Rapid entry into the cryptophycin core via an acyl-beta-lactam macrolactonization: total synthesis of cryptophycin-24

[see structure]. An efficient, concise approach to the macrolide core of the cryptophycins, potent antimitotic agents, has been achieved. The reaction sequence features a novel macrolactonization utilizing a reactive acyl-beta-lactam intermediate that incorporates the beta-amino acid moiety within the 16-membered macrolide core. This highly modular approach, which allows for multiple alterations throughout the structure, was successfully applied to the total synthesis of cryptophycin-24.

Induction of polyclonal prostate cancer-specific CTL using dendritic cells transfected with amplified tumor RNA

Polyvalent cancer vaccines targeting the entire antigenic spectrum on tumor cells may represent a superior therapeutic strategy for cancer patients than vaccines solely directed against single Ags. In this study, we show that autologous dendritic cells (DC) transfected with RNA amplified from microdissected tumor cells are capable of stimulating CTL against a broad set of unidentified and critical prostate-specific Ags. Although the polyclonal CTL responses generated with amplified tumor RNA-transfected DC encompassed as a subcomponent a response against prostate-specific Ag (PSA) as well as against telomerase reverse transcriptase, the tumor-specific CTL were consistently more effective than PSA or telomerase reverse transcriptase CTL to lyse tumor targets, suggesting the superiority of the polyclonal response. Although tumor RNA-transfected DC stimulated CTL, which recognized not only tumor but also self-Ags expressed by benign prostate tissue, these cross-reactive CTL were exclusively specific for the PSA, indicating an immunodominant role of PSA in the prostate cancer-specific immune response. Our data suggest that tumor RNA-transfected DC may represent a broadly applicable, potentially clinically effective vaccine strategy for prostate cancer patients, which is not limited by tumor tissue availability for Ag preparation and may minimize the risk of clonal tumor escape.

Critical stenosis of bicarotid trunk and left subclavian artery with severe coronary artery disease - a management dilemma

A 48 yr. old patient suffering from bicarotid trunk and left subclavian artery stenosis with severe coronary artery disease was managed successfully by angioplasty and stenting of the bicarotid trunk and subclavian artery. This was followed by coronary artery bypass grafting after one month. He was free of angina and cerebrovascular symptoms at one and a half year follow up.

Total synthesis of cryptophycin-24 (Arenastatin A) amenable to structural modifications in the C16 side chain

Two efficient protocols for the synthesis of tert-butyl (5S,6R,2E, 7E)-5-[(tert-butyldimethylsilyl)oxy]-6-methyl-8-phenyl-2, 7-octadienoate, a major component of the cryptophycins, are reported. The first utilized the Noyori reduction and Frater alkylation of methyl 5-benzyloxy-3-oxopentanoate to set two stereogenic centers, which became the C16 hydroxyl and C1' methyl of the cryptophycins. The second approach started from 3-p-methoxybenzyloxypropanal and a crotyl borane reagent derived from (-)-alpha-pinene to set both stereocenters in a single step and provided the dephenyl analogue, tert-butyl (5S,6R,2E)-5-[(tert-butyldimethylsilyl)oxy]-6-methyl-2, 7-octadienoate, in five steps. This compound was readily converted to the 8-phenyl compound via Heck coupling. The silanyloxy esters were efficiently deprotected and coupled to the C2-C10 amino acid fragment to provide desepoxyarenastatin A and its dephenyl analogue. The terminal olefin of the latter was further elaborated via Heck coupling. Epoxidation provided cryptophycin-24 (arenastatin A).

A subset of human monocyte-derived dendritic cells expresses high levels of interleukin-12 in response to combined CD40 ligand and interferon-gamma treatment

Dendritic cells (DCs) may arise from multiple lineages and progress through a series of intermediate stages until fully mature, at which time they are capable of optimal antigen presentation and T-cell activation. High cell surface expression of CD83 is presumed to correlate with full maturation of DCs, and a number of agents have been shown to increase CD83 expression on DCs. We hypothesized that interleukin 12 (IL-12) expression would be a more accurate marker of functionally mature DCs capable of activating antigen-specific T cells. We used combinations of signaling through CD40, using CD40 ligand trimer (CD40L), and interferon gamma to demonstrate that CD83 expression is necessary but not sufficient for optimal production of IL-12 by DCs. Phenotypically mature DCs could be induced to produce high levels of IL-12 p70 only when provided 2 simultaneous stimulatory signals. By intracellular cytokine detection, we determined that only a subset of cells that express high levels of CD80 and CD83 generate large amounts of IL-12. DCs matured with both signals are superior to DCs stimulated with the individual agents in activating antigen-specific T cell in vitro. These findings have important implications regarding the identification, characterization, and clinical application of functionally mature DCs.

Induction of cytotoxic T cell responses and tumor immunity against unrelated tumors using telomerase reverse transcriptase RNA transfected dendritic cells

The polypeptide component of telomerase (TERT) is an attractive candidate for a broadly expressed tumor rejection antigen because telomerase is silent in normal tissues but is reactivated in more than 85% of cancers. Here we show that immunization against TERT induces immunity against tumors of unrelated origin. Immunization of mice with TERT RNA-transfected dendritic cells (DC) stimulated cytotoxic T lymphocytes (CTL), which lysed melanoma and thymoma tumor cells and inhibited the growth of three unrelated tumors in mice of distinct genetic backgrounds. TERT RNA-transfected human DC stimulated TERT-specific CTL in vitro that lysed human tumor cells, including Epstein Barr virus (EBV)-transformed B cells as well as autologous tumor targets from patients with renal and prostate cancer. Tumor RNA-transfected DC were used as surrogate targets in the CTL assays, obviating the difficulties in obtaining tumor cells from cancer patients. In one instance, where a tumor cell line was successfully established in culture from a patient with renal cancer, the patient's tumor cells were efficiently lysed by the CTL. Immunization with tumor RNA was generally more effective than immunization with TERT RNA, suggesting that an optimal immunization protocol may have to include TERT as well as additional tumor antigens.

Phenotypic and functional maturation of dendritic cells mediated by heparan sulfate

Primary immune responses are thought to be induced by dendritic cells. To promote such responses, dendritic cells must be activated by exogenous agonists, such as LPS, or by products of activated leukocytes, such as TNF-alpha and IL-1. How dendritic cells might be activated in the absence of exogenous stimuli, or without the immediate presence of activated leukocytes, as might occur in immunity to tumor cells or transplants, is unknown. We postulated that heparan sulfate, an acidic, biologically active polysaccharide associated with cell membranes and extracellular matrices, which is rapidly released under conditions of inflammation and tissue damage, might provide such a stimulus. Incubation of immature murine dendritic cells with heparan sulfate induced phenotypic maturation evidenced by up-regulation of I-A, CD40, CD54 (ICAM-1), CD80 (B7-1), and CD86 (B7-2). Dendritic cells exposed to heparan sulfate exhibited a markedly lowered rate of Ag uptake and increased allostimulatory capacity. Stimulation of dendritic cells with heparan sulfate induced release of TNF-alpha, IL-1beta, and IL-6, although the maturation of dendritic cells was independent of these cytokines. These results suggest that soluble heparan sulfate chains, as products of the degradation of heparan sulfate proteoglycan, might induce maturation of dendritic cells without exogenous stimuli, thus contributing to the generation and maintenance of primary immune responses.

Involvement of an ATP-dependent peptide chaperone in cross-presentation after DNA immunization

Immunization with plasmid DNA holds promise as a vaccination strategy perhaps useful in situations that currently lack vaccines, since the major means of immune induction may differ from more conventional approach. In the present study, we demonstrate that exposure of macrophages to plasmid DNA encoding viral proteins or OVA generates Ag-specific material that, when presented in vitro by dendritic cells to naive T cells, induces primary CTL response or elicits IL-2 production from an OVA peptide-specific T-T hybridoma. The immunogenic material released was proteinaceous in nature, free of apoptotic bodies, and had an apparent m.w. much larger than a 9-11-aa CTL-recognizable peptide. The macrophage-released factor(s) specifically required a hydrolyzable ATP substrate and was inhibited by procedures that removed or hydrolyzed ATP; in addition, anti-heat-shock protein 70 antiserum abrogated the activity to a large extent. These results indicate the possible involvement of a heat-shock protein 70-linked peptide chaperone in a cross-priming method of immune induction by DNA vaccination. Such a cross-priming process may represent a principal mechanism by which plasmid DNA delivered to cells such as myocytes effectively shuttle Ag to DC or other APC to achieve CTL induction in vivo.

Effectiveness of combined interleukin 2 and B7.1 vaccination strategy is dependent on the sequence and order: a liposome-mediated gene therapy treatment for bladder cancer

We have developed a novel liposome-mediated immunogene therapy using interleukin 2 (IL-2) and B7.1 in a murine bladder cancer model. A carcinogen-induced murine bladder cancer cell line, MBT-2, was transfected with cationic liposome 1,2-dimyristyloxypropyl-3-dimethyl-hydroxyethyl ammonium bromide/dioleolylphosphatidylethanolamine and IL-2 plasmid. The optimized transfection condition generated IL-2 levels of 245-305 ng/10(6) cells/24 h, 100-fold higher than the levels seen with retrovirus transfection. Ninety percent of the peak level of IL-2 production was maintained for up to 11 days after transfection. Animal studies were conducted in C3H/HeJ female mice with 2 x 10(4) MBT-2 cells implanted orthotopically on day 0. Multiple vaccination schedules were performed with i.p. injection of 5 x 10(6) IL-2 and/or B7.1 gene-modified cell preparations. The greatest impact on survival was observed with the day 5, 10, and 15 regimen. Control animals receiving retrovirally gene-modified MBT-2/IL-2 cell preparations had a median survival of 29 days. Animals receiving the IL-2 liposomally gene-modified cell preparation alone had a median survival of 46 days. Seventy-five percent of animals receiving IL-2 followed by B7.1 gene-modified tumor vaccines were the only group to show complete tumor-free survival at day 60. All of these surviving animals rejected the parental MBT-2 tumor rechallenge and survived at day 120 with a high CTL response. In conclusion, liposome-mediated transfection demonstrates a clear advantage as compared with the retroviral system in the MBT-2 model. Multi-agent as opposed to single-agent cytokine gene-modified tumor vaccines were beneficial. These "targeted" sequential vaccinations using IL-2 followed by B7.1 gene-modified tumor cells significantly increased a systemic immune response that translated into increased survival.

Induction of cytotoxic T lymphocytes with dendritic cells transfected with human papillomavirus E6 and E7 RNA: implications for cervical cancer immunotherapy

Human papillomavirus (HPV) infection is associated with cervical cancer. The high-risk HPV E6 and E7 oncoproteins are constitutively expressed in most cervical carcinoma cells, and are, therefore, attractive antigens for cytotoxic T-lymphocyte (CTL)-mediated immunotherapy. The objective of this study was to evaluate the use of dendritic cells (DCs) transfected with RNA encoding the E6 and E7 protein for cervical cancer immunotherapy. The authors have shown that DCs transfected with RNA-encoding antigen stimulate potent antigen-specific CTL responses in vitro and in vivo. In this study, they tried to determine whether DCs transfected with E6 and E7 RNA stimulate primary, antigen-specific CTL responses in vitro. The results show that DCs pulsed with E6 or E7 RNA stimulate antigen-specific CTL responses that recognize and lyse DCs transfected with E6 and E7 RNA and human cervical carcinoma cells expressing the E6 and E7 products, and the lysis was comparable to that achieved with E6 and E7 peptide-pulsed DCs. Dendritic cells cotransfected with both E6 and E7 RNA stimulate CTLs that are more effective at lysing human cervical cancer cells. This study provides a rationale for the development of cervical carcinoma immunotherapy using DCs transfected with HPV E6 and E7 RNA.

External exposure to radionuclides accumulated in shoreline sediments with an application to the lower Clinch River

A simple analytical method was developed to estimate external doses from exposure to contaminated riverine shorelines. The method consists of deriving an adjustment factor that accounts for the geometry of the riverine shoreline; the adjustment factor is applied to the dose-rate coefficients already available for infinite contaminated surfaces. Such a geometry factor circumvents very complex radiation transport calculations which would otherwise be necessary to model exposures to a finite contaminated surface. For instance, for radionuclides emitting gamma rays of energies above 600 keV (e.g., 137Cs), the published dose-rate coefficients must be reduced by 75%, 60%, 50%, and 33% for shoreline widths of 4, 10, 20, and 50 m, respectively. The geometry factor changes only mildly with the energy of the gamma radiation. This property allows for the geometry factor to be used for radionuclides emitting multiple gamma rays of various energies. If a quick analysis is desired, the geometry factors derived for 137Cs can be used for all radionuclides. More refined analysis can be performed by deriving geometry factors for each radionuclide according to its gamma spectrum. Also, the mild variation with energy allows the geometry factors to be applied to the case when radionuclides are accumulated in layers under the soil surface, and not only to the case when radionuclides are deposited onto the soil surface. Empirical relationships between the geometry factor and the dimension of the shoreline were provided so that one can obtain values of the geometry factor for any shoreline width. These relationships can be easily used to account for the uncertainty in the dimension of the shoreline. The method was applied to derive similar adjustment factors for contaminated surfaces of other simple geometries (e.g., circular surfaces). An example of how this method can be applied to its full extent is presented for the case of external exposure to the shores of the lower Clinch River. This river received large amounts of 137Cs, 60Co, 106Ru, 95Zr, 95Nb, 144Ce, and 90Sr released during 1944-1991 from the Oak Ridge Reservation in Oak Ridge, Tennessee.

Human dendritic cells transfected with RNA encoding prostate-specific antigen stimulate prostate-specific CTL responses in vitro

Although immunological tolerance to self Ags represents an important mechanism to prevent normal tissue injury, there is growing evidence that tolerance to tumor Ags, which often represent normal peripherally expressed proteins, is not absolute and can be effectively reverted. Prostate-specific Ag (PSA) is a self Ag expressed by both normal and malignant prostatic epithelium, and therefore offers a unique opportunity to examine the ability of self Ags to serve as specific CTL targets. In this study, we investigated the efficacy of autologous dendritic cells (DC) transfected with mRNA encoding PSA to stimulate CTL against PSA Ags in vitro. Ag in form of RNA carries the advantage to encode multiple epitopes for many HLA alleles, thus permitting induction of CTL responses among many cancer patients independent of their HLA repertoire. In this study, we show that PSA mRNA-transfected DC were capable of stimulating primary CTL responses against PSA Ags in vitro. The PSA-specific CTL did not cross-react with kallikrein Ags, a protein, which shares significant homology with PSA, suggesting that harmful autoimmune toxicity may not represent a significant problem with this approach. PSA RNA-transfected DC generated from male or female healthy volunteers or from cancer patients were equally effective in stimulating PSA-specific CTL in vitro, implying that neither natural tolerance to PSA Ags nor tumor-mediated T cell anergy may represent major barriers for CTL generation against the self Ag PSA. This study provides a preclinical rationale for using PSA RNA-transfected DC in active or adoptive immunization protocols.

A radioiodine speciation, deposition, and dispersion model with uncertainty propagation for the Oak Ridge dose reconstruction

Between 1944 and 1956, radioactive 131I was released into the atmosphere from operations at the Oak Ridge National Laboratory in Oak Ridge, TN. The releases occurred from stacks and from building vents and openings in three different chemical forms: elemental, organic, and particulate. During their transport in the atmosphere, different forms of iodine react differently with other atmospheric chemicals and moisture, and are removed from the plume at different rates by the processes of dry and wet deposition. A modified Gaussian plume model was developed to address the processes of radioiodine speciation, deposition, depletion, and dispersion in the atmosphere, and to propagate uncertainties in input parameter values through to the ground-level concentrations of 131I in air. A unique approach was used to develop an implicitly correlated set of hourly meteorological parameters for any day of a month for each month of the year from ten years of available data between 1987 and 1996. The model was validated for both annual average and short-term releases. For the annual average releases, the predictions of ground-level concentrations of 131I from the model were within a factor of 2 of measured field data. For two of the three sets of available weekly data, the measurements fell within the 95% subjective confidence interval of model predictions. Predictions of ground-level air concentrations were made on an annual average basis for the entire period of release and on a short-term, episodic basis for a 1954 accident.

RNA transfected dendritic cells as cancer vaccines

Immunization with dendritic cells loaded with tumor antigens could represent a powerful method of inducing antitumor immunity. Studies from several laboratories have shown that immunization with dendritic cells pulsed with specific antigens prime cytotoxic T-cells and engender tumor immunity. This review will focus on the use of dendritic cells transfected with RNA as cancer vaccines, with emphasis on the potential advantages of using RNA. The majority of cancer patients who lack an identified tumor antigen and/or cannot provide sufficient tumor tissue for antigen preparation will be excluded from treatment with cancer vaccines based on using either specific tumor antigens or mixtures of tumor-derived antigens in the form of peptides or proteins isolated from tumor cells. Vaccination with the mRNA content of tumor cells would extend the scope of vaccination to this group of patients as well because RNA can be amplified from very few cancer cells.

Induction of tumor immunity and cytotoxic T lymphocyte responses using dendritic cells transfected with messenger RNA amplified from tumor cells

Unique patient-specific tumor antigens may constitute the dominant antigens in the antitumor immune response. Hence, vaccination with the patient's own repertoire of tumor antigens may offer a superior strategy to elicit protective immunity. We have shown previously that dendritic cells transfected with mRNA isolated from tumor cells stimulate potent CTL responses and engender protective immunity in tumor-bearing mice. In the current study, we demonstrate that tumor mRNA, isolated from murine tumor cell lines or from primary human tumor cells microdissected from frozen tissue sections, can be amplified without loss of function. This study provides the foundations for an effective and broadly applicable treatment that does not require the characterization of the relevant antigenic profile in each patient and will not be limited by tumor tissue availability for antigen preparation.

Induction of carcinoembryonic antigen (CEA)-specific cytotoxic T-lymphocyte responses in vitro using autologous dendritic cells loaded with CEA peptide or CEA RNA in patients with metastatic malignancies expressing CEA

The application of dendritic cells (DC) to the active immunotherapy of cancer currently relies on the generation of potent DC capable of presenting tumor antigens such as carcinoembryonic antigen (CEA). It is unknown whether the T cells of patients with advanced malignancies can be reliably stimulated against tumor antigens by their autologous DC. In this study, starting with the peripheral blood mononuclear cells (PBMC) of patients with metastatic malignancies expressing CEA, autologous DCs were generated in vitro in serum-free media supplemented with GM-CSF and IL-4. The DCs from HLA A2 positive patients were loaded with the CEA peptide CAP-1 and the DCs from HLA A2 negative patients were depleted of bystander lymphocytes and loaded with mRNA encoding CEA. The DC preparations were tested to determine their phenotype and were used to stimulate autologous PBMC twice, separated by 10-14 days. The stimulated cells were then tested for their ability to lyse CEA-expressing target cells. We successfully generated an adequate number of DC for a clinical trial from all patients. The harvested DC preparations contained 49% DC and 87% DC if depleted of bystander lymphocytes. Phenotypic analysis showed the typical pattern of CD11c+ CD40+ CD86+ HLA-DR+ CD80(low) CD83(low) CD14(low). All preparations but one were able to stimulate CEA-specific cytotoxic T-lymphocyte (CTL) activity, suggesting that the majority of patients are not anergic to CEA and possess functional DC. The CTL activity was similar for the CEA peptide and CEA RNA-loaded DC.

Induction of carcinoembryonic antigen (CEA)-specific cytotoxic T-lymphocyte responses in vitro using autologous dendritic cells loaded with CEA peptide or CEA RNA in patients with metastatic malignancies expressing CEA

The application of dendritic cells (DC) to the active immunotherapy of cancer currently relies on the generation of potent DC capable of presenting tumor antigens such as carcinoembryonic antigen (CEA). It is unknown whether the T cells of patients with advanced malignancies can be reliably stimulated against tumor antigens by their autologous DC. In this study, starting with the peripheral blood mononuclear cells (PBMC) of patients with metastatic malignancies expressing CEA, autologous DCs were generated in vitro in serum-free media supplemented with GM-CSF and IL-4. The DCs from HLA A2 positive patients were loaded with the CEA peptide CAP-1 and the DCs from HLA A2 negative patients were depleted of bystander lymphocytes and loaded with mRNA encoding CEA. The DC preparations were tested to determine their phenotype and were used to stimulate autologous PBMC twice, separated by 10-14 days. The stimulated cells were then tested for their ability to lyse CEA-expressing target cells. We successfully generated an adequate number of DC for a clinical trial from all patients. The harvested DC preparations contained 49% DC and 87% DC if depleted of bystander lymphocytes. Phenotypic analysis showed the typical pattern of CD11c+ CD40+ CD86+ HLA-DR+ CD80(low) CD83(low) CD14(low). All preparations but one were able to stimulate CEA-specific cytotoxic T-lymphocyte (CTL) activity, suggesting that the majority of patients are not anergic to CEA and possess functional DC. The CTL activity was similar for the CEA peptide and CEA RNA-loaded DC.

Induction of carcinoembryonic antigen (CEA)-specific cytotoxic T-lymphocyte responses in vitro using autologous dendritic cells loaded with CEA peptide or CEA RNA in patients with metastatic malignancies expressing CEA

The application of dendritic cells (DC) to the active immunotherapy of cancer currently relies on the generation of potent DC capable of presenting tumor antigens such as carcinoembryonic antigen (CEA). It is unknown whether the T cells of patients with advanced malignancies can be reliably stimulated against tumor antigens by their autologous DC. In this study, starting with the peripheral blood mononuclear cells (PBMC) of patients with metastatic malignancies expressing CEA, autologous DCs were generated in vitro in serum-free media supplemented with GM-CSF and IL-4. The DCs from HLA A2 positive patients were loaded with the CEA peptide CAP-1 and the DCs from HLA A2 negative patients were depleted of bystander lymphocytes and loaded with mRNA encoding CEA. The DC preparations were tested to determine their phenotype and were used to stimulate autologous PBMC twice, separated by 10-14 days. The stimulated cells were then tested for their ability to lyse CEA-expressing target cells. We successfully generated an adequate number of DC for a clinical trial from all patients. The harvested DC preparations contained 49% DC and 87% DC if depleted of bystander lymphocytes. Phenotypic analysis showed the typical pattern of CD11c+ CD40+ CD86+ HLA-DR+ CD80(low) CD83(low) CD14(low). All preparations but one were able to stimulate CEA-specific cytotoxic T-lymphocyte (CTL) activity, suggesting that the majority of patients are not anergic to CEA and possess functional DC. The CTL activity was similar for the CEA peptide and CEA RNA-loaded DC.

Optimization of the sequence of antigen loading and CD40-ligand-induced maturation of dendritic cells

Dendritic cells (DCs), matured by CD40-ligand (CD40L), undergo marked changes in their ability to process and present antigen, resulting in augmented lymphocyte stimulatory activity. We demonstrate that the form of the tumor antigen (peptide or genetic material) used to load the DCs dictates the required sequence of antigen loading and maturation for antitumor immunotherapy. Optimal stimulation of carcinoembryonic antigen (CEA)-specific CTLs by peptide-loaded DCs occurs when DCs from cancer patients are matured with CD40L before exposure to CEA peptide, whereas optimal stimulation by RNA-transfected DCs occurs when the DCs are loaded with CEA RNA before maturation with CD40L.

Dendritic cell/macrophage precursors capture exogenous antigen for MHC class I presentation by dendritic cells

Presentation of MHC class I antigens by professional antigen-presenting cells (APC) is an important pathway in priming cytotoxic T lymphocyte responses in vivo. This study sought to identify the nature of the professional APC responsible for indirect class I presentation by examining a special feature of professional APC, namely their ability to process exogenous forms of antigen for class I presentation. Incubation of highly purified bone marrow-derived precursor cells with chicken ovalbumin (OVA) led to the efficient presentation of the major class I-restricted OVA determinant by mature dendritic cells (DC), but not by macrophages (Mphi) derived from the precursor population. DC as well as macrophages were, however, able to mediate class II presentation of OVA, suggesting that macrophages were deficient in class I processing but not in capturing exogenous OVA. The majority of mature DC, i.e. over 80 %, generated from the precursor cells pulsed with OVA, presented the class I OVA epitope. Upon maturation, class I presentation of OVA by DC was greatly reduced, suggesting that class I processing of exogenous antigen is modulated during DC maturation in a manner similar to class II antigen processing. This study shows that bone marrow-derived DC/ME progenitors capture exogenous antigen for class I presentation, and that cells of the DC lineage can be functionally distinguished from cells of the macrophage lineage based on their ability to process exogenous antigen for class I presentation.

Induction of primary carcinoembryonic antigen (CEA)-specific cytotoxic T lymphocytes in vitro using human dendritic cells transfected with RNA

Dendritic cells (DC) generated from the peripheral blood mononuclear cells of healthy individuals or from cancer patients transfected with carcinoembryonic antigen (CEA) mRNA stimulate a potent CD8+ cytotoxic T lymphocyte (CTL) response in vitro. DCs are effectively sensitized with RNA in the absence of reagents commonly used to facilitate mammalian cell transfection. RNA encoding a chimeric CEA/LAMP-1 lysosomal targeting signal enhances the induction of CEA-specific CD4+ T cells, providing a strategy to induce T-help that may be necessary to generate and/or maintain an optimal CD8+ CTL response in vivo. CEA RNA-transfected DCs also serve as effective targets in cytotoxicity assays, thus providing a general method for inducing, as well as measuring, CEA-specific CTL responses across a broad spectrum of HLA haplotypes.