Boosting T cell costimulation in cancer: the possibilities seem endless

Enterotoxins can support CAR T cells against solid tumors

Responses of solid tumors to chimeric antigen receptor (CAR) T cell therapy are often minimal. This is potentially due to a lack of sustained activation and proliferation of CAR T cells when encountering antigen in a profoundly immunosuppressive tumor microenvironment. In this study, we investigate if inducing an interaction between CAR T cells and antigen-presenting cells (APCs) in lymphoid tissue, away from an immunosuppressive microenvironment, could enhance solid-tumor responses. We combined CAR T cell transfer with the bacterial enterotoxin staphylococcal enterotoxin-B (SEB), which naturally links a proportion of T cell receptor (TCR) Vβ subtypes to MHC-II, present on APCs. CAR T cell proliferation and function was significantly enhanced by SEB. Solid tumor-growth inhibition in mice was increased when CAR T cells were administered in combination with SEB. CAR T cell expansion in lymphoid tissue was demonstrated, and inhibition of lymphocyte egress from lymph nodes using FTY720 abrogated the benefit of SEB. We also demonstrate that a bispecific antibody, targeting a c-Myc tag on CAR T cells and cluster of differentiation 40 (CD40), could also enhance CAR T cell activity and mediate increased antitumor activity of CAR T cells. These model systems serve as proof-of-principle that facilitating the interaction of CAR T cells with APCs can enhance their ability to mediate antitumor activity.

Intratumoral delivery of vector mediated IL-2 in combination with vaccine results in enhanced T cell avidity and anti-tumor activity

Systemic IL-2 is currently employed in the therapy of several tumor types, but at the price of often severe toxicities. Local vector mediated delivery of IL-2 at the tumor site may enhance local effector cell activity while reducing toxicity. To examine this, a model using CEA-transgenic mice bearing established CEA expressing tumors was employed. The vaccine regimen was a s.c. prime vaccination with recombinant vaccinia (rV) expressing transgenes for CEA and a triad of costimulatory molecules (TRICOM) followed by i.t. boosting with rF-CEA/TRICOM. The addition of intratumoral (i.t.) delivery of IL-2 via a recombinant fowlpox (rF) IL-2 vector greatly enhanced anti-tumor activity of a recombinant vaccine, resulting in complete tumor regression in 70-80% of mice. The anti-tumor activity was shown to be dependent on CD8(+) cells and NK1.1(+). Cellular immune assays revealed that the addition of rF-IL-2 to the vaccination therapy enhanced CEA-specific tetramer(+) cell numbers, cytokine release and CTL lysis of CEA(+) targets. Moreover, tumor-bearing mice vaccinated with the CEA/TRICOM displayed an antigen cascade, i.e., CD8(+) T cell responses to two other antigens expressed on the tumor and not the vaccine: wild-type p53 and endogenous retroviral antigen gp70. Mice receiving rF-IL-2 during vaccination demonstrated higher avidity CEA-specific, as well as higher avidity gp70-specific, CD8(+) T cells when compared with mice vaccinated without rF-IL-2. These studies demonstrate for the first time that the level and avidity of antigen specific CTL, as well as the therapeutic outcome can be improved with the use of i.t. rF-IL-2 with vaccine regimens.

CTLA-4 expressed by chemoresistant, as well as untreated, myeloid leukaemia cells can be targeted with ligands to induce apoptosis

We have previously reported that about 80% of acute myeloid leukaemia (AML) samples tested at diagnosis constitutively expressed cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4). The present study compared CTLA-4 expression and function of leukaemic cells from AML patients at diagnosis with those from AML patients resistant to conventional chemotherapy. We also explored the possibility of targeting CTLA-4 for apoptosis induction in chemoresistant AML cells. AML cells either from untreated patients (n = 15) or in chemoresistant phase (n = 10) were analysed for CTLA-4 protein and transcript expression by flow cytometry and reverse transcription-polymerase chain reaction respectively. CTLA-4 expression was similar in untreated and in chemoresistant samples and was not associated with patients' clinical features. In chemoresistant AML cells, CTLA-4 transduced an apoptotic signal on engagement with its recombinant ligands r-CD80 and r-CD86, which induced an average of 71% and 62% apoptotic cells, respectively, at highest concentration. Apoptosis was equally induced in untreated leukaemic cells accompanied by cleavage of procaspase-8 and -3. Thus, this study provides the first evidence that killing of leukaemic cells from AML patients may be obtained by the engagement of CTLA-4 with its ligands, opening the way to a novel potential therapeutic approach based on triggering the CTLA-4 molecule to circumvent chemoresistance in AML.

PANVAC-VF: poxviral-based vaccine therapy targeting CEA and MUC1 in carcinoma

PANVAC is a cancer vaccine therapy delivered through two viral vectors--recombinant vaccinia and recombinant fowlpox--which are given sequentially. Both vectors contain transgenes for the tumor-associated antigens epithelial mucin 1 and carcinoembryonic antigen, which are altered or overexpressed in most carcinomas. The vectors also contain transgenes for three human T cell costimulatory molecules required to enhance immune response: B7.1, intracellular adhesion molecule-1 and leukocyte function-associated antigen-3. PANVAC is injected subcutaneously and processed by the body's antigen-presenting cells. Preclinical studies have demonstrated the efficacy of PANVAC in inducing both carcinoembryonic antigen- and mucin 1-specific cytotoxic T lymphocyte responses in vitro and in murine models. Other strategies that enhance the immune response include the use of granulocyte-macrophage colony-stimulating factor and a prime-boost administration sequence. Clinical trials have demonstrated PANVAC's safety and its ability to induce antigen-specific T cell responses. Early clinical trials are evaluating PANVAC alone and in combination with conventional chemotherapy and/or radiation. Studies to date hold promise for the use of PANVAC as a means to stimulate the immune system against malignancies and to provide clinical benefit.

Development of the PANVAC-VF vaccine for pancreatic cancer

PANVAC-VF is a vaccine regimen composed of a priming dose of recombinant vaccinia virus and booster doses of recombinant fowlpox virus expressing carcinoembryonic antigen, mucin-1 and a triad of costimulatory molecules (TRICOM), which include B7.1, intercellular adhesion molecule-1 and leukocyte function-associated antigen-3. Vaccination is administered by subcutaneous injection followed by 4 days of local recombinant adjuvant granulocyte-macrophage colony-stimulating factor at the vaccination site. The vaccine has been developed for patients with advanced pancreatic cancer and has now entered a randomized Phase III clinical trial. This review will describe the background of recombinant poxvirus technology for tumor vaccine development, detail the key preclinical studies supporting the regimen, review the clinical trials supporting the current Phase III study, and highlight the key challenges and future obstacles to successful implementation of PANVAC-VF for pancreatic cancer.

B7-1-HSA (CD80-CD24), a recombinant hybrid costimulatory molecule retains ligand binding and costimulatory functions

Optimal activation of naïve T lymphocyte requires two signals; an antigen-specific signal initiated by engagement of TCR with the antigen-MHC complex and a costimulatory signal independent of the antigen receptor complex. Without the costimulatory signal, T cells become anergic. Various adhesion molecules, such as B7-1 (CD80) and heat stable antigen (HSA, CD24), expressed on antigen presenting cells have been demonstrated to provide costimulatory signals to T cells. It was reported that the combinations of different adhesion molecules could induce even stronger immune response. In this study, we made a hybrid costimulatory molecule, B7-1-HSA, and tested its T cell stimulatory function. Chinese hamster ovary (CHO) cells expressing this hybrid molecule bound both anti-CD80 and anti-CD24 monoclonal antibodies, and induced stronger T cell proliferation than CHO cells expressing B7-1 or HSA alone. These results suggest that the B7-1-HSA hybrid molecule can deliver two costimulatory signals simultaneously that can synergize in inducing T cell proliferation. The purified B7-1-HSA protein reacted with both anti-B7-1 and anti-HSA mAbs in Western blotting and specifically mediated adhesion of Jurkat cells. Furthermore, purified B7-1-HSA molecule spontaneously incorporated onto cell membrane through its glycolipid anchor suggesting that this hybrid costimulatory molecule can be used in protein transfer to develop effective cancer vaccines.

Therapeutic peptidomimetic strategies for autoimmune diseases: costimulation blockade*

Cognate interactions between immune effector cells and antigen-presenting cells (APCs) govern immune responses. Specific signals occur between the T-cell receptor peptide and APCs and nonspecific signals between pairs of costimulatory molecules. Costimulation signals are required for full T-cell activation and are assumed to regulate T-cell responses as well as other aspects of the immune system. As new discoveries are made, it is becoming clear how important these costimulation interactions are for immune responses. Costimulation requirements for T-cell regulation have been extensively studied as a way to control many autoimmune diseases and downregulate inflammatory reactions. The CD28:B7 and the CD40:CD40L families of molecules are considered to be critical costimulatory molecules and have been studied extensively. Blocking the interaction between these molecules results in a state of immune unresponsiveness termed 'anergy'. Several different strategies for blockade of these interactions are explored including monoclonal antibodies (mAbs), Fab fragments, chimeric, and/or fusion proteins. We developed novel, immune-specific approaches that interfere with these interactions. Using experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis mediated by central nervous system (CNS)-specific T-cells, we developed a multi-targeted approach that utilizes peptides for blockade of costimulatory molecules. We designed blocking peptide mimics that retain the functional binding area of the parent protein while reducing the overall size and are thus capable of blocking signal transduction. In this paper, we review the role of costimulatory molecules in autoimmune diseases, two of the most well-studied costimulatory pathways (CD28/CTLA-4:B7 and CD40:CD40L), and the advantages of peptidomimetic approaches. We present data showing the ability of peptide mimics of costimulatory molecules to suppress autoimmune disease and propose a mechanism for disease suppression.