Hyun Il Cho

HIF-1α regulates function and differentiation of myeloid-derived suppressor cells in the tumor microenvironment.

The hypoxic environment of tumors dictates the phenotype of local myeloid-derived suppressor cells (MDSCs) via HIF-1a expression; hypoxia converts splenic MDSCs from specific into nonspecific suppressors.

Chemotherapy enhances tumor cell susceptibility to CTL-mediated killing during cancer immunotherapy in mice

Cancer immunotherapy faces a serious challenge because of low clinical efficacy. Recently, a number of clinical studies have reported the serendipitous finding of high rates of objective clinical response when cancer vaccines are combined with chemotherapy in patients with different types of cancers. However, the mechanism of this phenomenon remains unclear. Here, we tested in mice several cancer vaccines and an adoptive T cell transfer approach to cancer immunotherapy in combination with several widely used chemotherapeutic drugs. We found that chemotherapy made tumor cells more susceptible to the cytotoxic effect of CTLs through a dramatic perforin-independent increase in permeability to GrzB released by the CTLs. This effect was mediated via upregulation of mannose-6-phosphate receptors on the surface of tumor cells and was observed in mouse and human cells. When combined with chemotherapy, CTLs raised against specific antigens were able to induce apoptosis in neighboring tumor cells that did not express those antigens. These data suggest that small numbers of CTLs could mediate a potent antitumor effect when combined with chemotherapy. In addition, these results provide a strong rationale for combining these modalities for the treatment of patients with advanced cancers.

Mechanism of T Cell Tolerance Induced by Myeloid-Derived Suppressor Cells

Ag-specific T cell tolerance plays a critical role in tumor escape. Recent studies implicated myeloid-derived suppressor cells (MDSCs) in the induction of CD8+ T cell tolerance in tumor-bearing hosts. However, the mechanism of this phenomenon remained unclear. We have found that incubation of Ag-specific CD8+ T cells, with peptide-loaded MDSCs, did not induce signaling downstream of TCR. However, it prevented subsequent signaling from peptide-loaded dendritic cells. Using double TCR transgenic CD8+ T cells, we have demonstrated that MDSC induced tolerance to only the peptide, which was presented by MDSCs. T cell response to the peptide specific to the other TCR was not affected. Incubation of MDSCs with Ag-specific CD8+ T cells caused nitration of the molecules on the surface of CD8+ T cells, localized to the site of physical interaction between MDSC and T cells, which involves preferentially only TCR specific for the peptide presented by MDSCs. Postincubation with MDSCs, only nitrotyrosine-positive CD8+ T cells demonstrated profound nonresponsiveness to the specific peptide, whereas nitrotyrosine-negative CD8+ T cells responded normally to that stimulation. MDSCs caused dissociation between TCR and CD3ζ molecules, disrupting TCR complexes on T cells. Thus, these data describe a novel mechanism of Ag-specific CD8+ T cell tolerance in cancer.

Optimized Peptide Vaccines Eliciting Extensive CD8 T-Cell Responses with Therapeutic Antitumor Effects

A major challenge for developing effective therapeutic vaccines against cancer is overcoming immunologic tolerance to tumor-associated antigens that are expressed on both malignant cells and normal tissues. Herein, we describe a novel vaccination approach, TriVax, that uses synthetic peptides representing CD8 T-cell epitopes, Toll-like receptor agonists that function as potent immunologic adjuvants and costimulatory anti-CD40 antibodies to generate large numbers of high-avidity antigen-reactive T cells capable of recognizing and killing tumor cells. Our results show that TriVax induced huge numbers of long-lasting antigen-specific CD8 T cells that displayed significant antitumor effects in vivo. The administration of a TriVax formulation containing a CD8 T-cell epitope derived from a melanosomal antigen (Trp2(180-188)) elicited antigen-specific CD8 T cells that induced systemic autoimmunity (vitiligo). More important, TriVax immunization was effective in eliciting potent protective antitumor immunity as well as remarkable therapeutic effects against established B16 melanoma. This therapeutic effect was mediated by CD8 T cells via perforin-mediated lysis and required the participation of type-I IFN but not IFNgamma. These results suggest that similar strategies would be applicable for the design of effective vaccination for conducting clinical studies in cancer patients.

PRDM1/Blimp-1 Controls Effector Cytokine Production in Human NK Cells

NK cells are major effectors of the innate immune response through cytolysis and bridge to the adaptive immune response through cytokine release. The mediators of activation are well studied; however, little is known about the mechanisms that restrain activation. In this report, we demonstrate that the transcriptional repressor PRDM1 (also known as Blimp-1 or PRDI-BF1) is a critical negative regulator of NK function. Three distinct PRDM1 isoforms are selectively induced in the CD56dim NK population in response to activation. PRDM1 coordinately suppresses the release of IFN-γ, TNF-α, and TNF-β through direct binding to multiple conserved regulatory regions. Ablation of PRDM1 expression leads to enhanced production of IFN-γ and TNF-α but does not alter cytotoxicity, whereas overexpression blocks cytokine production. PRDM1 response elements are defined at the IFNG and TNF loci. Collectively, these data demonstrate a key role for PRDM1 in the negative regulation of NK activation and position PRDM1 as a common regulator of the adaptive and innate immune response.

In vivo Expansion, Persistence, and Function of Peptide Vaccine- Induced CD8 T Cells Occur Independently of CD4 T Cells

Significant efforts are being devoted toward the development of effective therapeutic vaccines against cancer. Specifically, well-characterized subunit vaccines, which are designed to generate antitumor cytotoxic CD8 T-cell responses. Because CD4 T cells participate at various stages of CD8 T-cell responses, it is important to study the role of CD4 T cells in the induction and persistence of antitumor CD8 T-cell responses by these vaccines. Recent evidence points to the requirement of CD4 T cells for the long-term persistence of memory CD8 T cells, which in the case of cancer immunotherapy would be critical for the prevention of tumor recurrences. The purpose of the present study was to assess whether CD4 T cells are necessary for the generation and maintenance of antigen-specific CD8 T cells induced by subunit (peptide or DNA) vaccines. We have used a vaccination strategy that combines synthetic peptides representing CD8 T-cell epitopes, a costimulatory anti-CD40 antibody and a Toll-like receptor agonist (TriVax) to generate large numbers of antigen-specific CD8 T-cell responses. Our results show that the rate of decline (clonal contraction) of the antigen-specific CD8 T cells and their functional state is not affected by the presence or absence of CD4 T cells throughout the immune response generated by TriVax. We believe that these results bear importance for the design of effective vaccination strategies against cancer.

Interferon γ limits the effectiveness of melanoma peptide vaccines

The development of effective therapeutic vaccines to generate tumor-reactive cytotoxic T lymphocytes (CTLs) continues to be a top research priority. However, in spite of some promising results, there are no clear examples of vaccines that eradicate established tumors. Most vaccines are ineffective because they generate low numbers of CTLs and because numerous immunosuppressive factors abound in tumor-bearing hosts. We designed a peptide vaccine that produces large numbers of tumor-reactive CTLs in a mouse model of melanoma. Surprisingly, CTL tumor recognition and antitumor effects decreased in the presence of interferon γ (IFNγ), a cytokine that can provide therapeutic benefit. Tumors exposed to IFNγ evade CTLs by inducing large amounts of noncognate major histocompatibility complex class I molecules, which limit T-cell activation and effector function. Our results demonstrate that peptide vaccines can eradicate large, established tumors in circumstances under which the inhibitory activities of IFNγ are curtailed.

BiVax: a peptide/poly-IC subunit vaccine that mimics an acute infection elicits vast and effective anti-tumor CD8 T-cell responses

Therapeutic vaccines for the treatment of cancer are an attractive alternative to some of the conventional therapies that are currently used. More importantly, vaccines could be very useful to prevent recurrences when applied after primary therapy. Unfortunately, most therapeutic vaccines for cancer have performed poorly due to the low level of immune responses that they induce. Previous work done in our laboratory in cancer mouse models demonstrated that vaccines consisting of synthetic peptides representing minimal CD8 T-cell epitopes administered i.v. mixed with poly-IC and anti-CD40 antibodies (TriVax) were capable of inducing massive T cell responses similar to those found during acute infections. We now report that some peptides are capable of inducing similarly large T cell responses after vaccination with poly-IC alone (BiVax). The results show that amphiphilic peptides are more likely to function as strong immunogens in BiVax and that systemic immunizations (i.v. or i.m.) were more effective than local (s.c.) vaccine administration. The immune responses induced by BiVax were found to be effective against established tumors in two mouse cancer models. The roles of various immune-related pathways such as type-I IFN, CD40 costimulation, CD4 T cells, TLRs and the MDA5 RNA helicase were examined. The present findings could facilitate the development of simple and effective subunit vaccines for diseases where CD8 T cells provide a therapeutic benefit.

A Potent Vaccination Strategy That Circumvents Lymphodepletion for Effective Antitumor Adoptive T-cell Therapy

Adoptive cell therapy using tumor-reactive T lymphocytes is a promising approach for treating advanced cancer. Successful tumor eradication depends primarily on the expansion and survival of the adoptively transferred T cells. Lymphodepletion using total body irradiation (TBI) and administering high-dose interleukin (IL)-2 have been used with adoptive cell therapy to promote T-cell expansion and survival to achieve maximal therapeutic effects. However, TBI and high-dose IL-2 increase the risk for major complications that impact overall survival. Here we describe an alternative approach to TBI and high-dose IL-2 for optimizing adoptive cell therapy, resulting in dramatic therapeutic effects against established melanomas in mice. Administration of a potent, noninfectious peptide vaccine after adoptive cell therapy dramatically increased antigen-specific T-cell numbers leading to enhancement in the survival of melanoma-bearing mice. Furthermore, combinations of peptide vaccination with PD1 blockade or IL-2/anti-IL-2 antibody complexes led to complete disease eradication and long-term survival in mice with large tumors receiving adoptive cell therapy. Our results indicate that PD1 blockade and IL-2/anti-IL-2 complexes enhance both the quantitative and qualitative aspects of the T-cell responses induced by peptide vaccination after adoptive cell therapy. These findings could be useful for the optimization of adoptive cell therapy in cancer patients without the need of toxic adjunct procedures.

Autophagy induced by conventional chemotherapy mediates tumor cell sensitivity to immunotherapy

Autophagy attenuates the efficacy of conventional chemotherapy but its effects on immunotherapy have been little studied. Here, we report that chemotherapy renders tumor cells more susceptible to lysis by CTL in vivo. Moreover, bystander tumor cells that did not express antigen were killed by CTL. This effect was mediated by transient but dramatic upregulation of the mannose-6-phosphate receptor (MPR) on the tumor cell surface. Antitumor effects of combined treatment related to the kinetics of MPR upregulation and abrogation of this event abolished the combined effect of immunotherapy and chemotherapy. MPR accumulation on the tumor cell surface during chemotherapy was observed in different mouse tumor models and in patients with multiple myeloma. Notably, this effect was the result of redistribution of the receptor caused by chemotherapy-inducible autophagy. Together, our findings reveal one molecular mechanism through which the antitumor effects of conventional cancer chemotherapy and immunotherapy are realized.