Autologous renal cell cancer vaccines using heat shock protein-peptide complexes

Prophylactic Antitumor Effect of Mixed Heat Shock Proteins/Peptides in Mouse Sarcoma

Background:

To develop a vaccine-based immunotherapy for sarcoma, we evaluated a mixture of heat shock proteins (mHSPs) as a vaccine for sarcoma treatment in a mouse model. Heat shock protein/peptides (HSP/Ps) are autoimmune factors that can induce both adaptive and innate immune responses; HSP/Ps isolated from tumors can induce antitumor immune activity when used as vaccines.

Methods:

In this study, we evaluated the effects of mHSP/Ps on prophylactic antitumor immunity. We extracted mHSP/Ps, including HSP60, HSP70, GP96, and HSP110, from the mouse sarcoma cell lines S180 and MCA207 using chromatography. The immunity induced by mHSP/Ps was assessed using flow cytometry, ELISPOT, lactate dehydrogenase release, and enzyme-linked immunosorbent assay.

Results:

Of S180 sarcoma-bearing mice immunized with mHSP/Ps isolated from S180 cells, 41.2% showed tumor regression and long-term survival, with a tumor growth inhibition rate of 82.3% at 30 days. Of MCA207 sarcoma-bearing mice immunized with mHSP/Ps isolated from MCA207 cells, 50% showed tumor regression and long-term survival with a tumor growth inhibition rate of 79.3%. All control mice died within 40 days. The proportions of natural killer cells, CD8⁺, and interferon-γ-secreting cells and tumor-specific cytotoxic T-lymphocyte activity were increased in the immunized group.

Conclusions:

Vaccination with a polyvalent mHSP/P cancer vaccine can induce an immunological response and a marked antitumor response to autologous tumors. This mHSP/P vaccine exerted greater antitumor effects than did HSP70, HSP60, or tumor lysates alone.

Regulatory T-cell depletion synergizes with gp96-mediated cellular responses and antitumor activity

Despite its potent immunostimulatory properties, vaccination with autologous tumor-derived gp96 has relatively modest antitumor effect in a range of clinical trials. Based on our previous study showing a gp96-mediated immune balance between CTL and Tregs, here we investigated possible synergy between gp96 vaccine and systemic Treg depletion on induction of antitumor T-cell immunity and the mechanisms accounting for synergistic efficacy. In gp96-peptide complex immunized BALB/c mice, anti-CD25 mAb treatment significantly increased IFN-γ-producing CD8(+) and CD4(+) T cells by about 1-2-fold in spleen and 40-50% in lymph node. A significantly higher number of peptide-specific CTL were observed under anti-CD25 mAb treatment compared with no treatment. Moreover, Treg depletion synergistically improved the anticancer activity of tumor-derived gp96 vaccine in the poorly immunogenic and highly tumorigenic B16 melanoma model in C57BL/6 J mice. While gp96 immunization alone led to the modest enhancement of CTL activities in spleen, the combination with Treg depletion dramatically increased tumor-specific CTL responses. In addition, the combination resulted in a significant increase of CD8(+) T-cell infiltration in tumor, which correlated with an enhanced inhibition of tumor growth. Our results provide evidence that targeting Tregs may provide a more efficient strategy to potentiate gp96-mediated T-cell responses and enhance the antitumor efficiency of gp96-based therapeutic vaccine.

Treg suppress CTL responses upon immunization with HSP gp96

HSP gp96-based vaccines have been trialled in rodent models and, more recently, in humans. Better understanding of gp96's immunomodulatory role will help with the design of more effective strategies for treatment of cancer and infectious diseases. In this study, we monitored the activities of T cells and activation of Treg in BABL/c mice after immunization using different doses of gp96 as adjuvant. We found that co-injection of gp96 simultaneously stimulated both CTL and Treg activity. Activation of CTL at low dose was far more pronounced than Treg activation. Treg population and suppression increased with gp96 dose, eventually abrogating the T-cell response induced by immunization. Low-dose cyclophosphamide treatment could restore the T-cell responses lost after high-dose gp96 adjuvant injection by suppression of Treg activation. We further examined the effect of different doses of gp96 or N355 peptide administration on tumor rejection. Our results provide new insights into the mechanisms of gp96-mediated balance between regulatory and responder T cells, which may facilitate future development of an effective gp96-based therapeutic vaccine.

Honokiol-mediated inhibition of PI3K/mTOR pathway: a potential strategy to overcome immunoresistance in glioma, breast, and prostate carcinoma without impacting T cell function

Inhibition of the phosphoinositide 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) pathway is an appealing method for decreasing the immunoresistance and augmenting T cell-mediated immunotherapy. A major impediment to this strategy is the impact of conventional PI3K/mTOR pathway inhibitors on T cell function. In particular, rapamycin, is a well-known immunosuppressant that can decrease the activity of the PI3K/mTOR pathway in tumor cells, but also has a profound inhibitory effect on T cells. Here we show that Honokiol, a natural dietary product isolated from an extract of seed cones from Magnolia grandiflora, can decrease PI3K/mTOR pathway-mediated immunoresistance of glioma, breast and prostate cancer cell lines, without affecting critical proinflammatory T cell functions. Specifically, we show that at doses sufficient to down-regulate levels of phospho-S6 and the negative immune regulator B7-H1 in tumor cells, Honokiol does not significantly impair T cell proliferation or proinflammatory cytokine production. In contrast to classic inhibitors, including LY294002, wortmannin, AKT inhibitor III and rapamycin, Honokiol specifically decreases the PI3K/mTOR pathway activity in tumor cells, but not in freshly stimulated T cells. Collectively, our data define a unique application for Honokiol and provide the impetus to more fully elucidate the mechanism by which T cells are resistant to the effects of this particular inhibitor. Honokiol is clinically available for human testing and may serve to augment T cell-mediated cancer immunotherapy.

Induction of leukemia-specific antibodies by immunotherapy with leukemia-cell-derived heat shock protein 70

Cancer immunotherapy using heat shock protein (HSP) derived from autologous tumor requires cluster of differentiation (CD)4(+) as well as CD8(+) T-cells for the prolongation of patient survival, suggesting that a humoral immune response through CD4(+) T-cells is important in addition to cellular immunity. However, the role of humoral responses in HSP-based autologous tumor immunotherapy remains unclear. In the present study, we investigated whether leukemia-specific antibodies and antibody-mediated cytotoxicity against autologous leukemia cells have a crucial role in a mouse A20 leukemia model by immunizing A20-derived HSP70. Immunization with A20-derived HSP70 induced the production of anti-A20-antibodies and the antibodies recognized HSP70-binding peptides derived from A20. One of those was a major histocompatibility complex (MHC) class-I binding peptide, which has been clarified as the target peptide of CD8+ cytotoxic T-cells (CTL) against A20. The anti-A20-antibodies produced by immunization with A20-derived HSP70 induced complement-dependent cytotoxicity (CDC) against A20 in vitro. In addition, immunization with A20-derived HSP70 increased intracellular interleukin-4 (IL4)-production of CD4(+) T-cells, confirming the activation of type-2 helper T-cells. Taken together, immunization with leukemia-cell-derived HSP70 induces antibodies against leukemia-cell-specific peptides and might play a crucial role in the eradication of leukemia cells by CDC in mice. These findings will enable future establishment of a novel therapeutic strategy using antileukemia antibodies in HSP-based autologous tumor immunotherapy.

Lessons from randomized phase III studies with active cancer immunotherapies--outcomes from the 2006 meeting of the Cancer Vaccine Consortium (CVC)

After years of effort to develop active cancer immunotherapies, seven candidate products achieved promising results in phase I/II studies that triggered phase III randomized studies. One candidate to date has received an approvable letter from the United States Food and Drug Administration (FDA), defining a clear path to licensure for sipuleucel-T (Provenge, Dendreon) within the next couple of years. The other phase III studies failed to achieve statistical criteria for some or all of the critical endpoints. Yet, there is widespread recognition that using a patient's own immune system to target and destroy cancer cells may offer an effective biological therapy with less toxicity than presently available anti-cancer therapies, and several candidates are still being evaluated in clinical studies. This review summarizes the lessons learned from these case studies, evaluates scientific, study design, and business factors that can affect study outcomes, identifies common challenges faced by sponsors developing these innovative therapies, and provides considerations for future study designs that may increase the likelihood of success.

Heat shock protein derivatives for delivery of antigens to antigen presenting cells

Delivery of antigens to antigen presenting cells (APCs) is a key issue for developing effective cancer vaccines. Controlling the tissue distribution of antigens can increase antigen-specific immune responses, including the induction of cytotoxic T lymphocytes (CTL). Heat shock protein 70 (Hsp70) forms complexes with a variety of tumor-related antigens via its polypeptide-binding domain. Because Hsp70 is taken up by APCs through recognition by Hsp receptors, such as CD91 and LOX-1, its application to antigen delivery systems has been examined both in experimental and clinical settings. A tissue distribution study revealed that Hsp70 is mainly taken up by the liver, especially by hepatocytes, after intravenous injection in mice. A significant amount of Hsp70 was also delivered to regional lymph nodes when it was injected subcutaneously, supporting the hypothesis that Hsp70 is a natural targeting system for APCs. Model antigens were complexed with or conjugated to Hsp70, resulting in greater antigen-specific immune responses. Cytoplasmic delivery of Hsp70-antigen further increased the efficacy of the Hsp70-based vaccines. These findings indicate that effective cancer therapy can be achieved by developing Hsp70-based anticancer vaccines when their tissue and intracellular distribution is properly controlled.

Renal cell carcinoma: Current status and emerging therapies

Renal cell carcinoma (RCC) accounts for about 3% of all adult malignancies and its incidence is increasing. Smoking, obesity, and end-stage renal disease are important risk factors. Localized RCC may be cured with surgical excision. However, over one-third of patients eventually develop metastatic disease. While chemotherapy and radiation therapy are relatively ineffective for RCC, immunotherapy modestly extends survival and may lead to tumor regression and long-term survival in a small minority of patients. Recently, research into the pathology of genetic syndromes associated with RCC has led to remarkable advances in our understanding of the pathogenesis of sporadic RCC. Rational therapeutic agents developed from this understanding have established new treatment paradigms for this disease.