Complement-induced cell death by rituximab depends on CD20 expression level and acts complementary to antibody-dependent cellular cytotoxicity

Interleukin-4 distinctively modifies responses of germinal centre-like and activated B-cell-like diffuse large B-cell lymphomas to immuno-chemotherapy

Diffuse large B-cell lymphomas (DLBCLs) can be classified into two subtypes: germinal-centre B-cell (GCB)-like and Activated B-cell (ABC)-like tumours, which are associated with longer or shorter patient overall survival, respectively. In our previous studies, we have shown that, although DLBCL tumours of GCB-like and ABC-like subtypes express similar levels of IL4 mRNA, they exhibit distinct patterns of IL-4-induced intracellular signalling and different expression of IL-4 target genes. We hypothesized that these differences may contribute to the different clinical behaviour and outcome of DLBCL subtypes. Herein, we demonstrated that IL-4 increased the sensitivity of GCB-like DLBCL to doxorubicin-induced apoptosis and complement-dependent rituximab cell killing. In contrast, IL-4 protected ABC-like DLBCL from the cytotoxic effects of doxorubicin and rituximab. The distinct effects of IL-4 on doxorubicin sensitivity in GCB-like and ABC-like DLBCL cells may be partially attributed to the contrasting effects of the cytokine on Bcl-2 and Bad protein levels in the DLBCL subtypes. These findings suggest that the different effects of IL-4 on chemotherapy and immunotherapy-induced cytotoxicity of GCB- and ABC-like DLBCL could contribute to the different clinical outcomes exhibited by patients with these two subtypes of DLBCL.

Molecular mechanisms of resistance to Rituximab and pharmacologic strategies for its circumvention

The introduction of Rituximab has greatly improved therapeutic options for patients with B-cell non-Hodgkin lymphoma (B-NHL). However, a substantial fraction of patients with aggressive B-NHL fails first-line therapy, and most patients with relapsing indolent B-NHL eventually acquire Rituximab resistance. Molecular understanding of the underlying mechanisms facilitates the development of pharmacologic strategies to overcome resistance. Rituximab exerts its activity on CD20-expressing B-cells by indirect and direct effector mechanisms. Indirect mechanisms are complement-dependent cytotoxicity (CDC), and antibody-dependent cell-mediated cytotoxicity (ADCC). Direct activities, such as growth inhibition, induction of apoptosis and chemosensitisation, have been reported, but are less defined. Moreover, the relative contribution of CDC, ADCC and direct mechanisms to the activity of Rituximab in vivo is unclear. Down-regulation of CD20 and expression of complement inhibitors have been described as escape mechanisms in B-NHL. Recent reports suggest that deregulated phosphoinositide-3-kinase (PI3K)/Akt, mitogen-activated kinases (MAPK) and nuclear-factor kappaB (NF-kappaB), as well as up-regulation of anti-apoptotic proteins may determine the efficacy of Rituximab to kill B-NHL cells in vitro and in vivo. The latter signalling pathways are attractive targets for pharmacologic modulation of resistance to Rituximab. With the advent of new inhibitors and antibodies, rationally designed clinical trials addressing Rituximab resistance are feasible.

Escape mechanisms from antibody therapy to lymphoma cells: downregulation of CD20 mRNA by recruitment of the HDAC complex and not by DNA methylation

Although rituximab is a critical monoclonal antibody therapy for CD20-positive B-cell lymphomas, rituximab resistance showing a CD20-negative phenotypic change has been a considerable clinical problem. Here we demonstrate that CD20 mRNA and protein expression is repressed by recruitment of a histone deacetylase protein complex to the MS4A1 (CD20) gene promoter in CD20-negative transformed cells after treatment with rituximab. CD20 mRNA and protein expression were stimulated by decitabine (5-Aza-dC) in CD20-negative transformed cells, and was enhanced by trichostation A (TSA). Immunoblotting indicated that DNMT1 expression was first downregulated 1 day after treatment with 5-Aza-dC, but IRF4 and Pu.1, the transcriptional regulators of MS4A1, were still expressed with or without 5-Aza-dC. Interestingly, CpG methylation of the MS4A1 promoter was not observed in CD20-negative transformed cells without 5-Aza-dC. A chromatin immunoprecipitation (ChIP) assay indicated that the Sin3A-HDAC1 co-repressor complex was recruited to the promoter and dissociated from the promoter with 5-Aza-dC and TSA, resulting in histone acetylation. Under these conditions, IRF4 and Pu.1 were continually recruited to the promoter with or without 5-Aza-dC and TSA. These results suggest that recruitment of the Sin3A-HDAC1 complex is related to downregulation of CD20 expression in CD20-negative B-cells after treatment with rituximab.

Fractionated subcutaneous rituximab is well-tolerated and preserves CD20 expression on tumor cells in patients with chronic lymphocytic leukemia

A pilot study previously demonstrated that thrice-weekly, fractionated-dose intravenous rituximab (RTX) limits CD20 loss from chronic lymphocytic leukemia (CLL) B cells, thereby enhancing immunotherapeutic targeting. Here, we investigated the feasibility of giving 20 mg rituximab subcutaneously thrice weekly for up to 12 weeks in 4 previously treated CLL patients. Subcutaneous rituximab was well-tolerated with minimal injection site reactions; a variable degree of efficacy was observed, likely influenced by the size of the patients' B cell/CD20 burden. Subcutaneous RTX largely preserved CD20 expression on leukemic cells but the most effective therapeutic dosing regimen needs to be established (ClinicalTrials.gov Identifier: NCT00366418).

[Molecular mechanisms of B lymphocyte depletion by CD20 immunotherapy]

Anti-CD20 antibody immunotherapy effectively treats non-Hodgkin's lymphoma and autoimmune disease. However, the cellular and molecular pathways for B cell depletion remain undefined and the in vivo effect of immunotherapy on tissue B cells and their subsets is generally unknown. To identify the mechanisms for B cell depletion in vivo, a new mouse model for anti-CD20 immunotherapy was developed using a panel of twelve mouse anti-mouse CD20 monoclonal antibodies. Anti-CD20 antibodies rapidly depleted the vast majority of circulating and tissue B cells in an isotype-restricted manner that was completely dependent on effector cell Fc receptor expression. B cell depletion utilized FcgammaRI-, FcgammaRIII- and FcgammaRIV-dependent pathways, while B cells were not eliminated in FcR common gamma chain-deficient mice. Monocytes were the dominant effector cells for B cell depletion, with no demonstrable role for T or NK cells. Although most anti-CD20 antibodies activated complement in vitro, B cell depletion was completely effective in mice with genetic deficiencies in C3 complement components. The considerable factors that determine the effectiveness of anti-CD20 immunotherapy are following: the expression level of CD20 on B cell surface; the dosage of anti-CD20 mAb; the association of Fcgamma receptor with the isotype of the antibies; B cell subpopulations within different tissues. These findings have important clinical implications for anti-CD20 and other antibody-based therapies.

Binding of submaximal C1q promotes complement-dependent cytotoxicity (CDC) of B cells opsonized with anti-CD20 mAbs ofatumumab (OFA) or rituximab (RTX): considerably higher levels of CDC are induced by OFA than by RTX

The CD20 mAb ofatumumab (OFA) is more effective than rituximab (RTX) in promoting complement-dependent cytotoxicity (CDC) of B cells via the classical pathway (CP) of complement. CP activation is initiated by C1q binding to cell-bound IgG. Therefore, we examined the role of C1q in the dynamics of complement activation and CDC of B cell lines and primary cells from patients with chronic lymphocytic leukemia, reacted with OFA or RTX. C1q binding, complement activation, and colocalization of C1q with cell-bound mAbs were determined by flow cytometry and high-resolution digital imaging. C1q binds avidly to OFA-opsonized Raji and Daudi cells (K(D) = 12-16 nM) and colocalizes substantially with cell-bound OFA. Cells opsonized with OFA undergo high levels of complement activation and CDC in C1q-depleted serum supplemented with low concentrations of C1q. Under comparable conditions, RTX-opsonized cells bind less C1q; in addition, even when higher concentrations of C1q are used to achieve comparable C1q binding to RTX-opsonized cells, less complement activation and CDC are observed. Greater CDC induced by OFA may occur because C1q is bound in close proximity and with high avidity to OFA, resulting in effective CP activation. Moreover, OFA binds to the small, extracellular CD20 loop, placing the mAb considerably closer to the cell membrane than does RTX. This may facilitate effective capture and concentration of activated complement components closer to the cell membrane, potentially shielding them from inactivation by fluid phase agents and promoting efficient generation of the membrane attack complex.

Tumor burden influences exposure and response to rituximab: pharmacokinetic-pharmacodynamic modeling using a syngeneic bioluminescent murine model expressing human CD20

Clinical studies have shown a large interindividual variability in rituximab exposure and its significant influence on clinical response in patients receiving similar doses of antibody. The aim of this study was to evaluate the influence of tumor burden on dose-concentration-response relationships of rituximab. Murine lymphoma cells (EL4, 8 × 103), transduced with human CD20 cDNA and transfected with luciferase plasmid (EL4-huCD20-Luc), were intravenously injected into C57BL/6J mice. Tumor burden detection, dissemination, and progression were evaluated quantitatively by in vivo bioluminescence imaging. Different doses of rituximab (6, 12, 20, or 40 mg/kg) were infused 13 days after lymphoma cell inoculation, and rituximab serum concentrations were measured by enzyme-linked immunosorbent assay. Without rituximab, all mice developed disseminated lymphoma and died within 30 days, whereas a significant dose-response relationship was observed in mice receiving rituximab. The 20-mg/kg dose was adequate to study interindividual variability in response because 23% of mice were cured, 59% had partial response, and 18% had disease progression. Rituximab concentrations were inversely correlated with tumor burden; mice with low tumor burden had high rituximab concentrations. Furthermore, rituximab exposure influenced response and survival. Finally, using a pharmacokinetic-pharmacodynamic model, we demonstrated that tumor burden significantly influenced rituximab efficacy.

Complement and cellular cytotoxicity in antibody therapy of cancer

The effective and practical use of mAbs in cancer therapy became a reality with the development of the chimeric anti-CD20 mAb, rituximab. Several additional mAbs have since been approved for clinical use. Despite these successes, the mechanisms by which mAbs mediate antitumor activity are still unclear. Preclinical studies indicate complement-dependent cytotoxicity (CDC) and antibody-dependent cellular cytotoxicity (ADCC) both can contribute to mAb-induced tumor cell lysis. However, evidence related to the relative clinical importance of each mechanism, and whether they are synergistic or antagonistic, is conflicting. New ways to enhance both CDC and ADCC are being developed in attempt to develop a more effective anticancer mAb. Continued research on the mechanisms of mAb therapy will be necessary if we are to take optimal advantage of the current mAbs and develop more effective mAbs in the future.

Responses to rituximab vary among follicular lymphoma B cells of different maturation stages

The chimeric anti-CD20 monoclonal antibody rituximab has been used for the treatment of non-Hodgkin's lymphomas with varying responses. Rituximab has been demonstrated to act by direct complement-dependent cytotoxity (CDC) and by inducing apoptosis, complement-, and antibody-dependent cellular cytotoxity. In the present study, we determined whether rituximab's effector mechanisms differed between two human follicular lymphoma cell lines that originate from different maturation stages of B cell germinal centre (GC) development. The tested HF-1 and HF-4b lymphoma cells represent GC centrocytes and centroblasts, respectively. Both cell lines responded to rituximab treatment by undergoing apoptosis yet the HF-1 cells were more sensitive. A major difference was seen in the proliferation response as only the proliferation of HF-1 cells was inhibited by rituximab. In the presence of normal human serum (NHS) rituximab almost completely inhibited DNA synthesis and induced necrosis of both cell lines because of CDC. Our results show that the CD20-positive HF-1 and HF-4b cells respond differentially to rituximab-induced apoptosis and inhibition of proliferation but similarly to complement-mediated killing. The increased sensitivity of the HF-1 cell line to apoptosis and inhibition of proliferation may reflect a tendency of centrocytic cells for negative selection and a role for CD20 in this process.

Adding fresh frozen plasma to rituximab for the treatment of patients with refractory advanced CLL

BACKGROUND

Many patients with chronic lymphocytic leukaemia (CLL) develop progressive, treatment-resistant disease. Rituximab (RTX), a monoclonal antibody targeting CD20 on B lymphocytes and widely used in other indolent B cell neoplasms is less efficacious in CLL, possibly due to associated complement deficiencies.

OBJECTIVE

To examine in open trial whether providing complement by concurrent administration of fresh frozen plasma (FFP) will enhance the effect of RTX in CLL.

SETTING

Outpatient haematology clinics in Israel and Greece.

PATIENTS

Five patients with severe treatment-resistant CLL. All had been previously treated with fludarabine and three also failed treatment with RTX.

INTERVENTION

Two units of FFP followed with RTX 375 mg/m(2) as a single agent, repeated every 1-2 weeks, as needed.

RESULTS

A rapid and dramatic clinical and laboratory response was achieved in all patients. Lymphocyte counts dropped markedly followed by shrinkage of lymph nodes and spleen and improvement of the anaemia and thrombocytopenia. This could be maintained over 8 months (median) with additional cycles if necessary. Treatment was well tolerated in all cases.

CONCLUSION

Adding FFP to RTX may provide a useful therapeutic option in patients with advanced CLL resistant to treatment.

Recombinant antibodies for cancer therapy

BACKGROUND

Recombinant antibodies have evolved into successful therapeutics with 10 approved for cancer and more in the pipeline. Four of the top ten cancer therapy drugs are recombinant antibodies.

OBJECTIVES

To survey the current state-of-the-art highlighting the reasons for this success and looking ahead to the next generation of antibody therapy.

METHODS

An analysis was carried out to identify preclinical and clinical examples and the underlying concepts and mechanisms that have shown how to design better therapies.

RESULTS/CONCLUSIONS

Greater understanding of the molecular basis of cancer has led to improved antibodies and a greater selection of targets. Fine tuning of successful antibodies through modification of glycosylation, affinity, size and other parameters are paying dividends. Fc-engineering is likely to be predominant in the near future but conjugates, fragments and fusion proteins will continue to be developed and find their place in the arsenal of antibody therapeutics.

An inducible caspase 9 safety switch can halt cell therapy-induced autoimmune disease

Transfer of either allogeneic or genetically modified T cells as a therapy for malignancies can be accompanied by T cell-mediated tissue destruction. The introduction of an efficient "safety switch" can potentially be used to control the survival of adoptively transferred cell populations and as such reduce the risk of severe graft-vs-host disease. In this study, we have tested the value of an inducible caspase 9-based safety switch to halt an ongoing immune attack in a murine model for cell therapy-induced type I diabetes. The data obtained in this model indicate that self-reactive T cells expressing this conditional safety switch show unimpaired lymphopenia- and vaccine-induced proliferation and effector function in vivo, but can be specifically and rapidly eliminated upon triggering. These data provide strong support for the evaluation of this conditional safety switch in clinical trials of adoptive cell therapy.

Multiple Myeloma Includes Phenotypically Defined Subsets of Clonotypic CD20+ B Cells that Persist During Treatment with Rituximab

Potential progenitor B cell compartments in multiple myeloma (MM) are clinically important. MM B cells and some circulating MM plasma cells express CD20, predicting their clearance by treatment with anti-CD20. Here we describe two types of clonotypic CD20+ B cell in peripheral blood of myeloma patients, identified by their expression of CD19 and CD20 epitopes, their expression of CD45RA and their light scatter properties. Thus, the circulating component of the MM clone includes at least two distinct CD19+ CD20+ B cell compartments, as well as CD138+ CD20+ plasma cells. To determine whether either or both B cell subsets and the CD20+ plasma cell subset were depleted by anti-CD20 therapy, they were evaluated before, during and after treatment of patients with rituximab (anti-CD20), followed by quantifying B cell subsets over a 5 month period during and after treatment. Overall, all three types of circulating B lineage cells persist despite treatment with rituximab. The inability of rituximab to prolong survival in MM may result from this failure to deplete CD20+ B and plasma cells in MM.

Sleeping Beauty transposon-mediated engineering of human primary T cells for therapy of CD19+ lymphoid malignancies

We have reported earlier that the non-viral Sleeping Beauty (SB) transposon system can mediate genomic integration and long-term reporter gene expression in human primary peripheral blood (PB) T cells. In order to test whether this system can be used for genetically modifying both PB T cells and umbilical cord blood (UCB) T cells as graft-versus-leukemia effector cells, an SB transposon was constructed to coexpress a single-chain chimeric antigen receptor (CAR) for human CD19 and CD20. PB and UCB were nucleofected with the transposon and a transposase plasmid, activated and then expanded in culture using anti-CD3/CD28 beads. Stable dual-gene expression was confirmed in both T-cell types, permitting enrichment by positive selection with Rituxan. The engineered CD4(+) T cells and CD8(+) T cells both exhibited specific cytotoxicity against CD19(+) leukemia and lymphoma cell lines, as well as against CD19 transfectants, and produced high-levels of antigen-dependent Th1 (but not Th2) cytokines. The in vivo adoptive transfer of genetically engineered T cells significantly reduced tumor growth and prolonged the survival of the animal. Taken together, these data indicate that T cells from PB and UCB can be stably modified using a non-viral DNA transfer system, and that such modified T cells may be useful in the treatment of refractory leukemia and lymphoma.

A safeguard eliminates T cell receptor gene-modified autoreactive T cells after adoptive transfer

By transfer of T cell receptor (TCR) genes, antigen specificity of T cells can be redirected to target any antigen. Adoptive transfer of TCR-redirected T cells into patients has shown promising results. However, this immunotherapy bears the risk of autoreactive side effects if the TCR recognizes antigens on self-tissue. Here, we introduce a safeguard based on a TCR-intrinsic depletion mechanism to eliminate autoreactive TCR-redirected T cells in vivo. By the introduction of a 10-aa tag of the human c-myc protein into murine (OT-I, P14) and human (gp100) TCR sequences, we were able to deplete T cells that were transduced with these myc-tagged TCRs with a tag-specific antibody in vitro. T cells transduced with the modified TCR maintained equal properties compared with cells transduced with the wild-type receptor concerning antigen binding and effector function. More importantly, therapeutic in vivo depletion of adoptively transferred T cells rescued mice showing severe signs of autoimmune insulitis from lethal diabetes. This safeguard allows termination of adoptive therapy in case of severe side effects.

Antibodies for HIV treatment and prevention: window of opportunity?

Monoclonal antibodies are routinely used as therapeutics in a number of disease settings and have thus also been explored as potential treatment for human immunodeficiency virus (HIV)-1 infection. Antibodies targeting viral antigens, and those directed to the cellular receptors, have been considered for use in prevention and therapy. For virus-targeted antibodies, attention has focused primarily on their neutralizing activity, but such antibodies also have the potential to exert antiviral effects via effector functions, such as antibody-dependent cellular cytotoxicity (ADCC), opsonization, or complement activation. Anti-cell antibodies act through occlusion or down-modulation of the viral receptors with notable impact in vivo, as recent trials have shown. This review summarizes the diverse specificities and modes of action of therapeutic antibodies against HIV-1 infection. Successes, challenges, and future opportunities of harnessing antibodies for therapy of HIV-1 infection are discussed.

NK-cell activation and antibody-dependent cellular cytotoxicity induced by rituximab-coated target cells is inhibited by the C3b component of complement

Antibody-dependent cellular cytotoxicity (ADCC) and complement fixation both appear to play a role in mediating antitumor effects of monoclonal antibodies (mAbs), including rituximab. We evaluated the relationship between rituximab-induced complement fixation, natural killer (NK)-cell activation, and NK cell-mediated ADCC. Down-modulation of NK- cell CD16 and NK-cell activation induced by rituximab-coated target cells was blocked by human serum but not heat-inactivated serum. This inhibition was also observed in the absence of viable target cells. C1q and C3 in the serum were required for these inhibitory effects, while C5 was not. An antibody that stabilizes C3b on the target cell surface enhanced the inhibition of NK-cell activation induced by rituximab-coated target cells. Binding of NK cells to rituximab-coated plates through CD16 was inhibited by the fixation of complement. C5-depleted serum blocked NK cell-mediated ADCC. These data suggest that C3b deposition induced by rituximab-coated target cells inhibits the interaction between the rituximab Fc and NK-cell CD16, thereby limiting the ability of rituximab-coated target cells to induce NK activation and ADCC. Further studies are needed to define in more detail the impact of complement fixation on ADCC, and whether mAbs that fail to fix complement will be more effective at mediating ADCC.

Mechanisms of killing by anti-CD20 monoclonal antibodies

CD20 is a cell-surface marker expressed on mature B cells and most malignant B cells, but not stem or plasma cells. It is an ideal target for monoclonal antibodies (mAb), such as rituximab and ofatumumab, as it is expressed at high levels on most B-cell malignancies, but does not become internalized or shed from the plasma membrane following mAb treatment. This allows mAb to persist on the cell surface for extended periods and deliver sustained immunological attack from complement and FcR-expressing innate effectors, particularly macrophages. CD20 can also generate transmembrane signals when engaged by certain mAb which, although unproven, might provide an important element of the therapeutic success of anti-CD20 mAb. These favourable characteristics have led to anti-CD20 mAb being developed and exploited for use in immunotherapy, where they have proven remarkably efficacious in both the treatment of malignant disease and autoimmune disorders by deleting malignant or normal B cells, respectively. In this review, we discuss how these mAb have driven research in the immunotherapy field over the last decade, detail their likely modes of action and their limitations in terms of effector exhaustion, and explore ways in which they might be enhanced and further exploited in the future.

The efficacy of rituximab plus Hyper-CVAD regimen in mantle cell lymphoma is independent of FCgammaRIIIa and FCgammaRIIa polymorphisms

Mantle cell lymphoma (MCL) accounts for 3-10% of all non-Hodgkin's lymphomas, with median overall survival not exceeding 3-4 years. Rituximab in combination with the Hyper-CVAD regimen appears the most promising regimen; thus, we adopted it as a first-line treatment strategy in a series of 24 patients. In addition to evaluation of clinical success of the regimen, we investigated a possible role of polymorphism in IgG Fc receptors, FCgammaRIIIa and FCgammaRIIa. The frequencies of FCgammaRIIIa-158 were as follows: V/V=4/24 (17%); V/F=16/24 (66%); F/F=4/24 (17%). Those of the FCgammaRIIa-131 polymorphism were H/H=11/24 (46%), H/R=9/24 (37%), R/R=4/24 (17%). The overall response rate was 62.5%, with 33% of complete responses (CRs) after four cycles of R-Hyper-CVAD. Two-year progression-free survival (PFS) was 78% for 158V/V patients vs 75% for cases carrying phenylalanine (p=0.88). When the FCgammaRIIa polymorphism was assessed, the 2-year PFS was 82% for 131H/H patients vs 75% for those carrying arginine (p=0.26). Eighty-three percent of cases achieved Polymerase Chain Reaction (PCR)-negativity: the progression rate was significantly influenced by the minimal residual disease clearance, with 12% progression in the subgroup of PCR-negative cases versus 67% progression in PCR-positive cases (p=0.008). The achievement of PCRnegativity was not significantly influenced by FCgammaR polymorphisms. Results confirm that rituximab plus Hyper-CVAD is an effective regimen for the induction of prolonged remission in patients with aggressive MCL and suggest that rituximab efficacy is independent of the FCgammaR polymorphisms.

NK cells stimulated with IL-15 or CpG ODN enhance rituximab-dependent cellular cytotoxicity against B-cell lymphoma

OBJECTIVE

Antibody-dependent cellular cytotoxicity (ADCC) is an important mechanism in the clinical activity of rituximab for treatment of B-cell malignancies. Natural killer (NK) cells, through the activating receptor FcgammaRIIIa (CD16), play a major role in rituximab-mediated ADCC. We have studied the in vitro effect of NK stimulators, such as interleukin-15 (IL-15) and CpG oligodeoxynucleotides A-Class (CpG ODN A), in the enhancement of rituximab-mediated ADCC against B-cell lymphoma.

METHODS

Peripheral blood mononuclear cells (PBMC), purified NK cells, or NK-depleted PBMC from healthy donors, were activated with IL-15 or CpG ODN A, and cocultured with B-lymphoma cells in the presence of rituximab to evaluate the enhancement of the cytotoxicity.

RESULTS

The rituximab-mediated ADCC of IL-15-activated PBMC was twofold compared to unstimulated PBMC (73% +/- 7% vs 37% +/- 5% respectively, p < 0.001). Similarly, rituximab-mediated ADCC was enhanced when PBMC were activated with CpG ODN A as compared to CpG ODN control (61% +/- 11% vs 36% +/- 8%, respectively, p = 0.02). Nevertheless, the ADCC of purified NK cells was increased only with IL-15. NK-depleted PBMC activated with either IL-15 or CpG ODN A showed no ADCC, suggesting that NK are the major effector cells. Furthermore, IL-15 or CpG ODN A-activated PBMC, but not activated purified NK cells, secreted large amounts of interferon-gamma in the presence of rituximab-coated lymphoma cells.

CONCLUSIONS

IL-15 and CpG ODN A enhance rituximab-mediated ADCC against B-cell lymphoma. Under these conditions, NK cells seem to be the main effector cells mediating ADCC. These findings suggest that these agents could be used as adjuvants in combination with rituximab for patients with B-cell lymphoma.

Rituximab-CD20 Complexes Are Shaved from Z138 Mantle Cell Lymphoma Cells in Intravenous and Subcutaneous SCID Mouse Models

Infusion of standard-dose rituximab (RTX) in chronic lymphocytic leukemia (CLL) patients promotes rapid complement activation and deposition of C3 fragments on CLL B cells. However, immediately after RTX infusions, there is substantial loss (shaving) of CD20 from circulating malignant cells. Because shaving can compromise efficacies of anticancer immunotherapeutic mAbs, we investigated whether shaving occurs in SCID mouse models. Z138 cells, a B cell line derived from human mantle cell lymphoma, were infused i.v. or s.c. The i.v. model recapitulates findings we previously reported for therapeutic RTX in CLL: i.v. infused RTX rapidly binds to Z138 cells in lungs, and binding is accompanied by deposition of C3 fragments. However, within 1 h targeted cells lose bound RTX and CD20, and these shaved cells are still demonstrable 40 h after RTX infusion. Z138 cells grow in tumors at s.c. injection sites, and infusion of large amounts of RTX (0.50 mg on each of 4 days) leads to considerable loss of CD20 from these cells. Human i.v. Ig blocked shaving, suggesting that FcgammaRI on cells of the mononuclear phagocytic system promote shaving. Examination of frozen tumor sections from treated mice by immunofluorescence revealed large areas of B cells devoid of CD20, with CD20 intact in adjacent areas; it is likely that RTX had opsonized Z138 cells closest to capillaries, and these cells were shaved by monocyte/macrophages. The shaving reaction occurs in neoplastic B cells in tissue and in peripheral blood, and strategies to enhance therapeutic targeting and block shaving are under development.

Rituximab and its role as maintenance therapy in non-Hodgkin lymphoma

Since rituximab, a chimeric monoclonal anti-CD20 antibody, was introduced into clinical practice in 1997, data regarding its benefit in terms of response rate, quality of response, progression-free survival and overall survival in B-cell lymphoid malignancies continues to expand. Rituximab has proven to be a relatively well-tolerated drug, with its major side effects being infusion related. Rituximab was approved initially by the US FDA and the European Medicines Agency for relapsed or refractory low-grade or follicular CD20+ B-cell non-Hodgkin lymphomas. Subsequently, its use has been extended to include first-line therapy in low-grade lymphoma as well as the treatment of more aggressive histological subtypes such as diffuse large B-cell lymphoma. In this article, we review the landmark trials that have impacted clinical practice in follicular and diffuse large B-cell lymphomas and the emerging data for use of rituximab as maintenance therapy in non-Hodgkin lymphoma.

Cancer therapeutic antibodies come of age: targeting minimal residual disease

Ten years after the first clinical application of Rituximab, an anti-CD20 recombinant monoclonal antibody, immunotherapy has become common practice in oncology wards. Thanks to the great diversity of the immune system and the powerful methodology of genetic engineering, the pharmacologic potential of antibody-based therapy is far from exhaustion. The recent application of Trastuzumab, an antibody to a receptor tyrosine kinase, in adjuvant breast cancer therapy marks the beginning of a new phase in cancer treatment. Here we discuss molecular mechanisms of antibody-based therapy, the emerging ability to target minimal disease and the therapeutic potential of combining antibodies with other modalities.