Rituximab-dependent cytotoxicity by natural killer cells: influence of FCGR3A polymorphism on the concentration-effect relationship

Elimination mechanisms of therapeutic monoclonal antibodies

Targeted therapies using monoclonal antibodies have achieved important therapeutic applications in the treatment of various human diseases. Understanding the factors that impact the pharmacokinetics of monoclonal antibodies is of high importance for effective therapy. Many factors related to the target antigen, antibody and patients can affect antibody elimination. Evaluation of these factors will facilitate the understanding of the processes involved in antibody elimination.

Engineered antibody Fc variants with enhanced effector function

Antibody-dependent cell-mediated cytotoxicity, a key effector function for the clinical efficacy of monoclonal antibodies, is mediated primarily through a set of closely related Fcgamma receptors with both activating and inhibitory activities. By using computational design algorithms and high-throughput screening, we have engineered a series of Fc variants with optimized Fcgamma receptor affinity and specificity. The designed variants display >2 orders of magnitude enhancement of in vitro effector function, enable efficacy against cells expressing low levels of target antigen, and result in increased cytotoxicity in an in vivo preclinical model. Our engineered Fc regions offer a means for improving the next generation of therapeutic antibodies and have the potential to broaden the diversity of antigens that can be targeted for antibody-based tumor therapy.

Antibody-dependent cellular cytotoxicity (ADCC) is mediated by genetically modified antigen-specific human T lymphocytes

In the context of transplantation, donor and virus-specific T-lymphocyte infusions have demonstrated the dramatic potential of T cells as immune effectors. Unfortunately, most attempts to exploit the T-cell immune system against nonviral malignancies in the syngeneic setting have been disappointing. In contrast, treatments based on monoclonal antibodies (Abs) have been clinically successful and have demonstrated the clinical relevance of several antigens as therapeutic targets and the importance of the antibody-dependent cellular cytotoxicity (ADCC) pathway. In the present study, we considered the possibility of arming specific T cells with a receptor that would enable them to mediate ADCC. After transduction with a CD16/gamma receptor gene, CD4(+) and CD8(+) cytotoxic T lymphocytes displayed stable expression of the CD16 receptor at their surface. In the absence of Ab, CD16/gamma expression did not affect the capacity of specific T lymphocytes to kill their target following "natural" T-cell receptor recognition. When tested against the autologous B-lymphoblastoid cell line (BLCL) coated with anti-CD20 mAb, the newly expressed Fc receptor enabled the T cells to kill the BLCL through ADCC. Adoptive transfer of such newly designed immune effector may be considered to increase antibody efficiency by harnessing the immune potential of T cells.

MT110: A novel bispecific single-chain antibody construct with high efficacy in eradicating established tumors

We have developed a novel single-chain Ep-CAM-/CD3-bispecific single-chain antibody construct designated MT110. MT110 redirected unstimulated human peripheral T cells to induce the specific lysis of every Ep-CAM-expressing tumor cell line tested. MT110 induced a costimulation independent polyclonal activation of CD4- and CD8-positive T cells as seen by de novo expression of CD69 and CD25, and secretion of interferon gamma, tumor necrosis factor alpha, and interleukins 2, 4 and 10. CD8-positive T cells made the major contribution to redirected tumor cell lysis by MT110. With a delay, CD4-positive cells could also contribute presumably as consequence of a dramatic upregulation of granzyme B expression. MT110 was highly efficacious in a NOD/SCID mouse model with subcutaneously growing SW480 human colon cancer cells. Five daily doses of 1 microg MT110 on days 0-4 completely prevented tumor outgrowth in all mice treated. The bispecific antibody construct also led to a durable eradication of established tumors in all mice treated with 1 microg doses of MT110 on days 8-12 after tumor inoculation. Finally, MT110 could eradicate patient-derived metastatic ovarian cancer tissue growing under the skin of NOD/SCID mice. MT110 appears as an attractive bispecific antibody candidate for treatment of human Ep-CAM-overexpressing carcinomas.

An engineered human IgG1 antibody with longer serum half-life

The serum half-life of IgG Abs is regulated by the neonatal Fc receptor (FcRn). By binding to FcRn in endosomes, IgG Abs are salvaged from lysosomal degradation and recycled to the circulation. Several studies have demonstrated a correlation between the binding affinity of IgG Abs to FcRn and their serum half-lives in mice, including engineered Ab fragments with longer serum half-lives. Our recent study extended this correlation to human IgG2 Ab variants in primates. In the current study, several human IgG1 mutants with increased binding affinity to human FcRn at pH 6.0 were generated that retained pH-dependent release. A pharmacokinetics study in rhesus monkeys of one of the IgG1 variants indicated that its serum half-life was approximately 2.5-fold longer than the wild-type Ab. Ag binding was unaffected by the Fc mutations, while several effector functions appeared to be minimally altered. These properties suggest that engineered Abs with longer serum half-lives may prove to be effective therapeutics in humans.

Lymphomas are sensitive to perforin-dependent cytotoxic pathways despite expression of PI-9 and overexpression of bcl-2

There is considerable interest in immunotherapeutic approaches for lymphoma. The expression of proteinase inhibitor 9 (PI-9), a molecule that inactivates granzyme B, is considered an immune escape mechanism in lymphoma. Further, lymphomas frequently overexpress the antiapoptotic molecule bcl-2, which is able to inhibit perforin-dependent cytotoxic pathways. In this study, the impact of PI-9 and bcl-2 expression on the sensitivity of lymphomas to T- and natural killer (NK) cell-mediated cytotoxicity was analyzed. We found PI-9 expression in 10 of 18 lymphoma cell lines and in 9 of 14 primary lymphomas. Overexpression of bcl-2 was found in 8 of 18 cell lines and in 12 of 14 primary lymphomas. All lymphoma cells were sensitive to cytolysis by specific T cells and cytokine-activated NK cells, and no difference in sensitivity was observed with respect to PI-9 or bcl-2 expression. Cytolysis was mediated predominantly through perforin-dependent pathways despite expression of PI-9 and bcl-2. Interestingly, the majority of lymphoma cells were resistant to cytolysis by resting allogeneic NK cells. This was due to the failure of lymphomas to induce degranulation of resting NK cells. These results show that resistance to perforin-dependent pathways is not a relevant immune escape mechanism in lymphoma and therefore is unlikely to impair clinical outcome of immunotherapeutic approaches.

Natural killer cells in human health and disease

Natural killer (NK) cells are lymphocytes of the innate immune system that are critical in host defense and immune regulation. They are activated or inhibited through the ligation of germline-encoded receptors and are involved in mediating cytotoxicity, in producing cytokines and in providing co-stimulation to cells of the adaptive immune system. NK cells play important roles in viral infections, autoimmunity, pregnancy, cancer and bone marrow transplantation. This review highlights recent developments in the understanding of the role of human NK cells in health and disease.

Pharmacokinetics and concentration–effect relationships of therapeutic monoclonal antibodies and fusion proteins

Although monoclonal antibodies (mAbs) constitute a major advance in therapeutics, their pharmacokinetic (PK) and pharmacodynamic (PD) properties are not fully understood. Saturable mechanisms are thought to occur in distribution and elimination of mAbs, which are protected from degradation by the Brambell's receptor (FcRn). The binding of mAbs to their target antigen explains part of their nonlinear PK and PD properties. The interindividual variability in mAb PK can be explained by several factors, including immune response against the biodrug and differences in the number of antigenic sites. The concentration-effect relationships of mAbs are complex and dependent on their mechanism of action. Interindividual differences in mAb PD can be explained by factors such as genetics and clinical status. PK and concentration-effect studies are necessary to design optimal dosing regimens. Because of their above-mentioned characteristics, the interindividual variability in their dose-response relationships must be studied by PK-PD modelling.

Variability factors in the clinical response to recombinant antibodies and IgG Fc-containing fusion proteins

Recombinant monoclonal antibodies and IgG Fc-containing fusion proteins represent major therapeutic advances in many diseases. However, despite their similarity with endogenous IgG, some patients respond to the treatment whilst others do not; thus raising the question of the origin of this variability. Some variability factors are now identified, of genetic origin or not, which influence either pharmacokinetics or pharmacodynamics of these drugs. Known variability factors are reviewed and classified according to their relationship with the paratope (antigen binding site) of the antibodies, with other parts of the IgGs (mostly Fc) or with IgG epitopes (antigenic motifs).

Pharmacogenetics and pharmacogenomics in oncology therapeutic antibody development

Pharmacogenetics and pharmacogenomics are keys to the success of personalized medicine, prescribing drugs based on a patien's individual genetic and biological profile. In this review, we will focus on the application of pharmacogenetics and pharmacogenomics in developing monoclonal antibody (MAb) therapeutics in oncology. The significance of pharmacogenomics in MAb therapeutics is highlighted by the association between polymorphisms in Fc receptors and clinical response to anti-CD20 MAb rituximab (Rituxan®) or anti-ganglioside GD2 MAb 3F8, as well as the potential link between polymorphisms in HER2 and cardiac toxicity in patients treated with the anti-HER2 MAb trastuzumab (Herceptin®). The dependence on gene copy number or expression levels ofHER2 and epidermal growth factor receptor (EGFR) for therapeutic efficacy of trastuzumab and cetuximab (Erbitux®), respectively, supports the importance of selecting suitable patient populations based on their pharmacogenetic profile. In addition, a better understanding of target mutation status and biological consequences will benefit MAb development and may guide clinical development and use of these innovative therapeutics. The application of pharmacogenetics and pharmacogenomics in developing MAb therapeutics will be largely dependent on the discovery of novel surrogate biomarkers and identification of disease- and therapeutics-relevant polymorphisms. Challenges and opportunities in biomarker discovery and validation, and in implementing clinical pharmacogenetics and pharmacogenomics in oncology MAb development and clinical practice will also be discussed.

The therapeutic potential of anti-CD20 "what do B-cells do?"

B-cells play a major role in the immunopathogenesis of autoimmune diseases. Not only do they produce autoantibodies, but they regulate other cell types, secrete cytokines, and present antigens. They are thus potential targets for therapeutic intervention. CD20 is a B-cell specific cell surface molecule of uncertain function. An anti-CD20 chimeric mAb (rituximab) has been FDA approved for treatment of B-cell lymphomas since 1997. Rituximab also depletes normal B-cells by several mechanisms, including ADCC. Over the past seven years, it has shown promise in a number of autoimmune diseases in phase I trials and anecdotal reports. Efficacy in rheumatoid arthritis has already been demonstrated in randomized control trials (RCTs), and RCTs in SLE, inflammatory myositis, and ANCA associated vasculitis are under way. Safety does not appear to be a major problem, but continued vigilance is warranted. The increased use of rituximab, other anti-CD20 agents, and other B-cell targeting therapies holds great promise for substantial clinical benefits, as well as providing special opportunities to understand better disease pathogenesis.

Flow cytometric assay for determination of FcgammaRIIIA-158 V/F polymorphism

A single nucleotide polymorphism (SNP) of the FCGR3A gene results in two allotypes of Fcgamma receptor IIIA (FcgammaRIIIA) with valine (V) or phenylalanine (F) at amino acid 158. Since the FcgammaRIIIA-158 V/F polymorphism is associated with the efficacy of monoclonal antibody (mAb) treatment and a risk factor for autoimmune disease, widely applicable methods to assess the SNP are needed. We developed a novel flow cytometric test for this polymorphism using a mAb that recognized only the FcgammaRIIIA-158 V allele (MEM-154) together with a mAb that detected both FcgammaRIIIA-158 alleles (3G8). The expression of both FcgammaRIIIA epitopes on natural killer (NK) cells from 37 healthy donors were measured and compared to the FCGR3A genotype determined by a 5' nuclease assay. FcgammaRIIIA expression levels in individuals with identical FCGR3A genotypes varied considerably, resulting in overlapping immunofluorescences by both 3G8 and MEM-154 between FcgammaRIIIA-158 V/F allotypes. However, the ratio between fluorescences measured using those mAbs in a single individual predicted the FCGR3A genotype with 100% sensitivity and specificity. The novel flow cytometric assay for the FcgammaRIIIA-158 V/F polymorphism that is based on the MEM-154/3G8 fluorescence ratio requires commercially available reagents and a three-color flow cytometer only.

CD16 polymorphisms and NK activation induced by monoclonal antibody-coated target cells

CD16 and natural killer (NK) cells appear to play a central role in mediating the anti-tumor effects of monoclonal antibody (mAb) therapy, yet little is known about changes in NK cells that result from interaction of the NK cells with mAb-coated tumor cells under physiologic conditions. We developed a system using peripheral blood mononuclear cells (PBMCs) and either transformed B cells or breast cancer cells to assess how mAbs impact on NK cell phenotype. Rituximab, apolizumab and trastuzumab induced modulation of CD16 and upregulation of CD54 on NK cells when the appropriate target cells were present. Higher concentrations of mAb were needed to induce these changes on NK cells from subjects with the lower affinity CD16 polymorphism. Phenotypic changes were greater in NK cells from subjects with the higher affinity polymorphism even when saturating concentrations of mAb were used, demonstrating increased concentration of mAb can overcome some, but not all, of the influence CD16 polymorphisms have on NK activation. These studies provide a straightforward and easily reproducible technique to measure the ability of mAb-coated tumor cells to activate NK cells in vitro which should be particularly useful as mAbs with varying affinity for both target antigen and Fc receptor (FcR) are developed.

Intralesional therapy with anti-CD20 monoclonal antibody rituximab: local and systemic efficacy in primary cutaneous B-cell lymphoma

Rituximab (MabThera, Roche) is a chimeric monoclonal antibody directed against the CD20 antigen. Its efficacy and safety were first demonstrated in the treatment of systemic B-cell lymphomas. We report the use of intralesional injections of rituximab into some but not all cutaneous lesions in a patient with multiple primary cutaneous follicular centre B-cell lymphoma. This treatment resulted in tumour regression, even of the lesions that had not been injected. We therefore hypothesize that there is systemic diffusion of rituximab from injected sites despite the low doses injected locally, or the induction of a specific antitumour immune response acting systemically.