Immunotherapeutic potential of tumor antigen-pulsed and unpulsed dendritic cells generated from murine bone marrow

Nasal administration of recombinant Neospora caninum secreting IL-15/IL-15Rα inhibits metastatic melanoma development in lung

BACKGROUND

Metastases are the leading cause of mortality in many cancer types and lungs are one of the most common sites of metastasis alongside the liver, brain, and bones. In melanoma, 85% of late-stage patients harbor lung metastases. A local administration could enhance the targeting of metastases while limiting the systemic cytotoxicity. Therefore, intranasal administration of immunotherapeutic agents seems to be a promising approach to preferentially target lung metastases and decrease their burden on cancer mortality. From observations that certain microorganisms induce an acute infection of the tumor microenvironment leading to a local reactivating immune response, microbial-mediated immunotherapy is a next-generation field of investigation in which immunotherapies are engineered to overcome immune surveillance and escape from microenvironmental cancer defenses.

METHODS

The goal of our study is to evaluate the potential of the intranasal administration of Neospora caninum in a syngeneic C57BL6 mouse model of B16F10 melanoma lung metastases. It also compares the antitumoral properties of a wild-type N. caninum versus N. caninum secreting human interleukin (IL)-15 fused to the sushi domain of the IL-15 receptor α chain, a potent activator of cellular immune responses.

RESULTS

The treatment of murine lung metastases by intranasal administration of an N. caninum engineered to secrete human IL-15 impairs lung metastases from further progression with only 0,08% of lung surface harboring metastases versus 4,4% in wild-type N. caninum treated mice and 36% in untreated mice. The control of tumor development is associated with a strong increase in numbers, within the lung, of natural killer cells, CD8⁺ T cells and macrophages, up to twofold, fivefold and sixfold, respectively. Analysis of expression levels of CD86 and CD206 on macrophages surface revealed a polarization of these macrophages towards an antitumoral M1 phenotype.

CONCLUSION

Administration of IL-15/IL-15Rα-secreting N. caninum through intranasal administration, a non-invasive route, lend further support to N. caninum-demonstrated clear potential as an effective and safe immunotherapeutic approach for the treatment of metastatic solid cancers, whose existing therapeutic options are scarce. Combination of this armed protozoa with an intranasal route could reinforce the existing therapeutic arsenal against cancer and narrow the spectrum of incurable cancers.

Targeted co-delivery of Trp-2 polypeptide and monophosphoryl lipid A by pH-sensitive poly (β-amino ester) nano-vaccines for melanoma

Dendritic cell (DC)-targeted vaccines based on nanotechnology are a promising strategy to efficiently induce potent immune responses. We synthesized and manufactured a mannose-modified poly (β-amino ester) (PBAE) nano-vaccines with easily tuneable and pH-sensitive characteristics to co-deliver the tumor-associated antigen polypeptide Trp-2 and the TLR4 agonist monophosphoryl lipid A (MPLA). To reduce immunosuppression in the tumor microenvironment, an immune checkpoint inhibitor, PD-L1 antagonist, was administrated along with PBAE nano-vaccines to delay melanoma development. We found that mannosylated Trp-2 and MPLA-loaded PBAE nano-vaccines can target and mature DCs, consequently boosting antigen-specific cytotoxic T lymphocyte activity against melanoma. The prophylactic study indicates that combination therapy with PD-L1 antagonist further enhanced anti-tumor efficacy by 3.7-fold and prolonged median survival time by 1.6-fold more than free Trp-2/MPLA inoculation. DC-targeting PBAE polymers have a great potential as a nanotechnology platform to design vaccines and achieve synergistic anti-tumor effects with immune checkpoint therapy.

Dendritic cells loaded with CD44+ CT-26 colon cell lysate evoke potent antitumor immune responses

Increasing evidence supports the concept that cancer stem cells (CSCs) are responsible for cancer progression and metastasis, therapy resistance and relapse. In addition to conventional therapies for colon cancer, the development of immunotherapies targeting cancer stem cells appears to be a promising strategy to suppress tumor recurrence and metastasis. In the present study, dendritic cells (DCs) were pulsed with whole-tumor cell lysates or total RNA of CD44⁺ colon cancer stem cells (CCSCs) isolated from mouse colon adenocarcinoma CT-26 cell cultures and investigated for their antitumor immunity against CCSCs in vivo and in vitro. In a model of colon adenocarcinoma using BALB/c mice, a sequential reduction in tumor volume and weight was associated with an extended survival in tumor-bearing mice vaccinated with DCs pulsed with RNA or CCSC lysate. In addition, a lactate dehydrogenase assay indicated that cytotoxic T-cells derived from the treated mice exhibited strong cytotoxic activity. Additionally, an enzyme-linked immunosorbent assay revealed that the cytotoxic T-cells of the treated mice released higher levels of interferon-γ against CCSCs compared with those of the control group. In all experiments, the antitumor efficacy of the lysate-pulsed DC-treated and RNA-pulsed DC-treated groups were significantly higher compared with that of the DC-treated and control groups. The results of the present study indicated the potential use of DCs pulsed with cancer stem cell lysates as a potent therapeutic antigen to target CSCs in colon cancer. Additionally, the results provided a rationale for using lysate-pulsed DCs in vivo to eliminate residual tumor deposits in post-operative patients.

Induction of suppressive phenotype in monocyte-derived dendritic cells by leukemic cell products and IL-1β

Professional antigen-presenting cells, dendritic cells (DCs) play an important role in controlling tumors. It is known that solid tumor cell products inhibit DC differentiation. Recently a similar effect produced by leukemic cell products has been demonstrated. In this case, leukemic cell products induced the secretion of IL-1β by monocytes undergoing differentiation. The aim of the present work was to characterize and to compare the development of monocyte-derived DCs under the influence of leukemic cell products (K562 supernatant) or exogenous IL-1β. It became clear that leukemic cell products and IL-1β differentially modulate some of the parameters studied on monocytes stimulated to differentiate into DCs. In the presence of K562 supernatant, the expression of the macrophage markers CD16 and CD68 were higher than in immature DCs control. Contrasting with IL-1β, leukemic cell products possibly favor the development of cells with macrophage markers. In addition, CD80 and CD83 expressions were also higher in the presence of tumor supernatant whereas HLA-DR was lower. In the presence of IL-1β, only CD80 was increased. Furthermore, it was observed that when monocytes were induced to differentiate into DCs in the presence of tumor supernatant and then activated, they expressed less CD80 and CD83 than activated DCs control. A reduced expression of CD83 following activation was also seen in cells differentiated with IL-1β. TGF-β and VEGF were found in the tumor supernatants. Moreover, the exposure to tumor supernatant or IL-1β stimulated IL-10 production while decreased IL-12 production by activated DCs. Finally, these results suggest that the addition of products released by leukemic cells or, more discreetly, the addition of IL-1β affects DC differentiation, inducing a suppressive phenotype.

Identification of CD123+ myeloid dendritic cells as an early-stage immature subset with strong tumoristatic potential

CD123 has been identified as a specific surface marker for plasmacytoid dendritic cells (PDCs). However, CD123 has recently been shown to be expressed on freshly isolated or in vitro generated myeloid dendritic cells (MDCs). In this article, we investigated whether the expression of CD123 on monocyte-derived MDCs was related to their function, especially to tumor-inhibiting potential. MDCs were induced from cord blood CD14+ monocytes with granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4) for 7 days, and then CD123+ cells were isolated by positive immunomagnetic cell selection. We observed that CD123+ cells lost monocyte CD14 expression, acquired immature myeloid dendritic cell phenotype and morphology. They exerted more significant endocytosis and less antigen-presenting function than CD123(-)MDCs which are often referred to as typical MDCs. Meanwhile, CD123+ MDCs exhibited more significant tumor-inhibiting activity toward hematological tumor cell lines of U937 and Jurkat even at a low effector:target ratio. CD123+ MDCs expressed higher level of cytoplasmic TNF-alpha-related apoptosis-inducing ligand (TRAIL), but no detectable surface TRAIL and very little soluble TRAIL. Pretreatment with recombinant human TRAIL receptor 2:Fc fusion protein significantly reduced the tumor-inhibiting effect of CD123+ MDCs, but not of CD123(-) MDCs. Overall, our data demonstrated that CD123+ MDCs were an early-stage immature DC subset, with a significant tumor-inhibiting activity partially via involvement of enhanced cytoplasmic TRAIL.

Immunisation with 'naïve' syngeneic dendritic cells protects mice from tumour challenge

Dendritic cells (DCs) ‘pulsed’ with an appropriate antigen may elicit an antitumour immune response in mouse models. However, while attempting to develop a DC immunotherapy protocol for the treatment of breast cancer based on the tumour-associated MUC1 glycoforms, we found that unpulsed DCs can affect tumour growth. Protection from RMA-MUC1 tumour challenge was achieved in C57Bl/6 MUC1 transgenic mice by immunising with syngeneic DCs pulsed with a MUC1 peptide. However, unpulsed DCs gave a similar level of protection, making it impossible to evaluate the effect of immunisation of mice with DCs pulsed with the specific peptide. Balb/C mice could also be protected from tumour challenge by immunisation with unpulsed DCs prior to challenge with murine mammary tumour cells (410.4) or these cells transfected with MUC1 (E3). Protection was achieved with as few as three injections of 50 000 naïve DCs per mouse per week, was not dependent on injection route, and was not specific to cell lines expressing human MUC1. However, the use of Rag2-knockout mice demonstrated that the adaptive immune response was required for tumour rejection. Injection of unpulsed DCs into mice bearing the E3 tumour slowed tumour growth. In vitro, production of IFN-γ and IL-4 was increased in splenic cells isolated from mice immunised with DCs. Depleting CD4 T cells in vitro partially decreased cytokine production by splenocytes, but CD8 depletion had no effect. This paper shows that naïve syngeneic DCs may induce an antitumour immune response and has implications for DC immunotherapy preclinical and clinical trials.

Hybrid-primed lymphocytes and hybrid vaccination prevent tumor growth of lewis lung carcinoma in mice

Dendritic cell (DC)-tumor cell hybrids are currently being evaluated as a novel antitumor vaccination strategy. We have explored in an animal model whether administration of DCs fused with poorly immunogenic carcinoma cells could elicit an antitumor response. Fusion of C57/BL6 mice bone marrow-derived DCs with Lewis lung carcinoma (LLC1) cells resulted in approximately 50% fusion efficiency. Hybrid cells (HCs) were used to explore 3 potential tumor therapy strategies: protective immunization, vaccination, and adoptive cellular therapy. Immunization with HCs induced activation of proliferating cytotoxic T cells, upregulation of distinct cytokines genes, and a significant retardation of tumor growth. Similar results were observed by vaccination with HCs in the tumor-bearing host. Finally, when T cells from HC-vaccinated mice were transferred into naive tumor-bearing mice, tumor growth was strongly retarded and an efficient proliferative and cytotoxic T-cell response was observed. Tumor growth was reduced by more than 50%, and tumor development was significantly delayed. Taken together, we demonstrate that HCs offer effective immunotherapy of poorly immunogenic carcinomas. This is independent of whether the HCs are taken for adoptive transfer or as a vaccine.

TWEAK Attenuates the Transition from Innate to Adaptive Immunity

Innate immunity is the first line of defense against infection, protecting the host during the development of adaptive immunity and critically affecting the nature of the adaptive response. We show that, in contrast to tumor necrosis factor alpha (TNF-alpha), the related protein TWEAK attenuates the transition from innate to adaptive mechanisms. TWEAK-/- mice had overabundant natural killer (NK) cells and displayed hypersensitivity to bacterial endotoxin, with their innate immune cells producing excess interferon (IFN)-gamma and interleukin (IL)-12. TWEAK inhibited stimulation of the transcriptional activator STAT-1 and induced p65 nuclear factor (NF)-kappaB association with histone deacetylase 1, repressing cytokine production. TWEAK-/- mice developed oversized spleens with expanded memory and T helper 1 (TH1) subtype cells upon aging and mounted stronger innate and adaptive TH1-based responses against tumor challenge. Thus, TWEAK suppresses production of IFN-gamma and IL-12, curtailing the innate response and its transition to adaptive TH1 immunity.

Inhibition of melanoma growth after treatment with dendritic cells in a Tyr-SV40E murine model requires CD4+ T cells but not CD8+ T cells

Melanomas are promising targets for immunotherapy, as they express a number of tissue-specific antigens against which immune responses can be elicited. We have previously described transgenic mice in which malignant cutaneous melanomas are produced. The 1042 melanoma cell line, derived from a primary melanoma in one of these mice, was used here to generate tumours by subcutaneous inoculation in syngeneic animals. All mice injected with 1 x 10(6) cells of the 1042 cell line developed a tumour. CD4+ T cells, CD8+ T cells and macrophages infiltrated the tumours. Treatment with dendritic cells pulsed with peptides from melanogenic proteins slowed tumour growth and resulted in increased numbers of infiltrating lymphocytes and macrophages, expansion of CD4+ T cells specific for 1042 cell antigens, and increased levels of 1042-specific immunoglobulin G1 (IgG1) and IgM in serum. The frequency of cytotoxic T lymphocytes (CTLs) specific for the MART-1 melanocytic antigen did not increase after dendritic cell treatment. Indeed, the presence of CD8+ T cells was apparently not required for the anti-tumour effects: slowing of tumour growth was not abrogated in animals depleted of CD8+ T cells using antibodies, or in syngeneic CD8-/- animals. In contrast, treatment with dendritic cells + peptides was ineffective after depletion of CD4+ T cells and in syngeneic CD4-/- mice. This experimental system therefore provides an opportunity to investigate CD4-dependent anti-tumour effector mechanisms, and for studies designed to activate the quiescent CTLs which infiltrate melanomas.

Dendritic cell-induced activation of adaptive and innate antitumor immunity

While studying Ag-pulsed syngeneic dendritic cell (DC) immunization, we discovered that surprisingly, unpulsed DCs induced protection against tumor lung metastases resulting from i.v. injection of a syngeneic BALB/c colon carcinoma CT26 or a syngeneic C57BL/6 lung carcinoma LL/2. Splenocytes or immature splenic DCs did not protect. The protection was mediated by NK cells, in that it was abrogated by treatment with anti-asialo-GM1 but not anti-CD8, and was induced by CD1(-/-) DCs unable to stimulate NKT cells, but did not occur in beige mice lacking NK cells. Protection correlated with increased NK activity, and increased infiltration of NK but not CD8(+) cells in lungs of tumor-bearing mice. Protection depended on the presence of costimulatory molecules CD80, CD86, and CD40 on the DCs, but surprisingly did not require DCs that could make IL-12 or IL-15. Unexpectedly, protection sensitive to anti-asialo-GM1 and increased NK activity were still present 14 mo after DC injection. As NK cells lack memory, we found by depletion that CD4(+) not CD8(+) T cells were required for induction of the NK antitumor response. The role of DCs and CD4(+) T cells provides a novel mechanism for NK cell induction and innate immunity against cancer that may have potential in preventing clinical metastases.

Dendritic cells transfected with interleukin-12 and pulsed with tumor extract inhibit growth of murine prostatic carcinoma in vivo

BACKGROUND

The induction of anti-tumor immune response by injection of dendritic cells loaded with specific antigen or transduced with genes encoding tumor-specific antigens have been studied in animal models and have shown promising anti-tumor effects. The impact of different routes of administration of dendritic cells on their anti-tumor effects is uncertain.

METHODS

We examined the effect of injection of cloned dendritic cells, which were stably transfected with IL-12 and exposed to an extract of murine RM-9 prostate carcinoma cell antigens on tumor growth in vivo. The cloned dendritic cells were injected intramuscularly, subcutaneously, or intraperitoneally into C57BL/6 mice. Seven days later, the mice were inoculated subcutaneously with 100,000 RM-9 cells. The sizes of the resulting tumors were measured every 3 days.

RESULTS

Compared with the wild type dendritic cells, the IL-12-transfected dendritic cells delayed tumor engraftment by 7 days (P=0.04), and reduced tumor growth by up to 80% (P=0.02). Among the three routes of injection, intramuscular injection was most effective. In contrast to wild type dendritic cells, IL-12-transfected dendritic cells induced infiltration of mononuclear cells into the tumors, and induced apoptosis and necrosis of tumor cells. Injection of IL-12-transfected dendritic cells also significantly delays tumor growth in the preexisting RM-9 tumors.

CONCLUSIONS

We conclude that antigen-exposed, IL-12-transfected dendritic cells have potential as an immunotherapy for prostate carcinoma. Routes of administration of dendritic cells are critical for maximal anti-tumor effect.

Generation of antigen-loaded dendritic cells in a serum-free medium using different cytokine combinations

Dendritic cells (DCs) are antigen-presenting cells that play a critical role in the induction of cytotoxic T-lymphocytes. An optimal method for the generation of DC for clinical use remains to be established. The aim of our study was to find an optimal cytokine combination for DC generation from peripheral blood stem cells (PBSC) and peripheral blood mononuclear cells (PBMC) in serum-free conditions. Serial immunophenotyping enabled us to observe changes in DC content during the culture as well as the development of maturation and activation markers. As a source for DC culture, we used PBSC from patients with multiple myeloma after stem cell mobilization using cyclophosphamide and G-CSF, or PBMC from healthy donors without mobilization. The cells were cultured in a serum-free medium with different cytokine combinations including GM-CSF, TNF-alpha, Flt-3, CD40L, IFN-gamma, IL-1alpha, IL-6, PGE1, and IL-4. The cell cultures were evaluated by immunophenotyping. For PBMC, interleukin-12 assay was performed. For PBSC, the yield of DC as determined by CD83+ cell count ranged from 0. 6 x 10(5) to 30.1 x 10(4) (mean: 9.4 x 10(4)) of DC generated per 1 x 10(6) of initially plated nucleated cells from apheresis. This yield corresponded to (0.3-19.1) x 10(5) (mean: 4.3 x 10(5)) per 1 x 10(6) of CD34+ cells in the apheresis products. For PBMC, the yield was (0.4-24.8) x 10(4) (mean: 2.4 x 10(4)) of DC generated per 1 x 10(6) of initially plated mononuclear cells from venous blood. The cultured cells expressed the mature immunophenotype. No significant differences in cell yield or immunophenotype were detected when comparing different cytokine combinations.

Human dendritic cells induce tumor-specific apoptosis by soluble factors

Dendritic cells (DCs) are the most potent antigen producing cells (APCs) for initiation of immune responses including anti-tumor immune responses. In previous reports, it has been shown that DCs efficiently take up and process apoptotic or necrotic bodies of tumor cells. It has also been shown that DCs pulsed with tumor cell apoptotic bodies, lysates or peptides generate potent anti-tumor immune responses. Direct interactions between DCs and viable tumor cells, however, have not been clearly elucidated. We report that monocyte-derived, CD1a+ immature DCs (iDCs) significantly inhibit the growth of breast tumor cells in coculture and transwell experiments in the presence of soluble CD40 ligand (sCD40L), LPS or both. The growth inhibition effects correlated with cell cycle arrest and apoptosis of breast tumor cells. The effects were associated with morphological changes of tumor cells from a round shape to a flat, spindle shape. In contrast, no inhibition of proliferation or morphological changes was observed on normal PBMC, K562 or breast fibroblasts. Interestingly, iDCs undergoing maturation induced by sCD40L+LPS induced a much stronger growth inhibitory effect than iDCs alone or mature DCs treated with sCD40L+LPS. Fractionation of supernatants showed the anti-tumor effects were mediated by a TNF-alpha-dependent and -independent mechanism. Soluble FasL and TRAIL were not involved. Our findings suggest that maturing DCs have the intrinsic ability to induce cell-cycle arrest and apoptosis of breast tumor cells through soluble factors, but not normal cells, in addition to their Ag presentation function.

The induction of systemic and mucosal immunity to protein vaccines delivered through skin sites exposed to UVB

It has been reported that common mucosal immunity can be efficiently induced in mice following immunization through the skin with vaccine formulations containing either the active form of vitamin D, or chemical agents capable of locally enhancing cyclic adenosine monophosphate levels. Herein, we report that exposure of skin to ultraviolet radiation B (UVB) can be employed as a means to alter systemic humoral immune responses and to promote the induction of mucosal immunity to protein antigens delivered into UVB-exposed skin sites. Our data indicates that the skin, as a vaccination site, can be manipulated to allow efficient induction of common mucosal and systemic immune responses.

Effects of lipofectin-antigen complexes on major histocompatibility complex class I-restricted antigen presentation pathway in murine dendritic cells and on dendritic cell maturation

We previously reported that exogenous antigens complexed with the cationic liposome lipofectin (LF) were efficiently presented via major histocompatibility complex (MHC) class I molecules on pulsed dendritic cells (DCs) in vitro. In the present study, we demonstrated that MHC class I-restricted antigen presentation on DC2.4 cells, a murine immature DC line, treated with LF-antigen complexes was remarkably suppressed through the inhibition of endocytosis, proteasome catalysis, and Golgi transport. We also found that LF did not influence expression of interleukin-12 p40 mRNA, MHC molecules, or co-stimulatory molecules in DC2.4 cells. These findings suggest that an antigen-loading procedure using LF could enhance delivery of exogenous antigens to the classical MHC class I pathway in DCs, but it does not initiate DC maturation.

Maturation of dendritic cells by recombinant human CD40L-trimer leads to a homogeneous cell population with enhanced surface marker expression and increased cytokine production

Dendritic cells (DC) have been shown to be potent inducers of specific cytotoxic T-cell responses both in vivo and in vitro. Furthermore, exposure to cytokines such as tumour necrosis factor (TNF)-alpha or CD40 triggering changes DC phenotype and cytokine production and may enhance the T-cell activating capacity of the DC. We studied DC phenotype and cytokine production as well as the T-cell proliferation and cytotoxic T lympocyte (CTL) activation induced by DC generated in vitro. In addition, the effect of exposure to recombinant human CD40L-trimer (huCD40LT) on these parameters was investigated. Effective differentiation of monocytes derived from freshly isolated peripheral blood mononuclear cells (PBMC) was obtained with granulocyte macrophage-colony stimulating factor (GM-CSF) and interleukin (IL)-4. The DC expression of human leucocyte antigen (HLA) molecules, CD80, CD83, and CD86 was markedly enhanced by exposure to huCD40LT even compared to TNF-alpha exposure. Only a moderate cytokine production was observed initially, while TNF-alpha addition or CD40 triggering, especially, induced enhanced production of IL-6 and IL-12 p40. Surprisingly, comparable induction of T-cell proliferation by a DC allostimulus or through the presentation of PPD, and influenza M1-peptide specific CTL activity was obtained with nonmaturated (CD83-) and maturated (CD83+) DC. In conclusion, a final maturation of monocyte-derived DC through huCD40LT resulted in a highly homogeneous cell population with enhanced surface marker expression and high production of pro-inflammatory cytokines. In addition, the induction of responses to allo or recall antigens presented by huCD40LT maturated DC was comparable to the responses obtained with the DC maturated through TNF-alpha exposure.

The involvement of TNF-alpha-related apoptosis-inducing ligand in the enhanced cytotoxicity of IFN-beta-stimulated human dendritic cells to tumor cells

TNF-alpha-related apoptosis-inducing ligand (TRAIL) is characterized by its preferential induction of apoptosis of tumor cells but not normal cells. Dendritic cells (DCs), besides their role as APCs, now have been demonstrated to exert cytotoxicity or cytostasis on some tumor cells. Here, we report that both human CD34(+) stem cell-derived DCs (CD34DCs) and human CD14(+) monocyte-derived DCs (MoDCs) express TRAIL and exhibit cytotoxicity to some types of tumor cells partially through TRAIL. Moderate expression of TRAIL appeared on CD34DCs from the 8th day of culture and was also seen on freshly isolated monocytes. The level of TRAIL expression remained constant until DC maturation. TRAIL expression on immature CD34DCs or MoDCs was greatly up-regulated after IFN-beta stimulation. Moreover, IFN-beta could strikingly enhance the ability of CD34DCs or MoDCs to kill TRAIL-sensitive tumor cells, but LPS did not have such an effect. The up-regulation of TRAIL on IFN-beta-stimulated DCs partially contributed to the increased cytotoxicity of DCS: Pretreatment of TRAIL-sensitive tumor cells with caspase-3 inhibitor could significantly increase their resistance to the cytotoxicity of IFN-beta-stimulated DCS: In contrast, NF-kappaB inhibitor could significantly increase the sensitivity of tumor cells to the killing by nonstimulated or LPS-stimulated DCS: Our studies demonstrate that IFN-beta-stimulated DCs are functionally cytotoxic. Thus, an innate mechanism of DC-mediated antitumor immunity might exist in vivo in which DCs act as effectors to directly kill tumor cells partially via TRAIL. Subsequently, DCs act as APCs involved in the uptake, processing, and presentation of apoptotic tumor Ags to cross-prime CD8(+) CTL cells.

In vitro immunization of patient T cells with autologous bone marrow antigen presenting cells pulsed with tumor lysates

Presentation of cell-associated antigen to T cells is a critical event in the initiation of an anti-tumor immune response but it appears to often be deficient or limiting. Here we report an experimental system for stimulation of human T lymphocytes using autologous antigen presenting cells (APCs) and autologous tumor cells. Two types of APCs were prepared from human bone marrow: MC and DC. MC were produced by using GM-CSF and SCF. DC were obtained with the same cytokines plus IL-4. DC and MC were generated in parallel from the same patients and their phenotypes and capacities to prime T lymphocytes were analyzed and compared. MC were CD14+, CD1a-, CD33+ and HLA-DR+. Two populations of DC were defined: immature DC were uniformly CD1a-; mature DC expressed CD1a, CD80, CD86, HLA-DR, CD54 and CD58 but lacked surface CD14. Stimulation of autologous T lymphocytes was studied by measuring their proliferation and cytotoxic function. In more than 80% of our experiments the proliferation of autologous T lymphocytes cocultured with APC pulsed or not with tumor cell lysates was higher than that of T cells cultured alone. DC were more effective than MC in stimulating proliferation of lymphocytes. The capacity of a patient's autologous bone marrow-derived APC to stimulate T cells when exposed to autologous tumor cell lysates suggest that such antigen-exposed APC may be useful in specific anti-tumor immunotherapy protocols.

Contrasting effects of myeloid dendritic cells transduced with an adenoviral vector encoding interleukin-10 on organ allograft and tumour rejection

Mouse bone marrow-derived myeloid dendritic cells (DC) propagated in granulocyte-macrophage colony-stimulating factor and transforming growth factor-beta1 (TGF-beta1) (so-called 'TGF-beta DC') are phenotypically immature, and prolong allograft survival. Interleukin-10 (IL-10) has been shown to inhibit the maturation of DC by down-regulating surface major histocompatibility complex (MHC) class II, co-stimulatory and adhesion molecule expression. Genetic engineering of TGF-beta DC to overexpress IL-10 might enhance their tolerogenic potential. In this study, adenoviral (Ad) vectors encoding the mouse IL-10 gene were transduced into B10 (H2b) TGF-beta DC. Transduction with Ad-IL-10 at a multiplicity of infection (MOI) of 50-100 resulted in a modest reduction in the incidence of DC expressing surface MHC class II, CD40, CD80 and CD86. Paradoxically, Ad-IL-10 transduction enhanced the allostimulatory activity of DC in mixed leucocyte reactions and cytotoxic T lymphocyte assays, and increased their natural killer cell stimulatory activity. Systemic injection of normal C3H recipients with Ad-IL-10-transduced B10-DC 7 days before organ transplantation, exacerbated heart graft rejection and augmented circulating anti-donor alloantibody titres. Contrasting effects were observed in relation to tumour growth. All mice preimmunized with Ad-IL-10-transduced, tumour antigen (B16F10)-pulsed DC developed palpable tumours, associated with significant inhibition of splenic anti-tumour cytotoxic T lymphocyte generation. Animals pretreated with control Ad-LacZ-transduced, B16F10-pulsed DC however, remained tumour free. These findings are consistent with the multifunctional immunomodulatory properties of mammalian IL-10.

Recombinant yellow fever viruses are effective therapeutic vaccines for treatment of murine experimental solid tumors and pulmonary metastases

We have genetically engineered an attenuated yellow fever (YF) virus to carry and express foreign antigenic sequences and evaluated the potential of this type of recombinant virus to serve as a safe and effective tumor vaccine. Live-attenuated YF vaccine is one of the most effective viral vaccines available today. Important advantages include its ability to induce long-lasting immunity, its safety, its affordability, and its documented efficacy. In this study, recombinant live-attenuated (strain 17D) YF viruses were constructed to express a cytotoxic T-lymphocyte epitope derived from chicken ovalbumin (SIINFEKL). These recombinant viruses replicated comparably to the 17D vaccine strain in cell culture and stably expressed the ovalbumin antigen, and infected cells presented the antigen in the context of major histocompatibility complex class I. Inoculation of mice with recombinant YF virus elicited SIINFEKL-specific CD8(+) lymphocytes and induced protective immunity against challenge with lethal doses of malignant melanoma cells expressing ovalbumin. Furthermore, active immunotherapy with recombinant YF viruses induced regression of established solid tumors and pulmonary metastases. Thus, recombinant YF viruses are attractive viral vaccine vector candidates for the development of therapeutic anticancer vaccines.

CD40-ligated dendritic cells effectively expand melanoma-specific CD8+ CTLs and CD4+ IFN-gamma-producing T cells from tumor-infiltrating lymphocytes

Professional APC, notably dendritic cells (DC), are necessary for stimulation and expansion of naive T cells. By means of murine models, the interaction between CD40 on DC and its ligand CD154 has been recognized as an important element for conditioning of DC to prime and expand CTL. We translated these findings into the human system, scrutinizing the ability of DC to initiate clonal expansion of single T cells. DC generated under completely autologous conditions from peripheral blood monocytes were cocultured at a rate of 0.3 cell/well with melanoma-infiltrating T cells; this procedure guaranteed that either a CD4+ or a CD8+ cell interacted with the DC, thus avoiding the contact of more than one T cell to the DC. In the absence of further stimulation, this cloning protocol yielded almost exclusively CD4+ T cell clones that predominantly exhibited a Th2 phenotype. However, cross-linking of CD40 on DC resulted in the induction of IFN-gamma-producing Th1 CD4+ T cell clones. In addition, CD40-activated DC were capable of expanding CD8+ CTL clones. The ratio of CD4 to CD8 T cell clones corresponded to the ratio present in the initial tumor-infiltrating lymphocyte preparation. The CTL clones efficiently lysed autologous tumor cells whereas autologous fibroblasts or MHC-mismatched melanoma cells were not killed. Our findings support the critical role of CD40/CD154 interactions for the induction of cellular immune responses.

The induction of systemic and mucosal immune responses to antigen-adjuvant compositions administered into the skin: alterations in the migratory properties of dendritic cells appears to be important for stimulating mucosal immunity

The properties of various vaccine-adjuvant formulations that are capable of inducing both systemic and common mucosal immunity subsequent to their intradermal administration are described. Effective mucosal adjuvants, including bacterial toxins, chemical enhancers of cyclic AMP, and the active form of vitamin D3, all shared the ability to promote dendritic cell migration from the skin to Peyer's patches subsequent to antigen induced maturation. Our data suggests that skin dendritic cells may function as effective antigen presenting cells for the induction of mucosal immune responses, if microenvironmental conditions are appropriately manipulated subsequent to their stimulation by antigen.

Anti-tumor vaccination in heterozygous congenic F1 mice: presentation of tumor-associated antigen by the two parental class I alleles

Peptide vaccination of homozygous mice against syngeneic tumors using single major histocompatibility complex (MHC) class I-restricted cytotoxic T lymphocyte (CTL) epitopes elicits effective immune responses against metastatic growth. So far, single-peptide vaccination of patients against their autologous tumors seems to elicit less satisfactory results. In this study, the authors tried to determine whether effective anti-metastatic immunity requires the presentation of peptides restricted by the two parental class I major histocompatibility complex alleles in heterozygous hosts. The immune response against the H-2b-derived 3LL Lewis lung carcinoma was evaluated in heterozygous recombinant congenic F1 mice (Kk x K(b)) and (Kd x K(b)). Vaccination of such heterozygous animals with dendritic cells expressing the two parental H-2K alleles, pulsed with total tumor extract, elicited a potent anti-metastatic response. A comparable response was obtained after vaccination with tumor cells genetically modified to express the two class I alleles. In contrast, vaccination of the heterozygous mice with dendritic cells expressing only one of the parental F1 H-2K alleles or with tumors expressing only one H-2K allele failed to elicit effective immunity against tumor metastasis in recombinant congenic F1 mice. It appears, therefore, that to achieve effective anti-metastatic immunotherapy in heterozygous organisms, presentation of cytotoxic T lymphocyte epitopes restricted by the two parental class I alleles is required.

Intramuscular administration of E7-transfected dendritic cells generates the most potent E7-specific anti-tumor immunity

Dendritic cells (DCs) are highly efficient antigen-presenting cells capable of priming both cytotoxic and helper T cells in vivo. Recent studies have demonstrated the potential use of DCs that are modified to carry tumor-specific antigens in cancer vaccines. However, the optimal administration route of DC-based vaccines to generate the greatest anti-tumor effect remains to be determined. This study is aimed at comparing the levels of immune responses and anti-tumor effect generated through different administration routes of DC-based vaccination. We chose the E7 gene product of human papillomavirus (HPV) as the model antigen and generated a stable DC line (designated as DC-E7) that constitutively expresses the E7 gene. Among the three different routes of DC-E7 vaccine administration in a murine model, we found that intramuscular administration generated the greatest anti-tumor immunity compared with subcutaneous and intravenous routes of administration. Furthermore, intramuscular administration of DC-E7 elicited the highest levels of E7-specific antibody and greatest numbers of E7-specific CD4+ T helper and CD8+ T cell precursors. Our results indicate that the potency of DC-based vaccines depends on the specific route of administration and that intramuscular administration of E7-transfected DCs generates the most potent E7-specific anti-tumor immunity.

Absence of herpesvirus DNA sequences in the 5T murine model of human multiple myeloma

Kaposi's sarcoma-associated herpesvirus (KSHV, also known as HHV-8) has been found in patients with multiple myeloma (MM) and postulated to be aetiologically associated with the development of this common plasma cell malignancy. A murine model of MM was previously established in which intravenous transfer of 5T myeloma cells into C57BL/KaLwRij mice resulted in characteristic features of human MM. In the present study, we sought to identify herpesvirus DNA sequences in this murine model of MM through polymerase chain reaction (PCR) analysis using primers specific for KSHV, murine herpesvirus 68 (MHV68) and murine cytomegalovirus (MCMV) as well as consensus primers designed from the highly conserved DNA polymerase genes of the Herpesviridae family. None of the DNA samples from whole bone marrow (n = 6) or dendritic cells enriched by long-term culture (n = 8) of 5T myeloma-bearing mice as well as the 5T myeloma cell lines (n = 3) maintained in long-term culture yielded specific amplification products in any of the PCR assays. Two KSHV-specific serological assays measuring antibodies to KSHV latent and lytic antigens also failed to detect the presence of anti-KSHV antibodies in mice that developed MM. These results suggest that the development of 5T murine MM is unlikely to be involved with KSHV or a KSHV-like murine herpesvirus.

Dendritic cells infected with a vaccinia vector carrying the human gp100 gene simultaneously present multiple specificities and elicit high-affinity T cells reactive to multiple epitopes and restricted by HLA-A2 and -A3

To investigate the ability of human dendritic cells (DC) to process and present multiple epitopes from the gp100 melanoma tumor-associated Ags (TAA), DC from melanoma patients expressing HLA-A2 and HLA-A3 were pulsed with gp100-derived peptides G9154, G9209, or G9280 or were infected with a vaccinia vector (Vac-Pmel/gp100) containing the gene for gp100 and used to elicit CTL from autologous PBL. CTL were also generated after stimulation of PBL with autologous tumor. CTL induced with autologous tumor stimulation demonstrated HLA-A2-restricted, gp100-specific lysis of autologous and allogeneic tumors and no lysis of HLA-A3-expressing, gp100+ target cells. CTL generated by G9154, G9209, or G9280 peptide-pulsed, DC-lysed, HLA-A2-matched EBV transformed B cells pulsed with the corresponding peptide. CTL generated by Vac-Pmel/gp100-infected DC (DC/Pmel) lysed HLA-A2- or HLA-A3-matched B cell lines pulsed with the HLA-A2-restricted G9154, G9209, or G9280 or with the HLA-A3-restricted G917 peptide derived from gp100. Furthermore, these DC/Pmel-induced CTL demonstrated potent cytotoxicity against allogeneic HLA-A2- or HLA-A3-matched gp100+ melanoma cells and autologous tumor. We conclude that DC-expressing TAA present multiple gp100 epitopes in the context of multiple HLA class I-restricting alleles and elicit CTL that recognize multiple gp100-derived peptides in the context of multiple HLA class I alleles. The data suggest that for tumor immunotherapy, genetically modified DC that express an entire TAA may present the full array of possible CTL epitopes in the context of all possible HLA alleles and may be superior to DC pulsed with limited numbers of defined peptides.

In vitro growth inhibition of a broad spectrum of tumor cell lines by activated human dendritic cells

Dendritic cells (DCs) are critical subsets of leukocytes providing antigen presentation for initiation of humoral and cellular immune responses. Their role as effector cells in tumor resistance, however, is less known. We report here that human DCs generated by culturing plastic-adherent peripheral blood monocytes in the presence of granulocyte-monocyte colony–stimulating factor (GM-CSF) and interleukin-4 have potent growth-inhibition activity in vitro on a wide spectrum of human tumor lines of different tissue origin. Proinflammatory stimuli lipopolysaccharide (LPS) and interferon-γ, but not tumor necrosis factor– and CD40 signaling, can further enhance DC-mediated inhibition of tumor growth. The growth inhibition requires contact between DCs and tumor cells while LPS treatment enhances the antitumor activity in DC culture supernatants. Our results suggest that in addition to their predominant role as regulatory cells, activated DCs are also potential effector cells in tumor immunity.

In vitro growth inhibition of a broad spectrum of tumor cell lines by activated human dendritic cells

Dendritic cells (DCs) are critical subsets of leukocytes providing antigen presentation for initiation of humoral and cellular immune responses. Their role as effector cells in tumor resistance, however, is less known. We report here that human DCs generated by culturing plastic-adherent peripheral blood monocytes in the presence of granulocyte-monocyte colony–stimulating factor (GM-CSF) and interleukin-4 have potent growth-inhibition activity in vitro on a wide spectrum of human tumor lines of different tissue origin. Proinflammatory stimuli lipopolysaccharide (LPS) and interferon-γ, but not tumor necrosis factor– and CD40 signaling, can further enhance DC-mediated inhibition of tumor growth. The growth inhibition requires contact between DCs and tumor cells while LPS treatment enhances the antitumor activity in DC culture supernatants. Our results suggest that in addition to their predominant role as regulatory cells, activated DCs are also potential effector cells in tumor immunity.

Immunogene therapy for murine melanoma using recombinant adenoviral vectors expressing melanoma-associated antigens

Adenoviral vectors expressing tumor-associated antigens can be used to evoke a specific immune response and inhibit tumor growth. In this study, we tested the efficacy of adenoviral vectors encoding human gp100 (Ad2/hugp100), murine gp100 (Ad2/mugp100), or murine TRP-2 (Ad2/muTRP-2) for their ability to elicit a specific cellular immune response and inhibit the growth of B16 melanoma tumor cells in the mouse. C57BL/6 mice were immunized with Ad2/hugp100, Ad2/mugp100, or Ad2/muTRP-2 either 2 weeks prior to B16-F10 tumor challenge (prophylactic treatment) or 3 days after tumor challenge (active treatment). Ad2/hugp100 and Ad2/muTRP-2 administered to two or more intradermal (i.d.) sites inhibited subsequent subcutaneous tumor growth in > or = 80% of the mice and elicited an antigen-specific cytotoxic T lymphocyte response, whereas other administration routes were not as effective. Ad2/mugp100 administered to two i.d. sites did not inhibit tumor growth or provoke cellular immunity. Immunization was less effective with active treatment where tumor growth was not significantly inhibited by a single dose of either Ad2/muTRP-2 or Ad2/hugp100. However, increasing the number of intradermal immunization sites and the number of doses resulted in progressive improvements in protection from tumor growth in the active treatment model. In conclusion, breaking host tolerance to elicit protective immunity by using adenoviral vectors expressing melanoma-associated antigens is dependent upon the choice of antigen, the site of administration, and the number of doses. These observations provide insights into the clinical applicability of adenoviral vaccines for immunotherapy of malignant diseases.

Dendritic cell biology and the application of dendritic cells to immunotherapy of multiple myeloma

Dendritic cells (DCs) are extremely efficient antigen-presenting cells that are potent stimulators of both B and T cell immune responses. Although DCs are normally present in extremely small numbers in the circulation, recent advances in DC biology have made it possible to generate DCs in culture. DCs can be generated in vitro from various cellular sources including bone marrow, cord blood and peripheral blood. Although culture conditions are extremely diverse, the majority of protocols grow DCs in GM-CSF and either TNF-alpha and/or IL-4. The addition of other growth factors such as SCF and Flt-3 ligand can dramatically enhance DC recovery. It is important to appreciate that DC subsets have been identified. Thus, DC at different stages of maturation, based on phenotype and capacity to capture antigen, can be obtained depending on culture conditions. For clinical applications, DCs can be generated in serum-free media and cryopreserved for future clinical applications. The ability to obtain DCs in numbers suitable for manipulating immune responses has pushed DC-based immunotherapies into the spotlight for treatment of various malignancies, including multiple myeloma, a B cell malignancy that is presently incurable. Although high-dose chemotherapy and transplantation have improved complete remission rates and overall survival in myeloma, immunotherapeutic strategies are needed for the additional cytoreduction needed to achieve a cure. Because DCs specialize in antigen capture and are extremely potent at stimulating T cell responses, they are ideally suited for generating anti-myeloma T cell responses in vivo. Several studies have demonstrated that myeloma protein, also called idiotype (Id), is sufficiently immunogenic and can be used to generate in vivo T cell responses in myeloma patients. Clinical trials using Id-pulsed DCs as a vaccine to treat minimal residual disease or relapsed myeloma are currently underway. Feasibility studies indicate that antigen-pulsed autologous DCs can be used to elicit in vivo Id-specific T cell responses. Additional studies are needed to optimize current DC vaccination protocols and determine clinical benefits associated with this approach. It is hoped that, following conventional therapies, a combination of adoptive immunotherapeutic modalities such as DCs together with myeloma-specific T cells may lead to improved clinical responses in multiple myeloma, and ultimately lead to complete remission and cure.

Generation of T-cell immunity to a murine melanoma using MART-1-engineered dendritic cells

The murine melanoma B16 expresses the murine counterpart of the human MART-1/Melan-A (MART-1) antigen, sharing a 68.6% amino acid sequence identity. In this study, mice were vaccinated with bone marrow-derived murine dendritic cells genetically modified with a replication-incompetent adenoviral vector to express the human MART-1 gene (AdVMART1). This treatment generated a protective response to a lethal tumor challenge of unmodified murine B16 melanoma cells. The response was mediated by major histocompatibility complex class I-restricted cytotoxic T lymphocytes specific for MART-1 antigen, which produced high levels of interferon-gamma when reexposed to MART-1 in vitro and lysed targets in a calcium-dependent mechanism suggestive of perforin/granzyme B lysis. MART-1 was presented by the dendritic cells used for vaccination and not by epitopes cross-presented by host antigen-presenting cells. In conclusion, dendritic cells genetically modified to express the human MART-1 antigen generate potent murine MART-1-specific protective responses to B16 melanoma.

Murine dendritic cells transfected with human GP100 elicit both antigen-specific CD8(+) and CD4(+) T-cell responses and are more effective than DNA vaccines at generating anti-tumor immunity

Dendritic cells (DCs) are potent inducers of cytotoxic T lymphocytes (CTLs) when pulsed with an antigenic peptide or tumor lysate. In this report, we have used liposome-mediated gene transfer to examine the ability of plasmid DNA encoding the human melanoma-associated antigen gp100 to elicit CD8(+) and CD4(+) T-cell responses. We also compared the efficacy between gp100 gene-modified DCs and naked DNA (pCDNA3/gp100)-based vaccines at inducing anti-tumor immunity. DCs were generated from murine bone marrow and transfected in vitro with plasmid DNA containing the gp100 gene. These gp100-modified DCs (DC/gps) were used to stimulate syngeneic naive spleen T cells in vitro or to immunize mice in vivo. Antigen-specific, MHC-restricted CTLs were generated when DC/gps were used to prime T cells both in vitro and in vivo. Thus, these CTLs were cytolytic for gp100-transfected syngeneic (H-2(b)) tumor MCA106 (MCA/gp) and vaccinia-pMel17/gp100-infected syngeneic B16 and MCA106, but not parental tumor MCA106 and B16, or gp100-transfected allogeneic tumor P815 (H-2(d)). Immunization with DC/gp protected mice from subsequent challenge with MCA/gp but not parental MCA106. Antibody-mediated T-cell subset depletion experiments demonstrate that induction of CTLs in vivo is dependent on both CD4(+) and CD8(+) T cells. Furthermore, DC/gp immunization elicits an antigen-specific CD4(+) T-cell response, suggesting that DC/gps present MHC class II epitopes to CD4(+) T cells. In addition, our data show that gene-modified, DC-based vaccines are more effective than the naked DNA-based vaccines at eliciting anti-tumor immunity in both prophylactic and therapeutic models. These results suggest that the use of DCs transfected with plasmid DNA containing a gene for TAA may be superior to peptide-pulsed DCs and naked DNA-based vaccines for immunotherapy and could provide an alternative strategy for tumor vaccine design.

CpG DNA: a potent signal for growth, activation, and maturation of human dendritic cells

DNA molecules containing unmethylated CpG-dinucleotides in particular base contexts ("CpG motifs") are excellent adjuvants in rodents, but their effects on human cells have been less clear. Dendritic cells (DCs) form the link between the innate and the acquired immune system and may influence the balance between T helper 1 (Th1) and Th2 immune responses. We evaluated the effects of CpG oligodeoxynucleotides alone or in combination with granulocyte-macrophage colony-stimulating factor (GMCSF) on different classes of purified human DCs. For primary dendritic precursor cells isolated from human blood, CpG oligonucleotides alone were superior to GMCSF in promoting survival and maturation (CD83 expression) as well as expression of class II MHC and the costimulatory molecules CD40, CD54, and CD86 of DCs. Both CD4-positive and CD4-negative peripheral blood dendritic precursor cells responded to CpG DNA which synergized with GMCSF but these DCs showed little response to lipopolysaccharide (LPS). In contrast, monocyte-derived DCs did not respond to CpG, but they were highly sensitive to LPS, suggesting an inverse correlation between CpG and LPS sensitivity in different subsets of DCs. Compared with GMCSF, CpG-treated peripheral blood DCs showed enhanced functional activity in the mixed lymphocyte reaction and induced T cells to secrete increased levels of Th1 cytokines. These findings demonstrate the ability of specific CpG motifs to strongly activate certain subsets of human DCs to promote Th1-like immune responses, and support the use of CpG DNA-based trials for immunotherapy against cancer, allergy, and infectious diseases.

Immunotherapeutic potential of dendritic cells generated in long-term stroma-dependent cultures

Long term cultures (LTC) producing dendritic cells (DC) have been established from spleen. A well developed stromal cell layer supported production of DC in numbers suitable for experimentation. Cells had obvious membrane pseudopodia and could be collected from culture every 2-3 days. Large cells produced in LTC stained with fluorescently labelled monoclonal antibodies specific for DC such as 33D1, and M1/70 which is specific for DC and myeloid cells. These staining patterns confirmed the presence of DC within the LTC population. LTC-DC were tested and shown capable of migration in vivo in B10.A(2R) mice following footpad inoculation. Most cells entered the spleen and a small number entered popliteal lymph node. LTC-DC have migratory capacity comparable with control spleen lymphocytes. LTC-DC were tested for capacity to induce an anti-tumour immune response after exposing cells to tumour cell membranes. LTC-DC pulsed with BL/VL3 tumour antigens were able to induce a BL/VL3-specific primary cytotoxic T lymphocyte (CTL) response detectable in popliteal lymph nodes and spleen of C57BL/6J mice within 6 days of priming. BL/VL3 tumour cells grew in sublethally irradiated C57BL/6J mice giving 100% mortality. Adoptive transfer of spleen cells from mice given BL/VL3 antigen-pulsed LTC-DC, two weeks previously, significantly slowed the growth of BL/VL3 tumour cells in mice. DC produced in LTC can function as antigen presenting cells (APC) when adoptively transferred into animals. Their capacity to migrate effectively, to induce a CTL response and to reduce tumour load suggests that DC grown using this in vitro system may have valuable clinical potential in humans.

Accessing Epstein-Barr virus-specific T-cell memory with peptide-loaded dendritic cells

The conventional means of studying Epstein-Barr virus (EBV)-induced cytotoxic T-lymphocyte (CTL) memory, by in vitro stimulation with the latently infected autologous lymphoblastoid cell line (LCL), has important limitations. First, it gives no information on memory to lytic cycle antigens; second, it preferentially amplifies the dominant components of latent antigen-specific memory at the expense of key subdominant reactivities. Here we describe an alternative approach, based on in vitro stimulation with epitope peptide-loaded dendritic cells (DCs), which allows one to probe the CTL repertoire for any individual reactivity of choice; this method proved significantly more efficient than stimulation with peptide alone. Using this approach we first show that reactivities to the immunodominant and subdominant lytic cycle epitopes identified by T cells during primary EBV infection are regularly detectable in the CTL memory of virus carriers; this implies that in such carriers chronic virus replication remains under direct T-cell control. We further show that subdominant latent cycle reactivities to epitopes in the latent membrane protein LMP2, though rarely undetectable in LCL-stimulated populations, can be reactivated by DC stimulation and selectively expanded as polyclonal CTL lines; the adoptive transfer of such preparations may be of value in targeting certain EBV-positive malignancies.

Experimental vaccine strategies for cancer immunotherapy

Recently, cancer immunotherapy has emerged as a therapeutic option for the management of cancer patients. This is based on the fact that our immune system, once activated, is capable of developing specific immunity against neoplastic but not normal cells. Increasing evidence suggests that cell-mediated immunity, particularly T-cell-mediated immunity, is important for the control of tumor cells. Several experimental vaccine strategies have been developed to enhance cell-mediated immunity against tumors. Some of these tumor vaccines have generated promising results in murine tumor systems. In addition, several phase I/II clinical trials using these vaccine strategies have shown extremely encouraging results in patients. In this review, we will discuss many of these promising cancer vaccine strategies. We will pay particular attention to the strategies employing dendritic cells, the central player for tumor vaccine development.

Vaccination with dendritic cells inhibits the growth of hepatic metastases in B6 mice

Dendritic cells (DC) are specialized antigen-presenting cells that can activate naive and mature T-cells, induce cellular immunity, and stimulate strong antitumor reactions in vivo. This study was undertaken to examine the function of DC vaccines in suppressing the growth of hepatic metastases in C57BL/6 mice. Experimental mice received two i.v. doses of 1 x 10(6) bone marrow-derived DC, either unpulsed or pulsed with MCA-106 fibrosarcoma cell lysates, on days -14 and -7. Controls were injected with HBSS. Hepatic metastases were established on day 0 through intrasplenic injections of 1 x 10(5) MCA-106 tumor cells. Animals were sacrificed on day 21 and their livers were excised to assess tumor burden. Splenocytes from DC-treated groups were cytotoxic against MCA-106 cells, but not against the L929 and CT26 (syngeneic fibroblast and colon tumor, respectively) cell lines. All control mice developed grossly evident hepatic metastases, while 62 and 44% of the mice receiving MCA-106 cell lysate-pulsed DC and unpulsed DC vaccines, respectively, were completely free of tumor. Mean hepatic mass for the controls, including tumor, was almost double that for treated animals. Antibody depletion of either CD4+ or CD8+ lymphocytes abrogated the protective effect of the vaccine. This study demonstrates that immunization with DC confers cellular immunity, with both CD4+ and CD8+ T-cells playing a significant role, and impedes the subsequent establishment and growth of hepatic metastases in mice. The antitumor capabilities of DC justify their use in immunotherapeutic vaccines against human cancers.