IL-10 Conditioning of Human Skin Affects the Distribution of Migratory Dendritic Cell Subsets and Functional T Cell Differentiation

In cancer patients pervasive systemic suppression of Dendritic Cell (DC) differentiation and maturation can hinder vaccination efficacy. In this study we have extensively characterized migratory DC subsets from human skin and studied how their migration and T cell-stimulatory abilities were affected by conditioning of the dermal microenvironment through cancer-related suppressive cytokines. To assess effects in the context of a complex tissue structure, we made use of a near-physiological skin explant model. By 4-color flow cytometry, we identified migrated Langerhans Cells (LC) and five dermis-derived DC populations in differential states of maturation. From a panel of known tumor-associated suppressive cytokines, IL-10 showed a unique ability to induce predominant migration of an immature CD14⁺CD141⁺DC-SIGN⁺ DC subset with low levels of co-stimulatory molecules, up-regulated expression of the co-inhibitory molecule PD-L1 and the M2-associated macrophage marker CD163. A similarly immature subset composition was observed for DC migrating from explants taken from skin overlying breast tumors. Whereas predominant migration of mature CD1a⁺ subsets was associated with release of IL-12p70, efficient Th cell expansion with a Th1 profile, and expansion of functional MART-1-specific CD8⁺ T cells, migration of immature CD14⁺ DDC was accompanied by increased release of IL-10, poor expansion of CD4⁺ and CD8⁺ T cells, and skewing of Th responses to favor coordinated FoxP3 and IL-10 expression and regulatory T cell differentiation and outgrowth. Thus, high levels of IL-10 impact the composition of skin-emigrated DC subsets and appear to favor migration of M2-like immature DC with functional qualities conducive to T cell tolerance.     

Exposure of CD34+ precursors to cytostatic anthraquinone-derivatives induces rapid dendritic cell differentiation: implications for cancer immunotherapy

Appropriate activation of dendritic cells (DC) is essential for successful active vaccination and induction of cell-mediated immunity. The scarcity of precursor cells, as well as long culture methods, have hampered wide-scale application of DC vaccines derived from CD34⁺ precursors, despite their suggested superior efficacy over the more commonly applied monocyte-derived DC (MoDC). Here, employing the CD34⁺/CD14⁺ AML-derived human DC progenitor cell line MUTZ3, we show that cytostatic anthraquinone-derivatives (i.e., the anthracenedione mitoxantrone and the related anthracyclin doxorubicin) induce rapid differentiation of CD34⁺ DC precursors into functional antigen-presenting cells (APC) in a three-day protocol. The drugs were found to act specifically on CD34⁺, and not on CD14⁺ DC precursors. Importantly, these observations were confirmed for primary CD34⁺ and CD14⁺ DC precursors from peripheral blood. Mitoxantrone-generated DC were fully differentiated within three days and after an additional 24 h of maturation, were as capable as standard 9-day differentiated and matured DC to migrate toward the lymph node-homing chemokines CCL19 and CCL21, to induce primary allogeneic T cell proliferation, and to prime functional MART1-specific CD8⁺ T lymphocytes. Our finding that anthraquinone-derivatives like mitoxantrone support rapid high-efficiency differentiation of DC precursors may have consequences for in vitro production of DC vaccines as well as for novel immunochemotherapy strategies.     

Dramatic efficacy improvement of a DC-based vaccine against AML by CD25 T cell depletion allowing the induction of a long-lasting T cell response

Dendritic cell (DC)-based vaccination is a promising approach to enhance anti-tumor immunity that could be considered for acute myeloid leukemia (AML) patients with high-risk of relapse. Our purpose was to study the efficiency and to optimize the immunogenicity of a DC-based vaccine in a preclinical AML murine model. In this report, C57BL6 mice were vaccinated with DC pulsed with peptides eluted (EP) from the syngeneic C1498 myelomonocytic leukemic cell line in a prophylactic setting. In this model, a natural antileukemic immunity mediated by NK cells was observed in the control unloaded DC-vaccinated group. On the other hand, we showed that the cytotoxic antileukemic immune response induced by vaccination with eluted peptides pulsed-DC (DC/EP), in vitro and in vivo, was mainly mediated by CD4⁺ T cells. Treatment with anti-CD25 antibody to deplete CD4⁺ CD25⁺ regulatory T cells before DC-vaccination dramatically improved the antileukemic immune response induced by immunization, and allowed the development of long-lasting immune responses that were tumor protective after a re-challenge with leukemic cells. Our results suggest that this approach could be successful against weakly immunogenic tumors such as AML, and could be translated in human.     

Immunologic hierarchy,class II MHC promiscuity,and epitope spreading of a melanoma helper peptide vaccine

Immunization with a combination melanoma helper peptide (6MHP) vaccine has been shown to induce CD4⁺ T cell responses, which are associated with patient survival. In the present study, we define the relative immunogenicity and HLA allele promiscuity of individual helper peptides and identify helper peptide-mediated augmentation of specific CD8⁺ T cell responses. Thirty-seven participants with stage IIIB-IV melanoma were vaccinated with 6MHP in incomplete Freund’s adjuvant. The 6MHP vaccine is comprised of 6 peptides representing melanocytic differentiation proteins gp100, tyrosinase, Melan-A/MART-1, and cancer testis antigens from the MAGE family. CD4⁺ and CD8⁺ T cell responses were assessed in peripheral blood and in sentinel immunized nodes (SIN) by thymidine uptake after exposure to helper peptides and by direct interferon-γ ELIspot assay against 14 MHC class I-restricted peptides. Vaccine-induced CD4⁺ T cell responses to individual epitopes were detected in the SIN of 63 % (22/35) and in the peripheral blood of 38 % (14/37) of participants for an overall response rate of 65 % (24/37). The most frequently immunogenic peptides were MAGE-A3_281–295 (49 %) and tyrosinase_386–406 (32 %). Responses were not limited to HLA restrictions originally described. Vaccine-associated CD8⁺ T cell responses against class I-restricted peptides were observed in 45 % (5/11) of evaluable participants. The 6MHP vaccine induces both CD4⁺ and CD8⁺ T cell responses against melanoma antigens. CD4⁺ T cell responses were detected beyond reported HLA-DR restrictions. Induction of CD8⁺ T cell responses suggests epitope spreading and systemic activity mediated at the tumor site.     

A long peptide from MELOE-1 contains multiple HLA class II T cell epitopes in addition to the HLA-A*0201 epitope: an attractive candidate for melanoma vaccination

CD4⁺ T cells contribute importantly to the antitumor T cell response, and thus, long peptides comprising CD4 and CD8 epitopes may be efficient cancer vaccines. We have previously identified an overexpressed antigen in melanoma, MELOE-1, presenting a CD8⁺ T cell epitope, MELOE-1_36–44, in the HLA-A*0201 context. A T cell repertoire against this epitope is present in HLA-A*0201+ healthy subjects and melanoma patients and the adjuvant injection of TIL containing MELOE-1 specific CD8⁺ T cells to melanoma patients was shown to be beneficial. In this study, we looked for CD4⁺ T cell epitopes in the vicinity of the HLA-A*0201 epitope. Stimulation of PBMC from healthy subjects with MELOE-1_26–46 revealed CD4 responses in multiple HLA contexts and by cloning responsive CD4⁺ T cells, we identified one HLA-DRβ1*1101-restricted and one HLA-DQβ1*0603-restricted epitope. We showed that the two epitopes could be efficiently presented to CD4⁺ T cells by MELOE-1-loaded dendritic cells but not by MELOE-1+ melanoma cell-lines. Finally, we showed that the long peptide MELOE-1_22–46, containing the two optimal class II epitopes and the HLA-A*0201 epitope, was efficiently processed by DC to stimulate CD4⁺ and CD8⁺ T cell responses in vitro, making it a potential candidate for melanoma vaccination.     

DC-based vaccine loaded with acid-eluted peptides in acute myeloid leukemia: the importance of choosing the best elution method

Tumor-associated peptides isolated by acid elution are frequently used for therapeutic immunization against various tumors both in mice and in humans. In acute myeloid leukemia (AML), the frequent accessibility of a large tumor burden allows for extraction of peptides from leukemia cells by using either citrate–phosphate (CP) or trifluoroacetic acid (TFA) buffer. To develop an optimal immunotherapeutic protocol for AML patients, we evaluated both in mice and in humans, the immunogenicity of peptides eluted from leukemia cells with the two acids (TFA or CP). Although ex vivo studies in mice showed that both prophylactic immunizations with mature dendritic cells (DC) loaded with TFA-peptides (DC/TFA), or CP-peptides (DC/CP), were able to stimulate specific antileukemia immune responses, only vaccination with DC/TFA was able to prevent leukemia outgrowth. Moreover, in humans, only DC/TFA generated significant antileukemia CD4⁺ and cytotoxic CD8⁺ T cell responses in vitro. In summary, these data demonstrate that the choice of the acid elution procedure to isolate immunogenic peptides strongly influences the efficacy of the antileukemia immune responses. These finding raise essential considerations for the development of immunotherapeutic protocols for cancer patients. In our model, our results argue for the use of the TFA elution method to extract immunogenic AML-associated peptides.Authors of submitted papers declare no conflict of interest or financial interest in the product or in potentially competing products held by them, their spouses and/or minor children.     

Autophagy,citrullination and cancer

A cell needs to maintain a balance between biosynthesis and degradation of cellular components to maintain homeostasis. There are 2 pathways, the proteasome, which degrades short-lived proteins, and the autophagy/lysosomal pathway, which degrades long-lived proteins and organelles. Both of these pathways are also involved in antigen presentation or the effective delivery of peptides to MHC molecules for presentation to T cells. Autophagy (macroautophagy) is a key player in providing substantial sources of citrullinated peptides for loading onto MHC-II molecules to stimulate CD4⁺ T cell responses. Stressful conditions in the tumor microenvironment induce autophagy in cancer cells as a mechanism to promote their survival. We therefore investigated if citrullinated peptides could stimulate CD4⁺ T cell responses that would recognize these modifications produced during autophagy within tumor cells. Focusing on the intermediate filament protein VIM (vimentin), we generated citrullinated VIM peptides for immunization experiments in mice. Immunization with these peptides induced CD4⁺ T cells in response to autophagic tumor targets. Remarkably, a single immunization with modified peptide, up to 14 d after tumor implant, resulted in long-term survival in 60% to 90% of animals with no associated toxicity. These results show how CD4⁺ cells can mediate potent antitumor responses against modified self-epitopes presented on tumor cells, and they illustrate for the first time how the citrullinated peptides produced during autophagy may offer especially attractive vaccine targets for cancer therapy.     

Modulation of p38 MAPK signaling enhances dendritic cell activation of human CD4+ Th17 responses to ovarian tumor antigen

The recent finding that Th17 infiltration of ovarian tumors positively predicts patient outcomes suggests that Th17 responses play a protective role in ovarian tumor immunity. This observation has led to the question of whether Th17 cells could be induced or expanded to therapeutic advantage by tumor vaccination. In this study, we show that treatment of ovarian tumor antigen-loaded, cytokine-matured human dendritic cells (DC) with a combination of IL-15 and a p38 MAP kinase inhibitor offers potent synergy in antagonism of CD4⁺ Treg induction and redirection toward CD4⁺ Th17 responses that correlate with strong CD8⁺ cytotoxic T lymphocyte (CTL) activation. Ovarian tumor antigen-specific CD4⁺ T cells secrete high levels of IL-17 and show reduced expression of CTLA-4, PD-1, and Foxp3 following activation with IL-15/p38 inhibitor-treated DC. We further show that modulation of p38 MAPK signaling in DC is associated with reduced expression of B7-H1 (PD-L1), loss of indoleamine 2,3-dioxygenase activity, and increased phosphorylation of ERK 1/2 MAPK. These observations may allow the development of innovative DC vaccination strategies to boost Th17 immunity in ovarian cancer patients.     

Costimulatory Effects of an Immunodominant Parasite Antigen Paradoxically Prevent Induction of Optimal CD8 T Cell Protective Immunity

Trypanosoma cruzi infection is controlled but not eliminated by host immunity. The T. cruzi trans-sialidase (TS) gene superfamily encodes immunodominant protective antigens, but expression of altered peptide ligands by different TS genes has been hypothesized to promote immunoevasion. We molecularly defined TS epitopes to determine their importance for protection versus parasite persistence. Peptide-pulsed dendritic cell vaccination experiments demonstrated that one pair of immunodominant CD4⁺ and CD8⁺ TS peptides alone can induce protective immunity (100% survival post-lethal parasite challenge). TS DNA vaccines have been shown by us (and others) to protect BALB/c mice against T. cruzi challenge. We generated a new TS vaccine in which the immunodominant TS CD8⁺ epitope MHC anchoring positions were mutated, rendering the mutant TS vaccine incapable of inducing immunity to the immunodominant CD8 epitope. Immunization of mice with wild type (WT) and mutant TS vaccines demonstrated that vaccines encoding enzymatically active protein and the immunodominant CD8⁺ T cell epitope enhance subdominant pathogen-specific CD8⁺ T cell responses. More specifically, CD8⁺ T cells from WT TS DNA vaccinated mice were responsive to 14 predicted CD8⁺ TS epitopes, while T cells from mutant TS DNA vaccinated mice were responsive to just one of these 14 predicted TS epitopes. Molecular and structural biology studies revealed that this novel costimulatory mechanism involves CD45 signaling triggered by enzymatically active TS. This enhancing effect on subdominant T cells negatively regulates protective immunity. Using peptide-pulsed DC vaccination experiments, we have shown that vaccines inducing both immunodominant and subdominant epitope responses were significantly less protective than vaccines inducing only immunodominant-specific responses. These results have important implications for T. cruzi vaccine development. Of broader significance, we demonstrate that increasing breadth of T cell epitope responses induced by vaccination is not always advantageous for host immunity.     

Priming of naive CD8+ T cells in the presence of IL-12 selectively enhances the survival of CD8<Superscript>+</Superscript>CD62L<Superscript>hi</Superscript> cells and results in superior anti-tumor activity in a tolerogenic murine model

During the antigen-dependant activation process several subsets CD8⁺ T cells appear with different phenotypic and functional characteristics. Recent studies indicate that the state of T cell differentiation radically affects their ability to effectively respond to tumor challenge, with early effector CD8⁺ T (CD62L^high) cells having better anti-tumor activity. Thus strategies aimed at optimizing the generation of such subpopulations could significantly enhance the effectiveness of adoptive cell therapy (ACT) for cancer. In this study, we show that priming of naïve CD8⁺ T cells in the presence of IL-12 selectively rescued early CD8⁺ CD62L^hi from activation induced cell death and resulted in the increased accumulation of this subset of CD8⁺ T cells. Furthermore, we demonstrated that IL-12 directly modulated the expression of CD62L on activated CD8⁺ T cells. When used for ACT, naïve CD8⁺ T cells primed in vitro in the presence of IL-12 showed superior anti-tumor activity toward B16 melanoma. Importantly, using the Pmel-1 model, priming pmel-1 cells in vitro with IL-12 reduced the state of functional tolerance associated with the non-mutated “self” tumor antigen gp100, as demonstrated by significant tumor responses in the absence of vaccination. Together, our results suggest that in vitro conditioning of naïve CD8⁺ T cells with IL-12 prior to ACT could significantly enhance their anti-tumor activity.     

Antitumor vaccination effect of dendritic cells can be augmented by locally utilizing Th1-type cytokines from OK432-reactive CD4+ T cells

 In order to enhance the antitumor vaccination effect of dendritic cells (DC) pulsed with class I tumor peptide, we tried to utilize the local cytokine help of CD4⁺ T cells reactive to a streptococcal preparation OK432. DC were prepared from murine bone marrow cells by culture with both granulocyte/macrophage-colony-stimulating factor and interleukin(IL)-4. The peritumoral injections of OK432 induced OK432-reactive CD4⁺ T cells in the draining lymph nodes, and their in vitro production of interferon γ was thus significantly enhanced by restimulation with OK432-pulsed DC. In addition, anti-P815 mastocytoma cytotoxic T lymphocytes were generated from the in vivo OK432-treated P815-draining lymph node cells only when the lymph node cells were restimulated in vitro with the DC pulsed with both P1A peptide and OK432. Moreover, the peritumoral injections of OK432 and the subsequent vaccination of the DC, pulsed with both OK432 and P1A peptide, significantly suppressed the growth of s.c. inoculated P815. Interestingly, a significant level of IL-12 was detected in the coculture supernatant of both OK432-pulsed DC and OK432-reactive CD4⁺ T cells. Collectively, our results suggest that the antitumor vaccination effect of DC pulsed with class I tumor peptide could thus be effectively augmented by locally utilizing the Th1-type cytokines from OK432-reactive CD4⁺ T cells. Received: 18 July 1997 / Accepted: 23 December 1997     

Adoptive cellular immunotherapy for the treatment of patients with breast cancer: A meta-analysis

BackgroundTo evaluate the therapeutic efficacy of dendritic cells (DC) alone, cytokine-induced killer (CIK) cells alone and the combination of DC and CIK cells in the treatment of breast cancer, we performed a systemic review of the relevant published clinical studies, collectively referred to as DC-CIK cell therapy.MethodsSix hundred thirty-three patients with breast cancer were assigned to cohorts, and a meta-analysis was conducted.ResultsThe treatment of breast cancer with DC-CIK cells was associated with a significantly improved 1-year survival (P = 0.0001). The Karnofsky performance status scale of the patients treated with DC-CIK cells was significantly improved compared with that of the non-DC-CIK group (P < 0.0001). The percentage of T cells (CD3⁺, CD4⁺ and CD4⁺CD8⁺), CD16⁺ monocytes, and CD3⁺CD56⁺ natural killer T cells in the peripheral blood of cancer patients was significantly increased (P ≤ 0.05), whereas the percentage of CD4⁺CD25⁺ regulatory T cells was not significantly decreased (P = 0.32) in the DC-CIK treatment group compared with the non-DC-CIK group. The levels of interleukin-2, interleukin-12, tumor necrosis factor-α, interferon-γ, and nucleolar organizer region protein in the peripheral blood of cancer patients, which reflect immune function, were significantly increased (P < 0.001) after DC-CIK cell treatment. Furthermore, after DC-CIK treatment, the average levels of the alpha-fetoprotein, cancer antigen embryonic antigen and carbohydrate antigen tumor markers were decreased (P < 0.00001).ConclusionsDC-CIK cell therapy markedly prolongs survival time, enhances immune function, and improves the efficacy of the treatment of breast cancer patients.     

An Efficient Large-Scale Retroviral Transduction Method Involving Preloading the Vector into a RetroNectin-Coated Bag with Low-Temperature Shaking

In retroviral vector-mediated gene transfer, transduction efficiency can be hampered by inhibitory molecules derived from the culture fluid of virus producer cell lines. To remove these inhibitory molecules to enable better gene transduction, we had previously developed a transduction method using a fibronectin fragment-coated vessel (i.e., the RetroNectin-bound virus transduction method). In the present study, we developed a method that combined RetroNectin-bound virus transduction with low-temperature shaking and applied this method in manufacturing autologous retroviral-engineered T cells for adoptive transfer gene therapy in a large-scale closed system. Retroviral vector was preloaded into a RetroNectin-coated bag and incubated at 4°C for 16 h on a reciprocating shaker at 50 rounds per minute. After the supernatant was removed, activated T cells were added to the bag. The bag transduction method has the advantage of increasing transduction efficiency, as simply flipping over the bag during gene transduction facilitates more efficient utilization of the retroviral vector adsorbed on the top and bottom surfaces of the bag. Finally, we performed validation runs of endoribonuclease MazF-modified CD4⁺ T cell manufacturing for HIV-1 gene therapy and T cell receptor-modified T cell manufacturing for MAGE-A4 antigen-expressing cancer gene therapy and achieved over 200-fold (≥10¹⁰) and 100-fold (≥5×10⁹) expansion, respectively. In conclusion, we demonstrated that the large-scale closed transduction system is highly efficient for retroviral vector-based T cell manufacturing for adoptive transfer gene therapy, and this technology is expected to be amenable to automation and improve current clinical gene therapy protocols.     

Identification of Prostate-Specific G-Protein Coupled Receptor as a Tumor Antigen Recognized by CD8+ T Cells for Cancer Immunotherapy

Background

Prostate cancer is the most common cancer among elderly men in the US, and immunotherapy has been shown to be a promising strategy to treat patients with metastatic castration-resistant prostate cancer. Efforts to identify novel prostate specific tumor antigens will facilitate the development of effective cancer vaccines against prostate cancer. Prostate-specific G-protein coupled receptor (PSGR) is a novel antigen that has been shown to be specifically over-expressed in human prostate cancer tissues. In this study, we describe the identification of PSGR-derived peptide epitopes recognized by CD8⁺ T cells in an HLA-A2 dependent manner.

Methodology/Principal Findings

Twenty-one PSGR-derived peptides were predicted by an immuno-informatics approach based on the HLA-A2 binding motif. These peptides were examined for their ability to induce peptide-specific T cell responses in peripheral blood mononuclear cells (PBMCs) obtained from either HLA-A2⁺ healthy donors or HLA-A2⁺ prostate cancer patients. The recognition of HLA-A2 positive and PSGR expressing LNCaP cells was also tested. Among the 21 PSGR-derived peptides, three peptides, PSGR3, PSGR4 and PSGR14 frequently induced peptide-specific T cell responses in PBMCs from both healthy donors and prostate cancer patients. Importantly, these peptide-specific T cells recognized and killed LNCaP prostate cancer cells in an HLA class I-restricted manner.

Conclusions/Significance

We have identified three novel HLA-A2-restricted PSGR-derived peptides recognized by CD8⁺ T cells, which, in turn, recognize HLA-A2⁺ and PSGR⁺ tumor cells. The PSGR-derived peptides identified may be used as diagnostic markers as well as immune targets for development of anticancer vaccines.     

Distinct responses of splenic dendritic cell subsets to infection with Listeria monocytogenes: maturation phenotype, level of infection, and T cell priming capacity ex vivo

To determine the relative contributions of DC subsets in the development of protective immunity to Listeria monocytogenes we examined the relationship between maturation, bacterial burden, and T cell priming capacity of four well characterized subsets of splenic DC following infection with Lm. CD8α⁺, CD4⁺, and CD8α⁻CD4⁻ DC and the B220⁺ plasmacytoid DC (pDC) were compared for abundance and costimulatory molecule expression at 24, 48, and 72 h post i.v. infection. We further determined the bacterial burden associated with each DC subset and their relative capacities to prime CD8⁺ T cells at 24 hpi. The CD8α⁺ DC displayed the highest level of maturation, association with live bacteria, and T cell activation potential. Second, the CD4⁺ DC were also mature, yet were associated with fewer bacteria, and stimulated T cell proliferation, but not IFN-γ production. The CD8α⁻CD4⁻ DC showed a modest maturation response and were associated with a high number of bacteria, but failed to induce T cell proliferation ex vivo. pDC displayed a strong maturation response, but were not associated with detectable bacteria and also failed to stimulate T cell activation. Finally, we measured the cytokine responses in these subsets and determined that IL-12 was produced predominantly by the CD8⁺ DC, correlating with the ability of this subset DC to induce IFN-γ production in T cells. We conclude that Listeria-specific CD8⁺ T cell activation in the spleen is most effectively achieved by infection-induced maturation of the CD8α⁺ DC subset.     

Dendritic cell-based multi-epitope immunotherapy of hormone-refractory prostate carcinoma

Background: Dendritic cell (DC)-based immunotherapy is a promising approach to augment tumor antigen-specific T cell responses in cancer patients. However, tumor escape with down-regulation or complete loss of target antigens may limit the susceptibility of tumor cells to the immune attack. Concomitant generation of T cell responses against several immunodominant antigens may circumvent this potential drawback. In this trial, we determined the immunostimulatory capacity of autologous DC pulsed with multiple T cell epitopes derived from four different prostate-specific antigens in patients with advanced hormone-refractory prostate cancer. Patients and methods: Autologous DC of HLA-A*0201⁺ patients with hormone-refractory prostate cancer were loaded with antigenic peptides derived from prostate stem cell antigen (PSCA_14–22), prostatic acid phosphatase (PAP_299–307), prostate-specific membrane antigen (PSMA_4–12), and prostate-specific antigen (PSA_154–163). DC were intradermally applied six times at biweekly intervals followed—in the case of an enhanced immune response—by monthly booster injections. Immune monitoring during the time of ongoing vaccinations (12–59 weeks) included ex vivo ELISPOT measurements, MHC tetramer analysis and in vitro cytotoxicity assays. Results: Of the initial six patients, three qualified for long-term multi-epitope DC vaccination. This regime was tolerated well by all three patients. The vaccination elicited significant cytotoxic T cell responses against all prostate-specific antigens tested. In addition, memory T cell responses against the control peptides derived from influenza matrix protein and tetanus toxoid were efficiently boosted. Clinically, the long-term DC vaccination was associated with an increase in PSA doubling time. Conclusions: DC-based multi-epitope immunotherapy with repeated boosting in men with hormone-refractory prostate carcinoma is feasible and generates efficient cellular antitumor responses. Grant sponsors: Cancer League St. Gallen-Appenzell; Swiss Cancer League; Foundation Propter Homines Vaduz Liechtenstein; Cancer Research Institute USA; Foundation for Clinical Cancer Research of Eastern Switzerland (OSKK)     

Vaccination with Embryonic Stem Cells Protects against Lung Cancer: Is a Broad-Spectrum Prophylactic Vaccine against Cancer Possible?

The antigenic similarity between tumors and embryos has been appreciated for many years and reflects the expression of embryonic gene products by cancer cells and/or cancer-initiating stem cells. Taking advantage of this similarity, we have tested a prophylactic lung cancer vaccine composed of allogeneic murine embryonic stem cells (ESC). Naïve C57BL/6 mice were vaccinated with ESC along with a source of granulocyte macrophage-colony stimulating factor (GM-CSF) in order to provide immunostimulatory adjuvant activity. Vaccinated mice were protected against subsequent challenge with implantable Lewis lung carcinoma (LLC). ESC-induced anti-tumor immunity was not due to a non-specific “allo-response” as vaccination with allogeneic murine embryonic fibroblasts did not protect against tumor outgrowth. Vaccine efficacy was associated with robust tumor-reactive primary and memory CD8⁺ T effector responses, Th1 cytokine response, higher intratumoral CD8⁺ T effector/CD4⁺CD25⁺Foxp3⁺ T regulatory cell ratio, and reduced myeloid derived suppressor cells in the spleen. Prevention of tumorigenesis was found to require a CD8-mediated cytotoxic T lymphocyte (CTL) response because in vivo depletion of CD8⁺ T lymphocytes completely abrogated the protective effect of vaccination. Importantly, this vaccination strategy also suppressed the development of lung cancer induced by the combination of carcinogen administration and chronic pulmonary inflammation. Further refinement of this novel vaccine strategy and identification of shared ESC/tumor antigens may lead to immunotherapeutic options for lung cancer patients and, perhaps more importantly, could represent a first step toward the development of prophylactic cancer vaccines.     

CD8+ cytotoxic T lymphocytes in cancer immunotherapy: A review

CD8⁺ cytotoxic T lymphocytes (CTLs) are preferred immune cells for targeting cancer. During cancer progression, CTLs encounter dysfunction and exhaustion due to immunerelated tolerance and immunosuppression within the tumor microenvironment (TME), with all favor adaptive immune-resistance. Cancer-associated fibroblasts (CAFs), macrophage type 2 (M2) cells, and regulatory T cells (Tregs) could make immunologic barriers against CD8 ⁺ T cell-mediated antitumor immune responses. Thus, CD8 ⁺ T cells are needed to be primed and activated toward effector CTLs in a process called tumor immunity cycle for making durable and efficient antitumor immune responses. The CD8 ⁺ T cell priming is directed essentially as a corroboration work between cells of innate immunity including dendritic cells (DCs) and natural killer (NK) cells with CD4 ⁺ T cells in adoptive immunity. Upon activation, effector CTLs infiltrate to the core or invading site of the tumor (so-called infiltrated–inflamed [I–I] TME) and take essential roles for killing cancer cells. Exogenous reactivation and/or priming of CD8 ⁺ T cells can be possible using rational immunotherapy strategies. The increase of the ratio for costimulatory to coinhibitory mediators using immune checkpoint blockade (ICB) approach. Programmed death-1 receptor (PD-1)–ligand (PD-L1) and CTL-associated antigen 4 (CTLA-4) are checkpoint receptors that can be targeted for relieving exhaustion of CD8 ⁺ T cells and renewing their priming, respectively, and thereby eliminating antigen-expressing cancer cells. Due to a diverse relation between CTLs with Tregs, the Treg activity could be dampened for increasing the number and rescuing the functional potential of CTLs to induce immunosensitivity of cancer cells.