Targeted delivery of CD40L promotes restricted activation of antigen-presenting cells and induction of cancer cell death

FcγRs and Their Relevance for the Activity of Anti-CD40 Antibodies

Inhibitory targeting of the CD40L-CD40 system is a promising therapeutic option in the field of organ transplantation and is also attractive in the treatment of autoimmune diseases. After early complex results with neutralizing CD40L antibodies, it turned out that lack of Fcγ receptor (FcγR)-binding is the crucial factor for the development of safe inhibitory antibodies targeting CD40L or CD40. Indeed, in recent years, blocking CD40 antibodies not interacting with FcγRs, has proven to be well tolerated in clinical studies and has shown initial clinical efficacy. Stimulation of CD40 is also of considerable therapeutic interest, especially in cancer immunotherapy. CD40 can be robustly activated by genetically engineered variants of soluble CD40L but also by anti-CD40 antibodies. However, the development of CD40L-based agonists is biotechnologically and pharmacokinetically challenging, and anti-CD40 antibodies typically display only strong agonism in complex with FcγRs or upon secondary crosslinking. The latter, however, typically results in poorly developable mixtures of molecule species of varying stoichiometry and FcγR-binding by anti-CD40 antibodies can elicit unwanted side effects such as antibody-dependent cellular cytotoxicity (ADCC) or antibody-dependent cellular phagocytosis (ADCP) of CD40 expressing immune cells. Here, we summarize and compare strategies to overcome the unwanted target cell-destroying activity of anti-CD40-FcγR complexes, especially the use of FcγR type-specific mutants and the FcγR-independent cell surface anchoring of bispecific anti-CD40 fusion proteins. Especially, we discuss the therapeutic potential of these strategies in view of the emerging evidence for the dose-limiting activities of systemic CD40 engagement.

Anti-CD40 Antibody Fused to CD40 Ligand Is a Superagonist Platform for Adjuvant Intrinsic DC-Targeting Vaccines

CD40 is a potent activating receptor expressed on antigen-presenting cells (APCs) of the immune system. CD40 regulates many aspects of B and T cell immunity via interaction with CD40L expressed on activated T cells. Targeting antigens to CD40 via agonistic anti-CD40 antibody fusions promotes both humoral and cellular immunity, but current anti-CD40 antibody-antigen vaccine prototypes require co-adjuvant administration for significant in vivo efficacy. This may be a consequence of dulling of anti-CD40 agonist activity via antigen fusion. We previously demonstrated that direct fusion of CD40L to anti-CD40 antibodies confers superagonist properties. Here we show that anti-CD40-CD40L-antigen fusion constructs retain strong agonist activity, particularly for activation of dendritic cells (DCs). Therefore, we tested anti-CD40-CD40L antibody fused to antigens for eliciting immune responses in vitro and in vivo. In PBMC cultures from HIV-1-infected donors, anti-CD40-CD40L fused to HIV-1 antigens preferentially expanded HIV-1-specific CD8+ T cells versus CD4+ T cells compared to analogous anti-CD40-antigen constructs. In normal donors, anti-CD40-CD40L-mediated delivery of Influenza M1 protein elicited M1-specific T cell expansion at lower doses compared to anti-CD40-mediated delivery. Also, on human myeloid-derived dendritic cells, anti-CD40-CD40L-melanoma gp100 peptide induced more sustained Class I antigen presentation compared to anti-CD40-gp100 peptide. In human CD40 transgenic mice, anti-CD40-CD40L-HIV-1 gp140 administered without adjuvant elicited superior antibody responses compared to anti-CD40-gp140 antigen without fused CD40L. In human CD40 mice, compared to the anti-CD40 vehicle, anti-CD40-CD40L delivery of Eα 52-68 peptide elicited proliferating of TCR I-Eα 52-68 CD4+ T cells producing cytokine IFNγ. Also, compared to controls, only anti-CD40-CD40L-Cyclin D1 vaccination of human CD40 mice reduced implanted EO771.LMB breast tumor cell growth. These data demonstrate that human CD40-CD40L antibody fused to antigens maintains highly agonistic activity and generates immune responses distinct from existing low agonist anti-CD40 targeting formats. These advantages were in vitro skewing responses towards CD8+ T cells, increased efficacy at low doses, and longevity of MHC Class I peptide display; and in mouse models, a more robust humoral response, more activated CD4+ T cells, and control of tumor growth. Thus, the anti-CD40-CD40L format offers an alternate DC-targeting platform with unique properties, including intrinsic adjuvant activity.

Controlled Modular Multivalent Presentation of the CD40 Ligand on P22 Virus-like Particles Leads to Tunable Amplification of CD40 Signaling

Ligands of the tumor necrosis factor superfamily (TNFSF) are appealing targets for immunotherapy research due to their integral involvement in stimulation or restriction of immune responses. TNFSF-targeted therapies are currently being developed to combat immunologically based diseases and cancer. A crucial determinant of effective TNFSF receptor binding and signaling is the trimeric quaternary structure of the ligand. Additionally, ligand multivalency is essential to propagate strong signaling in effector cells. Thus, designing a synthetic platform to display trimeric TNFSF ligands in a multivalent manner is necessary to further the understanding of ligand-receptor interactions. Viral nanocages have architectures that are amenable to genetic and chemical modifications of both their interior and exterior surfaces. Notably, the exterior surface of virus-like particles can be utilized as a platform for the modular multivalent presentation of target proteins. In this study, we build on previous efforts exploring the bacteriophage P22 virus-like particle for the exterior multivalent modular display of a potent immune-stimulating TNFSF protein, CD40 ligand (CD40L). Using a cell-based reporter system, we quantify the effects of tunable avidity on CD40 signaling by CD40L displayed on the surface of P22 nanocages. Multivalent presentation of CD40L resulted in a 53.6-fold decrease of the half maximal effective concentration (EC₅₀) compared to free CD40L, indicating higher potency. Our results emphasize the power of using P22-based biomimetics to study ligand-receptor interactions within their proper structural context, which may contribute to the development of effective immune modulators.

Rapid Capture of Cancer Extracellular Vesicles by Lipid Patch Microarrays

Extracellular vesicles (EVs) contain various bioactive molecules such as DNA, RNA, and proteins, and play a key role in the regulation of cancer progression. Furthermore, cancer-associated EVs carry specific biomarkers and can be used in liquid biopsy for cancer detection. However, it is still technically challenging and time consuming to detect or isolate cancer-associated EVs from complex biofluids (e.g., blood). Here, a novel EV-capture strategy based on dip-pen nanolithography generated microarrays of supported lipid membranes is presented. These arrays carry specific antibodies recognizing EV- and cancer-specific surface biomarkers, enabling highly selective and efficient capture. Importantly, it is shown that the nucleic acid cargo of captured EVs is retained on the lipid array, providing the potential for downstream analysis. Finally, the feasibility of EV capture from patient sera is demonstrated. The demonstrated platform offers rapid capture, high specificity, and sensitivity, with only a small need in analyte volume and without additional purification steps. The platform is applied in context of cancer-associated EVs, but it can easily be adapted to other diagnostic EV targets by use of corresponding antibodies.

Receptor Oligomerization and Its Relevance for Signaling by Receptors of the Tumor Necrosis Factor Receptor Superfamily

With the exception of a few signaling incompetent decoy receptors, the receptors of the tumor necrosis factor receptor superfamily (TNFRSF) are signaling competent and engage in signaling pathways resulting in inflammation, proliferation, differentiation, and cell migration and also in cell death induction. TNFRSF receptors (TNFRs) become activated by ligands of the TNF superfamily (TNFSF). TNFSF ligands (TNFLs) occur as trimeric type II transmembrane proteins but often also as soluble ligand trimers released from the membrane-bound form by proteolysis. The signaling competent TNFRs are efficiently activated by the membrane-bound TNFLs. The latter recruit three TNFR molecules, but there is growing evidence that this is not sufficient to trigger all aspects of TNFR signaling; rather, the formed trimeric TNFL–TNFR complexes have to cluster secondarily in the cell-to-cell contact zone for full TNFR activation. With respect to their response to soluble ligand trimers, the signaling competent TNFRs can be subdivided into two groups. TNFRs of one group, designated as category I TNFRs, are robustly activated by soluble ligand trimers. The receptors of a second group (category II TNFRs), however, failed to become properly activated by soluble ligand trimers despite high affinity binding. The limited responsiveness of category II TNFRs to soluble TNFLs can be overcome by physical linkage of two or more soluble ligand trimers or, alternatively, by anchoring the soluble ligand molecules to the cell surface or extracellular matrix. This suggests that category II TNFRs have a limited ability to promote clustering of trimeric TNFL–TNFR complexes outside the context of cell–cell contacts. In this review, we will focus on three aspects on the relevance of receptor oligomerization for TNFR signaling: (i) the structural factors which promote clustering of free and liganded TNFRs, (ii) the signaling pathway specificity of the receptor oligomerization requirement, and (iii) the consequences for the design and development of TNFR agonists.

Ad-CD40L mobilizes CD4 T cells for the treatment of brainstem tumors

BACKGROUND

Diffuse midline glioma, formerly DIPG (diffuse intrinsic pontine glioma), is the deadliest pediatric brainstem tumor with median survival of less than one year. Here, we investigated (i) whether direct delivery of adenovirus-expressing cluster of differentiation (CD)40 ligand (Ad-CD40L) to brainstem tumors would induce immune-mediated tumor clearance and (ii) if so, whether therapy would be associated with a manageable toxicity due to immune-mediated inflammation in the brainstem.

METHODS

Syngeneic gliomas in the brainstems of immunocompetent mice were treated with Ad-CD40L and survival, toxicity, and immune profiles determined. A clinically translatable vector, whose replication would be tightly restricted to tumor cells, rAd-Δ24-CD40L, was tested in human patient-derived diffuse midline gliomas and immunocompetent models.

RESULTS

Expression of Ad-CD40L restricted to brainstem gliomas by pre-infection induced complete rejection, associated with immune cell infiltration, of which CD4+ T cells were critical for therapy. Direct intratumoral injection of Ad-CD40L into established brainstem tumors improved survival and induced some complete cures but with some acute toxicity. RNA-sequencing analysis showed that Ad-CD40L therapy induced neuroinflammatory immune responses associated with interleukin (IL)-6, IL-1β, and tumor necrosis factor α. Therefore, to generate a vector whose replication, and transgene expression, would be tightly restricted to tumor cells, we constructed rAd-Δ24-CD40L, the backbone of which has already entered clinical trials for diffuse midline gliomas. Direct intratumoral injection of rAd-Δ24-CD40L, with systemic blockade of IL-6 and IL-1β, generated significant numbers of cures with readily manageable toxicity.

CONCLUSIONS

Virus-mediated delivery of CD40L has the potential to be effective in treating diffuse midline gliomas without obligatory neuroinflammation-associated toxicity.

Membrane-bound TNF mediates microtubule-targeting chemotherapeutics-induced cancer cytolysis via juxtacrine inter-cancer-cell death signaling

Microtubule-targeting agents (MTAs) are a class of most widely used chemotherapeutics and their mechanism of action has long been assumed to be mitotic arrest of rapidly dividing tumor cells. In contrast to such notion, here we show—in many cancer cell types—MTAs function by triggering membrane TNF (memTNF)-mediated cancer-cell-to-cancer-cell killing, which differs greatly from other non-MTA cell-cycle-arresting agents. The killing is through programmed cell death (PCD), either in way of necroptosis when RIP3 kinase is expressed, or of apoptosis in its absence. Mechanistically, MTAs induce memTNF transcription via the JNK-cJun signaling pathway. With respect to chemotherapy regimens, our results establish that memTNF-mediated killing is significantly augmented by IAP antagonists (Smac mimetics) in a broad spectrum of cancer types, and with their effects most prominently manifested in patient-derived xenograft (PDX) models in which cell–cell contacts are highly reminiscent of human tumors. Therefore, our finding indicates that memTNF can serve as a marker for patient responsiveness, and Smac mimetics will be effective adjuvants for MTA chemotherapeutics. The present study reframes our fundamental biochemical understanding of how MTAs take advantage of the natural tight contact of tumor cells and utilize memTNF-mediated death signaling to induce the entire tumor regression.

Prognosticating Outcomes in Interstitial Lung Disease by Mediastinal Lymph Node Assessment. An Observational Cohort Study with Independent Validation

RATIONALE

Mediastinal lymph node (MLN) enlargement on chest computed tomography (CT) is prevalent in patients with interstitial lung disease (ILD) and may reflect immunologic activation and subsequent cytokine-mediated immune cell trafficking.

OBJECTIVES

We aimed to determine whether MLN enlargement on chest CT predicts clinical outcomes and circulating cytokine levels in ILD.

METHODS

MLN measurements were obtained from chest CT scans of patients with ILD at baseline evaluation over a 10-year period. Patients with sarcoidosis and drug toxicity-related ILD were excluded. MLN diameter and location were assessed. Plasma cytokine levels were analyzed in a subset of patients. The primary outcome was transplant-free survival (TFS). Secondary outcomes included all-cause and respiratory hospitalizations, lung function, and plasma cytokine concentrations. Cox regression was used to assess mortality risk. Outcomes were assessed in three independent ILD cohorts.

MEASUREMENTS AND MAIN RESULTS

Chest CT scans were assessed in 1,094 patients (mean age, 64 yr; 52% male). MLN enlargement (≥10 mm) was present in 66% (n = 726) and strongly predicted TFS (hazard ratio [HR], 1.53; 95% confidence interval [CI], 1.12-2.10; P = 0.008) and risk of all-cause and respiratory hospitalizations (internal rate of return [IRR], 1.52; 95% CI, 1.17-1.98; P = 0.002; and IRR, 1.71; 95% CI, 1.15-2.53; P = 0.008, respectively) when compared with subjects with MLN <10 mm. Patients with MLN enlargement had lower lung function and decreased plasma concentrations of soluble CD40L (376 pg/ml vs. 505 pg/ml, P = 0.001) compared with those without MLN enlargement. Plasma IL-10 concentration >45 pg/ml predicted mortality (HR, 4.21; 95% CI, 1.21-14.68; P = 0.024). Independent analysis of external datasets confirmed these findings.

CONCLUSIONS

MLN enlargement predicts TFS and hospitalization risk in ILD and is associated with decreased levels of a key circulating cytokine, soluble CD40L. Incorporating MLN and cytokine findings into current prediction models might improve ILD prognostication.

Targeting the CD40-CD40L pathway in autoimmune diseases: Humoral immunity and beyond

CD40 is a TNF receptor superfamily member expressed on both immune and non-immune cells. Interactions between B cell-expressed CD40 and its binding partner, CD40L, predominantly expressed on activated CD4+ T cells, play a critical role in promoting germinal center formation and the production of class-switched antibodies. Non-hematopoietic cells expressing CD40 can also engage CD40L and trigger a pro-inflammatory response. This article will highlight what is known about the biology of the CD40-CD40L axis in humans and describe the potential contribution of CD40 signaling on both hematopoietic and non-hematopoietic cells to autoimmune disease pathogenesis. Additionally, novel therapeutic approaches to target this pathway, currently being evaluated in clinical trials, are discussed.

IL-15 and a Two-Step Maturation Process Improve Bone Marrow-Derived Dendritic Cell Cancer Vaccine

In the last 20 years, dendritic cells (DCs) have been largely used as a platform for therapeutic vaccination in cancer patients. However, despite its proven safety and ability to induce cancer specific immune responses, the clinical benefits of DC-based immunotherapy are currently very limited. Thus, novel approaches are still needed to boost its efficacy. Our group recently showed that squaric acid treatment of antigens is an important adjuvant that can increase vaccine-induced downstream immune responses and therapeutic outcomes. Here we further improved this dendritic cell vaccine formulation by developing a new method for differentiating and maturing DCs from their bone marrow precursors. Our data demonstrate that bone marrow-derived DCs differentiated with GM-CSF and IL-15 and matured with a maturation cocktail in two steps present a more mature and immunogenic phenotype, compared to standard DC preparations. Further suppression of the prostaglandin E₂ pathway achieved even more immunogenic DC phenotypes. This vaccine was more potent at delaying tumor growth, improved animal survival and induced a more immunogenic and Th1-skewed T cell response in an ovarian cancer mouse model. These promising results support future efforts for the clinical translation of this approach.

The promise and challenges of immune agonist antibody development in cancer

Immune cell functions are regulated by co-inhibitory and co-stimulatory receptors. The first two generations of cancer immunotherapy agents consist primarily of antagonist antibodies that block negative immune checkpoints, such as programmed cell death protein 1 (PD1) and cytotoxic T lymphocyte protein 4 (CTLA4). Looking ahead, there is substantial promise in targeting co-stimulatory receptors with agonist antibodies, and a growing number of these agents are making their way through various stages of development. This Review discusses the key considerations and potential pitfalls of immune agonist antibody design and development, their differentiating features from antagonist antibodies and the landscape of agonist antibodies in clinical development for cancer treatment.

Nanoparticles for the Induction of Antigen-Specific Immunological Tolerance

Antigen-specific immune tolerance has been a long-standing goal for immunotherapy for the treatment of autoimmune diseases and allergies and for the prevention of allograft rejection and anti-drug antibodies directed against biologic therapies. Nanoparticles have emerged as powerful tools to initiate and modulate immune responses due to their inherent capacity to target antigen-presenting cells (APCs) and deliver coordinated signals that can elicit an antigen-specific immune response. A wide range of strategies have been described to create tolerogenic nanoparticles (tNPs) that fall into three broad categories. One strategy includes tNPs that provide antigen alone to harness natural tolerogenic processes and environments, such as presentation of antigen in the absence of costimulatory signals, oral tolerance, the tolerogenic environment of the liver, and apoptotic cell death. A second strategy includes tNPs that carry antigen and simultaneously target tolerogenic receptors, such as pro-tolerogenic cytokine receptors, aryl hydrocarbon receptor, FAS receptor, and the CD22 inhibitory receptor. A third strategy includes tNPs that carry a payload of tolerogenic pharmacological agents that can “lock” APCs into a developmental or metabolic state that favors tolerogenic presentation of antigens. These diverse strategies have led to the development of tNPs that are capable of inducing antigen-specific immunological tolerance, not just immunosuppression, in animal models. These novel tNP technologies herald a promising approach to specifically prevent and treat unwanted immune reactions in humans. The first tNP, SEL-212, a biodegradable synthetic vaccine particle encapsulating rapamycin, has reached the clinic and is currently in Phase 2 clinical trials.

Antigen presentation of the Oct4 and Sox2 peptides by CD154-activated B lymphocytes enhances the killing effect of cytotoxic T lymphocytes on tumor stem-like cells derived from cisplatin-resistant lung cancer cells

The present study investigated whether antigen presentation of the Oct4 and Sox2 peptides by CD154-activated B lymphocytes can enhance the killing effect of CD8⁺ cytotoxic T lymphocytes (CTLs) on lung stem-like cancer cells (SLCCs). The CTLs were generated using an accelerated co-cultured dendritic cells (DC) (acDC) assay by incubating human peripheral blood mononuclear cells (PBMCs) from non-small-cell lung cancer patients with antigen peptides of Oct4 and Sox2 in the presence of several DC-activating agents. CD154⁺ NIH3T3 cells prepared by CD154 lentiviral transfection were used as feeder layer to activate primary B cells (CD19⁺) obtained from PBMCs. Activated B cells were co-cultured with CTLs to present antigen peptides of Oct4 and Sox2. CTLs co-cultured with activated B cells were evaluated for the levels of secreted inflammatory cytokines using ELISA. In addition, the killing effect of the CTLs on SLCCs derived from cisplatin-resistant strain of human lung cancer cell line PC9 was evaluated by flow cytometry using CFSE labeling of the target cells. After the acDC assay, the PBMCs exhibited a significant (p<0.01) increase in the population of CD8⁺/CD3⁺ cells, indicating successful preparation of CTLs. The primary B cells cultured on the CD154⁺ NIH3T3 feeder layer resulted in significant (p<0.01) increase in the proportions of population expressing CD80, CD86, or HLA-A, indicating successful activation of the B cells. The co-culture of CTLs with CD154-activated B cells presenting the Oct4 and Sox2 peptides caused significant increase in the levels of secretory inflammatory cytokines and exhibited enhanced killing of the SLCCs derived from cisplatin-resistant PC9 cells. Antigen presentation of the Oct4 and Sox2 peptides by CD154-activated B cells can enhance the killing effect of CTLs towards lung SLCCs.

A versatile pretargeting approach for tumour-selective delivery and activation of TNF superfamily members

TNFR superfamily (TNFRSF) members have important immunoregulatory functions and are of clear interest for cancer immunotherapy. Various TNFRSF agonists have been clinically evaluated, but have met with limited efficacy and/or toxicity. Recent insights indicate that 'first-generation' TNFRSF agonists lack efficacy as they do not effectively cross-link their corresponding receptor. Reversely, ubiquitous TNFRSF receptor(s) cross-linking by CD40 and Fas agonistic antibodies resulted in dose-limiting liver toxicity. To overcome these issues, we developed a novel pretargeting strategy exploiting recombinant fusion proteins in which a soluble form of TRAIL, FasL or CD40L is genetically fused to a high-affinity anti-fluorescein scFv antibody fragment (scFvFITC). Fusion proteins scFvFITC:sTRAIL and scFvFITC:sFasL induced potent target antigen-restricted apoptosis in a panel of cancer lines and in primary patient-derived cancer cells, but only when pretargeted with a relevant FITC-labelled antitumour antibody. In a similar pretargeting setting, fusion protein scFvFITC:sCD40L promoted tumour-directed maturation of immature monocyte-derived dendritic cells (iDCs). This novel tumour-selective pretargeting approach may be used to improve efficacy and/or reduce possible off-target toxicity of TNFSF ligands for cancer immunotherapy.

Antibody-Based Cancer Therapy: Successful Agents and Novel Approaches

Since their discovery, antibodies have been viewed as ideal candidates or "magic bullets" for use in targeted therapy in the fields of cancer, autoimmunity, and chronic inflammatory disorders. A wave of antibody-dedicated research followed, which resulted in the clinical approval of a first generation of monoclonal antibodies for cancer therapy such as rituximab (1997) and cetuximab (2004), and infliximab (2002) for the treatment of autoimmune diseases. More recently, the development of antibodies that prevent checkpoint-mediated inhibition of T cell responses invigorated the field of cancer immunotherapy. Such antibodies induced unprecedented long-term remissions in patients with advanced stage malignancies, most notably melanoma and lung cancer, that do not respond to conventional therapies. In this review, we will recapitulate the development of antibody-based therapy, and detail recent advances and new functions, particularly in the field of cancer immunotherapy. With the advent of recombinant DNA engineering, a number of rationally designed molecular formats of antibodies and antibody-derived agents have become available, and we will discuss various molecular formats including antibodies with improved effector functions, bispecific antibodies, antibody-drug conjugates, antibody-cytokine fusion proteins, and T cells genetically modified with chimeric antigen receptors. With these exciting advances, new antibody-based treatment options will likely enter clinical practice and pave the way toward more successful control of malignant diseases.

Use of single chain antibody derivatives for targeted drug delivery

Single chain antibodies (scFvs), which contain only the variable domains of full-length antibodies, are relatively small molecules that can be used for selective drug delivery. In this review, we display how scFv antibodies help improve the specificity and efficiency of drugs. Small interfering RNA (siRNA) delivery using scFv-drug fusion peptides, siRNA delivery using scFv-conjugated nanoparticles, targeted delivery using scFv-viral peptide- fusion proteins, use of scFv in fusion with cell penetrating peptides for effective targeted drug delivery, scFv-mediated targeted delivery of inorganic nanoparticles, scFv-mediated increase of tumor killing activity of granulocytes, use of scFv for tumor imaging, site-directed conjugation of scFv molecules to drug carrier systems, use of scFv to relieve pain, use of scFv for increasing drug loading efficiency are among the topics that are discussed here.

Soluble CD40 in plasma and malignant pleural effusion with non-small cell lung cancer: A potential marker of prognosis

OBJECTIVE

Soluble CD40 (sCD40) is a potential modulator for both antitumor responses and CD40-based immunotherapy; however the levels and significance of sCD40 in non-small cell lung cancer (NSCLC) patients with malignant pleural effusion are unknown.

METHODS

Forty-eight patients with lung cancer were treated in our institutions from January 2008 to January 2010. Peripheral blood and pleural effusion samples were collected from each subject. sCD40 levels in plasma and malignant pleural effusions supernatant were measured. The CD40L expression on CD3t T-cells was confirmed by flow cytometric direct immunofluorescence analysis. All patients were followed up after the study ended on January 1, 2010.

RESULTS

Patients with malignant pleural effusion of NSCLC had elevated circulating and pleural effusion levels of sCD40, and these elevated sCD40 levels were associated with advanced diseases and a poor prognosis.

CONCLUSIONS

These findings indicate that elevated sCD40 may have a role in modulating antitumor responses and may also be a useful prognostic marker.