Murine dendritic cells pulsed with an anti-idiotype antibody induce antigen-specific protective antitumor immunity

In this study, using the carcinoembryonic antigen (CEA)-expressing C15 murine colon carcinoma system in syngeneic C57BL/6 mice, we have evaluated the efficacy of bone marrow-derived dendritic cells (DCs) pulsed with the murine anti-idiotype antibody 3H1 as a tumor vaccine. Anti-idiotype 3H1 mimics a distinct and specific epitope of CEA and can generate anti-CEA immunity in mice, rabbits, monkeys, and humans when used with a conventional immune adjuvant. Our goal was to determine whether the use of DC as direct antigen-presenting cells would improve the potency of 3H1 as vaccine. Bone marrow-DC pulsed with 3H1 and injected into na?ve mice induced both humoral and cellular anti-3H1, as well as anti-CEA immunity. Specific killing of C15 cells in in vitro antibody-dependent cellular cytotoxicity has been observed by immune sera. Immune-splenic lymphocytes when stimulated in vitro with 3H1 or CEA, showed increased proliferative CD4(+) Th1 type T-cell response and secreted significantly high levels of Th1 cytokines [IFN-gamma, interleukin (IL)-2] and low levels of Th2 cytokines (IL-4, IL-10). This vaccine also induced MHC class I antigen-restricted CD8(+) T-cell responses. The up-regulation of activation markers CD69 and CD25 on CD8(+) CTLs correlated with antigen-specific strong CTL responses in vitro. The immunity induced in mice resulted in a complete rejection of CEA-expressing C15 tumor cells in 100% of experimental mice, whereas no protection was observed when 3H1-pulsed DC-vaccinated mice were challenged with CEA-negative MC-38 cells. The tumor rejection in 3H1-pulsed DC-treated mice was associated with the induction of a memory response that helped those mice to survive a second challenge with a lethal dose of C15 cells.     

Similar immune responses and antitumor effects of murine dendritic cells loaded with either exogenous or endogenous-synthesized protein

Conceptually, dendritic cells (DCs) take up and process exogenous antigens that are presented on MHC (major histocompatibility complex) class II molecules to stimulate CD4+ T cells, and present endogenously-produced proteins to CD8+ T cells through an MHC class I-dependent pathway. In this study, we compared the antitumor effects generated in vivo after vaccinations with DCs either loaded with exogenous protein (DCs-exo) or presenting antigens derived from endogenous-synthesized protein (DCs-endo). We used the murine MC26SC31 colon carcinoma cell line expressing on the cell surface the human CD4 (hCD4) molecule as a model tumor-associated antigen (TAA). Bone marrow (BM)-derived DCs-endo were obtained from histocompatible transgenic mice constitutively expressing hCD4; BM-derived DCs-exo were obtained after in vitro loading DCs, from syngenic normal mice, with purified soluble hCD4 protein (shCD4). Altogether, our results show that intravenous (i.v.) administration of DCs-exo and DCs-endo can trigger similar cytotoxic and humoral protecting immune responses against a lethal tumor challenge. hCD4 antigen-specific T cell-mediated cytotoxic immune response was not accompanied by elevated INF-gamma serum levels. This suggests, in the case of DCs-exo, a possible in vivo CTL cross-priming triggering a CD8+ T cell-mediated immune response in the absence of de novo antigen synthesis within the DCs.     

Endogenous HeLa p53 proteins are easily detected in HeLa cells transfected with mouse deletion mutant p53 gene

It has been reported [Matlashewski et al. (1986). Eur. J. Biochem., 154, 665-672] that HeLa cells contain no detectable p53 protein, although they contain p53 mRNA which is translationally active. Here it is shown that endogenous HeLa p53 proteins were easily detected in HeLa cells transiently expressing mouse deletion mutant p53 gene after transfection with the appropriate recombinant plasmid. This detection was obtained by immunoprecipitation coupled with SDS-PAGE as well as by Western blotting experiments. Our results strongly suggest that HeLa p53 mRNA is actually translated in vivo, generating an extremely unstable p53 protein. Considering that the HeLa cell line is a HPV-18-positive human cervical carcinoma cell line, this high instability of HeLa p53 proteins is in keeping with the finding that E6 oncoprotein encoded by human papillomavirus 16 or 18 promotes the degradation of p53 proteins [Scheffner et al. (1990). Cell, 63, 1129-1136].     

Dendritic cells transfected with hepatocellular carcinoma (HCC) total RNA induce specific immune responses against HCC in vitro and in vivo

Background

Immunotherapy is an effective method for preventing metastasis and recurrence of carcinoma. Hepatocellular carcinoma (HCC) is a common malignancy with a high rate of recurrence, and has not successfully been introduced to immunotherapy.

Methods

Peripheral blood mononuclear cells were isolated from whole blood of HCC patients and stimulated to transform into dendritic cells (DCs). These DCs were then transfected with RNA extracted from HepG-2 hepatoma cells to induce expression of specific antigens.

Results

The transfected DCs stimulated T lymphocytes to produce cytotoxic T lymphocytes, which specifically attacked HepG-2 cells. Injection of T lymphocytes from HCC patients and transfected DCs into severe combined immunodeficiency mice limited the growth of HepG-2 tumors.

Conclusion

A specific immune response against hepatoma can be generated in vivo by administering DCs transfected with RNA from a specific tumor. This method may have therapeutic application in humans to reduce recurrence of HCC.     

UCN-01 and camptothecin induce DNA double-strand breaks in p53 mutant tumor cells, but not in normal or p53 negative epithelial cells

Previous research has shown synergistic growth inhibition between UCN-01 and camptothecin (CPT) in tumor cells with mutant p53 versus tumor cells with wild-type p53. To determine the possible role of p53 in this drug combination, we tested the hypothesis that the synergistic growth inhibition is due to the absence of p53, and can result from the induction of DNA double-strand breaks (DSBs). Experiments were performed with the use of normal human mammary epithelial cells (HMEC); HMEC transfected with HPV16 E6 protein which inactivates p53 (HE6), or p53-mutant MDA-MB-231 tumor cells. CPT, UCN-01, or a 1:1 combination of both, in either HMEC or HE6 cells did not induce DSBs. In contrast, simultaneous treatment of MDA-MB-231 cells with both UCN-01 and CPT induced significant levels of DSBs while treatment with either drug alone did not. While UCN-01 was surprisingly potent against HMEC, the growth inhibition was only additive between UCN-01 and CPT against these cells. HE6 cells were much less sensitive than HMEC to UCN-01 and slightly less sensitive to the combined treatment with UCN-01 and CPT. The drug combination was synergistic against HE6 cells, due to their lower sensitivity to UCN-01. Unlike what was observed previously in MDA-MB-231 cells, UCN-01 did not abrogate CPT-induced inhibition of DNA synthesis in either HMEC or HE6 cells. These data indicate that synergistic growth inhibition by UCN-01 and CPT against p53 mutant MDA-MB-231 tumor cells may be due to induction of DSBs however the loss of p53 function alone does not sensitize normal cells to the combination of both drugs.     

恶性造血细胞表面Flt3受体的表达及其对Flt3配体的反应性研究

目的 :研究恶性造血细胞表面Flt3受体的表达 ,TNFα和地塞米松 (DXM )对Flt3受体表达的作用及重组人Flt3配体 (rhFL)对恶性造血细胞增殖的影响。方法 :用流式细胞仪测定 18株体外培养的恶性造血细胞株细胞表面Flt3受体 ,用MTT法测定rhFL对恶性造血细胞增殖的影响。结果 :5株细胞表面存在Flt3受体。B淋巴瘤细胞株Raji、Daudi及多发性骨髓瘤细胞株 82 6 6表达高水平Flt3受体 ;髓系白血病细胞株HL 6 0和多发性骨髓瘤细胞株XG 6表达低水平的Flt3受体。用 10 -6mol/LDXM培养 2 4h后 ,上述细胞Flt3受体表达降低 ;用2 0ng/mlTNFα培养 2 4h后 ,Raji和 82 6 6细胞Flt3受体表达降低 ,HL 6 0和XG 6细胞Flt3受体表达增高 ,Daudi细胞Flt3受体表达不受影响。rhFL在 10～ 10 0ng/ml浓度时 ,刺激Raji和HL 6 0细胞的增殖 (P <0 0 5 ) ,但对绝大多数的恶性造血细胞体外无刺激作用。结论 :多数恶性造血细胞不表达Flt3受体 ;rhFL也不引起此类细胞的增殖。地塞米松降低Flt3受体的表达 ,有可能用于防止或降低FL对部分恶性造血细胞的刺激作用 ,使FL的应用更为安全。     

转染p16基因对人肺腺癌细胞放射效应的影响

目的 :探讨p16基因与人肺腺癌细胞放射效应的关系。方法 :免疫组化、Westernblot方法检测人肺腺癌细胞株Anip973、AGZY83a的p16蛋白表达 ,FuGene转染方法把 p16表达载体转入这两个细胞株 ,进行细胞存活曲线、流式细胞仪 (FCM )分析细胞周期分布。结果 :p16蛋白表达AGZY83a为 87.4 % ,明显高于Anip973(5 2 % ) ,细胞存活曲线显示低表达的Anip973与转染后Anip973p16的Dq值有显著性差异 (P <0 .0 5 ) ,D0 值间无显著差异 (P >0 .0 5 )。p16蛋白高表达的AGZY83a与AGZY83ap16间D0 值、Dq值均无显著性差异 (P >0 .0 5 ) ;流式细胞仪测定细胞周期结果显示 ,Anip973转染 p16基因后出现G2 M期比例增加 ,S期比例减少。结论 :转染 p16基因后可能通过改变细胞周期分布及抑制细胞对照射后的亚致死性损伤修复 ,来改变p16蛋白低表达的人肺腺癌细胞株Anip973的放射效应 ,而对于高表达的AGZY83a则无显著影响。     

14-3-3 zeta down-regulates p53 in mammary epithelial cells and confers luminal filling

Recent progress in diagnostic tools allows many breast cancers to be detected at an early preinvasive stage. Thus, a better understanding of the molecular basis of early breast cancer progression is essential. Previously, we discovered that 14-3-3 zeta is overexpressed in >40% of advanced breast cancers, and this overexpression predicts poor patient survival. Here, we examined at what stage of breast disease 14-3-3 zeta overexpression occurs, and we found that increased expression of 14-3-3 zeta begins at atypical ductal hyperplasia, an early stage of breast disease. To determine whether 14-3-3 zeta overexpression is a decisive early event in breast cancer, we overexpressed 14-3-3 zeta in MCF10A cells and examined its effect in a three-dimensional culture model. We discovered that 14-3-3 zeta overexpression severely disrupted the acini architecture resulting in luminal filling. Proper lumen formation is a result of anoikis, apoptosis due to detachment from the basement membrane. We found that 14-3-3 zeta overexpression conferred resistance to anoikis. Additionally, 14-3-3 zeta overexpression in MCF10A cells and in mammary epithelial cells (MEC) from 14-3-3 zeta transgenic mice reduced expression of p53, which is known to mediate anoikis. Mechanistically, 14-3-3 zeta induced hyperactivation of the phosphoinositide 3-kinase/Akt pathway which led to phosphorylation and translocation of the MDM2 E3 ligase resulting in increased p53 degradation. Ectopic expression of p53 restored luminal apoptosis in 14-3-3 zeta-overexpressing MCF10A acini in three-dimensional cultures. These data suggest that 14-3-3 zeta overexpression is a critical event in early breast disease, and down-regulation of p53 is one of the mechanisms by which 14-3-3 zeta alters MEC acini structure and increases the risk of breast cancer.     

Improving antitumor immune responses by circumventing immunoregulatory cells and mechanisms.

Although numerous immunotherapeutic strategies have been studied in patients with cancer, consistent induction of clinical responses remains a formidable challenge. Cancer vaccines are often successful at generating elevated numbers of tumor-specific T lymphocytes in peripheral blood, however, despite this, tumors usually continue to grow unabated. Recent evidence suggests that endogenous regulatory cells, known to play a major role in the induction of immune tolerance to self and prevention of autoimmunity, as well as suppressive myeloid cells invoked in the tumor-bearing state, may be largely responsible for preventing effective antitumor immune responses. This review will focus on the major regulatory cell subtypes, including CD4(+)CD25(+) T-regulatory cells, type 1 regulatory T cells, natural killer T cells, and immature myeloid cells. Studies in humans and in animal models have shown a role for all of these cells in tumor progression, although the mechanisms by which they act to suppress immunity remain largely undefined. Elucidation of the dominant molecular mechanisms mediating immune suppression in vivo will allow more precise targeting of the relevant regulatory cell populations, as well as the development of novel strategies and clinical reagents that will directly block molecules that induce the suppression of antitumor immunity.     

Glypican-3 reexpression regulates apoptosis in murine adenocarcinoma mammary cells modulating PI3K/Akt and p38MAPK signaling pathways

Glypican-3 (GPC3) is a proteoglycan involved in proliferation and cell survival. Several reports demonstrated that GPC3 is downregulated in some tumors, such as breast cancer. Previously, we determined that GPC3 reexpression in the murine mammary adenocarcinoma LM3 cells induced an impairment of their invasive and metastatic capacities, associated with a decrease of their motility and an increase of their cell death. We demonstrated that GPC3 inhibits canonical Wnt signaling, as well as it activates non canonical pathway. Now, we identified signaling pathways responsible for the pro-apoptotic role of GPC3 in LM3 cells. We found for the first time that GPC3 inhibits the PI3K/Akt anti-apoptotic pathway while it stimulates the p38MAPK stress-activated one. We report a concomitant modulation of CDK inhibitors as well as of pro- and anti-apoptotic molecules. Our results provide new clues regarding the mechanism involved in the modulation induced by GPC3 of mammary tumor cell growth and survival.     

Coexpression of Flt3 ligand and GM-CSF genes modulates immune responses induced by HER2/neu DNA vaccine

DNA vaccine and dendritic cells (DCs)-based vaccine have emerged as promising strategies for cancer immunotherapy. Fms-like tyrosine kinase 3-ligand (Flt3L) and granulocyte-macrophage-colony-stimulating factor (GM-CSF) have been exploited for the expansion of DC. It was reported previously that combination of plasmid encoding GM-CSF with HER2/neu DNA vaccine induced predominantly CD4(+) T-cell-mediated antitumor immune response. In this study, we investigated the modulation of immune responses by murine Flt3L and GM-CSF, which acted as genetic adjuvants in the forms of bicistronic (pFLAG) and monocistronic (pFL and pGM) plasmids for HER2/neu DNA vaccine (pN-neu). Coexpression of Flt3L and GM-CSF significantly enhanced maturation and antigen-presentation abilities of splenic DC. Increased numbers of infiltrating DC at the immunization site, higher interferon-gamma production, and enhanced cytolytic activities by splenocytes were prominent in mice vaccinated with pN-neu in conjunction with pFLAG. Importantly, a potent CD8(+) T-cell-mediated antitumor immunity against bladder tumors naturally overexpressing HER2/neu was induced in the vaccinated mice. Collectively, our results indicate that murine Flt3L and GM-CSF genes coexpressed by a bicistronic plasmid modulate the class of immune responses and may be superior to those codelivered by two separate monocistronic plasmids as the genetic adjuvants for HER2/neu DNA vaccine.     

Resistance to anticancer drugs in NIH3T3 cells transfected with c-myc and/or c-H-ras genes

NIH3T3 cells transfected with c-H-ras and/or c-myc genes were examined for differences in drug sensitivity. The five transfectants used were N8, NIH3T3-nm-1, pT22-3-nm-2, pP1-4 and pT22-3. They were transfected with pKOneo alone, pKOneo and c-myc, pKOneo and c-myc plus activated c-H-ras, normal c-H-ras and activated c-H-ras genes, respectively. The IC50s of cisplatin, 4-hydroperoxycyclophosphamide, adriamycin, melphalan, and CPT-11 were significantly higher for NIH3T3-nm-1 abd pT22-3-nm-2 than for the parental NIH3T3 and N8 cells. Transfection with normal and activated C-H-ras oncogenes only led to increases in the IC50s of alkylating agents. There was no significant difference between the IC50s of N8 and those of NIH3T3 parental cells to any of these anticancer agents. These results strongly suggest that the expression of the c-myc gene plays a role in the acquisition of drug resistance. The c-myc gene may therefore provide us with an important clue in determining the mechanism of drug resistance.     

Local administration of IL-12-transfected dendritic cells induces antitumor immune responses to colon adenocarcinoma in the liver in mice

Colorectal cancer is one of the most common fatal malignancies in the United States, with an incidence second only to lung cancer. The liver is the most common site of colorectal metastases and frequently the only affected organ once the primary tumor has been surgically removed. The only potentially curative treatment for metastatic colorectal cancer in the liver is surgery, although most patients are not eligible for resection. We have therefore, evaluated the therapeutic efficacy of dendritic cells (DCs) engineered to express IL-12 in a liver metastasis model. Direct administration of DCs into the portal vein significantly inhibited the growth of established MC38 colon carcinoma in the liver in C57BL/6 mice. This effect was accompanied by an intratumoral accumulation of CD4+, CD8+, and NLDC-145+ immune effector cells, and also resulted in a systemic immune response as determined by enhanced production of IFN-gamma by T lymphocytes isolated from both spleen and draining lymph nodes. Evaluation of homing of Cy3-labeled DCs following the portal vein injection confirmed their distribution in the liver and lymphoid tissue. Thus, a local delivery of DCs transduced with the IL-12 gene can not only inhibit colorectal tumor growth in vivo but also mount systemic antitumor immune responses. This approach is likely to improve the outcome of immunotherapy for metastatic colorectal cancer since high numbers of tumor-associated DCs positively correlate with a more favorable prognosis. Simultaneous local gene therapy with IL-12 will further improve clinical efficacy without placing the patient at risk for systemic toxicity.     

Interleukin 2-antibody and tumor necrosis factor-antibody fusion proteins induce different antitumor immune responses in vivo.

Two fusion proteins, composed of interleukin 2 (IL-2) or tumor necrosis factor (TNF) coupled to an antibody [fusion protein (FuP); IL-2-FuP or TNF-FuP], were capable of retarding growth of a human malignant melanoma in the severe combined immunodeficient mouse depending on the concomitant application of human peripheral blood leukocytes. Here we have analyzed the mechanisms that determine the therapeutic effect. Tumor-bearing severe combined immunodeficient mice received once per week an i.v. injection of HLA-matched peripheral blood leukocytes and twice per week i.v. or intratumoral injections of FUPS: Leukocyte recovery and their activation state were monitored. The number of draining lymph node cells (LNCs) and tumor-infiltrating leukocytes increased continuously, and the yield of draining LNCs was improved significantly when the FuPs were applied locally. In IL-2-FuP-treated mice, the majority of draining LNCs and tumor-infiltrating lymphocytes expressed T-cell activation markers and IL-2, thus being classified as T helper type 1 cells. These cells displayed strong proliferative activity and initiated activation of lymphokine-activated killer cells and CTLS: TNF-FuP supported activation of CTLs and of monocytes as revealed by TNF expression and cytostatic activity. Neither the antibody, nor IL-2, nor TNF, nor the mixture of antibody and cytokines exhibited the full-fledged activational potency of the FUPS: Notably, activation of immune effector mechanisms was much stronger when the FuPs were applied intratumorally. This is the first report to show that FuPs are efficient immunostimulants in vivo for native leukocytes. Although IL-2-FuP induced a T helper type 1 response with recruitment of LAK and CTL, TNF-FuP efficiently recruited and activated monocytes and, in a less pronounced manner, CTLS:     

MMP-3和p53蛋白在乳腺癌组织中的表达及其与肿瘤转移的关系

目的细胞外基质金属蛋白酶-3(MMP-3)和p53在乳腺癌组织中的表达及临床意义。方法 采用免疫组化S-P法检测58例临床资料完整的乳腺癌组织标本中MMP-3和p53的表达情况并进行对比观察, 结合临床资料作统计学分析。结果 58例乳腺癌组织中MMP-3的阳性表达为44.83%, MMP-3的高表达与肿瘤的淋巴结转移呈正相关, P＜0.05;p53的阳性表达为37.93%, 其表达与肿块大小有相关性, P＜0.05。结论 MMP-3和p53在乳腺浸润性导管癌中的表达可以作为估计乳腺癌预后及术后综合治疗的生物学指标。     

Mutant p53 can provoke apoptosis in p53-deficient Hep3B cells with delayed kinetics relative to wild-type p53

Wild-type (wt) p53 frequently induces apoptosis when expressed in tumor cells whereas mutant p53 acts as an oncoprotein and consequently, stimulates cell proliferation. We report here exceptions to that rule. p53 conformational mutant 175H and DNA contact mutant 273H provoke apoptosis in human p53-deficient Hep3B hepatoma cells with delayed kinetics relative to wt p53. Similarly, c-Myc strongly stimulates apoptosis in these cells. In contrast, viral oncoproteins E1A and E7, and the cellular oncoprotein MDM-2, fail to elicit cytocidal responses. Efficient apoptotic cell death by mutant p53 requires oligomerization as 175H and 273H with deletions between amino acid residues 326 and 347 of the oligomerization domain are nontoxic. Apoptosis by mutant or wt p53 was significantly inhibited by the serine protease inhibitor AEBSF but not by the inactive analog AEBSA. Together, these results suggest that a wt p53-independent control mechanism is operational in Hep3B cells that eliminates cells upon sensing illegitimate proliferation signals originating from certain oncoproteins, including mutant p53 and Myc. We suggest that some tumor cell types lack p53 altogether because they tolerate neither wild-type nor mutant forms of the protein.     

Association of p16 homozygous deletions with clinicopathologic characteristics and EGFR/KRAS/p53 mutations in lung adenocarcinoma

PURPOSE: The p16 gene is frequently inactivated in lung adenocarcinoma. In particular, homozygous deletions (HD) have been frequently detected in cell lines; however, their frequency and specificity is not well-established in primary tumors. The purpose of this study was to elucidate the prevalence and the timing for the occurrence of p16 HDs in lung adenocarcinoma progression in vivo. EXPERIMENTAL DESIGN: Multiple ligation-dependent probe amplification was used for the detection of p16 HDs in 28 primary small-sized lung adenocarcinomas and 22 metastatic lung adenocarcinomas to the brain. Cancer cells were isolated from primary adenocarcinoma specimens by laser capture microdissection. HDs were confirmed by quantitative real-time genomic PCR analysis. RESULTS: HDs were detected in 8 of 28 (29%) primary tumors, including 2 of 8 (25%) noninvasive bronchioloalveolar carcinomas, and 5 of 22 (26%) brain metastases, respectively. No significant associations were observed between p16 HDs and gender, age, smoking history, stage, and prognosis. HDs were detected with similar frequencies (17-29%) among adenocarcinomas with epidermal growth factor receptor (EGFR) mutations, with KRAS mutations, and without EGFR/KRAS mutations, and with similar frequencies (22-28%) between adenocarcinomas with and without p53 mutations. CONCLUSIONS: p16 HDs occur early in the development of lung adenocarcinomas and with similar frequencies among EGFR type, KRAS type, and non-EGFR/KRAS type lung adenocarcinomas. Tobacco carcinogens would not be a major factor inducing p16 HDs in lung adenocarcinoma progression.     

Expression and stability of p53 protein in normal human mammary epithelial cells

To examine the p53 protein expressed in human mammary epithelialcell strains grown in vitro we first established the presenceof only wild-type p53 and lack of any missense mutations ina representative normal mammary epithelial cell strain, 76N,by cloning and sequencing the entire coding region of the p53mRNA. The p53 protein expressed in this cell strain and a numberof similarly derived normal mammary epithelial cell strainswas compared with mammary epithelial tumor cell lines havingknown p53 mutations and with fibroblasts derived from normalmammary tissue. In all cell strains, immunoprecipitation frommetabolically labelled cells using monoclonal antibodies (mAb)PAb 1801 and PAb 122 revealed easily detectable p53 protein.Surprisingly, mAb PAb 1620 (wild type-specific) and PAb 240(mutant-specific) each immunoprecipitated p53 protein from bothnormal and tumor cells. Furthermore, p53 protein in normal mammaryepithelial cells was shown to be markedly more stable (half-lifeof     

Immunization with wild-type p53 gene sequences coadministered with Flt3 ligand induces an antigen-specific type 1 T-cell response.

We examined the ability of immunization with sequential adenovirus/plasmid DNA vectors expressing human wild-type p53 to stimulate a type 1 T-cell response and induce protection against challenge from a metastatic tumor that expresses mutated murine p53. We found that tumor protection and an antigen (Ag)-specific immune response were enhanced by prior injection of Flt3 ligand (Flt3L) at a dose and schedule that significantly increased dendritic cell (DC) number and frequency. Preliminary studies using enzyme-linked immunospot and Winn assays suggested that Ag-specific CD8 cells, with their significant increase in IFN-gamma-secreting activity (Tc1 cells), were responsible for the tumor protection. The delayed-type hypersensitivity response to p53 was increased in mice immunized with p53 alone or p53 and Flt3L compared with a negative control. In contrast, spleen cells from mice immunized with p53 and Flt3L exhibited a higher Ag-specific proliferative response than mice immunized with p53 alone. The frequencies of Ag-specific IFN-gamma and interleukin (IL)-4-secreting cells were determined using an enzyme-linked immunospot assay, which demonstrated that the frequency of IFN-gamma-secreting cells was significantly higher in mice immunized with p53 and Flt3L than in mice receiving Flt3L, excipient, or p53 treatment alone. In contrast, the frequency of IL-4-secreting cells did not differ significantly among these groups. We also observed an increased frequency of IL-12 and IFN-gamma-secreting cells (but not IL-4 or IL-10) in the spleens of mice immediately after 10 days of Flt3L treatment, which was also the day of p53 priming. This observation supports the likelihood that there are multiple mechanisms of Flt3L adjuvant activity, including expansion of DC and type 1 T-cell number. Overall, these results suggest that immunization with p53 genetic sequences after in vivo expansion of DC, using Flt3L, provides a useful strategy to induce p53-specific, and protective, type 1 T-cell responses.