Background
The use of antigen-specific T cells for adoptive immunotherapy of patients with advanced cancers is emerging as a promising treatment modality [1]-[3]. Recent trials using genetic modification of T cells to introduce chimeric antigen receptors (CAR's) or T cell receptors (TCR's) and redirect their target specificity to tumor cells can be remarkably effective in reducing tumor burden and providing durable remissions in B cell malignancies and some solid tumors [4]-[10]. However, the regulatory and logistical hurdles of gene transfer can be prohibitive and issues such as receptor mispairing (for TCRs), target antigen affinity, and serious, occasionally life-threatening, even lethal on-target toxicities remain to be fully addressed [11],[12]. Although once fully characterized, these genetically modified approaches may be quite expedient, they first require a priori possession of the relevant receptor sequence from the cognate antibody for a CAR or a T cell clone for a TCR as well as rigorous validation, all of which limit the flexibility of this approach and incur significant obstacles to bringing a cell product to the clinic V体育ios版.
An alternative approach, involves the isolation of circulating endogenous antigen-specific T cells from the peripheral blood (Endogenous T Cell Therapy or ETC) and ex vivo expansion for adoptive transfer. Although these tumor-reactive T cells can be present at very low frequency, the feasibility of isolating and expanding endogenous antigen-specific CTL from the peripheral blood of patients for adoptive therapy has been demonstrated in trials targeting melanocyte antigens such as gp100 and MART-1 in melanoma, with intriguing evidence of clinical efficacy [2],[13]. The endogenous frequency of CTL targeting melanocyte antigens such as MART-1 is particularly high (up to 1%) enabling facile generation of MART-1-specific T cells using conventional approaches [2],[13],[14]. However, for more commonly expressed tumor antigens such as WT-1, MAGE family antigens and NY-ESO-1, the generation of antigen-specific cytotoxic T lymphocytes (CTL) has been labor and resource-intensive and largely unsuccessful on a routine basis due to their relatively rare endogenous precursor frequencies (<1:10,000) VSports最新版本.
With the exception of MART-1 and some tumor-associated viral antigens, generation of antigen-specific T cells using a conventional approach involving repeated cycles of autologous PBMC stimulation using peptide-pulsed dendritic cells (DC's) often fails to enrich low frequency tumor-reactive CTL to numbers sufficient for expansion and adoptive transfer.
To address this issue, we previously discovered that the addition of IL-21 during the initial priming period could increase the total number of antigen-specific CD8 T cells by >20-fold and, at the clonal level, enrich for a population of high-affinity CD8 T cells with sustained elevation of CD28 levels and a helper-independent phenotype. This enrichment can be further enhanced by depletion of CD25+ Treg cells from the responder PBMC prior to in vitro stimulation [15]-[17], leading to a synergistic increase in the yield of antigen-specific CTL to 2-300 fold greater than those cultures that were CD25 replete and not exposed to IL-21 [18],[19] VSports注册入口.
Therefore, to broaden the scope of patients eligible for adoptive therapy and the tumors that can be treated, we chose to target a prototypic cancer-testis antigen, NY-ESO-1, expressed by several solid tumor malignancies, including breast cancer, lung cancer, melanoma, sarcoma and ovarian cancer V体育官网入口. We developed a strategy where NY-ESO-1 specific T cells were first enriched through in vitro stimulation of CD25 depleted PBMC [17] with peptide pulsed dendritic cells in the presence of IL-21, followed by tetramer guided cell sorting to isolate and expand autologous NY-ESO-1-specific CTL from the peripheral blood of patients with sarcoma under clinically compliant manufacturing conditions.
To determine whether highly avid, oligoclonal NY-ESO-1 specific CD8+ T cells recognizing NY-ESO-1 positive tumor cell lines could be consistently isolated from patients who might benefit from NY-ESO-1 targeted therapy, we focused on patients with synovial sarcoma (SS) and myxoid/round cell liposarcoma (MRCL) because these tumors homogenously express NY-ESO-1, often with high intensity [20],[21]. We successfully isolated NY-ESO-1 specific T cells from 6 of 6, NY-ESO-1 expressing sarcoma patients using a clinical grade INFLUX cell sorter (Becton Dickson) and propagated these highly enriched populations to sufficient numbers for adoptive immunotherapy VSports在线直播.