Immune Checkpoints and CAR-T Cells: The Pioneers in Future Cancer Therapies?

Although the ever-increasing number of cancer patients pose substantial challenges worldwide, finding a treatment with the highest response rate and the lowest number of side effects is still undergoing research. Compared to chemotherapy, the relatively low side effects of cancer immunotherapy have provided ample opportunity for immunotherapy to become a promising approach for patients with malignancy. However, the clinical translation of immune-based therapies requires robust anti-tumoral immune responses. Immune checkpoints have substantial roles in the induction of an immunosuppressive tumor microenvironment and tolerance against tumor antigens. Identifying and targeting these inhibitory axes, which can be established between tumor cells and tumor-infiltrating lymphocytes, can facilitate the development of anti-tumoral immune responses. Bispecific T-cell engagers, which can attract lymphocytes to the tumor microenvironment, have also paved the road for immunological-based tumor elimination. The development of CAR-T cells and their gene editing have brought ample opportunity to recognize tumor antigens, independent from immune checkpoints and the major histocompatibility complex (MHC). Indeed, there have been remarkable advances in developing various CAR-T cells to target tumoral cells. Knockout of immune checkpoints via gene editing in CAR-T cells might be designated for a breakthrough for patients with malignancy. In the midst of this fast progress in cancer immunotherapies, there is a need to provide up-to-date information regarding immune checkpoints, bispecific T-cell engagers, and CAR-T cells. Therefore, this review aims to provide recent findings of immune checkpoints, bispecific T-cell engagers, and CAR-T cells in cancer immunotherapy and discuss the pertained clinical trials.

Epigenetic regulation of tumor necrosis factor α (TNFα) release in human macrophages by HIV-1 single-stranded RNA (ssRNA) is dependent on TLR8 signaling.

Human macrophages at mucosal sites are essential targets for acute HIV infection. During the chronic phase of infection, they are persistent reservoirs for the AIDS virus. HIV virions gain entry into macrophages following ligation of surface CD4-CCR5 co-receptors, which leads to the release of two copies of HIV ssRNA. These events lead to reverse transcription and viral replication initiation. Toll-like receptors TLR7 and TLR8 recognize specific intracellular viral ssRNA sequences, but in human alveolar macrophages, their individual roles in TLR-mediated HIV ssRNA recognition are unclear. In the current study, HIV-1 ssRNA induced TNFα release in a dose-dependent manner in adherent human macrophages expressing both intracellular TLR7 and TLR8. This response was reduced by inhibiting either endocytosis (50 µm dynasore) or endosomal acidification (1 µg/ml chloroquine). Either MYD88 or TLR8 gene knockdown with relevant siRNA reduced HIV-1 ssRNA-mediated TNFα release, but silencing TLR7 had no effect on this response. Furthermore, HIV-1 ssRNA induced histone 4 acetylation at the TNFα promoter as well as trimethylation of histone 3 at lysine 4, whereas TLR8 gene knockdown reduced these effects. Taken together in human macrophages, TLR8 binds and internalizes HIV ssRNA, leading to endosomal acidification, chromatin remodeling, and increases in TNFα release. Drugs targeting macrophage TLR8-linked signaling pathways may modulate the innate immune response to acute HIV infection by reducing viral replication.

Direct CD1d-mediated stimulation of APC IL-12 production and protective immune response to virus infection in vivo.

CD1d-restricted NKT cells rapidly stimulate innate and adaptive immunity through production of Th1 and/or Th2 cytokines and induction of CD1d(+) APC maturation. However, therapeutic exploitation of NKT cells has been hampered by their paucity and defects in human disease. NKT cell-APC interactions can be modeled by direct stimulation of human APCs through CD1d in vitro. We have now found that direct ligation with multiple CD1d mAbs also stimulated bioactive IL-12 release from CD1d(+) but not CD1d knockout murine splenocytes in vitro. Moreover, all of the CD1d mAbs tested also induced IL-12 as well as both IFN-gamma and IFN-alpha in vivo from CD1d(+) but not CD1d-deficient recipients. Unlike IFN-gamma, CD1d-induced IFN-alpha was at least partially dependent on invariant NKT cells. Optimal resistance to infection with picornavirus encephalomyocarditis virus is known to require CD1d-dependent APC IL-12-induced IFN-gamma as well as IFN-alpha. CD1d ligation in vivo enhanced systemic IL-12, IFN-gamma, and IFN-alpha and was protective against infection by encephalomyocarditis virus, suggesting an alternative interpretation for previous results involving CD1d "blocking" in other systems. Such protective responses, including elevations in Th1 cytokines, were also seen with CD1d F(ab')(2)s in vivo, whereas an IgM mAb (with presumably minimal tissue penetration) was comparably effective at protection in vivo as well as cytokine induction both in vivo and in vitro. Although presumably acting immediately "downstream," CD1d mAbs were protective later during infection than the invariant NKT cell agonist alpha-galactosylceramide. These data indicate that NKT cells can be bypassed with CD1d-mediated induction of robust Th1 immunity, which may have therapeutic potential both directly and as an adjuvant.

Effects of the administration of high-dose interleukin-2 on immunoregulatory cell subsets in patients with advanced melanoma and renal cell cancer.

PURPOSE: High-dose recombinant human interleukin-2 (IL-2) therapy is of clinical benefit in a subset of patients with advanced melanoma and renal cell cancer. Although IL-2 is well known as a T-cell growth factor, its potential in vivo effects on human immunoregulatory cell subsets are largely unexplored. EXPERIMENTAL DESIGN: Here, we studied the effects of high-dose IL-2 therapy on circulating dendritic cell subsets (DC), CD1d-reactive invariant natural killer T cells (iNKT), and CD4(+)CD25(+) regulatory-type T cells. RESULTS: The frequency of both circulating myeloid DC1 and plasmacytoid DC decreased during high-dose IL-2 treatment. Of these, only a significant fraction of myeloid DC expressed CD1d. Although the proportion of Th1-type CD4(-) iNKT increased, similarly to DC subsets, the total frequency of iNKT decreased during high-dose IL-2 treatment. In contrast, the frequency of CD4(+)CD25(+) T cells, including CD4(+)Foxp3(+) T cells, which have been reported to suppress antitumor immune responses, increased during high-dose IL-2 therapy. However, there was little, if any, change of expression of GITR, CD30, or CTLA-4 on CD4(+)CD25(+) T cells in response to IL-2. Functionally, patient CD25(+) T cells at their peak level (immediately after the first cycle of high-dose IL-2) were less suppressive than healthy donor CD25(+) T cells and mostly failed to Th2 polarize iNKT. CONCLUSIONS: Our data show that there are reciprocal quantitative and qualitative alterations of immunoregulatory cell subsets with opposing functions during treatment with high-dose IL-2, some of which may compromise the establishment of effective antitumor immune responses.

Novel HIV-1 miRNAs stimulate TNFα release in human macrophages via TLR8 signaling pathway.

PURPOSE: To determine whether HIV-1 produces microRNAs and elucidate whether these miRNAs can induce inflammatory response in macrophages (independent of the conventional miRNA function in RNA interference) leading to chronic immune activation. METHODS: Using sensitive quantitative Real Time RT-PCR and sequencing, we detected novel HIV-derived miRNAs in the sera of HIV+ persons, and associated with exosomes. Release of TNFα by macrophages challenged with HIV miRNAs was measured by ELISA. RESULTS: HIV infection of primary alveolar macrophages produced elevated levels of viral microRNAs vmiR88, vmiR99 and vmiR-TAR in cell extracts and in exosome preparations from conditioned medium. Furthermore, these miRNAs were also detected in exosome fraction of sera from HIV-infected persons. Importantly, vmiR88 and vmiR99 (but not vmiR-TAR) stimulated human macrophage TNFα release, which is dependent on macrophage TLR8 expression. These data support a potential role for HIV-derived vmiRNAs released from infected macrophages as contributing to chronic immune activation in HIV-infected persons, and may represent a novel therapeutic target to limit AIDS pathogenesis. CONCLUSION: Novel HIV vmiR88 and vmiR99 are present in the systemic circulation of HIV+ persons and could exhibit biological function (independent of gene silencing) as ligands for TLR8 signaling that promote macrophage TNFα release, and may contribute to chronic immune activation. Targeting novel HIV-derived miRNAs may represent a therapeutic strategy to limit chronic immune activation and AIDS progression.

Circulating myeloid dendritic cells of advanced cancer patients result in reduced activation and a biased cytokine profile in invariant NKT cells.

CD1d-restricted invariant NKT (iNKT) cells play important regulatory roles in various immune responses, including antitumor immune responses. Previous studies have demonstrated quantitative and qualitative defects in iNKT cells of cancer patients, and these defects are clinically relevant as they are associated with poor prognosis. In this study we demonstrate that defects in the iNKT cell population can, at least in part, be attributed to defective interactions between iNKT cells and CD1d-expressing circulating myeloid dendritic cells (mDC), as mDC of patients with advanced melanoma and renal cell cancer reduced the activation and Th1 cytokine production of healthy donor-derived iNKT cells. Interestingly, this reduced activation of iNKT cells was restricted to patients with low circulating iNKT cell numbers and could be reversed by IL-12 and in part by the neutralization of TGF-beta, but it was further reduced by the neutralization of IL-10 in vitro. Additional experiments revealed discordant roles for TGF-beta and IL-10 on human iNKT cells, because TGF-beta suppressed iNKT cell activation and proliferation and IFN-gamma production while IL-10 was identified as a cytokine involved in stimulating the activation and expansion of iNKT cells that could subsequently suppress NK cell and T cell responses.

CD1d ligation on human monocytes directly signals rapid NF-kappaB activation and production of bioactive IL-12.

Natural killer T cells (NKT cells) expressing a semi-invariant CD1d-reactive T cell receptor (invariant NKT, iNKT) can be rapidly activated by monocytes or immature dendritic cells (iDCs) bearing a CD1d-presented glycolipid antigen and can in turn stimulate these myeloid cells to mature and produce IL-12. Previous studies have shown that iNKT-produced IFNgamma and CD40 ligand contribute to this dendritic cell maturation. This study demonstrates that CD1d ligation alone, in the absence of iNKT, could rapidly (within 24 h) stimulate production of bioactive IL-12p70 by CD1d+ human peripheral blood monocytes as well as iDCs. IFNgamma alone had no effect, but it markedly enhanced CD1d-stimulated IL-12 production. Monocyte differentiation, as assessed by CD40 and CD1a up-regulation, was also accelerated by CD1d stimulation, consistent with this representing a physiological response. CD1d ligation on the human monocytic cell line THP-1 similarly specifically stimulated IL-12 production. Biochemical studies showed that IL-12 release correlated with rapid phosphorylation of IkappaB, a critical step in NF-kappaB activation. Selective NF-kappaB inhibition blocked this CD1d-stimulated IL-12 production. Finally, CD1d ligation could also enhance IL-12 production in the presence of suboptimal LPS or CD40 stimulation. These findings demonstrate an innate immune signaling function for CD1d and provide a mechanism for the rapid activation of monocytes and iDCs by CD1d-reactive T cells.