Application of xCELLigence real-time cell analysis to the microplate assay for pertussis toxin induced clustering in CHO cells.

The microplate assay with Chinese Hamster Ovary (CHO) cells is currently used as a safety test to monitor the residual pertussis toxin (PT) amount in acellular pertussis antigens prior to vaccine formulation. The assay is based on the findings that the exposure of CHO cells to PT results in a concentration-dependent clustering response which can be used to estimate the amount of PT in a sample preparation. A major challenge with the current CHO cell assay methodology is that scoring of PT-induced clustering is dependent on subjective operator visual assessment using light microscopy. In this work, we have explored the feasibility of replacing the microscopy readout for the CHO cell assay with the xCELLigence Real-Time Cell Analysis system (ACEA BioSciences, a part of Agilent). The xCELLigence equipment is designed to monitor cell adhesion and growth. The electrical impedance generated from cell attachment and proliferation is quantified via gold electrodes at the bottom of the cell culture plate wells, which is then translated into a unitless readout called cell index. Results showed significant decrease in the cell index readouts of CHO cells exposed to PT compared to the cell index of unexposed CHO cells. Similar endpoint concentrations were obtained when the PT reference standard was titrated with either xCELLigence or microscopy. Testing genetically detoxified pertussis samples unspiked or spiked with PT further supported the sensitivity and reproducibility of the xCELLigence assay in comparison with the conventional microscopy assay. In conclusion, the xCELLigence RTCA system offers an alternative automated and higher throughput method for evaluating PT-induced clustering in CHO cells.

Replacing the in vivo toxin challenge test with an in vitro assay for assessment of potency for diphtheria toxoid containing vaccines.

Replacement of the potency tests for diphtheria vaccines is a high priority for the international initiative to reduce, refine, and replace animal use in vaccine testing. Diphtheria toxoid containing vaccine products marketed in the US currently require potency testing by the United States Public Health Service (USPHS) test, which includes an in vivo passive protection test with a diphtheria toxin challenge. Here we describe an in vitro Diphtheria Vero Cell (DVC) assay which combines the immunization approach from the USPHS test and the use of a cell based neutralization assay for serological testing of vaccine potency. The DVC assay reduces the overall number of animals used compared to other serological potency tests and eliminates the in vivo toxin challenge used in the US test. The DVC assay can be used to test vaccine products with a low or high diphtheria toxoid dose. It has been optimized and validated for use in a quality control testing environment. Results demonstrate similar sera antibody unitage as well as agreement between the serum neutralization values determined using the USPHS test and the DVC assay and thus support the use of the DVC assay for routine and stability testing for diphtheria toxoid containing vaccine products.

Preclinical qualification of a new multi-antigen candidate vaccine for metastatic melanoma.

New therapies are urgently required for the treatment of patients with melanoma. Here we describe the generation and preclinical evaluation of 3 new recombinant ALVAC(2) poxviruses vCP2264, vCP2291, and vCP2292 for their ability to induce the desired cellular immune responses against the encoded melanoma-associated antigens. This was done either in HLA-A2/K transgenic mice or using in vitro antigen-presentation studies. These studies demonstrated that the vaccine was able to induce HLA-A*0201-restricted T-cell responses against gp100 and NY-ESO-1, detectable directly ex vivo, in HLA-A2/K-transgenic mice. The in vitro antigen presentation studies, in the absence of appropriate animal models, demonstrated that target cells infected with the vaccine construct were lysed by MAGE-1, MAGE-3 or MART-1 peptide-specific T cells. These data indicate that ALVAC(2)-encoded melanoma-associated antigens can be properly processed and presented to induce antigen-specific cytotoxic T-cell responses. To enhance the immunogenicity of the melanoma antigens, a TRIad of COstimulatory Molecules (TRICOM) were also cloned into all 3 vectors. Increased in vitro proliferation and IFN-γ production was observed with all ALVAC(2) poxviruses encoding TRICOM, confirming the immune-enhancing effect of the ALVAC-encoded TRICOM. These studies demonstrated that all components of the vaccine were functionally active and provide a rationale for moving this candidate vaccine to the clinic.

Combination chemotherapy and ALVAC-CEA/B7.1 vaccine in patients with metastatic colorectal cancer.

PURPOSE: The combination of vaccines and chemotherapy holds promise for cancer therapy, but the effect of cytotoxic chemotherapy on vaccine-induced antitumor immunity is unknown. This study was conducted to assess the effects of systemic chemotherapy on ALVAC-CEA/B7.1-induced T-cell immunity in patients with metastatic colorectal cancer. EXPERIMENTAL DESIGN: Patients with metastatic colorectal cancer were treated with fluorouracil, leucovorin, and irinotecan and were also given ALVAC-CEA/B7.1 vaccine with or without tetanus toxoid adjuvant. Eligible patients were randomized to ALVAC followed by chemotherapy and booster vaccination (group 1), ALVAC and tetanus toxoid followed by chemotherapy (group 2), or chemotherapy alone followed by ALVAC in patients without disease progression (group 3). Humoral immune responses were measured by standard ELISA assay, and carcinoembryonic antigen (CEA)-specific T-cell responses were measured by IFN-gamma enzyme-linked immunospot assay. RESULTS: One hundred eighteen patients were randomized to receive either ALVAC before and concomitantly with chemotherapy (n = 39), ALVAC with tetanus adjuvant before and concomitantly with chemotherapy (n = 40), or chemotherapy followed by ALVAC (n = 39). Serious adverse events were largely gastrointestinal (n = 30) and hematologic (n = 24). Overall, 42 patients (40.4%) showed objective clinical responses. All patients developed antibody responses against ALVAC, but increased anti-CEA antibody titers were detected in only three patients. Increases in CEA-specific T cells were detected in 50%, 37%, and 30% of patients in groups 1, 2, and 3, respectively. There were no differences in clinical or immune responses between the treatment groups. CONCLUSION: The combination of ALVAC-CEA/B7.1 vaccine and systemic chemotherapy has an acceptable safety profile in patients with metastatic colorectal cancer. Systemic chemotherapy did not affect the generation of CEA-specific T-cell responses following vaccination.