Improved efficacy of therapeutic vaccination with viable human umbilical vein endothelial cells against murine melanoma by introduction of OK432 as adjuvant

Vaccines targeting angiogenesis in melanoma

Angiogenesis has a significant role in metastasis and progression of melanoma. Even small tumors may be susceptible to metastasis and hence lead to a worse outcome in patients with melanoma. One of the anti-angiogenic treatment approaches that is undergoing comprehensive study is specific immunotherapy. While tumor cells are challenging targets for immunotherapy due to their genetic instability and heterogeneity, endothelial cells (ECs) are genetically stable. Therefore, vaccines targeting angiogenesis in melanoma are appropriate choices that target both tumor cells and ECs while capable of inducing strong, anti-tumor immune responses with limited toxicity. The main targets of angiogenesis are VEGFs and their receptors but other potential targets have also been investigated, especially in preclinical studies. Various types of vaccines that target angiogenesis in melanoma have been studied including DNA, peptide, protein, dendritic cell-based, and endothelial cell vaccines. This review outlines a number of target antigens that are important for potential progress in developing vaccines for targeting angiogenesis in melanoma. We also discuss different types of vaccines that have been investigated, delivery mechanisms and popular adjuvants, and suggest ways to improve future clinical outcomes.

Low-dose docetaxel enhances the anti-tumour efficacy of a human umbilical vein endothelial cell vaccine

Our previous studies have indicated that human umbilical vein endothelial cell (HUVEC) vaccination appears to be a potentially promising anti-angiogenesis therapy, but the modest therapeutic anti-tumour efficiency limits its clinical use. This highlights the importance of identifying more potent therapeutic HUVEC vaccine strategies for clinical testing. In the present study, the immune-modulating doses of docetaxel (DOC) was combined with 1 × 10⁶ viable HUVECs as a means to enhance the therapeutic anti-tumour efficiency of the HUVEC vaccine. Our results demonstrated that 5 mg/kg DOC administrated prior to HUVEC vaccine could most effectively assist HUVEC vaccine to display a remarkable suppression of tumour growth and metastasis as wells as a prolongation of survival time in a therapeutic procedure. CD31 immunohistochemical analysis of the excised tumours confirmed a significant reduction in vessel density after treatment with the HUVEC vaccine with 5 mg/kg DOC. Additionally, an increased HUVEC-specific antibody level, activated CTLs and an elevated IFN-γ level in cultured splenocytes were revealed after treatment with HUVEC vaccine with 5 mg/kg DOC. Finally, 5 mg/kg DOC coupled with the HUVEC vaccine led to induction of significant increases in CD8⁺T cells and decrease in Tregs in the tumour microenvironment. Taken together, all the results verified that 5 mg/kg DOC could assist HUVEC vaccine to elicit strong HUVEC specific humoral and cellular responses, which could facilitate the HUVEC vaccine-mediated inhibition of cancer growth and metastasis. These findings provide the immunological rationale for the combined use of immune-modulating doses of DOC and HUVEC vaccines in patients with cancer.

Improved Antitumor Efficacy of Combined Vaccine Based on the Induced HUVECs and DC-CT26 Against Colorectal Carcinoma

Angiogenesis is essential for the development, growth, and metastasis of solid tumors. Vaccination with viable human umbilical vein endothelial cells (HUVECs) has been used for antitumor angiogenesis. However, the limited immune response induced by HUVECs hinders their clinical application. In the present study, we found that HUVECs induced by a tumor microenvironment using the supernatant of murine CT26 colorectal cancer cells exerted a better antiangiogenic effect than HUVECs themselves. The inhibitory effect on tumor growth in the induced HUVEC group was significantly better than that of the HUVEC group, and the induced HUVEC group showed a strong inhibition in CD31-positive microvessel density in the tumor tissues. Moreover, the level of anti-induced HUVEC membrane protein antibody in mouse serum was profoundly higher in the induced HUVEC group than in the HUVEC group. Based on this, the antitumor effect of a vaccine with a combination of induced HUVECs and dendritic cell-loading CT26 antigen (DC-CT26) was evaluated. Notably, the microvessel density of tumor specimens was significantly lower in the combined vaccine group than in the control groups. Furthermore, the spleen index, the killing effect of cytotoxic T lymphocytes (CTLs), and the concentration of interferon-γ in the serum were enhanced in the combined vaccine group. Based on these results, the combined vaccine targeting both tumor angiogenesis and tumor cells may be an attractive and effective cancer immunotherapy strategy.

In vivo antitumor activity evaluation of cancer vaccines prepared by various antigen forms in a murine hepatocellular carcinoma model

Cancer cell vaccines with strong specificity and low tolerance have been revealed to be a promising option for oncology treatment. Various antigen forms, including tumor cell lysate and glutaraldehyde-fixed tumor cells, have been intensively used in cancer vaccine preparation. However, the most effective antigen form has not yet been identified. In the present study, the antitumor efficiency of vaccines prepared by these two antigen forms was systematically investigated. Murine H22 hepatocellular carcinoma cell lysate and glutaraldehyde-fixed H22 hepatocellular carcinoma cells were conjugated with Freund's adjuvant to prepare vaccines, H22-TCL and Fixed-H22-CELL, respectively. H22-TCL and Fixed-H22-CELL were administrated by subcutaneous immunization in prophylactic and therapeutic strategies. The results of the present study revealed that H22-TCL immunization induced more significant inhibition on tumor growth and metastasis compared with Fixed-H22-CELL injection. Furthermore, histopathological observation demonstrated that H22-TCL vaccine induced larger areas of continuous necrosis within tumors compared to the Fixed-H22-CELL vaccine, which was associated with the extent of tumor inhibition. More importantly, the H22-TCL vaccine injection elicited more evident antigen-specific antibody responses compared with the Fixed-H22-CELL injection. Splenocytes from H22-TCL vaccinated mice also exhibited a more significant T lymphocytes proliferation compared with that from Fixed-H22-CELL-treated mice. All the results indicated that whole tumor cell lysate may be a more effective antigen form in cancer vaccine preparation compared with glutaraldehyde-fixed tumor cells, which elicited more marked antigen specific humoral and cellular immune responses resulted with a superior antitumor efficiency. This would have important clinical signification for cancer vaccine preparation and serve a role in prompting this to other researchers.

Assessment of in vivo anti-tumor activity of human umbilical vein endothelial cell vaccines prepared by various antigen forms

Human umbilical vein endothelial cell (HUVEC) vaccine has been proved as an effective whole-cell vaccine, but the modest therapeutic anti-tumor efficiency limits its clinical use. Various antigen forms, including paraformaldehyde-fixed HUVEC, glutaraldehyde-fixed HUVEC, HUVEC lysate and live HUVEC, have been intensively used in HUVEC vaccine preparation, however, the most effective antigen form has not yet been identified. In the present study, these four commonly used antigen forms were used to prepare vaccines named Para-Fixed-EC, Glu-Fixed-EC, Lysate-EC, and Live-EC respectively, and the anti-tumor efficacy of these four vaccines was investigated. Results showed that Live-EC exhibited the most favorable anti-tumor growth and metastasis effects among the four vaccines in both H22 hepatocellular carcinoma and Lewis lung cancer models. High titer anti-HUVEC antibodies were detected in Live-EC immunized mice sera, and the immune sera of Live-EC group could significantly inhibit HUVEC proliferation and tube formation. Moreover, T cells isolated from Live-EC immunized mice exhibited strong cytotoxicity against HUVEC cells, with an increasing IFN-γ and decreasing Treg production in Live-EC immunized mice. Finally, CD31 immunohistochemical analysis of the excised tumors verified a significant reduction in vessel density after Live-EC vaccination, which was in accordance with the anti-tumor efficiency. Taken together, all the results proved that live HUVEC was the most effective antigen form to induce robust HUVEC specific antibody and CTL responses, which could lead to the significant inhibition of tumor growth and metastasis. We hope the present findings would provide a rationale for the further optimization of HUVEC vaccine.

Dendritic cells loading autologous tumor lysate promote tumor angiogenesis

Dendritic cells (DC) have been exploited for vaccination against cancer for years. DC loading autologous tumor lysate (ATL-DC) have been assessed in ongoing clinical trials, but frequently do not meet expectation. In this study, we found that mice immunized with ATL-DC induced less protective anti-tumor effect than immunized with DC alone. The percentage of CD8+ T cells and the lysis efficiency of CTLs to auto tumor cells in ATL-DC vaccination group was less than that of DC group. Moreover, vaccination of mice with ATL-DC also promoted tumor angiogenesis by analyzing the CD31 positive microvessel density and hemoglobin content of tumor specimens. Human umbilical vein endothelial cells (HUVEC) have been proved effective in the anti-angiogenesis immunity against cancer. However, in the following research we found that the anti-tumor effect was attenuated while immunized mice with HUVEC combined with ATL-DC (HUVEC + ATL-DC). Furthermore, immunized mice with HUVEC + ATL-DC profoundly increased the tumor angiogenesis by analyzing the microvessel density and hemoglobin content of tumor specimens. These data suggest that vaccination using ATL-DC antagonized HUVEC induced anti-angiogenesis effect. Our research for the first time indicated that ATL-DC have the potential to promote the process of tumor angiogenesis in vivo. As vaccines based on DC loading autologous tumor lysate have been used in clinical, this find warned that the safety of this kind of vaccine should be taken into consideration seriously.