ALBERT

Description: Abstract 377 Hemophilia B represents a promising model for the development of adeno-associated viral (AAV) vectors-based gene therapeutics. In the first clinical trial for AAV serotype 2 mediated gene transfer of Factor IX (F.IX) to the liver of severe hemophilia B subjects, transgene expression was short-lived with a gradual decline of F.IX levels. The loss of transgene expression was accompanied by a transient transaminitis, which we hypothesized to be the result of the reactivation of a pool of capsid-specific memory CD8+ T cells originated from a previous exposure to wild-type AAV. These results were unanticipated since previous work in small and large animal models showed that AAV administration is uneventful, allowing prolonged expression of F.IX transgene at therapeutic levels. We developed an in vitro cytotoxicity assay using a human hepatocyte cell line expressing HLA-B*0702, a common MHC class I allele for which the AAV capsid immunodominant epitope VPQYGYLTL was identified. Using this model, we demonstrated that HLA-matched AAV-specific effector CD8+ T cells were able to lyse target hepatocytes transduced with AAV-2. We now use this in vitro model of CTL killing of AAV-transduced hepatocytes to demonstrate the efficacy of a novel strategy to circumvent undesirable immune response through the engagement of regulatory T cells. A recently characterized MHC Class II-restricted T cell epitope (Tregitope) in the Fc fragment of IgG has been shown to induce regulatory T cells in vitro and in vivo (Blood, 2008; 112: 3303-3311). AAV-specific HLA-B*0702 effector cells expanded in the presence of a human Tregitope peptide resulted in 79% to 89% inhibition of cytotoxic activity against peptide-pulsed and AAV-transduced target cells, respectively. These results were confirmed using PBMCs from 5 different donors. A similar degree of inhibition of CTL activity was observed for the HLA allele A*0101, which binds to the AAV-derived epitope SADNNNSEY; co-culture of effector cells with the Tregitope inhibited CTL-mediated killing by 60%. Interestingly, the same Tregitope efficiently mediated suppression of CTL activity in subjects carrying different HLA alleles, indicating a high level of promiscuity of Tregitope binding. Staining for the regulatory T cell markers CD4, CD25, and FoxP3 supported the hypothesis that Tregitopes suppress T cell responses by expanding regulatory T cells; 62.2% of the CD4+ population stained positive for CD25 and FoxP3 in PBMCs expanded against AAV epitopes in the presence of Tregitope, compared with PBMCs expanded against an AAV epitope alone (3.63%), or against an AAV epitope and an irrelevant control peptide (1.94%). Polyfunctional analysis for markers for T cell activation showed that CD8+ T cells incubated in the presence of Tregitope had an approximately 5-fold decrease in production of IL-2 and IFN-γand a 2-fold reduction in TNF-α production, indicating levels of activation close to naïve CD8+ T cells. We further characterized the mechanism of action of Tregitopes by showing that Tregitopes are required at the time of CD8+ T cell priming, as CTL activity of AAV-expanded CD8+ T cells against transduced hepatocytes was not inhibited by the CD4+ T cell fraction of PBMC expanded separately in vitro with Tregitopes only. We conclude that the use of Tregitopes represents a promising strategy for antigen-specific, Treg-mediated modulation of capsid-specific T cell responses. Disclosures: Martin: EpiVax: Employment. De Groot:EpiVax, Inc.: Employment, Equity Ownership.

Description: Most immune responses to protein antigens are dependent on T-cell recognition of discrete peptide epitopes presented in an MHC groove. The pattern of peptide recognition can be predicted from the primary structure of a given protein based on residues that bind (anchor) to a given HLA phenotype. Algorithms such as EpiMatrix can be applied to identify such epitopes and measure the potential immunogenicity of proteins based on epitope content. One approach to reduce immunogenicity is to generate recombinant proteins whose constituent epitopes have been modified so as to reduce their HLA binding. Modification of the sequence can be performed in silico using algorithms such as OptiMatrix. This “de-immunization” method has been used effectively with a number of therapeutic proteins already in use in clinical trials. It may therefore also be possible to target those residues of fVIII that, while contributing to HLA binding, can be mutated without altering the functional ability of fVIII to initiate clotting. We have begun this de-immunization process with the fVIII, starting with C2 domain because C2 has been confirmed to be a major target of both T cells and inhibitory antibodies. Using EpiMatrix, we selected 10 peptides in human fVIII that would be predicted to bind to eight class II HLA DR molecules that encompass over 95% of the U.S. population. These epitopes were synthesized and eight of the ten were assayed in vitro and found to bind to HLA at IC50

Description: Background: Bleomycin-containing chemotherapy regimens have become the mainstay of treatment in Hodgkin’s Disease (HD). The risk of bleomycin pulmonary toxicity (BPT) ranges from 0–46% and mortality rates range from 0–27%. Although there is no excepted standard treatment for BPT, corticosteroid treatment, withholding bleomycin from subsequent chemotherapy, and proceeding with a non-bleomycin containing regimen is the most common approach. We reviewed our experience to better delineate outcome and appropriate treatment in these patients. Methods: We reviewed all patients managed for HD at Mayo Clinic, Rochester, from January 1986 to February 2003. BPT was defined by the presence of pulmonary symptoms, bilateral interstitial infiltrates, and no evidence for an infectious etiology. Results: A retrospective review identified 141 patients with HD treated with a bleomycin-containing regimen. The mean age of patients at diagnosis was 34 years. Fifty four percent were males. The histology was nodular sclerosing in 85%. The Hasenclever index was 0 in 15%, 1 in 35%, 2 in 24%, 3 in 16%, 4 in 9%, and 〉5 in 1%. Frontline chemotherapy included ABVD in 57%, MOPP-ABV(D) in 33%, COPP-ABV in 8%, BEACOPP in 3%, and Stanford V in 2%. Forty one percent of patients received radiation. The 5-year overall survival (OS) and progression free survival (PFS) for all patients were 87% and 79% respectively. BPT was observed in 18% of patients (25/141). There was a significant decrease in OS, 63% in patients with BPT versus 90% in non-BPT patients at 5 years (p=0.0013). The mortality from BPT was 4.2% (6/141) in all patients and 24% (6/25) in patients who developed the pulmonary syndrome. These 6 patients all died within 9 months of their HD diagnosis from BPT. The Hasenclever index was 3 or less in 5 of these 6 patients. CR rates were equal at 91% and 93% in BPT and non-BPT patients respectively (p=0.299). Twenty two percent (31/141) of patients, either symptomatic or asymptomatic, had bleomycin omitted at any time from their regimen with no difference in OS or PFS, 83% versus 88% (p=0.369) and 82% versus 78% (p=0.853) respectively. The mean bleomycin dose was 84 mg/m2 (range of 20–180 mg/m2). Bleomycin dose had no impact on OS or PFS. In BPT patients subsequent non-bleomycin therapy included AVD 44%, MOPP-AV 31%, or no further chemotherapy 25%. The five-year OS was equal between the AVD and MOPP-AV groups at 91%. However in patients who received no further chemotherapy 5-year OS was 30% (p=0.0001). Conclusion: Bleomycin pulmonary toxicity (BPT) results in a significant decrease in OS survival at 5 years in patients being treated for Hodgkin’s Disease. In patients who do not die acutely from pulmonary toxicity both OS and PFS appear equal despite the omission of bleomycin.

Description: 1. A case of coexistent hereditary spherocytosis and sicklemia in a Negro female is reported. Hematologic and clinical amelioration followed splenectomy. 2. Study of three generations of the family of the propositus revealed one additional case of hereditary spherocytosis-sicklemia and 10 cases of hereditary spherocytosis in the Negro. 3. Further evidence is adduced that the combination of this heterozygous hemoglobinopathy with the red blood cell defect of hereditary spherocytosis produces an illness which is not grossly different from hereditary spherocytosis associated with normal hemoglobin.

Description: Background: In Hodgkin’s Disease (HD), G-CSF has been used to maintain maximum dose intensity by avoiding neutropenia and treatment delays. Pre-clinical data and anecdotal reports have shown an association between G-CSF administration and bleomycin pulmonary toxicity (BPT). This complication may cause access morbidity and have a detrimental impact on survival in this otherwise good prognosis population. We embarked on a retrospective analysis to determine if G-CSF increased the incidence of this complication or had an impact on outcomes. Methods: We reviewed all patients managed for HD at Mayo Clinic, Rochester, from January 1986 to February 2003. BPT was defined by the presence of pulmonary symptoms, bilateral interstitial infiltrates, and no evidence for an infectious etiology. Patients who received G-CSF support with one or more of their bleomycin-containing chemotherapy cycles were considered as being treated with G-CSF. Results: A retrospective review identified 141 patients with HD treated with a bleomycin-containing regimen. The mean age of patients at diagnosis was 34 years. Fifty four percent were males. The histology was nodular sclerosing in 85%. The Hasenclever index was 0 in 15%, 1 in 35%, 2 in 24%, 3 in 16%, 4 in 9%, and ≥ 5 in 1%. The G-CSF and non G-CSF groups were balanced for poor prognosis risk factors including Hasenclever index. Frontline chemotherapy included ABVD in 57%, MOPP-ABV(D) in 33%, COPP-ABV in 8%, BEACOPP in 3%, and Stanford V in 2%. Forty one percent of patients received radiation. The 5-year overall survival (OS) and progression free survival (PFS) for all patients were 87% and 79% respectively. G-CSF was administered to 52% (74/141) of patients. BPT occurred in 18% of patients (25/141). A higher rate of BPT was observed in patients receiving G-CSF, 26% (19/74) versus 9% (6/67) in non G-CSF patients (p=0.0141). In this population, G-CSF administration was the only factor associated with an increased risk of BPT. There was no difference between the two groups for BPT associated risk factors including radiation, bleomycin dose, renal insufficiency, smoking history, and underlying lung disease. Additionally these risk factors showed no correlation with the development of BPT. The mortality from BPT was 4.2% (6/141) in all patients and 24% (6/25) in patients who developed the pulmonary syndrome. Of the 6 patients who died acutely, 83% (5/6) received G-CSF. CR rates were equal between the G-CSF and non G-CSF groups at 92% and 94% respectively. Five year OS and PFS were equal between the G-CSF and non G-CSF groups at 82% versus 89% (p=0.473) and 74% versus 84% (p=0.152) respectively. Conclusion: G-CSF administration increases the incidence of pulmonary toxicity in HD patients treated with bleomycin based chemotherapy. The major impact was on treatment related morbidity as 5-year OS and PFS were equal between the G-CSF and non G-CSF groups.

Description: Abstract 2207 Development of anti-factor VIII (FVIII) antibodies that neutralize FVIII activity is a major obstacle of replacement therapy in hemophilia A. To create a less immunogenic therapeutic protein, recombinant FVIII can be modified to reduce binding of FVIII sequences to HLA, based on predicted anchoring residues. This process is known as ‘de-immunization’. Previously, we found that immunogenic peptide epitopes in the C2 domain of FVIII could be modified to reduce MHC class II binding resulting in lower antigenicity in vitro in hemophilic E16 mice (H-2b). Here, we extended these studies to HLA-DR transgenic mice and identified immunodominant C2 peptides in E16, DR3 and DR4 mice as well as in DR3 mice crossed to E16 mice (DR3×E16). E16 and DR transgenic mice were immunized with the designated original high class II-binding peptides (ORG) or modified peptides (MOD) emulsified in CFA, and lymph node (LN) cells were tested in T-cell proliferation and ELISpot assays against the ORG and MOD peptides. We found that while p2191-2210 dominantly stimulates H-2b, p2271-89 is immunodominant in DR3 transgenic animals; DR3×E16 T cells recognized both epitopes as would be predicted. On the other hand, p2231-51 and p2310-30 were immunodominant in DR4 mice. We also found that modifications of dominant epitope peptides 2191, 2271, 2231, 2310 showed lower HLA class II binding and T-cell proliferation in corresponding mouse strains; stimulation of IL17-a and IFNγ cytokine production were reduced with modified 2191 in DR3xE16 mice. Direct immunization with rFVIII containing modified peptides is required to validate potential immunogenicity. These results will be utilized to design and produce a functional full-length modified rFVIII that can be used as a less immunogenic therapeutic protein for hemophilia A patients. (Supported by NIH grant R43 HL088834-01 to ADG.) Disclosures: Moise: EpiVax: Employment. Tassone: EpiVax: Employment. McClaine: EpiVax: Employment. Martin: EpiVax: Employment, Equity Ownership, Patents & Royalties. DeGroot: EpiVax: Employment, Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties. Scott: EpiVax: Consultancy.

Description: Abstract 3769 Recent advances in adeno-associated viral (AAV) vector-mediated gene transfer continue to offer hope for the correction of monogenic disorders such as hemophilia B. However, unanticipated T cell responses directed against viral capsid epitopes may limit the efficacy of AAV gene transfer. A phase I clinical study in which an AAV2 vector expressing human factor IX (FIX) was delivered systemically provided the first evidence that AAV vector administration at high doses may trigger the expansion of memory CD8+ T cells directed against AAV capsid epitopes. This response was associated with the loss of FIX transgene expression and a transient increase in liver enzymes. Additional studies in human subjects undergoing AAV gene transfer suggest that the capsid antigen load is an important determinant of capsid-specific T cell activation. Thus, strategies for the modulation of capsid T cell responses could contribute to achieving sustained transgene expression following high dose delivery of AAV. MHC class II peptide ligands identified within the human IgG Fc fragment (Tregitopes, Blood 2008;112:3303) have been shown to expand regulatory T cells (Tregs). Restimulation of human peripheral blood mononuclear cells (PBMC) in vitro with AAV capsid antigen in the presence of Tregitopes resulted in the suppression of capsid-specific CD8+ T cells and in the expansion of CD4+CD25+FoxP3+ Tregs. To better define the nature of Tregitope-induced Tregs, we depleted CD25+ cells from PBMC prior to in vitro restimulation. This completely prevented capsid-specific CTL suppression and the expansion of Tregs, suggesting that Tregitopes act by expanding natural Tregs. Cytokine ELISA on conditioned media from PBMC co-cultured with AAV antigen and Tregitopes showed a 50% decrease in IL-2 levels and a 〉500-fold increase in IL-10 levels. These results suggest that the effect of Tregitopes may be cytokine mediated. To test this hypothesis, we used a transwell system in which the CD4+ T cell fraction of Tregitope-restimulated PBMC was co-cultured with the capsid-specific CD8+ T cells. Without cell contact, a nearly 50% suppression of anti-capsid CD8+ T cell responses was observed. Further evidence supporting the role of cytokine-mediated suppression came from the observation that Tregitope-treated capsid-specific CD8+ T cells appeared to be anergic, and depletion of CD4+ T cells (Tregs) followed by a 24-hour incubation of CD8+CD4− T cells with IL-2 restored 〉80% of CTL activity. Finally, antigen specificity of Tregitope-induced Tregs was tested by expanding PBMC in vitro with HLA-B*0702-restricted epitopes from either the AAV capsid or the Epstein-Barr Virus (EBV). After in vitro restimulation, negatively-isolated CD4+ T cells expanded in the presence of EBV antigen and Tregitopes were co-incubated with either CD8+ T cells expanded against the AAV capsid or against EBV. Suppression of CTL activity was observed only when EBV Tregs were co-incubated with EBV CD8+ T cells. Similarly, Tregs isolated from AAV and Tregitope cultures suppressed AAV-specific CD8+ T cells but not EBV-specific CD8+T cells. These results suggest that inhibition of CD8+ T cell responses is antigen-specific. We conclude that Tregitopes induce the expansion of Tregs, which can mediate a potent antigen-specific inhibition of CD8+ T cell responses directed to the AAV capsid. Disclosures: Hui: Children's Hospital of Philadelphia: Patents & Royalties. Martin:EpiVax: Employment, Equity Ownership, Patents & Royalties. DeGroot:EpiVax: Employment, Equity Ownership. High:Children's Hospital of Philadelphia: Patents & Royalties. Mingozzi:Children's Hospital of Philadelphia: Patents & Royalties.

Description: Five cases of erythroleukemia of the acute or incomplete variety form the basis of this report. Four of the patients were women. The ages of these five patients ranged from 19 to 73 years at time of admission to the Mayo Clinic. Studies were made on the blood and peripheral marrow for varying periods throughout the course of the disease. All five patients had anemia and extreme immaturity of the erythrocytes in the peripheral blood and bone marrow. Leukopenia was eventually present in four cases as was thrombopenia. Splenectomy was performed on one patient. One patient lived six years after the condition developed, two died within thirteen months of the time of diagnosis, one was not followed, and the fifth was still living at last report. Relatively few cases of erythroleukemia have been reported in the literature and most of those reported have been cases of the chronic variety. The erythrocytic picture in the chronic variety differs from that in the acute variety. In the acute type acute erythremia is associated with leukemia and in the chronic type polycythemia is associated with it. Either the erythrocytic abnormality or the leukocytic may appear first. Our studies and those reported in the literature suggest excessive activity of the blast cell in two directions.

Description: The high cytosolic aldehyde dehydrogenase (ALDH) activity in hematopoietic progenitor cell (HPC) populations allows flow sorting of ALDH bright (ALDHbr), side scatter low cell populations highly enriched for human cells with long-term hematopoietic repopulating capacity. We are determining whether human ALDHbr populations and their CD34+ and CD34neg subsets sorted from umbilical cord blood (UCB) or adult G-CSF-mobilized peripheral blood (MPB) can engraft murine embryos and generate chimeric mice with partial human contribution. For each cell population, 50 – 75 sorted cells were injected into 3.5-day C57BL/6 blastocysts that were then transferred to surrogate mothers. We harvested 4 – 10 viable embryos/group at day 12.5 – 15.5; the ratio of viable embryos recovered/blastocysts transferred was not significantly different among the groups. Because cells in ALDHbr populations express surface markers characteristic of several stem cell types, and because some HPC may contribute to development in other tissues, we analyzed human cell content in both hematopoeitic and non-hematopoeitic tissues of the resulting animals. Human DNA was detected in dissected embryonic tissues by real-time PCR analysis of the repetitive α-satellite DNA on human chromosome 17. The detection limit for human content was 0.00003% (1 human cell / 3.3x106 mouse cells). The frequencies of positive tissues were similar among embryos produced using ALDHbr UCB cells (n=10), ALDHbrCD34+ UCB cells (n=6), and ALDHbrCD34neg MPB cells (n=10): 10–20% for brain and placenta, 20 – 50% for liver, 30 – 80% for lung and yolk sac (p=0.0001 compared to brain and placenta), and 60 – 100% for heart (p

Description: We have identified a set of putative natural T regulatory epitopes (Tregitopes) which, when co-administered with an antigen, cause the expansion of antigen-specific adaptive Tregs in vitro and in vivo. They have the following characteristics: they bind, in most cases, with high affinity to multiple MHC class II molecules and, when co-administered with antigen, they suppress effector T cell immune responses to the antigen and up-regulate Treg associated cytokines and chemokines. T cells responding to Tregitopes exhibit a T regulatory phenotype (CD4+/CD25hiFoxP3+). To test whether Tregitopes derived from immunoglobulin (Ig) suppress immune responses to antigen co-administered in vivo, we performed two types of experiments. In the first, we dosed three groups of HLA DR4 mice every other week for six weeks with either a peptide antigen (pAg) alone, pAg with murine Fc, or pAg with mTregitope289, the murine homolog of the human Tregitope289. Mice were sacrificed and spleens harvested for assay. While the mice dosed with murine Fc demonstrated a reduced IL-4 ELIspot response to pAg, remarkably, the reduction was even greater in the mice treated with Tregitope. In a second model, C57Bl/6 mice were injected with LPS-stimulated B cells that were pulsed with either ovalbumin (OVA) alone, mTregitopes 167 and 289 or with OVA together with the two mTregitopes. One week later, mice were challenged with OVA 323–339 peptide in adjuvant. Two weeks after challenge, draining lymph nodes were harvested and LN cells stimulated with OVA 323–339 for measurement of T-cell proliferation by thymidine incorporation and by IFN-γ secretion by ELIspot. The mice receiving B cells previously pulsed with OVA alone demonstrated a robust IFN-gamma response to OVA re-stimulation. In contrast, the mice receiving B cells previously pulsed with OVA + Tregitopes demonstrated a comparatively reduced response. When sera were assayed for anti-OVA antibodies by ELISA, antibody response to OVA also declined following treatment with B cells co-administered with Tregitope. The mechanism of suppression appears to be due to the induction of antigen-specific adaptive tolerance induction (De Groot AS et al. Activation of natural regulatory T cells by IgG Fc-derived Peptide “Tregitopes” Blood112: in press, 2008).