Our Science – Greiner Website
John W. Greiner, Ph.D.
Dr. Greiner's research interests are in cancer vaccines and immune adjuvants.
The Cytokine Group studies the interactions of cytokines and T cell checkpoint inhibitors on the different arms of the immune system to optimize antitumor responses to recombinant vaccines and monoclonal antibody therapy. We are working to define novel strategies for the delivery and use of cytokines and T cell checkpoint inhibitors as biologic adjuvants and immunotherapeutics. Additionally, we are involved in the development of new animal models for the analysis of new vaccines and vaccine strategies.
Vector-based Delivery of Tumor Antigens, T-cell Costimulation and Cytokines in the Induction of Immune Responses and Anti-Tumor Immunity: Experimental Systems
Two types of recombinant orthopox vectors are currently being evaluated for the delivery and expression of transgenes for tumor-associated antigens (TAAs), costimulatory molecules, and cytokines. These vectors are the replication competent vaccinia recombinants, and the replication defective avipox recombinants. Experimental studies have determined that the induction of an immune response to a given TAA can be amplified by priming the immune system with a recombinant vaccinia vector followed by multiple booster vaccinations with a recombinant avipox vector. These studies have formed the basis for clinical trials using diversified prime and boost vaccine strategies. Initial studies demonstrated that the insertion of the B7.1 costimulatory molecule transgene gene into an orthopox vector along with a TAA gene can greatly enhance the CD4 and CD8 responses to the TAA. We have now designed and studied recombinant orthopox vectors containing the following costimulatory molecule transgenes: B7.2, ICAM-1 LFA-3, and CD70. Analysis of these recombinants alone and in combinations has demonstrated that a TRIad of COstimulatory Molecules (B7.1, ICAM-1 and LFA-3; acronym TRICOM) will synergize to enhance T-cell responses to levels far greater than that achieved by any one or 2 costimulatory molecules. Recombinant vaccinia and avipox TRICOM vectors have been designed and are in the process of being analyzed; studies to date have demonstrated that when antigen-presenting cells (APC) are infected with TRICOM vectors and pulsed with peptide, the activated T-cells are markedly enhanced for production of type 1 cytokines, but do not undergo any enhanced level of apoptosis. Recombinant orthopox vectors have also been designed that contain the transgene for a model TAA (e.g., carcinoembryonic antigen, CEA) and 3 costimulatory molecule transgenes. These rV-CEA-TRICOM and avipox-CEA-TRICOM vectors are being evaluated in animal models to better form the basis for their subsequent use in clinical trials in patients with CEA-expressing carcinomas. Studies are ongoing and planned to better understand the interactions between the level of signal 1 (through the T-cell receptor) and the level of signal 2 (costimulatory signal(s)) in both the activation of naive T-cells or the induction and maintenance of memory T-cells. Other groups have previously shown that the use of recombinant cytokines such as GM-CSF and low dose IL-2 can enhance T-cell responses to a peptide as protein-based vaccine. We have now shown that the actual delivery of GM-CSF via an avipox-GM-CSF recombinant can lead to enhanced levels of APC, and duration of APC, in regional nodes as compared to the use of recombinant GM-CSF protein. Studies are now planned to determine how to better employ recombinant GM-CSF avipox vectors in vaccine strategies using protein or peptide immunogens and immunogens delivered through orthopox recombinant vectors, and will form the basis for subsequent use in clinical trials. Recent studies have shown the immunotherapeutic potential of several T cell checkpoint inhibitors that target PD-L1. Mechanistically, these antibodies have inherent antitumor properties by unleashing a constitutive antigen-specific T cell response to the tumor. Those observations provide the rationale to embark on studies in in which the T cell checkpoint inhibitors are combined with active immunization protocols. Studies are ongoing and planned in experimental transgenic models to define and understand the synergy between vector-based delivery of signal 1, signal 2 (through 1 or multiple costimulatory molecules) and cytokines/immune modulators in the activation and/or regulation of both naive and memory T-cell responses, and in the induction of anti-tumor responses.
Development of More Valid Animal Models for the Analysis of New Vaccine Strategies
Emphasis is currently being placed on the development of new animal models that are more appropriate for the analysis of new vaccines and vaccine strategies than the conventional prevention or treatment models, where vaccines are given a few days before or after transplant of a rapidly growing tumor. A particular interest has developed in mouse bladder tumor models that utilize intravital imaging of orthotopically instilled bladder tumors. A CEA-transgenic (Tg) mouse, where CEA is a 'self antigen' and is expressed in levels and tissues similar to those in humans, is being employed along with experimental liver metastases expressing CEA positive colon carcinoma cells. Moreover, CEA Tg mice have been crossed with min+ Tg mice; min+ Tg mice contain a mutant APC gene and develop numerous colonic polyps that ultimately cause their death. We have now developed a min+ x CEA+ double transgenic model in which spontaneous colon tumors arise that express CEA. Studies are planned to evaluate new vaccines and vaccine strategies in this and other Tg models. Studies are also ongoing and planned to develop and evaluate other murine models that develop spontaneous tumors, which contain a 'self antigen' as a potential vaccine target.
For a complete list of publications from the Cytokine Group, see 'Links'.
This page was last updated on 6/25/2014.