HLA class II antibodies in the treatment of hematologic malignancies

The small molecule antibody mimic SH7139 targets a family of HLA-DRs expressed by B-cell lymphomas and other solid cancers

Selective high-affinity ligands (SHALs) belong to a novel class of small-molecule cancer therapeutics that function as targeted prodrugs. SH7139, the most advanced of the SHAL drugs designed to bind to a unique β-subunit structural epitope located on HLA-DR10, has exhibited exceptional preclinical efficacy and safety profiles. A comparison of SH7139 and SH7129, a biotin derivative of the drug developed for use as a diagnostic, showed the incorporation of a biotin tag did not alter the SHALs ability to target or kill HLA-DR10 expressing Raji cells. The use of SH7129 in an immuno-histochemical type assay to stain peripheral blood mononuclear cells (PBMCs) obtained from individuals expressing specific HLA-DRB1 alleles has also revealed that in addition to HLA-DR10, seven other more commonly expressed HLA-DRs are targeted by the drug. Computational dockings of the SHAL's recognition ligands to a number of HLA-DR structures explain, in part, why the targeting domains of SH7129 and SH7139 bind to some HLA-DRs but not others. The results also substantiate the selectivity of SH7129 and suggest it may prove useful as a companion diagnostic for pre-screening biopsy samples to identify those patients whose tumours should respond to SH7139 therapy.

IMMU-140, a Novel SN-38 Antibody-Drug Conjugate Targeting HLA-DR, Mediates Dual Cytotoxic Effects in Hematologic Cancers and Malignant Melanoma

HLA-DR is a member of the MHC class II antigen family expressed on hematologic and solid tumors. Antibodies directed against HLA-DR have demonstrated some clinical success, but toxicities limited development. IMMU-140 is an anti-HLA-DR antibody-drug conjugate composed of the active metabolite of irinotecan, SN-38, conjugated to a humanized anti-HLA-DR IgG₄ antibody (IMMU-114); the IgG₄ naked antibody is devoid of immune functions. Our aim was to determine if SN-38, the metabolite of a drug not commonly used in hematopoietic cancers, would be effective and safe when targeted to HLA-DR-expressing tumors. IMMU-140 had dual-therapeutic mechanisms, as evidenced by its retention of nonoverlapping anti-HLA-DR nonclassical apoptotic signaling and classical apoptosis mediated by its SN-38 payload. In seven human disease models [acute lymphocytic leukemia (ALL), chronic lymphocytic leukemia (CLL), multiple myeloma (MM), acute myeloid leukemia (AML), diffuse large B-cell lymphoma (DLBCL), Hodgkin lymphoma (HL), and melanoma], IMMU-140 provided significant therapeutic efficacy compared with controls, in vitro, in 3D spheroid models, and in vivo Except for MM and HL, IMMU-140 imparted significantly improved antitumor effects compared with parental IMMU-114. Even in intractable AML and ALL, where IMMU-114 only had modest antitumor effects, IMMU-140 therapy mediated >80% improvement in survival. Therapy was well tolerated, as demonstrated by no marked loss in body weight. Combined with doxorubicin, IMMU-140 produced significantly greater antitumor effects in HL than with monotherapy and without any added toxicity. The dual-therapeutic action of IMMU-140 resulted in promising therapeutic activity in a range of hematopoietic tumors and melanoma, and therefore warrants clinical development. Mol Cancer Ther; 17(1); 150-60. ©2017 AACR.

Structurally Defined αMHC-II Nanobody-Drug Conjugates: A Therapeutic and Imaging System for B-Cell Lymphoma

Antibody-drug conjugates (ADCs) of defined structure hold great promise for cancer therapies, but further advances are constrained by the complex structures of full-sized antibodies. Camelid-derived single-domain antibody fragments (VHHs or nanobodies) offer a possible solution to this challenge by providing expedited target screening and validation through switching between imaging and therapeutic activities. We used a nanobody (VHH7) specific for murine MHC-II and rendered "sortase-ready" for the introduction of oligoglycine-modified cytotoxic payloads or NIR fluorophores. The VHH7 conjugates outcompeted commercial monoclonal antibodies (mAbs) for internalization and exhibited high specificity and cytotoxicity against A20 murine B-cell lymphoma. Non-invasive NIR imaging with a VHH7-fluorophore conjugate showed rapid tumor targeting on both localized and metastatic lymphoma models. Subsequent treatment with the nanobody-drug conjugate efficiently controlled tumor growth and metastasis without obvious systemic toxicity.

Targeted Radionuclide Therapy of Human Tumors

Targeted radionuclide therapy is one of the most intensively developing directions of nuclear medicine. Unlike conventional external beam therapy, the targeted radionuclide therapy causes less collateral damage to normal tissues and allows targeted drug delivery to a clinically diagnosed neoplastic malformations, as well as metastasized cells and cellular clusters, thus providing systemic therapy of cancer. The methods of targeted radionuclide therapy are based on the use of molecular carriers of radionuclides with high affinity to antigens on the surface of tumor cells. The potential of targeted radionuclide therapy has markedly grown nowadays due to the expanded knowledge base in cancer biology, bioengineering, and radiochemistry. In this review, progress in the radionuclide therapy of hematological malignancies and approaches for treatment of solid tumors is addressed.

Combating non-Hodgkin lymphoma by targeting both CD20 and HLA-DR through CD20-243 CrossMab

Although rituximab has revolutionized the treatment of hematological malignancies, the acquired resistance is one of the prime obstacles for cancer treatment, and development of novel CD20-targeting antibodies with potent anti-tumor activities and specificities is urgently needed. Emerging evidence has indicated that lysosomes can be considered as an "Achilles heel" for cancer cells, and might serve as an effective way to kill resistant cancer cells. HLA-DR antibody L243 has been recently reported to elicit potent lysosome-mediated cell death in lymphoma and leukemia cells, suggesting that HLA-DR could be used as a potential target against lymphoma. In this study, we generated a bispecific immunoglobulin G-like antibody targeting both CD20 and HLA-DR (CD20-243 CrossMab) through CrossMab technology. We found that the CrossMab could induce remarkably high levels of complement-dependent cytotoxicity, antibody-dependent cell-mediated cytotoxicity and anti-proliferative activity. Notably, although HLA-DR is expressed on normal and malignant cells, the CrossMab exhibited highly anti-tumor specificity, showing efficient eradication of hematological malignancies both in vitro and in vivo. Our data indicated that combined targeting of CD20 and HLA-DR could be an effective approach against malignancies, suggesting that CD20-243 CrossMab would be a promising therapeutic agent against lymphoma.

Antitumour effects of single or combined monoclonal antibodies directed against membrane antigens expressed by human B cells leukaemia

Background

The increasing availability of different monoclonal antibodies (mAbs) opens the way to more specific biologic therapy of cancer patients. However, despite the significant success of therapy in breast and ovarian carcinomas with anti-HER2 mAbs as well as in non-Hodkin B cell lymphomas with anti-CD20 mAbs, certain B cell malignancies such as B chronic lymphocytic leukaemia (B-CLL) respond poorly to anti-CD20 mAb, due to the low surface expression of this molecule. Thus, new mAbs adapted to each types of tumour will help to develop personalised mAb treatment. To this aim, we analyse the biological and therapeutic properties of three mAbs directed against the CD5, CD71 or HLA-DR molecules highly expressed on B-CLL cells.

Results

The three mAbs, after purification and radiolabelling demonstrated high and specific binding capacity to various human leukaemia target cells. Further in vitro analysis showed that mAb anti-CD5 induced neither growth inhibition nor apoptosis, mAb anti-CD71 induced proliferation inhibition with no early sign of cell death and mAb anti-HLA-DR induced specific cell aggregation, but without evidence of apoptosis. All three mAbs induced various degrees of ADCC by NK cells, as well as phagocytosis by macrophages. Only the anti-HLA-DR mAb induced complement mediated lysis. Coincubation of different pairs of mAbs did not significantly modify the in vitro results. In contrast with these discrete and heterogeneous in vitro effects, in vivo the three mAbs demonstrated marked anti-tumour efficacy and prolongation of mice survival in two models of SCID mice, grafted either intraperitoneally or intravenously with the CD5 transfected JOK1-5.3 cells. This cell line was derived from a human hairy cell leukaemia, a type of malignancy known to have very similar biological properties as the B-CLL, whose cells constitutively express CD5. Interestingly, the combined injection of anti-CD5 with anti-HLA-DR or with anti-CD71 led to longer mouse survival, as compared to single mAb injection, up to complete inhibition of tumour growth in 100% mice treated with both anti-HLA-DR and anti-CD5.

Conclusions

Altogether these data suggest that the combined use of two mAbs, such as anti-HLA-DR and anti-CD5, may significantly enhance their therapeutic potential.

In vitro affinity maturation of HuCAL antibodies: complementarity determining region exchange and RapMAT technology

Monoclonal antibodies gain ever-increasing importance in the treatment of human diseases across a broad range of indications. Diverse technologies currently exist, which are used to generate recombinant therapeutic antibodies that are basically indistinguishable from naturally occurring human immunoglobulins. We describe how human combinatorial antibody libraries are used together with unique optimization techniques to produce such therapeutically relevant proteins, for instance in the areas of oncology and inflammation.

Evaluation of anti-human leukocyte antigen-DR monoclonal antibody therapy in spontaneous canine lymphoma

A pilot study of anti-human leukocyte antigen (HLA)-DR monoclonal antibody (mAb) in dogs with lymphoma was undertaken to verify the suitability of a canine model to address therapeutically relevant endpoints prior to a full trial in dogs, and ultimately human investigation. In vitro studies demonstrated that L243, a murine IgG1 anti-HLA-DR, binds to normal and malignant canine lymphocytes and induces apoptosis in canine lymphoma cells. Moreover, L243 was administered safely to normal dogs and dogs with lymphoma, and bound to malignant cells in nodal tissue. Preliminary evidence of transient disease stabilization was observed in a subset of dogs with advanced-stage lymphoma following L243 immunotherapy. hL243γ4P (IMMU-114), a humanized IgG4 anti-HLA-DR, currently under evaluation preclinically for human trials, was also shown to bind malignant canine lymphocytes, and safety and pharmacokinetic data from the administration of IMMU-114 to normal dogs indicate similar behavior to L243 in these assessments. These findings provide a rationale for the use of dogs with lymphoma in safety and efficacy evaluations of anti-HLA-DR mAbs for both veterinary and human applications.

A recombinant bispecific single-chain fragment variable specific for HLA class II and Fc alpha RI (CD89) recruits polymorphonuclear neutrophils for efficient lysis of malignant B lymphoid cells

Bispecific Abs offer new perspectives for cancer immunotherapy. In this study, we describe a recombinant bispecific single-chain fragment variable (bsscFv) directed against Fc alpha RI (CD89) on polymorphonuclear neutrophils (PMNs) or monocytes/macrophages and HLA class II on lymphoma target cells. Fc alpha RI and HLA class II-directed single-chain fragment variable (scFv) fragments were isolated from phage display libraries, established from the hybridomas A77 and F3.3, respectively. The two scFv molecules were connected with a 20 aa flexible linker sequence. After expression in SF21 insect cells and chromatographic purification, the bispecific molecule showed specific binding to both Ags at K(D) values of 148 +/- 42 nM and 113 +/- 25 nM for the anti-Fc alpha RI and anti-HLA class II scFv components in the bsscFv, respectively. In Ab-dependent cytotoxicity assays with PMNs as effectors and a series of lymphoma-derived cell lines (ARH-77, RAJI, REH, NALM-6, RS4;11), the bsscFv was significantly more cytotoxic than the parental murine IgG1 and its chimeric IgG1 derivative. When targeting primary tumor cell isolates from six patients with B cell malignancies, the killing capacity of the (Fc alphaRI x HLA class II) bsscFv compared favorably to conventional HLA class II mAb. Importantly, the cell lines NALM-6 and RS411, as well as two primary tumor cell isolates, were exclusively lysed by the bsscFv. To our knowledge, this is the first report of an Fc alpha RI-directed bsscFv effectively recruiting PMNs for redirected cytotoxicity against human B cell malignancies. Our data show that an (Fc alpha RI x HLA class II) bsscFv is an interesting candidate for further engineering of small, modular immunopharmaceuticals.

A humanized HLA-DR antibody (hu1D10, apolizumab) in combination with granulocyte colony-stimulating factor (filgrastim) for the treatment of non-Hodgkin's lymphoma: A pilot study

Apolizumab is a humanized monoclonal antibody against a polymorphic epitope on HLA DRbeta that demonstrated evidence for therapeutic activity in follicular lymphoma patients. In pre-clinical studies, we previously reported that granulocyte colony-stimulating factor (G-CSF) treatment significantly enhanced lymphoma cell killing by HLA class II antibodies, including apolizumab. These results suggested a combination trial of apolizumab and G-CSF (filgrastim). In this trial, we treated six patients with relapsed or refractory 1D10-positive non-Hodgkin's lymphoma with filgrastim and variable doses of apolizumab ranging from 0.15 to 1.5 mg/m2. The combination was clinically well tolerated, with only two patients experiencing grade III/IV hematological toxicity (thrombocytopenia and autoimmune hemolytic anemia). Another patient developed a pruritic skin rash, which was probably a treatment-related grade II skin toxicity. Interestingly, two patients with follicular lymphoma who received intensified apolizumab treatment on a three times weekly schedule experienced prolonged stabilization of their disease for 12 and more than 36 months. In conclusion, this small pilot study suggests that a combination of HLA class II antibodies and G-CSF is clinically feasible.

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

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

Fully human antibody exhibits pan-human leukocyte antigen-DR recognition and high in vitro/vivo efficacy against human leukocyte antigen-DR-positive lymphomas

HD8, a fully human monoclonal antibody specific for human leukocyte antigen-DR (HLA-DR), was generated by using the transchromosome mouse that bears the human immunoglobulin genes. HD8 could bind to all 13 tested HLA-DR-positive cell lines and 35 B-cells from healthy donors. Epitope mapping revealed that while the antibody recognizes the most polymorphic region of the HLA-DRB chain, its critical epitope residues are conserved in the major alleles. Indeed, HD8 could recognize 99.2% of HLA-DRB alleles. Since its essential epitope residues are also largely conserved in HLA-DP and HLA-DQ, HD8 could recognize 100% and 66% of the HLA-DP and HLA-DQ alleles tested, respectively. HD8 exerted strong antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity in vitro, and significantly extended the life span of immunocompromised mice inoculated with non-Hodgkin lymphoma cell lines. The HD8 antibody may be highly useful in HLA-DR-targeted immunotherapy as it is likely to evoke similarly strong responses in individuals carrying different HLA-DR alleles.

Comparative biodistributions of pretargeted radioimmunoconjugates targeting CD20, CD22, and DR molecules on human B-cell lymphomas

Pretargeted radioimmunotherapy (PRIT) using streptavidin (SA)-conjugated antibodies (Abs), followed by clearing agent and radiolabeled biotin is a promising method that can increase the effectiveness of RIT, while decreasing the toxicities associated with directly labeled Abs. Although CD20 has been the traditional target antigen for RIT of non-Hodgkin lymphoma (NHL), studies targeting HLA DR and CD22 have yielded promising results. Targeting all 3 antigens at once may further augment the effect of PRIT. This study compares the targeting of Ramos, Raji, and FL-18 lymphoma xenografts with either anti-CD20 Ab/SA (1F5/SA), anti-HLA DR Ab/SA (Lym-1/SA), anti-CD22 Ab/SA (HD39/SA), or all 3 conjugates in combination, followed 24 hours later by a biotin-N-acetyl-galactosamine clearing agent, and 3 hours after that by (111)In-DOTA-biotin. The Ab/SA conjugate yielding the best tumor uptake and tumor-to-normal organ ratios of radioactivity varied depending on the target antigen expression on the cell line used, with 1F5/SA and Lym-1/SA yielding the most promising results overall. Also, the best tumor-to-normal organ ratios of absorbed radioactivity were obtained using single conjugates optimized for target tumor antigen expression rather than the combination therapy. This study highlights the importance of screening the antigenic expression on lymphomas to select the optimal reagent for PRIT.

Emerging drugs for chronic lymphocytic leukaemia

Although the philosophy of management of patients with chronic lymphocytic leukaemia (CLL) has been altered with the advent of fludarabine-based therapies, impact on long-term survival is unclear and a significant proportion of patients will develop resistance to fludarabine. Similar to other haematological malignancies, a potential for 'cure' is likely to be achieved only if 'high-quality' complete remissions (CRs) are achieved. Treatment options for patients who develop resistance to fludarabine continue to be limited, with only a proportion obtaining a response (usually not CRs) with salvage therapies. This review summarises novel therapies that are being evaluated in patients with CLL, specifically those targeting the antiapoptotic Bcl-2 family of proteins and receptors (e.g., CD40, CD80, HLA-DR) involved in mediating survival signals from the microenvironment.

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

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

Regulation of MHC class II gene expression by the class II transactivator

MHC class II molecules are pivotal for the adaptive immune system, because they guide the development and activation of CD4+ T helper cells. Fulfilling these functions requires that the genes encoding MHC class II molecules are transcribed according to a strict cell-type-specific and quantitatively modulated pattern. This complex gene-expression profile is controlled almost exclusively by a single master regulatory factor, which is known as the class II transactivator. As we discuss here, differential activation of the three independent promoters that drive expression of the gene encoding the class II transactivator ultimately determines the exquisitely regulated pattern of MHC class II gene expression.

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

AIM

Anti-HLA-DR and anti-CD20 monoclonal antibodies (MAbs) have been effective for immunotherapy and radioimmunotherapy in non-Hodgkin's lymphoma (NHL). The aim of our study was to compare the antilymphoma effects of Lym-1 and rituximab in human lymphoma cell lines, using assays of viability, apoptosis, antibody-dependent cellular cytotoxicity (ADCC), and complement-dependent cytotoxicity (CDC), under conditions relevant to the clinic.

METHODS

To characterize response relationships at varied concentrations of Lym-1 and rituximab, growth inhibition and cell death were assayed over 96 hours in four NHL cell lines derived from Burkitt's or large-cell lymphoma patients. Untreated cells and cells treated with an mLym-1 isotype-matched MAb were used as negative controls for direct assays. Western blot was used to detect apoptosis through the activation of caspase-3 and cleavage of poly (ADP-ribase) polymerase (PARP). The indirect cytotoxicity of Lym-1 and rituximab was assayed at varied concentrations, using ADCC activity in the presence of purified peripheral blood leukocytes and CDC activity in the presence of human donor serum.

RESULTS

Lym-1 and rituximab showed significant direct and indirect antilymphoma effects. Lym-1 had a substantial, and statistically greater, effect than rituximab over longer intervals of time. In Raji and B35M cells, Lym-1 induced potent growth inhibition reflected by 90% and 94% reductions in viable cells, respectively, whereas rituximab induced 63% and 56% reductions. Concurrently, Lym-1 increased nonviable cells by 372% and 153% in these cells, respectively, whereas rituximab induced 139% and 43% increases. Lym-1-induced apoptosis was greater than that of rituximab in all cell lines tested. Lym-1, both the chimeric form and the mouse parent, mediate ADCC more effectively, in the presence of a total peripheral blood leukocyte (PBL) population, than does rituximab, although the results for CDC activity were mixed.

CONCLUSIONS

In conclusion, Lym-1 had more potent direct and indirect cytotoxic effects than rituximab in lymphoma cells under conditions achievable in patients. Because the HLA-DR target antigen of Lym-1 is enriched on most B-cell lymphomas, these results support its complementary use in patients as an alternative to CD20 for monoimmunotherapy and for combination immunotherapy with rituximab, because the HLA-DR and CD20 antigens are physically and functionally coupled on human B cells.

Antiproliferative activity of a humanized anti-CD74 monoclonal antibody, hLL1, on B-cell malignancies

The humanized anti-CD74 monoclonal antibody (mAb) hLL1 is under evaluation as a therapeutic agent. The effects of hLL1-at times in comparison with the CD20 mAb rituximab-were assessed on non-Hodgkin lymphoma (NHL) and multiple myeloma (MM) cell lines and in tumor-bearing SCID mice. In vitro, hLL1 caused growth inhibition and induction of apoptosis in B-cell lines when cross-linked with an antihuman immunoglobulin G (IgG) second antibody. The sensitivity profile of the cell lines was different for hLL1 and rituximab, and antiproliferative activity was augmented when the 2 mAbs were combined. Unlike rituximab, hLL1 did not induce antibody-dependent cellular cytotoxicity or complement-mediated cytotoxicity. In xenograft models of NHL and MM, treatment with hLL1 yielded significant survival benefits without cross-linking agents. Efficacy was greater in the MM model, in which median survival time was increased more than 4.5-fold. Thus, hLL1 has therapeutic potential as a naked mAb for B-cell malignancies because of high antigen expression on malignant cells, specifically MM, with limited expression on normal tissue, and because of its antiproliferative activity. Further, hLL1 may be a therapeutic candidate for rituximab-resistant disease because the 2 antibodies apparently act through distinct mechanisms and exhibit different expression and sensitivity profiles, and activity can be augmented when the mAbs are combined.

A recombinant bispecific single-chain Fv antibody against HLA class II and FcgammaRIII (CD16) triggers effective lysis of lymphoma cells

Bispecific antibodies offer the possibility of improving effector-cell recruitment for antibody therapy. For this purpose, a recombinant bispecific single-chain Fv antibody (bsscFv), directed against FcgammaRIII (CD16) and human leucocyte antigen (HLA) class II, was constructed and tested in functional assays. RNA from the hybridomas 3G8 and F3.3, reacting with CD16 and HLA class II, respectively, was used to generate phage display libraries. From these libraries, reactive phages were isolated and the bsscFv was constructed by connecting both single-chain Fv components through a 20 amino acid flexible linker. After expression in SF21 insect cells and chromatographic purification, the bsscFv bound specifically and simultaneously to both antigens. The affinities of the anti-CD16 and the anti-HLA class II scFv components of the bsscFv were 8.6 x 10(-8) mol/l and 13.7 x 10(-8) mol/l, respectively, which was approximately sevenfold lower than the F(ab) fragments of the parental antibodies. In antibody-dependent cellular cytotoxicity experiments with human mononuclear cells as effectors, the bsscFv-mediated specific lysis of both HLA class II-positive, malignant human B-lymphoid cell lines and primary cells from patients with chronic B-cell lymphocytic leukaemia. Optimal lysis was obtained at bsscFv concentrations of approximately 400 ng/ml, similar to the concentration required for maximum lysis by the corresponding chemically linked bispecific antibody. Thus, this recombinant bsscFv-antibody is an efficient molecule for effector-cell mediated lysis of malignant human B-lymphoid cells.

Defective class II transactivator expression in a B lymphoma cell line

Loss of MHC class II expression in B-cell lymphoma has been associated with a higher tumorigenicity resulting from lower titers of tumor-infiltrating lymphocytes. This report aims towards the identification of the molecular mechanism leading to defective MHC class II expression in a B-cell lymphoma cell line, Rec-1. We evidenced a coordinated alteration of HLA-D gene transcription, reminiscent of B lymphoblastoid cell lines from patients with MHC class II deficiency. Genetic complementation performed between these cell lines and the lymphoma cells indicated that Rec-1 is altered in the MHC2TA gene. MHC2TA encodes the class II transactivator (CIITA), the master regulator of HLA-D gene expression. However, the coding sequence of the Rec-1 CIITA transcript did not reveal any mutation that could hamper the activity of the encoded protein. In agreement with the genetic complementation analysis, we evidenced a highly residual CIITA protein expression in the Rec-1 cell line resulting from a transcriptional defect affecting MHC2TA expression. Anti-HLA-DR monoclonal antibody treatment has proved efficient in the destruction of B lymphoma cells. Our data indicate that the appearance of variants losing CIITA, and thereby HLA-DR, expression will require a thorough monitoring during such immunotherapy protocols.

Antibody-induced intracellular signaling works in combination with radiation to eradicate lymphoma in radioimmunotherapy

Radioimmunotherapy (RIT) has emerged as an effective treatment for lymphoma, however the underlying mechanisms are poorly understood. We therefore investigated the relative contributions of antibody and targeted radiation to the clearance of tumor in vivo, using 2 different syngeneic murine B-cell lymphoma models. Although RIT with 131I–anti–major histocompatibility complex class II (MHCII) was effective in targeting radiation to tumor, no improvement in survival was seen by escalating the radiation dose alone and there were no long-term survivors. In contrast, using the combination of 131I anti-MHCII in the presence of unlabeled anti-idiotype (anti-Id), 100% prolonged disease-free survival was seen in both B-cell lymphoma models at the higher radiation dose. Using in vivo tracking we show that treatment with radiation plus anti-Id monoclonal antibody (mAb) results in a substantially greater reduction of splenic tumor cells than with either treatment alone. Prolonged survival could also be achieved using 131I anti-MHCII plus the signaling anti-CD19 mAb. Furthermore, the ability of these anti–B-cell mAbs to improve survival with targeted radiotherapy appeared to correlate with their ability to initiate intracellular signal transduction. Together these data illustrate that using 1 mAb to target radiation to tumor and a second to induce cell signaling is an effective new strategy in RIT.