Cyclophosphamide potentiates the antitumor effect of immunization with injection of immature dendritic cells into irradiated tumor

Cyclophosphamide augments the efficacy of in situ vaccination in a mouse melanoma model

Introduction

We have previously shown that an intratumoral (IT) injection of the hu14.18-IL2 immunocytokine (IC), an anti-GD2 antibody linked to interleukin 2, can serve as an in situ vaccine and synergize with local radiotherapy (RT) to induce T cell-mediated antitumor effects. We hypothesized that cyclophosphamide (CY), a chemotherapeutic agent capable of depleting T regulatory cells (Tregs), would augment in situ vaccination. GD2+ B78 mouse melanoma cells were injected intradermally in syngeneic C57BL/6 mice.

Methods

Treatments with RT (12Gy) and/or CY (100 mg/kg i.p.) started when tumors reached 100-300 mm3 (day 0 of treatment), followed by five daily injections of IT-IC (25 mcg) on days 5-9. Tumor growth and survival were followed. In addition, tumors were analyzed by flow cytometry.

Results

Similar to RT, CY enhanced the antitumor effect of IC. The strongest antitumor effect was achieved when CY, RT and IC were combined, as compared to combinations of IC+RT or IC+CY. Flow cytometric analyses showed that the combined treatment with CY, RT and IC decreased Tregs and increased the ratio of CD8+ cells/Tregs within the tumors. Moreover, in mice bearing two separate tumors, the combination of RT and IT-IC delivered to one tumor, together with systemic CY, led to a systemic antitumor effect detected as shrinkage of the tumor not treated directly with RT and IT-IC. Cured mice developed immunological memory as they were able to reject B78 tumor rechallenge.

Conclusion

Taken together, these preclinical results show that CY can augment the antitumor efficacy of IT- IC, given alone or in combination with local RT, suggesting potential benefit in clinical testing of these combinations.

Establishment of Synergistic Chemoimmunotherapy for Head and Neck Cancer Using Peritumoral Immature Dendritic Cell Injections and Low-Dose Chemotherapies

The lack of available tumor antigens with strong immunogenicity, human leukocyte antigen restriction, and immunosuppression via regulatory T-cells (Tregs) and myeloid-derived suppressor cells are limitations for dendritic cell (DC)–based immunotherapy in patients with advanced head and neck cancer (HNC). We sought to overcome these limitations and induce effective antitumor immunity in the host. The effect of low-dose docetaxel (DTX) treatment on DC maturation was examined in an ex vivo study, and a phase I clinical trial of combination therapy with direct peritumoral immature DC (iDC) injection with OK-432 and low-dose cyclophosphamide (CTX) plus DTX was designed. Low-dose DTX did not negatively affect iDC viability and instead promoted maturation and IL-12 production. Five patients with metastatic or recurrent HNC were enrolled for the trial. All patients experienced grade 1 to 3 fevers. Intriguingly, elevated CD8+ effector T-cells and reduced Tregs were observed in four patients who completed two treatment cycles. All patients were judged to have progressive disease, but tumor regressions were observed in a subset of targeted metastatic lesions in two of five patients. Our results show that the combination of direct peritumoral iDC injection with OK-432 and low-dose CTX plus DTX is well tolerated and should give rise to changing the immune profile of T-cell subsets and improvement of immunosuppression in advanced HNC patients. Additionally, our ex vivo data on the effect of low-dose DTX treatment on DC maturation may contribute to developing new combination therapies with low-dose chemotherapy and immunotherapy.

Combination of cancer immunotherapy with clinically available drugs that can block immunosuppressive cells

Although cancer immunotherapy, which is able to target specifically cancer cells without detrimental effects to normal cell functions, would serve as an ideal therapeutic modality, most of the randomized clinical trials of cancer immunotherapy have not demonstrated a meaningful survival benefit to cancer patients over preexisting therapeutic modalities. Due to the discrepancy between the impressive preclinical results and the limited clinical results, the cancer immunotherapy is not accepted generally as a standard therapy for cancers. A variety of immune escape mechanisms are thought to be involved in this ineffectiveness of cancer immunotherapy. Therefore, elimination of immunosuppressive activities in tumor microenvironment will enhance the effectiveness of cancer immunotherapy, which is currently focused on activation of tumor-specific immune responses. Since there are now increasing evidences showing that many cytotoxic anticancer drugs including targeted agents given in lower-than-therapeutic doses have not only the ability to eliminate tumor cells but can also block the immunosuppressive activities in tumor microenvironments and consequently favor the development of anticancer immune responses, clinically available drugs can be considered for their rapid application to cancer immunotherapies to enhance the efficacy of cancer immunotherapies with marginal effects on cancer treatment.

Negative regulation of myeloid-derived suppressor cells in cancer

Myeloid-derived suppressor cells (MDSC) are a heterogeneous population of immature myeloid cells with suppressive function on immune response. In this review, we discuss recent studies about mechanisms of expansion and suppressive function of MDSCs during inflammation, infection and autoimmune diseases, as well as pro-angiogenic and pro-metastatic functions of these cells in tumor development. Further, we focus on novel studies of MDSCs and therapeutic approaches to eliminate these cells in cancer.

Resveratrol analogue HS-1793 induces the modulation of tumor-derived T cells

Recent advances in the understanding of the mechanisms responsible for tumor progression suggest the possibility to control cancer growth, not only through chemotherapy-induced cancer cell destruction, but also by stimulating anticancer immunity. However, immune tolerance against tumor antigens disturbs diverse forms of immunotherapy. One of the most potent and well-studied tumor-induced immunosuppressive phenotypes found in the tumor microenvironment is the regulatory subpopulation cells (CD4(+)CD25(+)FoxP3(+) Treg cells). Among the great number of natural agents derived from plants and potentially useful for application in the complementary therapy of cancer, resveratrol is gaining attention for its immunomodulating properties in breast cancer, since the ineffectiveness of numerous immunotherapy strategies may be related, in part, to their negative effects on Treg cells. The present study was undertaken to examine whether HS-1793, a synthetic resveratrol analogue free from the restriction of the metabolic instability and high dose requirement of resveratrol, shows a direct effect on immune responses by enhancing lymphocyte proliferation or an immunomodulatory effect by inducing changes in the Treg cell population in FM3A breast tumor-bearing mice. Although HS-1793 had no direct immunostimulatory effect, it dose-dependently decreased IL-2 secretion and increased IL-4 secretion of concanavalin A-stimulated lymphocytes from tumor-bearing mice, which suggest that HS-1793 may induce changes in the subpopulations of tumor-derived T lymphocytes. The CD4(+)CD25(+) cell population from tumor-bearing mice decreased after HS-1793 treatment in a dose-dependent manner, while the CD4(+) T cell population remained unchanged. FoxP3(+)-expressing cells among the CD4(+)CD25(+) population showed a similar pattern. In contrast, the CD8(+) T cell population as well as the interferon (IFN)-γ-expressing CD8(+) T cell population and IFN-γ secretion of splenocytes from tumor-bearing mice were significantly upregulated by HS-1793 treatment. These results suggest that HS-1793 induces the modulation of tumor-derived T lymphocytes, particulary having a suppressive effect on the Treg cell population, likely contributing to enhanced tumor-specific cytotoxic T lymphocyte responses and CD4(+) T cells involving antitumor immunity. Therefore, HS-1793 may serve as a promising adjuvant therapeutic reagent in breast cancer immunotherapy.

Cancer vaccines and carbohydrate epitopes

Tumor-associated carbohydrate antigens (TACA) result from the aberrant glycosylation that is seen with transformation to a tumor cell. The carbohydrate antigens that have been found to be tumor-associated include the mucin related Tn, Sialyl Tn, and Thomsen-Friedenreich antigens, the blood group Lewis related Lewis(Y), Sialyl Lewis(X) and Sialyl Lewis(A), and Lewis(X) (also known as stage-specific embryonic antigen-1, SSEA-1), the glycosphingolipids Globo H and stage-specific embryonic antigen-3 (SSEA-3), the sialic acid containing glycosphingolipids, the gangliosides GD2, GD3, GM2, fucosyl GM1, and Neu5GcGM3, and polysialic acid. Recent developments have furthered our understanding of the T-independent type II response that is seen in response to carbohydrate antigens. The selection of a vaccine target antigen is based on not only the presence of the antigen in a variety of tumor tissues but also on the role this antigen plays in tumor growth and metastasis. These roles for TACAs are being elucidated. Newly acquired knowledge in understanding the T-independent immune response and in understanding the key roles that carbohydrates play in metastasis are being applied in attempts to develop an effective vaccine response to TACAs. The role of each of the above mentioned carbohydrate antigens in cancer growth and metastasis and vaccine attempts using these antigens will be described.