Selective apoptosis of neoplastic cells by the HLA-DR-specific monoclonal antibody

Development of therapeutic monoclonal antibodies against DKK1 peptide-HLA-A2 complex to treat human cancers

BACKGROUND

Targeted immunotherapy with monoclonal antibodies (mAbs) is an effective and safe method for the treatment of malignancies. Development of mAbs with improved cytotoxicity, targeting new and known tumor-associated antigens, therefore continues to be an active research area. We reported that Dickkopf-1 (DKK1) is a good target for immunotherapy of human cancers based on its wide expression in different cancers but not in normal tissues. As DKK1 is a secreted protein, mAbs binding directly to DKK1 have limited effects on cancer cells in vivo.

METHODS

The specificity and antibody-binding capacity of DKK1-A2 mAbs were determined using indirect ELISA, confocal imaging, QIFIKIT antibody-binding capacity and cell surface binding assays. The affinity of mAbs was determined using a surface plasmon resonance biosensor. A flow cytometry-based cell death was performed to detect tumor cell apoptosis. Antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) assays were used to evaluate the ability of DKK1-A2 mAbs to mediate ADCC and CDC activities against tumor cells in vitro. Flow cytometry data were collected with an FACSymphony A3 cell analyzer and analyzed with FlowJo V.10.1 software. Human cancer xenograft mouse models were used to determine the in vivo therapeutic efficacy and the potential safety and toxicity of DKK1-A2 mAbs. In situ TUNEL assay was performed to detect apoptosis in tumors and mouse organs.

RESULTS

We generated novel DKK1-A2 mAbs that recognize the DKK1 P20 peptide presented by human HLA-A*0201 (HLA-A2) molecules (DKK1-A2 complexes) that are naturally expressed by HLA-A2+DKK1+ cancer cells. These mAbs directly induced apoptosis in HLA-A2+DKK1+ hematologic and solid cancer cells by activating the caspase-9 cascade, effectively lysed the cancer cells in vitro by mediating CDC and ADCC and were therapeutic against established cancers in their xenograft mouse models. As DKK1 is not detected in most human tissues, DKK1-A2 mAbs neither bound to or killed HLA-A2+ blood cells in vitro nor caused tissue damage in tumor-free or tumor-bearing HLA-A2-transgenic mice.

CONCLUSION

Our study suggests that DKK1-A2 mAbs may be a promising therapeutic agent to treat human cancers.

Monoclonal Antibody Therapies for Hematological Malignancies: Not Just Lineage-Specific Targets

Today, monoclonal antibodies (mAbs) are a widespread and necessary tool for biomedical science. In the hematological cancer field, since rituximab became the first mAb approved by the Food and Drug Administration for the treatment of B-cell malignancies, a number of effective mAbs targeting lineage-specific antigens (LSAs) have been successfully developed. Non-LSAs (NLSAs) are molecules that are not restricted to specific leukocyte subsets or tissues but play relevant pathogenic roles in blood cancers including the development, proliferation, survival, and refractoriness to therapy of tumor cells. In consequence, efforts to target NLSAs have resulted in a plethora of mAbs-marketed or in development-to achieve different goals like neutralizing oncogenic pathways, blocking tumor-related chemotactic pathways, mobilizing malignant cells from tumor microenvironment to peripheral blood, modulating immune-checkpoints, or delivering cytotoxic drugs into tumor cells. Here, we extensively review several novel mAbs directed against NLSAs undergoing clinical evaluation for treating hematological malignancies. The review focuses on the structure of these antibodies, proposed mechanisms of action, efficacy and safety profile in clinical studies, and their potential applications in the treatment of hematological malignancies.

Clinical safety and pharmacological profile of the HLA-DR antibody 1D09C3 in patients with B cell chronic lymphocytic leukemia and lymphoma: results from a phase I study

1D09C3 is a human monoclonal IgG4-type antibody against human leukocyte antigen-DR (HLA-DR) which has demonstrated pro-apoptotic activity against lymphoid tumors in vitro and in vivo. We report results from a phase I dose-escalation study which aimed to identify tolerated dosing, and the pharmacokinetic and pharmacodynamic profile of 1D09C3. Fourteen patients with relapsed/refractory B cell type leukemia/lymphoma were treated and followed after up to 4 weekly infusions of 1D09C3, administered in 6 dose levels at 0.25-8 mg/kg/day. Treatment was tolerated well with mostly mild side effects. The most common grade III-IV toxicities were hematological events observed in 4 patients. In one patient, treated at 8.0 mg/kg/day, a dose limiting toxicity occurred, identified as an invasive catheter-related infection. Adverse events resolved completely without long-term sequelae. 1D09C3 reduced peripheral blood B cells and monocytes by a median of 73-81 % in all patients, with a nadir reached 30-60 min after infusion and sustained for <96 h. Granulocytes and natural killer cells predominantly increased with variable time courses. Pharmacokinetic assessments showed detectable drug concentrations at doses 4-8 mg/kg/day and a terminal half-life of 0.7-7.9 h. Effective saturation of HLA-DR on peripheral blood B cells/monocytes was achieved, varying consistently with available serum concentrations and the cell-reducing activity of 1D09C3. In summary, 1D09C3 could be administered safely in patients with advanced B cell malignancies. Pharmacodynamic studies demonstrated a strong dose dependent but transient reduction of peripheral blood B cells and monocytes, consistent with a short drug serum availability.

Emerging drugs for chronic lymphocytic leukaemia

Although the philosophy of management of patients with chronic lymphocytic leukaemia (CLL) has been altered with the advent of fludarabine-based therapies, impact on long-term survival is unclear and a significant proportion of patients will develop resistance to fludarabine. Similar to other haematological malignancies, a potential for 'cure' is likely to be achieved only if 'high-quality' complete remissions (CRs) are achieved. Treatment options for patients who develop resistance to fludarabine continue to be limited, with only a proportion obtaining a response (usually not CRs) with salvage therapies. This review summarises novel therapies that are being evaluated in patients with CLL, specifically those targeting the antiapoptotic Bcl-2 family of proteins and receptors (e.g., CD40, CD80, HLA-DR) involved in mediating survival signals from the microenvironment.

Targeting beta2-microglobulin for induction of tumor apoptosis in human hematological malignancies

We discovered that monoclonal antibodies (mAbs) specific to human beta(2)-microglobulin (beta(2)M) induce apoptosis in vitro and were therapeutic in mouse models of myeloma and other hematological tumor cells. Cell death occurred rapidly, without the need for exogenous immunological effector mechanisms. The mAbs induced cell death via recruiting MHC class I molecules to lipid rafts and activating Lyn and PLCgamma2, leading to activated JNK and inhibited PI3K/Akt and ERK, compromised mitochondrial integrity, and caspase-9-dependent cascade activation. Although the expression of beta(2)M on normal hematopoietic cells is a potential safety concern, the mAbs were selective to tumor-transformed cells and did not induce apoptosis of normal cells. Therefore, such mAbs offer the potential for a therapeutic approach to hematological malignancies.

High numbers of tumour-infiltrating activated cytotoxic T lymphocytes, and frequent loss of HLA class I and II expression, are features of aggressive B cell lymphomas of the brain and testis

Loss of both HLA class I and class II expression in B cell lymphomas is a mechanism of escape from a cytotoxic T lymphocyte (CTL) immune response and will therefore give a strong selective survival advantage in tumours expressing strong immunogenic antigens. We investigated loss of HLA expression using specific antibodies on tissue sections from 254 B cell lymphomas originating from nodal and different extranodal sites in relation to numbers of tumour-infiltrating T cells. Complete loss of HLA class I and II was observed in a minority of the nodal, stomach, and skin lymphomas but in the majority of the lymphomas originating from the testis and the CNS. Interestingly, relatively high percentages of activated CTLs were detected in both primary testicular and CNS lymphomas compared to lymphomas at other sites, with highest percentages in the testis (p < 0.0001). We conclude that loss of both HLA class I and II expression occurs very frequently in lymphomas originating from the testis and the CNS as compared to nodal and some other extranodal sites. The presence of high percentages of activated CTLs in the testicular and CNS lymphomas suggests that loss of HLA expression provides a strong growth advantage for lymphoma cells in these immune-privileged sites.

Tocotrienol-Rich Fraction from Palm Oil and Gene Expression in Human Breast Cancer Cells

Vitamin E is important not only for its cellular antioxidant and lipid-lowering properties, but also as an antiproliferating agent. It has also been shown to contribute to immunoregulation, antibody production, and resistance to implanted tumors. It has recently been shown that tocotrienols are the components of vitamin E responsible for growth inhibition in human breast cancer cells in vitro as well as in vivo through estrogen-independent mechanisms. Although tocotrienols act on cell proliferation in a dose-dependent manner and can induce programmed cell death, no specific gene regulation has yet been identified. In order to investigate the molecular basis of the effect of a tocotrienol-rich fraction (TRF) from palm oil, we performed a cDNA array analysis of cancer-related gene expression in estrogen-dependent (MCF-7) and estrogen-independent (MDA-MB-231) human breast cancer cells. The human breast cancer cells were incubated with or without 8 mug/mL of tocotrienols for 72 h. RNA was subsequently extracted and subjected to reverse transcription before being hybridized onto cancer arrays. Tocotrienol supplementation modulated significantly 46 out of 1200 genes in MDA-MB-231 cells. In MCF-7 cells, tocotrienol administration was associated with a lower number of affected genes. Interestingly, only three were affected in a similar fashion in both cell lines: c-myc binding protein MM-1, 23-kDa highly basic protein, and interferon-inducible protein 9-27 (IFITM-1). These proteins are most likely involved in the cell cycle and can exert inhibitory effects on cell growth and differentiation of the tumor cell lines. These data suggest that tocotrienols are able to affect cell homeostasis, possibly independent of their antioxidant activity.

Major histocompatibility complex status in breast carcinogenesis and relationship to apoptosis

Major histocompatibility complex (MHC) molecules are of central importance in regulating the immune response against tumors. In this study we used immunohistochemistry to study human leukocyte antigen (HLA) class I and II antigen expression in normal breast tissues and benign, preneoplastic, primary, and metastatic breast lesions using antibodies against beta-2-microglobulin (beta2-m), heavy-chain, and HLA-DR antigens. Whereas all normal tissues and benign lesions were positive for beta2-m and HLA-A, -B, and -C antigens, total loss of HLA class I antigens was found in 37% (11 of 30) of in situ carcinomas, in 43% (56 of 131) of the primary tumors, and in 70% (31 of 45) of the lymph node metastases. HLA-DR was also underexpressed in breast cancer cells; thus 20% (6 of 30) of in situ carcinomas, 15% of invasive carcinomas (20 of 131), and only 1 metastatic case were positive for this antigen. Both HLA class I and II antigen expression were more frequently down-regulated in metastatic lesions than in primary breast lesions (P <0.05), and a tendency toward a simultaneous defective expression of HLA class I and II antigens was observed in primary carcinomas (P = 0.07). However, no correlation was found between the expression of any of the aforementioned molecules and pathological parameters or survival. Interestingly, HLA class I expression was expressed more frequently in tissues with high apoptotic activity and was significantly associated with the expression of the proapoptotic bax gene (P = 0.02), and was inversely associated with expression of the antiapoptotic bcl-2 gene (P = 0.03). We conclude that alterations in HLA class I and II antigen expression are early events in breast carcinogenesis and play significant roles in metastatic progression. In addition, their expression is correlated with apoptosis-regulating proteins, which may influence the cytotoxicity of T cells against HLA class I-specific tumor antigens.

HLA class II antibodies in the treatment of hematologic malignancies

Promising results have suggested human leukocyte antigen (HLA) class II as potential target for antibody-based lymphoma therapy. Thus, antibodies against HLA class II induced apoptosis in vitro, as well as complement-dependent cytotoxicity (CDC) and effector cell-mediated cytotoxicity (ADCC). Furthermore, animal models demonstrated strong antitumor effects in vivo. Importantly, early clinical studies with antibodies Lym-1 or Hu1D10, both against HLA-DR variants, suggested therapeutic potential. However, the increased risk of serious toxicity may require an improved understanding of the clinically relevant mechanisms of action of HLA class II-directed antibodies, which may then allow generation of optimized antibody constructs to achieve optimal therapeutic efficacy.

MHC class II antigen signaling induces homotypic and heterotypic cluster formation of human mature monocyte derived dendritic cells in the absence of cell death

Cellular aggregation in response to surface antigen signaling is a regulated process important for cell-cell interaction and cell migration. We studied dendritic cell (DC) aggregation in response to major histocompatibility complex (MHC) class II antigen ligation using human monocyte derived mature DCs. Crosslinking of MHC class II antigens by monoclonal antibodies in DCs matured by different stimuli, but not in immature DCs, induced the formation of large and long-lived homotypic cell clusters within 1 hour. These aggregates were completely resistant to mechanical disruption and displayed no signs of increased cell death. Heterotypic conjugate formation of mature DCs with lymphocytes and monocytes following addition of MHC class II antibodies occurred as well. DC aggregation required antigen dimerization, the presence of serum and energy, an intact cytoskeleton, and could not be blocked by EDTA, mannan, and monoclonal antibodies specific for integrins. These data underscore the positive role of MHC class II signaling in mature DCs suggesting the possibility of reverse DC activation in the course of antigen specific interaction with lymphocytes.

Induction of complete remission of hypoplastic leukemia with antithymocyte globulin

A 13-year-old boy was admitted to a local hospital because of pancytopenia. A bone marrow aspiration and biopsy revealed severely hypocellular marrow with no obvious leukemic cells. The diagnosis was severe aplastic anemia, and the patient was treated with antithymocyte globulin and cyclosporin A. A trilineage response was obtained, and the patient became transfusion-independent within 2 weeks. Two months later, the peripheral blood count normalized with an increased bone marrow cellularity. However, the patient was readmitted 5 months later for recurrence of the pancytopenia. A bone marrow aspiration revealed hypocellular marrow with morphologically blastoid cells. A surface marker study revealed the presence of a single clone that was positive for CD7, CD33, CD34, and HLA-DR. A diagnosis of hypoplastic leukemia was made on the basis of morphology and the surface marker studies. Retrospectively, the laboratory findings were the same as those seen at the onset of the disease. The patient did not respond to combination chemotherapy consisting of vincristine, prednisolone, cyclophosphamide, L-asparaginase, and doxorubicin, but administration of etoposide resulted in complete remission. An in vitro study revealed that >95% of the leukemic cells of this patient could be lysed after an incubation with antithymocyte globulin and human AB serum or baby rabbit serum. These findings suggest the efficacy of antithymocyte globulin in treating certain hypoplastic leukemias.

Fully human, HLA-DR-specific monoclonal antibodies efficiently induce programmed death of malignant lymphoid cells

The Human Combinatorial Antibody Library (HuCAL) was screened for antibodies specific to human leukocyte antigen-DR (HLA-DR) that induce programmed death of lymphoma/leukemia cells expressing the target antigen. The active Fab fragments were affinity-matured, and engineered to IgG(4) antibodies of sub-nanomolar affinity. The antibodies exhibited potent in vitro tumoricidal activity on several lymphoma and leukemia cell lines and on chronic lymphocytic leukemia patient samples. They were also active in vivo in xenograft models of non-Hodgkin lymphoma. Cell death occurred rapidly, without the need for exogenous immunological effector mechanisms, and was selective to activated/tumor-transformed cells. Although the expression of HLA-DR on normal hematopoietic cells is a potential safety concern, the antibodies caused no long-lasting hematological toxicity in primates, in vivo. Such monoclonal antibodies offer the potential for a novel therapeutic approach to lymphoid malignancies.

Antigenic characterization of medullary carcinoma of the breast: HLA-DR expression in lymph node positive cases

Medullary carcinoma of the breast has attracted attention because of its relatively good prognosis, in spite of its high cytologic grade. It has, by definition, a consistent, florid tumor infiltrating lymphocyte (TIL) population, probably the result of cytotoxic T-lymphocytes recognizing tumor cells in an HLA-DR-restricted manner. HLA-DR tends to be more highly expressed on primary medullary carcinoma cells than on ductal carcinoma cells; however, the MHC-class II antigenicity of the tumor cells themselves has not been analyzed extensively, and as yet there has been no comparative study of HLA-DR expression in medullary and ductal carcinomas metastatic to lymph nodes. Eleven cases of medullary carcinoma and 15 cases of ductal carcinoma, primaries, and respective lymph node metastases were analyzed by immunoperoxidase staining for HLA-DR and lymphocytes antigens. Polymerase chain reaction (PCR) analysis to identify HLA-DR subtypes from the paraffin blocks was performed on selected cases of primaries and nodal metastases of both tumor types. Immunoperoxidase staining for HLA-DR antigen revealed a marked difference in antigen expression between medullary and ductal carcinomas. In the medullary carcinomas, the mean percentage of cells staining for HLA-DR was 74.5% in the primary tumors and 67.3% in the nodal metastases. For the ductal carcinomas, the mean percentage of cells staining was 17.7% in the primaries and 7% in the metastases. There was a tendency for the level of HLA-DR expression to remain high in medullary carcinoma metastatic to nodes, whereas whatever HLA-DR was present within ductal primaries tended to diminish when cells metastasized to regional nodes. PCR analysis of the HLA-DR within the two tumor types revealed no emerging subtype or variant that could be associated with either the medullary or the ductal carcinomas. Medullary carcinoma cells express much greater quantities of HLA-DR, on the whole, than ductal carcinomas. Expression of HLA-DR is retained on medullary carcinoma cells that have spread to lymph nodes, whereas the smaller quantities of HLA-DR present within ductal primaries tend to diminish even further when the tumor cells are found in lymph nodes. No discernible HLA-DR mutations or predominant subtypes emerged on PCR analysis, and the authors therefore conclude that it is the quantity and not the quality of HLA-DR expression in medullary carcinoma that maintains the characteristic TIL infiltrate, not seen in ductal carcinomas.

A Caspase-Independent Pathway of MHC Class II Antigen-Mediated Apoptosis of Human B Lymphocytes

MHC class II molecules have a crucial role in thymic selection and in generating Ag-specific T cell responses. There is extensive evidence for second messenger generation via MHC class II molecules, which can lead to apoptosis of B lymphocytes. We have examined HLA class II-mediated apoptosis in both normal and tumoral human B lymphocytes. Phosphatidylserine exposure and DNA fragmentation were observed in B cells within 24 h of stimulation via HLA class II. In marked comparison with Fas, the cell-permeable and irreversible caspase inhibitors zVAD-fmk and DEVD-fmk failed to inhibit HLA-DR-mediated apoptosis. No direct activation of caspase 3 was detected, and cleavage of pro-caspase 3 was not observed. Cleavage of poly(ADP-ribose) polymerase was detected via Fas but not via HLA class II. Although phosphatidylinositol-3-kinase has been implicated in HLA class I-mediated apoptosis, neither wortmannin nor LY294002 affected HLA class II-mediated apoptosis. CD95-sensitive cells were used to reveal that death occurred independently of CD95-CD95 ligand interactions. Overall, these data reveal a pathway of HLA-DR-mediated apoptosis that neither requires nor involves caspases. Moreover, it is phosphatidylinositol-3-kinase independent and Fas/CD95 independent. This pathway of HLA class II-mediated apoptosis could have an important role in the regulation of APC populations or in the control of malignant B lymphocyte proliferations.

HLA-DR inhibits granulocytic differentiation without inducing apoptosis of CD34 cells

Hematopoietic progenitors express HLA-DR molecules. However the significance of HLA-class II molecules on CD34+ cells remains unknown. The primary role of HLA-class-II molecules is antigen presentation although a second role, that of signal transduction, has been established in B cells. The role of HLA-DR in hematopoiesis was examined by determining the ability of CD34+ progenitor cells to differentiate to "Colony Forming Unit Granulocyte-Macrophage" (CFU-GM) and "Burst Forming Unit Erythrocyte" (BFU-E) in the presence of anti-HLA-DR monoclonal antibody. We observed a reduction in the number of CFU-GM which was due in part to down regulation of granulocyte rather than monocyte differentiation. These observations suggest that HLA-DR signals can regulate myelopoiesis. We point out especially the role of the HLA-DR molecule in the switch of CFU-GM between granulocyte or monocyte lineages. Although HLA-DR mediated apoptosis has been described in mature B lymphocytes apoptosis of CD34+ cells was excluded as a mechanism.