Treatment of relapsed B-cell non-Hodgkin's lymphoma with a combination of chimeric anti-CD20 monoclonal antibodies (rituximab) and G-CSF: final report on safety and efficacy.

Antibody-dependent cellular cytotoxicity (ADCC) is one of the possible mechanisms of action of the chimeric CD20 monoclonal antibody IDEC-C2B8 (rituximab). As granulocyte-colony stimulating factor (G-CSF) greatly enhances the cytotoxicity of neutrophils in ADCC, the efficacy of rituximab might be enhanced by the addition of G-CSF. In a phase I/II clinical trial, we investigated the safety and efficacy of the combination of rituximab and G-CSF (5 microg/kg/day, administered for 3 days, starting 2 days before each infusion) in 26 relapsed low-grade lymphoma patients. Adverse events occurred in 25/26 patients and mainly consisted of (grade I/II) fever (29%) and allergic reactions (19%). In phases I and II (375 mg/m(2) rituximab+G-CSF), 19 patients were evaluable for efficacy. The response rate was 42% (8/19; 95% CI 20-67%), with 16% (3/19) complete remissions and 26% (5/19) partial remissions. The median duration of response was 18 months, the median time to progression was 24 months. We conclude that the combination of rituximab and G-CSF is well tolerated. Although the overall response rate seems comparable to that reported for rituximab monotherapy, remission duration in this pilot phase II study is remarkably long. Randomized comparison with rituximab monotherapy should substantiate this promising finding.     

Granulocyte-colony stimulating factor enhances chimeric antibody Nd2 dependent cytotoxicity against pancreatic cancer mediated by polymorphonuclear neutrophils

Nd2 is a monoclonal antibody against pancreatic cancer. We have previously reported that human/mouse chimeric antibody Nd2 (c-Nd2) can induce antibody-dependent cell-mediated cytotoxicity (ADCC) with peripheral blood mononuclear cells (PBMs) as effectors. In this study, we investigated whether c-Nd2 can induce ADCC with poly-morphonuclear neutrophils (PMNs) as effector cells and the effects of granulocyte-colony stimulating factor (G-CSF) in enhancing this cytotoxicity. Cytotoxicities for pancreatic cancer cell line, SW1990 were dose-dependently increased by c-Nd2 during co-culture with PMNs and these cytotoxicities were significantly suppressed by the addition of neutralizing antibodies against CD16, which is Fcgamma receptor expressed on PMN membranes. PMNs treated with G-CSF significantly enhanced in vitro ADCC activity against SW1990 induced by c-Nd2. The in vivo growth of subcutaneously transplanted SW1990 tumor in nude mouse was significantly inhibited by i.p. administration of c-Nd2 compared to control (non-specific IgG1). In addition, this inhibitory effect was enhanced by the combination of c-Nd2 and G-CSF. Immunohistochemical study with anti-mouse neutrophil elastase antibody demonstrated strong infiltrations of PMNs into and around the transplanted tumor, treated with c-Nd2 and G-CSF. These results suggest that PMNs play an important role in c-Nd2 inducing ADCC and that combination immunotherapy of c-Nd2 with G-CSF may have clinical applications in the treatment of patients with pancreatic cancer by enhancing ADCC.     

Effector Cell Analysis of Human Multidrug-resistant Cell Killing by Mouse-Human Chimeric Antibody against P-Glycoprotein

A mouse-human chimeric monoclonal antibody (mAb), MH162, against P-glycoprotein was previously found to be more effective than an all-mouse mAb (MRK16) in lysis of multidrug-resistant (MDR) tumor cells by blood mononuclear cells. The present study was performed to identify the effector cells responsible for the chimeric mAb-dependent cell-mediated cytotoxicity (ADCC) against MDR cells. The ADCC reaction was assessed by a 6-h ⁵¹Cr release assay. Highly purified lymphocytes (>99%), monocytes (>99%) and neutrophils (>96%) were obtained from peripheral blood of the same healthy donors. A comparison of these three effector cell populations showed no difference between MH162 and its all-murine counterpart MRK16 in MDR cell lysis by monocytes or neutrophils. But MH162 was more effective than MRK16 in lymphocyte-mediated lysis of the MDR cells. The lymphocytes responsible for this ADCC had CD16+ Fc receptors. Pretreatment of monocytes with colony-stimulating factors (IL-3, GM-CSF and M-CSF) caused significant increase in their MH162-mediated lysis of MDR cells. Another anti-P-glycoprotein chimeric mAb (MH171) was also more effective than its murine counterpart MRK17 in lymphocyte-mediated lysis of MDR cells. These findings suggest that mouse-human chimeric mAbs may be useful therapeutically for in vivo destruction of MDR cancer cells by the ADCC reaction.     

Effector cell analysis of human multidrug-resistant cell killing by mouse-human chimeric antibody against P-glycoprotein.

A mouse-human chimeric monoclonal antibody (mAb), MH162, against P-glycoprotein was previously found to be more effective than an all-mouse mAb (MRK16) in lysis of multidrug-resistant (MDR) tumor cells by blood mononuclear cells. The present study was performed to identify the effector cells responsible for the chimeric mAb-dependent cell-mediated cytotoxicity (ADCC) against MDR cells. The ADCC reaction was assessed by a 6-h 51Cr release assay. Highly purified lymphocytes (greater than 99%), monocytes (greater than 99%) and neutrophils (greater than 96%) were obtained from peripheral blood of the same healthy donors. A comparison of these three effector cell populations showed no difference between MH162 and its all-murine counterpart MRK16 in MDR cell lysis by monocytes or neutrophils. But MH162 was more effective than MRK16 in lymphocyte-mediated lysis of the MDR cells. The lymphocytes responsible for this ADCC had CD16+ Fc receptors. Pretreatment of monocytes with colony-stimulating factors (IL-3, GM-CSF and M-CSF) caused significant increase in their MH162-mediated lysis of MDR cells. Another anti-P-glycoprotein chimeric mAb (MH171) was also more effective than its murine counterpart MRK17 in lymphocyte-mediated lysis of MDR cells. These findings suggest that mouse-human chimeric mAbs may be useful therapeutically for in vivo destruction of MDR cancer cells by the ADCC reaction.     

Chimeric and humanized anti-HM1.24 antibodies mediate antibody-dependent cellular cytotoxicity against lung cancer cells

HM1.24 antigen (CD317) was originally identified as a cell surface protein that is preferentially overexpressed on multiple myeloma cells. Immunotherapy using anti-HM1.24 antibody has been performed in patients with multiple myeloma as a phase I study. The aim of this study was to evaluate the anti-tumor activity of mouse-human chimeric and humanized anti-HM1.24 monoclonal antibodies (mAbs) against lung cancer cells in vitro. Human peripheral blood lymphocytes and monocytes separated from mononuclear cells (PBMCs) were used as effector cells. Antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) of chimeric and humanized anti-HM1.24 mAbs against lung cancer cells were determined by chromium-release assay. In some experiments, target or effector cells were pretreated with various cytokines. Chimeric and humanized anti-HM1.24 mAbs effectively induced ADCC against lung cancer cells mediated more efficiently by lymphocytes than monocytes. The cytotoxic activity correlated with the level of HM1.24 expression on lung cancer cells. Natural killer cells were identified as the major effector cells in ADCC mediated by the anti-HM1.24 mAb. The treatment of lymphocytes or monocytes with IL-2, IL-12, IL-15, M-CSF, or IFN-gamma significantly increased the ADCC activity. Moreover, the culture of lung cancer cells with IFN-beta or IFN-gamma augmented their susceptibility to ADCC and CDC. PBMCs from patients with lung cancer induced a level of ADCC comparable to that induced by PBMCs from healthy donors. Chimeric or humanized anti-HM1.24 mAbs have potential as a new therapeutic tool in lung cancer, and in combination with interleukins and interferons, could be useful for enhancing ADCC.     

Clinically effective monoclonal antibody 3F8 mediates nonoxidative lysis of human neuroectodermal tumor cells by polymorphonuclear leukocytes.

Most studies of antibody-dependent cellular cytotoxicity (ADCC) by polymorphonuclear leukocytes (PMN) have supported oxidative lytic processes. This may be because the studies used nonhuman or nonneoplastic cells that were highly sensitive to reactive oxygen species or were small enough to be phagocytosed by PMN. We therefore investigated whether oxygen radicals participate in PMN cytotoxicity toward human neuroectodermal solid tumor cells sensitized by 3F8, which is an anti-ganglioside GD2 murine IgG3 monoclonal antibody with documented anticancer activity in humans. A 4-h 51Cr release assay was used to assess tumor cell lysis by hydrogen peroxide, superoxide, and hypochlorite. Nine of 11 GD2(+) human melanoma and neuroblastoma cell lines had equal or greater resistance to these oxidants as compared to a GD2(-) human carcinoma line (SKBr1-III) found by others (and confirmed by us) to be significantly more resistant to oxidative lysis than a murine cell line (P388D1) representative of those commonly used in cytotoxicity assays. To facilitate detection of oxidant-mediated lysis, subsequent studies of 3F8-mediated ADCC used GD2(+) targets that were relatively sensitive and others that were relatively resistant to oxygen radicals. Normal PMN and PMN obtained from children with chronic granulomatous disease, which do not generate reactive oxygen species, were equally effective in ADCC. Granulocyte-macrophage colony-stimulating factor, which primes oxidative responses of normal but not of chronic granulomatous disease PMN, enhanced ADCC by both kinds of PMN. During ADCC of 3F8-sensitized targets, with or without granulocyte-macrophage colony-stimulating factor, GD2(-) "innocent bystander" tumor cells (including P388D1) were not lysed, a finding consistent with unimportant extracellular release of cytotoxic mediators. Finally, antioxidant and antimyeloperoxidase moieties did not block ADCC. We conclude that oxidants are not key factors in 3F8-mediated lysis by PMN of human neuroectodermal tumor cells.     

Phase I clinical trial of the bispecific antibody MDX-H210 (anti-FcgammaRI x anti-HER-2/neu) in combination with Filgrastim (G-CSF) for treatment of advanced breast cancer

A phase I study of the bispecific antibody MDX-H210 in combination with granulocyte colony-stimulating factor (G-CSF) was performed in stage IV breast carcinoma patients, overexpressing HER-2/neu. MDX-H210, constructed by crosslinking antigen binding fragments (F(ab') fragments) of monoclonal antibody (mAb) H22 to Fc gamma receptor I (FcgammaRI), and mAb 520C9 to HER-2/neu, respectively, mediates the lysis of tumour cells in vitro, and in human FcgammaRI transgenic mouse models. The proto-oncogene HER-2/neu is overexpressed in approximately 30% of breast cancer patients, and represents a promising target for antibody-based immunotherapy. Fc gamma receptor I (CD64) is an effective trigger molecule, which is expressed on monocytes/macrophages, immature dendritic cells, and G-CSF-primed polymorphonuclear cells (PMN). Patients received G-CSF (Filgrastim) for 8 consecutive days, and cohorts of three patients were treated on day 4 with escalating, single doses of MDX-H210. A total of 30 patients were included, and treatment was generally well tolerated, without reaching dose-limiting toxicity. Side effects consisted mainly of fever and short periods of chills, which were timely related to elevated plasma levels of interleukin 6 and tumour necrosis factor alpha. In the last two cohorts, MDX-H210 plasma levels exceeded 1 microg ml(-1), and on circulating myeloid cells >50% saturation of FcgammaRI was found until day 4. These effector cells were highly effective in antibody-dependent cell-mediated cytotoxicity. Immunohistochemical analyses of tumour biopsies in individual patients documented infiltration of monocytes and PMN after MDX-H210 infusion. Although the clinical course of the disease was not altered by the single dose of MDX-H210, a favourable toxicity profile--even at high doses--and remarkable biological effects were seen when combined with G-CSF. Therefore, the combination of G-CSF and MDX-H210 should be evaluated in further immunotherapeutical strategies.     

Enhancement of polymorphonuclear cell-mediated tumor cell killing on simultaneous engagement of fcgammaRI (CD64) and fcalphaRI (CD89)

Antibodies can efficiently induce antitumor responses via recruitment of Fc receptor-bearing cytotoxic cells. Polymorphonuclear (PMN) cells represent attractive effector cells for antibody-directed immunotherapy. This, because activated PMN cells coexpress the class I receptors for IgG (FcgammaRI, CD64) and IgA (FcalphaRI, CD89), which are potent cytotoxic trigger molecules. Both receptors, however, require the FcR gamma chain for signaling. In this study, we show that FcgammaRI and FcalphaRI can trigger function independently of one another and do not cross-compete for the FcR gamma chain. FcalphaRI proved more efficient in initiating early signaling events and effector functions, such as redirected tumor cell killing and generation of superoxide. In addition, simultaneous engagement of FcgammaRI and FcalphaRI resulted in enhanced tumor cell lysis. These data support the development of concepts in which both FcgammaRI and FcalphaRI on PMN cells are targeted for tumor therapy.     

Mechanisms of action of CD20 antibodies

Therapeutic monoclonal antibodies (mAbs) that target the CD20 antigen on B cells are successfully used in the clinic for the depletion of B cells to treat various forms of cancer and autoimmune diseases. The first CD20 mAb, approved by the FDA in 1998, was rituximab (RTX) and since then it has been widely used to treat more than one million patients thus far. The success of RTX has led to a general interest in the mechanism of action of CD20 mAbs. CD20 mAbs can induce tumor killing via various mechanisms, such as direct induction of apoptosis, antibody-dependent cell-mediated cytotoxicity (ADCC) or complement-dependent lysis (CDC). Although we now understand these mechanisms better, it is still unclear which of these mechanisms is the most important for in vivo RTX action. Not every patient respond to RTX treatment and eventually the overwhelming majority will experience a relapse. Therefore, there is an urgent need to improve the efficacy of CD20 mAbs. This review aims to summarize our current understanding on the mechanism of action of CD20 mAbs.     

Expression of the ULBP ligands for NKG2D by B‐NHL cells plays an important role in determining their susceptibility to rituximab‐induced ADCC

Antibody‐dependent cellular cytotoxicity (ADCC) is a major antitumor mechanism of action of therapeutic monoclonal antibodies (mAbs). The aim of this study was to identify tumor‐associated factors which determine susceptibility to rituximab‐induced ADCC. Thirty different CD20+ non‐Hodgkin lymphoma cell lines were phenotyped for characteristics such as level of expression of NKG2D ligands, and the influence thereof on susceptibility to rituximab‐induced ADCC was established. The present study demonstrated that tumor cell susceptibility to rituximab‐induced ADCC was determined by 3 major tumor‐associated factors: (i) the amount of the target molecule, CD20; (ii) the amount of the ligands for inhibitory killer Ig‐like receptors, major histocompatibility complex class I; and (iii) the amounts of some of the NKG2D ligands, especially UL16‐binding protein (ULBP) 1–3. The importance of the ULBPs was confirmed using antibody blockade. In conclusion, this is the first report to show the importance for rituximab‐induced ADCC of ULBPs expressed on tumor cells. The ULBPs could be valuable diagnostic biological markers and significant targets for immunotherapy to improve efficacy not only of rituximab but also of other therapeutic mAbs. © 2009 UICC     

Different types of FCgamma-receptors are involved in anti-Lewis Y antibody induced effector functions in vitro

Stimulation of monocytes by interaction of monoclonal antibodies (mAbs) with Fc gamma receptors (FcgammaRs) results in the activation of various monocyte effector functions. In the present investigation we show that the anti-Lewis Y (LeY) anti-tumour mAb ABL 364 and its mouse/human IgG1 chimaera induce both antibody-dependent cellular cytotoxicity (ADCC) and the release of tumour necrosis factor alpha (TNF-alpha) during mixed culture of monocytes with LeY+ SKBR5 breast cancer cells in vitro. Although anti-LeY mAb-mediated TNF-alpha release paralleled ADCC activity, cytokine release required a higher concentration of sensitizing mAb than the induction of cytolysis. The determination of the FcgammaR classes involved in the induction of the distinct effector functions showed that anti-LeY mAb-induced cytolysis was triggered by interaction between anti-LeY mAbs and FcgammaRI. In contrast, mAb-induced TNF-alpha release mainly depended on the activation of monocyte FcgammaRII. Neutralization of TNF-alpha showed no influence on monocyte ADCC activity towards SKBR5 target cells. Our data indicate an independent regulation of anti-LeY mAb induced effector functions of ADCC and TNF-alpha release which seemed to be triggered by activation of different types of FcgammaR.     

CpG-A and B oligodeoxynucleotides enhance the efficacy of antibody therapy by activating different effector cell populations

Immunostimulatory CpG oligodeoxynucleotides (ODNs) can enhance the therapeutic effect of monoclonal antibodies (mAbs) by enhancing antibody-dependent cell-mediated cytotoxicity (ADCC). Distinct classes of CpG ODNs have been found recently to stimulate different effector cell populations. We used murine cancer models to explore the role of various effector cell populations in the antitumor activity seen with mAbs combined with CpG ODNs of the A and B classes. In the 38C13 syngeneic murine lymphoma model, both CpG A and CpG B enhanced the efficacy of murine antilymphoma mAb. Depletion of natural killer (NK) cells alone markedly decreased the efficacy of therapy with mAbs plus CpG A. In contrast, depletion of both NK cells and granulocytes was required to decrease the efficacy of mAb plus CpG B. A human (h) Fc gamma receptor I (FcgammaRI)-expressing transgenic (Tg) mouse model was used to explore the role of FcgammaRI in therapy with mAb and CpG ODN. CpG B induced up-regulation of FcgammaRI in hFcgammaRI Tg mice, whereas CpG A did not. In vitro CpG B also enhanced ADCC of HER-2/neu-expressing tumor cells by the FcgammaRI-directed bispecific antibody MDX-H210 using hFcgammaRI-positive effector cells. In a solid tumor model, tumor growth was inhibited in Tg mice treated with a combination of MDX-H210 and CpG B. These data suggest that CpG A enhance ADCC largely by activating NK cells. In contrast, other effector cell populations, including granulocytes, contribute to the antitumor activity of CpG B and mAbs. FcgammaRI plays an important role in this activity.     

Anti-GD3 monoclonal antibody effects on lymphocytes and antibody-dependent cellular cytotoxicity

PURPOSE: Antibodies targeting GD3 gangliosides highly expressed on melanomas mediate immune effector functions in vitro and inhibit animal model melanoma tumor growth in vivo. Because GD3 is expressed also on a subpopulation of human lymphocytes, we characterized the in vitro immune effects of murine R24 and a chimeric anti-GD3 antibody (KW-2871). DESIGN: Anti-GD3 complement-mediated (CMC) and antibody-dependent cellular cytotoxicity (ADCC) were tested against cell line Mel-624. Antibody-mediated lymphocyte expression of interleukin (IL)-2, IL-4, IL-10, and interferon-gamma (IFN-gamma) was quantified. The effect of antibody and antibody-treated lymphocyte supernates on effector cell ADCC and Fc receptor expression were evaluated. RESULTS: R24 and KW-2871 antibodies mediated CMC and ADCC to the Mel-624 cell line. R24 induced potent lymphocyte proliferation and enhanced lymphocyte RNA expression of IL-4 (2-4 logs), IL-10, and IFN-gamma (> 10-fold). KW-2871 induced no lymphocyte proliferation and had minimal effects on lymphokine expression (< 5-fold). Preincubation of effector cells with either antibody inhibited ADCC and reduced monocyte expression of FcgammaRI and II. Supernates of effector cells preincubated with either antibody were able to inhibit ADCC. CONCLUSIONS: R24 and KW-2871 antibody differ in their lymphocyte proliferation and lymphokine release activity but have similar inhibition of lymphocyte ADCC and FcgammaR expression in vitro.     

Immunomodulatory drug lenalidomide (CC-5013, IMiD3) augments anti-CD40 SGN-40-induced cytotoxicity in human multiple myeloma: clinical implications

SGN-40, a humanized immoglobulin G1 (IgG1) anti-CD40 monoclonal antibody, mediates cytotoxicity against human multiple myeloma (MM) cells via suppression of interleukin (IL)-6-induced proliferative and antiapoptotic effects as well as antibody-dependent cell-mediated cytotoxicity (ADCC). Here, we studied the clinical significance of an immunomodulatory drug lenalidomide on SGN-40-induced cytotoxicity against CD138(+)CD40(+) MM lines and patient MM cells. Pretreatment with lenalidomide sensitized MM cells to SGN-40-induced cell death. Combined lenalidomide and SGN-40 significantly induced MM apoptosis, evidenced by enhanced cleavage of caspase-3/8/poly(ADP-ribose)polymerase and increased sub-G(0) cells, compared with either single agent at the same doses. Pretreatment of effector cells with lenalidomide augmented SGN-40-induced MM cell lysis, associated with an increased number of CD56(+)CD3(-) natural killer (NK) cells expressing CD16 and LFA-1. Importantly, pretreatment with lenalidomide or lenalidomide and SGN-40 markedly enhanced NK-cell-mediated lysis of autologous patient MM cells triggered by SGN-40. Lenalidomide also up-regulated CD40L on CD56(+)CD3(-) NK cells, facilitating IL-2-mediated activation of NK cells. In addition, lenalidomide induced the CD56(dim) NK subset, which are more potent mediators of ADCC against target MM cells than the CD56(bright) NK subset. Finally, pretreatment of both effector and target MM cells with lenalidomide markedly enhanced SGN-40-mediated ADCC against CD40-expressing MM cells. These studies, therefore, show that the addition of lenalidomide to SGN-40 enhances cytotoxicity against MM cells, providing the framework for combined lenalidomide and SGN-40 in a new treatment paradigm to both target MM cells directly and induce immune effectors against MM.     

Recombinant antibodies against ganglioside expressed on tumor cells

Several gangliosides such as GM2, GD2, and GD3 have been thought of as target molecules for active or passive immunotherapy of human cancers because of their dominant expression on the tumor cell surface, especially in tumors of neuroectodermal origin. We established a number of mouse or rat monoclonal antibodies (mAbs) to a series of gangliosides to investigate the nature of the molecules on the cell surface. Some of those mAbs were converted to chimeric or humanized mAbs with the aim of developing immunotherapy for human cancer. It is desirable for mAbs to remain on the cell surface for a long time so that they can exert effector functions such as complement-dependent cytotoxicity (CDC) and antibody-dependent cellular cytotoxicity (ADCC). We found that mAbs to GM2, GD2, and GD3 remain on the cell surface for ₨ min after binding, while mAbs to other types of carbohydrate such as sialy Le^a are quickly internalized. A chimeric mAb to GD3, KM871, was generated by linking cDNA sequences encoding light- and heavy-chain variable regions of mouse mAb KM641 with cDNAs encoding the constant region of human immunoglobulin ų (IgG-1). KM871 bound to a variety of tumor cell lines, especially melanoma cells, including some cell lines to which R24 failed to bind. In a preclinical study, intravenous injection of KM871 markedly suppressed tumor growth and radio-labeled KM871 efficiently targeted the tumor site in a nude mouse model. This chimeric mAb is being evaluated in a phase I clinical trial in melanoma patients. The chimeric mAb KM966 and humanized mAb KM8969 to GM2 originated from a mouse IgM mAb. When human serum and human peripheral blood mononuclear cells were used as effectors in CDC and ADCC, respectively, KM966 and KM8969 killed GM2-expressing tumor cells effectively. In addition, these mAbs may induce apoptosis of a small cell lung cancer cell line cultured under conditions mimicking physiological tumor conditions.     

Enhanced cytotoxicity against colon carcinoma by combinations of noncompeting monoclonal antibodies to the 17-1A antigen

The purpose of this report was to investigate the binding specificities and ability to generate antibody dependent cell mediated cytotoxicity (ADCC) or antibody dependent complement mediated cytotoxicity of three novel monoclonal antibodies (mAbs), designated M74, M77, and M79, raised against the colorectal carcinoma antigen 17-1A. As determined by indirect radioimmunoassay, all three mAbs, as well as mAb 17-1A, bound to a similar extent to adherent cultures of the human colon carcinoma cell line, HT-29. Scatchard analysis of direct binding data for mAbs 17-1A, M74, M77, and M79 to HT-29 cells demonstrated equivalent association constants (7.54-9.77 X 10(7) liters/mol) and molecules bound per cell (2.15-2.69 X 10(5)). In contrast to mAbs M77 and M79, mAb M74 inhibited the binding of 125I-labeled mAb 17-1A to HT-29 cells. Similar to mAb 17-1A, incubation of human lymphocytes and blood monocytes with mAbs M74, M77, or M79 generated ADCC activity against HT-29 colon carcinoma cells. Various combinations of noncompeting mAbs to the 17-1A antigen (17-1A and M74; M77 and M79; M74 and either M77 or M79) but not competing mAbs (17-1A and M74; M77 and M79) resulted in a heightened level of ADCC activity. Under optimum conditions (saturation of antigenic sites with mAb), ADCC generated by the combination of noncompeting mAbs to the 17-1A antigen was additive to the activity seen with the respective mAbs alone. Under suboptimum conditions, the combination of noncompeting mAbs to the 17-1A antigen resulted in tumor cell cytotoxicity which was synergistic to the lysis obtained with the respective mAbs alone. No mAb used alone was able to generate antibody dependent complement mediated cytotoxicity against a panel of 17-1A positive colon carcinoma cells. Similarly, no antibody dependent complement mediated cytotoxicity activity was obtained with the combination of competing mAbs to the 17-1A antigen. However, HT-29 cells treated with noncompeting mAbs to the 17-1A antigen antigen were rendered susceptible to lysis by human complement. We conclude that the combination of mAbs recognizing different epitopes on the same tumor antigen could have important implications for the passive immunotherapy of cancer.     

Active specific immunotherapy of renal cell carcinoma: cellular and humoral immune responses

We investigated the effect of vaccinating renal cell carcinoma (RCC) patients with irradiated autologous or allogeneic tumor cells and Newcastle disease virus (NDV) as adjuvant on cellular and humoral antitumor immunity. By Western blot analysis, we found that vaccination induced antibody formation in 33 of 34 patients against NDV proteins but not against tumor cell related antigens. NDV proteins detected had molecular weights of 53 kDa, 55-56 kDa, and 66 kDa. ADCC by patients' isolated PBMC and patients' sera against autologous or allogeneic tumor cells was not enhanced after vaccine treatment in a nonradioactive cytotoxicity assay. Target cells infected with NDV were lysed more effectively (p < 0.05) in ADCC after vaccination than noninfected targets. Natural cellular cytotoxicity of patients' isolated PBMC was not altered during vaccine treatment. Specific lysis rates against autologous and allogeneic RCC cells not exceeded 10% (effector:target ratio 50:1). Specific lysis of K-562 cells was > 20%; a slight decrease in lysis during vaccination was not significant. Numbers of lymphocyte subsets from patients' peripheral blood analyzed by FACS revealed significant expression of CD20+ (p < 0.02) and CD39+ (p < 0.03) cell numbers by vaccine therapy. Cytokine detection in patients' sera by ELISA showed significant increases (p < 0.05) for IFN-gamma and TNF-alpha but not for IFN-alpha four h post vaccination. Thus, immunomodulation with autologous or allogeneic RCC tumor cell vaccines is mainly due to cytokine induction, whereas tumor specific humoral or cellular responses are not detectable in patients' peripheral blood.     

Novel humanized anti-CD20 monoclonal antibodies with unique germline VH and VL gene recruitment and potent effector functions

The anti-CD20 chimeric monoclonal antibody (mAb) rituximab is the most widely used therapeutic antibody for B-cell malignancies. However, approximately 50% of non-Hodgkin's lymphoma (B-NHL) patients respond to treatment with this antibody. Novel humanized antibodies target membrane CD20 with enhanced effector properties should improve treatment for a broader patient population with relapsed and refractory disease. A novel chimerized form of the murine anti-CD20 1K1791 exerts more potent antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) activities and induces cell death by a non-caspase dependent process. Humanized mAbs derived from 1K1791 were designed using four different humanization techniques and characterized. In contrast to rituximab or 2F2 (human anti-CD20 mAb), several of these exhibited superior ADCC, CDC, inhibition of cell growth and cell death. There was a wide range of functional differences among the humanized forms of 1K1791 despite a modest replacement of amino acid residues in the CDRs. To determine whether the superior activities exhibited by parental murine mAb 1K1791 were due to differences in VH and VL rearrangement, we analyzed its germline and compared it to other anti-CD20 mAbs. A remarkable conservation of VH and Vk (VL kappa) gene usage was observed in the murine anti-CD20 mAbs. 18/23 used the same germline gene J558.42 and 4/23 used closely related genes of the 'J558' group. Thus, 22/23 belonged to VH1 family. One exception was the mAb 1K1791, which was derived from the VH9.12 germline gene. 1K1791 was also unique in its use of a Vk19/28 family gene whereas most other mAbs (21/23) used Vk4/5 family genes. A formal relationship between the particular germline gene recruitment and antibody functionality has not been established, however, the present findings identified humanized mAbs with functional activities that were superior to rituximab and 2F2. These in vitro results support future in vivo animal testing and subsequent clinical trials.     

HLA class II antibodies in the treatment of hematologic malignancies

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

Enhanced natural killer cell binding and activation by low-fucose IgG1 antibody results in potent antibody-dependent cellular cytotoxicity induction at lower antigen density.

PURPOSE: Recent studies have revealed that fucose removal from the oligosaccharides of human IgG1 antibodies results in a significant enhancement of antibody-dependent cellular cytotoxicity (ADCC) via improved IgG1 binding to FcgammaRIIIa. In this report, we investigated the relationship between enhanced ADCC and antigen density on target cells using IgG1 antibodies with reduced fucose. EXPERIMENTAL DESIGN: Using EL4 cell-derived transfectants with differential expression levels of exogenous human CC chemokine receptor 4 or human CD20 as target cells, ADCC of fucose variants of chimeric IgG1 antibodies specific for these antigens were measured. We further investigated IgG1 binding to natural killer (NK) cells and NK cell activation during ADCC induction to elucidate the mechanism by which low-fucose IgG1 induces ADCC upon target cells with low antigen expression. RESULTS: Low-fucose IgG1s showed potent ADCC at low antigen densities at which their corresponding high-fucose counterparts could not induce measurable ADCC. The quantitative analysis revealed that fucose depletion could reduce the antigen amount on target cells required for constant degrees of ADCC induction by 10-fold for CC chemokine receptor 4 and 3-fold for CD20. IgG1 binding to NK cells was increased by ligating IgG1 with clustered antigen, especially for low-fucose IgG1. Up-regulation of an activation marker, CD69, on NK cells, particularly the CD56(dim) subset, in the presence of both the antibody and target cells was much greater for the low-fucose antibodies. CONCLUSIONS: Our data showed that fucose removal from IgG1 could reduce the antigen amount required for ADCC induction via efficient recruitment and activation of NK cells.