Abstract 5380: Prophylactic MUC1/Poly-ICLC vaccine in individuals with the history of advanced colorectal adenoma

Background MUC1 is aberrantly expressed in a hypoglycosylated form with lack of luminal polarity in variety of human adenocarcinomas including colon cancer. Aberrant MUC1 is also highly expressed in colonic adenomas where it may promote malignant transformation by interacting withβ-catenin known to be an important pathway in colon carcinogenesis. We hypothesized that induction of an immune response against aberrant MUC1 in individuals with a recent history of adenoma may prevent adenoma recurrence and/or their progression to colon cancer. We conducted a clinical study using MUC1 peptide and Poly-ICLC adjuvant vaccine to evaluate the safety and immunogenicity in individuals who are cancer free but at high risk for developing colorectal cancer because of a recent history of advanced adenoma. Method Patients with advanced colorectal adenoma which meets at least one of following criteria: 1) ≥ 1cm in maximal diameter, 2) villous or tubulovillous histology, 3) high-grade dysplasia, were vaccinated with 100μg of 100aa MUC1 peptide (H2N-(GVTSAPDTRPAPGSTAPPAH)5-CONH2) admixed with 500μg of Poly-ICLC (TLR-3 agonist) as adjuvant, on week 0, 2, 10 and one year later. Bloods were collected two weeks after each injection for monitoring of general immunocompetence, development of anti-MUC1 antibody and safety. Results The vaccine was well tolerated without any adverse event grade 2 or higher. Among 36 evaluable patients, anti MUC1 IgG antibody was elicited in 17 patients as measured on week12 (response rate 47.2%). This response rate and the high levels of IgG have never been seen in response to MUC1 vaccines in cancer patients. Antibody titers declined over time but could be boosted to previous or higher levels at 1 year, showing development of immune memory. Vaccine responders were distributed across most HLA-DR and DQ types with similar frequency as in the general population, indicating that the MUC1 peptide could be presented by multiple Class II alleles. Immune competence of colon adenoma patients evaluated by cytokine production of lymphocyte and regulatory T cell frequency was generally equal to healthy individuals, however myeloid derived suppressor cells (MDSCs) were significantly increased in colon adenoma patients. Increase in MDSCs was especially pronounced in non-responders to the vaccine. Conclusion MUC1 poly-ICLC vaccine is highly immunogenic in this prophylactic setting and no significant adverse events have been seen. Vaccine immunogenicity is reduced in individuals with increased numbers of MDSC and this immunosuppressive population might be used as a biomarker to select patients most likely to respond.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5380. doi:1538-7445.AM2012-5380

Abstract A16: A phase I/II clinical trial of a MUC1-glycopeptide dendritic cell vaccine in castrate resistant non-metastatic prostate cancer patients

Background: Current treatment options for prostate cancer (PCa) patients with rising PSA despite castrate testosterone levels are limited. A number of immunotherapeutic approaches for the treatment of PCa have been studied with varying efficacy. MUC1 has been an antigen of interest for immunotherapy, however, tolerance to the peptide epitopes has led to limited immune response. A glycosylated version of the antigen, Tn-100mer-MUC1, was shown to be effective in overcoming tolerance in pre-clinical studies. Dendritic cells (DC) take up and process Tn-100mer-MUC1 and present both glycopeptide and peptide epitopes. We report the results of a phase I/II clinical trial of an autologous DC vaccine loaded with Tn-100mer-MUC1 and KLH in patients with castrate resistant, non-metastatic PCa.

Methodology: Eight consenting patients with rising PSA were enrolled into the study; however one patient progressed with bone metastases before receiving the first vaccine dose. To generate the autologous DC vaccine, patient's monocytes were elutriated from apheresis product and cultured under conditions suitable for the generation of mature and motile DCs. Tn-100mer-MUC1 glycopeptide and clinical-grade KLH, as a control antigen, were loaded onto the DCs. The final vaccine product consisting of Tn-100mer-MUC1 and KLH loaded DCs mixed 10:1 was cryopreserved and tested before release and administration to patients. Patients were treated with 3 vaccine injections every two weeks administered intradermally (i.d.) and intranodally (i.n.) to a single inguinal node for the first dose only. Booster i.d. vaccinations were given 6 and 12 months following the first dose in patients showing stable disease. Each dose consisted of the administration of a total of 1.2 × 107 DCs. Toxicity and biologic effects of the vaccine were evaluated by physical, imaging and clinical chemistry examinations at regular intervals. PSA doubling times were determined using the Memorial Sloan-Kettering Cancer Center PSA doubling time calculator.

Results: The vaccine was safe; there were no serious vaccine-related adverse events. Toxicity was limited to grade 1 and 2 injection site reactions. Four of 7 patients treated were withdrawn after 6 months because of radiologic progression or elevated PSA. Three patients showed stable disease and received all five vaccinations. Our primary endpoint, reduction in PSA, was not achieved. However, the rate of PSA rise decreased in 6 of 7 patients. Overall the PSA doubling time increased from a median of 2.9 months prior to treatment to 7.5 months during vaccination.

Conclusions: These results suggest that the DC-Tn-MUC1 vaccination is safe and induces a biological response reflected by an increase in PSA doubling time in most patients. These early results are encouraging and warrant further testing in a larger number of patients.

This study was supported by CANVAC with funds from the Networks of Centres of Excellence of Canada.

Citation Format: Pierre Major, Louis Lacombe, Yves Fradet, Ronan Foley, Elizabeth Scheid, Alain Bergeron, Som Mukherjee, Olivera J. Finn, Jean Gariepy, Rafick P. Sekaly, Sebastien Hotte, Sheila Chou. A phase I/II clinical trial of a MUC1-glycopeptide dendritic cell vaccine in castrate-resistant nonmetastatic prostate cancer patients [abstract]. In: Proceedings of the AACR Special Conference on Advances in Prostate Cancer Research; 2012 Feb 6-9; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(4 Suppl):Abstract nr A16.

MUC1 protein expression in tumor cells regulates transcription of proinflammatory cytokines by forming a complex with nuclear factor-κB p65 and binding to cytokine promoters: importance of extracellular domain

MUC1 is a transmembrane glycoprotein abnormally expressed in all stages of development of human adenocarcinomas. Overexpression and hypoglycosylation of MUC1 in cancer cells compared with normal epithelial cells are likely to alter its function and affect the behavior of cancer cells. The extracellular domain, specifically the highly O-glycosylated VNTR (variable number of tandem repeats) region, plays an important role in cell-cell communication; however, we show here that it also participates intracellularly in activation of the NF-κB pathway. Transfection of MUC1(-) tumor cells with cDNA encoding MUC1 with 22 tandem repeats (MUC1/22TR) or two tandem repeats (MUC1/2TR) or two isoforms that lack the VNTR region (MUC1/Z and MUC1/Y) showed that the highest expression levels of NF-κB family members correlated with the presence of VNTR and the highest number of tandem repeats. Because expression of MUC1 with VNTR on tumors was previously associated with chemotactic activity for cells of the innate immune system, we investigated the influence of MUC1 expression on the NF-κB-dependent transcriptional regulation of proinflammatory cytokines. ChIP and real-time PCR experiments revealed that MUC1/22TR up-regulated IL-6 and TNF-α expression by binding to their promoter regions in a NF-κB p65-dependent manner in both MUC1-transfected and human breast cancer cells that express endogenous MUC1. This newly detected complex of MUC1 and p65 is a novel mechanism that tumors can use to promote inflammation and cancer development.

IL-33 synergizes with TCR and IL-12 signaling to promote the effector function of CD8+ T cells

The effector functions of CD8(+) T cells are influenced by tissue inflammatory microenvironments. IL-33, a member of the IL-1 family, acts as a danger signal after its release during cell necrosis. The IL-33/ST2 axis has been implicated in various Th2 responses. Its role in CD8(+) T-cell-mediated immune response is, however, not known. Here we find that type 1 cytotoxic T (Tc1) cells cultured in vitro unexpectedly express high levels of the IL-33 receptor ST2. Interestingly, the expression of ST2 in Tc1 cells is dependent on T-bet, a master Th1/Tc1 transcription factor. In addition, IL-33 enhances TCR-triggered IFN-γ production. IL-33 together with IL-12 can stimulate IFN-γ production in Tc1 cells. Moreover, IL-33 synergizes with IL-12 to promote CD8(+) T-cell effector function. The synergistic effect of IL-33 and IL-12 is partly mediated by Gadd45b. Together, these in vitro data establish a novel role of IL-33 in promoting effector type 1 adaptive immune responses.

Abstract CN08-04: Testing cancer vaccines in the setting of premalignant disease: State of immunity and determinants of response

The overarching hypothesis we are testing is that the best therapeutic approach to cancer is to prevent it either by preventing development of precursor lesions in high-risk individuals or arresting their progression from early lesions to invasive cancer. In the history of medicine, the most effective disease prevention has been achieved through vaccination. There is now solid evidence that tumors are recognized by the immune system and their development can be stopped or controlled long term through a process known as immunosurveillance. Immune recognition and tumor elimination are mediated by the adaptive immune system and directed against specific tumor antigens.

We have explored the potential of one such antigen, MUC1, to be a good immunogen as well as a good target of anti-tumor immunity. The experiments have involved in vitro trials, animal models and Phase I and II clinical trials. All MUC1 vaccines tested by us and others have been “therapeutic,” administered to patients with late stage cancer and often after failing standard toxic therapies. In that setting there was very low immunogenicity and limited therapeutic efficacy. It is now clear that the immune system of a cancer patient is under the influence of multiple stress pathways, both tumor induced and host induced, which have a profound immunosuppressive effect, especially on the adaptive immune cells responsible for eliminating tumor cells.

We took advantage of the fact that MUC1 that is abnormally expressed on tumor cells is also abnormally expressed on precursor lesions that can progress to cancer. For example, MUC1 is a tumor antigen on colon tumors but also abnormally expressed on all different types of colonic polyps, precursors to colon cancer. We conducted a clinical trial testing a MUC1 vaccine in individuals diagnosed with villous colonic adenomas, the immediate precursor lesions for colon cancer. Our hypothesis was that the immune system of these individuals would not have experienced the stress pathways associated with the cancer microenvironment and thus would generate a good immune response to the vaccine, which could prevent adenoma recurrence or their progression to colon cancer.

We vaccinated 40 individuals with a 100aa-long MUC1 peptide combined with the TLR3 agonist adjuvant Poly-ICLC (HiltonolÒ). The vaccine was given at Day 0, week 2, week 10 and week 52 (1-year booster). 47% of individuals responded vigorously to the vaccine as measured by anti-MUC1 IgG. All responders had a vigorous memory response at 1 year. There was no toxicity of any kind.

We also focused our attention on the 53% who were non-responders. There was no correlation between response to the vaccine and age or race and only a slight correlation with gender. The surprise came when we examined the immunocompetence of these individuals by evaluating the state of CD4 and CD8 T cells and the presence or absence of Treg and MDSCs. Treg and MDSC have been found in increased numbers at the tumor site and in circulation of advanced cancer patients. They have not been reported in people with premalignant lesions. We found a highly statistically significant correlation between high percentages of MDSCs in the blood and non-responsiveness to the vaccine. We also found that, unlike in cancer, there was no increase in Treg in premalignancy. Furthermore, again unlike in cancer patients, once MDSCs are removed, the T cells function normally and have a normal effector phenotype rather than the phenotype of exhausted T cells.

We draw three important conclusions from this trial: 1) the MUC1 plus Poly-ICLC adjuvant is an immunogenic vaccine; 2) progressive premalignant disease can also create a “stressful” environment that can interfere with effective immunosurveillance. Cancer vaccines should be administered before MDSC expand or in combination with treatments that would control or eliminate MDSC function.

Citation Information: Cancer Prev Res 2011;4(10 Suppl):CN08-04.

Epidemiologic perspective on immune-surveillance in cancer

Common 'themes' in epidemiology related to cancer risk beg a comprehensive mechanistic explanation. As people age, risk for cancer increases. Obesity and smoking increase the risk for many types of cancer. History of febrile childhood diseases lowers the risk for melanomas, leukemias, non-Hodgkin's lymphoma (NHL), and ovarian cancer. Increasing number of ovulatory cycles uninterrupted by pregnancies correlate positively with breast, endometrial, and ovarian cancer risk while pregnancies and breastfeeding lower the risk for these cancers as well as cancers of the colon, lung, pancreas, and NHL. Chronic inflammatory events such as endometriosis or mucosal exposure to talc increase the risk for several types of cancer. Mechanisms so far considered are site specific and do not explain multiple associations. We propose that most of these events affect cancer immunosurveillance by changing the balance between an effective immune response and immune tolerance of an emerging cancer. We review recently published data that suggest that immune mechanisms underlie most of these observed epidemiologic associations with cancer risk.

Tumor antigen epitopes interpreted by the immune system as self or abnormal-self differentially affect cancer vaccine responses

Epitope selection is an important consideration in the design of cancer vaccines, but factors affecting selection are not fully understood. We compared the immune responses to peptides and glycopeptides from the common human tumor antigen MUC1, a mucin that is coated with O-linked carbohydrates in its variable number of tandem repeats (VNTR) region. MUC1 expressed on tumor cells is characteristically underglycosylated, creating peptide and glycopeptide neoepitopes that are recognized by the immune system. The response to VNTR peptides is weaker in MUC1-transgenic mice (MUC1-Tg mice) than in wild-type (WT) mice, whereas the response to VNTR glycopeptides is equally strong in the two strains. Thus, glycopeptides seem to be recognized as foreign, whereas peptides, although immunogenic, are perceived as self. To explore this further, we generated MUC1 peptide- and glycopeptide-specific T-cell receptor transgenic mice and studied the function of their CD4 T cells when adoptively transferred into MUC1-Tg or WT mice. Peptide-specific T-cell precursors were not centrally deleted in MUC1-Tg mice and did not acquire a T regulatory phenotype. However, their response to the cognate peptide was reduced in MUC1-Tg mice compared with WT mice. In contrast, glycopeptide-specific CD4 T cells responded equally well in the two hosts and, when simultaneously activated, also enhanced the peptide-specific T-cell responses. Our data show that the immune system differentially recognizes various epitopes of tumor-associated antigens either as self or as foreign, and this controls the strength of antitumor immunity. This represents an important consideration for designing safe and effective cancer vaccines.

Anti-MUC1 antibodies and ovarian cancer risk: prospective data from the Nurses' Health Studies

BACKGROUND

The surface epithelial glycoprotein MUC1 becomes overexpressed and hypoglycosylated in adenocarcinomas; similar changes occur during nonmalignant inflammatory events. Antibodies developed against tumor-like MUC1 in response to such events could be one way through which ovarian cancer risk factors operate.

METHODS

We evaluated the association between anti-MUC1 antibodies and risk of ovarian cancer in a prospective nested case-control study in the Nurses' Health Studies. We used an ELISA to measure plasma anti-MUC1 antibodies in 117 ovarian cancer cases collected at least 3 years before diagnosis and 339 matched controls.

RESULTS

In controls, younger women (P-trend = 0.03), those with a tubal ligation (P = 0.03), and those with fewer ovulatory cycles (P-trend = 0.04) had higher antibody levels. In cases, women with late-stage disease (P = 0.04) and those whose specimen was >11 years remote from diagnosis (P = 0.01) had higher antibody levels. Overall, increasing anti-MUC1 antibody levels were associated with a nonsignificant trend for lower risk for ovarian cancer, but there was highly significant heterogeneity by age (P-heterogeneity = 0.005). In women <64 years, the antibody level in quartiles 2 to 4 versus quartile 1 were associated with reduced risk (relative risk = 0.53; 95% confidence interval, 0.31-0.93; P-trend = 0.03), whereas in women > or = 64 years, the corresponding relative risk was 2.11 (95% confidence interval, 0.73-6.04); P-trend = 0.05).

CONCLUSION

Anti-MUC1 antibodies evaluated several years before diagnosis may be associated with lower risk of subsequent ovarian cancer in women <64 years old at assessment.

IMPACT

Key elements of an "immune model" to explain ovarian cancer risk factors are confirmed and should be evaluated in larger prospective studies.

Vaccines based on abnormal self-antigens as tumor-associated antigens: immune regulation

Abnormal expression of "self" antigens on tumors compared with normal cells provides opportunities and challenges for development of cancer vaccines. We review recent work in pre-clinical transgenic mouse models and in clinical trials that has elucidated multiple regulatory mechanisms that interfere with the induction of effective immunity. We discuss these as being either part of the normal function of the immune system or being driven by the tumor microenvironment. Collectively this work shows that it is possible to design vaccines based on tumor-associated antigens and elicit effective immunity against abnormal expression of these antigens on tumors without causing autoimmunity.

Vaccine against MUC1 antigen expressed in inflammatory bowel disease and cancer lessens colonic inflammation and prevents progression to colitis-associated colon cancer

Association of chronic inflammation with an increased risk of cancer is well established, but the contributions of innate versus adaptive immunity are not fully delineated. There has furthermore been little consideration of the role played by chronic inflammation-associated antigens, including cancer antigens, and the possibility of using them as vaccines to lower the cancer risk. We studied the human tumor antigen MUC1 which is abnormally expressed in colon cancers and also in inflammatory bowel disease (IBD) that gives rise to colitis-associated colon cancer (CACC). Using our new mouse model of MUC1(+) IBD that progresses to CACC, interleukin-10 knockout mice crossed with MUC1 transgenic mice, we show that vaccination against MUC1 delays IBD and prevents progression to CACC. One mechanism is the induction of MUC1-specific adaptive immunity (anti-MUC1 IgG and anti-MUC1 CTL), which seems to eliminate abnormal MUC1(+) cells in IBD colons. The other mechanism is the change in the local and the systemic microenvironments. Compared with IBD in vaccinated mice, IBD in control mice is dominated by larger numbers of neutrophils in the colon and myeloid-derived suppressor cells in the spleen, which can compromise adaptive immunity and facilitate tumor growth. This suggests that the tumor-promoting microenvironment of chronic inflammation can be converted to a tumor-inhibiting environment by increasing adaptive immunity against a disease-associated antigen.

Cancer vaccines: emphasis on pediatric cancers

The success that vaccines have had in the fight with infectious diseases has not been mirrored in their use in the fight against cancer. The major differences are that cancer vaccines have been tested in the therapeutic rather than the prophylactic setting, and in older adults rather than in the pediatric population. Cancers, as well as current standard treatments, are highly immunosuppressive, which further compromises the success of therapeutic vaccines. Cancer is considered to be primarily a disease of the older age and yet many children suffer from or succumb to cancers such as leukemias, glioblastomas, neuroblastomas and sarcomas. Standard therapy, even when curative, is accompanied by serious side effects, including secondary tumors later in life. Due to the greater capacity of a young immune system to recover after cancer treatment, therapeutic vaccines are expected to have a better chance to elicit protective immunity and prevent cancer recurrence in children. In this review, we discuss the current efforts at designing and testing cancer vaccines in children with the focus on specific tumor antigens expressed by pediatric cancers.

Aberrant expression of MUC1 mucin in pediatric inflammatory bowel disease

Mucin 1 (MUC1) glycoprotein is normally expressed at low levels on the luminal side of healthy colonic epithelial cells. In colon cancer and other epithelial tumors, MUC1 is overexpressed and hypoglycosylated. Antibodies specific for this "tumor form" of MUC1 are found in cancer patients. We hypothesized that MUC1 expression might be altered in chronic inflammation, such as in inflammatory bowel disease (IBD). Furthermore, we hypothesized that these alterations might induce antibody responses. The aims of this study were to characterize MUC1 expression in IBD and to examine whether pediatric patients with IBD have an MUC1-specific antibody. Colon biopsies were examined for MUC1 expression by immunochemistry using anti-MUC1 antibodies that detect normal or abnormal forms of MUC1. Sera were analyzed by Enzyme Linked Immunosorbent Assay (ELISA) for evidence of anti-MUC1 antibody. We found marked overexpression of MUC1 in IBD, most of which was hypoglycosylated. On colon specimens from healthy age-matched controls, we found low levels of luminal MUC1 and no alteration in its glycosylation. We detected antibody to MUC1 in sera of IBD patients as well as controls, and in a limited number of IBD samples examined longitudinally, we could correlate the rise and fall of antibody levels with clinical disease severity. MUC1 is overexpressed and hypoglycosylated in pediatric IBD and may play an important role in the pathogenesis of IBD, and thus warrants further study as a potential therapeutic target. Similarly, antibodies to MUC1 may influence IBD and should be explored as potential diagnostic or prognostic markers.

The prioritization of cancer antigens: a national cancer institute pilot project for the acceleration of translational research

The purpose of the National Cancer Institute pilot project to prioritize cancer antigens was to develop a well-vetted, priority-ranked list of cancer vaccine target antigens based on predefined and preweighted objective criteria. An additional aim was for the National Cancer Institute to test a new approach for prioritizing translational research opportunities based on an analytic hierarchy process for dealing with complex decisions. Antigen prioritization involved developing a list of "ideal" cancer antigen criteria/characteristics, assigning relative weights to those criteria using pairwise comparisons, selecting 75 representative antigens for comparison and ranking, assembling information on the predefined criteria for the selected antigens, and ranking the antigens based on the predefined, preweighted criteria. Using the pairwise approach, the result of criteria weighting, in descending order, was as follows: (a) therapeutic function, (b) immunogenicity, (c) role of the antigen in oncogenicity, (d) specificity, (e) expression level and percent of antigen-positive cells, (f) stem cell expression, (g) number of patients with antigen-positive cancers, (h) number of antigenic epitopes, and (i) cellular location of antigen expression. None of the 75 antigens had all of the characteristics of the ideal cancer antigen. However, 46 were immunogenic in clinical trials and 20 of them had suggestive clinical efficacy in the "therapeutic function" category. These findings reflect the current status of the cancer vaccine field, highlight the possibility that additional organized efforts and funding would accelerate the development of therapeutically effective cancer vaccines, and accentuate the need for prioritization.

Immunity against cyclin B1 tumor antigen delays development of spontaneous cyclin B1-positive tumors in p53 (-/-) mice

We previously identified cyclin B1-specific T cells and antibodies in cancer patients with cyclin B1-positive (+) tumors and also in some healthy individuals. We also demonstrated that these responses may be important in cancer immunosurveillance by showing that vaccination against cyclin B1 prevents growth of transplantable cyclin B1(+) tumors in mice. Constitutive overexpression of cyclin B1 was determined to correlate with the lack of p53 function. This allowed us to use p53(-/-) mice as a model that better approximates human disease. These p53(-/-) mice spontaneously develop cyclin B1(+) tumors. At 5-6 weeks of age, when the mice were still healthy with no evidence of tumor, they received the cyclin B1 vaccine and were then observed for tumor growth. We demonstrate that cyclin B1 vaccination delays spontaneous cyclin B1(+) tumor growth and increases median survival of tumor-bearing p53(-/-) mice.

Tumor-associated MUC1 glycopeptide epitopes are not subject to self-tolerance and improve responses to MUC1 peptide epitopes in MUC1 transgenic mice

Human adenocarcinomas overexpress a hypoglycosylated, tumor-associated form of the mucin-like glycoprotein MUC1 containing abnormal mono- and disaccharide antigens, such as Tn, sialyl-Tn, and TF, as well as stretches of unglycosylated protein backbone in the variable number of tandem repeats (VNTR) region. Both peptide and glycopeptide epitopes generated from the VNTR are candidates for cancer vaccines and we performed experiments to evaluate their relative potential to elicit tumor-MUC1-specific immunity. We show here that immunization with the 100 amino acid-long VNTR peptide (MUC1p) elicits weaker responses in MUC1 transgenic mice compared to wild type mice suggesting self-tolerance. In contrast, when glycosylated with tumor-associated Tn antigen (GalNAc-O-S/T), TnMUC1 induces glycopeptide-specific T cell and antibody responses in both strains of mice and helps enhance responses to MUC1p in MUC1 transgenic mice. Using newly derived MUC1-specific mouse T cell hybridomas we show that the only antigen-presenting cells able to cross-present TnMUC1 glycopeptide are dendritic cells (DCs). This is likely due to their exclusive expression of receptors capable of binding TnMUC1. We conclude that MUC1 glycopeptides induce stronger immunity in MUC1-Tg mice because they are recognized as 'foreign' rather than ;self' and because they are cross-presented preferentially by DCs.

Lentiviral vectors encoding human MUC1-specific, MHC-unrestricted single-chain TCR and a fusion suicide gene: potential for universal and safe cancer immunotherapy

MUC1 tumor antigen is a target for immunotherapy of most human adenocarcinomas and some hematological malignancies. Expression of a MUC1-specific, MHC-unrestricted single-chain T cell receptor (scTCR) on cells of both innate and adaptive immune system through reconstitution of lethally irradiated mice by retroviral vector-transduced bone marrow cells, had been shown to effectively control the growth of MUC1(+) tumors independent of their MHC type, suggesting that this receptor is a good candidate for broadly applicable gene therapy/immunotherapy. However, the translational application of this immuno-gene therapy modality was discouraged by the progressive transgene silencing in reconstituted T and B cells, as well as the potential of tumorogenesis intrinsic to oncoretroviral vectors. To overcome these problems and facilitate the future clinical use of this receptor, we have constructed a panel of novel self-inactivating lentiviral vectors (LVs) which harbor two independent internal promoters, one driving expression of the scTCR gene and the other of a fusion suicide gene, the HSV-TK-EGFP fusion gene, allowing the transduced cells to be destroyable by the pro-drug ganciclovir. Despite the large size of insert, these vectors were efficiently packaged into high titer virus that transferred the expression of transgene in both T cell lines and primary T cells. Sustained expression was maintained in a T cell line for over 4 months in vitro, suggesting its efficient resistance to transgene silencing. Both scTCR and HSV-TK-EGFP genes were functional in the transduced cells, as evidenced by their specific recognition of MUC1(+) tumors and efficient eradication by ganciclovir.

Antigen dose over-rides DC phenotype in the control of CD4+ regulatory T cell induction through reduced Akt/mTOR signaling (89.30)

There is no consensus regarding which features of dendritic cells (DC) are optimal for inducing Foxp3+ regulatory T cells (Treg). Immature DC (iDC) have been shown to induce Tregs in response to foreign and allo-antigens. However, in the autoimmunity setting, mature (mDC) induce tolerance to self antigens by inducing Treg expansion and Th2 differentiation.

We compared the induction of islet autoantigen-specific Treg by mDC, and iDC populations that have distinct phenotypes and cytokine profiles. CD4+ T cells from BDC2.5 TCR Tg mice were cultured in the absence of exogenous TGFβ or IL-2 with iDC or mDC pulsed with high- or low-affinity antigenic peptides.

DC presenting low peptide doses induced weak TCR signaling via the Akt/mTOR pathway, resulting in significant expansion of Foxp3+ Treg. Higher doses of antigenic peptide induced strong Akt/mTOR signaling and favored the expansion of Foxp3- Th cells. The inverse correlation of Foxp3 and Akt/mTOR signaling was also observed in DO11.10 (OVA) and VFT (MUC1) TCR-Tg T cells and could be recapitulated with anti-CD3/CD28 stimulation in the absence of any DC.

These studies indicate that the strength of Akt/mTOR signaling is a critical T cell-intrinsic determinant for Treg vs Th induction. Furthermore, appropriately adjusting the dose of antigenic peptide can override the effect that DC phenotype and cytokine production may play.

Tumor-associated antigen MUC1 contains self epitopes subject to self-tolerance and tumor-associated “foreign” epitopes that elicit effective immunity: important distinction for cancer vaccines (41.60)

Human adenocarcinomas express tumor-associated antigen (TAA) MUC1 that presents to the immune system peptide epitopes as well as glycopeptide epitopes carrying tumor specific carbohydrates. In MUC1-Tg mice responses to MUC1-peptides are suppressed while vaccination with tumor-associated glycopeptides results in effective anti-MUC1 immunity. Transgene negative mice respond equally to both antigens. Using our newly generated TCR transgenic mice with peptide and glycopeptide specific TCRs, we show for the first time that peptide specific CD4 T cells transferred to MUC1-Tg mice are suppressed through mechanisms of peripheral tolerance that are not induced against MUC1-glycopeptide specific CD4 T cells. This tolerance is due to MUC1-peptide epitope presentation in the periphery of healthy MUC1-Tg mice, previously thought to occur primarily in tumor bearing mice. MUC1 glycopeptide epitopes are tumor specific and thus treated as foreign in MUC1-Tg mice, resulting in effective activation of CD4 T cells. Furthermore, glycopeptide-specific T cells provide help to enhance peptide-specific T cell responses. We conclude that TAA contain epitopes that are subject to self tolerance and also tumor specific (foreign) epitopes not affected by self tolerance. It is important to maintain this distinction in attempts to develop effective and safe cancer vaccines. (Supported by NIH T32CA82084, RO1CA56103, CBCRA/CCS)

Humoral immune response to abnormal MUC1 in subjects with colorectal adenoma and cancer

Colorectal cancer (CRC) expresses a hypoglycosylated (abnormal) form of MUC1 different than MUC1 expressed in normal colon, which elicits antibodies in patients with CRC. This form of MUC1 is expressed in other abnormal but non-malignant lesions in the colon, such as adenomatous polyps, precursors to CRC. Estimates of the prevalence of anti-MUC1 antibodies in subjects with these lesions are lacking. We evaluated IgM and IgG anti-MUC1 antibodies in 148 subjects with non-advanced adenomas (NAA), advanced adenomas (AA), colorectal cancer, hyperplastic polyps (HPP), and normal controls. We hypothesized that the prevalence of anti-MUC1 antibodies would increase along the adenoma-carcinoma sequence as more dysplastic tissues express more abnormal MUC1. Anti-MUC1 IgM was found in 5/47 (10.6%) of normals, 5/45 (11.1%) of NAA, 7/47 (14.9%) of AA, and 4/20 (20.0%) of CRC (p=0.70). The prevalence of anti-MUC1 IgG was 8/47 (17.0%) of normals, 14/45 (31.1%) of NAA, 14/47 (29.8%) of AA, and 6/20 (30.0%) of CRC (p=0.36). We found no significant differences in the prevalence of anti-MUC1 antibodies between subjects along the adenoma-carcinoma sequence. However, in an exploratory analysis, the median normalized anti-MUC1 IgG OD level of the combined abnormal groups (NAA, AA, CRC) was significantly higher than the normals (0.045 OD vs. 0.030 OD; p=0.017). Our data support further studies into the potential role of anti-MUC1 immunity in preventing progression of premalignant colon lesions to colon cancer.