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Wiskott-Aldrich syndrome (WAS) is an inherited immunodeficiency characterized by high incidence of autoantibody-mediated autoimmune complications. Such a feature has been associated with defective suppressor activity of WAS protein-deficient, naturally occurring CD4+CD25+Foxp3+ regulatory T cells on responder T cells. However, it remains to be established whether the altered B-cell tolerance reported in WAS patients and Was knockout (WKO) mice is secondary to abnormalities in the direct suppression of B-cell function by nTreg cells or to impaired regulation of T-helper function. Because activated nTreg cells are known to induce granzyme B–mediated B-cell killing, we decided to evaluate the regulatory capabilities of WKO nTregs on B lymphocytes. We found that preactivated WKO nTreg cells failed to effectively suppress B-cell proliferation and that such a defect was associated with reduced killing of B cells and significantly decreased degranulation of granzyme B. Altogether, these results provide additional mechanistic insights into the loss of immune tolerance in WAS.

Gene transfer into hematopoietic stem cells has been used successfully to treat a variety of human genetic diseases. Although protocols have shown positive clinical outcomes, the successes of clinical trials have been tempered by adverse events in which the use of gamma-retroviral vectors (GV) containing full-length long terminal repeats (LTRs) with strong enhancer activity increased transcription of cancer-related genes, and thereby contributed to development of leukemia. Assessing safety of integrating viral vectors for future clinical use is therefore of paramount importance. The negative control region (NCR) is a particularly well-conserved sequence among mammalian gamma-retroviruses with demonstrated regulating a transcription activity of GV in hematopoietic cells. This suggests that the NCR might play a crucial role of insertional oncogenesis after gene transfer into hematopoietic progenitors. In a series of safety studies of viral gene transfer constructs, we used an in vitro assay of murine bone marrow (BM) cell immortalization and compared the consequences of hematopoietic stem cell transduction with three different kinds of viral vectors, including Moloney murine leukemia virus- (MMLV), lentivirus- (LV), and foamy virus (FV)-based constructs. To evaluate critical elements for cell immortalization by MMLV vectors, we also tested four different MMLV LTR variants deleted of either 1) most of the two 75-bp repeats associated with the viral enhancer (delE1), 2) all of the two 75-bp repeats and the NCR (delE2), 3) only the NCR (delNCR), or 4) carrying a deleterious mutation of the NCR NFAT motif (ΔNFAT). All vectors carried an internal expression cassette including the eGFP gene under the control of a UCOE (ubiquitously acting chromatin opening element) promoter. In this assay, BM cells are harvested from C57BL6 mice, exposed to retroviral supernatants and cultured long-term. Derived lines are considered immortalized based on their ability to continue to grow in vitro for more than six weeks in the presence of interleukin-3 and stem cell factor. Real-time PCR was performed to verify comparable transduction efficiency of bone marrow cells by different vectors. In our analysis of MMLV LTR mutants, full-MMLV and delE1 transduction of 92 and 108 cultures, respectively, resulted in 37 and 37 immortalized lines (40% and 34% immortalization rate, respectively). The difference in immortalization rate between full-MMLV and delE1 was not statistically significant. Transductions using delE2-, delNCR- and ΔNFAT-carrying vectors of 60, 36 and 35 cultures resulted in 10, 3 and 10 immortalized lines (17%, 8.3% and 29% immortalization rate, respectively). The difference between the immortalization caused by delE1 and delE2 vectors was statistically significant (p These results confirm that GV are prone to causing immortalization of hematopoietic cells and indicate that deletion of the whole viral enhancer sequences may not be adequate to eliminate the insertional oncogenesis risk. Importantly, our data point to the NCR as a crucial element for immortalization and justify additional studies to evaluate its specific role in MMLV-mediated insertional oncogenesis. Finally, our results suggest that vectors based on LV and FV backbones are safer alternatives for clinical gene transfer into hematopoietic stem cells. Disclosures: No relevant conflicts of interest to declare.

Abstract 2049 Gene transfer into hematopoietic stem cells has been used successfully to treat a variety of human genetic diseases. Although protocols have shown positive clinical outcomes, the successes of clinical trials have been tempered by adverse events in which the integration of the viral vectors increased transcription of cancer-related genes and thereby contributed to development of leukemias. The use of gamma-retroviral vectors containing full-length, long terminal repeats (LTRs) with strong promoter and enhancer activity has been well documented to have the potential of resulting in activation of expression of genes neighboring the vector insertion site. Assessing safety of integrating viral vectors for future clinical use is therefore of paramount importance. In preparation for gene therapy approaches for the Wiskott-Aldrich syndrome (WAS), we used an in vitro assay of murine bone marrow (BM) cell immortalization to compare the consequences of hematopoietic stem cell transduction by three different kinds of viral vectors, including Moloney murine leukemia virus (MMLV), lentivirus (LV), and foamy virus (FV) constructs. To evaluate critical elements for cell immortalization by MMLV vectors, we also tested five different MMLV LTR forms: unmodified (full-MMLV), deleted of most of the two 75-bp repeats associated with the viral enhancer (delE1), deleted of all the two 75-bp repeats and negative control region (NCR) (delE2), deleted of the viral promoter sequences (delP), and with full deletion of enhancer and promoter sequences (delEP). All vectors carried an internal expression cassette including the eGFP gene under the control of a UCOE (ubiquitously acting chromatin opening element) or the WAS endogenous promoter (WASp). In this assay, BM cells are harvested from C57BL6 mice, exposed to retroviral supernatants and cultured long-term. Derived lines are considered immortalized based on their ability to continue to grow in vitro for more than six weeks in the presence of interleukin-3 and stem cell factor. Real-time PCR was performed to verify comparable transduction efficiency of bone marrow cells by different vectors. To date, full-MMLV and delE1 transduction of 123 and 132 cultures, respectively, has given rise to 48 and 43 immortalized lines (39.0% and 32.5% immortalization rate, respectively). The difference in immortalization rate between full-MMLV and delE1 was not statistically significant. In contrast, transduction of 114 and 62 cultures with LV and FV vectors, respectively, resulted in no immortalized lines. In our analysis of MMLV LTR mutants, full-MMLV and delE1 transduction of 56 and 72 cultures, respectively, has given rise to 24 and 26 immortalized lines (43% and 36% immortalization rate). Again, the difference in immortalization rate between full-MMLV and delE1 was not statistically significant. In contrast, delE2, delP and delEP transduction of 24 cultures each has given rise to 2, 5 and 3 immortalized lines (8.3%, 21% and 13% immortalized ratio, respectively). The difference between the immortalization caused by delE1 and delE2 vectors was statistically significant (p These preliminary results confirm that gamma-retroviral vectors are prone to causing immortalization of hematopoietic cells and indicate that deletion of viral enhancer and/or promoter sequences may not be adequate to eliminate the insertional oncogenesis risk. Importantly, our data point to the NCR as a crucial element for immortalization and justify additional studies to evaluate its specific role in MMLV-mediated insertional oncogenesis. Finally, our results suggest that vectors based on LV and FV backbones are safer alternatives for clinical gene transfer into hematopoietic stem cells. Disclosures: No relevant conflicts of interest to declare.

Abstract 3116 Therapeutic gene transfer has been used successfully to treat a variety of human genetic diseases. Although protocols have shown positive clinical outcomes, the success of clinical trials were tempered by adverse events, in which integration of the viral vectors increased transcription of cancer-related genes and thereby contributed to development of leukemia. In all documented cases of insertional mutagenesis, the viral vectors used contained full-length, gamma-retrovirus long terminal repeats (LTRs) that are able to exert strong promoter and enhancer activity driving not only the expression of the transgene carried by the vector, but also that of genes neighboring the insertion site. Assessing safety of integrating viral vectors for future clinical use is therefore of paramount importance. In preparation for gene therapy approaches for the Wiskott-Aldrich syndrome (WAS), we used an in vitro assay of murine bone marrow (BM) cell immortalization to compare the consequences of transduction by four different kinds of viral vectors, including a full-length LTR Moloney leukemia virus (MLV), a self-inactivating MLV carrying a 3' LTR deleted of the viral enhancer region (SIN), a lentivirus (LV), and a foamy virus (FV) construct. All vectors carried EGFP under the control of a ubiquitously acting chromatin opening element (UCOE) or the WAS endogenous promoter (WASp). In this assay, BM cells are harvested from C57BL6 mice, exposed to retroviral supernatants and cultured long-term. Derived lines are considered immortalized based on their ability to continue to grow in vitro for more than 6 weeks in the presence of interleukin-3 and stem cell factor. To date, MLV and SIN transduction of 123 and 132 cultures, respectively, gave rise to 48 and 43 immortalized lines (39.0% and 32.6% immortalization rate). The difference in immortalization rate between MLV and SIN vectors was not statistically significant (Chi square: p=0.30). As expected, immortalized cells were negative/low for IgER, cKit and Sca1 expression, and positive to different degrees for expression of the myeloid markers CD11b/Mac1 and Ly6g/Gr1. Transduction of 114 and 62 cultures with LV and FV vectors, respectively, resulted in no immortalized lines. Real-time PCR was performed to evaluate transduction efficiency of bone marrow cells and immortalized lines. Integrated vector sequences in bone marrow cells transduced by LV and FV were detected in significantly higher quantities than in cells transduced with MLV and SIN vectors. However, expression of the EGFP transgene was markedly reduced in LV- and FV-transduced cells compared to cells exposed to MLV vectors (MFI: 14.0, 1.88, 93.2, respectively). These preliminary results confirm that gamma-retroviral gene transfer vectors are prone to causing immortalization of hematopoietic cells and suggest the vectors based on LV and FV backbones may be safer alternatives for WAS and other genetic disorders, provided that effective gene expression levels can be achieved in the biological model system under study.Table.Summary of immortalization results using MLV, SIN, LV and FV vectorsVirusMOITransduction efficiencyTransduction experiments% ImmortalizationMLV/UCOE/EGFP2067%5643MLV/WASp/EGFP2065%6736SIN/UCOE/EGFP532%7236SIN/WASp/EGFP537%6028LV/UCOE/EGFP1040%570LV/WASp/EGFP1049%570FV/UCOE/EGFP1027%280FV/WASp/EGFP1022%340negativeN.A.N.A.720 Disclosures: No relevant conflicts of interest to declare.

Hypersensitivity to mosquito bites (HMB) is a rare disease classified into chronic active EB Virus (EBV) infection (CAEBV), characterized by clonal expansion of EBV-infected NK cells. The immunological background of the disease has not been elucidated yet. In this report we extensively studied EBV infected NK cells of a patient with HMB in view of several aspects, including latency, usage of promoter Cp/Wp and Qp of EBNAs, and induction of CD8+ cytotoxic T lymphocytes (CTL) to peptide antigens in order to know the relation between latency of EBV infected NK cells and induction of CTL. Case report: A female patient aged 19 complained of skin symptoms after a mosquito bite. A blister developed at the bite site that subsequently transformed into ulcer. The patient also had general fever and liver dysfunction. Past medical history showed that she suffered from HMB when she was 7 years old. The titers of serum antibodies to EBV were as follows: viral capsid antigen (VCA) IgG, 1280X; IgA, 80X; IgM, 10X; EBNA, 20X; EA DR IgG, 160X and IgA, 10X. These data strongly indicated lytic type of EBV infection. Subset analysis of peripheral blood lymphocytes revealed CD3+ lymphocytes, 50.2%; CD4+, 34.2%; CD8+, 12.7%; CD19, 10.0% and CD56/16+, 22.6%. Real time polymerase chain analysis of her peripheral mononuclear cells showed markedly increased copy number of EBV genome (5 x 10^5 copies/μgDNA). Purification of each lymphocyte fraction by immunomagnetic beads and subsequent PCR analysis showed that EBV infected lymphocytes were NK cells. Latency and Cp and Qp of EBNA promoter usage analyses: In order to determine the latency of EBV infected NK cells RT-PCR was carried out. EBNA1, EBNA2, LMP1, LMP2A, and EBER1 were positive and BZLF was negative. These results indicated that EBV infection in NK cells is associated with type III latency. RT-PCR analyses confirmed that both promoters Cp/Wp and Qp were involved in this disease. Through bisulfite PCR analysis, eighty four % of Cp was found to be methylated, on the other hand, only 6% of Qp was methylated. These methylation patterns were similar to those of hemophagocytic syndrome with latency III, also known in a few patients with CAEBV. Detection and expansion of EBV specific CD8+ CTL: We used HLA-A24 restricted BRLF1, EBNA3A, EBNA3B and LMP2 tetramers for quantification of specific CTL and we found 0.48% of BRLF1 and 0.15% of EBNA3 peptide-specific CTL among CD8+ cells. These cells could be expanded to 6.6% for BRLF1 and 0.22% for EBNA3A peptide-specific CTL after stimulation with an autologous lymphoblastoid cell line (LCL) for 10 days and then with LCL and IL-2 for 7 days. Conclusion: In this study we reported a long-term survivor of HMB with EBV infected NK cell proliferation. Promoter usage of EBNA genes and their methylation patterns might be important to determine latency and host immune responses against EBV infected cells.