Intrinsic Expression of Immune Checkpoint Molecule TIGIT Could Help Tumor Growth in vivo by Suppressing the Function of NK and CD8+ T Cells.

TIGIT, an immune checkpoint molecule widely expressed on NK cells, activated T cells and Tregs, has been involved in delivering inhibitory signals through the interaction with PVR. The blockade of TIGIT/PVR interaction is a promising approach in cancer immunotherapy. Here, we unexpectedly discovered the expression of TIGIT in murine tumor cells. To elucidate the mechanism of such intrinsic expression, TIGIT knockout murine colorectal CT26 and MC38 cell lines were generated by using CRISPR/Cas9 system. Although TIGIT knockout showed no effects on proliferation and colony formation of tumor cells in vitro, the tumor growth in mice was considerably inhibited. TIGIT knockout led to the increase of IFN-γ secretion by NK and CD8+ T cells. Further, in BABL/c nude mice, CD8+ T cells depleting mice and NK cells depleting nude mice, the promotion of tumor growth was significantly diminished, suggesting that both NK cells and CD8+ T cells were involved in the tumor promoting process mediated by intrinsic TIGIT. In addition, blocking TIGIT/PVR interaction by the antibody or recombinant PVR protein could elicit anti-tumor effects by facilitating the tumor infiltration and restoring the function of CD8+ T cells, and the antibody-mediate TIGIT blockade could inhibit MC38 tumor growth through blocking TIGIT expressed on tumor cells. We therefore propose a novel TIGIT/PVR interaction mode that tumor intrinsic TIGIT delivers inhibitory signals to CD8+ T cells and NK cells by engaging with PVR.

LncSox4 promotes the self-renewal of liver tumour-initiating cells through Stat3-mediated Sox4 expression.

Liver cancer has a tendency to develop asymptomatically in patients, so most patients are diagnosed at a later stage. Accumulating evidence implicates that liver tumour-initiating cells (TICs) as being responsible for liver cancer initiation and recurrence. However, the molecular mechanism of liver TIC self-renewal is poorly understood. Here we discover that a long noncoding RNA (lncRNA) termed LncSox4 is highly expressed in hepatocellular carcinoma (HCC) tissues and in liver TICs. We find that LncSox4 is required for liver TIC self-renewal and tumour initiation. LncSox4 interacts with and recruits Stat3 to the Sox4 promoter to initiate the expression of Sox4, which is highly expressed in liver TICs and required for liver TIC self-renewal. The expression level of Sox4 correlates with HCC development, clinical severity and prognosis of patients. Altogether, we find that LncSox4 is highly expressed in liver TICs and is required for their self-renewal.

The immunogenicity of a novel cytotoxic T lymphocyte epitope from tumor antigen PL2L60 could be enhanced by 4-chlorophenylalanine substitution at position 1.

PIWIL2, a member of PIWI/AGO family, is expressed in germline stem cells and precancerous stem cells, but not in adult somatic cells. PIWIL2 plays an important role in tumor development. It is considered as a cancer­testis antigen (CT80). It has been reported that the spliced fragment of PIWIL2, PL2L60, was widely expressed in cancer cell lines. In this study, HLA-A2-restricted epitopes from PL2L60 were predicted by online tools. To improve the activity of the native epitope, a candidate peptide P281 with potent binding affinity was chosen to investigate the modification strategy. A series of aromatic amino acids were introduced to substitute the first residue of P281. Then, we tested the binding affinity and stability of the peptide analogs and their ability to elicit specific immune responses both in vitro and in vivo. Our results indicated that the cytotoxic T lymphocytes (CTLs) induced by [4-Cl-Phe1]P281 could elicit more potent activities than that of P281 and other analogs. The CTLs induced by this analog could lyze target cells in HLA-A2-restricted and antigen-specific manners. [4-Cl-Phe1]P281 also showed the best resistance against degradation in human serum. In conclusion, the introduction of the unnatural amino acid, 4-Cl-Phe, into the first position could enhance the activity of the native epitope to induce cytotoxic T lymphocytes. It might be a good strategy to modify other promising native epitopes. The novel epitopes identified in this study could be used as novel candidates to the immunotherapy of HLA-A2 positive patients with tumors expressing PL2L60.

In vitro and in vivo identification of a novel cytotoxic T lymphocyte epitope from Rv3425 of Mycobacterium tuberculosis.

The identification of novel cytotoxic T lymphocyte (CTL) epitopes is important to analysis of the involvement of CD8(+) T cells in Mycobacterium tuberculosis infection as well as to the development of peptide vaccines. In this study, a novel CTL epitope from region of difference 11 encoded antigen Rv3425 was identified. Epitopes were predicted by the reversal immunology approach. Rv3425-p118 (LIASNVAGV) was identified as having relatively strong binding affinity and stability towards the HLA-A*0201 molecule. Peripheral blood mononuclear cells pulsed by this peptide were able to release interferon-γ in healthy donors (HLA-A*02(+) purified protein derivative(+)). In cytotoxicity assays in vitro and in vivo, Rv3425-p118 induced CTLs to specifically lyse the target cells. Therefore, this epitope could provide a subunit component for designing vaccines against Mycobacterium tuberculosis.

Identification of novel T cell epitopes from efflux pumps of Mycobacterium tuberculosis.

Cytotoxic T lymphocytes (CTLs) play an important role in the immunity of Mycobacterium tuberculosis (Mtb) infection. In the present study, the identification of novel CTL epitopes from efflux pumps, Rv1258c and Rv1410c, was reported. Candidate native peptides and their analogues were predicted with prediction programs. Rv1410c-p510 (TLAPQVEPL) and Rv1410c-p510-1Y9V (YLAPQVEPV) showed potent binding affinity and stability towards HLA-A*0201 molecule. In enzyme-linked immunospot (ELISPOT) assay, the CTLs induced from peripheral blood mononuclear cells (PBMCs) by these peptides could release interferon-γ (IFN-γ) in at least one healthy donor (HLA-A*02(+), PPD(+)). In cytotoxicity assay in vitro and in vivo, the CTLs induced by Rv1410c-p510-1Y9V could specifically lyse peptide-loaded T2 cells. This is the first report to identify CTL epitopes from the efflux pumps of Mtb. The novel epitope identified could serve as candidate to the multivalent peptide vaccine against drug-resistant M. tuberculosis.