Ganglioside-based vaccines and anti-idiotype antibodies for active immunotherapy against cancer

One-Pot Enzymatic Synthesis and Biological Evaluation of Ganglioside GM3 Derivatives as Potential Cancer Immunotherapeutics

Cancer is a leading cause of death worldwide. Recent research studies have revealed that GM3 derivatives have considerable promise as potential therapeutic agents for cancer. To discover novel GM3 derivatives as potential antitumor agents, a one-pot enzymatic synthesis was established, yielding 14 GM3 derivatives in high total yields (22-41%). Subsequently, the inhibitory activities of GM3 derivatives were assessed by wound-healing assays and Transwell assays and tumor-bearing animal models. Among all the GM3 derivatives, N-12 showed excellent migration and invasion inhibitory effects in cells and marked antitumor activity in C57BL/6 mice. The subsequent analysis of cancer tissues and serum samples revealed that N-12 induces tumor inhibition, which was closely related to immune response. Taken together, N-12 can be further developed as an effective therapeutic for the treatment of cancer. An RNA-sequencing (RNA-seq) analysis was then performed and indicated that the antitumor mechanism of N-12 involved focal adhesion and ECM-receptor interaction signaling pathways.

Frequent co-expression of EGFR and NeuGcGM3 ganglioside in cancer: it's potential therapeutic implications

Interaction between epidermal growth factor receptor (EGFR) signaling with GM3 ganglioside expression has been previously described. However, little is known about EGFR and NeuGcGM3 co-expression in cancer patients and their therapeutic implications. In this paper, we evaluate the co-expression of EGFR and NeuGcGM3 ganglioside in tumors from 92 patients and in two spontaneous lung metastasis models of mice (Lewis lung carcinoma (3LL-D122) in C57BL/6 and mammary carcinoma (4T1) in BALB/c). As results, co-expression of EGFR and NeuGcGM3 ganglioside was frequently observed in 63 of 92 patients (68 %), independently of histological subtype. Moreover, EGFR is co-expressed with NeuGcGM3 ganglioside in the metastasis of 3LL-D122 and 4T1 murine models. Such dual expression appears to be therapeutically relevant, since combined therapy with mAbs against these two molecules synergistically increase the survival of mice treated. Overall, our results suggest that NeuGcGM3 and EGFR may coordinately contribute to the tumor cell biology and that therapeutic combinations against these two targets might be a valid strategy to explore.

Recent Advance in Tumor-associated Carbohydrate Antigens (TACAs)-based Antitumor Vaccines

Cancer cells can be distinguished from normal cells by displaying aberrant levels and types of carbohydrate structures on their surfaces. These carbohydrate structures are known as tumor-associated carbohydrate antigens (TACAs). TACAs were considered as promising targets for the design of anticancer vaccines. Unfortunately, carbohydrates alone can only evoke poor immunogenicity because they are unable to induce T-cell-dependent immune responses, which is critical for cancer therapy. Moreover, immunotolerance and immunosuppression are easily induced by using natural occurring TACAs as antigens due to their endogenous property. This review summarizes the recent strategies to overcome these obstacles: (1) covalently coupling TACAs to proper carriers to improve immunogenicity, including clustered or multivalent conjugate vaccines, (2) coupling TACAs to T-cell peptide epitopes or the built-in adjuvant to form multicomponent glycoconjugate vaccines, and (3) developing vaccines based on chemically modified TACAs, which is combined with metabolic engineering of cancer cells.

Superior Efficacy and Safety of a Nonemulsive Variant of the NGcGM3/VSSP Vaccine in Advanced Breast Cancer Patients

NGcGM3 ganglioside is a tumor-specific antigen expressed in human breast tumors. The NGcGM3/VSSP vaccine, consisting in very small-sized proteoliposomes (VSSP) obtained by the incorporation of NGcGM3 into the outer membrane protein complex of Neisseria meningitidis, has been previously tested in a Phase II trial in patients with metastatic breast cancer (MBC) but emulsified with Montanide ISA 51. An Expanded Access study was carried out in MBC patients aiming to find if a nonemulsive formulation of NGcGM3/VSSP, without Montanide ISA 51, could be more safe and effective. A total of 104 patients were vaccinated with the nonemulsive formulation (900 μg), subcutaneously (SC), or with the emulsive formulation (200 μg), intramuscularly (IM). An intent-to-treat analysis of efficacy was performed with all patients, and 93 patients were split off according to the site of metastases (visceral/nonvisceral). Of note, SC-treated patients exhibited a superior median overall survival (OS) than IM-treated patients (23.6 vs. 8.2 months; log rank P = 0.001). Even though in the subset of patients with nonvisceral metastases SC vaccination duplicated the median OS compared to the alternative option (31.6 vs. 16.5 months), this difference did not reach statistical significance (log rank P = 0.118). Curiously, in patients with visceral metastases, the advantage of the nonemulsive formulation was more apparent (median OS 21.0 vs. 6.2 months; log rank P = 0.005). The vaccine was safe for both formulations.

Induction of leukocyte infiltration at metastatic site mediates the protective effect of NGcGM3-based vaccine

While the NGcGM3/VSSP vaccine, a preparation consisting in very small sized proteoliposomes (VSSP) obtained by the incorporation of the NGcGM3 ganglioside into the outer membrane protein (OMP) complex of Neisseria meningitides, is currently studied in late stage clinical trials in breast cancer and melanoma patients, mechanisms involved in the vaccine's antitumor effect are insufficiently understood. Here we have addressed the role of adaptive and innate immune cells in mediating the protective effect of the vaccine. To this aim we selected the 3LL-D122 Lewis lung spontaneous metastasis model. Unexpectedly, inoculation of the vaccine in tumor bearing C57BL/6 mice, either by subcutaneous (sc) or intraperitoneal (ip) routes, induced similar anti-metastatic effect. Regardless the T-independent nature of NGcGM3 ganglioside as antigen, the antimetastatic effect of NGcGM3/VSSP is dependent on CD4(+) T cells. In a further step we found that the vaccine was able to promote the increase, maturation, and cytokine secretion of conventional DCs and the maturation of Bone Marrow-derived plasmacytoid DCs. In line with this result the in vivo IFNα serum level in ip vaccinated mice increased as soon as 2h after treatment. On the other hand the infiltration of NK1.1(+)CD3(-) and NK1.1(+)CD3(+) cells in lungs of vaccinated mice was significantly increased, compared with the presence of these cells in control animal lungs. In the same way NGcGM3/VSSP mobilized acquired immunity effector cells into the lungs of vaccinated tumor bearing mice. Finally and not less noteworthy, leukocyte infiltration in lungs of tumor bearing mice correlates with vaccine induced inhibition of lung metastization.

Carbohydrate antigen delivery by water soluble copolymers as potential anti-cancer vaccines

Tumor associated carbohydrate antigens (TACAs) are overexpressed on tumor cells, which renders them attractive targets for anti-cancer vaccines. To overcome the poor immunogenicity of TACAs, we designed a polymer platform for antigen presentation by co-delivering TACA and helper T (Th) cell epitope on the same chain. The block copolymer was synthesized by cyanoxyl-mediated free radical polymerization followed by conjugation with a TACA Tn antigen and a mouse Th-cell peptide epitope derived from polio virus (PV) to afford the vaccine construct. The glycopolymer vaccine elicited an anti-Tn immune response with significant titers of IgG antibodies, which recognized Tn-expressing tumor cells.

Antibody recognition of cancer-related gangliosides and their mimics investigated using in silico site mapping

Modified gangliosides may be overexpressed in certain types of cancer, thus, they are considered a valuable target in cancer immunotherapy. Structural knowledge of their interaction with antibodies is currently limited, due to the large size and high flexibility of these ligands. In this study, we apply our previously developed site mapping technique to investigate the recognition of cancer-related gangliosides by anti-ganglioside antibodies. The results reveal a potential ganglioside-binding motif in the four antibodies studied, suggesting the possibility of structural convergence in the anti-ganglioside immune response. The structural basis of the recognition of ganglioside-mimetic peptides is also investigated using site mapping and compared to ganglioside recognition. The peptides are shown to act as structural mimics of gangliosides by interacting with many of the same binding site residues as the cognate carbohydrate epitopes. These studies provide important clues as to the structural basis of immunological mimicry of carbohydrates.

Recent Development in Carbohydrate Based Anti-cancer Vaccines

The development of carbohydrate based anti-cancer vaccines is of high current interests. Herein, the latest development in this exciting field is reviewed. After a general introduction about tumor associated carbohydrate antigens and immune responses, the review is focused on the various strategies that have been developed to enhance the immunogenecity of these antigens. The results from animal studies and clinical trials are presented.

Intravenous immunoglobulin-based immunotherapy: an arsenal of possibilities for patients and science

The use of intravenous immunoglobulin (IVIG) concentrated from pooled healthy donors' plasma has gained increasing popularity. IVIG therapy has become important as a replacement therapy in primary and acquired humoral immunodeficiencies, and it has been extended to autoimmune, neurodegenerative and inflammatory conditions and transplantation therapy. Recurrent pregnancy failure and cancer are rather new platforms, where IVIG has shown its beneficial effects. This manuscript is focused on these two off-labelled usages. The immunomodulatory mechanisms of IVIG therapy appear as a coordinated orchestration of different functions, resulting in a synergistic effect. Treatment monitoring and detailed molecular analyses reveal how such treatments may interfere with disease pathogenesis. These finding may foster the development of novel therapeutic and/or preventive strategies. Studying this field with bidirectional bench-to-bedside and bedside-to-bench approaches fit well into 'the two-way road' paradigm of translational medicine.

NGcGM3 ganglioside: a privileged target for cancer vaccines

Active specific immunotherapy is a promising field in cancer research. N-glycolyl (NGc) gangliosides, and particularly NGcGM3, have received attention as a privileged target for cancer therapy. Many clinical trials have been performed with the anti-NGc-containing gangliosides anti-idiotype monoclonal antibody racotumomab (formerly known as 1E10) and the conjugated NGcGM3/VSSP vaccine for immunotherapy of melanoma, breast, and lung cancer. The present paper examines the role of NGc-gangliosides in tumor biology as well as the available preclinical and clinical data on these vaccine products. A brief discussion on the relevance of prioritization of cancer antigens in vaccine development is also included.

Tumour-associated carbohydrate antigens in breast cancer

Glycosylation changes that occur in cancer often lead to the expression of tumour-associated carbohydrate antigens. In breast cancer, these antigens are usually associated with a poor prognosis and a reduced overall survival. Cellular models have shown the implication of these antigens in cell adhesion, migration, proliferation and tumour growth. The present review summarizes our current knowledge of glycosylation changes (structures, biosynthesis and occurrence) in breast cancer cell lines and primary tumours, and the consequences on disease progression and aggressiveness. The therapeutic strategies attempted to target tumour-associated carbohydrate antigens in breast cancer are also discussed.

Anti-idiotypic antibody mimicking a T-antigen-specific lectin inhibits human epithelial tumor cell proliferation

Cancer-associated mucins show frequent alterations of oligosaccharide chain profile. Terminal structures may be deleted, thereby exposing normally 'cryptic' structures such as Tn (GalNAcα-O-Ser/Thr) and T antigen (Galβ1-3GalNAcα-O-Ser/Thr). Overexpression of these commonly hidden glycoforms, and reduced level of naturally occurring anti-T or anti-Tn antibodies, is associated with epithelial tumor progression and aggressiveness. The lectin from the common edible mushroom Agaricus bisporus (ABL) shows high affinity binding to T antigen, and reversible noncytotoxic inhibitory effect on epithelial tumor cell proliferation. The aim of this study was to induce immune response with tumor-associated glycan specificity and biological activity similar to those of ABL. An anti-idiotypic (Id) antibody strategy was developed using ABL as first template. ABL was purified by affinity chromatography and assayed as immunogen in rabbit. Rabbit IgG was purified from anti-ABL serum using a protein G column, and specific anti-ABL IgG was obtained by affinity chromatography using immobilized ABL. Affinity-purified anti-ABL IgG contained an antibody fraction that recognizes the carbohydrate-binding site of ABL. This IgG was used as immunogen in mouse to yield anti-Id antibody recognizing tumor-associated glycans such as Tn and T antigen. Competitive assays showed that α-anomeric GalNAc is the main binding subsite of anti-Id antibody in glycan recognition. Anti-Id antibody bound human epithelial tumor cells, as shown by cell enzyme-linked immunosorbent assay and immunofluorescence. Anti-Id antibody raised by immunization with affinity-purified anti-ABL IgG had antiproliferative effect on human epithelial tumor cells through apoptosis induction similar to that of ABL. The anti-Id immune response developed here has potential application in cancer therapy.

Detection and characterization of N-glycolyated gangliosides in Wilms tumor by immunohistochemistry

Gangliosides are glycolipids present on the cell surface. The N-glycolylated ganglioside NeuGc-GM3 has been described in some neoplasms, such as breast carcinoma and melanoma, but is usually not detected in normal human cells. Our aim was to evaluate the presence of NeuGc-GM3 in Wilms tumor by immunohistochemistry. Postchemotherapy tumors were grouped into different histologic subtypes considering the main preserved component. Formalin-fixed, paraffin-embedded tumor samples were cut into 5-microm sections. The monoclonal antibody 14F7, a mouse IgG1 that specifically recognizes NeuGc-GM3, and a peroxidase-labeled polymer conjugated to secondary antibodies were used. Sections from breast carcinoma were employed as positive controls. Presence of NeuGc-GM3 was evident in 22 of 25 (88%) cases. The staining was stronger in the epithelial component, with a membrane pattern and cytoplasmic diffusion. The stromal component expressed cytoplasmic NeuGc-GM3 in cells with rhabdomyoblastic differentiation. Tubules of adjacent renal tissue were also positive, but no expression of NeuGc-GM3 was detected in nontumoral fetal kidney. Until now, the expression of N-glycolylated gangliosides in pediatric solid tumors has not been investigated. The present study evidenced the expression of NeuGc-GM3 in a high proportion of Wilms tumors, suggesting its potential utility as a specific target of immunotherapy.

Exogenous incorporation of neugc-rich mucin augments n-glycolyl sialic acid content and promotes malignant phenotype in mouse tumor cell lines

Background

Carbohydrates embedded in the plasma membrane are one of the main actors involved in the communication of cells with the microenvironment. Neuraminic sialic acids are glycocalyx sugars that play important roles in the modulation of malignant cell behaviour. N-glycolylneuraminic acid (NeuGc) is synthesized by the cytidine monophospho-N-acetylneuraminic acid hydroxylase (CMAH), an enzyme expressed in all mammals except humans. In mice, this sugar is synthesized in several somatic tissues.

Methods

We used the B16 melanoma and F3II mammary carcinoma mouse tumor cell lines. By CMAH directed RT-PCR and NeuGc detection with the specific anti-NeuGc-GM3 antibody 14F7 we evaluated enzyme and ganglioside expression in tumor cells, respectively. Expression of NeuGc-GM3 ganglioside was reached by in vitro incubation with NeuGc-rich bovine submaxillary mucin and evaluated by slot-blot and immunohistochemistry assays using the 14F7 antibody. Tumor cells treated with mucin or purified NeuGc were injected s.c. and i.v. in syngeneic mice to evaluate tumor and metastatic growth.

Results

In the present work we demonstrated the absence of expression of CMAH enzyme in B16 melanoma and F3II mammary carcinoma cells. In vitro incubation of these NeuGc-negative cells with NeuGc-rich mucin increased the presence of NeuGc in cell membranes for at least 48-72 h, as a component of the GM3 ganglioside. Preincubation with NeuGc-rich mucin reduced tumor latency and increased the metastatic potential of tumor cells in syngeneic animals. Similar results were obtained when cells were incubated with purified NeuGc alone.

Conclusion

Our results indicate that B16 and F3II mouse tumor cell lines do not express NeuGc in cell membranes but they are able to incorporate NeuGc from an exogenous source, contributing to the malignant phenotype of melanoma and mammary carcinoma cells.

De-N-acetyl GM3 promotes melanoma cell migration and invasion through urokinase plasminogen activator receptor signaling-dependent MMP-2 activation

We have recently discovered that de-N-acetyl GM3 [NeuNH(2)LacCer, d-GM3], a derivative of ganglioside GM3, is specifically expressed in metastatic tumor cells and that its expression correlates with an enhanced metastatic phenotype. Although the classic N-acetylated form of GM3 (NeuAcLacCer, c-GM3) is found in both normal and tumor cells, metastatic tumor cells (but not other cells) predominantly express d-GM3 (82-95% of total GM3). d-GM3 expression is mainly found in metastatic melanomas, but not in benign nevi or the majority of primary melanomas. Using metastatic (d-GM3-positive) and poorly invasive (d-GM3-negative) human melanoma cell lines, we found that d-GM3 stimulates cell migration and invasion by increasing the expression and activation of urokinase-like plasminogen activator (uPA). Further studies showed that d-GM3 activates matrix metalloproteinase-2 (MMP-2), but not MMP-9, when uPA receptor signaling is activated. These results implicate d-GM3 as a specific marker for metastatic melanoma and a novel therapeutic target for neoplastic diseases.

Innate-immunity cytokines induced by very small size proteoliposomes, a Neisseria-derived immunological adjuvant

Neisserial outer membrane proteins have been combined with monosialoganglioside GM3 to form very small size proteoliposomes (VSSP), a nanoparticulated formulation used as a cancer vaccine for the treatment of cancer patients with GM3-positive tumours. VSSP were shown to elicit anti-GM3 and anti-tumour immune responses. VSSP have also been shown to be an efficient adjuvant for tumour-cell and peptide-antigen vaccines in mice. In vitro studies showed that VSSP promote maturation of both murine and human dendritic cells, suggesting that VSSP could be used as efficient adjuvants. In order to study further the capacity of VSSP to elicit innate immune responses, human peripheral blood mononuclear cells and monocytes derived thereof were assessed for in vitro secretion of interleukin (IL)-10, IL-6, IL-12 and interferon (IFN)-gamma. VSSP most prominently induced the secretion of IL-6. IL-10 was secreted at a lower level. IL-12 p40 (but no p70) was also detected. IFN-gamma response was observed in 56% of the tested samples. Cytokine secretion was not related to lipopolysaccharide (LPS) content and involved Toll-like receptor 2 (TLR2)-mediated signal transduction. VSSP also induced DC maturation and a cytokine secretion pattern (high IL-6/low IL-10) which differs from that induced by LPS. The observed proinflammatory cytokine secretion pattern and the capacity of VSSP to drive DC maturation are examined in the light of the properties of other bacterial derivatives currently being user for immunotherapy purposes. Our results suggest that VSSP could be tested in clinical settings where T helper 1-type immune responses would be beneficial.

Glycosphingolipid expression in squamous cell carcinoma of the upper aerodigestive tract

Glycosphingolipids are integral constituents of cellular membrane, arranged in rafts, and with neoplasic cell antisocial behavior, like uncontrolled cell growth, invasiveness, and metastatic potential.

Aim

However, there are few studies about glycosphingolipids (GSL) expression in squamous cell carcinoma (SCC). Since GSL are known to be tumor-associated markers we decided to perform a prospective study on the GSL profiles of SCC.

Method

Specimens of 33 SCC and normal mucosa were obtained and GSLs were extracted and purified by reverse-phase chromatography on C18 column and alkaline hydrolysis in methanol. GSLs were quantified using densitometry of orcinol-stained HPTLC plates.

Result

A significant increase of GSLs in SCC (3.57µg/mg) was observed as compared to normal mucosa (1.92µg/mg). In SCC, an increase of 2 to 3 times in the amounts of CDH, CTH, Globoside, and GM3 was observed in comparison to normal mucosa. The identification of GM3 as well as its increased expression in SCC was confirmed unequivocally by HPTLC immunostaining and indirect immunofluorescence using MAb DH2 (anti-GM3). BY analyzing SCC and normal mucosa CMHs by GC/MS, normal mucosa expresses only glucosylceramide whereas SCC cells express both glucosylceramide and galactosylceramide.

Conclusion

The increase in the amount of GSLs in tumor tissue may represent changes of cell membrane microdomains resulting from the malignant transformation process, which is responsible for greater cell-cell or cell-matrix interaction thereby increasing their potential for infiltration and metastasis.

Human gliosarcoma-associated ganglioside composition is complex and distinctive as evidenced by high-performance mass spectrometric determination and structural characterization

Gangliosides (GGs), involved in malignant alteration and tumor progression/invasiveness, are considered as tumor biomarkers or therapeutic targets. Here, we describe the first systematic GG composition characterization in human gliosarcoma versus normal brain tissue using our recently developed mass spectrometry (MS) methods, based on nano-electrospray (nano-ESI), Fourier-transform ion cyclotron resonance (FT-ICR), and chip nano-ESI quadrupole time-of-flight (QTOF), complemented by thin-layer chromatographic (TLC) analysis and quantification. Combined MS enabled detection and structural assignment of 73 distinct GG species: many more than reported so far for investigated gliomas. Apart from the 7.4-times lower total GG content, gliosarcoma contained all major brain-associated species, however, in very altered proportions, exhibiting a highly distinctive pattern: GD3 (48.9%)>GD1a/nLD1>GD2/GT3>GM3>GT1b>GM2>GM1a/GM1b/nLM1>LM1>GD1b>GQ1b. MS also revealed abundant O-Ac-GD3; its sequencing provided structural evidence to postulate a novel O-Ac-GD3 isomer O-acetylated at the inner Neu5Ac-residue, previously not structurally confirmed. The high sensitivity and mass accuracy permitted the assignment of unusual minor species: GM4, Hex-HexNAc-nLM1, Gal-GD1, Fuc-GT1, GalNAc-GT1, O-Ac-GM3, di- O-Ac-GD3O-Ac-GD3, and O-Ac-GT3, not previously reported as glioma-associated. The gliosarcoma-expressed GA2 might represent a marker distinguishing astrocytic from oligodendroglial tumors. This is, to our knowledge, so far the most complete GG composition characterization of certain glioma, which demonstrates that our MS-based approach could provide essential structural information relevant to glycosphingolipid role(s) in brain tumor biology, differential diagnosis/prognosis and novel treatment concepts.

Ganglioside GM3 promotes carcinoma cell proliferation via urokinase plasminogen activator-induced extracellular signal-regulated kinase-independent p70S6 kinase signaling

Overexpression of NeuAcalpha2-3Galbeta1-4Glcbeta1-Cer (GM3), a major ganglioside of cutaneous tumor cell membranes, inhibits ligand-dependent and ligand-independent activation of the epidermal growth factor (EGF) receptor in normal and neoplastic epithelial cells. This leads to the suppression of Ras/extracellular signal-regulated kinase (ERK) activation and, in the presence of EGF or fibronectin, inhibits cell proliferation. However, some tumor cells show increased levels of GM3, and vaccines that target GM3 can inhibit the growth of neoplastic cells in vivo, especially melanomas. We report that in the presence of urokinase plasminogen activator (uPA), overexpression of GM3 paradoxically increases the proliferation of carcinoma cells by augmenting ERK-independent p70S6 kinase activation. Functional blockade of uPA receptor (uPAR) or inhibition of p70S6 kinase, but not inhibition of Ras/ERK signaling, suppresses this GM3-induced stimulation of cell proliferation. The ERK-independent activation of p70S6 kinase involves phosphorylation at threonine-389, threonine-421/serine-424, and serine-411 sites with intermediate phosphatidylinositol 3 kinase and protein kinase C-zeta activation. These studies implicate gangliosides as enhancers of uPAR-related signaling and suggest that the response to GM3 depends on the local concentration of uPA. Therapeutic modalities that target or supplement gangliosides may require concomitant treatment that suppresses EGFR or uPAR signaling, respectively, to control neoplastic cell proliferation.

Cellular and humoral immune response to N-Glycolyl-GM3 elicited by prolonged immunotherapy with an anti-idiotypic vaccine in high-risk and metastatic breast cancer patients

In this study, the immunogenicity and toxicity profile of 1E10, an anti-idiotypic vaccine mimicking the N-glycolyl-GM3 ganglioside, was investigated with an extended vaccination protocol. The year-long vaccination scheme consisted of 6 biweekly intradermal injections (induction phase), followed by 10 monthly boosters (maintenance). Nineteen patients with high-risk (stage III) or metastatic breast cancer were vaccinated with different dose levels of 1E10 (0.5, 1, and 2 mg). The humoral and cellular responses to 1E10 and the targeted ganglioside were assessed at baseline and throughout the treatment. Local skin reactions represented the most common adverse event (National Cancer Institute Toxicity Criteria (NCIC) grades I and II), followed by mild flu-like symptoms lasting for 1 to 2 days. Two patients were removed from the study because of vaccine-related hypersensitivity reactions. A third patient was removed from the study after a transient loss of consciousness with uncertain relation to the vaccine. All patients showed a strong antibody response to the targeted ganglioside. In addition, ganglioside-specific T-cell responses were recorded in 5 of 13 evaluable patients. Vaccination with 1E10 was immunogenic and relatively well tolerated. Because similar results were observed with the 3 tested dose levels, the 0.5-mg dose level was selected for future trials.