ALBERT

Description: Eradication of residual disease remains a critical problem in patients with chronic myeloid leukemia (CML). Donor lymphocyte infusion (DLI) for the treatment of relapsed CML after transplantation is a robust example of the graft-versus-leukemia (GvL) effect, producing complete durable remission in 75% of patients. Since CML originates as a clonal stem cell disorder, we hypothesize that the curative effect of DLI results from immunologic targeting of the self-renewing CML progenitor cell. We have focused on B cell responses as a critical element in effective tumor immunity after observing significant B cell lymphocytosis in 7 responders of DLI at 6 and 9 months following DLI compared to pre-treatment levels (p=0.03; p=0.04, respectively), which was not seen in 5 DLI nonresponders. Moreover, some DLI responders showed marrow plasmacytosis at the time of cytogenetic response. To identify targets of this visible B cell response, we used post-DLI plasma as a source of immunoglobulin to probe two complementary immunoproteomic platforms and identify antigens eliciting increased reactivity compared to pre-DLI plasma. In the first approach, plasma from 7 individual responders was screened for binding to proteins expressed from a CML cDNA phage library (SEREX). In the second approach, plasma from 3 of the 7 responders was screened for binding to proteins expressed from approximately 5000 open reading frames spotted on a protein microarray (ProtoArray, Invitrogen). Screening by SEREX yielded 24 and by ProtoArray 58 candidate antigens. Analysis of datasets generated from normal and malignant myeloid cells on HG-Focus and HG-U133A Affymetrix microarrays confirmed that most candidate targets were expressed in CML progenitor cells. Of the antigens represented on the microarrays, 83% (10 of 12) and 64% (18 of 28) of the SEREX- and ProtoArray-identified antigens, respectively, were expressed in CML CD34+ cells. EXOSC5 was expressed on CML CD34+ cells and was identified by both platforms. Four of 16 ProtoArray-identified antigens (RAB38, TBCE, DUSP12, RPS6KC1) were expressed at higher levels in CML compared to normal CD34+ and mature myeloid lineage cells (p

Description: Background:Spleen tyrosine kinase (SYK) is a nonreceptor cytoplasmic tyrosine kinase primarily expressed in cells of hematopoietic lineage. Constitutive activation of SYK in acute myeloid leukemia (AML) has been reported and targeted inhibition of SYK induced differentiation in vitro and demonstrated anti-leukemia activity in AML mouse models. SYK has also been shown to directly phosphorylate the FLT3 receptor, modulating its activation and possibly promoting its role in leukemogenesis. Entospletinib is an orally bioavailable, selective inhibitor of SYK shown to be clinically active in B-cell malignancies. Here we evaluate the combination of entospletinib in patients with untreated AML using a 14-day window phase to assess single-agent activity, then adding standard intensive chemotherapy. Methods: In this phase 1b/2 study (NCT02343939), patients age 18 to 70 years with previously untreated AML, preserved organ function, and ECOG ≤ 2 were eligible to receive dose escalated entospletinib for 14 days as monotherapy (days -14 to 0) followed by combination with daunorubicin 60 mg/m2/d, cycle 1 day 1 to 3, and cytarabine 100 mg/m2/d, cycle 1 day 1 to 7. All patients received entospletinib monotherapy for up to 14 days prior to starting induction. Chemotherapy could be initiated after 5 days of monotherapy (and entospletinib continued for 4+ weeks) in patients with leukemia-related complications necessitating chemotherapy. Patients enrolled to dose level (DL) 0 and DL 1 received entospletinib 200 mg po BID and 400 mg po BID, respectively. Patients with residual disease two weeks after chemotherapy received a second induction cycle identical to the first. Entospletinib was continued without interruption until remission was assessed at count recovery. Results:Twelve patients enrolled with a median age of 54 (range, 18-69) years. Patients were in the following European LeukemiaNet genetic risk groups: favorable (n=1), intermediate I (n=3), intermediate II (n=2), and adverse (n=4), respectively. Three patients were not evaluable for dose limiting toxicity (DLT) assessment and were replaced (due to detection of CNS disease requiring non-study therapy (n=1), and withdrawal of consent unrelated to drug toxicity (n=2)). Single-agent entospletinib during the window period was well tolerated; toxicities after combination with intensive chemotherapy were common and typical. Among 3 patients treated at 200mg BID, no DLT was observed. Of 3 patients treated at 400mg BID, a patient with documented fungal pneumonia developed grade 3 pneumonitis that was possibly related to entospletinib. Although this did not meet DLT criteria, DL 1 was expanded with 3 additional patients, none of whom experienced DLT. Overall, the most common non hematologic adverse events (inclusive of intensive chemotherapy periods) were febrile neutropenia, nausea, and diarrhea. Based on this clinical experience and compiled pharmacokinetic data demonstrating lack of benefit to further dose escalation, 400 mg BID was selected as the recommended phase 2 dose. Responses were seen at both levels. Among the 3 patients treated at 200 mg BID, two required a second induction but all achieved a complete remission (CR) (3/3; 100%). Of the 6 patients treated at 400mg BID, none required a second induction and the CR rate was also 100%. Remarkably, an 18 year old male with 11q23-rearranged AML achieved morphologic and cytogenetic CR after only the 14 day entospletinib monotherapy window (prior to chemotherapy). Another patient with 11q23-rearranged AML had significant platelet response during the window period (this patient refused disease evaluation by marrow aspiration prior to chemotherapy). Conclusions: Entospletinib appears to have significant clinical activity in AML, and its combination at doses up to 400mg BID with intensive chemotherapy is well tolerated. An extended phase 2 program is now underway. Patients with 11q23-rearranged AML may be uniquely sensitive to SYK inhibition by entospletinib. Detailed molecular analysis of these patients is ongoing and will be presented. Disclosures Walker: Gilead Sciences: Research Funding. Bhatnagar:Karyopharm: Research Funding. Marcondes:Gilead Sciences: Employment, Equity Ownership. DiPaolo:Gilead Sciences: Employment, Equity Ownership. Abella-Dominicis:Gilead Sciences: Employment, Equity Ownership.

Description: To elucidate the basis of the potent graft versus leukemia (GvL) immune response that is initiated with donor lymphocyte infusion (DLI), we hypothesized the existence of an endogenous adjuvant that enhances antigen-specific immunity. In patients with chronic myeloid leukemia (CML) who achieved molecular remission after DLI, we previously identified a panel of CML-associated antigens that are targets of antibodies present in post-DLI sera and are predicted to bind nucleic acids. Recent studies in SLE have identified immunostimulatory nucleic-acid antibody complexes in patient sera, which can stimulate Toll-like receptors (TLRs) in plasmacytoid dendritic cells (pDCs). To identify immunostimulatory factors associated with GvL, we studied 6 patients that responded to DLI without clinically significant GvHD. Consistent with our prediction that sera from DLI responders contain an immunostimulatory activity, we measured a 3 to 50-fold increase in the expression of MIP-1α, TNF-α, IP-10 and IFN-α transcripts in normal peripheral blood mononuclear cells (PBMC) induced by exposure to 5 of 6 post-DLI sera. No increase in cytokine/chemokine expression was observed upon exposure to sera from pre DLI sera from the same patients, from 3 of 3 DLI non-responders, nor from 3 of 3 CML patients who achieved molecular remission after imatinib treatment. To identify the cell type that responds to the immunostimulatory activity in post-DLI sera, we isolated B, T, NK cells, monocytes, myeloid DCs and pDCs, and cultured them with pre- or post-DLI responder sera. In contrast to published findings that SLE sera stimulate pDCs, we found that post DLI sera induced normal monocytes to express high levels of MIP-1α, IP-10, MCP, TNF-α, IFN-α, IL-6, IL-8 and IL-12. Pretreatment of post-DLI sera with DNase, RNase, papain or pepsin resulted in marked decrease in IL-8 induction, demonstrating that this endogenous immunostimulatory factor requires both nucleic acid and protein for its adjuvant activity. Four active post-DLI sera were then used to stimulate stable HEK transfectants expressing TLR2, 3, 4, 8 or 9. IL-8 expression increased only in the TLR8 and TLR9-expressing cells lines that are known to be responsive to RNA and DNA respectively. IL-8 expression was further induced by post-DLI sera in TLR9-expressing cell lines co-transfected with CD32, suggesting that internalization by FcR may enhance delivery of nucleic acids to endosomal TLR8/9. None of the TLR transfectants could be activated by pre-DLI sera from the same responder patients, nor by post-DLI sera from non-responders. Finally, sera from responders collected between 2 weeks to several months after DLI consistently activated TLR8 and TLR9 suggesting that endogenous TLR8/9 activation may contribute to the early immunologic events that lead to an effective DLI response. Ongoing studies are focused on precisely identifying the TLR8/TLR9 agonists in DLI responders, studying the immunologic effects of this endogenous adjuvant and determining the association of our previously identified CML antigens with nucleic acids that activate TLR8 and TLR9. In summary, we demonstrate for the first time that effective tumor immunity is correlated with the presence of endogenous adjuvant-immunoglobulin complexes in patient sera, and propose that these observations form the basis for novel tumor vaccine strategies.

Description: Regulatory T cells (Treg) play a key role in controlling immune responses following allogeneic hematopoietic stem cell transplantation (HSCT). In murine models, infusion of purified CD4+CD25+ Treg at the time of transplant is sufficient to prevent acute GVHD. In humans, development of acute as well as chronic GVHD has been associated with reduced numbers of Treg following allogeneic HSCT, suggesting that defective reconstitution of this functional cell type can contribute to exacerbation of alloimmune responses. Based on these results, adoptive cellular therapy using purified and in vitro expanded populations of Treg has been proposed as a therapeutic strategy to correct chronic GVHD. Treg are mainly characterized by the constitutive expression of the IL-2 receptor ? chain, CD25 and proliferate in response to IL-2 in vitro. In vivo, the effects of IL-2 on Treg populations are unknown. To examine this question we quantified changes in Treg in 9 patients with CML who previously received low dose IL-2 following allogeneic HSCT. Patients enrolled in this protocol received a daily intravenous infusion of 2 X 105 U IL-2/m2 for 3 months, starting 3 months after CD6 depleted allogeneic bone marrow transplantation (BMT). No patient developed GVHD following IL-2 administration and overall toxicity was minimal. The predominant immunologic effect of IL-2 reported in the initial study was a marked increase in NK cell populations characterized as CD3-CD16+CD56+ as well as total CD56+ cells. In this retrospective analysis we investigated populations of CD4+CD25+ T cells before and 1 to 2 months after the beginning IL-2 treatment. Using RNA extracted from patient PBMC we also assessed the level of expression of the specific transcription factor FOXP3 by quantitative PCR as an alternate marker of Treg in vivo. As initially reported, all 9 patients showed a marked increase in CD3-CD56+ cells 1 to 2 months post IL-2 administration. In contrast, the percent of CD3+ T cells were either unchanged or slightly decreased. The percent of CD4+CD25+ cells within the CD3+ T cell population increased during IL-2 treatment (median: 5.8 pre IL-2 vs 7.6 post IL-2, p-value=0.02). Likewise, FOXP3 expression in the CD3+ population showed 5 to 19 fold increase in 8 of 9 patients during this period (median: 3817 AU pre IL-2 vs. 18924 AU post IL-2, p-value=0.055). These results indicate that administration of low dose IL-2 can augment Treg cells in vivo as reflected by increased ratio of CD4+CD25+/CD3+ T cells as well as higher levels of FOXP3 expression. These studies suggest that prolonged treatment with low dose IL-2 can effectively expand CD4+CD25+ Treg in vivo. This represents a novel strategy for expanding regulatory T cells in vivo and may be useful alone or in conjunction with adoptive cellular therapy with Treg.

Description: Abstract 1892 Patients with advanced hematological malignancies remain at high risk for eventual disease progression following reduced intensity conditioning (RIC) allogeneic hematopoietic stem cell transplantation (allo-HSCT). We hypothesized that vaccination with whole leukemia cells during the critical period of immune reconstitution early after transplant may enhance antitumor immunity and facilitate expansion of leukemia-reactive T cell responses. We tested this hypothesis in a prospective clinical trial, in which patients with advanced chronic lymphocytic leukemia (CLL) received up to 6 vaccine doses initiated between day 30–45 following RIC allo-HSCT. Each vaccine consisted of 1×107 irradiated autologous tumor cells admixed with 1×107 irradiated K562 bystander cells secreting GM-CSF (GM-K562). All patients received tacrolimus and mini-methotrexate as graft-versus-disease (GvHD) prophylaxis. Tacrolimus was maintained at therapeutic levels during the vaccination period without taper. Twenty-two patients were enrolled, all with advanced disease (median number of prior therapies 3; range 2–11). Many of the leukemias expressed markers associated with aggressive disease (e.g. unmutated IgVH - 68%) and displayed high-risk cytogenetic abnormalities (sole del(11q) - 41%; sole del(17p) - 23%; del(11q and 17p) - 18%). Greater than 50% (n=13) of patients had persistent marrow involvement (≥10%) at time of allo-HSCT. Eighteen of 22 subjects were vaccinated after allo-HSCT and received a median of 6 (range 1–6) vaccines. The remaining 4 patients were precluded from vaccination due to development of acute GvHD before day 45. Vaccines were generally well tolerated, but mild, transient injection site erythema was common. Only one grade 4 event (neutropenia) with a possible attribution to treatment occurred. We observed a similar incidence of grade II-IV aGvHD at 1 year in the 18 vaccinated patients (39%; 95% CI: 17–61%) and 42 control CLL patients that underwent RIC allo-HSCT at our institution from 2004–2009 (31%; 95%CI: 18–46%). At a median follow-up of 2.9 (range 1–4) years, the estimated 2-year rates of progression-free survival and overall survival of vaccinated study participants were 80% (95% CI: 54–92%) and 84% (95% CI: 58–95%). With these promising clinical results, we next focused on gaining insight into the mechanism that generated the observed clinical graft-versus-leukemia (GvL) responses. To delineate the specific contribution of vaccination to the overall GvL effect, we performed T cell assays to detect CLL-specific reactivity in serial pre- and post-HSCT samples obtained from vaccinated patients (n=9) who received median of 6 vaccines (range 3–6). In comparison, we examined T cell responses in study subjects (n=4) that developed aGvHD at a median of 44.5 days (range 26–56) after HSCT; and control CLL patients (n=4; no vaccine, no GvHD in the early post-transplant period) that were not enrolled in the study. Although early post-transplant vaccination had no impact on recovering absolute T cell numbers, reactivity of CD8+ T cells from the vaccinated patients was consistently directed against autologous tumor cells but not alloantigen bearing-recipient cells (PHA T cell blasts and fibroblasts) in IFNγ ELISpot assays. A peak response against autologous tumor cells was reached at day 60 after allo-HSCT (average 221 SFC/5×105 cells vs. 29 and 33 average SFC/5×105cells for PHA blasts and fibroblasts, respectively). CD8+ T cell clones were isolated from 4 vaccinated study subjects by limiting dilution and 17% (range 13–33%) reacted solely against CLL-associated antigens. In contrast, broad CD8+ T cell reactivity indicating an alloantigen response was observed in GvHD patients, while no increase in T cell reactivity against tumor-associated or alloantigens was seen in control patients. Tumor-reactive CD8+ T cells isolated from vaccinated patients secreted a broad profile of effector cytokines (GM-CSF, TNFα and IP10). Moreover, the amount of cytokines secreted by these CLL-specific CD8+ T cells steadily increased following early post-transplant vaccination, but not after allo-HSCT alone or in relation to GvHD. Our studies reveal that vaccination with autologous whole CLL/GM-K562 cells between days 30–100 after allo-HSCT is associated with induction of immunity against recipient CLL cells, and suggest that this is an effective strategy for promoting GvL following RIC allo-HSCT. Disclosures: Brown: Genzyme, Celgene: Research Funding; Calistoga, Celgene, Genentech, Pharmacyclics, Novartis, Avila: Consultancy. Cutler:Pfizer, inc: Research Funding; Astellas, Inc: Consultancy, Research Funding.

Description: Graft-versus-host disease (GVHD) is a major cause of morbidity and mortality following allogeneic hematopoietic stem cell transplantation (HSCT). Advances in molecular typing of major histocompatibility complex (MHC) alleles have decreased but not eliminated the occurrence of acute GVHD. Minor histocompatibility antigen (mHA) disparities between patients and their molecularly HLA-identical donors are likely to represent the residual targets of donor immunity. The majority of mHAs are encoded by SNPs which are disparate between patient and donor. Identification of these immunogenic SNPs would provide both a clinical benefit as well as insight into the biology of GVHD. We used Affymetrix high-density arrays to assess 10,043 SNPs spanning the entire genome. We have examined genomic DNA from 36 patient/donor pairs (21 with acute GVHD grades II-IV and 15 without GVHD). All patients and donors were HLA and sex-matched siblings and all patients received T-cell depleted transplants. T cell depletion is important in this context as it removes the potential pharmacogenomic confounding factor of differential sensitivity to immunosuppressive agents. Because the donors and recipients are related, large areas of the genome are identical by descent. Similarly sized blocks of chromosome are disparately inherited. We hypothesized that genomic regions important to the immunopathogenesis of GVHD would be more likely to be disparately inherited in pairs with GVHD than in pairs without GVHD. As a control of our method we compared the area of chromosome 6 surrounding the MHC complex and demonstrated that there was minimal SNP disparity in either GVHD pairs or asymptomatic pairs. We also focused our attention on the region of chromosome 6 outside the MHC area, hypothesizing that disparities in this area would have to result from recombination events. Interestingly the only major area of disparity on Chr 6 was in the gene GMDS, which has been proposed to play a role in the extravasation of activated lymphocytes. We then examined other chromosomes for evidence of genomic regions that that were selectively disparate in GVHD pairs. We were able to identify several genomic regions that appeared to be associated with this outcome. The Lander-Green algorithm was used to estimate the allele sharing between the siblings for each SNP marker and then the disparity score was defined as the average allele sharing of the GVHD group - average allele sharing of the asymptomatic group. The five genomic regions with the highest disparity scores (ranked in order of score) and the gene closest to the region are: 11q14.3 (gene cysteine and histidine-rich domain (CHORD)-containing, zinc binding protein 1), 9p22.2 (gene SH3GL2), 5p15 (gene KIAA0947), 10p15.1 (gene aldo-keto reductase family 1, member C4), and 9p21.2 (Chr 9 ORF 72). The highly disparate regions ranged between 70 and 2200 kb in size. Interestingly the total number of disparate SNPs was not different between pairs with GVHD and pairs without GVHD, supporting the hypothesis that a limited number of SNPs are important immunologic targets. This technique of genome-wide disparity analysis is a promising addition to our ability to define important mHA.

Description: Donor lymphocyte infusions (DLIs) induce effective graft-versus-tumor responses in patients with multiple myeloma who relapse after allogeneic hematopoietic stem-cell transplantation. The graft-versus-myeloma response is presumably mediated primarily by donor T cells, but recent studies have also demonstrated the presence of antibodies specific for a variety of myeloma-associated antigens in patients who achieve complete remission after DLI. One of the B-cell antigens identified in these studies was B-cell maturation antigen (BCMA), a transmembrane receptor of the tumor necrosis factor (TNF) superfamily that is selectively expressed by mature B cells. The present studies were undertaken to characterize the functional significance of antibodies to BCMA in vivo. Using transfected cells expressing BCMA, antibodies in patient serum were found to react with the cell-surface domain of BCMA. Post-DLI patient serum was able to induce complement-mediated lysis and antibody-dependent cellular cytotoxicity (ADCC) of transfected cells and primary myeloma cells expressing BCMA. BCMA antibodies were only found in post-DLI responders and not in other allogeneic transplant patients or healthy donors. These results demonstrate that BCMA is a target of donor B-cell immunity in patients with myeloma who respond to DLI. Antibody responses to cell-surface BCMA may contribute directly to tumor rejection in vivo.

Description: Key Points Marrow CD8+ T-cell infiltrates may be a novel predictor of response to donor lymphocyte infusions in patients with relapsed CML. Reversal of T-cell exhaustion is tightly linked to effective antileukemia responses to donor lymphocyte infusions.

Description: Previous trials of allogeneic bone marrow transplantation (BMT) in patients with multiple myeloma (MM) have demonstrated high response rates but also high transplantation-related mortality (TRM) and high relapse rates. Exploitation of this strategy remains of interest because donor lymphocyte infusions (DLIs) can induce a potent graft-versus-myeloma (GVM) effect. CD6 T-cell–depleted allogeneic BMT was combined with prophylactic CD4+ DLI administered 6 to 9 months after BMT in an effort to reduce TRM and to induce a GVM response after BMT. Twenty-four patients with matched sibling donors and chemotherapy-sensitive disease underwent BMT. CD6 T-cell depletion of donor bone marrow was the sole method of graft-versus-host disease (GVHD) prophylaxis. GVHD after BMT was minimal, 1 (4%) grade III and 4 (17%) grade II GVHD. Fourteen patients received DLI, 3 in complete response and 11 with persistent disease after BMT. Significant GVM responses were noted after DLI in 10 patients with persistent disease, resulting in 6 complete responses and 4 partial responses. After DLI, 50% of patients developed acute (≥ II) or extensive chronic GVHD. Two-year estimated overall survival and current progression-free survival (PFS) for all 24 patients is 55% and 42%, respectively. The 14 patients receiving DLI had an improved 2-year current PFS (65%) when compared with a historical cohort of MM patients who underwent CD6-depleted BMT survived 6 months with no GVHD and did not receive DLI (41%) (P = .13). Although this study suggests that prophylactic DLI induces significant GVM responses after allogeneic BMT, only 58% of patients were able to receive DLI despite T-cell–depleted BMT. Therefore, less toxic transplantation strategies are needed to allow a higher proportion of patients to receive DLI and the benefit from the GVM effect after transplantation.

Description: Following myeloablative therapy, it is unknown to what extent age-dependent thymic involution limits the generation of new T cells with a diverse repertoire. Normal T-cell receptor gene rearrangement in T-cell progenitors results in the generation of T-cell receptor rearrangement excision circles (TRECs). In this study, a quantitative assay for TRECs was used to measure T-cell neogenesis in adult patients with leukemia who received myeloablative therapy followed by transplantation of allogeneic hematopoietic stem cells. Although phenotypically mature T cells had recovered by 1 to 2 months after bone marrow transplantation (BMT), TREC levels remained low for 3 months after BMT. T-cell neogenesis became evident by 6 months, and normal levels of adult thymic function were restored at 6 to 12 months after BMT. Subsequent leukemia relapse in some patients was associated with reduced TREC levels, but infusion of mature donor CD4+ T cells resulted in rapid restoration of thymic function. These studies demonstrate that T-cell neogenesis contributes to immune reconstitution in adult patients and suggest that thymic function can be manipulated in vivo.