Modifying an immunogenic epitope on a therapeutic protein: a step towards an improved system for antibody-directed enzyme prodrug therapy (ADEPT)

Carboxypeptidase G2 (CP) is a bacterial enzyme, which is targeted to tumours by an antitumour antibody for local prodrug activation in antibody-directed enzyme prodrug therapy (ADEPT). Repeated cycles of ADEPT are desirable but are hampered by human antibody response to CP (HACA). To address this, we aimed to identify and modify clinically important immunogenic sites on MFECP, a recombinant fusion protein of CP with MFE-23, a single chain Fv (scFv) antibody. A discontinuous conformational epitope at the C-terminus of the CP previously identified by the CM79 scFv antibody (CM79-identified epitope) was chosen for study. Modification of MFECP was achieved by mutations of the CM79-identified epitope or by addition of a hexahistidine tag (His-tag) to the C-terminus of MFECP, which forms part of the epitope. Murine immunisation experiments with modified MFECP showed no significant antibody response to the CM79-identified epitope compared to A5CP, an unmodified version of CP chemically conjugated to an F(ab)(2) antibody. Success of modification was also demonstrated in humans because patients treated with His-tagged MFECP had a significantly reduced antibody response to the CM79-identified epitope, compared to patients given A5CP. Moreover, the polyclonal antibody response to CP was delayed in both mice and patients given modified MFECP. This increases the prospect of repeated treatment with ADEPT for effective cancer treatment.     

Sub-class of IgG in allergic disease. I. IgG sub-class antibodies in immediate and non-immediate food allergy

Previous studies have suggested that, apart from IgE-mediated reactions, some of the symptoms of food allergy may be caused by IgG antibodies to food proteins. This study was carried out to see if there were any distinctive features of the IgG sub-class antibody response to dietary antigens which occurs in food allergic patients. IgG sub-class antibodies were measured using a quantitative enzyme-linked immuno-sorbent assay (ELISA) to wheat gliadin, ovalbumin and bovine casein in twenty patients who had coeliac disease and in twenty-eight egg allergic patients. These were compared with twenty-one atopic dermatitis patients who did not have food allergy and twenty-six healthy control subjects. Coeliac disease patients tended to have raised IgG antibody levels (especially IgG1) to all three antigens but these overlapped considerably with that seen in egg allergic and atopic dermatitis patients. Coeliacs who avoided gluten had anti-gliadin antibody levels which did not differ from those seen in healthy subjects but nevertheless had raised anti-ovalbumin and casein-specific antibodies. The IgG antibody was largely restricted to IgG1 and IgG4 sub-class although the relative amount of each varied with the antigen. Although gliadin-specific antibodies were mainly IgG1, ovalbumin-specific antibodies were mainly IgG4. The increased antibody levels to all three antigens in coeliacs were caused by a raised IgG1 response, IgG4 antibodies were usually normal. Egg allergic patients also had raised IgG1 but not IgG4 antibodies to ovalbumin. These data show that the response to different dietary antigens can vary with the antigen. The fact that IgG1 and not IgG4 antibodies were raised to all three antigens in patients with coeliac disease suggests that they are a secondary consequence of the disease, perhaps reflecting increased transport of antigens across a damaged gut mucosa rather than a specific immunopathological reaction. However, the observation that antibodies to gliadin, and not ovalbumin or casein, fell following gluten avoidance shows that the response to gliadin, at least, is dependent upon continued exposure to antigen.     

Posttransplantation lymphoproliferative disorder in liver recipients: characteristics, management, and outcome.

Posttransplantation lymphoproliferative disorder (PTLD) is a well-recognized complication of organ transplantation. The aim of this study, performed over 9 years, was to examine the histopathological findings, clinical course, and outcome of patients who, having undergone orthotopic liver transplantation (OLT), developed PTLD. The sample included 7 adult liver allograft recipients (1.7%), 4 men and 3 women, with a mean age of 53 years (range, 40 to 61 years) who developed PTLD 1 to 36 months post-OLT (mean, 6 months). Four patients received either antithymocyte globulin as primary immunosuppression or OKT3 for steroid-resistant cellular rejection. Four patients had localized hepatic tumor with or without regional lymph node involvement, 2 patients had extralymphoreticular disease (head of pancreas and chest wall), and 1 patient had spleen and lymph node involvement. All tumors were B-cell lymphomas; three polymorphic and four monomorphic. Clonality was assessed by immunostaining for kappa and lambda and gene rearrangement. Monoclonality was found in 4 patients and polyclonality in 2 (1 of whom progressed to monoclonality); in 2 patients, clonality could not be determined. Immunohistochemistry findings for the presence of the Epstein-Barr virus (EBV)-determined nuclear antigen and the latent membrane protein 1 were noted in lymphoma tissue in 6 patients. Immunosuppressive therapy was decreased in all patients. Polyclonal tumors were treated with acyclovir (1 patient is in complete remission and 1 patient died), and monoclonal tumors with systemic chemotherapy (2 patients are in complete remission and 2 patients died). One patient was treated with monoclonal antibodies (CD20) but failed to respond, and 1 patient was treated with excision and is in complete remission. The mortality rate was 43%; for the remainder, median survival is 21 months (range, 10 to 42 months). We conclude that PTLD may re-present early after OLT. EBV has a special role in the pathogenesis, combined with immunosuppressive therapy. The outcome is poor, and new therapeutic approaches are needed.     

Somatically mutated regions of immunoglobulin on human B-cell lymphomas code for peptides that bind to autologous major histocompatibility complex class I, providing a potential target for cytotoxic T cells.

Lymphoma-derived immunoglobulin idiotype (Id) is a well-characterized, tumor-specific antigen on B-cell malignancies. Immunotherapy using lymphoma immunoglobulin can lead to clinical responses mostly associated with anti-Id antibody. We cloned the Id from B-cell lymphomas, sequenced them, and used bioinformatics to select autologous MHC class I binding peptides from somatically mutated regions of the lymphoma Id. Peptides from patients who were HLA-A1, HLA-A2, HLA-A3, or HLA-A11 positive were analyzed in the T2 stabilization assay and a competitive peptide-binding assay. By both methods, approximately half of the peptides analyzed, regardless of HLA type, bound with intermediate or high affinity. Peptide binding affinity was similar to viral peptide sequences known to provide targets for cytotoxic T cells. Further investigation of lymphocyte responses to stimulation by autologous Id peptides versus Id peptides from other patients revealed that three of five patients in complete remission or with low volume, stable disease responded to self-peptides by IFN-gamma secretion greater than that seen with non-self peptides, whereas none of five patients with progressive disease responded to their own lymphoma Id. We have shown that mutated regions of lymphoma Id contain MHC class I binding peptides that are potential targets for cytotoxic T cells. Immunotherapy using the tumor-specific mutated regions from lymphoma Id avoids the need to break innate tolerance toward the germ-line protein sequences present on normal and malignant B cells.     

Subacute immune response to primary EBV infection leading to post-transplant lymphoproliferative disease in a renal transplant patient

A 23-year-old man sero-negative for Epstein-Barr virus (EBV) developed recurrent sore throats 3 and 6 months after a renal transplant from an EBV sero-positive donor. Tonsillar biopsy at 9 months post-transplant showed post-transplant lymphoproliferative disease (PTLD) caused by EBV. Following reduction of immunosuppressive treatment, he developed further signs and symptoms, and serological evidence of infectious mononucleosis followed by resolution of lymphadenopathy. This case emphasizes the difficulty in interpreting EBV serology in immunosuppressed patients and the importance of pre-transplant EBV serology.     

Rearrangement of TCR gamma chain gene involving JP1 suggests early thymocyte origin of peripheral T-cell lymphoma

Peripheral T-cell lymphomas (PTL) are morphologically and immunophenotypically heterogeneous. We have examined a series of cases to determine whether this heterogeneity is reflected at the level of developmentally specific T-cell receptor (TCR) gene rearrangement. 4 of 5 cases had clonal rearrangements of TCR beta and gamma chain genes; one of these also had a probable DQ52-J immunoglobulin heavy chain gene rearrangement. 2 of the 4 TCR gamma gene rearrangements involved the most 5' J region, JP1, a characteristic of immature thymocytes. These 2 cases also had immunophenotypic features of immaturity. Taken together, our results suggest that TCR gene rearrangement is correlated with surface marker data and shows that in some cases PTL may arise from a very early stage of thymocyte maturation.     

Collagen production by human mesothelial cells in vitro

Serous effusions from a variety of malignant and non-malignant conditions were found to contain cells which had the morphological, histochemical and ultrastructural characteristics of mesothelial cells. In culture they were the predominant cell type and synthesised large quantities of the interstitial collagens type I and III, with the proportion of type III frequently approaching or exceeding 50 per cent. There was no evidence that they synthesised basement membrane collagen chains of type IV or type V. Since mesothelial cells are assumed to secrete the mesothelial basement membrane, the synthesis of interstitial collagens by desquamated mesothelial cells appears to reflect a change in the phenotype of collagen synthesis. We suggest that this change may be an important factor in the fibrosis of the serosal wall which frequently accompanies diseases with chronic serious effusion.