The mutational status of p53 can influence its recognition by human T-cells.

p53 was reported to be an attractive immunotherapy target because it is mutated in approximately half of human cancers, resulting in its inactivation and often accumulation in tumor cells. Peptides derived from p53 are presented by class I MHC molecules and may act as tumor-associated epitopes which could be targeted by p53-specific T cells. Interestingly, it was recently shown that there is a lack of significant correlation between p53 expression levels in tumors and their recognition by p53-TCR transduced T cells. To better understand the influence of the mutational status of p53 on its presentation by the MHC system and on T cell antitumor reactivity, we generated several mutant p53 constructs and expressed them in HLA-A2+/p53- cells. Upon co-culture with p53-specific T cells, we measured the specific recognition of p53-expressing target cells by means of cytokine secretion, marker upregulation and cytotoxicity, and in parallel determined p53 expression levels by intracellular staining. We also examined the relevance of antigen presentation components on p53 recognition and the impact of mutant p53 expression on cell-cycle dynamics. Our results show that selected p53 mutations altering protein stability can modulate p53 presentation to T cells, leading to a differential immune reactivity inversely correlated with measured p53 protein levels. Thus, p53 may behave differently than other classical tumor antigens and its mutational status should therefore be taken into account when elaborating immunotherapy treatments of cancer patients targeting p53.

Isolation of neoantigen-specific T cells from tumor and peripheral lymphocytes.

Adoptively transferred tumor-infiltrating T lymphocytes (TILs) that mediate complete regression of metastatic melanoma have been shown to recognize mutated epitopes expressed by autologous tumors. Here, in an attempt to develop a strategy for facilitating the isolation, expansion, and study of mutated antigen-specific T cells, we performed whole-exome sequencing on matched tumor and normal DNA isolated from 8 patients with metastatic melanoma. Candidate mutated epitopes were identified using a peptide-MHC-binding algorithm, and these epitopes were synthesized and used to generate panels of MHC tetramers that were evaluated for binding to tumor digests and cultured TILs used for the treatment of patients. This strategy resulted in the identification of 9 mutated epitopes from 5 of the 8 patients tested. Cells reactive with 8 of the 9 epitopes could be isolated from autologous peripheral blood, where they were detected at frequencies that were estimated to range between 0.4% and 0.002%. To the best of our knowledge, this represents the first demonstration of the successful isolation of mutation-reactive T cells from patients' peripheral blood prior to immune therapy, potentially providing the basis for designing personalized immunotherapies to treat patients with advanced cancer.

Nanomedicine for Cancer Immunotherapy: Tracking Cancer-Specific T-Cells in Vivo with Gold Nanoparticles and CT Imaging.

Application of immune cell-based therapy in routine clinical practice is challenging due to the poorly understood mechanisms underlying success or failure of treatment. Development of accurate and quantitative imaging techniques for noninvasive cell tracking can provide essential knowledge for elucidating these mechanisms. We designed a novel method for longitudinal and quantitative in vivo cell tracking, based on the superior visualization abilities of classical X-ray computed tomography (CT), combined with state-of-the-art nanotechnology. Herein, T-cells were transduced to express a melanoma-specific T-cell receptor and then labeled with gold nanoparticles (GNPs) as a CT contrast agent. The GNP-labeled T-cells were injected intravenously to mice bearing human melanoma xenografts, and whole-body CT imaging allowed examination of the distribution, migration, and kinetics of T-cells. Using CT, we found that transduced T-cells accumulated at the tumor site, as opposed to nontransduced cells. Labeling with gold nanoparticles did not affect T-cell function, as demonstrated both in vitro, by cytokine release and proliferation assays, and in vivo, as tumor regression was observed. Moreover, to validate the accuracy and reliability of the proposed cell tracking technique, T-cells were labeled both with green fluorescent protein for fluorescence imaging, and with GNPs for CT imaging. A remarkable correlation in signal intensity at the tumor site was observed between the two imaging modalities, at all time points examined, providing evidence for the accuracy of our CT cell tracking abilities. This new method for cell tracking with CT offers a valuable tool for research, and more importantly for clinical applications, to study the fate of immune cells in cancer immunotherapy.

An NCR1-based chimeric receptor endows T-cells with multiple anti-tumor specificities.

The Ral (Ras-like) GTP-binding proteins (RalA and RalB), as effectors of the proto-oncogene Natural killer (NK) cells are an important component of the anti-tumor response. Tumor recognition by NK cells was found to be partly triggered by molecules termed natural cytotoxic receptors (NCRs). Adoptive transfer of genetically-engineered tumor-reactive T-lymphocytes can mediate remarkable tumor regressions mostly in melanoma and leukemia patients. Yet, the application of such treatments to other cancers is needed and dependent on the isolation of receptors that could facilitate efficient recognition of these malignancies. Herein, we aimed at combining NK tumor recognition capability with the genetic modification of T-cells to provide the latter with a means to recognize several tumors in a non-MHC restricted way. Consequently, we generated and evaluated several chimeric receptors based on the extracellular domain of NCR1 (NKp46) fused to multiple signaling moieties and assess their antitumor activity when retrovirally expressed in T-cells. Following co-culture with different tumors, primary human T-lymphocytes expressing a chimeric NCR1 molecule recognized target cells derived from lung, cervical carcinoma, leukemia and pancreatic cancer. In addition, this receptor mediated an upregulation of surface activation markers and significant antitumor cytotoxicity both in vitro and in vivo. These results have meaningful implications for the immunotherapeutic treatment of cancer using gene-modified T-cells.

Human T cells engineered to express a programmed death 1/28 costimulatory retargeting molecule display enhanced antitumor activity.

Adoptive transfer of T cells genetically modified to express cancer-specific receptors can mediate impressive tumor regression in terminally ill patients. However, T cell function and persistence over time could be hampered by the activation of inhibitory costimulatory pathways, such as programmed death 1 (PD1)/programmed death ligand 1, leading to T cell exhaustion and providing tumor cells with an escape mechanism from immunosurveillance. In addition, the lack of positive costimulation at the tumor site can further dampen T cell response. Thus, as T cell genetic engineering has become clinically relevant, we aimed at enhancing T cell antitumor activity by genetically diverting T cell-negative costimulatory signals into positive ones using chimeric costimulatory retargeting molecules and which are composed of the PD1 extracellular domain fused to the signaling domains of positive costimulatory molecules such as CD28 and 4-1BB. After characterizing the optimal PD1 chimera, we designed and optimized a tripartite retroviral vector that enables the simultaneous expression of this chimeric molecule in conjunction with a cancer-specific TCR. Human T cells, transduced to express a PD1/28 chimeric molecule, exhibited enhanced cytokine secretion and upregulation of activation markers upon coculture with tumor cells. These engineered cells also proliferated better compared with control cells. Finally, we tested the function of these cells in two xenograft models of human melanoma tumors and show that PD1/28-engineered human T cells demonstrated superior antitumor function. Overall, we propose that engineering T cells with a costimulatory retargeting molecule can enhance their function, which bears important implications for the improvement of T cell immunotherapy.

Enhanced antitumor activity mediated by human 4-1BB-engineered T cells.

4-1BB (CD137) is a costimulatory molecule transiently expressed on the T-cell surface after TCR engagement, whereas its ligand 4-1BBL can be found on professional antigen-presenting cells, but more importantly, also on tumor cells. As the role of the 4-1BB/4-1BBL pathway has emerged central to CD8(+) T-cell responses and survival, we sought to test its relevance in the context of genetically modified human T cells. To that end, T cells purified from healthy donors and from vaccinated-melanoma patients were transduced to express high levels of constitutive 4-1BB. 4-1BB-transduced T cells were cocultured with melanoma tumor lines and exhibited enhanced cytokine secretion, upregulation of activation markers as well as increased cytotoxicity in a chick-chorioallantoic membrane model of human melanoma tumors. In addition, these cells expanded and proliferated at a higher rate, expressed heightened levels of the antiapoptotic molecule Bcl(XL) and were also relatively insensitive to immunosuppression mediated by transforming growth factor-ß, compared to control cells. We also show that 4-1BBL expression on the target cell is essential to 4-1BB-mediated functional improvement. Overall, we conclude that the modification of human T cells with 4-1BB yields enhanced antitumor function which may have important applications in therapies based on the genetic modification of patient lymphocytes.

Incorporation of transmembrane hydrophobic mutations in the TCR enhance its surface expression and T cell functional avidity.

TCR-gene transfer represents an effective way to redirect the specificity of T lymphocytes for therapeutic purposes. Recent successful clinical trials have underscored the potential of this approach in which efficient expression of the exogenous TCR has been directly linked to the efficacy of T cell activity. It has been also demonstrated that the TCR exhibits a lack of stability associated with the presence of positively charged residues in its transmembrane (TM) region. In this study, we designed an original approach selectively to improve exogenous TCR stability by increasing the hydrophobic nature of the TCRα TM region. Incorporation of hydrophobic residues at evolutionarily permissive positions resulted in an enhanced surface expression of the TCR chains, leading to an improved cellular avidity and anti-tumor TCR activity. Furthermore, this strategy was successfully applied to different TCRs, enabling the targeting of human tumors from different histologies. We also show that the combination of these hydrophobic mutations with another TCR-enhancing approach further improved TCR expression and function. Overall, these findings provide information regarding TCR TM composition that can be applied for the improvement of TCR-gene transfer-based treatments.

Selected murine residues endow human TCR with enhanced tumor recognition.

TCR-gene transfer can mediate tumor regression in terminally ill melanoma patients. However, the formation of mix dimers between endogenous and transduced TCR chains may result in the surface dilution of the introduced TCR, which translates in poorer cellular avidity. Recently, we reported that murinization of human TCRs (i.e., the replacement of human C regions by murine ones) can improve TCR function. However, because xenogenic sequences may trigger immunogenicity, we sought to identify the essential murine residues that mediate this enhanced functional effect. We constructed murine/human chimeras of alpha- and beta-chains and assessed for their surface expression and function. We identified an evolutionary-unique lysine residue in Cbeta, central to murine TCR function. The mapping of Calpha revealed that a few short stretches of amino acids play a role in enhancing TCR function, one of the most important ones being the SDVP sequence. This information led us to design improved and minimally murinized human TCR C regions that mediate increased tumor recognition. This also enabled us to suggest a structural model that could explain the role of the aforementioned residues in promoting the preferential pairing and stability of murinized TCRs. Overall, these findings could have implications for the treatment of malignant diseases using TCR-gene transfer.