Antilymphoma effects of anti-HLA-DR and CD20 monoclonal antibodies (Lym-1 and Rituximab) on human lymphoma cells

Estimation for general birth-death processes

Birth-death processes (BDPs) are continuous-time Markov chains that track the number of "particles" in a system over time. While widely used in population biology, genetics and ecology, statistical inference of the instantaneous particle birth and death rates remains largely limited to restrictive linear BDPs in which per-particle birth and death rates are constant. Researchers often observe the number of particles at discrete times, necessitating data augmentation procedures such as expectation-maximization (EM) to find maximum likelihood estimates. For BDPs on finite state-spaces, there are powerful matrix methods for computing the conditional expectations needed for the E-step of the EM algorithm. For BDPs on infinite state-spaces, closed-form solutions for the E-step are available for some linear models, but most previous work has resorted to time-consuming simulation. Remarkably, we show that the E-step conditional expectations can be expressed as convolutions of computable transition probabilities for any general BDP with arbitrary rates. This important observation, along with a convenient continued fraction representation of the Laplace transforms of the transition probabilities, allows for novel and efficient computation of the conditional expectations for all BDPs, eliminating the need for truncation of the state-space or costly simulation. We use this insight to derive EM algorithms that yield maximum likelihood estimation for general BDPs characterized by various rate models, including generalized linear models. We show that our Laplace convolution technique outperforms competing methods when they are available and demonstrate a technique to accelerate EM algorithm convergence. We validate our approach using synthetic data and then apply our methods to cancer cell growth and estimation of mutation parameters in microsatellite evolution.

Autophagy plays a critical role in ChLym-1-induced cytotoxicity of non-hodgkin's lymphoma cells

Autophagy is a critical mechanism in both cancer therapy resistance and tumor suppression. Monoclonal antibodies have been documented to kill tumor cells via apoptosis, antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC). In this study, we report for the first time that chLym-1, a chimeric anti-human HLA-DR monoclonal antibody, induces autophagy in Raji Non-Hodgkin’s Lymphoma (NHL) cells. Interestingly, inhibition of autophagy by pharmacological inhibitors (3-methyladenine and NH₄Cl) or genetic approaches (siRNA targeting Atg5) suppresses chLym-1-induced growth inhibition, apoptosis, ADCC and CDC in Raji cells, while induction of autophagy could accelerate cytotoxic effects of chLym-1 on Raji cells. Furthermore, chLym-1-induced autophagy can mediate apoptosis through Caspase 9 activation, demonstrating the tumor-suppressing role of autophagy in antilymphoma effects of chLym-1. Moreover, chLym-1 can activate several upstream signaling pathways of autophagy including Akt/mTOR and extracellular signal-regulated kinase 1/2 (Erk1/2). These results elucidate the critical role of autophagy in cytotoxicity of chLym-1 antibody and suggest a potential therapeutic strategy of NHL therapy by monoclonal antibody chLym-1 in combination with autophagy inducer.

Novel antibodies against follicular non-Hodgkin's lymphoma

The anti-CD20 monoclonal antibody rituximab has revolutionized the treatment of patients with follicular B-cell lymphoma. With the combination of chemotherapy and rituximab the overall survival rate has increased with approximately 30%. Unfortunately, there is resistance to rituximab with relapse of the disease in about 60% of the patients during the first five years of treatment and eventually in all patients. To this end, there is a need to develop improved anti-CD20 monoclonal antibodies and antibodies that target other attractive molecules expressed on the follicular lymphoma cell. This review describes the development and clinical achievements so far of next generation anti-CD20 and other antibodies in the treatment of follicular B-cell lymphoma.

Combination immunotherapy with anti-CD20 and anti-HLA-DR monoclonal antibodies induces synergistic anti-lymphoma effects in human lymphoma cell lines

Rituximab is effective in about one half of patients with indolent lymphoma. Even these patients relapse and develop rituximab resistance. To increase potency and circumvent resistance, the anti-lymphoma effects of rituximab, an anti-CD20 MAb(1), combined with chLym-1(2), an anti-HLA-DR MAb, were assessed in human lymphoma cell lines by examining growth inhibition and cell death, apoptosis induction, ADCC(3) and CDC(4). There were additive effects in all assays and synergism in cell lines, such as B35M, which displayed resistance to either MAb alone. In B35M cells, combined rituximab and chLym-1 induced a 27-fold direct reduction in viable cells, whereas equivalent concentrations of rituximab or chLym-1 alone induced only a 1-fold and 10-fold reduction in viable cells, respectively. Because these results occurred at MAb concentrations readily achievable in patients, they suggest that this combination immunotherapy regimen may increase the potency and range of effectiveness of these MAbs in lymphoma patients.

Generation of a human IgM monoclonal antibody directed against HLA class II molecules: a potential agent in the treatment of haematological malignancies

Major histocompatibility complex (MHC) class II molecules have been considered as a good target molecule for use in immunotherapy, because of the high expression in some lymphoma and leukaemia cells and, also, because of their restricted expression on human cells (monocytes, dendritic, B lymphocytes, thymic epithelial cells, and some cytokine-activated cells, such as T lymphocytes). We have obtained a human IgM monoclonal antibody directed against human leukocyte antigen (HLA) class II molecules, using transgenic mice carrying human Ig genes. The antibody BH1 (IgM/kappa isotype) recognises HLA-class II on the surface of tumour cells from patients suffering from haematological malignancies, such as chronic and acute lymphocytic leukaemias, non-Hodgkin lymphomas and myeloid leukaemias. Interestingly, functional studies revealed that BH1 mAb recognises and kills very efficiently tumour cells from several leukaemia patients in the presence of human serum as a source of complement. These results suggest that this human IgM monoclonal antibody against HLA-class II could be considered as a potential agent in the treatment of several malignancies.

MHC class II structural requirements for the association with Igalpha/beta, and signaling of calcium mobilization and cell death

Emerging evidence indicates that in addition to their well-characterized role in antigen presentation, MHC II molecules transmit signals that induce death of APCs. Appropriately timed APC death is important for prevention of autoimmunity. Though the exact mechanism of MHC II-mediated cell death signaling is unknown, the response appears independent of caspase activation and does not involve Fas-FasL interaction. Here we investigated MHC II structural requirements for mediation of cell death signaling in a murine B cell lymphoma. We found that neither the transmembrane spanning regions nor the cytoplasmic tails of MHC II, which are required for MHC II-mediated cAMP production and PKC activation, are required for the death response. However, mutations in the connecting peptide region of MHC II alpha chain (alphaCP), but not the beta chain (betaCP), resulted in significant impairment of the death response. The alphaCP mutant was also unable to mediate calcium mobilization responses, and did not associate with Igalpha/beta. Knock-down of Igbeta by shRNA eliminated the MHC II-mediated calcium response but not cell death. We propose that MHC II mediates cell death signaling via association with an undefined cell surface protein(s), whose interaction is partially dependent on alphaCP region.

Lym-1-induced apoptosis of non-Hodgkin's lymphomas produces regression of transplanted tumors

Lym-1 was one of the first antibodies to be used successfully for the radioimmunotherapy of the human malignant lymphomas. This antibody, which recognizes the HLA-DR10 antigen preferentially expressed in B-cell lymphomas, was recently shown to induce apoptosis upon binding to lymphoma cells. In this study, Lym-1-induced apoptosis was studied to identify the potential molecular pathways of programmed cell death and to demonstrate the clinical potential of this antibody in the treatment of the human malignant lymphomas. Immunofluorescence microscopy revealed that Lym-1 stained focal areas of the cell surface, consistent with the fact that the HLA-DR10 antigen is associated with lipid rafts, a known prerequisite for apoptosis signaling. Likewise, Annexin V/propidium iodide staining and TUNEL assays demonstrated that both murine Lym-1 and chimeric Lym-1 induced both early and late apoptosis, respectively, unlike anti-CD20 rituximab. Furthermore, Lym-1 was found to produce a rapid loss of mitochondrial membrane potential and mitochondrial release of cytochrome C 14 hours post-Lym-1 treatment. Although it was found to activate caspase-3, inhibitors of caspase pathways showed that the Lym-1-induced apoptosis in lymphoma cell lines is independent of caspase induction. Finally, treatment studies in vivo demonstrated that, compared with murine anti-CD20 (2B8), Lym-1 was more effective in inducing the regression of human lymphoma xenografts. Based upon these results, chimeric Lym-1 should be especially effective in treating lymphoma patients, as, in addition to being able to elicit immune effector functions such as chimeric anti-CD20, it can also induce apoptosis directly upon cell binding.

Direct antilymphoma activity of novel, first-generation "antibody mimics" that bind HLA-DR10-positive non-Hodgkin's lymphoma cells

A first-generation series of novel small molecules, collectively known as selective high-affinity ligands (SHALs), were designed and synthesized to mimic the binding of Lym-1, a monoclonal antibody (mAb) shown to be an effective cytotoxic and radionuclide carrier molecule for targeting non-Hodgkin's lymphoma (NHL). Created as radionuclide targeting molecules, these SHALs were intended to have the human leukocyte antigen-DR (HLA-DR) selectivity of Lym-1 mAb and the pharmacokinetics of a small molecule. Because of the remarkable bioactivity of Lym-1 in vitro, the direct antilymphoma activity of three of these SHALs was tested. Two of these SHALs were bidentate and consisted of two ligands connected to the carboxyl and amino groups of lysine and polyethylene glycol (PEG); the third SHAL was a dimeric version of one of the former two SHALs linked with PEG. The three SHALs tested were: LeLPLDB, that contained one deoxycholate and one 5-leu-enkephalin as ligands; (LeacPLD)2LPB, a bis version of LeLPLDB intended to improve "functional affinity"; and ItPLDB, that contained the ligands, deoxycholate and triiodothyronine. Micromolar concentrations of all three SHALs showed binding to Raji, an HLA-DR10-positive human malignant B-cell line but no binding to CEM or Jurkat's, HLA-DR10-negative malignant T-cell lines. Additionally, the Raji cell membrane distributions of all three SHALs and of Lym-1 were remarkably similar. Unlike Lym-1, which causes substantial growth inhibition and cell death in NHL cell lines, these SHALs had no direct antilymphoma activity. In summary, three first-generation SHALs lacked direct antilymphoma activity, although they had selective NHL B-cell binding like Lym-1 mAb. Because of their small size, these SHALs have potential as radionuclide carrier substitutes for Lym-1 mAb to target the HLA-DR10 NHL-related cell-surface protein.

Cure of incurable lymphoma

The most potent method for augmenting the cytocidal power of monoclonal antibody (MAb) treatment is to conjugate radionuclides to the MAb to deliver systemic radiotherapy (radioimmunotherapy; RIT). The antigen, MAb, and its epitope can make a difference in the performance of the drug. Additionally, the radionuclide, radiochemistry, chelator for radiometals and the linker between the MAb and chelator can have a major influence on the performance of drugs (radiopharmaceuticals) for RIT. Smaller radionuclide carriers, such as antibody fragments and mimics, and those used for pretargeting strategies, have been described and evaluated. All of these changes in the drugs and strategies for RIT have documented potential for improved performance and patient outcomes. RIT is a promising new therapy that should be incorporated into the management of patients with B-cell non-Hodgkin's lymphoma (NHL) soon after these patients have proven incurable. Predictable improvements using better drugs, strategies, and combinations with other drugs seem certain to make RIT integral to the management of patients with NHL, and likely lead to cure of currently incurable NHL.

Antibody Targeting to a Class I MHC-Peptide Epitope Promotes Tumor Cell Death

Therapeutic mAbs that target tumor-associated Ags on the surface of malignant cells have proven to be an effective and specific option for the treatment of certain cancers. However, many of these protein markers of carcinogenesis are not expressed on the cells' surface. Instead these tumor-associated Ags are processed into peptides that are presented at the cell surface, in the context of MHC class I molecules, where they become targets for T cells. To tap this vast source of tumor Ags, we generated a murine IgG2a mAb, 3.2G1, endowed with TCR-like binding specificity for peptide-HLA-A*0201 (HLA-A2) complex and designated this class of Ab as TCR mimics (TCRm). The 3.2G1 TCRm recognizes the GVL peptide (GVLPALPQV) from human chorionic gonadotropin beta presented by the peptide-HLA-A*0201 complex. When used in immunofluorescent staining reactions using GVL peptide-loaded T2 cells, the 3.2G1 TCRm specifically stained the cells in a peptide and Ab concentration-dependent manner. Staining intensity correlated with the extent of cell lysis by complement-dependent cytotoxicity (CDC), and a peptide concentration-dependent threshold level existed for the CDC reaction. Staining of human tumor lines demonstrated that 3.2G1 TCRm was able to recognize endogenously processed peptide and that the breast cancer cell line MDA-MB-231 highly expressed the target epitope. The 3.2G1 TCRm-mediated CDC and Ab-dependent cellular cytotoxicity of a human breast carcinoma line in vitro and inhibited in vivo tumor implantation and growth in nude mice. These results provide validation for the development of novel TCRm therapeutic reagents that specifically target and kill tumors via recognition and binding to MHC-peptide epitopes.

Characterization of a humanized IgG4 anti-HLA-DR monoclonal antibody that lacks effector cell functions but retains direct antilymphoma activity and increases the potency of rituximab

HLA-DR is under investigation as a target for monoclonal antibody (mAb) therapy of malignancies. Here we describe a humanized IgG4 form of the anti-HLA-DR mAb L243, hL243gamma4P (IMMU-114), generated to provide an agent with selectivity toward neoplastic cells that can kill without complement-dependent cytotoxicity (CDC) or antibody-dependent cellular-cytotoxicity (ADCC), so as to reduce reliance on intact immunologic systems in the patient and effector mechanism-related toxicity. In vitro studies show that replacing the Fc region of hL243gamma1, a humanized IgG1 anti-HLA-DR mAb, with the IgG4 isotype abrogates the effector cell functions of the antibody (ADCC and CDC) while retaining its antigen-binding properties, antiproliferative capacity (in vitro and in vivo), and the ability to induce apoptosis concurrent with activation of the AKT survival pathway. Growth inhibition was evaluated compared with and in combination with the anti-CD20 mAb rituximab, with the combination being more effective than rituximab alone in inhibiting proliferation. Thus, hL243gamma4P is indistinguishable from hL243gamma1 and the parental murine mAb in assays dependent on antigen recognition. The abrogation of ADCC and CDC, which are believed to play a major role in side effects of mAb therapy, may make this antibody an attractive clinical agent. In addition, combination of hL243gamma4P with rituximab offers the prospect for improved patient outcome.

Treatment of Non-Hodgkin’s Lymphoma (NHL) With Radiolabeled Antibodies (mAbs)

Most patients with non-Hodgkin's lymphoma (NHL) achieve remission but, despite newer drugs, the natural history of this disease has not improved during the last 20 years. Less than one half of patients with aggressive NHL are cured, and few of those with low-grade NHL are curable. Furthermore, NHL becomes progressively more chemoresistant while remaining responsive to external beam radiation therapy. Radioimmunotherapy (RIT) is a logical strategy for the treatment of NHL because this disease is multifocal and radiosensitive. Because of their remarkable effectiveness for RIT, 2 anti-CD20 monoclonal antibodies (mAbs), one labeled with (111)In for imaging or (90)Y for therapy and a second labeled with (131)I for imaging and therapy, have been approved for use in patients with NHL. These drugs have proven remarkably effective and safe. Evidence for the importance of the radionuclide is manifested by the data in the randomized pivotal phase III trial of (90)Y-ibritumomab that revealed response rates were several times greater in the (90)Y-ibritumomab arm than in the rituximab arm. A second drug for RIT, (131)I-tositumomab, was compared in a pivotal trial with the efficacy of the last chemotherapy received by each patient. Once again, response rates were much higher for RIT. Both (90)Y-ibritumomab and (131)I-tositumomab require preinfusion of several hundred milligrams of unlabeled anti-CD20 mAb to obtain "favorable" biodistribution, that is, targeting of NHL. Response rates for other mAbs and radionuclides in NHL also have been high but these drugs have not reached the approval stage. These drugs can be used safely by physicians who have suitable training and judgment. Unlike chemotherapy, RIT is not associated with mucositis, hair loss, or persistent nausea or vomiting. Although hematologic toxicity is dose limiting, hospitalization for febrile neutropenia is uncommon. Randomized trials of RIT in different formulations have not been conducted, but there is evidence to suggest that the mAb, antigen, radionuclide, chelator, linker, and dosing strategy may make a difference in the outcome.