Cancer vaccines: challenges and potential solutions

Efficient glycoengineering of GM3 on melanoma cell and monoclonal antibody-mediated selective killing of the glycoengineered cancer cell

To verify the principal of a new immunotherapeutic strategy for cancer, a monoclonal antibody 2H3 against N-phenylacetyl GM3, an unnatural form of the tumor-associated antigen GM3, was prepared and employed to demonstrate that murine melanoma cell B16F0 could be effectively glycoengineered by N-phenylacetyl-d-mannosamine to express N-phenylacetyl GM3 and that 2H3 was highly cytotoxic to the glycoengineered B16F0 cell in the presence of complements. It was further demonstrated that B16F0 cell could be glycoengineered 4-5 times more effectively than 3T3 A31 cell, a normal murine embryo fibroblast cell, and that the antibody and complement mediated cytotoxicity was at least 200 times more potent to the glycoengineered B16F0 cell than to the N-phenylacetyl-d-mannosamine-treated 3T3 A31 cell. These results show the promise for developing useful melanoma immunotherapies based on vaccination against N-phenylacetyl GM3 followed by treatment with N-phenylacetyl-d-mannosamine.

Cytokine gene transfer for cancer therapy

The possibility of inducing a strong immune response to impair tumor growth by ectopically expressing cytokines, followed by the generation of an antitumor memory raised great hopes and enthusiasm as a therapeutic approach. However, the efficacy of this strategy on established tumor models appeared low and the initial results in the clinics were disappointing. Recently, new evidence indicates that cytokine gene combination or the combined use of cytokine genes with additional gene therapy approaches induces a synergistic effect supporting the use of cytokine gene therapy to improve the clinical outcome for cancer patients.

Preparation of multifunctional glyconanoparticles as a platform for potential carbohydrate-based anticancer vaccines

A novel platform for anticancer vaccines has been prepared using glyconanotechnology recently developed in our laboratory. Ten different multifunctional gold glyconanoparticles incorporating sialylTn and Lewis(y) antigens, T-cell helper peptides (TT) and glucose in well defined average proportions and with differing density have been synthesised in one step and characterised using NMR and TEM. Size and nature of the linker were crucial to control kinetics of S-Au bond formation and to achieve the desired ligand ratio on the gold clusters. The technology presented here opens the way for tailoring polyvalent anticancer vaccines candidates and drug delivery carriers with defined average chemical composition.

Improving the antigenicity of sTn antigen by modification of its sialic acid residue for development of glycoconjugate cancer vaccines

Sialyl Tn (sTn) antigen is a sialylated disaccharide abundantly expressed by many tumors. To search for effective cancer immunotherapies based on sTn antigen, we designed and synthesized a series of unnatural N-acyl derivatives of sTn and studied their immunological properties. For this purpose, an efficient method was developed to synthesize the natural and unnatural forms of sTn antigen and their protein conjugates. The resultant glycoconjugates were used to immunize C57BL/6 mice, and the immune response was assessed by enzyme-linked immunosorbent assay (ELISA). Whereas the keyhole limpet hemocyanin (KLH) conjugate of sTn elicited low levels of IgM antibodies, the KLH conjugates of N-iso-butanoyl sTn and N-phenylacetyl sTn, especially the latter, induced high titers of antigen-specific IgG antibodies, showing a T-cell-dependent response that is critical for the antitumor activity. The results suggest that the modified forms of sTn, especially N-phenylacetyl sTn, have improved antigenicity and promising immunological properties for use as cancer vaccines.

Combination of vaccination and chimeric receptor expressing T cells provides improved active therapy of tumors

We have generated murine T cells expressing chimeric immune receptors (CR) against human 5T4 oncofetal Ag (h5T4) and evaluated their tumor therapeutic efficacy alone and in combination with immunization using a replication-defective adenovirus encoding h5T4 (Rad.h5T4) and bone marrow-derived dendritic cells (BMDC). The h5T4-specific engineered T cells demonstrated Ag-specific, non-MHC-restricted cytolysis of h5T4-positive B16 and CT26 tumor cells in vitro by cytotoxicity assay and antitumor activity in vivo using a Winn assay. In the s.c. injected B16h5T4 melanoma model, early local but not systemic i.v. administration of syngeneic h5T4-specific CR T cells significantly increased mice survival. This improvement was further enhanced when combined with immunization with Rad.h5T4, followed by post-CR T cell treatment with BMDC in the active therapy model, possibly through mechanisms of enhancing Ag-specific cellular immune responses. This synergistic effect was lost without delivery of the BMDC. Our findings suggest that combining engineered T cells with specific vaccination strategies can improve the active tumor therapy.

Efficient metabolic engineering of GM3 on tumor cells by N-phenylacetyl-D-mannosamine

Abnormal carbohydrates expressed on tumor cells, which are termed tumor-associated carbohydrate antigens (TACAs), are potential targets for the development of cancer vaccines. However, immune tolerance to TACAs has severely hindered progress in this area. To overcome this problem, we have developed a novel immunotherapeutic strategy based on synthetic cancer vaccines and metabolic engineering of TACAs on tumor cells. One critical step of this new strategy is metabolic engineering of cancer, namely, to induce expression of an artificial form of a TACA by supplying tumors with an artificial monosaccharide precursor. To identify the proper precursor for this application, N-propionyl, N-butanoyl, N-isobutanoyl, and N-phenylacetyl derivatives of d-mannosamine were synthesized, and their efficiency as biosynthetic precursors in modifying sialic acid and inducing expression of modified forms of GM3 antigen on tumor cells was investigated. For this purpose, tumor cells were incubated with different N-acyl-d-mannosamines, and modified forms of GM3 expressed on tumor cells were analyzed by flow cytometry using antigen-specific antisera. N-Phenylacetyl-d-mannosamine was efficiently incorporated in a time- and dose-dependent manner to bioengineer GM3 expression by several tumor cell lines, including K562, SKMEL-28, and B16-F0. Moreover, these tumor cell lines also exhibited ManPAc-dependent sensitivity to cytotoxicity mediated by anti-PAcGM3 immune serum and complement. These results provide an important validation for this novel therapeutic strategy. Because N-phenylacetyl GM3-protein conjugates are particularly immunogenic, the combination of an N-phenylacetyl GM3 conjugate vaccine with systemic N-phenylacetyl-d-mannosamine treatment is a promising immunotherapy for future development and application to melanoma and other GM3-bearing tumors.

Synthesis and immunological properties of N-modified GM3 antigens as therapeutic cancer vaccines

The problem of immunotolerance to GM3, an important tumor-associated trisaccharide antigen, seriously hinders its usage in cancer vaccine development. To solve this problem, the keyhole limpet hemocyanin (KLH) conjugates of a series of GM3 derivatives were synthesized and screened as therapeutic cancer vaccines. First, the beta-linked anomeric azides of differently N-acylated GM3 analogues were prepared by a highly convergent procedure. Next, a pentenoyl group was linked to the reducing end of the carbohydrate antigens following selective reduction of the azido group. The linker was thereafter ozonolyzed to give an aldehyde functionality permitting the conjugation of the antigens to KLH via reductive amination. Finally, the immunological properties of the resultant glycoconjugates were studied in C57BL/6 mice by assessing the titers of specific antibodies induced by the GM3 analogues. While KLH-GM3 elicited low levels of immune response, the KLH conjugates of N-propionyl, N-butanoyl, N-iso-butanoyl, and N-phenylacetyl GM3s induced robust immune reactions with antibodies of multiple isotypes, indicating significantly improved and T-cell dependent immune responses that lead to isotype switching, affinity maturation, and the induction of immunological "memory". It was suggested that GM3PhAc-KLH is a promising vaccine candidate for glycoengineered immunotherapy of cancer with GM3 as the primary target.

Therapeutic vaccination with tumor cells that engage CD137

Therapeutic cancer vaccination is based on the finding that tumors in both humans and experimental animals, such as mice, express potential immunological targets, some of which have high selectivity for cancer cells. In contrast to the successful vaccination against some infectious diseases, where most vaccines induce neutralizing antibodies that act prophylactically, the aim of therapeutic cancer vaccines is to treat established tumors (primarily micrometastases). Since most tumor-destructive immune responses are cell-mediated, therapeutic cancer vaccination needs to induce and expand such responses and also to overcome "escape" mechanisms that allow tumors to evade immunological destruction. Tumor antigens (as with other antigens) are presented by "professional" antigen-presenting cells, most notably dendritic cells (DC). Therefore DC that have been transfected or "pulsed" to present antigen provide a logical source of tumor vaccines, and some encouraging results have been obtained clinically as well as in preclinical models. An alternative and more physiological approach is to develop vaccines that deliver tumor antigen for in vivo uptake and presentation by the DC. Vaccines of the latter type include tumor cells that have been modified to produce certain lymphokines or express costimulatory molecules, as well as cDNAs, recombinant viruses, proteins, peptides and glycolipids which are often given together with an adjuvant. Several studies over the past 5 years have demonstrated dramatic therapeutic responses against established mouse tumors as a result of repeated injections of agonistic monoclonal antibodies (MAbs) to the costimulatory molecule CD137 (4-1BB). However, the clinical use of such MAbs may be problematic since they depress antibody formation, for example, to infectious agents. The alternative approach to transfect tumor cells to express the CD137 ligand (CD137L) increases their immunogenicity, but vaccination with tumor cells expressing CD137L is ineffective in several systems where injection of anti-CD137 MAb produces tumor regression. Recent findings indicate that a more effective way to engage CD137 towards tumor destruction is to transfect tumor cells to express a cell-bound form of anti-CD137 single-chain Fv fragments (scFv). Notably, tumors from melanoma K1735, growing either subcutaneously or in the lung, could be eradicated following vaccination with K1735 cells that expressed anti-CD137 scFv. This was in spite of the fact that K1735, as with many human neoplasms, expresses very low levels of MHC class I and has low immunogenicity. Similar results were subsequently obtained with other tumors of low immunogenicity, including sarcoma Ag104. We hypothesize that the concomitant expression of tumor antigen and anti-CD137 scFv effectively engages NK cells, monocytes and dendritic cells, as well as activated CD4(+) and CD8(+) T cells (all of which express CD137) so as to induce and expand a tumor-destructive Th1 response. While vaccines in the form of transfected tumor cells can be effective, at least in mouse models, the logical next step is to construct vaccines that combine genes that encode molecularly defined tumor antigens with a gene that encodes anti-CD137 scFv. Before planning any clinical trials, vaccines that engage CD137 via scFv need to be compared in demanding mouse models for efficacy and side effects with vaccines that are already being tested clinically, including transfected DC and tumor cells producing granulocyte-macrophage colony-stimulating factor.

Single-chain antigen recognition receptors that costimulate potent rejection of established experimental tumors

Tumor cells are usually weakly immunogenic as they largely express self-antigens and can down-regulate major histocompatability complex/peptide molecules and critical costimulatory ligands. The challenge for immunotherapies has been to provide vigorous immune effector cells that circumvent these tumor escape mechanisms and eradicate established tumors. One promising approach is to engineer T cells with single-chain antibody receptors, and since T cells require 2 distinct signals for optimal activation, we have compared the therapeutic efficacy of erbB2-reactive chimeric receptors that contain either T-cell receptor zeta (TCR-zeta) or CD28/TCR-zeta signaling domains. We have demonstrated that primary mouse CD8(+) T lymphocytes expressing the single-chain Fv (scFv)-CD28-zeta receptor have a greater capacity to secrete Tc1 cytokines, induce T-cell proliferation, and inhibit established tumor growth and metastases in vivo. The suppression of established tumor burden by cytotoxic T cells expressing the CD28/TCR-zeta chimera was critically dependent upon their interferon gamma (IFN-gamma) secretion. Our study has illustrated the practical advantage of engineering a T-cell signaling complex that codelivers CD28 activation, dependent only upon the tumor's expression of the appropriate tumor associated antigen.

Calreticulin binding and other biological activities of survival peptide Y-P30 including effects of systemic treatment of rats

Neuron survival-promoting peptide Y-P30, purified from oxidatively stressed neural cell lines, inhibits the appearance of microglia and rescues neurons 1 week after direct application to lesions of the rat cerebral cortex (7). Y-P30 affinity matrices treated with solubilized membranes from a variety of cell lines including human neuroblastoma SY5Y, mouse hippocampal cells HN 33.1, and human promonocytes HL-60, as well as with cerebral cortex tissue from both humans and rats, showed highly specific binding to calreticulin, a ubiquitous calcium binding protein that may be critical for integrin function. Treatment of cultures with 0.1 nM Y-P30 stabilized all these cell types whether differentiated or not, while 1 microM peptide also inhibited the morphological differentiation of the HL-60 cells into macrophages. Western analysis of the medium of SY5Y cell cultures suggested Y-P30-stimulated release of calreticulin, a result consistent with its other biological activities. Likewise, single dose systemic application of Y-P30 in unoperated rats and in rats with cerebral cortex lesions produced significant reductions in cerebral cortex membrane-associated calreticulin. Both direct and intravenous treatment with peptide also reduced cortical neuron atrophy 4 days after these lesions but only direct application consistently inhibited the appearance of ED-1(+) monocyte derivatives. We suggest that in vitro and in vivo mechanisms of Y-P30 effects are similar and involve the targeting of calreticulin. The results also suggest that some of these activities are apparent in the cerebral cortex after systemic application of this peptide.

Identification of a survival-promoting peptide in medium conditioned by oxidatively stressed cell lines of nervous system origin

A survival-promoting peptide has been purified from medium conditioned by Y79 human retinoblastoma cells and a mouse hippocampal cell line (HN 33.1) exposed to H2O2. A 30 residue synthetic peptide was made on the basis of N-terminal sequences obtained during purification, and it was found to exhibit gel mobility and staining properties similar to the purified molecules. The peptide maintains cells and their processes in vitro for the HN 33.1 cell line treated with H2O2, and in vivo for cortical neurons after lesions of the cerebral cortex. It has weak homology with a fragment of a putative bacterial antigen and, like that molecule, binds IgG. The peptide also contains a motif reminiscent of a critical sequence in the catalytic region of calcineurin-type phosphatases; surprisingly, like several members of this family, the peptide catalyzes the hydrolysis of para-nitrophenylphosphate in the presence of Mn2+. Application of the peptide to one side of bilateral cerebral cortex lesions centered on area 2 in rats results in an increase in IgG immunoreactivity in the vicinity of the lesions 7 d after surgery. Microglia immunopositive for IgG and ED-1 are, however, dramatically reduced around the lesions in the treated hemisphere. Furthermore, pyramidal neurons that would normally shrink, die, or disintegrate were maintained, as determined by MAP2 immunocytochemistry and Nissl staining. These survival effects were often found in both hemispheres. The results suggest that this peptide operates by diffusion to regulate the immune response and thereby rescue neurons that would usually degenerate after cortical lesions. The phosphatase activity of this molecule also suggests the potential for direct neuron survival-promoting effects.