Stressed target cancer cells drive nongenetic reprogramming of CAR T cells and solid tumor microenvironment

The poor efficacy of chimeric antigen receptor T-cell therapy (CAR T) for solid tumors is due to insufficient CAR T cell tumor infiltration, in vivo expansion, persistence, and effector function, as well as exhaustion, intrinsic target antigen heterogeneity or antigen loss of target cancer cells, and immunosuppressive tumor microenvironment (TME). Here we describe a broadly applicable nongenetic approach that simultaneously addresses the multiple challenges of CAR T as a therapy for solid tumors. The approach reprograms CAR T cells by exposing them to stressed target cancer cells which have been exposed to the cell stress inducer disulfiram (DSF) and copper (Cu)(DSF/Cu) plus ionizing irradiation (IR). The reprogrammed CAR T cells acquire early memory-like characteristics, potent cytotoxicity, enhanced in vivo expansion, persistence, and decreased exhaustion. Tumors stressed by DSF/Cu and IR also reprogram and reverse the immunosuppressive TME in humanized mice. The reprogrammed CAR T cells, derived from peripheral blood mononuclear cells of healthy donors or metastatic female breast cancer patients, induce robust, sustained memory and curative anti-solid tumor responses in multiple xenograft mouse models, establishing proof of concept for empowering CAR T by stressing tumor as a promising therapy for solid tumors.

Stressed target cancer cells drive nongenetic reprogramming of CAR T cells and tumor microenvironment, overcoming multiple obstacles of CAR T therapy for solid tumors

The poor efficacy of chimeric antigen receptor T-cell therapy (CAR T) for solid tumor is due to insufficient CAR T cell tumor infiltration, in vivo expansion, persistence, and effector function, as well as exhaustion, intrinsic target antigen heterogeneity or antigen loss of target cancer cells, and immunosuppressive tumor microenvironment (TME). Here we describe a broadly applicable nongenetic approach that simultaneously addresses the multiple challenges of CAR T as a therapy for solid tumors. The approach massively reprograms CAR T cells by exposing them to stressed target cancer cells which have been exposed to the cell stress inducer disulfiram (DSF) and copper (Cu)(DSF/Cu) plus ionizing irradiation (IR). The reprogrammed CAR T cells acquired early memory-like characteristics, potent cytotoxicity, enhanced in vivo expansion, persistence, and decreased exhaustion. Tumors stressed by DSF/Cu and IR also reprogrammed and reversed immunosuppressive TME in humanized mice. The reprogrammed CAR T cells, derived from peripheral blood mononuclear cells (PBMC) of healthy or metastatic breast cancer patients, induced robust, sustained memory and curative anti-solid tumor responses in multiple xenograft mouse models, establishing proof of concept for empowering CAR T by stressing tumor as a novel therapy for solid tumor.

Improving the Therapeutic Efficacy of Sorafenib for Hepatocellular Carcinoma by Repurposing Disulfiram

Background

Sorafenib, a kinase inhibitor, is a standard treatment for advanced hepatocellular carcinoma (HCC) but provides only a limited survival benefit. Disulfiram (DSF), a drug for treating alcoholism and a chelator of copper (Cu), forms a complex with Cu (DSF/Cu). DSF/Cu is a potent inducer of autophagic apoptosis of cancer stem cells, which can demonstrate drug resistance. Thus, we hypothesized that DSF/Cu could increase the sensitivity of HCC cells to sorafenib by targeting hepatic cancer stem cells.

Methods

The synergistic effect of DSF/Cu and sorafenib on human HCC cell lines was assessed by cell viability MTT assay. Changes in stemness gene expression in HCC cells were investigated by assessing the presence of hepatic cancer stem cells (HCSCs) (defined as ALDH+ cells) using flow cytometry, sphere formation ability as an index of in vitro tumorigenicity, and expression of stemness gene-encoded proteins by western blot. Autophagic apoptosis and the ERK signaling pathway were also assessed by western blot. Most importantly, the in vivo anti-tumor efficacy of DSF/Cu and sorafenib was tested using orthotopic HCC xenografts in mice.

Results

Compared with sorafenib alone, DSF/Cu + sorafenib synergistically inhibited proliferation of all HCC cell lines, decreased the stemness of HCC cells, and increased the autophagy and apoptosis of HCC cells. The mechanism by which DSF/Cu mediated these phenomena with sorafenib was sustained activation of the ERK pathway. The combination of DSF/Cu (formed with endogenous Cu2+) and sorafenib was significantly more effective than sorafenib alone in inhibiting the growth of orthotopic HCC xenografts in mice. This in vivo anti-tumor efficacy was associated with decreased stemness in treated HCC tumors.

Conclusions

DSF/Cu and sorafenib can synergistically and effectively treat HCC by targeting HCSCs in vitro and in vivo. Our data provide a foundation for clinical translation.

Targeting Radiation-Resistant Prostate Cancer Stem Cells by B7-H3 CAR T Cells

Radiotherapy (RT) is a key treatment for prostate cancer. However, RT resistance can contribute to treatment failure. Prostate cancer stem cells (PCSCs) are radioresistant. We recently found that fractionated irradiation (FIR) upregulates expression of the immune checkpoint B7-H3 (CD276) on PCSCs and bulk cells in each prostate cancer cell line tested. These findings prompted us to investigate whether B7-H3 targeting chimeric antigen receptor (CAR) T cells, which may abrogate function of an immune checkpoint and mediate lysis of targeted cells, can target RT-resistant PCSCs in vitro and in vivo. B7-H3 expression is naturally higher on PCSCs than bulk prostate cancer cells and cytotoxicity of B7-H3 CAR T cells to PCSCs is more potent than to bulk prostate cancer cells. Furthermore, FIR significantly upregulates B7-H3 expression on PCSCs and bulk prostate cancer cells. The duration of FIR or single-dose irradiation-induced further upregulation of B7-H3 on bulk prostate cancer cells and PCSCs lasts for up to 3 days. B7-H3 CAR T-cell cytotoxicity against FIR-resistant PCSCs at a low effector to target ratio of 1:1 was assessed by flow cytometry and sphere formation assays. Further upregulation of B7-H3 expression by FIR made PCSCs even more sensitive to B7-H3 CAR T-cell-mediated killing. Consequently, the FIR and B7-H3 CAR T-cell therapy combination is much more effective than FIR or CAR T cells alone in growth inhibition of hormone-insensitive prostate cancer xenografts in immunodeficient mice. Our work provides a sound basis for further development of this unique combinatorial model of RT and B7-H3 CAR T-cell therapy for prostate cancer. SIGNIFICANCE: We demonstrate that FIR significantly upregulates B7-H3 expression by RT-resistant PCSCs and bulk cells; cytotoxicity of B7-H3 CAR T cells to FIR-treated PCSCs is potent and results in significantly improved antitumor efficacy in mice.

The p53 Saga: Early Steps in the Development of Tumor Immunotherapy

This year marks the 40th anniversary of the initial identification of p53 as a transformation-related Ag, which was the result of our effort to identify an antigenically distinct tumor Ag of a chemically induced mouse tumor and develop a cancer vaccine. Many researchers at the time viewed this effort as folly. Since then, its characterization has progressed from being an attractive cancer vaccine candidate to recognition as a key player in regulating critical pathways controlling the cell cycle and oncogenesis. Advances in molecular immunology and oncology have enhanced the role of p53 in both fields. It is now apparent that p53 plays a critical role in controlling immune recognition and responses in normal tissues as well as the tumor microenvironment. Together with the advances in clinical implementation of p53-based cancer immunotherapy, they highlight the importance of p53 in many areas of basic and translational cancer research.

Targeting cancer stem cells by disulfiram and copper sensitizes radioresistant chondrosarcoma to radiation

Overcoming the radiosensitivity of chondrosarcoma (CS), the second most common primary bone tumor, is needed. Radioresistance is attributed to cancer stem cells (CSCs) in many malignancies. Disulfiram (DSF), an FDA-approved anti-alcoholism drug, complexed with Cu (DSF/Cu) can radiosensitize epithelial CSCs. This prompted us to investigate the radiosensitizing effect of DSF/Cu on CS CSCs (CCSCs). The radiosensitizing effects of DSF/Cu on CCSCs were investigated in vitro using cell lines SW1353 and CS-1. Stemness was identified independently by flow cytometry for CCSCs (ALDH⁺CD133⁺), sphere-forming ability, and Western blot analysis of stemness gene protein expression. The radiosensitizing effect of DSF/Cu was studied in an orthotopic CS xenograft mouse model by analyzing xenograft growth and residual xenografts for stemness. CCSCs were found to be resistant to single-dose (IR) and fractionated irradiation (FIR). IR and FIR increased CS stemness. Combined with DSF/Cu in vitro and in vivo, IR and FIR eliminated CS stemness. RT + DSF/Cu was safer and more effective than either RT ± DSF in inhibiting growth of orthotopic CS xenografts. In conclusion, DSF/Cu radiosensitizes CCSCs. These results can be translated into clinical trials for CS patients requiring RT for improved outcomes.

Induction of autophagy-dependent apoptosis in cancer cells through activation of ER stress: an uncovered anti-cancer mechanism by anti-alcoholism drug disulfiram

Due to its potent anticancer activity, there is interest in repurposing of the FDA-approved anti-alcoholism drug, disulfiram (DSF). DSF forms potent complexes with copper (DSF/Cu) that induce apoptosis of many types of cancer cells. Here, we investigated the role of DSF/Cu in autophagy, a mechanism of cell death or survival, and its interplay with DSF/Cu induced apoptosis of human pancreatic and breast cancer cells.

METHODS

Levels of autophagy and apoptosis were assessed by Western blot, flow cytometry and immunofluorescence analysis. Cell viability was measured by MTT assays. Activation of inositol-requiring enzyme 1α (IRE1α)-mRNA X-box binding protein 1 (XBP1) pathway and spliced XBP1 (XBP1s) expression were analyzed by Western blot, Phos-tag gel assay, RT-PCR, qRT-PCR and flow cytometry.

RESULTS

The apoptosis induced by DSF/Cu in pancreatic and breast cancer cells is autophagy dependent. This is accomplished by activating IRE1α, the sensor of unfolded protein response (UPR) via promotion of phosphorylation of IRE1α and its downstream XBP1 splicing into active XBP1s.

CONCLUSIONS

DSF/Cu induces ER-stress through activation of IRE1α-XBP1 pathway which is responsible, at least in part, for induction of autophagy-dependent apoptosis of cancer cells. Insight into the ER-stress inducing ability by DSF/Cu may open a new research area for rational design of innovative therapeutic strategies for pancreatic and breast cancers.

Phenotype of p53 wild-type epitope-specific T cells in the circulation of patients with head and neck cancer

CD8⁺ cytotoxic T-cell (CTL) specific for non-mutated, wild type (wt) sequence p53 peptides derived from wt or mutant p53 molecules expressed in head and neck squamous cell carcinomas (HNSCC) have been detected in the circulation of patients with this disease. The frequency and differentiation/maturation phenotypes of these anti-tumor specific CTL can reflect the host’s immunologic response. Therefore, we investigated the frequency and phenotypes of wt sequence p53 peptide-specific CTL in patients with HNSCC (n = 33) by flow cytometric analysis using HLA-A*0201 tetrameric peptides (tet) complexed with the wt sequence p53_264–272 or p53_149–157 peptide and co-staining with phenotypic markers. One main finding was that increasing frequencies of tet⁺ CD8⁺ T cells in patients’ circulation correlated with increased frequencies of inactive naïve tet⁺ cells, while those with effector memory and terminally differentiated phenotypes, which are associated with positive anti-tumor immune responses, decreased. We also found that the frequency of circulating tet⁺ CD8⁺ T cells negatively correlated with p53 expression in tumor tissues and tumor stage. Our findings support further clinical-based investigations to define the frequencies and phenotypes of wt sequence p53 peptide-specific CD8⁺ T cells to predict disease severity, enhance selection of patients for inclusion in vaccination trials and highlight prerequisites to enhance immune susceptibility by activation of inactive naïve tet⁺ T cells and/or enhancing circulating effector T cell activity by checkpoint blockage.

Targeting cancer stem cells with p53 modulators

Cancer stem cells (CSC) typically over-express aldehyde dehydrogenase (ALDH). Thus, ALDH^bright tumor cells represent targets for developing novel cancer prevention/treatment interventions. Loss of p53 function is a common genetic event during cancer development wherein small molecular weight compounds (SMWC) that restore p53 function and reverse tumor growth have been identified. Here, we focused on two widely studied p53 SMWC, CP-31398 and PRIMA-1, to target ALDH^bright CSC in human breast, endometrial and pancreas carcinoma cell lines expressing mutant or wild type (WT) p53. CP-31398 and PRIMA-1 significantly reduced CSC content and sphere formation by these cell lines in vitro. In addition, these agents were more effective in vitro against CSC compared to cisplatin and gemcitabine, two often-used chemotherapeutic agents. We also tested a combinatorial treatment in methylcholantrene (MCA)-treated mice consisting of p53 SMWC and p53-based vaccines. Yet using survival end-point analysis, no increased efficacy in the presence of either p53 SMWC alone or with vaccine compared to vaccine alone was observed. These results may be due, in part, to the presence of immune cells, such as activated lymphocytes expressing WT p53 at levels comparable to some tumor cells, wherein further increase of p53 expression by p53 SMWC may alter survival of these immune cells and negatively impact an effective immune response. Continuous exposure of mice to MCA may have also interfered with the action of these p53 SMWC, including potential direct interaction with MCA. Nonetheless, the effect of p53 SMWC on CSC and cancer treatment remains of great interest.

Inhibition of Soluble Tumor Necrosis Factor Prevents Chemically Induced Carcinogenesis in Mice

TNF is a potent promoter of carcinogenesis and potentially important target for cancer prevention. TNF is produced as functionally distinct transmembrane and soluble molecules (tmTNF and sTNF, respectively), but their individual roles in carcinogenesis are unexplored. We investigated the participation of tmTNF and sTNF in chemically induced carcinogenesis in mice. We found that injection of XPro1595, a dominant-negative TNF biologic (DN-TNF) and specific antagonist of sTNF, decreased tumor incidence and growth, and prolonged survival of 3-methylcholanthrene (MCA)-injected mice. Similar results were obtained following the exclusion of both TNF forms by either TNF-receptor 2-Fc fusion protein (TNFR2-Fc) treatment or TNF gene deletion. In addition, gene deletion of TNFR1, which is preferentially triggered by sTNF, was temporarily blocked, whereas gene deletion of TNFR2, which is preferentially triggered by tmTNF, enhanced MCA-induced carcinogenesis. Concomitantly with carcinogenesis induction, MCA increased circulating IL1α, accumulation of myeloid-derived suppressor cells (MDSC), STAT3 phosphorylation, and immunosuppression in the spleen. In sharp contrast, DN-TNF treatment dramatically decreased IL1α and increased the essential immunoregulatory cytokines IL1β, IL12p70, and IL17 in the peripheral blood of MCA-injected mice. In addition, MDSC accumulation, STAT3 phosphorylation, and immunosuppression in MCA-injected mice were prevented by DN-TNF treatment, TNFR2-Fc treatment, and/or gene deletion of TNF or TNFR1, but not deletion of TNFR2. These findings reveal that sTNF is both an essential promoter of carcinogenesis and a pivotal regulator of MDSCs, and indicate that sTNF could be a significant target for cancer prevention and therapy. Cancer Immunol Res; 4(5); 441-51. ©2016 AACR.

Abstract 3639: Combinatorial therapy for triple negative breast cancer

In the US, about 10-20% of breast cancers are found to be triple-negative breast cancer (TNBC). In comparison to other types of breast cancer, TNBC is biologically more aggressive and more prevalent in younger women. Recent molecular analysis of TNBC has suggested that these tumors might be enriched with cancer initiating cells (CICs). According to the cancer stem cell theory, CICs play a major role in disease recurrence and metastatic spread, the two major causes of patient morbidity and mortality. Therefore, an effective therapy must both eliminate differentiated and CICs in TNBC, and counteract the escape mechanisms utilized by tumor cells to avoid destruction. We have designed a novel strategy which combines cell- and antibody-based immunotherapy with metronomic chemotherapy. The molecules selected as targets of T cell- and monoclonal antibody (mAb)-based immunotherapy are aldehyde dehydrogenase 1A1 (ALDH1A1) and chondroitin sulfate proteoglycan 4 (CSPG4). The latter is also expressed on activated tumor-associated pericytes. Immunodeficient SCID mice were orthotopically inoculated with TNBC MDA-MB-231 cells (1 million cells per mouse) and then subjected to the combinatorial treatment. Tumor volume was monitored twice weekly, and primary tumors were collected at the time of sacrifice and digested for mammosphere assays. Next, we examined the anti-tumor efficacy of the combinatorial therapy on tumor recurrence and survival using a post-surgery model. Immunodeficient SCID mice were orthotopically inoculated with MDA-MB-231 cells and on day 80, when the average tumor diameter reached 0.8 cm, all primary tumors were surgically removed. Mice were then subjected to the combinatorial treatment. The combinatorial treatment effectively inhibited primary tumor growth by 71.2%, which is significantly higher than that inhibited by the individual agents or any combination of two agents. Furthermore, the cells digested from primary tumors removed from mice treated with the combinatorial treatment formed less mammospheres (2) than those (at least 15) from any other groups. Importantly, the mice in the combinatorial treatment group exhibited only 20% tumor recurrence in comparison to 100% recurrence in all other groups by day 143. Moreover, the combinatorial treatment effectively prolonged the survival of mice after surgical removal of the primary tumors. By day 155, mice in the combinatorial treatment group exhibited 80% survival, in comparison to 0% survival in any other groups by day 143. Our findings strongly indicate that the combination of the CSPG4-specific mAb 225.28, ALDH1A1-specific CD8+ T cells, and metronomic chemotherapy with cyclophosphamide effectively targets both differentiated and CICs in TNBC, resulting in inhibition of both primary tumor growth and post-surgery tumor recurrence, and in prolonging post-surgery survival of mice orthotopically inoculated with TNBC cells. Thus, our described approach may provide a novel therapy for TNBC.

Citation Format: Yangyang Wang, Shalin S. Patel, Juan Cong, Nan Zhang, Yuan Qi, Francesco Sabbatino, Steven Isakoff, Albert B. DeLeo, Soldano Ferrone, Xinhui Wang. Combinatorial therapy for triple negative breast cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3639. doi:10.1158/1538-7445.AM2014-3639

PRAME expression in head and neck cancer correlates with markers of poor prognosis and might help in selecting candidates for retinoid chemoprevention in pre-malignant lesions

OBJECTIVES

PRAME (Preferentially Expressed Antigen in Melanoma) is a tumor-associated antigen recognized by immunocytes, and it induces cytotoxic T cell-mediated responses in melanoma. PRAME expression in tumors interferes with retinoic acid receptor (RAR) signaling thus promoting tumor progression. Here, we study PRAME expression in head and neck squamous cell carcinoma (HNSCC) to determine its potential clinical significance.

MATERIALS AND METHODS

PRAME expression in HNSCC was evaluated by immunohistochemistry in tissue microarrays of primary tumors (n=53), metastatic lymph nodes (n=8) and normal oral mucosa (n=11). Biopsies of dysplastic oral lesions (n=12) were also examined. PRAME expression levels in tissues were correlated with markers of poor prognosis in HNSCC. PRAME mRNA in HNSCC cell lines and in normal immortalized human keratinocytes (HaCaT cell line) was measured by qRT-PCR, and the protein expression by flow cytometry and western blots.

RESULTS

PRAME was expressed in HNSCC cell lines and HNSCC lesions. PRAME expression in dysplastic mucosa was variable. No or only weak expression was found in normal cells or tissues. PRAME expression levels significantly correlated with the tumor grade, size, nodal involvement and the clinical status of HNSCC patients.

CONCLUSIONS

Elevated PRAME expression associates with clinicopathologic markers of poor outcome in HNSCC and might identify potential candidates with pre-cancerous lesions for chemoprevention with retinoids.

17β Hydroxysteroid dehydrogenase type 12 (HSD17B12) is a marker of poor prognosis in ovarian carcinoma

OBJECTIVE

17β-hydroxysteroid dehydrogenase isoform 12 (HSD17B12) overexpression is associated with poor clinical outcome in invasive ductal carcinoma of the breast. Here, we evaluated HSD17B12 overexpression and its activity in ovarian carcinoma (OvCa) to determine its role in the growth and progression of this tumor.

METHODS

Immunohistochemical analysis of HSD17B12 expression was performed in 100 tissue samples of untreated OvCa and was correlated with clinicopathologic characteristics and patient outcome. In A2780 OvCa cell line expressing HSD17B12, siRNA knockdown of the enzyme was performed, and its effects on tumor cell growth and Annexin V binding were determined.

RESULTS

HSD17B12 expression was detected in all tumor samples, but the staining intensity was variable. Normal ovarian epithelium was negative. Patients with tumor showing weak/moderate expression of HSD17B12 had a better overall survival than those with strongly positive tumors (p<0.001). The time to first recurrence was longer for patients with tumors with heterogeneous staining relative to patients with tumors that were uniformly positive (p<0.001). Upon silencing of HSD17B12 in tumor cells, their growth was inhibited (p<0.005) and apoptosis was increased (p<0.05). Arachidonic acid but not estradiol reversed the growth inhibition mediated by HSD17B12 knockdown.

CONCLUSION

HSD17B12 overexpression is shown to be a marker of poor survival in patients with OvCa. Expression in the tumor and function of this enzyme facilitates OvCa progression.

Targeting ALDH(bright) human carcinoma-initiating cells with ALDH1A1-specific CD8⁺ T cells

PURPOSE

Cancer-initiating cells (CIC) are considered to represent the subpopulation of tumor cells that is resistant to conventional cancer treatments, highly tumorigenic in immunodeficient mice, and responsible for tumor recurrence and metastasis. Based on an elevated aldehyde dehydrogenase (ALDH) activity attributable to ALDH1/3 isoforms, ALDH(bright) cells have been identified and isolated from tumors and shown to have characteristics of CIC. The ALDH1A1 isoform was previously identified as a tumor antigen recognized by CD8(+) T cells. This study examines the ability of ALDH1A1-specific CD8(+) T cells to eliminate ALDH(bright) cells and control tumor growth and metastases.

EXPERIMENTAL DESIGN

ALDH(bright) cells were isolated by flow cytometry using ALDEFLUOR from HLA-A2(+) human head and neck, breast, and pancreas carcinoma cell lines and tested for their tumorigenicity in immunodeficient mice. ALDH1A1-specific CD8(+) T cells were generated in vitro and tested for their ability to eliminate CICs in vitro and in vivo by adoptive transfer to immunodeficient mice bearing human tumor xenografts.

RESULTS

ALDH(bright) cells isolated by flow cytometry from HLA-A2(+) breast, head and neck, and pancreas carcinoma cell lines at low numbers (500 cells) were tumorigenic in immunodeficient mice. ALDH(bright) cells present in these cell lines, xenografts, or surgically removed lesions were recognized by ALDH1A1-specific CD8(+) T cells in vitro. Adoptive therapy with ALDH1A1-specific CD8(+) T cells eliminated ALDH(bright) cells, inhibited tumor growth and metastases, or prolonged survival of xenograft-bearing immunodeficient mice.

CONCLUSIONS

The results of this translational study strongly support the potential of ALDH1A1-based immunotherapy to selectively target CICs in human cancer.

Identification of Hydroxysteroid (17β) dehydrogenase type 12 (HSD17B12) as a CD8+ T-cell-defined human tumor antigen of human carcinomas

Hydroxysteroid (17β) dehydrogenase type 12 (HSD17B12) is a multifunctional isoenzyme functional in the conversion of estrone to estradiol (E2), and elongation of long-chain fatty acids, in particular the conversion of palmitic to archadonic (AA) acid, the precursor of sterols and the inflammatory mediator, prostaglandin E(2). Its overexpression together with that of COX-2 in breast carcinoma is associated with a poor prognosis. We have identified the HSD17B12(114-122) peptide (IYDKIKTGL) as a naturally presented HLA-A*0201 (HLA-A2)-restricted CD8(+) T-cell-defined epitope. The HSD17B12(114-122) peptide, however, is poorly immunogenic in its in vitro ability to induce peptide-specific CD8(+) T cells. Acting as an "optimized peptide", a peptide (TYDKIKTGL), which is identical to the HSD17B12(114-122) peptide except for threonine at residue 1, was required for inducing in vitro the expansion of CD8(+) T-cell effectors cross-reactive against the HSD17B12(114-122) peptide. In IFN-γ ELISPOT assays, these effector cells recognize HSD17B12(114-122) peptide-pulsed target cells, as well as HLA-A2(+) squamous cell carcinoma of the head and neck (SCCHN) and breast carcinoma cell lines overexpressing HSD17B12 and naturally presenting the epitope. Whereas growth inhibition of a breast carcinoma cell line induced by HSD17B12 knockdown was only reversed by AA, in a similar manner, the growth inhibition of the SCCHN PCI-13 cell line by HSD17B12 knockdown was reversed by E2 and AA. Our findings provide the basis for future studies aimed at developing cancer vaccines for targeting HSD17B12, which apparently can be functional in critical metabolic pathways involved in inflammation and cancer.

CD8+ T cell recognition of polymorphic wild-type sequence p53(65-73) peptides in squamous cell carcinoma of the head and neck

The TP53 tumor suppressor gene contains a well-studied polymorphism that encodes either proline (P) or arginine (R) at codon 72, and over half of the world's population is homozygous for R at this codon. The wild-type sequence (wt) p53 peptide, p53(65-73), has been identified as a CD8+ T cell-defined tumor antigen for use in broadly applicable cancer vaccines. However, depending on the TP53 codon 72 polymorphism of the recipient, the induced responses to the peptides incorporating R (p53(72R)) or P (p53(72P)) can be "self" or "non-self." Thus, we sought to determine which wt p53(65-73) peptide should be used in wt p53-based cancer vaccines. Despite similar predicted HLA-A2-binding affinities, the p53(72P) peptide was more efficient than the p53(72R) peptide in HLA-A2 stabilization assays. In vitro stimulation (IVS) of CD8+ T cells obtained from healthy HLA-A2(+) donors with these two peptides led to the generation of CD8+ T cell effectors in one-third of the samples tested, at a frequency similar to the responsiveness to other wt p53 peptides. Interestingly, regardless of their p53 codon 72 genotype, CD8+ T cells stimulated with either p53(72P) or p53(72R) peptide were cross-reactive against T2 cells pulsed with either peptide, as well as HLA-A2(+) head and neck cancer (HNC) cell lines presenting p53(72P) and/or p53(72R) peptides for T cell recognition. Therefore, the cross-reactivity of CD8+ T cells for the polymorphic wt p53(65-73) peptides, irrespective of their p53 codon 72 polymorphism, suggests that employing either peptide in wt p53-based vaccines can result in efficient targeting of this epitope.

CSPG4 in cancer: multiple roles

Chondroitin sulfate proteoglycan 4 (CSPG4), also known as High Molecular Weight-Melanoma Associated Antigen, is a cell surface proteoglycan which has been recently shown to be expressed not only by melanoma cells, but also by various types of human carcinoma and sarcoma. Furthermore, at least in squamous cell carcinoma of head and neck and in basal breast carcinoma, CSPG4 is expressed by cancer stem cells. CSPG4 plays an important role in tumor cell growth and survival. These CSPG4-associated functional properties of tumor cells are inhibited by CSPG4-specific monoclonal antibodies (mAb) in vitro. Moreover, CSPG4-specific mAb can also inhibit tumor growth and metastasis in vivo. The anti-tumor effects of CSPG4-specific mAb are likely to reflect the blocking of important migratory, mitogenic and survival signaling pathways in tumor cells. These results indicate that CSPG4 is a promising new target to implement mAb-based immunotherapy of various types of cancer.

Abstract 3339: Elimination of cancer stem cells in pancreatic cancer cell lines by a combinatorial therapy

Cancer stem cells (CSC) are tumor initiating cells and considered resistant to current conventional chemo and radio therapies. Consequently, novel strategies are needed to target these cells. Tumor cells expressing elevated levels of aldehyde dehydrogenase 1 family member A1 activity (ALDHbright cells) have been shown to have many properties attributed to CSC, including tumorigenicity in immunodeficient mice. We used FACS analysis to identify and sort ALDHbright cells from several human pancreatic cell lines using ALDEFLUOR (Stem Cell Technologies, Vancouver Canada). We show that ALDHbright but not ALDHnegative cells sorted from the human MiaPaCa-2 pancreatic adenocarcinoma cell are highly tumorigenic at low inoculum of 500 cells in immunodeficient NOD.SCID mice, a critical property of CSC. Previously, we identified the ALDH1A188–96 peptide as an HLA-A2-restricted, cytotoxic T cell (CTL)-defined tumor antigen. Using a flow cytometry-based assay, ALDHbright cells in the HLA-A2+ MiaPaCa-2 cell line were selectively eliminated in vitro by ALDH1A188–96 peptide-specific CTL. The Hedgehog (Hh) stem cell signaling pathway has been shown to play a critical role in invasion and metastasis in pancreatic cancer. Treatment of the MiaPaCa-2 cell line with the Hg inhibitor, cyclopamine, significantly eliminated ALDH+ MiaPaCA-2 cells compared to treatment with conventional chemotherapeutic agents. The efficacy of a combinatorial therapy consisting of adoptive transfer of ALDH1A1-specific CTL combined with systemic administration of cyclopamine in vitro and in vivo on ALDHbright cells and in vivo growth inhibition of MIA PaCa-2-derived xenografts is detailed.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3339.

Abstract 5605: Targeting cancer stem cells in squamous cell carcinoma of the head and neck with combinatorial adoptive immunotherapy

According to current views, in order for cancer immunotherapy to be successful it must target cancer stem cells (CSC) and counteract the multiple mechanisms involved in immune escape. Guided by these concepts, we have developed a combinatorial adoptive immunotherapeutic strategy which utilizes a monoclonal antibody (mAb) and cytotoxic T lymphocytes (CTL) in combination with continuous administration of low dose cyclophosphamide (metronomic chemotherapy) to target CSC and differentiated tumor cells, as well as activated pericytes in the tumor microenvironment. The targets selected are aldehyde dehydrogenase 1 family member A1 (ALDH1A1) and chondroitin sulfate proteoglycan 4 (CSPG4). We now report that ALDHbright cells in squamous cell carcinoma of the head and neck (SCCHN) cell lines, which express high levels of ALDH1A1, are tumorigenic at low inoculum in immunodeficient mice, and particularly sensitive to recognition by ALDH1A1-specific T cells. The ALDHbright cells express CSPG4, a cell surface antigen functional in adhesion and migration. CSPG4 is also expressed on tumor associated activated pericytes which stabilize tumor blood vessels and provide vascular endothelial cells with survival signals. Administration of CSPG4-specific mAb and metronomic chemotherapy combined with intralesional adoptive transfer of ALDH1A1 peptide-specific CTL to mice bearing human SCCHN PCI-13-derived xenografts significantly reduced tumor growth and number of tumor cells with CSC phenotype. The antitumor effects of the immunotherapy we have developed were significantly higher than those of its individual components. These results argue in favor of the possibility that this combinatorial strategy may enhance the clinical efficacy of adoptive immunotherapy in SCCHN patients.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5605.

Abstract 2414: Comparable effect of p53 peptide vaccine in adjuvant or pulsed on dendritic cells in ovarian cancer patients: A gynecologic oncology group study

Purpose: Peptide antigens have been administered by different approaches in cancer vaccine therapy, including direct injection or pulsed onto dendritic cells; however, the optimal delivery method is still debatable. In this study, we describe the immune response elicited by the wild-type (wt) p53 vaccine using two approaches.

Experimental Design: Twenty-one HLA-A2.1 patients with stage III, IV, or recurrent ovarian cancer overexpressing the p53 protein with no evidence of disease were treated in two cohorts. Arm A received subcutaneous wt p53:264-272 peptide admixed with Montanide and GM-CSF. Arm B received wt p53:264-272 peptide-pulsed dendritic cells intravenously. Interleukin-2 (IL-2) was administered in both cohorts in alternative cycles. The immunologic response was assessed by ELISPOT and tetramer assays.

Results: Nine of 13 patients (69%) in arm A and 5 of 6 patients (83%) in arm B had an immunologic response. The vaccine caused no serious systemic side effects. IL-2 administration resulted in grade 3 and 4 toxicities in both arms and directly induced expansion of T regulatory cells. The median overall survival was 40.8 and 29.6 months for arm A and B, respectively; the median progression-free survival was 4.2 and. 8.7 months, respectively.

Conclusion: We demonstrated that using either vaccination approach could generate comparable specific immune responses against the wt p53 peptide with minimal toxicity. Accordingly, our findings support the utilization of the less demanding subcutaneous method. Furthermore, as IL-2 may add toxicity and induce T regulatory cells, which can suppress the immune response, therefore, it may not be needed in future trials.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2414.

Spontaneous apoptosis of tumor-specific tetramer+ CD8+ T lymphocytes in the peripheral circulation of patients with head and neck cancer

BACKGROUND

In cancer, tumor escape from the host immune system includes apoptosis of circulating CD3(+)CD8(+) effector T lymphocytes. Here, we compare sensitivity to apoptosis of virus- with tumor-specific circulating CD8(+) T cells in patients with head and neck cancer.

METHODS

Wild-type p53 peptide-specific (p53(264-272) and p53(149-157)) and viral peptide-specific (EBV BMLF(259-267) and CMVpp65(495-503)) tetramers were used to measure the frequency of reactive T cells by flow cytometry. Annexin V (ANX) binding to circulating 7-amino-actinomycin D-negative but tetramer(+)CD8(+) T cells in PBMC obtained from 21 patients with head and neck cancer and 11 normal controls (NC) was evaluated.

RESULTS

In patients with head and neck cancer, a higher percentage of tetramer(+)CD8(+) than tetramer(-)CD8(+) T cells bound ANX (p < .023-.005). Although most tumor-epitope(+)CD8(+) T cells bound ANX, lower percentages of virus-specific CD8(+) T cells were ANX(+) in the same patients.

CONCLUSIONS

Preferential demise of circulating tumor-specific CD8(+) T cells and their paucity in head and neck cancer contribute to tumor escape.

Identification of a 17beta-hydroxysteroid dehydrogenase type 12 pseudogene as the source of a highly restricted BALB/c Meth A tumor rejection peptide

Mass spectrometric analysis identified the peptide recognized by a cytotoxic T lymphocyte (CTL) specific for the chemically induced BALB/c Meth A sarcoma as derived from a 17beta-hydroxysteroid dehydrogenase type 12 (Hsd17b12) pseudogene present in the BALB/c genome, but only expressed in Meth A sarcoma. The sequence of the peptide is TYDKIKTGL and corresponds to Hsd17b12(114-122) with threonine instead of isoleucine at codon 114 and is designated Hsd17b12(114T). Immunization of mice with an Hsd17b12(114T) peptide-pulsed dendritic cell-based vaccine or a non-viral plasmid construct expressing the Hsd17b12(114T) peptide protected the mice from lethal Meth A tumor challenge in tumor rejection assays. A Hsd17b12(114-122) peptide-pulsed vaccine was ineffective in inducing resistance in mice to Meth A sarcoma. These results confirm the immunogenicity of the identified tumor peptide, as well as demonstrate the efficacies of these vaccine vehicles. These findings suggest that the role of the human homolog of Hsd17b12, HSD17B12, as a potential human tumor antigen be explored.

CD4+ T cell responses to HLA-DP5-restricted wild-type sequence p53 peptides in patients with head and neck cancer

Wild-type sequence (wt) p53 peptides are attractive candidates for broadly applicable cancer vaccines. Evidence has been accumulating which indicates that CD4+ Th cells have an important role in generating and maintaining antitumor immune responses. To elucidate the nature of CD4+ Th responses to wt p53 epitopes in patients with squamous cell carcinoma of the head and neck (SCCHN), peripheral blood mononuclear cells (PBMCs) from HLA-DP5+ patients were stimulated with HLA-DP5-restricted wt p53 peptides, p53(108-122) or p53(153-166), and tested for the release of IFN-gamma and IL-5 in ELISPOT assays. Immunohistochemistry for p53 accumulation in tumors, and ELISA for serum antibodies to p53 were also performed. Eleven (57.9%) of 19 HLA-DP5+ patients but none of 5 healthy donors had detectable Th1 and/or Th2 responses to wt p53 peptides by ELISPOT assay. Among these 11 responding patients, 9 (81.8%) and all 11 (100%) patients had a tumor burden and p53 accumulation, respectively. On the other hand, two responding patients were in post-operative condition. Interestingly, among nine patients with a tumor burden, four patients with early disease showed either Th1-polarized or mixed Th1/Th2 responses, while five patients with advanced disease showed either Th2-polarized or mixed Th1/Th2 responses. Our results suggest that wt p53(108-122) and p53(153-166) peptides stimulate both Th1- and Th2-type CD4+ T cell responses in patients with SCCHN, and anti-p53 Th responses may persist even after surgical resection of the tumor; however, the presence of a tumor and its progression may affect the nature of immune responses to wt p53 peptides.

Development of multi-epitope vaccines targeting wild-type sequence p53 peptides

Loss of p53 tumor-suppressor function is the most common abnormality in human cancer, which can result in enhanced presentation to immune cells of wild-type (wt)-sequence peptides from tumor p53 molecules, thus providing the rationale for wt p53 peptide-based cancer vaccines. We review evidence from preclinical murine tumor models and preclinical studies that led to the clinical introduction of wt p53 peptide-based vaccines for cancer immunotherapy. Overall, this review illustrates the complex process of wt p53 epitope selection and the issues and concerns involved in the application of p53-based vaccines for patients with cancer.

Identification of human aldehyde dehydrogenase 1 family member A1 as a novel CD8+ T-cell-defined tumor antigen in squamous cell carcinoma of the head and neck

Few epitopes are available for vaccination therapy of patients with squamous cell carcinoma of the head and neck (SCCHN). Using a tumor-specific CTL, aldehyde dehydrogenase 1 family member A1 (ALDH1A1) was identified as a novel tumor antigen in SCCHN. Mass spectral analysis of peptides in tumor-derived lysates was used to determine that the CTL line recognized the HLA-A*0201 (HLA-A2) binding ALDH1A1(88-96) peptide. Expression of ALDH1A1 in established SCCHN cell lines, normal mucosa, and primary keratinocytes was studied by quantitative reverse transcription-PCR and immunostaining. Protein expression was further defined by immunoblot analysis, whereas ALDH1A1 activity was measured using ALDEFLUOR. ALDH1A1(88-96) peptide was identified as an HLA-A2-restricted, naturally presented, CD8(+) T-cell-defined tumor peptide. ALDH1A1(88-96) peptide-specific CD8(+) T cells recognized only HLA-A2(+) SCCHN cell lines, which overexpressed ALDH1A1, as well as targets transfected with ALDH1A1 cDNA. Target recognition was blocked by anti-HLA class I and anti-HLA-A2 antibodies. SCCHN cell lines overexpressing ALDH1 had high enzymatic activity. ALDH1A1 protein was expressed in 12 of 17 SCCHN, and 30 of 40 dysplastic mucosa samples, but not in normal mucosa. ALDH1A1 expression levels in target cells correlated with their recognition by ALDH1A1(88-96) peptide-specific CD8(+) T cells. Our findings identify ALDH1A1, a metabolic antigen, as a potential target for vaccination therapy in the cohort of SCCHN subjects with tumors overexpressing this protein. A smaller cohort of subjects with SCCHN, whose tumors express little to no ALDH1A1, and thus are deficient in conversion of retinal to retinoic acid, could benefit from chemoprevention therapy.

Toward the development of multi-epitope p53 cancer vaccines: an in vitro assessment of CD8(+) T cell responses to HLA class I-restricted wild-type sequence p53 peptides

Wild-type sequence (wt) p53 peptides are attractive candidates for broadly applicable cancer vaccines. Six HLA-A2 or HLA-A24-restricted wt p53 peptides were evaluated for their ex vivo immunogenicity and their potential for use in cancer vaccines. Peripheral blood mononuclear cells (PBMC) obtained from HLA-A*0201(+) and/or HLA-A*2402(+) normal donors and subjects with squamous cell carcinoma of the head and neck (SCCHN) were analyzed for p53 peptide-specific reactivity in ELISPOT IFN-gamma assays. CD8(+) T cells in 7/10 normal donors (HD) and 11/23 subjects with SCCHN responded to at least one of the wt p53 peptides. CD8(+) T cell precursors responsive to wt p53 epitopes were detected in the circulation of most subjects with early disease, and an elevated blood Tc(1)/Tc(2) ratio distinguished wt p53 peptide responders from non-responders. The identification of multiple wt p53 peptides able to induce cytolytic T lymphocytes in most subjects with cancer promotes the development of multi-epitope p53 vaccines.

Immunological characterization of missense mutations occurring within cytotoxic T cell-defined p53 epitopes in HLA-A*0201+ squamous cell carcinomas of the head and neck

Previous analyses of p53 in 40 HLA-A*0201(HLA-A2)(+) squamous cell carcinomas of the head and neck (SCCHN) indicated that 6/13 p53 missense mutations that were detected, S149C, T150R, V157F, Y220C, Y220H and E271K, occurred within HLA-A2-restricted cytotoxic T lymphocyte (CTL)-defined p53 epitopes. Of the 6, the p53 S149C, Y220C and Y220H peptides were immunogenic. Anti-p53 mutant S149C and Y220H effector cells cross-reacted against the parental wild type sequence (wt) p53 peptides, whereas anti-p53 Y220C effector cells were specific for the mutant peptide, p53 Y220C cDNA-transfected HLA-A2(+) SaOS cells, and an HLA-A2(+) SCCHN cell line naturally expressing the mutation. These results indicate that the p53 Y220C mutation can be processed and presented for CD8(+) T cell recognition. Furthermore, using an autologous PBMC/tumor system, anti-p53 Y220C peptide-effector cells recognizing the autologous tumor could also be generated. Our analysis of p53 in 10 additional HLA-A2(+) SCCHN tumors detected the p53 Y220C in 2/10 tumors raising the overall frequency of the p53 Y220C mutation to 6/50 (12%) HLA-A2(+) SCCHN tumors. In contrast, independent of their HLA class I genotypes, the p53 Y220C mutation frequency for all human tumors analyzed to date is approximately 1.5%. This unexpectedly high frequency of the p53 Y220C mutation in HLA-A2(+) SCCHN suggests that vaccines targeting this mutation would not only be expected to induce robust anti-tumor immune responses in HLA-A2(+) subjects, but also be more widely applicable than previously envisioned for any given p53 missense mutation.

The wild-type sequence (wt) p53(25-35) peptide induces HLA-DR7 and HLA-DR11-restricted CD4+ Th cells capable of enhancing the ex vivo expansion and function of anti-wt p53(264-272) peptide CD8+ T cells

Tumor peptide-based vaccines are more effective when they include tumor-specific Th cell-defined as well as CTL-defined peptides. Presently, two overlapping wild-type sequences (wt) p53 helper peptides, p53(108-122) and p53(110-124), have been identified as HLA-DR1- and/or HLA-DR4-restricted epitopes. These HLA-DR alleles are expressed by approximately 35% of subjects with cancer. To identify Th cell-defined wt p53 peptides suitable for use on the remaining subject population, a dendritic cell (DC)-based coculture system was developed. CD4+ T cells isolated from PBMC obtained from HLA-DR4- normal donors were stimulated ex vivo with autologous DC transfected with wt p53 or mutant p53 cDNA. Reactivity of T cells was tested in ELISPOT IFN-gamma assays against DC pulsed individually with a panel of algorithm-predicted, multiple HLA-DR-binding wt p53 peptides. The wt p53(25-35) peptide was identified as capable of inducing and being recognized by CD4+ T cells in association, at a minimum, with HLA-DR7 and -DR11 molecules, each of which is expressed by approximately 15% of the population. In addition, the presence of anti-p53(25-35) CD4+ Th cells was shown to enhance the in vitro generation/expansion of HLA-A2-restricted, anti-wt p53(264-272) CD8+ T cells, which from one donor were initially "nonresponsive" to the wt p53(264-272) peptide. The wt p53(25-35) peptide has attributes of a naturally presented Th cell-defined peptide, which could be incorporated into antitumor vaccines applicable to a broader population of subjects for whom a wt p53 helper peptide is presently unavailable, as well as used for monitoring anti-p53 Th cell activity in cancer subjects receiving p53-based immunotherapy.

Role of antigen-processing machinery in the in vitro resistance of squamous cell carcinoma of the head and neck cells to recognition by CTL

Squamous cell carcinoma of the head and neck (SCCHN) cells are poorly recognized in vitro by CTL despite expressing the restricting HLA class I allele and the targeted tumor Ag (TA). Several lines of evidence indicate that the lack of SCCHN cell recognition by CTL reflects defects in targeted TA peptide presentation by HLA class I Ag to CTL because of Ag-processing machinery (APM) dysfunction. First, lack of recognition of SCCHN cells by CTL is associated with marked down-regulation of the IFN-gamma-inducible APM components low-m.w. protein 2, TAP1, TAP2, and tapasin. Second, SCCHN cell recognition by CTL is restored by pulsing cells with exogenous targeted TA peptide. Third, the restoration of CTL recognition following incubation of SCCHN cells with IFN-gamma is associated with a significant (p = 0.001) up-regulation of the APM components TAP1, TAP2, and tapasin. Lastly, and most conclusively, SCCHN cell recognition by CTL is restored by transfection with wild-type TAP1 cDNA. Our findings may explain the association between APM component down-regulation and poor clinical course of the disease in SCCHN. Furthermore, the regulatory nature of the APM defects in SCCHN cells suggests that intralesional administration of IFN-gamma may have a beneficial effect on the clinical course of the disease and on T cell-based immunotherapy of SCCHN by restoring SCCHN cell recognition by CTL.

Increased frequencies of CD8+ T lymphocytes recognizing wild-type p53-derived epitopes in peripheral blood correlate with presence of epitope loss tumor variants in patients with hepatocellular carcinoma

Wild-type (WT) sequence p53 peptides are attractive candidates for broadly applicable cancer vaccines. The aim of this study was to evaluate the potential of a WT p53-based immunotherapeutic approach for patients with hepatocellular carcinoma (HCC). Circulating CD8+ T cells specific for WT p53(149-157) and WT p53(264-272) HLA-A*0201 restricted epitopes were directly identified in the peripheral blood by the use of peptide/HLA-A2.1 tetramers in 24 HCC patients. Cytotoxic T lymphocyte (CTL) activity after WT p53 peptide-specific stimulation was assessed by analysis of granzyme B and interferon-gamma mRNA transcription, using a quantitative real-time polymerase chain reaction assay. Tumor immunophenotyping was performed to evaluate the p53 status, the expression of major histocompatibility complex (MHC) and costimulatory molecules in freshly isolated tumor cells. HCC patients exhibited significantly higher frequencies of WT p53-specific memory CD8+ T cells and stronger WT p53-specific CTL activity, when compared with healthy controls. Increased frequencies of p53-specific CD8+ T cells and their activity correlated with selective HLA-A2 allele loss and reduced costimulatory molecule expression of tumor cells. Moreover, augmented numbers of p53-specific T cells coincided with high MHC class II expression in tumor cells but were inversely related to the T status of the tumor node metastasis staging system. Our results indicate the existence of natural immunosurveillance and tumor immune evasion, involving a T cell response against WT p53 tumor antigen in patients with HCC. These findings may have important implications for the future development of cancer vaccines.

Immune responses to p53 in patients with cancer: enrichment in tetramer+ p53 peptide-specific T cells and regulatory T cells at tumor sites

OBJECTIVE

A majority of human cancers, including head and neck cancer (HNC), "overexpress" p53. Although T cells specific for wild-type (wt) sequence p53 peptides are detectable in the peripheral blood of patients with HNC, it is unknown whether such T cells accumulate in tumor-involved tissues. Also, the localization of "regulatory" T cells (Treg) to tumor sites in HNC has not been investigated to date.

METHODS

Tumor infiltrating lymphocytes (TIL), tumor-involved or non-involved lymph node lymphocytes (LNL) and peripheral blood mononuclear cells (PBMC) were obtained from 24 HLA-A2.1+ patients with HNC. Using tetramers and four-color flow cytometry, the frequency of Treg and CD3+CD8+ T cells specific for wt p53 epitopes as well as their functional attributes were determined.

RESULTS

The CD3+CD8+ tetramer+ cell frequency was significantly higher (P<0.001) in TIL than autologous PBMC as was the percentage of CD4+CD25+ T cells (P<0.003). TIL were enriched in FOXp3+, GITR+ and CTLA-4+ Treg. CD8+ TIL had low Zeta expression and produced little IFN-gamma after ex vivo stimulation relative to autologous PBMC or PBMC from NC.

CONCLUSIONS

Anti-wt p53 epitope-specific T cells and Treg preferentially localize to tumor sites in patients with HNC. However, despite enrichment in tumor peptide-specific T cells, the effector cell population (CD3+CD8+) in TIL or PBMC was unresponsive to activation in the tumor microenvironment enriched in Treg.

Impact of p53-based immunization on primary chemically-induced tumors

In mice as well as humans, cytotoxic T lymphocytes (CTL) specific for wild-type-sequence (wt) p53 peptides have been shown to react against a wide range of tumors, but not normal cells. As such, they are attractive candidates for developing broadly applicable cancer vaccines. Of particular interest is the potential of using p53-based vaccines in high-risk individuals to prevent cancer. Methylcholanthrene, an immunosuppressive polycyclic hydrocarbon carcinogen implicated as a causative agent in human cancers, has long been used to induce murine tumors with a high incidence of genetic alterations and sensitivity to wt p53-specific CTL. To analyze the potential of p53-based vaccines on primary tumors, we evaluated the efficacy of DNA and dendritic cell vaccines targeting wt p53 peptides given to methylcholanthrene-treated mice in the protection or therapy settings. The results indicate that the efficacy of these vaccines relative to reducing tumor incidence were severely compromised by vaccine-induced tumor escape. As compared to tumors induced in non-immunized mice, a higher incidence of epitope-loss tumors was detected in tumors from the immunized mice. The increase in tumor escape arose as a consequence of either increased frequencies of mutations within/flanking p53 epitope-coding regions or downregulation of expression of the major histocompatibility complex Class I molecules that present these epitopes for T cell recognition These findings are consistent with current views of immunoselection occurring in patients receiving tumor peptide-based immunotherapy, and impact on the design and implementation of p53-based vaccines, in particular, those aimed at treating individuals at high risk for developing cancer.

P53(110-124)-specific human CD4+ T-helper cells enhance in vitro generation and antitumor function of tumor-reactive CD8+ T cells

Current evidence suggests that the optimal vaccines for cancer should incorporate tumor-specific cytotoxic as well as helper epitopes. Wild-type sequence (wt) p53 peptides are attractive candidates for broadly applicable cancer vaccines, which could combine multiple tumor epitopes defined by CD8(+) CTLs, as well as CD4(+) T-helper cells. To test this possibility, we generated anti-p53 CD4(+) T cells from peripheral blood obtained from an HLA-DRB1*0401(+) donor by in vitro stimulation with dendritic cells and recombinant human p53 protein. We identified the wt p53(110-124) peptide as a naturally presented epitope. In a series of ex vivo experiments, performed in an autologous human system, we then demonstrated the ability of anti-wt p53(110-124) CD4(+) T cells to enhance the generation and antitumor functions of CD8(+) effector cells. The results demonstrate the crucial role of T helper-defined epitopes in shaping the immune response to multiepitope cancer vaccines targeting p53. This model of tumor-specific CD8(+) and CD4(+) T-cell interactions suggests that future vaccination strategies targeting tumor cells should incorporate helper and cytotoxic T cell-defined epitopes.

Frequencies of tetramer+ T cells specific for the wild-type sequence p53(264-272) peptide in the circulation of patients with head and neck cancer

Immunization with wild-type sequence (wt) p53 epitopes represents a novel therapeutic strategy for cancer patients with tumors accumulating mutant p53. To evaluate usefulness of p53-derived peptides as future cancer vaccines, frequencies of wt p53(264-272) peptide-specific CD8+ T cells were determined in the peripheral circulation of patients with squamous cell carcinoma of the head and neck (SCCHN). T cells of 30 HLA-A2.1+ patients and 31 HLA-A2.1+ healthy individuals were evaluated by multicolor flow cytometry analysis using peptide-HLA-A2.1 complexes (tetramers). T cells specific for an influenza matrix peptide (a model recall antigen) or an HIV reverse transcriptase peptide (a model novel antigen) were studied in parallel. Patients with SCCHN had a significantly higher mean frequency of CD8+ T cells specific for wt p53(264-272) than normal donors (P = 0.0041). Surprisingly, the frequency of epitope-specific T cells in the circulation of patients did not correlate with p53 accumulation in the tumor. In patients whose tumors had normal p53 expression or had p53 gene mutations preventing presentation of this epitope, high frequencies of wt p53(264-272)-specific CD8+ T cells were found, of which many were memory T cells. In contrast, patients whose tumors accumulated p53 had low frequencies of wt p53(264-272)-specific CD8+ T cells, which predominantly had a naive phenotype and were unable to proliferate ex vivo in response to the epitope, as reported by us previously (T. K. Hoffmann, J. Immunol., 165: 5938-5944, 2000). This seemingly contradictory relationship between the high frequency of epitope-specific T cells and wt p53 expression in the tumor suggests that other factors may contribute to the observed anti-p53 responses. Human papillomavirus-16 E6/E7 expression is common in SCCHN, and E6 is known to promote presentation of wt p53 epitopes. Although human papillomavirus-16 E6/E7 expression was detected in 46% of the tumors, it did not correlate with the frequency of wt p53(264-272)-specific CD8+ T cells or with p53 expression in the tumor. These findings emphasize the complexity of interactions between the tumor and the host immune system, and, thus, have particularly important implications for future p53-based immunization strategies.

In vitro generated cytolytic T lymphocytes reactive against head and neck cancer recognize multiple epitopes presented by HLA-A2, including peptides derived from the p53 and MDM-2 proteins

In previous studies, we were successful in generating HLA-A2-restricted CD8+ CTLs reactive with head and neck carcinomas (HNCs) in 4/10 cases using traditional mixed lymphocyte tumor cultures (MLTCs) employing a semi-allogeneic HLA-A2+ HNC cell line, PCI-13, as the stimulator of normal HLA-A2+ donor T lymphocytes. However, these T cell lines contained only 1-1.5% HLA-A2-restricted, tumor-reactive CD8+ CTLs, as assessed by both limiting dilution and IFN-gamma ELISPOT assays. In order to increase the success rate in generating such HNC-reactive CTL lines, we modified the procedure to allow for T cell crosspriming by autologous DCs pulsed with PCI-13 lysates. In all three attempts, HLA-A2-restricted effector T cell lines were obtained that contained PCI-13-reactive CD8+ T cells at frequencies as high as 1 in 6. These cultured bulk lines recognized at least five predominant HLA-A2-restricted epitopes based on ELISPOT fingerprinting of HPLC-fractionated, naturally presented PCI-13-derived peptides. Two of these epitopes appear to be derived from the p53 and MDM-2 proteins overexpressed by the PCI-13 cell line. Interestingly, the synthetic wild type sequence p53 (264-272) and MDM-2 (53-61) peptides were able to drive in vitro generation of tumor-specific CTLs from the PBMCs of normal HLA-A2+ donors. However, this MDM-2 peptide was not able to elicit responses from HLA-A2+ patients with HNC in short-term in vitro cultures. Overall, these data suggest that tumor lysate-loaded DCs elicit a broad repertoire of CTL responses, some of which are directed against peptides derived from cell cycle regulatory proteins that may prove to be of clinical significance in the therapy of HNC.

The ability of variant peptides to reverse the nonresponsiveness of T lymphocytes to the wild-type sequence p53(264-272) epitope

Recently, we observed that CTL specific for the wild-type (wt) sequence p53(264-272) peptide could only be expanded ex vivo from PBMC of a subset of the HLA-A2.1(+) normal donors or cancer patients tested. Surprisingly, the tumors of the responsive patients expressed normal levels of wt p53 and could be considered unlikely to present this epitope. In contrast, tumors of nonresponsive patients accumulated mutant p53 and were more likely to present this epitope. We sought to increase the responsive rate to the wt p53(264-272) peptide of PBMC obtained from normal donors and patients by identifying more immunogenic variants of this peptide. Two such variants were generated by amino acid exchanges at positions 6 (6T) and 7 (7W) of the peptide. These variants were capable of inducing T cells from PBMC of nonresponsive donors that recognized the parental peptide either pulsed onto target cells or naturally presented by tumors. TCR Vbeta analysis of two T cell lines isolated from bulk populations of effectors reactive against the wt p53(264-272) peptide, using either the parental or the 7W variant peptide, indicated that these T cells were expressing identical TCR Vbeta13.6/complementarity-determining region 3/J region sequences. This finding confirms the heteroclitic nature of at least one of the variant peptides identified in this study. The use of variant peptides of the wt p53(264-272) epitope represents a promising approach to overcoming the nonresponsiveness of certain cancer patients to this self epitope, thereby enhancing its potential use in tumor vaccines for appropriately selected cancer patients.

Immunogenicity of enhanced green fluorescent protein (EGFP) in BALB/c mice: identification of an H2-Kd-restricted CTL epitope

Enhanced green fluorescent protein (EGFP) is a novel marker gene product, which is readily detectable using techniques of fluorescence microscopy, flow cytometry, or macroscopic imaging. In the present studies, we have examined the immunogenicity of EGFP in murine models. A stable transfectant of the transplantable CMS4 sarcoma of BALB/c origin expressing EGFP, CMS4-EGFP-Zeo, was generated. Splenocytes harvested from mice immunized with a recombinant adenovirus expressing EGFP (Ad-EGFP) were restimulated in vitro with CMS4-EGFP-Zeo. Effector lymphocytes displayed strong cytotoxicity against CMS4-EGFP-Zeo, but not against mock-transfected CMS4-Zeo tumor cells. A number of candidate H2-Kd-binding peptides derived from the EGFP protein were chosen according to an epitope prediction program and synthesized. These peptides were tested for their ability to bind to H2-Kd molecules and stimulate IFNgamma-production by splenocytes harvested from Ad-EGFP-immunized mice. Using this methodology, the peptide, HYLSTQSAL (corresponding to EGFP200-208) which strongly binds to H2-Kd molecules, was identified as a naturally occurring epitope of EGFP. These results should facilitate the use of EGFP as a model tumor antigen in BALB/c mice.

Competition of peptide-MHC class I tetrameric complexes with anti-CD3 provides evidence for specificity of peptide binding to the TCR complex

BACKGROUND

Major histocompatibility complex (MHC)-peptide tetrameric complexes (tetramers) are valuable tools for detecting and characterizing peptide-specific T cells. Because the frequency of these cells is generally very low, it may be difficult to discriminate between nonspecific and specific tetramer binding.

METHODS

A four-color flow cytometric assay that simultaneously measures tetramer, CD3, CD8, and CD14 was used to investigate the sensitivity and specificity of MHC class I tetramer staining. This was accomplished by using the influenza virus matrix protein peptide, GILGFVFTL (FLU), as a model recall antigen and the human immunodeficiency virus (HIV) reverse transcriptase peptide, ILKEPVHGV (HIV), as a model novel antigen. Peripheral blood mononuclear cells (PBMC) from 31 HLA-A2.1(+) and 10 HLA-A2.1(-) healthy individuals were stained with the tetramers.

RESULTS

The lower limit of detection was established at approximately 1/8,000. In HLA-A2(+) PMBC, frequencies of tetramer-positive CD8(+) T cells were log normally distributed and were high for FLU (1/910) but low for HIV (1/6,067). A novel competition assay, in which tetramer binding was shown to diminish subsequent staining with anti-CD3 antibody, was used to confirm the specificity of tetramer binding to the T-cell receptor (TCR) complex. The competition assay was validated by evaluating several anti-CD3 antibodies and showing that in PBMC from HLA-A2(-) subjects, spurious tetramer-positive events (1/20,000) failed to compete with CD3 binding. For the "recall" FLU tetramer, the degree of competition was proportional to the frequency, suggesting a selection of high avidity cells. Although CD3 competition was also highly correlated with the intensity of tetramer staining, competition allowed the identification of false positive cases with relatively high tetramer staining intensity.

CONCLUSION

The data indicate that competition of CD3 binding allows confirmation of the specificity of tetramer binding to the TCR, extending the usefulness of tetramers in the frequency analysis of peptide-specific T lymphocytes.

Generation of T cells specific for the wild-type sequence p53(264-272) peptide in cancer patients: implications for immunoselection of epitope loss variants

Alterations in the p53 gene occur frequently and can lead to accumulation of p53 protein in squamous cell carcinomas of the head and neck (SCCHN). Since accumulation of p53 is associated with enhanced presentation of wild-type sequence (wt) p53 peptides to immune cells, the development of pan vaccines against SCCHN has focused on wt p53 epitopes. We used the HLA-A2.1-restricted wt p53(264-272) epitope to generate CTL from circulating precursor T cells of HLA-A2.1(+) healthy donors and patients with SCCHN. Autologous peptide-pulsed dendritic cells were used for in vitro sensitization. CTL specific for the wt p53(264-272) peptide were generated from PBMC obtained from two of seven normal donors and three of seven patients with SCCHN. These CTL were HLA class I restricted and responded to T2 cells pulsed with p53(264-272) peptide as well as HLA-A2-matched SCCHN cell lines naturally presenting the epitope. Paradoxically, none of the tumors in the three patients who generated CTL could adequately present the epitope; two had a wt p53 genotype and no p53 protein accumulation, while the third tumor expressed a point mutation (R to H) in codon 273 that prevents presentation of the p53(264-272) epitope. In contrast, patients who did not generate CTL had tumors that accumulated altered p53 and potentially could present the p53(264-272) epitope. These findings suggest that in vivo, CTL specific for the wt p53(264-272) peptide might play a role in the elimination of tumor cells expressing this epitope and in immunoselection of epitope-loss tumor cells. Immunoselection of tumors that become resistant to anti-p53 immune responses has important implications for future p53-based vaccination strategies.

A wild-type sequence p53 peptide presented by HLA-A24 induces cytotoxic T lymphocytes that recognize squamous cell carcinomas of the head and neck

Evidence has accumulated indicating that HLA-A2-restricted CTLs specific for human wild-type sequence p53 epitopes lyse tumor cells expressing mutant p53. To explore the possibility that wild-type sequence p53 peptides could also be used in vaccines for patients expressing HLA-A24 antigen, another frequent HLA class I allele, we investigated the induction of HLA-A24-restricted p53-specific CTLs from the peripheral blood lymphocytes of normal donors. Of six p53-derived peptides possessing an HLA-A24 binding motif, the p53 peptide 125-134 (p53(125-134)) was found to have a high binding capacity and induced peptide-specific CTLs from peripheral blood mononuclear cells, using peptide-pulsed autologous dendritic cells and subsequent cultivation with cytokines interleukin 2 and interleukin 7. Bulk CTL populations lysed peptide-pulsed HLA-A24+ targets as well as HLA-A24+ squamous cell carcinoma of the head and neck (SCCHN) cell lines. However, IFN-gamma pretreatment of HLA-A24+ SCCHN cell lines was necessary for lysis, suggesting that a ligand density higher than that normally expressed by tumor cells is required for these CTLs to mediate lysis. Moreover, a cloned CTL, designated TH#99, isolated from the bulk population by limiting dilution, lysed HLA-A24+ SCCHN targets more efficiently than the bulk CTL population. Lysis was inhibited by anti-HLA class I monoclonal antibody but not by anti-HLA-DR monoclonal antibody. These results indicate that HLA-A24-restricted CTLs recognizing the wild-type sequence p53(125-134) can be generated using autologous dendritic cells from precursors present in peripheral blood lymphocytes obtained from normal HLA-A24+ donors. This finding suggests that vaccine strategies targeting wild-type sequence p53 epitopes can be extended to a wider range of cancer patients.

Dendritic cell-based genetic immunization in mice with a recombinant adenovirus encoding murine TRP2 induces effective anti-melanoma immunity

BACKGROUND

The induction of cellular immune responses to melanocyte-specific enzymes such as the tyrosinase family of proteins is the goal of various clinical studies for the immunotherapy of melanoma. Tyrosinase-related protein-2 (TRP2) is an attractive model antigen for preclinical studies in C57BL/6 mice because it is naturally expressed by the murine B16 melanoma and can be recognized by self-reactive cytolytic T lymphocytes (CTL). Here we describe efforts to develop genetic immunization with dendritic cells (DC) for the immunotherapy of melanoma in this clinically relevant system.

METHODS

Recombinant adenoviruses encoding green fluorescent protein (Ad-EGFP) and murine TRP2 (Ad-mTRP2) were constructed using Cre-loxP-mediated recombination. DC were generated in vitro from precursors in bone marrow and transduced with Ad-EGFP or Ad-mTRP2. Mice were immunized by direct injection of adenovirus or by injection of Ad-transduced DC. Induction of tumor immunity was assessed by intravenous challenge with B16 melanoma cells and enumeration of experimentally induced lung metastases.

RESULTS

Flowcytometric analysis of DC transduced with Ad-EGFP demonstrated endogenous fluorescence due to cytoplasmatic expression of EGFP in 30-60% of cells. Ad-EGFP-transduced DC simultaneously displayed the DC-specific marker NLDC145 and high levels of MHC and costimulatory molecules on their cell surface. Transduction of DC with Ad-mTRP2 resulted in strong intracellular expression of TRP2 which could be readily detected by immunostaining. Importantly, immunization of mice with cultured Ad-mTRP2-transduced DC completely prevented the development of lung metastases following an intravenous challenge with B16 melanoma cells. This striking protective effect was observed with both the intravenous and the subcutaneous route of DC immunization. In vivo depletion of T-cell subsets suggested that the protective effect of an immunization with Ad-mTRP2-transduced DC involved both CD8+ and CD4+ T-cells.

CONCLUSIONS

Our results demonstrate that DC-based genetic immunization of mice with TRP2, a clinically relevant melanocyte-specific self-antigen, induces effective cellular immunity and prevents metastatic growth of B16 melanoma cells in vivo.

Generation of anti-p53 cytotoxic T lymphocytes from human peripheral blood using autologous dendritic cells

CTLs recognizing the HLA-A2.1-restricted, wild-type sequence p53 epitopes p53(149-157) and p53(264-272) were generated from CD8-enriched populations of nonadherent peripheral blood lymphocytes (PBLs) obtained from healthy donors. The PBLs were restimulated in vitro with peptide-pulsed granulocyte macrophage colony-stimulating factor- and interleukin (IL)-4-induced autologous dendritic cells in the presence of IL-6 and IL-12 and subsequently cultivated with IL-1alpha, IL-2, IL-4, IL-6, and IL-7. Bulk anti-p53(264-272) CTL populations were generated from PBLs obtained from two of five donors. Both CTL populations were cytotoxic against peptide-pulsed HLA-A2+ target cells, but not against untreated target cells. A CD8+ anti-p53 CTL clone designated p264#2 was isolated from one of the bulk populations. It was found to have an intermediate affinity of approximately 10(-9) M for the epitope and to mediate cytotoxicity against several human tumor cell lines, including the squamous cell carcinoma of the head and neck cell line SCC-9, which is known to present the wild-type sequence p53(264-272) epitope. In addition, CTLs reactive against p53(149-157)-pulsed targets as well as a HLA-A2+ tumor cell line were cloned from a bulk population of antitumor CTLs obtained from one of the five normal PBLs restimulated with this epitope. The results indicate that CTLs recognizing wild-type sequence epitopes can be generated from precursors present in PBLs obtained from some normal individuals using autologous dendritic cells as antigen-presenting cells and suggest that vaccine strategies targeting these epitopes can lead to antitumor CTL generation, thereby emphasizing the therapeutic potential of p53-based cancer vaccines.

Co-delivery of T helper 1-biasing cytokine genes enhances the efficacy of gene gun immunization of mice: studies with the model tumor antigen beta-galactosidase and the BALB/c Meth A p53 tumor-specific antigen

DNA-based immunization is currently being investigated as a new method for the induction of cellular and humoral immunity directed against viral disease and cancer. In the present study we characterized and compared the immune responses induced in mice following particle-bombardment of the skin ('gene gun' immunization) with those elicited by intracutaneous injection of a recombinant adenoviral vector. Using the well characterized beta-galactosidase (beta gal) model Ag system we find that both in vivo gene transfer systems elicit potent and long-lasting anti-beta gal-specific CD8+ and CD4+ T cell responses. However, gene gun immunization predominantly promotes the production of anti-beta gal antibodies of the gamma 1 isotype, indicative of a Th2-biased immune response, while intradermal injection of recombinant adenovirus primarily leads to the production of anti-beta gal gamma 2a antibodies, indicative of a Th1-biased immune response. Since viral infections are generally associated with the production of large amounts of IFN-alpha and IL-12, we investigated whether administration of expression plasmids encoding these Th1-associated cytokines along with antigen-encoding cDNA can influence the nature of the immune response resulting from gene gun immunization. We observed that co-delivery of IFN-alpha or IL-12 resulted in increased production of anti-beta gal gamma 2a antibodies. This suggests a shift towards a Th1 phenotype of the resulting immune response, thus mimicking a viral infection. Importantly, gene gun immunization of mice with a naturally occurring tumor antigen, the tumor-specific p53 mutant antigen expressed by the chemically induced BALB/c Meth A sarcoma, required co-delivery of IL-12 for the induction of effective antitumor immunity. These results have important implications for the design of clinically relevant gene gun immunization strategies for tumor immunotherapy.

p53-based immunotherapy of cancer

Immunotherapy targeting p53 missense mutations, which occur in nearly half of all human tumors, is limited by several factors, including the constraints of antigen processing and presentation. Due to the accumulation of mutated p53 molecules in tumors expressing p53 mutations, an alternative approach would be to target wild-type sequence, CTL-defined p53 epitopes. Obviously, the possibility of an autoimmune response is a major potential drawback to this therapy. Immunization of BALB/c mice with bone marrow-derived dendritic cells (DC) generated in the presence of GM-CSF/IL-4 and prepulsed with the H-2Kd-binding wild-type p53(232-240) peptide has been shown to induce anti-peptide CTL. These effectors were cross-reactive against sarcomas expressing p53 missense mutations outside of the p53(232-240) epitope, but not within it. Mitogen-activated splenocytes, which express elevated levels of p53, were not sensitive to these CTL. The p53 peptide-pulsed DC-based vaccine was shown to be effective in inducing tumor rejection in immunization and therapy models in the absence of any observable deleterious effect on naive mice. The murine model has now been extended to include the use of genetically modified DC-based vaccines as well.

Genetically modified bone marrow-derived dendritic cells expressing tumor-associated viral or "self" antigens induce antitumor immunity in vivo

The clinical application of synthetic tumor peptide-based vaccines is currently limited to patients with specified major histocompatibility complex (MHC) class I alleles. Such logistic limitations may be overcome using tumor gene-based approaches. Here we describe the effective generation of dendritic cells (DC) expressing tumor peptide-MHC complexes as a result of particle-mediated transfer of genes encoding tumor-associated antigens (TAA). Bone marrow-derived DC were transfected with plasmid DNA encoding the tumor-associated viral antigen E7 derived from human papilloma virus (HPV) 16. When applied as a vaccine, these genetically modified DC induced antigen-specific CD8+ cytotoxic T lymphocytes (CTL) in vivo and promoted the rejection of a subsequent, normally lethal challenge with an HPV 16-transformed tumor cell line. Of greatest interest, immunization of mice with syngeneic DC genetically modified to enhance their presentation of a constitutive "self" epitope derived from the tumor-suppressor gene product p53 caused a significant reduction in the in vivo growth of a chemically induced p53-positive sarcoma. These results suggest that cancer vaccines consisting of DC genetically modified to express TAA of viral or "self" origin effectively induce antitumor immunity in vivo.

Bone marrow-derived dendritic cells serve as potent adjuvants for peptide-based antitumor vaccines

Dendritic cells (DCs) are considered the most effective antigen-presenting cells (APCs) for primary immune responses. Since presentation of antigens to the immune system by appropriate professional APCs is critical to elicit a strong immune reaction and DCs seem to be quantitatively and functionally defective in the tumor host, DCs hold great promise to improve cancer vaccines. Even though they are found in lymphoid organs, skin and mucosa, the difficulty of generating large numbers of DCs has been a major limitation for their use in vaccine studies. A simple method for obtaining DCs from mouse bone marrow cells cultured in the presence of GM-CSF + interleukin 4 is now available. In four different tumor models, mice injected with DCs grown in GM-CSF plus interleukin 4 and prepulsed with a cytotoxic T lymphocyte-recognized tumor peptide epitope developed a specific cytotoxic T lymphocyte response and were protected against a subsequent tumor challenge with tumor cells expressing the relevant tumor antigen. Moreover, treatment of day 5-14 tumors with peptide-pulsed DCs resulted in sustained tumor regression in five different tumor models. These results suggest that presentation of tumor antigens to the immune system by professional APCs is a promising method to circumvent tumor-mediated immunosuppression and is the basis for ongoing clinical trials of cancer immunotherapy with tumor peptide-pulsed DCs.

Therapy of murine tumors with p53 wild-type and mutant sequence peptide-based vaccines

The BALB/c Meth A sarcoma carries a p53 missense mutation at codon 234, which occurs in a peptide, termed 234CM, capable of being presented to cytotoxic T lymphocytes (CTL) by H-2Kd molecules (Noguchi, Y., E.C. Richards, Y.-T. Chen, and L.J. Old. 1994. Proc. Natl. Acad. Sci. USA. 91:3171-3175). Immunization of BALB/c mice with bone marrow-derived dendritic cells (DC), generated in the presence of granulocyte macrophage colony-stimulating factor and interleukin 4, and prepulsed with the Meth A p53 mutant peptide, induced CTL that specifically recognized peptide-pulsed P815 cells, as well as Meth A cells naturally expressing this epitope. Immunization with this vaccine also protected naive mice from a subsequent tumor challenge, and it inhibited tumor growth in mice bearing day 7 subcutaneous Meth A tumors. We additionally determined that immunization of BALB/c mice with DC pulsed with the p53 peptide containing the wild-type residue at position 234, 234CW, induced peptide-specific CTL that reacted against several methylcholanthrene-induced BALB/c sarcomas, including CMS4 sarcoma, and rejection of CMS4 sarcoma in vaccination and therapy (day 7) protocols. These results support the efficacy of DC-based, p53-derived peptide vaccines for the immunotherapy of cancer. The translational potential of this strategy is enhanced by previous reports showing that DC can readily be generated from human peripheral blood lymphocytes.