Adoptive transfer of T cells that have been genetically modified to express an antitumor T‐cell receptor (TCR) is a potent immunotherapy, but only if TCR avidity is sufficiently high. Endogenous TCRs specific to shared (self) tumor‐associated antigens (TAAs) have low affinity due to central tolerance. Therefore, for effective therapy, anti‐TAA TCRs with higher and optimal avidity must be generated. Here, we describe a new in vitro system for directed evolution of TCR avidity using somatic hypermutation (SHM), a mechanism used in nature by B cells for antibody optimization. We identified 44 point mutations to the Pmel‐1 TCR, specific for the H‐2Db‐gp10025‐33 melanoma antigen. Primary T cells transduced with TCRs containing two or three of these mutations had enhanced activity in vitro. Furthermore, the triple‐mutant TCR improved in vivo therapy of tumor‐bearing mice, which exhibited improved survival, smaller tumors and delayed or no relapse. TCR avidity maturation by SHM may be an effective strategy to improve cancer immunotherapy.
For many years, clinicians and scientists attempt to develop methods to stimulate the immune system to target malignant cells. Recent data suggest that effective cancer vaccination requires combination immunotherapies to overcome tumor immune evasion. Through presentation of both MHC-I and II molecules, DCs-based vaccine platforms are effective in generating detectable CD4 and CD8 T cell responses against tumor-associated antigens. Several platforms include DC transfection with mRNA of the desired tumor antigen. These DCs are then delivered to the host and elicit an immune response against the antigen of interest. We have recently established an mRNA genetic platform which induced specific CD8 cytotoxic T cell response by DC vaccination against melanoma. In our study, an MHC-II mRNA DCs vaccine platform was developed to activate CD4 T cells and to enhance the anti-tumor response. The invariant chain (Ii) was modified and the semi-peptide CLIP was replaced with an MHC-II binding peptide sequences of melanoma antigens. These chimeric MHC-II constructs are presented by DCs and induce proliferation of tumor specific CD4 T cells. When administered in combination with the MHC-I platform into tumor bearing mice, these constructs were able to inhibit tumor growth, and improve mouse survival. Deciphering the immunological mechanism of action, we observed an efficient CTLs killing in addition to higher levels of Th1 and Th2 subsets in the groups immunized with a combination of the MHC-I and MHC-II constructs. These universal constructs can be applied in multiple combinations and offer an attractive opportunity to improve cancer treatment.
Lynch Syndrome (LS) is an autosomal dominant genetic condition that causes a high risk of colorectal cancer. The hallmark of LS is genetic instability as a result of mismatch repair (MMR) deficiency, particularly in repetitive low complexity regions called microsatellites (MS). MLH1−/− mice deficient in MMR are prone to developing tumors in the colon, upon oral administration of dextran sodium sulfate (DSS), at a rate of more than 70%. Using this LS mouse model, we found a novel tumor neo‐antigen from a deletion mutation of the coding MS in the SENP6 gene that prevented tumorigenesis or hindered tumor growth rate in immunized mice. This was accomplished via high throughput exome sequencing of DSS‐induced colorectal tumors in the MLH1−/− mice and predicting the most highly immunogenic mutant gene products processed and presented as antigens in C57BL/6 MHC‐I molecules. Throughout our study, we were able to prove the validity of the vaccine by analyzing the colorectal tumors in immunized DSS‐treated mice using either our epitope, called Sp6D1, or an unrelated peptide as a negative control. Tumors developed in this context were found to be antigenic and Sp6D1‐specific CD8+ tumor infiltrating lymphocytes were detected by flow cytometry and cytotoxic T lymphocytes (CTL) killing assays. Additionally, immunohistochemistry showed that tumor‐adjacent tertiary lymphoid organs were a potentially significant source of CD8+ lymphocytes. Altogether, our results indicate that there may be a protective effect to patients carrying LS mutations through the induction of a peptide‐specific CTL response from the use of neoepitope vaccination.
A T‐cell receptor (TCR) with optimal avidity to a tumor antigen can be used to redirect T cells to eradicate cancer cells via adoptive cell transfer. Cancer testis antigens (CTAs) are attractive targets because they are expressed in the testis, which is immune‐privileged, and in the tumor. However, CTAs are self‐antigens and natural TCRs to CTAs have low affinity/avidity due to central tolerance. We previously described a method of directed evolution of TCR avidity using somatic hypermutation. In this study, we made several improvements to this method and enhanced the avidity of the hT27 TCR, which is specific for the cancer testis antigen HLA‐A2‐MAGE‐A1278‐286. We identified eight point mutations with varying degrees of improved avidity. Human T cells transduced with TCRs containing these mutations displayed enhanced tetramer binding, IFN‐γ and IL2 production, and cytotoxicity. Most of the mutations have retained specificity, except for one mutant with extremely high avidity. We demonstrate that somatic hypermutation is capable of optimizing avidity of clinically relevant TCRs for immunotherapy.
Background Chimeric antigen receptor (CAR)-T cell therapy has shown incredible clinical success for hematopoietic malignancies, but for solid tumors is limited by "on-target offtumor" toxicity to vital organs due to lack of target specificity. We have developed dual CAR-T cells consisting of a canonical activating CAR (aCAR), intended to elicit efficacy in solid tumors, and an inhibitory CAR (iCAR) designed to effectively suppress aCAR activation in normal tissues. The iCAR and aCAR bind distinct cell-surface antigens that are widely co-expressed in normal tissues. The iCAR is allele specific, and targets an antigen that is commonly lost in cancer due to chromosomal loss-of heterozygosity (LOH). Therefore, whereas healthy cells express the iCAR antigen and are protected, tumors have irreversibly lost iCAR antigen expression via LOH and are killed. Methods In this study we developed dual CARs with an aCAR targeting Her2 and iCAR targeting HLA-A2. We screened bicistronic dual CARs in human PBMCs following lentiviral transduction against target cell lines that express normal levels of both antigens paired with targets following CRISPR KO of the HLA-A2 to mimic LOH. In-vitro assays included Luciferase-based killing assays, live-imaging killing assays, and cytokine secretion. In-vivo studies were performed in NSG-mice inoculated with either the HLA-A2+ or HLA-A2 KO targets. Results We optimized the iCAR scFv, hinge, signaling domain, and bicistronic linker to generate dual CARs with high potency and tumor-specificity. These dual CARs were highly active against HLA-A2 KO targets ("tumor") and inhibited against HLA-A2+ targets ("normal tissue"). Conclusions These results show that the iCAR enables the tremendous therapeutic potential of CAR-T therapy to transition to solid tumors while maintaining safety and tumor specificity.
The NRAS oncoprotein is highly mutated in melanoma. However, to date, no comprehensive proteomic study has been reported for NRAS. Here, we utilized the endogenous epitope tagging (EET) approach for the identification of novel NRAS binding partners. Using EET, an epitope tag is added to the endogenously expressed protein, via modification of its genomic coding sequence. Existing EET systems are not robust, suffer from high background, and are labor-intensive. To this end, we present a polyadenylation signal-trap construct for N'-tagging that generates a polycistronic mRNA with the gene of interest. This system requires the integration of the tagging cassette in frame with the target gene to be expressed. Using this design, we demonstrate, for the first time, endogenous tagging of NRAS in melanoma cells allowing the identification of the E3 ubiquitin ligase c-CBL as a novel NRAS binding partner. Thus, our developed EET technology allows the characterization of new RAS effectors, which could be beneficial for the design of future drugs that inhibit constitutive signaling of RAS oncogenic mutants.
Chimeric antigen receptor (CAR)-T cell therapy is a groundbreaking cancer treatment that has produced remarkable clinical efficacy for hematopoietic malignancies, yet “on-target off-tumor” toxicity due to lack of target specificity limits the therapeutic potential of CAR-T cells in solid tumors. We are developing dual CAR-T cells composed of a canonical activator CAR (aCAR), intended to elicit efficacy in solid tumors, and an inhibitory CAR (iCAR) designed to efficiently inhibit the aCAR activity in normal tissue and vital organs. The iCAR and aCAR scFvs of this system bind distinct cell-surface antigens that are widely co-expressed on the normal epithelial from which solid tumors originate. Upon antigen binding, signal propagation through iCAR cytoplasmic domain (iDomain) counteracts aCAR induction of CAR T-cell activation and killing; thus protecting normal tissue. Dual CAR-T cells are activated and kill when exposed to tumor cells that have lost iCAR target expression due to chromosomal loss-of-heterozygosity (LOH) which is common in all cancers. iCAR-targeted LOH generates absolute and irreversible tumor specificity therefore tumor-specific overexpression of the iCAR or aCAR targets is not required. We have carried out a comprehensive screen using human T-cells to identify the most effective inhibitory iDomains derived from cell-surface receptors that naturally inhibit or moderate immune cell activation. The cell-based assay suite developed for this screen consisted of cell lines that co-express iCAR and aCAR target at clinically relevant levels and isogenic partners that mimic LOH through CRISPR editing of the iCAR target. The expression of dual CARs in T cells as biscistronic constructs introduced with lentiviral vectors was successful in a limited number of cases, and it was necessary to develop alternative methods of iCAR aCAR co-expression to complete the screen. Combining aCAR transduction with iCAR mRNA Electroporation (T-REP) proved to be a useful method to disentangle iDomain potency and expression level. The screen identified new iDomains that may expand the potential of iCAR technology in developing strategies to treat solid tumors without compromising efficacy for safety. Citation Format: David Bassan, Jason Yi, Neta Chaim, Nir Bujanover, Sarit Tabak, Tanya Kim, Yael Lopesco, Leehee Weinberger, Kristina Vucci, Michael Weist, Caitlin Schnair, Gregor B. Adams, Orit Foord, Frank J. Calzone, Rick Kendall, Adi Sharbi-Yunger. Incorporation of inhibitory signaling domains into chimeric antigen receptors (iCAR) designed for self-regulation of canonical CAR-T to treat solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2848.
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