Lack of evidence for an immunosuppressive role for MUC1

Human MUC1 Mucin: A Multifaceted Glycoprotein

Human MUC1 mucin, a membrane-bound glycoprotein, is a major component of the ductal cell surface of normal glandular cells. MUC1 is overexpressed and aberrantly glycosylated in carcinoma cells. The role MUC1 plays in cancer progression represents two sides of one coin: on the one hand, loss of polarity and overexpression of MUC1 in cancer cells interferes with cell adhesion and shields the tumor cell from immune recognition by the cellular arm of the immune system, thus favoring metastases; on the other hand, MUC1, in essence a self-antigen, is displaced and altered in malignancy and induces immune responses. Tumor-associated MUC1 has short carbohydrate sidechains and exposed epitopes on its peptide core; it gains access to the circulation and comes into contact with the immune system provoking humoral and cellular immune responses. Natural antibodies to MUC1 present in the circulation of cancer patients may be beneficial to the patient by restricting tumor growth and dissemination: early stage breast cancer patients with a humoral response to MUC1 have a better disease-specific survival. Several MUC1 peptide vaccines, differing in vectors, carrier proteins and adjuvants, have been tested in phase I clinical trials. They are capable of inducing predominantly humoral responses to the antigen, but evidence that these immune responses may be effective against the tumor in humans is still scarce.

Specific tumor cell targeting by a recombinant MVA expressing a functional single chain antibody on the surface of intracellular mature virus (IMV) particles

Recombinant vaccinia virus with tumor cell specificity may provide a versatile tool either for direct lysis of cancer cells or for the targeted transfer of genes encoding immunomodulatory or toxic molecules. We report the expression of a tumor-specific single-chain antibody on the surface of intracellular mature vaccinia virus particles (IMV). The wild-type p14 externally membrane-associated protein p14 (A27L gene), which is not required for viral binding and replication, was replaced by p14 fusion molecules carrying a single-chain antibody directed against the tumor-associated antigen MUC-1. MUC-1 mucin is an epithelial cell antigen whose aberrant expression plays a role in autoimmunity and tumor immunity in the majority of human carcinomas and multiple myeloma. Fusion protein carrying the single-chain antibody at the NH2-terminal position was expressed and exposed at the envelope of the corresponding recombinant virus. The construct containing the antibody was able to bind a MUC-1 specific 60mer peptide. Moreover, targeted virus infects MUC-1-expressing cells in vitro more efficiently.

MUC1 as a target antigen for cancer immunotherapy

The cancer-associated antigen MUC1 is overexpressed and modified by tumor cells in over half of all cancer cases. Despite various complexities associated with this antigen, it is well worth pursuing as a vaccine for the immunotherapy of cancer. In this review, the authors describe the discovery of MUC1 and its association with cancer, recent observations showing that the immunology of MUC1 is complicated, animal data showing that it can be a target for immune-mediated tumor rejection, and finally, preliminary clinical results to show that vaccine-based immunotherapy with MUC1 does have an impact on the therapy of cancer.

Metastatic Breast Tumour Regression Following Treatment by a Gene-Modified Vaccinia Virus Expressing MUC1 and IL-2

MUC1 is expressed by glandular epithelial cells. It is overexpressed in the majority of breast tumours, making it a potential target for immune therapy. The objectives of the present study were to evaluate the anti-tumour activity and tolerance of repeated administration of TG1031 (an attenuated recombinant vaccinia virus containing sequences coding for human MUC1 and the immune stimulatory cytokine IL-2) in patients with MUC1-positive metastatic breast cancer. This was an open-label, randomised study comparing two dose levels, 5 x 10E6 and 5 x 10E7, with 14 patients in each arm. The treatment was administered intramuscularly every 3 weeks for the first 4 doses and every 6 weeks thereafter, until progression. Two patients had a partial tumour regression ( > 50%), and 15 patients had stable disease as their best overall response until at least the 5th injection. Partial regression lasted for 11 months in one patient and for 12 months in the second patient who then underwent surgical resection of her hepatic metastases. The most frequent adverse events included inflammation at injection site: 7 patients, itching or pain at injection site: 5 patients, and moderate fever: 6 patients. One responding patient developed antinuclear, anti-DNA, and increased anti-TPO antibodies after the fifth injection, and which resolved at the end of treatment. The treatment regimes were well tolerated with a low toxicity profile. Although clinical efficacy remains limited, this study demonstrates the potential use of MUC1-based immune therapy in breast cancer.

Phase I immunotherapy with a modified vaccinia virus (MVA) expressing human MUC1 as antigen-specific immunotherapy in patients with MUC1-positive advanced cancer

BACKGROUND

The MUC1 protein is a highly glycosylated mucin normally found at the apical surface of mucin-secreting epithelial cells in many types of tissues. MUC1 is expressed, but heavily underglycosylated, in different human tumors. TG4010 is a viral suspension of a recombinant vaccinia vector (MVA) containing DNA sequences coding for the human MUC1 antigen and interleukin-2 (IL-2). This product was developed for use as a vaccine in cancer patients whose tumors express the MUC1 antigen. The objective of the present study was to determine the safety of the product and to define the dose of TG4010 to be used in further clinical trials.

MATERIALS AND METHODS

Thirteen patients with different solid tumors were treated by repeated intramuscular injection with increasing doses of TG4010 in two separate phase I studies, one in Europe (Basel-CR) and one in the United States (UCLA-RF): a total of 6 patients were treated at a dose of 5 x 10(6) pfu, 3 patients at 5 x 10(7) pfu, and 4 patients at 10(8) pfu. Safety, efficacy, and different immunological tests were the endpoints of the study.

RESULTS

Tolerance of TG4010 was excellent, and side effects mainly consisted of injection site pain and influenza-like symptoms. There was no apparent detrimental effect of repeated injections of the vaccinia virus. Four of thirteen evaluable patients showed stabilization of their disease for 6 to 9 months. One lung cancer patient who was initially progressing after the first injections later showed a marked decrease in the size of his metastases that lasted for 14 months. Some T cell proliferative immune responses were seen in five patients.

CONCLUSIONS

The administration of TG4010 was generally well tolerated in patients with metastatic tumors, and transient disease stabilization was observed in several patients, warranting further clinical studies with the product.

Form and pattern of MUC1 expression on T cells activated in vivo or in vitro suggests a function in T-cell migration

MUC1 is a transmembrane mucin that is expressed on ductal epithelial cells and epithelial malignancies and has been proposed as a target antigen for immunotherapy. The expression of MUC1 has recently been reported on T and B cells. In this study we demonstrate that following activation in vivo or activation by different stimuli in vitro, human T cells expressed MUC1 at the cell surface. However, the level of expression in activated human T cells was significantly lower than that seen on normal epithelial cells or on breast cancer cells. In contrast, resting T cells did not bind MUC1-specific monoclonal antibodies (mAbs), nor was MUC1 mRNA detectable by reverse transcription-polymerase chain reaction (RT-PCR) or Northern blot analysis in these cells. The profile of activated T-cell reactivity with different MUC1-specific antibodies suggested that the glycoform of MUC1 expressed by the activated T cells carried core 2-based O-glycans, as opposed to the core 1 structures that dominate in the cancer-associated mucin. Confocal microscopy revealed that MUC1 was uniformly distributed on the surface of activated T cells. However, when the cells were polarized in response to a migratory chemokine, MUC1 was found on the leading edge rather than on the uropod, where other large mucin-like molecules on T cells are trafficked. The concentration of MUC1 at the leading edge of polarized activated human T cells suggests that MUC1 could be involved in early interactions between T cells and endothelial cells at inflammatory sites.

MUC1 and the immunobiology of cancer

The membrane epithelial mucin MUC1 is expressed at the luminal surface of most simple epithelial cells, but expression is greatly increased at lactation and in most breast carcinomas. The increase in level of expression of MUC1 in breast cancer is accompanied by changes in the profile of glycosyl transferases involved in the synthesis of the O-glycans attached to the MUC1 core protein. The cancer-associated mucin is therefore structurally different from the normal mucin, and expresses novel B cell epitopes. MUC1 antibodies are used for in vivo targeting of breast and ovarian tumors, and there is considerable interest in MUC1 as a possible target antigen for the immunotherapy of breast cancer. The different glycoforms can affect cell interactions differently, depending on whether specific interactions with lectins occur. In the absence of such lectin interactions, the long sialylated and negatively charged molecule can inhibit intercellular interactions between other cell surface molecules. The potential role of the different components of the immune system in MUC1 responses are discussed within the framework of how to develop logical strategies for designing clinical studies.

Targeted macrophage cytotoxicity using a nonreplicative live vector expressing a tumor-specific single-chain variable region fragment

Antigen-specific recognition and subsequent destruction of tumor cells is the goal of vaccine-based immunotherapy of cancer. Often, however, tumor antigen-specific cytotoxic T lymphocytes (CTLs) are either not available or in a state of anergy. In addition, MHCI expression on tumor cells is often downregulated. Either or both of these situations can allow tumor growth to proceed unchecked by CTL control. We have shown previously that tumor antigen-specific monoclonal antibodies can be expressed in vaccinia virus and that activated macrophages infected with this virus acquire the ability to kill tumor cells expressing that antigen. Here we show that a membrane-anchored form of the scFv portion of the MUC1 tumor antigen-specific monoclonal antibody, SM3, can be expressed on activated macrophages with the highly attenuated poxvirus, modified vaccinia Ankara (MVA), as a gene transfer vector. Cells infected with the MVA-scFv construct were shown to express the membrane-bound scFv by Western blot and FACS analysis. That cells expressing the membrane-anchored scFv specifically bind antigen was shown by FACS and by BIAcore analysis. GM-CSF-activated macrophages were infected with the construct and shown to recognize specifically MUC1-expressing tumor cells as measured by IL-12 release. Furthermore, activated macrophages expressing the membrane-bound scFv specifically lyse target cells expressing the MUC1 antigen but not cells that do not express MUC1.

Lack of evidence for MHC-unrestricted (atypical) recognition of mucin by mucinous pancreatic tumour-reactive T-cells

Cytotoxic T-cells generated against heterologous, mucinous pancreatic tumour cells were shown to recognize mucin in a major histocombatibility complex (MHC)-unrestricted fashion. In contrast, the present study demonstrates a typical allogeneic response of heterologous cytotoxic T-cells established against mucin-expressing pancreatic tumour cells. Heterologous cytotoxic T cells lysed targets that were used as stimulators and other targets that shared human leucocyte antigen (HLA) with the stimulator. These cytotoxic T-cells lysed mucin-expressing stimulator cells but not autologous tumour cells in spite of expressing mucin on their surface. Likewise, tumour-infiltrating CD4+ T-cells proliferated against its own tumour cell target, while such T-cells did not respond to heterologous, mucin-expressing pancreatic tumour cells. Culturing heterologous tumour-specific cytotoxic T-cells with purified pancreatic tumour cell-mucin rendered them unresponsive to their target cells. Furthermore, purified mucin did not produce a mucin-specific response in mucinous pancreatic tumour patients' primary T-cells even in the presence of antigen-presenting cells. Our study finds no evidence for MHC-unrestricted recognition of mucin by pancreatic cancer patients' T-cells.