ALBERT

Description: Key Points Human IgM memory B cells possess immunoregulatory properties analogous to transitional B cells. IL-10–producing B cells are deficient in cGVHD.

Description: Patients with CLL experience generalized immune suppression, susceptibility to infections and secondary malignancies that likely involve complex bi-directional interactions between leukemic cells, components of the tumor microenvironment and immune effectors. CLL cells are capable of secreting IL-10 and exhibit regulatory functions comparable to that of normal B10 cells, a regulatory B cell subset that suppresses effector T-cell function through STAT3-mediated production of IL-10. However, the underlying mechanisms governing IL-10 production by CLL cells are not fully understood. The chemokine CXCL12 is constitutively secreted by bone marrow stroma in CLL, and binds CXCR4 to direct chemotaxis, support tumor survival and activate various signaling pathways, including STAT3. Thus, we investigated if CXCL12 can enhance IL-10 production by activating the STAT3 pathway in CLL. Using peripheral blood mononuclear cells (PBMC) from 24 CLL patients who had not received therapy for ≥2 years, we showed that CXCL12 can enhance IL-10 production by CLL cells by activating S727-STAT3. This effect was CXCR4-mediated since blocking the CXCR4-CXCL12 interaction with a blocking antibody abolished CXCL12-induced IL-10 production. Addition of the STAT3 inhibitor curcubitacin to the culture also abrogated CXCL12-induced IL-10 production, confirming an important role for S727-STAT3 as a mediator of CXCL12-CXCR4-induced IL-10 production by CLL cells. We next determined if activation of the CXCR4-CXCL12-STAT3-IL10 pathway in CLL is important in mediating their immunoregulatory function. Culture of primary CLL withCXCL12 induced significantly more suppression of CD3+ T cell function, including TNF-α, IFN-γ and IL-2 production, and CD107a degranulation, compared to CD3+ T cells cultured with untreated CLL cells or with CXCL12 alone. The addition of IL-10 blocking antibody to the co-culture completely reversed T cell dysfunction, supporting an important for IL-10 in CLL-mediated T-cell suppression. IL-10 has been reported to induce T cell suppression through phosphorylation of Y705-STAT3.. Blocking IL-10 also prevented CLL-induced phosphorylation of Y705-STAT3 in T cells, confirming an important role for CLL-derived IL-10 in activation of Y705-STAT3 and induction of T cell dysfunction. Lenalidomide is an immune-modulatory drug with clinical efficacy in CLL and was recently reported to inhibit STAT3 phosphorylation. To investigate if lenalidomide can inhibit CXCL12-induced STAT3 phosphorylation, we treated CLL cells with lenalidomide and measured p-S727-STAT3 levels. Exposure of CLL cells to 10µM/ml lenalidomide prevented CXCL12-induced increase in p-S727-STAT3 and resulted in significant reduction in the IL-10 response by CLL cells. Lenalidomide also suppressed IL-10-induced Y705-STAT3 phosphorylation in healthy T cells, thus reversing CLL-induced T cell dysfunction. We next confirmed the in vivo relevance of our findings using PBMC cryopreserved from patients treated with lenalidomide monotherapy (NCT00535873). When compared to pretreatment samples, CLL cells from on-treatment samples produced less IL-10 and showed significantly improved T cell function. We thus conclude that the capacity of CLL to produce IL-10 is mediated by the CXCL12-CXCR4-STAT3 pathway and may contribute to immunodeficiency in patients. Lenalidomide can reverse CLL-induced immunosuppression through multiple mechanisms that involve abrogation of the CXCL12-CXCR4-S727STAT3-mediated IL-10 response by CLL B cells and prevention of IL-10-induced phosphorylation of Y705-STAT3 in T cells. Disclosures Estrov: incyte: Consultancy, Research Funding. Wierda:Glaxo-Smith-Kline Inc.: Research Funding; Celgene Corp.: Consultancy. Rezvani:Pharmacyclics: Research Funding.

Description: Natural killer (NK) cells are a major component of the innate immune system, possessing the ability to lyse their targets without the need for prior sensitization or specificity for antigen. Besides their classical role in providing potent antitumor and antiviral immunity, NK cells can reduce the risk of graft-versus-host disease (GVHD) by targeting host antigen-presenting cells, as well as activated alloreactive donor T cells, indicating that NK-mediated graft-versus-leukemia (GVL) responses may occur in the absence of GVHD. Although most groups have relied on autologous or adult peripheral blood donor-derived NK cells, we have studied umbilical CB as a potential source of NK cells because of their availability as an "off-the-shelf" frozen product and their potent preclinical activity against leukemia cells. To overcome the obstacle of limited numbers of NK cells in a single CB unit, we have established GMP-compliant conditions for the ex vivo expansion of clinically relevant doses of such cells. By using GMP grade K562-based artificial antigen-presenting cells (aAPCs), which express membrane-bound IL-21 (clone 9.mbIL21), to numerically expand highly functional and mature CB-derived NK cells. To further enhance the GVL effect independent of KIR-ligand mismatch, we have genetically modified human CB-derived NK cells with a retroviral vector, CAR19-CD28-zeta-2A-IL15 (CAR19/IL15), which incorporates the genes for CAR-CD19, IL-15 to enhance proliferation and survival, and the inducible caspase-9 molecule. CB-NK cells could be stably transduced with CAR19/IL15, proliferated efficiently in vitro and maintained superior effector function against CD19-expressing leukemia cell lines and primary CLL cells. Moreover, the effector functions of both NK-CAR and nontransduced NK cells against K562 were comparable, indicating that the genetic modification of CB-NK cells does not alter their intrinsic cytotoxicity against NK-sensitive targets. Because of concerns over autonomous, uncontrolled NK cell growth due to autocrine production of IL15, we also incorporated into our construct a suicide gene based on the inducible caspase-9 (IC9) gene. The addition of as little as 10 nM of the small molecule dimerizer CID AP20187 to cultures of iC9/CAR19/IL15+ NK cells induced apoptosis/necrosis of 〉60% of transgenic cells within 4 hours as assessed by annexin-V-7AAD staining. The infusion of CAR.CD19.IL15-transduced CB-NK cells into a NOD-SCID-gamma null model of lymphoblastic lymphoma (Raji model) resulted in impressive anti-tumor responses (Fig. 1). Moreover, adoptively infused CAR-transduced CB NK persisted for up to 70 days post-infusion (Fig. 2), supporting our hypothesis that IL-15 enhances the proliferation and survival of the engineered CB-NK cells. Based on these promising data, we now propose to manufacture a GMP-grade CAR19-CD28-zeta-2A-IL15 vector for a phase 1 dose escalation trial in patients with high risk B-cell leukemia. Disclosures Wierda: Celgene Corp.: Consultancy; Glaxo-Smith-Kline Inc.: Research Funding. Rezvani:Pharmacyclics: Research Funding.

Description: Adoptive immunotherapy with ex vivo expanded virus-specific T-cell lines from transplant donors has emerged as a potentially curative approach for the treatment of drug-refractory viral infections complicating allogeneic hematopoietic cell transplants (HSCT). In these studies, viral-specific T cells are generated in compliance with current good manufacturing practice (cGMP) following repeated rounds of antigen-driven stimulation over a number of weeks. Such protocols are logistically and technically demanding, requiring access to specialized GMP units and are difficult to apply in urgent clinical settings. The cytokine-capture (gamma-catch) procedure is a fast and simple method that takes

Description: Natural killer (NK) cells are the first lymphocyte population to reconstitute following allogeneic hematopoietic stem cell transplantation (HSCT) and are key players in immune defense against viral infections and malignant transformation. NK cell numbers generally recover within the first month post-transplant, but the acquisition of mature NK cell phenotype and full functional competency can take over 6 months and is influenced by various host and donor factors. Cytomegalovirus (CMV) infection has been shown to modulate NK cell maturation after HSCT. The diversity of the NK cell repertoire is dictated by a variety of combinatorially expressed activating and inhibitory receptors that dictate the NK activation status. Moreover, whereas the expression of inhibitory receptors is primarily genetically determined, environmental factors such as viral infections influence the expression of activating receptors to a great extent.. We propose that assessment of diversity could provide a different perspective for the evaluation of the NK cell compartment after HSCT, since it is a quantitative measure that takes into account both the number and evenness of the different NK subpopulations. To better understand the factors that influence NK cell recovery after cord blood (CB) transplant (CBT) and specifically the influence of cytomegalovirus (CMV) infection on NK cell maturity, we used 40-parameter mass cytometry (CyTOF) to interrogate the NK cell repertoire. A panel including 37 monoclonal antibodies was designed to recognize NK cells lineage markers and receptors as well as intracellular markers such as transcription factors and adaptor proteins. We first evaluated and compared the diversity of NK cells in 10 CB units and peripheral blood (PB) from 20 healthy donors. We then examined the diversity of NK cells before and after CBT in 22 serially collected blood samples from in 10 CBT recipients. NK cell diversity was significantly lower in CB (mean 574, range 417-891) compared to PB samples from healthy donors (mean 3792, range 1284-5079; P=0.001), indicating less diversification within the naive CB NK compartment. After CBT, NK cell diversity was lower at earlier time point (Day30) (mean 1129, range 428-1768) compared to PB from healthy donors; P=0.01. The diversity of NK cells increased gradually over time following CBT (Day 30 mean 1129 range 428-1768; Day 60, mean 1185, range 515-1864; 4 months, mean 1711 range 597-2640). We also compared the diversity of NK cells in the PB of healthy CMV seronegative (n=10) and seropositive adult donors (n=10). The diversity of NK cells was higher in CMV seropositive vs. CMV seronegative healthy donors (3887 vs 2473; P=0.04). This difference in NK diversity was even more pronounced within the KIR positive (mean 1701, range, 981-2152) compared to the KIR negative subset (mean 551, range 456-647; P=0.02), indicating that CMV infection increases the richness of mature NK cells. In keeping with these findings, CMV infection after CBT was associated with a significantly greater diversity of NK cells, especially within the KIR positive compartment (mean 604, range 207-1035) compared to the KIR negative subset (mean 283, 257-457; P=0.025). However, in CMV negative patients, we found no difference in diversity within the KIR positive and negative subsets (mean 1120 vs. 1366; P=0.28). Taken together, these data suggest that NK cell diversity reflects NK cells differentiation and maturation, and that CMV shapes NK cell diversity, especially within the KIR positive compartment. To further understand how CMV influences NK cells diversity, we examined the top 15 NK cell subsets and their distribution at multiple timepoints before and after CMV reactivation post-CBT. CMV infection post-CBT was associated with a significant change in the distribution of NK subsets within the KIR positive population, with the top 15 subsets prior to CMV reactivation being mostly replaced by the emergence of new subsets. In contrast, the top 15 subsets within the KIR negative NK population remained stable. These data suggest that CMV drives NK cell maturation by differentiating KIR positive NK cells. In summary, we used high-dimensional single-cell data to evaluate NK cell reconstitution following HSCT. These data can help us better understand the biology of NK cell recovery after HSCT and discover the functional significance of NK cell diversity in the setting of viral infections. Disclosures Champlin: Ziopharm Oncology: Equity Ownership, Patents & Royalties; Intrexon: Equity Ownership, Patents & Royalties.

Description: Clinical manifestations of BKV hemorrhagic cystits (HC) following hematopoietic stem cell transplantation (HSCT) range from microscopic hematuria to bladder hemorrhage and renal failure. Pharmacologic treatments for HC have limited efficacy and significant adverse effects. Here, we report the preliminary analysis of adoptive immunotherapy with most closely HLA-matched third party BKV-specific CTL lines (BKV-CTLs) generated by ex vivo expansion.We generated a bank of BKV-specific CTLs from 17 virus-immune healthy donors (mean age, 55; range, 25 to 75 years). Mononuclear cells enriched from donor buffy coats were stimulated with BKV peptide mix from capsid proteins VP1, VP2, VP3, large T antigen (LT) and small T antigen (ST) in the presence of IL-2, IL-7 and IL-15 for 14 days. At the end of culture, the cells were harvested and cryopreserved until use. Patients with symptomatic BKV cystitis after HSCT for leukemia or lymphoma were eligible. Patients with acute GVHD grades II-IV, those receiving 〉0.5 mg/kg systemic steroids/day or on treatment with cidofovir or leflunomide were excluded. A search for the most closely HLA-matched donor was initiated through the MDACC cell therapy donor bank. BKV-specific T cells were infused intravenously directly after thawing. Patients could receive up to 2 infusions. BKV PCR and clinical symptoms were monitored every week for 28 days after infusion. Complete response was defined as complete resolution of symptoms and gross hematuria and partial response (PR) as decrease in grade of HC from 3 (urinary blood clots) or 4 (red cell transfusion requirement/renal impairment) to 2 (macroscopic hematuria) or 3 respectively. Patients with stable disease (SD) or progression had insufficient changes to qualify as PR or had an increase in symptoms or worsening hematuria, respectively. To date, 10 patients (2 HLA-matched related, 5 HLA-matched unrelated and 3 haploidentical HSCT recipients) have received BKV-CTLs for BK cystitis. The median number of BKV-specific CD3+IFN-gamma+ and CD3+IL-2+ T-cells infused was 10e3/kg and 4.8e3/kg, respectively. The ratio of BKV-specific CD4+/CD8+ T cells in the infused product was 7.8 (range 3.1-22.1). There were no infusion-related adverse effects. Based on end-organ response, BKV-CTLs controlled infection in 9/9 evaluable patients with BKV cystitis (4 CRs and 5 PRs)- one patient was not evaluable due to disease relapse, sepsis and anuria. All patients achieved a response by day 14 post-infusion. Two of 5 patients with PR received a second BK CTL infusion from a different donor. One had an initial PR to the first CTL infusion but symptoms progressed after 6 weeks. A second infusion resulted in a PR with reduction in BKV PCR and symptoms. The other patient achieved CR within 28 days of the second infusion. The time to second infusion was 6 and 3 weeks, respectively. The response in all patients was sustained. Following infusion, we detected high frequencies of polyfunctional BKV-specific CD4+ and CD8+ T-cells, capable of producing IL-2, IFN-gamma and TNF-alpha in response to ex vivo stimulation with BKV peptide pools (VP1, VP2, VP3, LT and ST). The response was mainly CD4+ T cell dominant, reflecting the composition of the infused BKV T cell line and consistent with previous reports of a predominantly CD4-mediated T cell response in BKV infection. De novo grade 2-4 acute graft versus host disease (aGVHD) occurred in 1/10 patients. The patient developed grade 2 duodenal GVHD 14 days following infusion. A second patient had recurrence of a prior skin GVHD and developed grade 2 aGVHD 9 days after infusion. Both were successfully treated with 1mg/kg/day systemic steroids. This analysis demonstrates the safety, feasibility and efficacy of administration of most closely HLA-matched BKV CTLs for the treatment of BKV cystitis in HSCT patients. The response rate of 100% in the first 10 patients treated with BKV CTLs is promising. Disclosures Ciurea: Cyto-Sen Therapeutics: Equity Ownership; Spectrum Pharmaceuticals: Other: Advisory Board.

Description: INTRODUCTION: The Bruton's tyrosine kinase (BTK) inhibitor ibrutinib is a covalent inhibitor of BTK, a member of the B-cell receptor (BCR) signaling pathway and induces objective clinical responses in the majority of CLL patients (Byrd et al., NEJM 2013). Interestingly this drug also inhibits L2-inducible T cell kinase (ITK), an essential enzyme for the development and effector function of Th2 and Th17 cells, and has been shown to shift the balance towards a Th1 response. The purpose of the study was to determine how ibrutinib influences the Th1/Th17/T regulatory cell response, expression of immune checkpoint blockade molecules on T cells and the functional pathogen-specific T cell recovery. METHODS: Here we present data from a clinical trial of ibrutinib versus ibrutinib + rituximab in previously treated patients (NCT02007044). Peripheral blood and serum were collected at baseline, 3 months and 6 months during therapy. Multicolor flow cytometry was used to characterize B cell subsets, T-cell subsets, expression of PD-1, PD-L1 and CTLA-4 and T-cell effector function. For statistical analysis of pre-treatment to on-treatment measurements the paired Student t-test was used. RESULTS: Here we report on the phenotypic and functional recovery of immune subsets in 41 CLL patients treated with ibrutinib (n=17) or ibrutinib + rituximab (n=25). Both PD-1 and PD-L1 were expressed at high levels on CLL cells. Interestingly, by 3 and 6 months, there was a significant decrease in PD-1 expression from a pre-treatment median of 15% to 4% (at 3 months) and 3% (at 6 months; P

Description: Chimeric antigen receptors to redirect T cell specificity against tumor antigens have shown remarkable clinical responses against CD19+ malignancies. However, the manufacture of an engineered autologous T cell product is expensive and cumbersome. Natural killer (NK) cells provide an alternative source of immune effectors for the treatment of cancer. NK cell cytolytic function can be directed towards specific targets by exploiting their ability to mediate antibody-dependent cellular cytotoxicity (ADCC) through the NK cell Fc receptor, CD16 (FcγRIIIa). AFM13 is a tetravalent bispecific antibody construct based on Affimed's ROCK™ platform. AFM13 is bispecific for CD30 and CD16A, designed for the treatment of CD30 expressing malignancies. It binds CD16A on the surface of NK cells, thus activating and recruiting them to CD30 expressing tumor cells and mediating subsequent tumor cell killing. Since autologous NK effector function is impaired in many patients with malignancies, we propose to overcome this by the use of allogeneic NK cells in combination with AFM13. Cord blood (CB) is a readily available ("off-the-shelf") source of allogeneic NK cells that can be expanded to large, highly functional therapeutic doses. The feasibility and safety of therapy with allogeneic ex vivo expanded CB-derived NK cells have been shown by our group and others. In this study, we hypothesized that we can redirect the specificity of NK cells against CD30+ malignancies by preloading ex vivo activated and expanded CB-derived NK cells with AFM13 prior to adoptive infusion. Briefly, mononuclear cells were isolated from fresh or frozen CB units by ficoll density gradient centrifugation. CD56+ NK cells were cultured with rhIL-12, rhIL-18 and rhIL-15 for 16 hrs, followed by ex vivo expansion with rhIL-2 and irradiated (100 Gy) K562-based feeder cells expressing membrane-bound IL-21 and CD137-ligand (2:1 feeder cell:NK ratio). After 14 days, NK cells were loaded with serial dilutions of AFM13 (0.1, 1, 10 and 100 mg/ml). After washing twice with PBS, we tested the effector function of AFM13-loaded NK-cells (AFM13-NK) compared to expanded CB-NK cells without AFM13 against Karpas-299 (CD30 positive) and Daudi (CD30 negative) lymphoma cell lines by 51Cr release and intracellular cytokine production assays. AFM13-NK cells killed Karpas-299 cells more effectively at all effector:target ratios tested than unloaded NK cells (Figure 1) and produced statistically more INFγ and CD107a (P=0.0034; P=0.0031 respectively, n=4). In contrast, AFM13-NK cells and unloaded NK cells exerted similar cytotoxicity against Daudi cells. Next, we established the optimal concentration of AFM13 for loading (determined to be 100 μg/ml) and the optimal incubation time to obtain maximal activity (1 h) in a series of in vitro experiments. We also confirmed that the activity of AFM13-NK cells against Karpas-299 cells remains stable for at least 72h post-wash (Figure 2). Additionally, we characterized the phenotype of AFM13-NK vs. unloaded NK cells by flow cytometry using monoclonal antibodies against 22 markers, including markers of activation, inhibitory receptors, exhaustion markers and transcription factors. Compared to unloaded NK cells, AFM13-NK cells expressed higher levels of CD25, CD69, TRAIL, NKp44, granzyme B and CD57, consistent with an activated phenotype. We next tested the in vivo anti-tumor efficacy of AFM13-NK cells in an immunodeficient mouse model of FFluc-Karpas-299. Briefly, six groups of NOD/SCID/IL2Rγc null mice (n=5 per group) were transplanted by tail-vein injection with 1 x 10e5 FFluc-transduced Karpas cells. Group 1 and 6 received tumor alone or tumor + AFM13 and served as a control. Groups 2-4 receive Karpas FFLuc with either expanded NK cells or AFM13-NK cells (NK cells loaded with AFM13) or expanded NK cells and AFM13 injected separately. Group 5 received AFM13-NK cells without tumor. Initial studies confirm the antitumor activity of AFM13-NK cells. In summary, we have developed a novel premixed product, comprised of expanded CB-NK cells loaded with AFM13 to 'redirect' their specificity against CD30+ malignancies. The encouraging in vitro and in vivo data observed in this study, provide a strong rationale for a clinical trial to test the strategy of an off-the-shelf adoptive immunotherapy with AFM13-loaded CB-NK cells in patients with relapsed/refractory CD30+ malignancies. Disclosures Champlin: Sanofi: Research Funding; Otsuka: Research Funding. Koch:Affimed GmbH: Employment. Treder:Affimed GmbH: Employment. Shpall:Affirmed GmbH: Research Funding. Rezvani:Affirmed GmbH: Research Funding.

Description: Background: CD123 is frequently expressed on hematologic malignancies including 96-98% of AML. CD123 has been a potential immunotherapeutic target in AML due to its association with leukemic stem cells that play an essential role in disease progression and relapse. Our previous study using T-cells secreting CD123/CD3-bispecific T-cell engagers (BiTEs) (CD123-ENG T-cells) showed a promising approach anti-AML activity, however T-cell persistence was limited. Interleukin-15 (IL15) has emerged as a candidate immunomodulator as it enhances T-cell expansion and persistence, and induces long-lasting memory T-cells. To improve the efficacy and persistence of CD123-ENG T-cells we developed IL15 expressing CD123-ENG T-cells. Here, we report on the characterization and efficacy of IL15-secreting CD123-ENG T cells in vitro and in vivo models of adult AML. Methods/Results: A cDNA encoding IL15 was cloned into retroviral vectors encoding CD123-ENG or CD19-ENG (CD123-ENG.IL15; CD19-ENG.IL15). ENG T-cells were generated from human peripheral blood mononuclear cells (PBMCs) from normal donors or T-cells from AML patients by retroviral transduction and in vitro expansion. Non-transduced (NT) T-cells and T-cells expressing CD123 (CD123-ENG T-cells) served as controls. IL15 production of CD19-ENG.IL15 and CD123-ENG.IL15 T cells was confirmed by ELISA (144-159 pg/ml vs 38 and 46 pg/ml of NT and CD123-ENG T cells, p

Description: Progressive multifocal leukoencephalopathy (PML) is a rare and often fatal demyelinating disorder of central nervous system caused by JC virus reactivation in patients with severe defects of cellular immunity. JC virus is genetically similar to BK virus. Both JC and BK virus express large tumor antigen (LT), small tumor antigen (ST), and the capsid proteins, VP1, VP2 and VP3 during replication. Due to antigenic epitope homology, ex vivo expanded BK virus specific T cells can also target JCV, especially for VP1 and LT. We developed a rapid, effective and GMP-compliant BK virus specific cytotoxic T lymphocyte (CTL) expansion method from peripheral blood mononuclear cells. Donor mononuclear cells were stimulated with a BK virus peptide mix in the presence of IL-2, IL-7 and IL-15 for 14 days. At the end of culture, the cells were harvested and cryopreserved until use. Here, we report the first two cases of PML treated with BK virus specific CTL from the most closely HLA-matched donor. Case 1. A 32-year-old female with a diagnosis of FLT3+ acute myeloid leukemia underwent double cord blood transplantation. Her post-transplant course was complicated by acute graft versus host disease involving skin and gastrointestinal tract, HHV-6 infection and BK virus related hemorrhagic cystitis. Twenty months after transplantation she presented with left-sided extremity weakness, slurred speech and mental confusion. The physical examination revealed ataxic gait and weakness of left lower extremity. MRI revealed abnormal pattern of parenchymal enhancement and signal abnormality in the posterior fossa, predominantly involving cerebellum and brain stem. Lumbar puncture revealed low levels of JC virus DNA (130 copies/ml). Repeat MRI three weeks later showed progression in the peduncle and right cerebellum with an increase in the CSF JC virus load to 700 copies/ml. At this point the patient received 105/kg BKV-specific CTLs expanded from a 3/6 HLA-matched allogeneic donor. There was no infusion-related toxicity. Two weeks later, there was a significant reduction in the JC virus titer to 78 copies/ml (limit of detection 72 copies/mL). HLA BW6+ donor CD4+ and CD8+ T-cells could be detected in the CSF 2 weeks after infusion, confirming that BK virus CTLs can home to inflammatory sites in the central nervous system. The lymphocytes in CSF showed a distinct phenotypic profile, mainly composed of recipient CD56bright NK cells and a mixture of donor and recipient CD4+ and CD8+ T cells. Donor T cells in CSF expressed very high levels of PD1 and CXCR3 compared to peripheral blood T-cells. Four weeks from the infusion, the neurological symptoms have resolved and repeat MRI confirmed near complete resolution of the lesions. The patient received a second CTL infusion 3 weeks after the first for persistent low positive JCV in the CSF. The patient remains essentially asymptomatic 4 months after BK virus specific CTL infusion with intermitted low positive JC virus DNA titers in the CSF. Donor T cells continue to be present in the CSF. Case 2. A 73-year-old female with JAK2 positive myeloproliferative disorder on treatment with ruxolitinib for 8 years presented with altered mental state, blurred vision and unsteady gait. MRI revealed parieto-occipital subcortical signals in left hemisphere extending to the posterior temporal lobe suggestive of PML. JC virus load in the CSF was 230,000 copies/ml. She received a 2/6 HLA-matched allogeneic BK virus specific CTLs. Three weeks after infusion JC virus titer in the CSF decreased to 5,200 copies/ml and her condition stabilized. The MRI remained stable. Donor-derived CD4+ and CD8+ T cells were detected in the CSF, with high expression of PD1 and inflammatory chemokines on T cells. The patient received a second dose of BK virus specific CTL from the same donor one month after the first infusion. The CSF viral load reduced further to 800 copies/ml but the there was no clinical or radiological improvement, suggestive of irreversible CNS damage. The patient remains alive. In this proof-of-principle study, we have used ex vivo expanded BK virus specific CTL to target PML, a disease without viable treatment strategies and with a universally fatal outcome. Both patients showed a remarkable reduction in the viral load and there was near complete resolution of symptoms and MRI findings in one case. Use of third party partially HLA-matched BK virus specific CTLs to treat PML holds promise. Disclosures Champlin: Ziopharm Oncology: Equity Ownership, Patents & Royalties; Intrexon: Equity Ownership, Patents & Royalties.