the expression of MG7-Ag in esophageal squamous cell carcinomas to assess its value as a prognostic indicator.

METHODS

The expression of MG7-Ag was detected in 112 cases of esophageal squamous cell carcinoma (SCC) by immunohistochemical analysis. The relation of MG7-Ag staining with various clinicopathological features was statistically analyzed.

RESULTS

The staining of MG7-Ag was detected in SCC, while not in normal epithelial cells. In esophageal SCC, MG7-Ag was found significantly correlated with depth of invasion (P = .012), in T4, T3 carcinomas but not in T2, T1 carcinomas, lymph node metastases (P = .029), pathological stage (P = .005). Consistently, the survival rate tended to be statistically lower in patients with MG7-Ag positive SCCs than in MG7-Ag negative SCCs (P = .005). However, no significant difference was observed between MG7-expression and patient age, sex, tumor location, differentiation, distant metastasis, and lymphatic invasion.

CONCLUSION

MG7-Ag might play a positive role in the process of carcinogenesis and progression of esophageal SCC, and it could be considered as one valuable prognostic indicator in esophageal SCC.