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Monoclonal antibodies coupled to drugs and toxic agents (immunotoxins) or radionuclides (radioimmunoconjugates) represent new tools for immunotherapy of haematological malignancies. Immunotoxins constructed with toxins of either plant or bacterial origin have shown a powerful antitumor activity both in vitro and in mice with severe combined immunodeficiency bearing various kinds of leukaemias and lymphomas. Preliminary clinical trials have shown an activity of these compounds at least in a proportion of patients. However, tumour responses have generally been partial and transient. The main problems with immunotoxin therapy remain the inability of immunotoxins to target tumour cells in the presence of a high burden of disease, the host immune response against both the antibody and the toxin moieties, which precludes repeated administration of immunotoxins, and the vascular leak syndrome. Targeting of tumour cells with specific antibodies armed with radionuclides (usually iodine-131 or yttrium-90) appears to be an even more attractive approach. Preliminary clinical studies have clearly demonstrated the ability of radioimmunoconjugates, especially when administered at high dose followed by bone marrow rescue, to induce durable complete remission in patients with non-Hodgkin's lymphomas refractory to conventional therapies. Radioimmunotherapy also overcomes the antigenic heterogeneity of the tumour cell population, since antigen negative tumour cells will be irradiated by the nearby targeted antigen-positive cells. Efforts should now be focused on defining more precisely the optimal clinical setting for administration of immunotoxin and radioimmunoconjugates (e.g. minimal residual disease), to reduce the immunogenicity of these compounds and solve the problem of vascular leak syndrome.

The human BCL-6 gene, which is rearranged in approximately 30% of diffuse large B cell lymphomas, encodes a 706-amino-acid nuclear protein of the Kruppel-type zinc finger transcription factors mainly expressed in normal germinal center B cells and related lymphomas. Four monoclonal antibodies (PG-B6, PG-B6a, PG-B6p, and PG-B6m), specifically directed against the human BCL-6 protein, were generated by immunizing BALB/c mice with a recombinant protein corresponding to the BCL-6 amino-terminal region (amino acids 3 to 484). The PG-B6 monoclonal antibody reacted with a BCL-6 epitope sensitive to fixatives and preserved in all mammalian species. PG-B6a (a is for avian) recognized the most evolutionarily conserved BCL-6 epitope (expressed in all animal species including avian). PG-B6p (p is for paraffin) recognized a fixative-resistant epitope of BCL-6 that was detectable on paraffin sections after microwave heating in 1 mmol/L EDTA buffer. PG-B6m (m is for mantle) was the least specific monoclonal antibody as, in addition to BCL-6, it reacted with a yet undefined antigen selectively located in the cytoplasm of mantle and marginal zone B cells. All monoclonal antibodies detected strong nuclear expression of BCL-6 in follicular lymphomas, diffuse large B cell lymphomas, Burkitt's lymphomas, and nodular, lymphocyte-predominance Hodgkin's disease. In diffuse large B cell lymphomas, BCL-6 expression was independent of BCL-6 gene rearrangements and did not correlate with expression of other markers or the proliferation index. BCL-6 was not expressed in B-CLL, hairy cell leukemia, mantle-cell- and marginal-zone-derived lymphomas. Labeling of paraffin sections with PG-B6p proved useful for differentiating proliferation centers in B-CLL (BCl-2+/BCL-6-) from trapped germinal centers in mantle cell lymphomas (BCL-2-/BCL-6+) and for identifying neoplastic cells in cases of nodular, lymphocyte-predominance Hodgkin's disease. Because of their high specificity, wide reactivity in humans and animal species including avians (PG-B6a), and suitability for labeling routine paraffin sections (PG-B6p), the reagents described in this paper should prove valuable in both research and diagnostics.

The anti-CD30 immunotoxin (IT) Ber-H2/saporin is effective in patients with refractory Hodgkin's disease. However, responses are short and partial, one of the main reasons being the inability to repeat IT doses because of formation of human antibodies against the murine antibody and/or the toxin. To overcome this problem, we constructed two new anti-CD30 ITs by covalently linking the mouse monoclonal antibody Ber-H2 to the type 1 ribosome-inactivating proteins (RIPs) momordin (MOM) and pokeweed antiviral protein from seeds (PAP-S), which do not cross-react with each other or with saporin. Both ITs inhibited protein synthesis by Hodgkin's disease and anaplastic large-cell lymphoma (ALCL)-derived CD30+ target cell lines with a very high efficiency (IC50 ranging from5 x 10(-13) M to 2.75 x 10(-11) M, as RIP). In a SCID mouse model of xenografted CD30+ human ALCL, a 3d treatment with non-toxin doses of Ber-H2/MOM (50%LD50), started 24 h after transplantation, prevented tumour development in about 40% of the animals and significantly delayed tumour growth rate in the others. Main toxicity signs in mice and rabbits were dose-related increase of serum transaminases (AST and ALT) and creatine phosphokinase (CPK). LD50 (as RIP) in Swiss mice was 7 mg/kg for Ber-H2/MOM and 0.45 mg/kg for Ber-H2/PAP-S. Sequential administration of two anti-CD30 ITs (Ber-H2/MOM and Ber-H2/saporin) was well tolerated and did not result in formation of antibodies cross-reacting and with the two plant toxins. The results presented in this paper suggest that in the future, sequential administration of anti-CD30 humanized antibodies linked to antigenically distinct type 1 RIPs (saporin, MOM, PAP-S) should be feasible.

The BCL-6 gene is frequently involved in translocations occurring at the 3q27 locus and is rearranged in approximately 30% of diffuse large cell lymphomas and in a small fraction of follicular lymphomas. The BCL-6 gene encodes for a Kruppel-type zinc-finger protein, the cell/tissue expression and function of which is unknown. In this study, we describe a new monoclonal antibody (PG-B6) that is specifically directed against a fixative-sensitive epitope on the amino-terminal region of the BCL-6 protein. By immunocytochemical analysis, BCL-6 localizes in the nucleus where PG-B6 staining gives a microgranular/diffuse pattern with exclusion of the nucleoli. The main reactivity of PG-B6 in tonsil and spleen is with the nuclei of germinal center B cells, whereas B cells within the mantle and marginal zones do not express BCL-6. No other lymphoid cells in the tonsil express BCL-6 except for a subset of CD3+/CD4+ intrafollicular and interfollicular T cells. A few lymphoid cells of unknown phenotype express BCL-6 in the thymus. Extra-lymphoid BCL-6 expression includes a weak nuclear positivity of epithelia. In non-Hodgkin's lymphomas, BCL-6 expression parallels that observed in normal lymphoid compartments, eg, expression in germinal center-derived tumors (follicular and diffuse large cell lymphomas), but not in mantle cell and marginal zone lymphomas. In most diffuse large cell lymphomas, the BCL-6 protein is expressed at high levels in cases with or without BCL-6 gene rearrangements. These findings indicate that BCL-6 expression is specifically regulated during B lymphocyte development and suggest that BCL-6 may play a role during B cell differentiation in the germinal center.

PG-M3 is a new monoclonal antibody (MoAb) specifically directed against a peptide sequence located in the aminoterminal region of the human PML protein. PML gene fuses with the retinoic acid receptor alpha (RAR alpha) gene during the t(15; 17) chromosomal translocation of acute promyelocytic leukemia (APL). The epitope recognized by PG-M3 is species-specific and fixative-resistant and is shared by most PML isoforms and PML/RAR alpha fusion proteins. PML is consistently located within the nucleus, although a minority of cells (about 20%), both in vitro and in vivo, show positivity for PML also in the cytoplasm. The nuclear staining pattern of PG-M3 varies from speckled (cells other than APL) to micropunctate (APL cells). Although two physiologically expressed PML isoforms are detectable by immunocytochemistry only or predominantly in the cytoplasm of transfected cells, the cytoplasmic localization of PML is a property also shared by the PML isoforms that predominantly localize to the nuclei. Immunohistologic analysis of normal human tissues with the PG-M3 MoAb showed variable PML expression, with the highest levels of the protein in postmitotic, differentiated cell types, such as endothelial cells, epithelia, and tissue macrophages, especially activated ones. In keeping with this in vivo finding, PML appears strongly upregulated in the U937 promonocyte cell line after exposure to agents that induce monocyte/macrophage activation (interferon gamma) or maturation (vitamin D3 and transforming growth factor beta 1).

The RING-finger promyelocytic leukemia (PML) protein is the product of the PML gene that fuses with the retinoic acid receptor-alpha gene in the t(15; 17) translocation of acute promyelocytic leukemia. Wild-type PML localizes in the nucleus with a typical speckled pattern that is a consequence of the concentration of the protein within discrete subnuclear domains known as nuclear bodies. Delocalization of PML from nuclear bodies has been documented in acute promyelocytic leukemia cells and suggested to contribute to leukemogenesis. In an attempt to get new insights into the function of the wild-type PML protein and to investigate whether it displays an altered expression pattern in neoplasms other than acute promyelocytic leukemia, we stained a large number of normal and neoplastic human tissues with a new murine monoclonal antibody (PG-M3) directed against the amino-terminal region of PML. As the PG-M3 epitope is partially resistant to fixatives, only cells that overexpress PML are detected by the antibody in microwave-heated paraffin sections. Among normal tissues, PML was characteristically up-regulated in activated epithelioid histiocytes and fibroblasts in a variety of pathological conditions, columnar epithelium in small active thyroid follicles, well differentiated foamy cells in the center of sebaceous glands, and hypersecretory endometria (Arias-Stella). Interferons, the PML of which is a primary target gene, and estrogens are likely to represent some of the cytokines and/or hormones that may be involved in the up-regulation of PML under these circumstances. In keeping with this concept, we found that PML is frequently overexpressed in Hodgkin and Reed-Sternberg cells of Hodgkin's disease, a tumor of cytokine-producing cells. Among solid tumors, overexpression of PML was frequently found in carcinomas of larynx and thyroid (papillary), epithelial thymomas, and Kaposi's sarcoma, whereas carcinomas of the lung, thyroid (follicular), breast, and colon were frequently negative or weakly PML+. We did not observe any changes in the levels of PML expression as the lesion progressed from benign dysplasia to carcinoma. Our immunohistological data are consistent with the hypothesized growth suppressor function of PML and strongly suggest that PML expression levels are likely to be modulated by a variety of stimuli, including cytokines and hormones.

Doxorubicin is the most effective single agent in the treatment of non‐Hodgkin's lymphoma (NHL). Its use is limited because of the cardiac toxicity primarily in elderly patients (pts) and in pts with history of cardiac disease. Liposomal doxorubicin has been proven to reduce cardiotoxicity. The aim of this retrospective study was the use of nonpeghylated liposomal doxorubicin (NPLD) in term of efficacy, response rate and incidence of cardiac events. We retrospectively collected the experience of 33 Hematological Italian Centers in using NPLD. Nine hundred and forty‐six consecutive pts treated with R‐COMP (doxorubicin was substituted with NPLD, Myocet) were collected. Median age was 74 years, the reasons for use of NPLD were: age (466 pts), cardiac disease (298 pts), uncontrolled hypertension (126 pts), other reasons (56 pts). According to clinicians' evaluation, 49.9% of pts would not have used standard doxorubicin for different situations (age, cardiomyopathy, previous use of doxorubicin, and uncontrolled hypertension). Overall 687 pts (72.6%) obtained a complete remission (CR). About 5% (n = 51) of subjects developed major cardiotoxic events including heart failure (N = 31), ischemic heart disease (N = 16), acute heart attack (N = 3), and acute pulmonary oedema (N = 1). After a median follow‐up of 32 months, 651 pts were alive and the overall survival (OS) was 72%. After a median observation period of 23 months disease free survival (DFS) was 58%. Either in univariate or in multivariate analysis OS and DFS were not significantly affected by age or cardiac disease. Our findings strongly support that including R‐COMP is effective and safe when the population is at high risk of cardiac events and negatively selected. Moreover, the use of this NPLD permitted that about half of our population had the opportunity to receive the best available treatment.

After FDA and EMA approval of the regimen containing polatuzumab vedotin plus rituximab and bendamustine (PolaBR), eligible relapsed/refractory diffuse large B-cell lymphoma (DLBCL) patients in Italy were granted early access through a Named Patient Program. A multicentric observational retrospective study was conducted focusing on the effectiveness and safety of PolaBR in everyday clinical practice. Fifty-five patients were enrolled. There were 26 females (47.3%), 32 patients were primary refractory and 45 (81.8%) resulted refractory to their last therapy. The decision to add or not bendamustine was at physician's discretion. Thirty-six patients underwent PolaBR, and 19 PolaR. The 2 groups did not differ in most of baseline characteristics. The final overall response rate was 32.7% (18.2% complete response rate), with a best response rate of 49.1%. Median disease-free survival was reached at 12 months, median progression-free survival at 4.9 months and median overall survival at 9 months, respectively. Overall, 88 adverse events (AEs) were registered during treatment in 31 patients, 22 of grade ≥3. Eight cases of neuropathy occurred, all of grades 1-2 and all related to polatuzumab. The two groups of treatment did not differ for effectiveness endpoints but presented statistically significant difference in AEs occurrence, especially in hematological AEs, in AEs of grade equal or greater than 3 and in incidence of neuropathy. Our data add useful information on the effectiveness of Pola(B)R in the setting of heavily pretreated DLBCL and may also suggest a better tolerability in absence of bendamustine without compromise of efficacy.