Activation requirements of circulating antigen-specific human CD8(+) memory T cells probed with insect cell-based artificial antigen-presenting cells

Stronger hepatitis C virus-specific CD8+ T-cell responses in HIV coinfection

Hepatitis C virus (HCV) is a widespread chronic infection that shares routes of transmission with human immunodeficiency virus (HIV). Thus, coinfection with these viruses is a relatively common and growing problem. In general, liver disease develops over years with HIV coinfection, when compared to decades in HCV monoinfection. The role of the immune system in the accelerated pathogenesis of liver disease in HIV/HCV coinfection is not clear. In this study, we compared the frequency, magnitude, breadth and specificity of peripheral blood CD4+ and CD8+ T-cell responses between HCV-monoinfected and HCV/HIV-coinfected individuals and between HIV/HCV-coinfected subgroups distinguished by anti-HCV antibody and HCV RNA status. While HIV coinfection tended to reduce the frequency and breadth of anti-HCV CD8+ T-cell responses in general, responses that were present were substantially stronger than in monoinfection. In all groups, HCV-specific CD4+ T-cell responses were rare and weak, independent of either nadir or concurrent CD4+ T-cell counts of HIV-infected individuals. Subgroup analysis demonstrated restricted breadth of CD8+ HCV-specific T-cell responses and lower B-cell counts in HIV/HCV-coinfected individuals without anti-HCV antibodies. The greatest difference between HIV/HCV-coinfected and HCV-monoinfected groups was substantially stronger HCV-specific CD8+ T-cell responses in the HIV-coinfected group, which may relate to accelerated liver disease in this setting.

Soluble HLA/peptide monomers cross-linked with co-stimulatory antibodies onto a streptavidin core molecule efficiently stimulate antigen-specific T cell responses

Soluble MHC-peptide complexes, commonly referred to as tetramers, have been shown to induce strong cross-linking of TCR and CD8, resulting in a vigorous activation followed by a rapid non-apoptotic CD8(+) T cell death. This has limited tetramer use for antigen-specific T cells isolation and cloning, as sorted tetramer positive cells were shown to possess compromised functional integrity. Here we show that the cross-linking of a secondary co-stimulatory signal into oligomeric MHC:peptide complexes prevents such cell death, and in contrast strongly stimulates antigen-specific T cell responses. Such soluble antigen-presenting complexes (sAPCs) containing MHC:peptide complexes linked to either anti-CD27 or anti-CD28 antibodies were capable of priming and expanding HLA-A*0201 restricted CMV specific T cells and also of generating functional HLA-A*0301 restricted BCR/ABL-specific T cell responses. These sAPCs constitute an encouraging alternative method for generating antigen-specific T cells that could be applied to a variety of antigens.

T-cell artificial focal triggering tools: linking surface interactions with cell response

T-cell activation is a key event in the immune system, involving the interaction of several receptor ligand pairs in a complex intercellular contact that forms between T-cell and antigen-presenting cells. Molecular components implicated in contact formation have been identified, but the mechanism of activation and the link between molecular interactions and cell response remain poorly understood due to the complexity and dynamics exhibited by whole cell-cell conjugates. Here we demonstrate that simplified model colloids grafted so as to target appropriate cell receptors can be efficiently used to explore the relationship of receptor engagement to the T-cell response. Using immortalized Jurkat T cells, we monitored both binding and activation events, as seen by changes in the intracellular calcium concentration. Our experimental strategy used flow cytometry analysis to follow the short time scale cell response in populations of thousands of cells. We targeted both T-cell receptor CD3 (TCR/CD3) and leukocyte-function-associated antigen (LFA-1) alone or in combination. We showed that specific engagement of TCR/CD3 with a single particle induced a transient calcium signal, confirming previous results and validating our approach. By decreasing anti-CD3 particle density, we showed that contact nucleation was the most crucial and determining step in the cell-particle interaction under dynamic conditions, due to shear stress produced by hydrodynamic flow. Introduction of LFA-1 adhesion molecule ligands at the surface of the particle overcame this limitation and elucidated the low TCR/CD3 ligand density regime. Despite their simplicity, model colloids induced relevant biological responses which consistently echoed whole cell behavior. We thus concluded that this biophysical approach provides useful tools for investigating initial events in T-cell activation, and should enable the design of intelligent artificial systems for adoptive immunotherapy.

Potent costimulation of human CD8 T cells by anti-4-1BB and anti-CD28 on synthetic artificial antigen presenting cells

The in vitro generation of cytotoxic T lymphocytes (CTLs) for anticancer immunotherapy is a promising approach to take patient-specific therapy from the bench to the bedside. Two criteria must be met by protocols for the expansion of CTLs: high yield of functional cells and suitability for good manufacturing practice (GMP). The antigen presenting cells (APCs) used to expand the CTLs are the key to achieving both targets but they pose a challenge: Unspecific stimulation is not feasible because only memory T cells are expanded and not rare naïve CTL precursors; in addition, antigen-specific stimulation by cell-based APCs is cumbersome and problematic in a clinical setting. However, synthetic artificial APCs which can be loaded reproducibly with MHC-peptide monomers and antibodies specific for costimulatory molecules could resolve these problems. The purpose of this study was to investigate the potential of complex synthetic artificial APCs in triggering the costimulatory molecules CD28 and 4-1BB on the T cell. Anti-4-1BB antibodies were added to an established system of microbeads coated with MHC-peptide monomers and anti-CD28. Triggering via CD28 and 4-1BB resulted in strong costimulatory synergy. The quantitative ratio between these signals determined the outcome of the stimulation with optimal results when anti-4-1BB and anti-CD28 were applied in a 3:1 ratio. Functional CTLs of an effector memory subtype (CD45RA(-) CCR7(-)) were generated in high numbers. We present a highly defined APC platform using off-the-shelf reagents for the convenient generation of large numbers of antigen-specific CTLs.

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.

Artificial Antigen-Presenting Cells Transduced with Telomerase Efficiently Expand Epitope-Specific, Human Leukocyte Antigen–Restricted Cytotoxic T Cells

Human telomerase reverse transcriptase (hTERT) is overexpressed in most human tumors, making it a potential target for cancer immunotherapy. hTERT-derived CTL epitopes have been identified previously, including p865 (RLVDDFLLV) and p540 (ILAKFLHWL), which are restricted by the human leukocyte antigen (HLA) class I A*0201 allele. However, it remains a major challenge to efficiently and consistently expand hTERT-specific CTLs from donor peripheral blood T lymphocytes. To bypass the need for generating conventional antigen-presenting cells (APC) on an autologous basis, we investigated the potential ability of fibroblast-derived artificial APCs (AAPC) to activate and expand HLA-A*0201-restricted CTLs. We show here that AAPCs stably expressing HLA-A*0201, human beta(2)-microglobulin, B7.1, intercellular adhesion molecule-1, and LFA-3, together with either p540 and p865 minigenes or the full-length hTERT, effectively stimulate tumoricidal, hTERT-specific CTLs. hTERT-expressing AAPCs stimulated both p540 and p865 CTLs as shown by peptide-specific cytolysis and tetramer staining, indicating that hTERT is processed by the AAPCs and that the two peptides are presented as codominant epitopes. The level of cytotoxic activity against a panel of tumors comprising hematologic and epithelial malignancies varied, correlating overall with the level of HLA-A2 and hTERT expression by the target cell. Starting from 100 mL blood, approximately 100 million hTERT-specific CTLs could be generated over the course of five sequential stimulations, representing an expansion of approximately 1 x 10(5). Our data show that AAPCs process hTERT antigen and efficiently stimulate hTERT-specific CTLs from human peripheral blood T lymphocytes and suggest that sufficient expansion could be achieved to be clinically useful for adoptive cell therapy.

Prime boost vaccination strategies: CD8 T cell numbers, protection, and Th1 bias

Vaccination strategies involving priming with DNA and boosting with a poxvirus vector have emerged as a preferred combination for the induction of protective CD8 T cell immunity. Using IFN-gamma ELISPOT and a series of DNA plasmid, peptide, and modified vaccinia Ankara (MVA) vaccine combinations, we demonstrate that the DNA/MVA combination was uniquely able to enhance IFN-gamma secretion by Ag-specific CD8 T cells. However, CD8 T cell populations induced by DNA/MVA vaccination failed to show an enhanced capability to mediate protection in an IFN-gamma-independent influenza challenge model. The DNA/MVA vaccine strategy was also not unique in its ability to induce high numbers of CD8 T cells, with optimal strategies simply requiring the use of vaccine modalities that individually induce high numbers of CD8 T cells. These experiments argue that rivals to DNA/poxvirus vaccination strategies for the induction of optimal protective CD8 T cell responses are likely to emerge.