ALBERT

Description: Through an immune-mediated graft-versus-leukemia effect, allogeneic hematopoietic stem cell transplantation (HSCT) affords durable clinical benefits for many patients with hematologic malignancies. Nonetheless, subjects with high-risk acute myeloid leukemia or advanced myelodysplasia often relapse, underscoring the need to intensify tumor immunity within this cohort. In preclinical models, allogeneic HSCT followed by vaccination with irradiated tumor cells engineered to secrete GM-CSF generates a potent antitumor effect without exacerbating the toxicities of graft-versus-host disease (GVHD). To test whether this strategy might be similarly active in humans, we conducted a Phase I clinical trial in which high-risk acute myeloid leukemia or myelodysplasia patients were immunized with irradiated, autologous, GM-CSF-secreting tumor cells early after allogeneic, nonmyeloablative HSCT. Despite the administration of a calcineurin inhibitor as prophylaxis against GVHD, vaccination elicited local and systemic reactions that were qualitatively similar to those previously observed in nontransplanted, immunized solid-tumor patients. While the frequencies of acute and chronic GVHD were not increased, 9 of 10 subjects who completed vaccination achieved durable complete remissions, with a median follow-up of 26 months (range 12–43 months). Six long-term responders showed marked decreases in the levels of soluble NKG2D ligands, and 3 demonstrated normalization of cytotoxic lymphocyte NKG2D expression as a function of treatment. Together, these results establish the safety and immunogenicity of irradiated, autologous, GM-CSF-secreting leukemia cell vaccines early after allogeneic HSCT, and raise the possibility that this combinatorial immunotherapy might potentiate graft-versus-leukemia in patients.

Description: Despite progress in the treatment of multiple myeloma (MM), the disease remains incurable. Therefore novel therapeutic approaches are required to achieve better outcome in patients. Development of peptide-based immunotherapy against tumor specific or associated antigens offers an attractive approach that may lead to tumor-targeted cellular therapy in MM patients. Recently, CS1 (CD2 subset 1, CRACC, SLAMF7), a cell surface glycoprotein of the CD2 family, was found to be highly expressed by the tumor cells of the majority of MM patients but not other normal tissues. Importantly, a novel anti-CS1 HuLuc63 mAb induced significant anti-myeloma killing in vitro and in vivo (Abstract #950059). In addition, CS1 may play a role in MM cell survival (Abstract #953659). In this study, we asked whether CS1 is a suitable myeloma-associated antigen for cellular therapy in MM. We wanted to identify potential immunogenic peptides derived from CS1 and tested whether these peptides evoke MM-specific cytotoxic T lymphocytes (CTLs). First, we predicted the potential peptide sequences of CS1 that could bind to HLA-A*0201 molecule using three databases (RANKPEP, BIMAS and NetMHC). A total of four peptides were selected and synthesized according to the high binding scores among all the databases. Next, peptide-T2 cells binding assay confirmed these peptides with high binding affinity to HLA-A*0201 molecule (Fluorescence index: 2.19, 3.28, 3.44 and 3.49). To generate the peptide-specific CTLs, HLA-A*0201-positive normal human CD8+ T lymphocytes were stimulated with autologuous dendritic cells (DCs) or T2 cells pulsed with candidate CS1-peptides. The CTL cell lines were established after several rounds restimulation. We have evaluated the immunogenicity of the expanded CTLs by the stimulation with peptide-pulsed or unpulsed T2 cells. Our data demonstrated that one peptide-induced CTLs (CS1-CTLs) possessed high antigen-specific immune responses with the HLA-A*0201-restriction relative to a certain level of immune responses displayed by another three peptide-induced CTLs. We further evaluated the proliferative activity of CS1-CTLs by 3H-TdR incorporation assay. Upon stimulation by peptide-pulsed T2 cells, the cell proliferation of CS1-specific CTLs increased approximately 55-fold, compared with unstimulated cells (pulsed vs. unpulsed: 22894 vs. 423 cpm). The activation of CS1-CTLs was monitored by the expression of CD25 (IL-2Rα chain) on peptide-stimulated CS1-CTLs (%CD25+ cells: pulsed vs. unpulsed: 98% vs. 13%). CS1-CTLs significantly secreted 14-fold higher levels of IFN- γ in response to peptide-pulsed T2 cells (pulsed vs. unpulsed: 615 vs. 46 pg/ml). Importantly, the expanded CS1-CTLs generated high cytotoxicity (93%) in response to peptide pulsed T2 cells. Furthermore, more than 30% of killing activity by CS1-CTLs against HLA-A*0201+CS1+ MCCAR cells was observed at the effector: target ratio of 20:1. In contrast, these CS1-CLTs did not kill HLA-A*0201+/CS1− U266 and HLA-A*0201−/CS1+ MM1S target cells. These results support CS1 as an antigenic target for the induction of peptide-specific CTLs against MM cells. Further functional studies are underway to confirm potential CS1-specific cellular therapy to treat MM.

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: Abstract 3022 Poster Board II-998 Dendritic cells (DC) are “professional” antigen-presenting cells (APC) that can prime T cells. Their characteristic morphology and phenotype segregate them from other APC. Many studies suggest that mature DC are able to induce potent antitumor T cell immunity that can reject tumors. Based on this, numerous cancer vaccine trials using ex vivo generated DC have been conducted in humans. However, the observed objective response rates in these studies have been disappointing. This could partially be attributed to difficulties in generating large numbers of clinical grade, optimally matured DC. Also, it is widely accepted that the quality and quantity of DC generated ex vivo vary substantially among individuals. We have hypothesized that the generation of standardized artificial DC (aDC) will overcome the time, expense, and suboptimal reproducibility of DC cultures and prompt the development of DC-based immunotherapy for cancer. Previously, we developed a renewable and standardized artificial APC (aAPC) by transducing HLA-A2, CD80, and CD83 to the human erythroleukemic suspension cell line, K562. This aAPC can naturally process and present HLA-A2-restricted peptides and uniquely support the priming and prolonged expansion of large numbers of antigen-specific CD8+ CTL. Generated antigen-specific CTL display a central ∼ effector memory phenotype consistent with in vivo persistence, possess potent effector function, and specifically recognize tumor cells. Furthermore, CTL can be maintained in vitro for a prolonged period of time up to 〉1 year without any feeder cells or cloning. Recent clinical trials have demonstrated that adoptive transfer of anti-tumor CTL with a memory phenotype generated ex vivo using this aAPC, IL-2, and IL-15 can persist in cancer patients as memory T cells for 〉6 months without any lymphodepletion, adjuvants, or cytokine administration. Clinical responses have also been observed in some patients. To develop a standardized aDC, we have undertaken an approach to differentiate our K562-based aAPC into aDC. In neurogenesis, it has been well established that a family of Rho GTPases (Rho, Rac, and Cdc42) critically regulates the outgrowth of neurites, i.e. dendrites and axon. We have found that the inhibition of Rho kinase (ROCK), which is a key effector molecule of Rho, can promote the differentiation of monocyte-derived immature DC into mature DC both morphologically and phenotypically. Intriguingly, when aAPC were forced to attach via a newly identified surface molecule, PladX, and ROCK activity was subsequently blocked, K562-derived aAPC “differentiated” into DC-like cells by acquiring dendrite extensions and growth cone-like structures at the end of the extensions (see picture). PladX-mediated strong attachment was critical for differentiation, since ROCK inhibition without attachment or following attachment via conventional adhesion molecules such as poly-L lysine, fibronectin, or collagen was not sufficient to induce dendrites. Confocal microscopy analysis revealed that dendrites were composed of F-actin rich filopodia and lamellipodia. Furthermore, F-actin and microtubules were differentially localized in the “growth cones” and “dendrite shafts” of aDC, respectively. While treatment with actin inhibitors blocked the generation of “growth cones” but not dendritic shafts, exposure to microtubule inhibitors abrogated the extension of dendritic shafts. Finally, we were able to demonstrate that aDC were more potent than aAPC in CD8+ T cell stimulatory activity. This was the case despite the fact that differentiation of aAPC into aDC does not alter the expression level of molecularly engineered immunoaccessory molecules MHC class I, CD80, and CD83. The effects of the differentiation on processing and presentation of antigenic peptides were negligible since CD8+ T cell antigen was exogenously pulsed as a fully processed synthetic peptide. Taken together, this result indicates that the dendrite formation and the resultant enlarged surface area are critical determinants of DC's enhanced immunogenicity. We have succeeded in producing infinite number of aDC with enhanced immunogenicity by differentiating our renewable and standardized K562-based aAPC, which has been already tested in the clinic. This novel aDC may overcome the cumbersome issues inherent to conventional DC and widen the applicability of DC-based immunotherapy for cancer. Disclosures No relevant conflicts of interest to declare.

Description: Abstract 2449 Poster Board II-426 Donor lymphocyte infusion (DLI) is a highly effective treatment for relapsed chronic myeloid leukemia (CML) after allogeneic hematopoietic stem cell transplantation (HSCT), in which 70-80% patients achieve curative responses. Despite its efficacy and established clinical use, the mechanism by which DLI achieves anti-tumor immunity remains incompletely understood. CML66 was discovered as an overexpressed nonpolymorphic CML-associated antigen that elicited a high-titer (〉1:50,000) antibody response in a patient who received CD4+ DLI for relapsed CML. CML66 is preferentially expressed on myeloid leukemia progenitor cells and the development of CML66 antibodies temporally correlated with attainment of molecular remission. Since CD4+ T cell responses are involved in generating both antigen-specific B cell and CD8+T cell responses, we queried whether development of potent B cell immunity was also associated with the development of cytolytic T cell immunity against CML66. To detect specific T cell responses, post-DLI PBMC from this patient were screened for reactivity against pools of overlapping 15- to 18-mer peptides encoding the entire protein sequence of CML66. Patient CD8+ T cells were found to be reactive against a single CML66-derived peptide pool, and specifically an 8 amino acid peptide (HDVDALLW), beginning at residue 459. This T cell epitope is positioned in a different region of the protein compared to the B cell epitope (at residues 198-217: GFYVSLEWVTISKKNQDNK). A peptide-specific T cell clone was isolated, whose MHC class I molecule binding was restricted to HLA B*4403. The CML66-reactive T cell clone recognized the HLA-B4403-expressing CD34+ AML cell line MUTZ-3, providing evidence that this epitope is naturally processed and presented by myeloid leukemia cells. Functional cytotoxic T cell responses to CML66 appeared to precede the appearance of antigen-specific antibody responses. While CML66-specific plasma antibody was only detectable starting 2-3 months after DLI, reactivity to the HLA-B4403-restricted epitope by peripheral blood-derived CD8+ T cells was detected by IFNγ ELISpot as early as one month following DLI. To sensitively detect CD8+ CML66-specific T cells in vivo, we sequenced the CDR3 region specific to the CML66-specific clone, and designed clone-specific quantitative PCR primers. Nested PCR of RNA directly extracted from patient PBMC revealed only minimal detection of the CML66-specific T cell clone prior to DLI, but then expansion between 1 to 6 months after DLI. Similar analysis of marrow-derived RNA also revealed the presence of CML66-specific T cell clone in patient marrow following DLI. Moreover, this clone was already detected in patient marrow prior to DLI, suggesting that marrow is a reservoir of leukemia-specific T cells following hematopoietic stem cell transplantation. Our studies provide the first description of coordinated adaptive immunity developing against a nonpolymorphic leukemia-associated antigen, in close temporal correlation with the attainment of long-lasting immune-mediated clinical remission after allogeneic HSCT. The detected cytolytic T cell response was associated with the secretion of high-titer IgG antibody specific for a distinct epitope in the same target protein. In this setting, our results indicate that infusion of CD4+ donor cells resulted in the rapid activation and expansion of pre-existing marrow-resident leukemia-specific CD8+ T cells, followed by a cascade of antigen-specific immune responses detectable in the periphery. Disclosures: No relevant conflicts of interest to declare.