Antitumor effect of CAR-T cells targeting transmembrane tumor necrosis factor alpha combined with PD-1 mAb on breast cancers

BACKGROUND

Our previous study showed that transmembrane tumor necrosis factor alpha (tmTNF-α) is overexpressed in primary breast cancers including triple-negative breast cancers (TNBCs). Chimeric antigen receptor engineered-T (CAR-T) cells have been successfully used mainly in B-cell malignancies.

METHODS

We generated CAR-T cells targeting tmTNF-α but not secreted tumor necrosis factor alpha and assessed the antitumor effect of the CAR-T cells on tmTNF-α-expressing breast cancer cells in vitro and in vivo.

RESULTS

Our tmTNF-α CAR-T cells showed potent cytotoxicity against tmTNF-α-expressing breast cancer cells but not tmTNF-α-negative tumor cells with increased secretion of interferon gamma (IFN-γ) and interleukin (IL)-2 in vitro. In tmTNF-α-overexpressing TNBC-bearing mice, the tmTNF-α CAR-T therapy induced evident tumor regression, prolonged survival and increased serum concentrations of IFN-γ and IL-2. However, we found thattmTNF-α induced programmed death-ligand 1 (PD-L1) expression through the p38 pathway via TNF receptor (TNFR) and through the NF-κB and AKT pathways via outside-to-inside (reverse) signaling, which might limit the efficacy of the CAR-T cell therapy. Blockage of the PD-L1/programmed death-1 (PD-1) pathway by PD-1 monoclonal antibody significantly enhanced the antitumor effect of the tmTNF-α CAR-T cell therapy in vitro and in vivo, and the combination was effective for antiprimary tumors and had a tendency to increase the antimetastasis effect of the CAR-T cell therapy.

CONCLUSION

Our findings suggest a potent antitumor efficacy of the tmTNF-α CAR-T cells that can be enhanced by anti-PD-L1/PD-1 because high PD-L1 expression in TNBC was induced by the tmTNF-α signaling, indicating a promising individual therapy for tmTNF-α-positive breast cancers including TNBC.

Transmembrane TNF and Its Receptors TNFR1 and TNFR2 in Mycobacterial Infections

Tumor necrosis factor (TNF) is one of the main cytokines regulating a pro-inflammatory environment. It has been related to several cell functions, for instance, phagocytosis, apoptosis, proliferation, mitochondrial dynamic. Moreover, during mycobacterial infections, TNF plays an essential role to maintain granuloma formation. Several effector mechanisms have been implicated according to the interactions of the two active forms, soluble TNF (solTNF) and transmembrane TNF (tmTNF), with their receptors TNFR1 and TNFR2. We review the impact of these interactions in the context of mycobacterial infections. TNF is tightly regulated by binding to receptors, however, during mycobacterial infections, upstream activation signalling pathways may be influenced by key regulatory factors either at the membrane or cytosol level. Detailing the structure and activation pathways used by TNF and its receptors, such as its interaction with solTNF/TNFRs versus tmTNF/TNFRs, may bring a better understanding of the molecular mechanisms involved in activation pathways which can be helpful for the development of new therapies aimed at being more efficient against mycobacterial infections.

Transmembrane tumor necrosis factor alpha attenuates pressure-overload cardiac hypertrophy via tumor necrosis factor receptor 2

Tumor necrosis factor-alpha (TNF-α) plays an important pathogenic role in cardiac hypertrophy and heart failure (HF); however, anti-TNF is paradoxically negative in clinical trials and even worsens HF, indicating a possible protective role of TNF-α in HF. TNF-α exists in transmembrane (tmTNF-α) and soluble (sTNF-α) forms. Herein, we found that TNF receptor 1 (TNFR1) knockout (KO) or knockdown (KD) by short hairpin RNA or small interfering RNA (siRNA) significantly alleviated cardiac hypertrophy, heart dysfunction, fibrosis, and inflammation with increased tmTNF-α expression, whereas TNFR2 KO or KD exacerbated the pathological phenomena with increased sTNF-α secretion in transverse aortic constriction (TAC)- and isoproterenol (ISO)-induced cardiac hypertrophy in vivo and in vitro, respectively, indicating the beneficial effects of TNFR2 associated with tmTNF-α. Suppressing TNF-α converting enzyme by TNF-α Protease Inhibitor-1 (TAPI-1) to increase endogenous tmTNF-α expression significantly alleviated TAC-induced cardiac hypertrophy. Importantly, direct addition of exogenous tmTNF-α into cardiomyocytes in vitro significantly reduced ISO-induced cardiac hypertrophy and transcription of the pro-inflammatory cytokines and induced proliferation. The beneficial effects of tmTNF-α were completely blocked by TNFR2 KD in H9C2 cells and TNFR2 KO in primary myocardial cells. Furthermore, we demonstrated that tmTNF-α displayed antihypertrophic and anti-inflammatory effects by activating the AKT pathway and inhibiting the nuclear factor (NF)-κB pathway via TNFR2. Our data suggest that tmTNF-α exerts cardioprotective effects via TNFR2. Specific targeting of tmTNF-α processing, rather than anti-TNF therapy, may be more useful for the treatment of hypertrophy and HF.

In contrast to detrimental effects of soluble tumor necrosis factor-alpha (TNF-α) via TNFR1, this study shows that transmembrane TNF-α protects the heart by suppressing pressure overload-induced cardiac hypertrophy and inflammation via TNFR2. Targeting tmTNF-α processing may be more useful than TNF-antagonist for treatment of hypertrophy and heart failure.

Unfolding transmembrane TNFα dynamics in cancer therapeutics

Cytokines are a group of glycoprotein signaling mediators, which play essential roles in maintaining several complex physiological functions of our body. TNFα is such a pleiotropic cytokine, which involves maintaining a plethora of immune responses. Initially, TNFα is synthesized as a 26 kDa full-length transmembrane form, which is enzymatically cleaved to produce the soluble circulating 17 kDa TNFα. Although the anti-cancer potential of soluble TNFα was discovered more than a century back, its dual ability to promote tumor, posed a major hindrance in finding its acceptance as a proper anti-cancer molecule. In contrast, the membrane-tethered tmTNFα holds the potential of tumor regression without initiating cell proliferation. The membrane-tethered form of TNFα is the physiological precursor of soluble TNFα that remains biologically active and is capable of initiating signaling cascades after binding with the TNFα receptors- TNFR I and TNFR II. In this review, we emphasize on the basic biology and molecular aspects of tmTNFα for its anti-cancer potential.

The Role of TNF-α as a Proinflammatory Cytokine in Pathological Processes

TNF-α is a member of the vast cytokine family being considered a proinflammatory substance produced many by macrophages and other cells belonging to the innate immunity, many of them classified as indeed Antigen Presenting Cells (APCs) involved in the complex chemotactic process of activation of the adaptive immunity. The aim of this work was to accomplish a literature review concerning the main pathologies that have TNF-α as a modulating agent in other to bring light to the main interactions present in the inflammation installed.

Exclusive expression of transmembrane TNF aggravates acute glomerulonephritis despite reduced leukocyte infiltration and inflammation

Tumor necrosis factor-α (TNF) is a cytokine mediating inflammatory kidney diseases such as immune complex glomerulonephritis. Its two receptors, TNFR1 and TNFR2, play distinct roles in this process, with TNFR2 strongly required for induction of disease. In contrast to soluble TNF (sTNF), transmembrane TNF robustly activates TNFR2. Thus, we examined the functional role of transmembrane TNF by inducing heterologous nephrotoxic serum nephritis in wild-type and transgenic TNFΔ1-9,K11E knock-in mice expressing transmembrane TNF but no sTNF (memTNF mice). Compared to wild-type, nephritis was exacerbated in memTNF mice on day 5, indicated by increased albuminuria, higher serum urea levels, and more pronounced glomerular deposits, together with higher numbers of dying and proliferating glomerular cells. This was associated with greater loss of glomerular endothelial cells, increased podocyte stress, and signs of augmented necroptosis in memTNF kidneys. Aggravation of nephritis was dependent on transmembrane TNF expression in parenchymal cells, but not leukocytes. Surprisingly, increased kidney injury was associated with reduced renal leukocyte infiltration in memTNF mice, which correlated with decreased renal mRNA expression of pro-inflammatory mediators. This effect was also present in isolated memTNF glomeruli stimulated with interleukin-1β in vitro. Thus, uncleaved transmembrane TNF is an important mediator of renal tissue damage characterized by increased renal cell death and loss of glomerular endothelial cells in murine glomerulonephritis. In contrast, sTNF predominantly mediates renal leukocyte recruitment and inflammation. These findings highlight the importance of transmembrane TNF in inflammatory kidney disease as a possible therapeutic target.

Transmembrane TNF-α preferentially expressed by leukemia stem cells and blasts is a potent target for antibody therapy

To design an effective antibody therapy to improve clinical outcomes in leukemia, the identification of novel cell surface antigens is needed. Herein, we demonstrate a role for transmembrane tumor necrosis factor-α (tmTNF-α) in leukemia. To characterize tmTNF-α expression in acute leukemia (AL), normal hematopoietic cells, and nonhematopoietic tissues, we used a monoclonal antibody, termed C1, which specifically recognizes the tmTNF-α domain. We found that tmTNF-α was preferentially expressed by AL and leukemia stem cells (LSCs). More abundant expression correlated with poor risk stratification, extramedullary infiltration, and adverse clinical parameters. Moreover, knockdown of tmTNF-α(+) expression rendered leukemia cells more sensitive to chemotherapy in vitro and delayed regeneration of leukemia in NOD-SCID mice. Targeting tmTNF-α by C1 resulted in leukemia cell killing via antibody-dependent cell-mediated and complement-dependent cytotoxicity in vitro and inhibited leukemia cell growth in vivo while simultaneously sparing normal hematopoietic cells. Notably, C1 administration impaired the regeneration of leukemia in secondary serial transplantation into NOD-SCID mice. In conclusion, tmTNF-α has a favorable AL- and LSC-associated expression profile and is important for the survival and proliferation of these cells. C1-mediated targeting shows potent anti-LSC activity, indicating that tmTNF-α represents a novel target antigen in AL.

Transmembrane tumor necrosis factor-alpha sensitizes adipocytes to insulin

Transmembrane TNF-α (tmTNF-α) acts both as a ligand, delivering 'forward signaling' via TNFR, and as a receptor, transducing 'reverse signaling'. The contradiction of available data regarding the effect of tmTNF-α on insulin resistance may be due to imbalance in both signals. Here, we demonstrated that high glucose-induced impairment of insulin-stimulated glucose uptake by 3T3-L1 adipocytes was concomitant with decreased tmTNF-α expression and increased soluble TNF-α (sTNF-α) secretion. However, when TACE was inhibited, preventing the conversion of tmTNF-α to sTNF-α, this insulin resistance was partially reversed, indicating a salutary role of tmTNF-α. Treatment of 3T3-L1 adipocytes with exogenous tmTNF-α promoted insulin-induced phosphorylation of IRS-1 and Akt, facilitated GLUT4 expression and membrane translocation, and increased glucose uptake while addition of sTNF-α resulted in the opposite effect. Furthermore, tmTNF-α downregulated the production of IL-6 and MCP-1 via NF-κB inactivation, as silencing of A20, an inhibitor for NF-κB, by siRNA, abolished this effect of tmTNF-α. However, tmTNF-α upregulated adiponectin expression through the PPAR-γ pathway, as inhibition of PPAR-γ by GW9662 abrogated both tmTNF-α-induced adiponectin transcription and glucose uptake. Our data suggest that tmTNF-α functions as an insulin sensitizer via forward signaling.

β-actin in the signaling of transmembrane TNF-α-mediated cytotoxicity

To study the role of β-actin in the signaling of transmembrane TNF-α (tmTNF-α)-mediated cytotoxicity, we mainly used bioassay and apoptosis assay, detection of the visual changes in β-actin and intracellular translocation of signal molecules in response to tmTNF-α, and analysis of the signal molecules coupled or uncoupled with TNFR2 complex. These protocols might also be used to investigate the signaling events mediated by other transmembrane cytokines or members of TNF superfamily, which have transmembrane and soluble forms, as well as the involvement of actin cytoskeleton in signal transduction pathways.

Transmembrane TNF-α promotes suppressive activities of myeloid-derived suppressor cells via TNFR2

It has been reported that TNFR2 is involved in regulatory T cell induction and myeloid-derived suppressor cell (MDSC) accumulation, two kinds of immunosuppressive cells contributing to tumor immune evasion. Because transmembrane TNF-α (tmTNF-α) is the primary ligand for TNFR2, we hypothesized that tmTNF-α is mainly responsible for the activation of MDSCs. Indeed, we found that tmTNF-α, rather than secretory TNF-α (sTNF-α), activated MDSCs with enhanced suppressive activities, including upregulating arginase-1 and inducible NO synthase transcription, promoting secretion of NO, reactive oxygen species, IL-10, and TGF-β, and enhancing inhibition of lymphocyte proliferation. This effect of tmTNF-α was mediated by TNFR2, as TNFR2 deficiency significantly impaired tmTNF-α-induced release of IL-10 and NO and inhibition of T cell proliferation by MDSC supernatant. Furthermore, tmTNF-α caused p38 phosphorylation and NF-κB activation, whereas inhibition of NF-κB or p38 with an inhibitor pyrrolidine dithiocarbamate or SB203580 abrogated tmTNF-α-mediated increased suppression of lymphocyte proliferation by MDSCs. Consistently, our in vivo study showed that ectopic expression of uncleavable tmTNF-α mutant by 4T1 cells significantly promoted tumor progression and angiogenesis, accompanied with more accumulation of MDSCs and regulatory T cells in the tumor site, increased production of NO, IL-10, and TGF-β, as well as poor lymphocyte infiltration. In contrast, enforced expression of sTNF-α mutant by 4T1 cells that only released sTNF-α without expression of surface tmTNF-α markedly reduced MDSC accumulation and induced more lymphocyte infiltration instead, showing obvious tumor regression. Our data suggest that tmTNF-α acts as a potent activator of MDSCs via TNFR2 and reveals another novel immunosuppressive effect of this membrane molecule that promotes tumor immune escape.