No abstract

Immunotherapy and chemotherapy are generally effective against small tumors in animal models of cancer. However, these treatment regimens are generally ineffective against large, bulky tumors. We have found that a multimodality treatment regimen using DNA vaccination in combination with chemotherapeutic agent epigallocatechin-3-gallate (EGCG), a compound found in green tea, is effective in inhibiting large tumor growth. EGCG was found to induce tumor cellular apoptosis in a dose-dependent manner. The combination of EGCG and DNA vaccination led to an enhanced tumor-specific T-cell immune response and enhanced antitumor effects, resulting in a higher cure rate than either immunotherapy or EGCG alone. In addition, combined DNA vaccination and oral EGCG treatment provided longterm antitumor protection in cured mice. Cured animals rejected a challenge of E7-expressing tumors, such as TC-1 and B16E7, but not a challenge of B16 7 weeks after the combined treatment, showing antigen-specific immune responses. These results suggest that multimodality treatment strategies, such as combining immunotherapy with a tumor-killing cancer drug, may be a more effective anticancer strategy than singlemodality treatments. [Cancer Res 2007;67(2):802-11]

Immune evasion is an important reason why the immune system cannot control tumor growth. To elucidate the mechanism for tumor immune evasion, we generated an immune-resistant human papillomavirus type 16 (HPV-16) E7-expressing tumor cell line by subjecting a susceptible tumor cell line to multiple rounds of in vivo immune selection with an E7-specific vaccine. Comparison of parental and immune-resistant tumors revealed that Akt is highly activated in the immune-resistant tumors. Retroviral transfer of a constitutively active form of Akt into the parental tumor significantly increased its resistance against E7-specific CD8(+) T-cell mediated apoptosis. The observed resistance against apoptosis was found to be associated with the upregulation of antiapoptotic molecules. We also observed that intratumoral injection of an Akt inhibitor enhanced the therapeutic efficacy of E7-specific vaccine or E7-specific CD8(+) T-cell adoptive transfer against the immune-resistant tumors. Thus, our data indicate that the activation of PI3K/Akt pathway represents a new mechanism of immune escape and has important implications for the development of a novel strategy in cancer immunotherapy against immune-resistant tumor cells.

Multiple classes of pharmacologic agents have the potential to induce the expression and release of pro-inflammatory factors from dying tumor cells. As a result, these cells can in theory elicit an immune response through various defined mechanisms to permanently eradicate disseminated cancer. However, the impact of chemotherapy on the tumor-specific immune response in the context of the tumor microenvironment is largely unknown. Within the tumor microenvironment, the immune response promoted by chemotherapy is antagonized by an immune-suppressive milieu, and the balance of these opposing forces dictates the clinical course of disease. Here we report that high antigen exposure within the tumor microenvironment following chemotherapy is sufficient to skew this balance in favor of a productive immune response. In elevating antigen exposure, chemotherapy can achieve long-term control of tumor progression without the need of an additional adjuvant. We found that chemotherapy initiated this phenomenon in the tumor microenvironment through an accumulation of dendritic cells, which stimulated CD8+ T cells and the type-I interferon pathway. From this conceptual base, we developed a simple approach to cancer therapy combining chemotherapy and vaccination that may be widely applicable.

Due to the exquisite specificity and potency of the immune system, vaccination is in theory the most precise and powerful approach for controlling cancer. However, current data from clinical trials indicate that vaccination rarely yields significant benefits for cancer patients in terms of tumor progression and long-term survival. The poor clinical outcomes of vaccination are primarily caused by mechanisms of immune tolerance, especially within the tumor microenvironment. Here we report that vaccination drives the evolution of tumor cells towards an immune-resistant and stem-like phenotype that promotes tumor growth and nullifies the cytotoxic T lymphocyte (CTL) response. The emergence of this phenotype required the transcription factor Nanog, which is induced as a consequence of immune selection. Nanog expression enhanced the stem-like features of tumor cells and protected them from killing by tumor-reactive CTLs. Delivery of siNanog into tumor-bearing mice rendered the tumor vulnerable to immune surveillance and strongly suppressed its growth. Together, our findings demonstrate tumor adaptation to vaccination through gain of an immune-resistant, stem-like phenotype and identify Nanog as a central molecular target in this process. Future vaccination technology should consider Nanog an important target to enhance the immunotherapeutic response.

We analyzed the in vivo tumor regression activity of high molecular mass poly-γ-glutamate (γ-PGA) from Bacillus subtilis sups. chungkookjang. C57BL/6 mice were orally administered 10-, 100-, or 2000-kDa γ-PGA or β-glucan (positive control), and antitumor immunity was examined. Our results revealed higher levels of NK cell-mediated cytotoxicity and IFN-γ secretion in mice treated with higher molecular mass γ-PGA (2000 kDa) vs those treated with lower molecular mass γ-PGA (10 or 100 kDa) or β-glucan. We then examined the effect of oral administration of 10- or 2000-kDa γ-PGA on protection against B16 tumor challenge in C57BL/6 mice. Mice receiving high molecular mass γ-PGA (2000 kDa) showed significantly smaller tumor sizes following challenge with the MHC class I-down-regulated tumor cell lines, B16 and TC-1 P3 (A15), but not with TC-1 cells, which have normal MHC class I expression. Lastly, we found that γ-PGA-induced antitumor effect was decreased by in vivo depletion of NK cells using mAb PK136 or anti-asialo GM1 Ab, and that was completely blocked in NK cell-deficient B6 beige mice or IFN-γ knockout mice. Taken together, we demonstrated that oral administration of high molecular mass γ-PGA (2000 kDa) generated significant NK cell-mediated antitumor activity in mice bearing MHC class I-deficient tumors.

A key factor in dendritic cell (DC)-based tumor immunotherapy is the identification of an immunoadjuvant capable of inducing DC maturation to enhance cellular immunity. The efficacy of a 50S ribosomal protein L7/L12 (rplL) from Mycobacterium tuberculosis Rv0652, as an immunoadjuvant for DC-based tumor immunotherapy, and its capacity for inducing DC maturation was investigated. In this study, we showed that Rv0652 is recognized by Toll-like receptor 4 (TLR4) to induce DC maturation, and pro-inflammatory cytokine production (TNF-alpha, IL-1beta, and IL-6) that is partially modulated by both MyD88 and TRIF signaling pathways. Rv0652-activated DCs could activate naïve T cells, effectively polarize CD4+ and CD8+ T cells to secrete IFN-gamma, and induce T cell-mediated-cytotoxicity. Immunization of mice with Rv0652-stimulated ovalbumin (OVA)-pulsed DCs resulted in induction of a potent OVA-specific CD8+ T cell response, slowed tumor growth, and promoted long-term survival in a murine OVA-expressing E.G7 thymoma model. These findings suggest that Rv0652 enhances the polarization of T effector cells toward a Th1 phenotype through DC maturation, and that Rv0652 may be an effective adjuvant for enhancing the therapeutic response to DC-based tumor immunotherapy.

The low response rate of current cancer immunotherapy suggests the presence of few antigen-specific T cells and a high number of immunosuppressive factors in tumor microenvironment (TME). Here, we develop a syringeable immunomodulatory multidomain nanogel (iGel) that overcomes the limitation by reprogramming of the pro-tumoral TME to antitumoral immune niches. Local and extended release of immunomodulatory drugs from iGel deplete immunosuppressive cells, while inducing immunogenic cell death and increased immunogenicity. When iGel is applied as a local postsurgical treatment, both systemic antitumor immunity and a memory T cell response are generated, and the recurrence and metastasis of tumors to lungs and other organs are significantly inhibited. Reshaping of the TME using iGel also reverts non-responding groups to checkpoint blockade therapies into responding groups. The iGel is expected as an immunotherapeutic platform that can reshape immunosuppressive TMEs and synergize cancer immunotherapy with checkpoint therapies, with minimized systemic toxicity.