CMV-specific T cells generated from naïve T cells recognize atypical epitopes and may be protective in vivo

Adoptive transfer of cytomegalovirus (CMV)-specific T cells derived from adult seropositive donors can effectively restore antiviral immunity after transplantation. However, CMV-seronegative donors lack CMV-specific memory T cells, which restricts the availability of virus-specific T cells for immunoprophylaxis. We demonstrate the feasibility of deriving CMV-specific T cells from naïve cells for T cell therapy. Naïve T cells primed to recognize CMV were restricted to different, atypical epitopes than T cells derived from CMV-seropositive individuals; however, these two cell populations had similar avidities. CMV-seropositive individuals also had T cells recognizing these atypical epitopes, but these cells had a lower avidity than those derived from the seronegative subjects, which suggests that high-avidity T cells to these epitopes may be lost over time. Indeed, recipients of cord blood (CB) grafts who did not develop CMV were found by clonotypic analysis to have T cells recognizing atypical CMVpp65 epitopes. Therefore, we examined unmanipulated CB units and found that T cells with T cell receptors restricted by atypical epitopes were the most common, which may explain why these T cells expanded. When infused to recipients, naïve donor-derived virus-specific T cells that recognized atypical epitopes were associated with prolonged periods of CMV-free survival and complete remission. These data suggest that naïve-derived T cells from seronegative patients may be an additional source of cells for CMV immunoprophylaxis.

Abstract IA22: Immunotherapy with virus-specific T cells

Epstein-Barr virus (EBV) reactivation post allogeneic hematopoietic stem cell transplantation (HSCT) can lead to the outgrowth of EBV-infected B cells and the development of post-transplant lymphoproliferative disease (EBV-PTLD). Since 1993 our group has used adoptive transfer of in vitro expanded EBV-specific T cells as a means to prevent or treat these EBV-driven lymphomas. In a series of Phase I and II clinical trials we have assessed the safety and clinical benefit associated with these transferred cells in allogeneic HSCT recipients. The T cell products infused were generated using 3 different manufacturing methodologies - [(i) EBV-transformed lymphoblastoid cell lines (EBV-LCLs) (~12 weeks manufacturing time), (ii) plasmid-nucloefected dendritic cells (DCs) (17 day manufacturing) and (iii) direct stimulation of PBMCs using overlapping peptide libraries (10 day manufacturing)] and were administered to either prevent (n=162) or treat (n=47) EBV reactivation/disease in a total of 209 allogeneic HSCT recipients ranging in age from 6 months to 63 years. Of 162 patients infused prophylactically only 1 (0.6%) developed EBV-PTLD, which occurred following the administration of steroids 3 weeks-post VST infusion. However, this patient responded to a second VST infusion after the steroids. 31 of 36 (86%) patients with elevated viral load (n=21) or biopsy-proven/probable LPD (n=15) achieved durable complete remissions and the infused cells persisted long term as demonstrated in 26 patients who received gene-marked VSTs that were detectable for up to 9 years post-infusion.

To extend the approach to additional viruses we initially developed methodology for using genetically modified antigen presenting cells approach to generate VSTs from donor peripheral blood that target CMV, EBV and adenovirus and showed that adoptively transferred donor-derived VSTs can reconstitute antiviral immunity to all three viruses and effectively treat established infections. However, the time taken to prepare patient-specific products and the lack of virus-specific memory T cells in cord blood and seronegative donors restricts application. More recently we have evaluated whether T-cell lines manufactured using overlapping peptide pools and extended the specificity to include HHV6 and BK. When administered to 11 recipients of allogeneic transplants, 8 of whom had up to four active infections with the targeted viruses, these VSTs proved safe in all subjects and produced an overall 94% virological and clinical response rate that was sustained long-term.

Another means of avoiding growing CTLs for individual patients is to bank lines that are then available as an off the shelf product of most closely HLA-matched allogeneic cytotoxic T lymphocyte lines. We evaluated this strategy in a multicenter study through the NHLBI Specialized Centers for Cell-Based Therapy (SCCT) program in HSCT recipients who had viral reactivation or infection refractory to standard therapy. The overall cumulative incidence of first CR/PR in 50 patients based on viral load by day 42 was 74.0% (73.9% for CMV, 66.7% for EBV and 77.8% for adenovirus). In a follow up study using the peptide induced VSTs that recognize 5 viruses, based on viral load measurements by quantitative PCR a single VST infusion successfully controlled active infections in 19/21 evaluable patients. These results demonstrate the feasibility and safety of 3rd party multivirus-directed VSTs, generated by direct stimulation of PBMCs with synthetic peptides and administered as an off the shelf product.

Citation Format: Helen E. Heslop, Ifigenia Tzannou, Bilal Omer, Malcolm K. Brenner, Ann M. Leen, Cliona M. Rooney. Immunotherapy with virus-specific T cells. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr IA22.

Anti-Tumor Effects after Adoptive Transfer of IL-12 Transposon-Modified Murine Splenocytes in the OT-I-Melanoma Mouse Model

Adoptive transfer of gene modified T cells provides possible immunotherapy for patients with cancers refractory to other treatments. We have previously used the non-viral piggyBac transposon system to gene modify human T cells for potential immunotherapy. However, these previous studies utilized adoptive transfer of modified human T cells to target cancer xenografts in highly immunodeficient (NOD-SCID) mice that do not recapitulate an intact immune system. Currently, only viral vectors have shown efficacy in permanently gene-modifying mouse T cells for immunotherapy applications. Therefore, we sought to determine if piggyBac could effectively gene modify mouse T cells to target cancer cells in a mouse cancer model. We first demonstrated that we could gene modify cells to express murine interleukin-12 (p35/p40 mIL-12), a transgene with proven efficacy in melanoma immunotherapy. The OT-I melanoma mouse model provides a well-established T cell mediated immune response to ovalbumin (OVA) positive B16 melanoma cells. B16/OVA melanoma cells were implanted in wild type C57Bl6 mice. Mouse splenocytes were isolated from C57Bl6 OT-I mice and were gene modified using piggyBac to express luciferase. Adoptive transfer of luciferase-modified OT-I splenocytes demonstrated homing to B16/OVA melanoma tumors in vivo. We next gene-modified OT-I cells to express mIL-12. Adoptive transfer of mIL-12-modified mouse OT-I splenocytes delayed B16/OVA melanoma tumor growth in vivo compared to control OT-I splenocytes and improved mouse survival. Our results demonstrate that the piggyBac transposon system can be used to gene modify splenocytes and mouse T cells for evaluating adoptive immunotherapy strategies in immunocompetent mouse tumor models that may more directly mimic immunotherapy applications in humans.

Abstract B17: Banked Epstein-Barr virus specific T-cells for treatment of EBV+ lymphoma

Standard intensive chemotherapy and hematopoietic stem cell transplant usually benefit patients with Hodgkin (HL) and Non-Hodgkin Lymphoma (NHL), but for those with T or NK-T NHL or who relapse, the prognosis is less favorable. Furthermore, substantially increased morbidity and mortality from the complications of aggressive chemotherapies is evident for many years, even in patients who are cured of their original disease. About 30% of all lymphomas carry the Epstein-Barr virus (EBV) genome and express 4 viral proteins (EBNA1, LMP1, LMP2 ± BARF1), a pattern termed Type 2 latency. T-cells specific for these antigens circulate with low frequency in healthy donors, but are rendered anergic in patients by their immunosuppressive tumors. We have previously shown that potent in vitro T-cell stimulation can reverse anergy. Virus-specific T-cells specific for the EBV antigens (EBVSTs) have produced complete remissions in 60% of patients with multiply relapsed EBV+ HL and NHL. Though successful, our earlier method was labor intensive and prolonged, and the requirement for live EBV and adenoviral (Ad) vectors increased costs and regulatory complexity. We have overcome these problems by replacing Ad vectors with peptide mixtures (pepmixes) and the EBV lymphoblastoid cell lines (LCL) with professional antigen presenting cells to provide costimulation. We therefore seek to produce a safe and effective immunotherapy for relapsed, refractory EBV+ lymphoma that can be implemented rapidly by creating and characterizing a bank of T-cells targeted to the four EBV antigens expressed in EBV+ HL and NHL. Thus far, we have successfully screened 30 eligible blood donors and manufactured several EBVST lines with specificity for the four Type 2 EBV latency proteins using the rapid pep-mix method. This strategy robustly and rapidly produces higher frequencies of EBV-specific T cells that kill LCLs that naturally express viral antigens, showing that the pepmixes are not recruiting low-avidity T-cells. T-cell lines will be selected and infused based on their ability to recognize EBV antigens through HLA alleles shared with the recipient. The in vivo expansion and persistence of the infused EBVSTs will be evaluated together with their ability to reactivate endogenous T-cells specific for non-viral tumor antigens. We hypothesize that allogeneic, partially HLA-matched T-cells can produce benefit in patients with lymphoma both by direct tumor cell killing and by creating a proinflammatory tumor microenvironment that reactivates and restores effective endogenous tumor-specific T-cells.

Citation Format: Rayne H. Rouce, Serena K. Perna, Gayatri Vyas, Sandhya Sharma, Natalia Lapteva, Ann Leen, Cliona M. Rooney, Helen E. Heslop. Banked Epstein-Barr virus specific T-cells for treatment of EBV+ lymphoma. [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy: A New Chapter; December 1-4, 2014; Orlando, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2015;3(10 Suppl):Abstract nr B17.

Abstract 4703: Improving CAR T cell function by reversing the immunosuppressive tumor microenvironment of pancreatic cancer

Adoptive transfer of T cells redirected to tumor-associated antigens (TAAs) by expression of chimeric antigen receptors (CARs) can produce tumor responses, even in patients with resistant malignancies. To target pancreatic ductal adenocarcinoma (PDAC), we generated T cells expressing a CAR directed to the TAA prostate stem cell antigen (PSCA). T cells expressing this CAR were able to kill PSCA(+) tumor cell lines CAPAN1 and K562-PSCA but not PSCA(-)293T cells (74±4%, 73±6% and 9±3% specific lysis, respectively, 10:1 E:T, n = 3). Although these CAR-T cells had potent anti-tumor activity, pancreatic tumors employ immune evasion strategies such as the production of inhibitory cytokines, which limit in vivo CAR-T cell persistence and effector function. Indeed, when we examined the serum of patients with pancreatic cancer (n = 8) we found the levels of the immunosuppressive cytokine IL4 to be elevated relative to patients with benign pancreatic disorders or normal healthy controls (14.25±19.48 pg/mL vs 7.28±9.03 vs 1.13±1.42 pg/mL). Thus, to protect our CAR-PSCA T cells from the negative influences of IL-4, we generated a chimeric cytokine receptor in which the IL4 receptor exodomain was fused to the IL7 receptor endodomain (IL4/7 ChR). Transgenic expression of this molecule in CAR-PSCA T cells should invert the inhibitory effects of tumor-derived IL4 and instead promote the proliferation of the effector CAR T cells. In preliminary experiments we successfully co-expressed both CAR-PSCA and IL4/7 ChR (47.5±12.3% double-positive cells, n = 4) on primary T cells. These T cells retained their tumor-specific activity (80±8% specific lysis against CAPAN1, 10:1 E:T, n = 3) and when cultured in conditions that mimic the tumor milieu (IL4 12.5 ng/ml), CAR-PSCA 4/7R ChR-modified T cells continued to expand (increase from 2×10e6 cells on day 0 to 5.53±8.46×10e10 cells on day 28), unlike unmodified CAR-PSCA T cells which plateaued at 3.84±5.43×10e8 cells (n = 4). Indeed, in the presence of IL4, transgenic cells had a selective advantage (comprising 44.8±11.0% of the population on day 0 and 87.6±10.0% on day 28; n = 4). However, even after prolonged cytokine exposure these T cells remained both antigen- and cytokine-dependent. In conclusion, CAR-PSCA 4/7 ChR-modified tumor-specific T cells can effectively target pancreatic cancer cells and should be equipped to expand, persist, and retain their cytotoxic function even in the presence of high levels of IL4 in the tumor microenvironment.

Citation Format: Somala Mohammed, Sujita Sukumaran, Pradip Bajgain, Usanarat Anurathapan, Helen E. Heslop, Cliona M. Rooney, Malcolm K. Brenner, Ann M. Leen, Juan F. Vera. Improving CAR T cell function by reversing the immunosuppressive tumor microenvironment of pancreatic cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4703. doi:10.1158/1538-7445.AM2015-4703

Antigen-specific T cell therapies for cancer

Adoptively transferred antigen-specific T cells that recognize tumor antigens through their native receptors have many potential benefits as treatment for virus-associated diseases and malignancies, due to their ability to selectively recognize tumor antigens, expand and persist to provide long-term protection. Infusions of T cells targeting Epstein-Barr virus (EBV) antigens have shown encouraging response rates in patients with post-transplant lymphoproliferative disease as well as EBV-positive lymphomas and nasopharyngeal cancer, although a recent study also showed that human papilloma virus-reactive T cells can induce complete regression of metastatic cervical cancer. This strategy is also being evaluated to target non-viral tumor-associated antigens. Targeting these less immunogenic antigens is more challenging, as tumor antigens are generally weak, and high avidity T cells specific for self-antigens are deleted in the thymus, but tumor responses have been reported. Current research focusses on defining factors that promote in vivo persistence of transferred cells and ameliorate the immunosuppressive microenvironment. To this end, investigators are evaluating the effects of combining adoptive transfer of antigen-specific T cells with other immunotherapy moieties such as checkpoint inhibitors. Genetic modification of infused T cells may also be used to overcome tumor evasion mechanisms, and vaccines may be used to promote in vivo proliferation.

Abstract B63: Improving CAR T cell function by reversing the immunosuppressive tumor environment of pancreatic cancer

Background: Adoptive transfer of T cells redirected to tumor-associated antigens (TAAs) by expression of chimeric antigen receptors (CARs) can produce tumor responses, even in patients with resistant malignancies. Although these CAR-T cells have potent anti-tumor activity in vitro and in vivo, pancreatic tumors employ immune evasion mechanisms, such as the production of inhibitory cytokines, which limit in vivo CAR-T cell persistence and effector function.

Methods: To target pancreatic ductal adenocarcinoma (PDAC), we generated T cells expressing a CAR directed to the TAA prostate stem cell antigen (PSCA). We also engineered a chimeric cytokine receptor in which the IL4 receptor exodomain was fused to the IL7 receptor endodomain (IL4/7 ChR). Expansion and selection profiles and short- and long-term anti-tumor activity of these transgenic T cells were assessed.

Results: T cells expressing CAR-PSCA kill PSCA(+) tumor cell lines CAPAN1 and K562-PSCA but not PSCA(-) targets, such as 293T (74±4%, 73±6% and 9±3% specific lysis, respectively, 10:1 E:T, n=3). Although these CAR-T cells had potent anti-tumor activity in vitro and in vivo, pancreatic tumors employ immune evasion mechanisms, such as the production of inhibitory cytokines, which limit in vivo CAR-T cell persistence and effector function. Indeed, when the serum of patients with pancreatic cancer (n=8) was examined, we found the levels of the immunosuppressive cytokine IL4 to be elevated relative to patients with benign pancreatic disorders or normal healthy controls (14.25±19.48 pg/mL vs 7.28±9.03 vs 1.13±1.42 pg/mL). Thus, to protect the CAR-PSCA T cells from the negative influences of IL-4, we generated a chimeric cytokine receptor in which the IL4 receptor exodomain was fused to the IL7 receptor endodomain (IL4/7 ChR). Transgenic expression of this molecule in CAR-PSCA T cells should invert the inhibitory effects of tumor-derived IL4 and instead promote the proliferation of the effector CAR T cells. In preliminary experiments we successfully co-expressed both CAR-PSCA and IL4/7 ChR (47.5±12.3% double-positive cells, n=4) on primary T cells. These T cells retained their tumor-specific activity (80±8% specific lysis against CAPAN1, 10:1 E:T, n=3) and when cultured in conditions that mimic the tumor milieu (IL4 12.5 ng/ml), CAR-PSCA 4/7R ChR-modified T cells continued to expand unlike unmodified CAR-PSCA T cells (from 2x106 cells on day 0 to 5.53x1010±8.46x1010 cells (CAR-PSCA 4/7R ChR) on day 28, in comparison to CAR-PSCA T cells that reached only 3.84x108±5.43x108 cells, n=4). Indeed, in the presence of IL4, transgenic cells had a selective advantage (comprising 44.8±11.0% of the population on day 0 and 87.6±10.0% on day 28, n=4), but even after prolonged cytokine exposure these T cells remained both antigen- and cytokine-dependent.

Conclusions: CAR-PSCA 4/7 ChR-modified tumor-specific T cells can effectively target pancreatic cancer cells and should be equipped to expand, persist, and retain their cytotoxic function even in the presence of high levels of IL4 in the tumor microenvironment.

Citation Format: Somala Mohammed, Sujita Sukumaran, Usanarat Anurathapan, Pradip Bajgain, Helen E. Heslop, Cliona M. Rooney, Malcolm K. Brenner, Ann M. Leen, Juan F. Vera. Improving CAR T cell function by reversing the immunosuppressive tumor environment of pancreatic cancer. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Innovations in Research and Treatment; May 18-21, 2014; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2015;75(13 Suppl):Abstract nr B63.

Peripheral blood-derived virus-specific memory stem T cells mature to functional effector memory subsets with self-renewal potency

Memory T cells expressing stem cell-like properties have been described recently. The capacity of self-renewal and differentiation into various memory/effector subsets make them attractive for adoptive T cell therapy to combat severe virus infections and tumors. The very few reports on human memory stem T cells (T(SCM)) are restricted to analyses on polyclonal T cells, but extensive data on Ag-specific T(SCM )are missing. This might be due to their very low frequency limiting their enrichment and characterization. In this article, we provide functional and phenotypic data on human viral-specific T(SCM), defined as CD8(+)CD45RA(+)CCR7(+)CD127(+)CD95(+). Whereas <1% of total T cells express the T(SCM) phenotype, human CMV-specific T(SCM) can be detected at frequencies similar to those seen in other subsets, resulting in ∼ 1 /10,000 human CMV-specific T(SCM). A new virus-specific expansion protocol of sort-purified T(SCM) reveals both upregulation of various T cell subset markers and preservation of their stem cell phenotype in a significant proportion, indicating both self-renewal and differentiation potency of virus-specific T cells sharing their TCR repertoire. Furthermore, we describe a simplified culture protocol that allows fast expansion of virus-specific T(SCM) starting from a mixed naive T/T(SCM) pool of PBLs. Due to the clinical-grade compatibility, this might be the basis for novel cell therapeutic options in life-threatening courses of viral and tumor disease.

Human Epidermal Growth Factor Receptor 2 (HER2) -Specific Chimeric Antigen Receptor-Modified T Cells for the Immunotherapy of HER2-Positive Sarcoma

PURPOSE

The outcome for patients with metastatic or recurrent sarcoma remains poor. Adoptive therapy with tumor-directed T cells is an attractive therapeutic option but has never been evaluated in sarcoma.

PATIENTS AND METHODS

We conducted a phase I/II clinical study in which patients with recurrent/refractory human epidermal growth factor receptor 2 (HER2) -positive sarcoma received escalating doses (1 × 10(4)/m(2) to 1 × 10(8)/m(2)) of T cells expressing an HER2-specific chimeric antigen receptor with a CD28.ζ signaling domain (HER2-CAR T cells).

RESULTS

We enrolled 19 patients with HER2-positive tumors (16 osteosarcomas, one Ewing sarcoma, one primitive neuroectodermal tumor, and one desmoplastic small round cell tumor). HER2-CAR T-cell infusions were well tolerated with no dose-limiting toxicity. At dose level 3 (1 × 10(5)/m(2)) and above, we detected HER2-CAR T cells 3 hours after infusion by quantitative polymerase chain reaction in 14 of 16 patients. HER2-CAR T cells persisted for at least 6 weeks in seven of the nine evaluable patients who received greater than 1 × 10(6)/m(2) HER2-CAR T cells (P = .005). HER2-CAR T cells were detected at tumor sites of two of two patients examined. Of 17 evaluable patients, four had stable disease for 12 weeks to 14 months. Three of these patients had their tumor removed, with one showing ≥ 90% necrosis. The median overall survival of all 19 infused patients was 10.3 months (range, 5.1 to 29.1 months).

CONCLUSION

This first evaluation of the safety and efficacy of HER2-CAR T cells in patients with cancer shows the cells can persist for 6 weeks without evident toxicities, setting the stage for studies that combine HER2-CAR T cells with other immunomodulatory approaches to enhance their expansion and persistence.

Activity of broad-spectrum T cells as treatment for AdV, EBV, CMV, BKV, and HHV6 infections after HSCT

It remains difficult to treat the multiplicity of distinct viral infections that afflict immunocompromised patients. Adoptive transfer of virus-specific T cells (VSTs) can be safe and effective, but such cells have been complex to prepare and limited in antiviral range. We now demonstrate the feasibility and clinical utility of rapidly generated single-culture VSTs that recognize 12 immunogenic antigens from five viruses (Epstein-Barr virus, adenovirus, cytomegalovirus, BK virus, and human herpesvirus 6) that frequently cause disease in immunocompromised patients. When administered to 11 recipients of allogeneic transplants, 8 of whom had up to four active infections with the targeted viruses, these VSTs proved safe in all subjects and produced an overall 94% virological and clinical response rate that was sustained long-term.

Early transduction produces highly functional chimeric antigen receptor-modified virus-specific T-cells with central memory markers: a Production Assistant for Cell Therapy (PACT) translational application

BACKGROUND

Virus-specific T-cells (VSTs) proliferate exponentially after adoptive transfer into hematopoietic stem cell transplant (HSCT) recipients, eliminate virus infections, then persist and provide long-term protection from viral disease. If VSTs behaved similarly when modified with tumor-specific chimeric antigen receptors (CARs), they should have potent anti-tumor activity. This theory was evaluated by Cruz et al. in a previous clinical trial with CD19.CAR-modified VSTs, but there was little apparent expansion of these cells in patients. In that study, VSTs were gene-modified on day 19 of culture and we hypothesized that by this time, sufficient T-cell differentiation may have occurred to limit the subsequent proliferative capacity of the transduced T-cells. To facilitate the clinical testing of this hypothesis in a project supported by the NHLBI-PACT mechanism, we developed and optimized a good manufacturing practices (GMP) compliant method for the early transduction of VSTs directed to Epstein-Barr virus (EBV), Adenovirus (AdV) and cytomegalovirus (CMV) using a CAR directed to the tumor-associated antigen disialoganglioside (GD2).

RESULTS

Ad-CMVpp65-transduced EBV-LCLs effectively stimulated VSTs directed to all three viruses (triVSTs). Transduction efficiency on day three was increased in the presence of cytokines and high-speed centrifugation of retroviral supernatant onto retronectin-coated plates, so that under optimal conditions up to 88% of tetramer-positive VSTs expressed the GD2.CAR. The average transduction efficiency of early-and late transduced VSTs was 55 ± 4% and 22 ± 5% respectively, and early-transduced VSTs maintained higher frequencies of T cells with central memory or intermediate memory phenotypes. Early-transduced VSTs also had higher proliferative capacity and produced higher levels of TH1 cytokines IL-2, TNF-α, IFN-γ, MIP-1α, MIP-1β and other cytokines in vitro.

CONCLUSIONS

We developed a rapid and GMP compliant method for the early transduction of multivirus-specific T-cells that allowed stable expression of high levels of a tumor directed CAR. Since a proportion of early-transduced CAR-VSTs had a central memory phenotype, they should expand and persist in vivo, simultaneously protecting against infection and targeting residual malignancy. This manufacturing strategy is currently under clinical investigation in patients receiving allogeneic HSCT for relapsed neuroblastoma and B-cell malignancies (NCT01460901 using a GD2.CAR and NCT00840853 using a CD19.CAR).

Evaluating the potential for undesired genomic effects of the piggyBac transposon system in human cells

Non-viral transposons have been used successfully for genetic modification of clinically relevant cells including embryonic stem, induced pluripotent stem, hematopoietic stem and primary human T cell types. However, there has been limited evaluation of undesired genomic effects when using transposons for human genome modification. The prevalence of piggyBac(PB)-like terminal repeat (TR) elements in the human genome raises concerns. We evaluated if there were undesired genomic effects of the PB transposon system to modify human cells. Expression of the transposase alone revealed no mobilization of endogenous PB-like sequences in the human genome and no increase in DNA double-strand breaks. The use of PB in a plasmid containing both transposase and transposon greatly increased the probability of transposase integration; however, using transposon and transposase from separate vectors circumvented this. Placing a eGFP transgene within transposon vector backbone allowed isolation of cells free from vector backbone DNA. We confirmed observable directional promoter activity within the 5'TR element of PB but found no significant enhancer effects from the transposon DNA sequence. Long-term culture of primary human cells modified with eGFP-transposons revealed no selective growth advantage of transposon-harboring cells. PB represents a promising vector system for genetic modification of human cells with limited undesired genomic effects.

Expanded cytotoxic T-cell lymphocytes target the latent HIV reservoir

Enhanced human immunodeficiency virus (HIV)-specific immunity may be required for HIV eradication. Administration of autologous, ex vivo expanded, virus-specific, cytotoxic T-lymphocytes derived from HIV-infected patients on suppressive antiretroviral therapy (HXTCs) are a powerful tool for proof-of-concept studies. Broadly specific, polyclonal HXTCs resulting from ex vivo expansion demonstrated improved control of autologous reservoir virus compared to bulk CD8(+) T cells in viral inhibition assays. Furthermore, patient-derived HXTCs were able to clear latently infected autologous resting CD4(+) T cells following exposure to the latency-reversing agent, vorinostat. HXTCs will be ideal reagents to administer with precise control in future in vivo studies in combination with latency-reversing agents.