In vitro mechanisms of action of rituximab on primary non-Hodgkin lymphomas

Pharmacokinetics of rituximab and its clinical use: thought for the best use?

Rituximab (MabThera, Rituxan) is a chimaeric monoclonal antibody increasingly used in the treatment of B-lymphoproliferative disorders and autoimmune diseases. Rituximab is now associated with chemotherapy for the treatment of non-Hodgkin's lymphoma and should be approved soon in maintenance strategies. During its rapid clinical development, rituximab schedules were dictated more often by logistical rather than by scientific considerations. In addition, early clinical phases have shown that rituximab exposure was variable in patients receiving similar doses and that clinical response was related to rituximab concentrations. There is however limited information on rituximab pharmacokinetics and on factors influencing individual exposure to this monoclonal antibody, although a better understanding of these factors is needed to optimise its dosing regimen. This review focuses on the current knowledge on rituximab pharmacokinetics and on factors influencing individual exposure and suggests ways to improve its clinical use.

Comparing antibody and small-molecule therapies for cancer

The 'magic bullet' concept of specifically targeting cancer cells at the same time as sparing normal tissues is now proven, as several monoclonal antibodies and targeted small-molecule compounds have been approved for cancer treatment. Both antibodies and small-molecule compounds are therefore promising tools for target-protein-based cancer therapy. We discuss and compare the distinctive properties of these two therapeutic strategies so as to provide a better view for the development of new drugs and the future direction of cancer therapy.

Rituximab but not Other anti-CD20 Antibodies Reverses Multidrug Resistance in 2 B lymphoma Cell Lines, Blocks the Activity of P-glycoprotein (P-gp), and Induces P-gp to Translocate out of Lipid Rafts

The objective of this study was to investigate the ability of the anti-CD20 antibody, Rituximab (RTX), to inhibit the activity of P-glycoprotein (P-gp), and reverse multidrug resistance (MDR) in 2 P-gp/CD20 lymphoma cell lines. We determined whether RTX would chemosensitize the 2 P-gp cell lines in vitro, and inhibit the ability of the cells to efflux Rhodamine 123. One cell line was infected with an MDR1 vector and the other was generated by drug selection. We also determined whether RTX induced P-gp to translocate out of lipid rafts. RTX chemosensitized 2 different MDR cell lines, inhibited the activity of P-gp in both, and induced P-gp to translocate out of lipid rafts in the 1 cell line that was studied in greater detail. In contrast, 3 other anti-CD20 antibodies did not chemosensitize, inhibit the activity of P-gp, or induce it to translocate out of rafts, despite the fact that 1 antibody recognized the same epitope on CD20. Our results suggest that RTX can chemosensitize 2 CD20/P-gp cell lines in vitro by inhibiting the activity of the P-gp pump. The inhibition of P-gp activity correlated with the ability of RTX to induce P-gp to translocate out of lipid rafts. Although the mechanisms by which RTX effects P-gp translocation and activity are not yet known, they are not associated with acid-sphingomyelinase activation in raft microdomains, as described for the antiproliferative activity of RTX.

The anti-lymphoma effect of antibody-mediated immunotherapy is based on an increased degranulation of peripheral blood natural killer (NK) cells

BACKGROUND

In patients treated with rituximab and alemtuzumab for lymphomas or CLL, antibody-dependent cellular cytotoxicity (ADCC) is a major mechanism of action. Therefore, assessment of ADCC is mandatory to understand the complex mechanisms leading to the anti-lymphoma effects of monoclonal antibodies (mAb). Due to methodical difficulties, little is yet known about the relevant cell subpopulations and effector mechanisms leading to tumor lysis in ADCC.

METHODS

We used a novel flow cytometric assay that detects CD107a as a marker for NK-cell degranulation to characterize and quantify peripheral blood natural killer (NK) cells mediating ADCC in vitro and in vivo.

RESULTS

We observed specific and dose-dependent NK-cell activation after administration of rituximab and alemtuzumab. The number of degranulating NK cells was closely related to the concentration of mAb and the effector:target ratio. We were able to quantify and characterize the peripheral blood NK cells mediating ADCC. The majority of degranulating NK cells had the phenotype: CD56(dim), CD69(+), NKG2D(+), NKp30(-), NKp46(-), and CD94(-). Furthermore, we found that the CD107a assay can also visualize ADCC under clinical conditions as we observed increased numbers of NK cells degranulating in response to CD20(+) lymphoma cell lines in patients with non-Hodgkin's lymphoma treated with rituximab.

CONCLUSIONS

We were able to quantify and characterize NK cells mediating ADCC with a new and feasible method. The CD107a assay may be useful for predicting treatment responses of individual patients and may help find the optimal dosage and timing for treatment with mAb.

Ex Vivo-activated Human Macrophages Kill Chronic Lymphocytic Leukemia Cells in the Presence of Rituximab: Mechanism of Antibody-dependent Cellular Cytotoxicity and Impact of Human Serum

Antibody-dependent cellular cytotoxicity (ADCC) is one of the mechanisms of tumor killing during antibody (Ab) immunotherapy, and a role for myeloid cells as effectors has been observed in several models. We are developing immunotherapy approaches based on administration of large numbers of ex vivo interferon-gamma-activated macrophages to cancer patients. With a quantitative assay measuring killing of nonproliferating tumor cells, we evaluated whether, in physiologic conditions, these macrophages synergize with the anti-CD20 Ab rituximab for killing primary B-cell chronic lymphocytic leukemia (B-CLL) cells. ADCC reached levels of 70% to 80% at effector to target ratios as low as 1:1. Macrophage recruitment by Ab-opsonized tumor cells did not result in enhanced cytokine secretion, suggesting that the cytokine shower observed in rituximab-treated patients is not caused by macrophage activation, and that cytokines have no role in CLL killing. We observed that uptake of tumor material by macrophages was not directly correlated to tumor killing. Nonetheless, experiments in the presence of cytochalasin D showed that ADCC occurred mainly by phagocytosis. Tumor killing was largely mediated by Fc gammaRI and inhibited by increasing concentration of serum. Importantly, complement deposition on B-CLL cells did not seem to enhance macrophage ADCC in this model, as complement-depleted and complement-repleted human plasmas exerted comparable inhibition.

The anti-CD20 antibody rituximab augments the immunospecific therapeutic effectiveness of an anti-CD19 immunotoxin directed against human B-cell lymphoma

The chimaeric anti-CD20 antibody rituximab (Rituxan) sensitises lymphoma cells to small molecule cytotoxic drugs and to protein toxins. We have explored the augmentive effect of rituximab on the anti-CD19 immunotoxin BU12-SAPORIN in a model of human lymphoma. Intact rituximab and its F(ab)2 derivative both augmented the immunospecific protein synthesis inhibitory effects of BU12-SAPORIN in a complement-independent manner. A combination of rituximab + BU12-SAPORIN completely abolished the proliferation of Ramos cells in vitro and also induced a significantly greater degree of apoptosis in these cells. Treatment with rituximab, BU12-SAPORIN or a combination of both induced poly(ADPribose) polymerase and caspase 3 cleavage, although this was always consistently greater in combination-treated cells. zVAD almost completely inhibited apoptosis in rituximab- or BU12-SAPORIN-treated cells but only partially in combination-treated cells. In severe combined immunodeficient (SCID)-Ramos mice the combination of rituximab + BU12-SAPORIN was significantly better therapeutically than either single agent. The immunological fidelity of the therapeutic effect because of combination treatment was demonstrated through the failure of rituximab to augment an irrelevant anti-CD7 immunotoxin. The therapeutic efficacy of rituximab and combination treatment was reduced in SCID-Ramos mice depleted of serum complement while natural killer cell depletion failed to show any convincing role for antibody-dependent cellular cytotoxicity. This study shows a clear therapeutic advantage from using rituximab to immunospecifically augment immunotoxin cytotoxicity warranting further investigation.

Epratuzumab, a CD22-targeting recombinant humanized antibody with a different mode of action from rituximab

Epratuzumab is a humanized anti-CD22 monoclonal antibody currently in clinical trials for treatment of non-Hodgkin lymphoma (NHL) and certain autoimmune diseases. Here we report the results of investigations of epratuzumab's mode of action in comparison to and in combination with the anti-CD20 mAb, rituximab. In vitro cell growth inhibition, induction of apoptosis, and the ability of the mAbs to mediate complement-dependent cytotoxicity (CDC) and antibody-dependent cellular cytotoxicity (ADCC) were evaluated. We also investigated the potential activity of epratuzumab in the regulation of B-cell antigen receptor (BCR) activation. Epratuzumab and rituximab displayed very distinct modes of action; epratuzumab acts as an immunomodulatory agent, while rituximab is an acutely cytotoxic therapeutic antibody. Epratuzumab has distinct effects on cell growth from rituximab. For example, rituximab+anti-human IgG Fcgamma yielded marked inhibition of proliferation in human NHL cell lines, while epratuzumab had little or no effect in this assay. However, when cells were immobilized and stimulated with anti-IgM, epratuzumab, but not rituximab, caused a significant antiproliferative effect. Unlike rituximab, no CDC could be detected, and ADCC was modest but significant with epratuzumab. Importantly, combining rituximab and epratuzumab did not decrease rituximab's ability to induce apoptosis, CDC, and ADCC. In fact, the combination is more effective than rituximab alone in inhibiting proliferation of Daudi Burkitt lymphoma cells in the presence of second antibody, and at least equally effective to rituximab in the absence of crosslinking. These observations suggest that it may be possible to enhance clinical efficacy by combination therapy comprised of anti-CD20 and anti-CD22 mAbs.

Allogeneic hematopoietic stem cell transplantation after rituximab-containing myeloablative preparative regimen for acute lymphoblastic leukemia

We explored the safety and efficacy of rituximab administered in combination with the standard transplant conditioning regimen of cyclophosphamide (Cy) 120 mg/kg and total body irradiation (TBI) 12 Gy for adult patients with acute lymphoblastic leukemia (ALL). Patients were eligible if their disease expressed CD20. Rituximab was administered at 375 mg/m2 weekly for four doses beginning on day -7 of the conditioning regimen. Graft-versus-host-disease (GVHD) prophylaxis consisted of tacrolimus and methotrexate. Thirty-five patients undergoing matched sibling (n = 23) or unrelated donor (n = 12) transplantation were studied, with a median age of 30 years (range 15-55 years). At 2 years, progression-free survival, treatment-related mortality, and overall survival were 30, 24, and 47%, respectively. There was no delay in engraftment or increased incidence of infection. The cumulative incidence of grade II-IV acute GVHD was 17%, and limited and extensive chronic GVHD was 43% at 2 years. The addition of rituximab to the standard Cy/TBI transplant conditioning regimen in ALL was safe and well tolerated, and there was a suggestion of decreased incidence of acute GVHD when compared to historically reported GVHD rates for this group of patients.

Nonfucosylated Therapeutic IgG1 Antibody Can Evade the Inhibitory Effect of Serum Immunoglobulin G on Antibody-Dependent Cellular Cytotoxicity through its High Binding to FcγRIIIa

PURPOSE

Recent studies have revealed that fucosylated therapeutic IgG1s need high concentrations to compensate for FcgammaRIIIa-competitive inhibition of antibody-dependent cellular cytotoxicity (ADCC) by endogenous human plasma IgG. Here, we investigated whether ADCC of nonfucosylated therapeutic IgG1 is also influenced by plasma IgG in the same way as fucosylated IgG1s.

EXPERIMENTAL DESIGN

Ex vivo ADCC upon CD20+ human B cells was induced by incubation of human whole blood with nonfucosylated and/or fucosylated anti-CD20 IgG1s rituximab, and quantified by measuring the remaining CD19+ human B cells using flow cytometry.

RESULTS

Nonfucosylated anti-CD20 showed markedly higher (over 100-fold based on EC50) ex vivo B-cell depletion activity than its fucosylated counterpart in the presence of plasma IgG. The efficacy of fucosylated anti-CD20 was greatly diminished in plasma, resulting in the need for a high concentration (over 1.0 microg/mL) to achieve saturated efficacy. In contrast, nonfucosylated anti-CD20 reached saturated ADCC at lower concentrations (0.01-0.1 microg/mL) with much higher efficacy than fucosylated anti-CD20 in all nine donors through improved FcgammaRIIIa binding. Noteworthy, the high efficacy of nonfucosylated anti-CD20 was inhibited by addition of fucosylated anti-CD20. Thus, the efficacy of a 1:9 mixture (10 microg/mL) of nonfucosylated and fucosylated anti-CD20s was inferior to that of a 1,000-fold dilution (0.01 microg/mL) of nonfucosylated anti-CD20 alone.

CONCLUSIONS

Our data showed that nonfucosylated IgG1, not including fucosylated counterparts, can evade the inhibitory effect of plasma IgG on ADCC through its high FcgammaRIIIa binding. Hence, nonfucosylated IgG1 exhibits strong therapeutic potential through dramatically enhanced ADCC at low doses in humans in vivo.

Analysis of changes in CD20, CD55, and CD59 expression on established rituximab-resistant B-lymphoma cell lines

Rituximab has markedly improved treatment results for B-cell lymphoma, but there are resistance problems similar to those of other chemotherapy drugs. With regard to the acquisition of rituximab resistance, there have been several reports describing the relation between rituximab and complement regulatory factors or CD20, but many points remain unclear. To further investigate acquisition of resistance to rituximab-related complement-dependent cytotoxicity (CDC), we established rituximab-resistant B-lymphoma cell lines (RAMOS) in vitro and then analyzed expression of CD20, CD55, and CD59 on these resistant cells by flow cytometry. With repeated exposure to a low concentration of rituximab and complement, RAMOS cells gradually acquired rituximab resistance, and selection and increase of CD55(bright) and CD59(bright) cell populations due to rituximab-related CDC were observed. With repeated exposure to a high concentration of rituximab and complement, RAMOS cells promptly acquired rituximab resistance, and CD20 expression of RAMOS cells was decreased. Not only selection of CD20(dim) cells but also down-modulation of CD20 caused by rituximab-related CDC appeared to cause the decrease in CD20 expression. We believe our findings will prove to be useful for prevention of or release from rituximab resistance in cases of B-cell lymphoma.

Antitumor efficacy of a combination of CMC-544 (inotuzumab ozogamicin), a CD22-targeted cytotoxic immunoconjugate of calicheamicin, and rituximab against non-Hodgkin's B-cell lymphoma

PURPOSE

CMC-544 is a CD22-targeted cytotoxic immunoconjugate, currently being evaluated in B-cell non-Hodgkin's lymphoma (B-NHL) patients. Rituximab is a CD20-targeted antibody commonly used in B-NHL therapy. Here, we describe antitumor efficacy of a combination of CMC-544 and rituximab against B-cell lymphoma (BCL) in preclinical models.

EXPERIMENTAL DESIGN

BCLs were cultured in vitro with CMC-544, rituximab, or their combination. BCLs were injected either s.c. or i.v. to establish localized s.c. BCL in nude mice or disseminated BCL in severe combined immunodeficient mice, respectively. I.p. treatment with CMC-544 or rituximab was initiated at various times either alone or in combination and its effect on s.c. BCL growth or survival of mice with disseminated BCL was monitored.

RESULTS

In vitro growth-inhibitory activity of CMC-544 combined with rituximab was additive. Rituximab but not CMC-544 exhibited effector functions, such as antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity. Rituximab was less effective in inhibiting growth of established BCL xenografts than developing xenografts. In contrast, CMC-544 was equally effective against both developing and established BCL xenografts. Although CMC-544 and rituximab individually caused partial inhibition of the growth of BCL xenografts at suboptimal doses examined, their combination suppressed xenograft growth by >90%. In a disseminated BCL model, 60% of CMC-544-treated mice and 20% of rituximab-treated mice survived for 125 days. In contrast, 90% of mice treated with the combination of CMC-544 and rituximab survived for longer than 125 days.

CONCLUSION

The demonstration of superior antitumor activity of a combination of CMC-544 and rituximab described here provides the preclinical basis for its clinical evaluation as a treatment option for B-NHL.

The Anti–Human Leukocyte Antigen-DR Monoclonal Antibody 1D09C3 Activates the Mitochondrial Cell Death Pathway and Exerts a Potent Antitumor Activity in Lymphoma-Bearing Nonobese Diabetic/Severe Combined Immunodeficient Mice

The fully human anti-HLA-DR antibody 1D09C3 has been shown to delay lymphoma cell growth in severe combined immunodeficient (SCID) mice. The present study was aimed at (a) investigating the mechanism(s) of 1D09C3-induced cell death and (b) further exploring the therapeutic efficacy of 1D09C3 in nonobese diabetic (NOD)/SCID mice. The chronic lymphocytic leukemia cell line JVM-2 and the mantle cell lymphoma cell line GRANTA-519 were used. Generation of reactive oxygen species (ROS) and mitochondrial membrane depolarization were measured by flow cytometry following cell incubation with dihydroethidium and TMRE, respectively. Western blot analysis was used to detect c-Jun-NH(2)-kinase (JNK) phosphorylation and apoptosis-inducing factor (AIF). NOD/SCID mice were used to investigate the activity of 1D09C3 in early- or advanced-stage tumor xenografts. In vitro, 1D09C3-induced cell death involves a cascade of events, including ROS increase, JNK activation, mitochondrial membrane depolarization, and AIF release from mitochondria. Inhibition of JNK activity significantly reduced 1D09C3-induced apoptosis, indicating that 1D09C3 activity involves activation of the kinase. In vivo, 1D09C3 induces long-term disease-free survival in a significant proportion of tumor-bearing mice treated at an early stage of disease. Treatment of mice bearing advanced-stage lymphoma results in a highly significant prolongation of survival. These data show that 1D09C3 (a) exerts a potent antitumor effect by activating ROS-dependent, JNK-driven cell death, (b) cures the great majority of mice treated at an early-stage of disease, and (c) significantly prolongs survival of mice with advanced-stage disease.

Treatment of primary central nervous system lymphoma with induction of complement-dependent cytotoxicity by intraventricular administration of autologous-serum-supplemented rituximab

We describe an immunocompetent 19-year-old man with CD20-positive primary central nervous system (CNS) lymphoma refractory to chemotherapy and irradiation. After intraventricular administration of rituximab, a chimeric anti-CD20 monoclonal antibody, supplemented with autologous serum, a remarkable response developed to the CNS parenchymal lymphoma. Cytotoxicity assays showed that untreated patient's serum with rituximab, but not that of heat-inactivated patient's serum with rituximab or rituximab alone, induced potent rituximab-mediated cytotoxicity against tumor cells in the patient's cerebrospinal fluid, suggesting induction of complement-dependent cytotoxicity against CNS lymphoma.

Blockade of bulky lymphoma-associated CD55 expression by RNA interference overcomes resistance to complement-dependent cytotoxicity with rituximab

Recently, anti-CD20 (rituximab) and anti-Her2/neu (trastuzumab) antibodies have been developed and applied to the treatment of malignant lymphoma and breast cancer, respectively. However, bulky lymphoma is known to be resistant to rituximab therapy, and this needs to be overcome. Fresh lymphoma cells were collected from 30 patients with non-Hodgkin's lymphoma, the expression of CD20 and CD55 was examined by flow cytometry, and complement-dependent cytotoxicity (CDC) assays were carried out. Susceptibility to CDC with rituximab was decreased in a tumor size-dependent manner (r=-0.895, P<0.0001), but not in a CD20-dependent manner (r=-0.076, P=0.6807) using clinical samples. One complement-inhibitory protein, CD55, contributed to bulky lymphoma-related resistance to CDC with rituximab. A decrease in susceptibility to CDC with rituximab was statistically dependent on CD55 expression (r=-0.927, P<0.0001) and the relationship between tumor size and CD55 expression showed a significant positive correlation (r=0.921, P<0.0001) using clinical samples. To overcome the resistance to rituximab by high expression of CD55 in bulky lymphoma masses, small interfering RNA (siRNA) was designed from the DNA sequence corresponding to nucleic acids 1-380 of the CD55 cDNA. Introduction of this siRNA decreased CD55 expression in the breast cancer cell line SK-BR3 and in CD20-positive cells of patients with recurrent lymphoma; resistance to CDC was also inhibited. This observation gives us a novel strategy to suppress bulky disease-related resistance to monoclonal antibody treatment.

A DeImmunized chimeric anti-C3b/iC3b monoclonal antibody enhances rituximab-mediated killing in NHL and CLL cells via complement activation

Complement-dependent cytotoxicity (CDC) is a key mechanism of Rituximab (RTX) action in killing non-Hodgkin's lymphoma (NHL) cells both in vitro and probably in vivo. A DeImmunized, mouse/human chimeric monoclonal antibody (Mab), H17, specific for cell-associated complement C3 cleavage products, C3b and iC3b, was generated to enhance RTX-mediated killing of target cells by CDC. When NHL cell lines were treated with RTX and H17 in the presence of complement for 1 h, there was 40-70% more cell death than that observed with RTX alone. The enhancing effect of H17 was also seen over longer treatment periods. H17 was tested ex vivo against primary cells from NHL and chronic lymphocytic leukemia (CLL) patients. In RTX-resistant NHL samples, H17 enhanced RTX-mediated killing; in the remaining samples RTX + complement alone promoted more than 80% killing, and no significant enhancement was observed. The H17 antibody also increased RTX-mediated killing in four out of nine CLL samples. H17 may have therapeutic applications in NHL and CLL treatment as an adjunctive therapy to RTX. It might also enhance the activity of other therapeutic antibodies that work through CDC.

Designing antibodies for oncology

The past five years have witnessed the emergence of monoclonal antibodies as important therapeutics for cancer treatment. Lower toxicity for antibodies versus small molecules, the potential for increased efficacy by conjugation to radioisotopes and cellular toxins, or the ability to exploit immune cell functions have led to clinical performances on par or superior to conventional drug therapies. This review outlines the various immunoglobulin design strategies currently available, techniques used to reduce Ig antigenicity and toxicity, and points to consider during the manufacture of antibodies for use in clinical oncology.

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).

Cholesterol depletion inhibits src family kinase-dependent calcium mobilization and apoptosis induced by rituximab crosslinking

The monoclonal antibody (mAb) rituximab produces objective clinical responses in patients with B-cell non-Hodgkin's lymphoma and antibody-based autoimmune diseases. Mechanisms mediating B-cell depletion by rituximab are not completely understood and may include direct effects of signalling via the target antigen CD20. Like most but not all CD20 mAbs, rituximab induces a sharp change in the solubility of the CD20 protein in the non-ionic detergent Triton-X-100, reflecting a dramatic increase in the innate affinity of CD20 for membrane raft signalling domains. Apoptosis induced by rituximab hypercrosslinking has been shown to require src family kinases (SFK), which are enriched in rafts. In this report we provide experimental evidence that SFK-dependent apoptotic signals induced by rituximab are raft dependent. Cholesterol depletion prevented the association of hypercrosslinked CD20 with detergent-insoluble rafts, and attenuated both calcium mobilization and apoptosis induced with rituximab. CD20 cocapped with the raft-associated transmembrane adaptor LAB/NTAL after hypercrosslinking with CD20 mAbs, regardless of their ability to induce a change in the affinity of CD20 for rafts. Taken together, the data demonstrate that CD20 hypercrosslinking via rituximab activates SFKs and downstream signalling events by clustering membrane rafts in which antibody-bound CD20 is localized in a high-affinity configuration.

Mesenchymal stem cells induce apoptosis of activated T cells

Mesenchymal stem cells (MSC) have recently been used successfully in humans to control severe graft-versus-host disease. However, the mechanisms involved in their immunomodulatory effects remain a matter of debate. Here, we show that MSC are unable to activate allogeneic T cells even in the presence of T-cell growth factors. We then found that MSC inhibit T-cell proliferation triggered either by allogeneic, mitogenic or antigen-specific stimuli. Interestingly, MSC inhibit T-cell proliferation by inducing apoptosis of activated T cells, but have no effect on resting T cells. Furthermore, we show that this apoptosis could be related to the conversion of tryptophan into kynurenine by indoleamine 2,3-dioxygenase expressed by MSC in the presence of IFNgamma. Moreover, we show that the inhibitory effect of MSC is neither abrogated nor modified during expansion in culture or after irradiation. Together, these results bring new insight to the mechanisms of immunosuppression induced by MSC and might help to develop their clinical use controlling immune-related adverse effects in humans.

Potent and specific antitumor efficacy of CMC-544, a CD22-targeted immunoconjugate of calicheamicin, against systemically disseminated B-cell lymphoma

PURPOSE

CMC-544 is a CD22-targeted immunoconjugate of calicheamicin and exerts a potent cytotoxic effect against CD22+ B-cell lymphoma. This study evaluated antitumor efficacy of CMC-544 against systemically disseminated B-cell lymphoma.

EXPERIMENTAL DESIGN

Scid mice received i.v. injections of CD22+ Ramos B-cell lymphoma cells for their systemic dissemination. CMC-544, G5/44, CD33-targeted CMA-676 (control conjugate) or rituximab were given i.p. 3, 9, 15, or 21 days after B-cell lymphoma dissemination. Diseased mice were monitored daily for hind-limb paralysis and death. Histopathological examination of CMC-544-treated and vehicle-treated diseased mice was also performed.

RESULTS

Mice with disseminated B-cell lymphoma developed hind-limb paralysis within 35 days. When given up to 15 days after B-cell lymphoma dissemination, CMC-544 extended survival of the diseased mice to >100 days, and these mice were considered cured. CMC-544 was efficacious when given during both the early initiation phase and the late established phase of the disease. A single dose of CMC-544 was effective in delaying the occurrence of hind-limb paralysis. In contrast, neither CMA-676 nor unconjugated G5/44 was effective. Rituximab was effective when given early in the disease process but not when the disease was established. Histopathological analysis revealed B-cell lymphoma infiltration in brain, spinal cord, bone marrow, and kidney in vehicle-treated but not in CMC-544-treated diseased mice. Consistent with its efficacy against the disseminated B-cell lymphoma, CMC-544 also caused regression of established Ramos B-cell lymphoma xenografts in scid mice.

CONCLUSIONS

CMC-544 confers strong therapeutic activity against systemic disseminated B-cell lymphoma and protects mice from hind-limb paralysis and death. These results support clinical evaluation of CMC-544 in the treatment of CD22+ lymphoid malignancies.

CD20 expression in normal canine B cells and in canine non-Hodgkin lymphoma

We examined the expression of CD20 in normal canine peripheral blood mononuclear cells, normal canine spleen, and canine non-Hodgkin lymphoma (NHL) to determine the feasibility of using this antigen as a diagnostic aid and as a possible target for therapy. An antibody generated against a C-terminal (intracytoplasmic) epitope of human CD20 recognized proteins of 32-36 kd in normal and malignant canine lymphocytes. This antibody showed restricted membrane binding in a subset of lymphocytes in peripheral blood, in the B-cell regions from a normal canine spleen and lymph node, and in malignant cells from 19 dogs with B-cell NHL, but not from 15 dogs with T-cell NHL. The patterns of CD20 reactivity in these samples overlapped those seen using an antibody that recognizes canine CD79a. This anti-CD20 antibody is therefore suitable as an aid to phenotype canine NHL. In contrast, normal canine B cells were not recognized by any of 28 antibodies directed against the extracellular domains of human CD20 (including the chimeric mouse-human antibody Rituximab) or by any of 12 antibodies directed against the extracellular domains of mouse CD20. Thus, the use of CD20 as a therapeutic target will require the generation of specific antibodies against the extracellular domains of canine CD20.

In vivo tumouricidal effects of LAD-1 monoclonal antibody on murine RL-male-1 lymphoma mediated by enhanced phagocytosis

We have reported previously that the LAD-4 monoclonal antibody (mAb) directed against a fibronectin receptor (FNR) on RL-male-1 T lymphoma cells in BALB/c mice partially inhibited their migration to the liver. In the present study, we examined the mechanism by which another anti-FNR mAb, LAD-1, exerts its antitumourigenic effects. Administration of LAD-1 significantly prolonged survival of BALB/c mice challenged previously with RL-male-1 cells. LAD-1 enhanced phagocytosis of RL-male-1 cells by hepatic macrophages and clodronate-mediated macrophage depletion abrogated the antitumour activity of LAD-1. In vitro experiments revealed that a pan-caspase inhibitor, zVAD-fmk, did not affect the ability of LAD-1 to inhibit the proliferation of RL-male-1 cells. These data suggest that the antitumour effects of LAD-1 may be dependent on stimulation of tumour cell phagocytosis and are apoptosis-independent. Thus, LAD-1-induced phagocytosis of lymphoma cells by hepatic macrophages in mice may, at least in part, be responsible for the prolonged survival of the mice.

Induction of Apoptosis Using Inhibitors of Lysophosphatidic Acid Acyltransferase- and Anti-CD20 Monoclonal Antibodies for Treatment of Human Non-Hodgkin's Lymphomas

PURPOSE

Lysophosphatidic acid acyltransferase-beta (LPAAT-beta) is a transmembrane enzyme critical for the biosynthesis of phosphoglycerides whose product, phosphatidic acid, plays a key role in raf and AKT/mTor-mediated signal transduction.

EXPERIMENTAL DESIGN

LPAAT-beta may be a novel target for anticancer therapy, and, thus, we examined the effects of a series of inhibitors of LPAAT-beta on multiple human non-Hodgkin's lymphoma cell lines in vitro and in vivo.

RESULTS

We showed that five LPAAT-beta inhibitors at doses of 500 nmol/L routinely inhibited growth in a panel of human lymphoma cell lines in vitro by >90%, as measured by [3H]thymidine incorporation. Apoptotic effects of the LPAAT-beta inhibitors were evaluated either alone or in combination with the anti-CD20 antibody, Rituximab. The LPAAT-beta inhibitors induced caspase-mediated apoptosis at 50 to 100 nmol/L in up to 90% of non-Hodgkin's lymphoma cells. The combination of Rituximab and an LPAAT-beta inhibitor resulted in a 2-fold increase in apoptosis compared with either agent alone. To assess the combination of Rituximab and a LPAAT-beta inhibitor in vivo, groups of athymic mice bearing s.c. human Ramos lymphoma xenografts were treated with the LPAAT-beta inhibitor CT-32228 i.p. (75 mg/kg) daily for 5 d/wk x 4 weeks (total 20 doses), Rituximab i.p. (10 mg/kg) weekly x 4 weeks (4 doses total), or CT-32228 plus Rituximab combined. Treatment with either CT-32228 or Rituximab alone showed an approximate 50% xenograft growth delay; however, complete responses were only observed when the two agents were delivered together.

CONCLUSIONS

These data suggest that Rituximab, combined with a LPAAT-beta inhibitor, may provide enhanced therapeutic effects through apoptotic mechanisms.

Controlling complement resistance in cancer by using human monoclonal antibodies that neutralize complement-regulatory proteins CD55 and CD59

Expression of the complement-regulatory proteins (CRP) CD46, CD55 and CD59 represents a strategy used by tumor cells to evade complement-dependent cell cytoxicity stimulated by monoclonal antibodies. We have isolated two single-chain variable fragments (scFv) to CD55 and CD59 from a human phage-display library and from these scFv we have produced two miniantibodies (MB), MB-55 (against CD55) and MB-59 (against CD59), containing the human hinge-CH2-CH3 domains of IgG1. The specificity of the two MB for the corresponding CRP was assessed by ELISA using purified CD46, CD55 and CD59. MB-55 and MB-59 neutralized the inhibitory activity of CD55 and CD59, respectively, restoring the complement-mediated lysis of sheep and guinea pig erythrocytes that was otherwise inhibited by the two CRP. FACS analysis revealed binding of MB-55 and MB-59 to the lymphoma cell line Karpas 422. The two MB induced a two-fold increase in the complement-dependent killing of these cells stimulated by Rituximab, a chimeric anti-CD20 monoclonal antibody. Transfection of HEK293T cells with vectors encoding MB-55 or MB-59 markedly reduced the expression of CD55 and CD59. We conclude that the human antibodies MB-55 and MB-59 may represent a therapeutic tool to increase the complement-dependent killing activity of Rituximab in the treatment of non-Hodgkin's lymphoma.

Rituximab mediates in vitro antileukemic activity in pediatric patients after allogeneic transplantation

Relapse is a major problem after allogeneic transplantation in children with acute B-lineage lymphoblastic leukemias (ALL) and lymphomas and additional therapeutic strategies are needed to increase graft versus leukemia effects without inducing graft versus host disease (GvHD). Several studies have shown the efficacy of a humanized CD20 antibody (rituximab) for treatment of CD20+ malignancies together with conventional chemotherapy but less is known about its post transplant usefulness. We studied the ability of rituximab to mediate antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) with effector cells and complement from patients who were transplanted with T-cell-depleted grafts from unrelated or mismatched related donors. Highest lytic activity (ADCC) was observed against leukemia-derived MHH4 cells and Burkitt's lymphoma-derived Raji cells in the first months after transplantation, corresponding to the high percentage of regenerating CD56+ CD16+ cells. Moreover, primary cryopreserved ALL-blasts from a pediatric patient were also efficiently lysed. Increased lysis was obtained after stimulation with interleukin-2. Combination of ADCC and CDC had additive effects. These findings encourage clinical trials on the use of rituximab for improving minimal residual disease control and relapse prevention after allogeneic high-risk transplantation in the small group of pediatric patients with CD20+ leukemias/lymphomas.

T cells armed with anti-CD3 x anti-CD20 bispecific antibody enhance killing of CD20+ malignant B cells and bypass complement-mediated rituximab resistance in vitro

OBJECTIVE

Resistance to rituximab, a chimeric monoclonal antibody that binds to CD20, is a major limitation for the successful treatment of patients with non-Hodgkin lymphoma and other CD20+ B-cell malignancies. To circumvent rituximab resistance in these patient populations, we have constructed a bispecific antibody (BiAb), anti-CD3 x anti-CD20 (CD20Bi), that combines rituximab targeting with non-major histocompatibility complex (non-MHC)-restricted cytotoxicity mediated by activated T cells (ATC).

MATERIALS AND METHODS

Activated T cells were obtained from anti-CD3 activated peripheral blood mononuclear cells (PBMC) of normal donors or the leukapheresis products of patients by culturing in the presence of interleukin-2 for 6-14 days. After ATC expansion, the cells were armed with CD20Bi. Killing activity was evaluated by 51Cr-release assay.

RESULTS

Arming ATC with as little as 5 ng CD20Bi/10(6) cells significantly increased cytotoxicity above unarmed ATC. CD20Bi-armed ATC (50 ng/10(6) cells) efficiently lysed CD20+ cell lines at E:T of 6.25-50, but not the nonhematologic, CD20- SK-BR-3 cell line. High levels of cytotoxicity mediated by CD20Bi-armed ATC (p < 0.05) could not be blocked by an 8000-fold excess of soluble rituximab. CD20Bi-armed ATC in the presence of complement killed ARH-77 cells, a rituximab-complement pathway-resistant multiple myeloma, significantly (p < 0.05) better than rituximab or unarmed ATC, suggesting that CD20Bi-armed ATC may be clinically effective for treatment of rituximab-resistant CD20+ hematologic malignancies.

CONCLUSIONS

Our findings demonstrate that CD20Bi-armed ATC enhance cytotoxicity against CD20+ B-cell lines and circumvent complement-mediated rituximab resistance, providing a strong rationale for this immune-based strategy for the treatment of rituximab-refractory CD20+ B-cell malignancies.

Rituxan (anti-CD20 antibody)-induced translocation of CD20 into lipid rafts is crucial for calcium influx and apoptosis

Rituxan, a chimeric anti-CD20 antibody, is the first antibody approved for immunotherapy in non-Hodgkin's B-cell lymphoma and other B-cell lymphoproliferative disorders. Additionally, efficacy of Rituxan treatment has been reported in nonmalignant autoimmune diseases such as rheumatoid arthritis. Crosslinking of CD20 molecules by Rituxan induces therapeutic B-cell depletion. CD20 is a B-lymphocyte specific integral membrane protein, proposed to function as a store-operated calcium channel, which is activated upon receptor-stimulated calcium depletion of intracellular stores. Crosslinking of CD20 by antibodies has been reported to induce a redistribution of CD20 molecules to specialized microdomains at the plasma membrane known as lipid rafts. Here, we report that in the absence of Rituxan, CD20 exhibits a low affinity to lipid rafts. However, binding of Rituxan significantly increases the affinity of CD20 for lipid rafts resulting in its redistribution to a fraction resistant to Triton X-100 solubilization. Furthermore, we demonstrate that disturbing the raft integrity by cholesterol extraction results in dissociation of CD20 from a Triton X-100 resistant fraction followed by complete inhibition of Rituxan-induced calcium entry and apoptosis. The integrity of lipid rafts seems to play a crucial role for CD20-induced caspase activation. These data show, for the first time, that Rituxan-induced translocation of CD20 to lipid rafts is important for increased intracellular Ca(2+) levels and downstream apoptotic signalling.

Cellular and molecular signal transduction pathways modulated by rituximab (rituxan, anti-CD20 mAb) in non-Hodgkin's lymphoma: implications in chemosensitization and therapeutic intervention

The clinical application of rituximab (chimeric mouse anti-human CD20 mAb, Rituxan, IDEC-C2B8), alone and/or combined with chemotherapy, has significantly ameliorated the treatment outcome of patients with relapsed and refractory low-grade or follicular non-Hodgkin's lymphoma (NHL). The exact in vivo mechanisms of action of rituximab are not fully understood, although antibody-dependent cell-mediated cytotoxicity (ADCC), complement-dependent cytotoxicity (CDC), and apoptosis have been suggested. We have proposed that modifications of the cellular signaling pathways by rituximab may be crucial for its clinical response. The B-cell restricted cell surface phosphoprotein CD20 is involved in many cellular signaling events including proliferation, activation, differentiation, and apoptosis upon crosslinking. Monomeric rituximab chemosensitizes drug-resistant NHL cells via selective downregulation of antiapoptotic factors through the type II mitochondrial apoptotic pathway. Several signaling pathways are affected by rituximab which are implicated in the underlying molecular mechanisms of chemosensitization. ARL (acquired immunodeficiency syndrome (AIDS)-related lymphoma) and non-ARL cell lines have been examined as in vitro model systems. In ARL, rituximab diminishes the activity of the p38MAPK signaling pathway resulting in inhibition of the interleukin (IL)-10/IL-10R autocrine/paracrine cytokine autoregulatory loop leading to the inhibition of constitutive STAT-3 activity and subsequent downregulation of Bcl-2 expression leading to chemosensitization. Rituximab upregulates Raf-1 kinase inhibitor protein (RKIP) expression in non-ARL cells. Through physical association with Raf-1 and nuclear factor kappaB (NF-kappa B)-inducing kinase (NIK), RKIP negatively regulates two major survival pathways, namely, the extracellular signal-regulated kinase1/2 (ERK1/2) and the NF-kappa B pathways, respectively. Downmodulation of the ERK1/2 and NF-kappa B pathways inhibits the transcriptional activity of AP-1 and NF-kappa B transcription factors, respectively, both of which lead to the downregulation of Bcl-(xL) (Bcl-2 related gene (long alternatively spliced variant of Bcl-x gene)) transcription and expression and sensitization to drug-induced apoptosis. Bcl-(xL)-overexpressing cells corroborated the pivotal role of Bcl-(xL) in chemosensitization. The specificity of rituximab-mediated signaling and functional effects were corroborated by the use of specific pharmacological inhibitors. Many patients do not respond and/or relapse and the mechanisms of unresponsiveness are unknown. Rituximab-resistant B-NHL clones were generated to investigate the acquired resistance to rituximab-mediated signaling, and chemosensitization. Resistant clones display different phenotypic, genetic and functional properties compared to wild-type cells. This review summarizes the data highlighting a novel role of rituximab as a signal-inducing antibody and as a chemosensitizing agent through negative regulation of major survival pathways. Studies presented herein also reveal several intracellular targets modified by rituximab, which can be exploited for therapeutic and prognostic purposes in the treatment of patients with rituximab- and drug-refractory NHL.

Importance of receptor density in alpha radioimmunotherapy in B cell malignancies: an in-vitro study

BACKGROUND

External beam radiotherapy and beta radioimmunotherapy (RIT) are effective treatments for lymphoid malignancies. The development of RIT with alpha emitters is attractive because of the high linear energy transfer (LET) and short path length, allowing higher tumour cell kill and lower toxicity to healthy tissues.

AIM

To assess the binding of rituximab to samples of B cell chronic lymphocytic leukaemia (B-CLL) and splenic lymphoma with villous lymphocytes (SLVL), and to evaluate the induction of apoptosis by conventional therapies as well as with Bi conjugated to rituximab.

METHOD

213Bi was eluted from a 225Ac generator and conjugated to CD20 antibody (rituximab) with CHX-A''-DTPA as chelator. Binding assays with 213Bi-rituximab were correlated to antibody binding capacity obtained by flow cytometry. Apoptosis was scored by flow cytometric analyses of the cells stained with annexin V-FITC and 7-amino-actinomycin D.

RESULTS

Binding of 213Bi-rituximab was significantly lower for B-CLL compared to SLVL samples (12+/-3 and 42+/-10 213Bi atoms per cell, respectively, at 370 kBq.ml(-1)). The induction of apoptosis did not differ significantly between the two groups (B-CLL and SLVL) after external gamma irradiation or treatment with methylprednisolone and fludarabine (17+/-12% and 18+/-11%; 23+/-14% and 21+/-12%; 9+/-9% and 11+/-8%, respectively; all results expressed as percentages of all cells). Rituximab conjugated or not to 213Bi induced significantly more apoptosis in SLVL (42+/-19% and 42+/-17%) compared to B-CLL samples (27+/-12% and 6+/-8%).

CONCLUSION

Binding assays confirm that SLVL samples present more CD20 antigens compared to B-CLL samples. Conventional therapies such as fludarabine, methylprednisolone or external gamma irradiation induce similar responses in the two populations but SLVL samples present higher sensitivity towards 213Bi-rituximab. These data are in favour of alpha-RIT in SLVL patients.

Preparation of purified lymphoma cells suitable for therapy

BACKGROUND

Very few tumoral Ags have yet been isolated in NHL B cells. It is nevertheless possible to use whole tumor cells as a source of tumor Ags. We describe the purification of large numbers of human NHL B cells directly from lymph node or spleen biopsies, and different preparations allowing their use in a clinical setting.

METHODS

The purification procedure consists of the negative selection of tumor B cells: cells to be eliminated are opsonized by CD2 Abs, and then coupled to magnetic beads for separation by the Isolex 300 magnetic separator.

RESULTS

The mean yield of the purification was 74% for CD19+ cells, with a mean purity of 87%, dependent on the initial fraction of tumor cells in the biopsy. Using this procedure, a large number of purified tumor cells can be recovered from a biopsy in sterile conditions. We also describe treatments of B cells that can enhance their uptake by APCs, a critical step in anti-tumor immunotherapy strategies. Cells were opsonized by rituximab, or induced in apoptosis by irradiation, or necrosis by heating. Cell lysates were directly prepared from purified tumor cells.

DISCUSSION

These procedures were reproducible on every lymphoma cell, and treated cells were phagocytosed by APCs. The methodology described here allows the evaluation of the immunological potential of apoptotic, necrotic, opsonized lymphoma cells, or their lysates, in a clinical setting.

[Rituximab: a original biotherapy in auto-immune disorders]

SUBJECT

After several decades of hegemony of the T lymphocyte, recent work has suggested the importance of the B lymphocyte in auto-immune diseases. As a consequence, there has emerged over the last few years the idea of using anti-B lymphocyte therapy, in particular rituximab (a chimeric anti-CD20 monoclonal antibody).

CURRENT TOPICS AND IMPORTANT RESULTS

This review addresses various current topics: a) the role of B lymphocytes in auto-immune diseases, notably their capacity to be antigen presenting cells and to be activated by original systems like Blys/Baff; b) the mechanism of action of rituximab (apoptosis, complement-dependent cytotoxicity and antibody-dependent cell cytotoxicity) and the phenomena explaining failures and cases escaping treatment, in particular among lymphoproliferations; c) The results include efficacy and tolerance data for the principal auto-immune affections. Among these, the most promising indications would seem to be for rheumatoid polyarthritis and systemic lupus erythematosis, although some preliminary open studies point to an effect in Goujerot-Sjögren's syndrome, neuropathies, auto-immune cytopenia, idiopathic thrombocytopenic purpura, cryoagglutinins, blistering cutaneous affections...

PERSPECTIVES AND PROJECTS

Controlled studies will be required to determine the true efficacy and tolerance of this molecule, as it is imperative to validate these new immunotherapeutic strategies, above all when they concern innovative and expensive therapy. Nevertheless, these different observations arouse great hopes and at the same time exciting questions, notably as to the role of B lymphocytes in auto-immune diseases.

An anti-CD20-IL-2 immunocytokine is highly efficacious in a SCID mouse model of established human B lymphoma

We have engineered an anti-CD20-interleukin 2 (IL-2) immunocytokine (ICK) based on the Leu16 anti-CD20 antibody and have deimmunized both the variable (V) regions as well as the junction between the heavy (H) chain constant region and IL-2. Mutations were made to remove potential T-cell epitopes identified by in silico binding to major histocompatibility complex (MHC) class II molecules. The resulting immunocytokine, DI-Leu16-IL-2, retained full anti-CD20 activity as assessed by fluorescence-activated cell-sorting (FACS) analysis, and had enhanced antibody-dependent cellular cytotoxicity (ADCC) effector function relative to the DI-Leu16 antibody or control anti-CD20 antibody (rituximab). In a severe combined immunodeficient (SCID) mouse model of disseminated, residual lymphoma, anti-CD20-IL-2 immunocytokines based on Leu16 were far more effective at a dose of 0.25 mg/kg than anti-CD20 antibody given at 25/mg/kg, despite a shorter half-life of the ICK. Anti-CD20-IL-2 was also far more effective than a control ICK targeted to an antigen with greatly reduced expression on Daudi tumor cells, or various combinations of anti-CD20 antibodies and IL-2. Antitumor activity of DI-Leu16-IL-2 was shown to partially but not entirely depend on Fc receptor (R) binding, suggesting that ADCC and targeting of IL-2 both play roles in the mechanism of tumor clearance. Based on these animal models, DI-Leu16-IL-2 could offer therapeutic potential for patients with CD20 positive lymphoma. Clinical trials are currently under development.

Apoptotic killing of B-chronic lymphocytic leukemia tumor cells by allicin generated in situ using a rituximab-alliinase conjugate

Allicin, a highly active component from freshly crushed garlic, is produced upon the reaction of the small molecular weight molecule alliin, with the enzyme alliinase (EC 4.4.1.4). Because allicin was shown to be toxic to various mammalian cells in vitro, we devised a novel approach for the therapy of B-cell malignancies based on site-directed generation of allicin. Alliinase was conjugated to the monoclonal antibody rituximab, which recognizes the CD20 antigen, and the resulting conjugate was targeted to CD20+ B chronic lymphocytic leukemia (B-CLL) and other B-cell lymphomas. Upon addition of alliin, allicin was formed in situ, killing the CD20+ tumor B cells via apoptosis. Following a 72-hour treatment, an 85% and 96% reduction was observed in the number of viable B-CLL and EBV-transformed B cells, respectively. Using the human/mouse radiation chimera for the evaluation of allicin targeting in a preclinical animal model, we showed a significant reduction in the number of recovered B-CLL, mantle cell lymphoma, or EBV-transformed B cells. We conclude that our system offers a new powerful and less toxic therapy for B-CLL and other B-cell malignancies. Furthermore, combining alliinase with the appropriate monoclonal antibody may extend the application of this approach to other conditions in which the elimination of a specific cell population is desired.

Immunochemotherapy with rituximab and cyclophosphamide, doxorubicin, vincristine, and prednisone significantly improves response and time to treatment failure, but not long-term outcome in patients with previously untreated mantle cell lymphoma: results of a prospective randomized trial of the German Low Grade Lymphoma Study Group (GLSG)

PURPOSE

Mantle cell lymphoma (MCL) is characterized by a poor prognosis with a low to moderate sensitivity to chemotherapy and a median survival of only 3 to 4 years. In an attempt to improve outcome, the German Low Grade Lymphoma Study Group (GLSG) initiated a randomized trial comparing the combination of cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) and rituximab (R-CHOP) with CHOP alone as first-line therapy for advanced-stage MCL.

PATIENTS AND METHODS

One hundred twenty-two previously untreated patients with advanced-stage MCL were randomly assigned to six cycles of CHOP (n = 60) or R-CHOP (n = 62). Patients up to 65 years of age achieving a partial or complete remission underwent a second randomization to either myeloablative radiochemotherapy followed by autologous stem-cell transplantation or interferon alfa maintenance (IFNalpha). All patients older than 65 years received IFNalpha maintenance.

RESULTS

R-CHOP was significantly superior to CHOP in terms of overall response rate (94% v 75%; P = .0054), complete remission rate (34% v 7%; P = .00024), and time to treatment failure (TTF; median, 21 v 14 months; P = .0131). No differences were observed for progression-free survival. Toxicity was acceptable, with no major differences between the two therapeutic groups.

CONCLUSION

The combined immunochemotherapy with R-CHOP resulted in a significantly higher response rate and a prolongation of the TTF as compared with chemotherapy alone. Hence, R-CHOP may serve as a new baseline regimen for advanced stage MCL, but needs to be further improved by novel strategies in remission.

Combination immunotherapy of B-cell non-Hodgkin's lymphoma with rituximab and interleukin-2: a preclinical and phase I study

PURPOSE

Cytokine-induced modulation of innate immunity is being explored to enhance the activity of monoclonal antibodies. Severe combined immunodeficient (SCID) mice engrafted with peripheral blood leukocytes (PBLs) from Epstein Barr virus-seropositive donors develop human B-cell non-Hodgkin's lymphomas [B-NHLs (hu-PBL-SCID mouse model)]. We used this hu-PBL-SCID mouse model to study the synergism between interleukin (IL)-2 and rituximab. We also conducted a phase I trial of IL-2 and rituximab in relapsed B-NHL to study whether expansion of natural killer (NK) cells and enhanced cellular cytotoxicity could be safely accomplished in vivo.

EXPERIMENTAL DESIGN

Hu-PBL-SCID mice were treated with various schedules of rituximab and IL-2, with survival as the end point. Patients with relapsed B-NHL received rituximab (375 mg/m2 weekly x 4) followed by daily low-dose IL-2 (1 MIU/m2/day x 4 weeks) with pulses of intermediate-dose IL-2 (3-15 MIU/m2). Toxicity, NK cell numbers, and cellular cytotoxicity were measured.

RESULTS

In the hu-PBL-SCID mouse, the combination of rituximab and IL-2 showed greater activity against B-NHL than either agent alone. Treatment was most effective when IL-2 was given before rituximab. Twelve patients with heavily pretreated B-NHL entered the phase I trial. Toxicity was manageable, and responses were observed. NK cell expansion and enhanced cellular cytotoxicity against a B-cell lymphoma target were observed but did not correlate with response.

CONCLUSIONS

The combination of IL-2 and rituximab is synergistic against B-NHL in the hu-PBL-SCID model. In the phase I trial, a sequential combination of rituximab and IL-2 was well tolerated and achieved biological end points. Responses were observed.

Folate receptor-targeted immunotherapy: Induction of humoral and cellular immunity against hapten-decorated cancer cells

We previously exploited the frequent overexpression of folate receptors on cancer cells to decorate malignant cell surfaces selectively with folate-hapten conjugates. In antihapten-immunized hosts, this targeted localization of foreign haptens to tumor cells led to rapid accumulation of autologous antihapten IgG, which in turn yielded potent antitumor activity upon stimulation with cytokines (IL-2, IFN-alpha). In an effort to understand the effector mechanisms responsible for tumor regression, we have now investigated the involvement of both humoral and cellular immune components in the tumor destruction process. We report that the dependence of therapeutic efficacy on folate-hapten concentration is bimodal, suggesting that the conjugate must bridge between a cell surface FR and an antihapten IgG in order to mediate killing. Studies with cancer cells in vitro further demonstrate that folate-fluorescein-marked tumor cells are killed primarily by antibody-dependent cellular cytotoxicity and phagocytosis, with no contribution from complement-dependent mechanisms. Investigations of specific immune cell involvement also reveal that asialo-GM1(+)-natural killer cells, macrophages, CD4+ T cells and CD8+ T cells contribute significantly to recognition/removal of the cancer mass, and that elimination of these cell types markedly compromises the therapy. Because the initial antibody-dependent stage of tumor cell killing is shown to lead to a long-term antibody-independent cellular immunity that involves both CD4+ and CD8+ T cells, we propose that F(c) receptor-expressing immune cells not only initiate destruction of the IgG-marked tumor cells, but also participate in presentation of endogenous tumor antigens in a manner that leads to long-term cellular immunity.

Overview on the use of therapeutic antibodies in drug discovery

The number of therapeutic antibodies approved by regulatory agencies as novel drugs and the number of antibodies in development has increased significantly. The modular nature of antibody structure has enabled researchers to more predictably design therapeutic antibodies by choosing appropriate functional features most appropriate for a given antibody target and clinical indication. Advances in recombinant antibody technologies have allowed the routine generation of antibodies that can satisfy stringent drug design criteria, such as low immunogenicity, high affinity, target specificity, and commercially viable manufacturing methods. Engineering design opportunities exist for both the variable and the constant regions that encompass, in addition to antigen specificity and affinity, effector functions that mediate immune complex clearance or pharmacokinetics. These are discussed in the context of relevant in vivo and in vitro technologies, such as human IgG transgenic mice, phage display, and biologics manufacturing. Finally, therapeutic antibodies are compared with traditional drugs with respect to target class, selectivity, route of administration, intellectual property issues, and lead discovery and optimization.

The Evolution of Antibodies into Versatile Tumor-Targeting Agents

In recent years, monoclonal antibodies have become important weapons in the arsenal of anticancer drugs, and in select cases are now the drugs of choice due to their favorable toxicity profiles. Originally developed to confer passive immunity against tumor-specific antigens, clinical uses of monoclonal antibodies are expanding to include growth factor sequestration, signal transduction modulation, and tumor-specific drug delivery. In this review, we shall present the origins of antibody therapeutics within the field of immunotherapy and their evolution into effective anticancer agents, then discuss their multiple mechanisms of action, the basis of their tumor selectivity, and their therapeutic properties compared with traditional therapies. Antibodies are complex molecules whose efficacy and toxicity depend on the antigen, the antibody, any conjugated groups, and even the patient. Finally, we shall present new technologies being developed to increase the efficacy and selectivity of antibody-based therapeutics. Interestingly, many of the new approaches straddle the middle ground between immunotherapy and the traditional modalities of chemotherapy and radiotherapy, and can be seen as ways of combining the selectivity of the former with the efficacy of the latter.

CD8+ T-Cell–Dependent Immunity Following Xenogeneic DNA Immunization against CD20 in a Tumor Challenge Model of B-Cell Lymphoma

The CD20 B-cell differentiation antigen is an attractive target for immunotherapy of B-cell lymphomas. In an experimental lymphoma model, BALB/c mice were immunized with mouse or human CD20 cDNA (mCD20 and hCD20, respectively) or their extracellular domains (minigenes). IFNγ secretion by CD8+ T cells against CD20 was detected in mice vaccinated with hCD20 or human minigene, indicating that hCD20-primed CD8+ T cells recognize syngeneic CD20. Systemic challenge with syngeneic A20 cells, an aggressive lymphoma, resulted in long-term survival in a subset of immunized mice. Overall long-term survival was 14% in groups vaccinated with the human minigene versus 4% in control groups (P &lt; 0.001). CD8+ T-cell depletion during the effector phase completely abrogated this effect. Antibodies against a recombinant mouse CD20 protein produced in insect cells were detected in mice immunized with hCD20 DNA and human and mouse minigene, but not in mice receiving mCD20 DNA. These results show that active immunization with xenogeneic DNA vaccines can induce CD8+ T cell–dependent immunity against CD20.

Improved access to CD20 following B cell receptor cross-linking at Burkitt's lymphoma cell surfaces

Here we report that B cell receptor (BCR) engagement rapidly improves the capacity of CD20 to be accessed by cognate antibody at model Burkitt's lymphoma cell surfaces. None of eight other surface molecules demonstrated such BCR-dependent enhancement of ligand binding while the quantity of accessible CD20 remained unchanged on either CD19 or CD40 engagement. Neither the actin-depolymerizing agent cytochalasin D nor inhibitors targeting signalling pathways associated with the BCR attenuated the CD20 increase that could be uncoupled from BCR endocytosis. Instead, a role for lipid rafts was indicated both from the inhibitory actions of cholesterol-sequestering methyl-beta-cyclodextrin and direct analysis of CD20 redistribution using sucrose density gradients and confocal microscopy. Whether such observations could find application in CD20-directed therapies where success can be compromised by otherwise low-level expression of target antigen is discussed.

Antibody-targeted therapy: a paradigm of innovative treatment strategies in indolent and aggressive B-cell non-Hodgkin lymphoma

PURPOSE OF REVIEW

This review outlines the principles of treatment of indolent and aggressive B-cell lymphoma based on current knowledge on the classification of hematologic malignancies and the rationale to implement new antibody-targeted immunotherapeutic approaches.

RECENT FINDINGS

An update is provided on the use of antibody-targeted therapies in clinical trials, with emphasis on new, emerging strategies of immunotherapy in B-cell non-Hodgkin lymphoma.

SUMMARY

The success of immune-mediated therapies has encouraged studies on antibody-targeted therapy in B-cell non-Hodgkin lymphoma. Promising new approaches combine classical dose-intense chemotherapy with "tumor-specific" antibody targeting during several phases of the disease. The safety and efficacy of anti-CD20 in the treatment of indolent and aggressive B-cell non-Hodgkin lymphoma at any stage of disease, either as a single agent or as part of multimodality regimes, as an unconjugated antibody or as radioimmunoconjugate have changed dramatically our treatment strategies. Increasing insights into basic molecular biology and immunology of B-cell non-Hodgkin lymphoma may identify subgroups of patients categorized in current classification systems who may benefit from tailored approaches with new modality antibody-targeted therapy in near future.

From the bench to the bedside: ways to improve rituximab efficacy

Rituximab (MabThera, Rituxan) is a chimeric IgG1 monoclonal antibody that specifically targets the CD20 surface antigen expressed on normal and neoplastic B-lymphoid cells. Rituximab is currently used in the treatment of both follicular and aggressive B-cell non-Hodgkin lymphomas. Despite its demonstrated clinical effectiveness, its in vivo mechanisms of action remain unknown and could differ by subtype of lymphoma. Rituximab has been shown to induce apoptosis, complement-mediated lysis, and antibody-dependent cellular cytotoxicity in vitro, and some evidence points toward an involvement of these mechanisms in vivo. Rituximab also has a delayed therapeutic effect as well as a potential “vaccinal” effect. Here, we review the current understanding of the mechanism of action of rituximab and discuss approaches that could increase its clinical activity. A better understanding of how rituximab acts in vivo should make it possible to develop new and more effective therapeutic strategies. (Blood. 2004;104:2635-2642)

Empowering targeted therapy: lessons from rituximab

Rituximab, a monoclonal antibody directed against the B cell-specific protein CD20, has revolutionized lymphoma treatment by providing a highly effective form of therapy with relatively mild toxic side effects. Effective as a single agent against some forms of B cell lymphoma, rituximab also has a chemosensitizing effect, enhancing the efficacy of chemotherapy against other forms of the disease. Although the mechanisms whereby rituximab achieves its effects remain incompletely understood, these seem to involve at least three distinct phenomena: (i) antibody-dependent cell-mediated cytotoxicity, (ii) complement-mediated cell lysis, and (iii) stimulation of apoptosis in target cells. The latter occurs through interaction of complexes of rituximab and CD20 in lipid rafts, with elements of a signaling pathway involving Src kinases. Effector molecules trigger various gene expression events, leading to sensitization of malignant cells to proapoptotic stimuli. Lessons learned from the research on rituximab may be applied to the rational development of antibody-based therapies against other forms of cancer.

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

The FCGR3A gene dimorphism generates two allotypes: FcgammaRIIIa-158V and FcgammaRIIIa-158F. The genotype homozygous for FcgammaRIIIa-158V (VV) is associated with higher clinical response to rituximab, a chimeric anti-CD20 IgG1 used in the treatment of B lymphoproliferative malignancies. Our objective was to determine whether this genetic association relates to rituximab-dependent cytotoxicity mediated by FcgammaRIIIa/CD16a+ cells. The number of CD16+ circulating monocytes, T cells, and natural killer (NK) cells in 54 donors was first shown to be unrelated to FCGR3A polymorphism. We then demonstrated that FcgammaRIIIa-158V displays higher affinity for rituximab than FcgammaRIIIa-158F by comparing rituximab concentrations inhibiting the binding of 3G8 mAb (anti-CD16) with VV NK cells and NK cells homozygous for FcgammaRIIIa-158F (FF). VV and FF NK cells killed Daudi cells similarly after FcgammaRIIIa engagement by saturating concentrations of rituximab or 3G8. However, the rituximab concentration resulting in 50% lysis (EC(50)) observed with NK cells from VV donors was 4.2 times lower than that observed with NK cells from FF donors (on average 0.00096 and 0.00402 microg/ml, respectively, P = 0.0043). Finally, the functional difference between VV and FF NK cells was restricted to rituximab concentrations weakly sensitizing CD20. This study supports the conclusion that FCGR3A genotype is associated with response to rituximab because it affects the relationship between rituximab concentration and NK cell-mediated lysis of CD20+ cells. Rituximab administration could therefore be adjusted according to FCGR3A genotype.

Rituximab infusion promotes rapid complement depletion and acute CD20 loss in chronic lymphocytic leukemia

Complement plays an important role in the immunotherapeutic action of the anti-CD20 mAb rituximab, and therefore we investigated whether complement might be the limiting factor in rituximab therapy. Our in vitro studies indicate that at high cell densities, binding of rituximab to human CD20(+) cells leads to loss of complement activity and consumption of component C2. Infusion of rituximab in chronic lymphocytic leukemia patients also depletes complement; sera of treated patients have reduced capacity to C3b opsonize and kill CD20(+) cells unless supplemented with normal serum or component C2. Initiation of rituximab infusion in chronic lymphocytic leukemia patients leads to rapid clearance of CD20(+) cells. However, substantial numbers of B cells, with significantly reduced levels of CD20, return to the bloodstream immediately after rituximab infusion. In addition, a mAb specific for the Fc region of rituximab does not bind to these recirculating cells, suggesting that the rituximab-opsonized cells were temporarily sequestered by the mononuclear phagocytic system, and then released back into the circulation after the rituximab-CD20 complexes were removed by phagocytic cells. Western blots provide additional evidence for this escape mechanism that appears to occur as a consequence of CD20 loss. Treatment paradigms to prevent this escape, such as use of engineered or alternative anti-CD20 mAbs, may allow for more effective immunotherapy of chronic lymphocytic leukemia.

Three new assays for rituximab based on its immunological activity or antigenic properties: analyses of sera and plasmas of RTX-treated patients with chronic lymphocytic leukemia and other B cell lymphomas

Rituximab (RTX) is a monoclonal antibody which targets CD20 and is approved for treatment of non-Hodgkin's lymphoma (NHL), with an approximate 50% overall response rate among NHL patients. Accurate determination of RTX concentrations in patient plasmas is important for proper dosing of patients and for correlating RTX concentrations with clinical responses. There is currently no assay available for RTX which utilizes easily obtainable commercial reagents. Therefore, we sought to develop such an assay, and in this report we describe three new assays for RTX concentration. One assay, based on flow cytometry, quantitates immunologically active RTX based on its ability to bind to CD20 on Raji cells. Two other methods, based on flow cytometry and ELISA, measure RTX based on its antigenic properties. The assays are accurate, in good agreement with one another, and can all measure RTX concentrations as low as approximately 1 microg/ml in both sera and plasmas. Use of these assays reveals that chronic lymphocytic leukemia (CLL) patients receiving RTX treatment have lower plasma RTX concentrations than patients with other B cell lymphomas at all times over the usual 4-week course of therapy. The level in CLL plasmas often declines to <1 microg/ml RTX 1 week after each RTX infusion, substantially lower than the values found in comparable non-CLL patient plasmas. RTX assay results also demonstrate that naïve CLL patient plasmas do not have levels of non-cell associated CD20 sufficient to either interfere with an in vitro assay of RTX or to block the potential therapeutic action of RTX in vivo.