Clinical immunogenicity outcomes from GENEr8-1, a phase 3 study of valoctocogene roxaparvovec, an AAV5-vectored gene therapy for hemophilia A.

Gene transfer therapies utilizing adeno-associated virus (AAV) vectors involve a complex drug design with multiple components that may impact immunogenicity. Valoctocogene roxaparvovec is an AAV serotype 5 (AAV5)-vectored gene therapy for treatment of hemophilia A that encodes a B-domain-deleted human factor VIII (FVIII) protein controlled by a hepatocyte-selective promoter. Following previous results from the first-in-human phase 1/2 clinical trial, we assessed AAV5 capsid- and transgene-derived FVIII-specific immune responses with 2 years of follow-up data from GENEr8-1, a phase 3, single-arm, open-label study in 134 adult men with severe hemophilia A. No FVIII inhibitors were detected following administration of valoctocogene roxaparvovec. Immune responses were predominantly directed toward the AAV5 capsid, with all participants developing durable anti-AAV5 antibodies. Cellular immune responses specific for the AAV5 capsid were detected in most participants by interferon-ᵧ enzyme-linked immunosorbent spot assay 2 weeks following dose administration and declined or reverted to negative over the first 52 weeks. These responses were weakly correlated with alanine aminotransferase elevations and showed no association with changes in FVIII activity. FVIII-specific cellular immune responses were less frequent and more sporadic compared with those specific for AAV5 and showed no association with safety or efficacy parameters.

Three-year outcomes of valoctocogene roxaparvovec gene therapy for hemophilia A.

BACKGROUND: Valoctocogene roxaparvovec transfers a human factor (F)VIII coding sequence into hepatocytes of people with severe hemophilia A to provide bleeding protection. OBJECTIVES: To present 3-year efficacy and safety in the multicenter, open-label, single-arm, phase 3 GENEr8-1 trial. METHODS: GENEr8-1 enrolled 134 adult males with severe hemophilia A who were receiving FVIII prophylaxis. Efficacy endpoints included annualized bleeding rate, annualized FVIII utilization, FVIII activity (chromogenic substrate assay; imputed as 1 IU/dL at baseline and 0 IU/dL after discontinuation), and the Haemophilia-Specific Quality of Life Questionnaire for Adults. Safety was assessed by adverse events (AEs). RESULTS: At week 156, 131 of 134 participants remained in the study; overall, 17 of 134 resumed prophylaxis. Mean annualized bleeding rate for treated bleeds decreased from 4.8 (SD, 6.5) bleeds/y at baseline to 0.8 (SD, 2.3; P < .0001) bleeds/y after prophylaxis (prophylaxis cessation to last follow-up) and 0.97 (SD, 3.48) bleeds/y during year 3. Annualized FVIII utilization decreased 96.8% from baseline after prophylaxis and 94.2% during year 3. At week 156, mean and median FVIII activity were 18.4 (SD, 30.8) and 8.3 IU/dL, respectively. FVIII activity decrease was lower between years 2 and 3 than between years 1 and 2. At the end of year 3, clinically meaningful improvements in the Haemophilia-Specific Quality of Life Questionnaire for Adults Total Score were observed (mean change from baseline, 6.6; 95% CI, 4.24-8.87; P < .0001). Mild alanine aminotransferase elevations remained the most common AE during year 3 (23.7% of participants). A serious AE of B-cell acute lymphoblastic leukemia was considered unrelated to treatment. CONCLUSION: Hemostatic efficacy was maintained, and safety remained unchanged from previous years.

Long-term safety and efficacy outcomes of valoctocogene roxaparvovec gene transfer up to 6 years post-treatment.

INTRODUCTION: Valoctocogene roxaparvovec uses an adeno-associated virus serotype 5 (AAV5) vector to transfer a factor VIII (FVIII) coding sequence to individuals with severe haemophilia A, providing bleeding protection. AIM: To assess safety and efficacy of valoctocogene roxaparvovec 5-6 years post-treatment. METHODS: In a phase 1/2 trial, adult male participants with severe haemophilia A (FVIII ≤1 IU/dL) without FVIII inhibitors or anti-AAV5 antibodies received valoctocogene roxaparvovec and were followed for 6 (6 × 1013 vg/kg; n = 7) and 5 (4 × 1013 vg/kg; n = 6) years. Safety, including investigation of potential associations between a malignancy and gene therapy, and efficacy are reported. RESULTS: No new treatment-related safety signals emerged. During year 6, a participant in the 6 × 1013  vg/kg cohort was diagnosed with grade 2 parotid gland acinar cell carcinoma; definitive treatment was uncomplicated parotidectomy with lymph node dissection. Target enrichment sequencing of tumour and adjacent healthy tissue revealed low vector integration (8.25 × 10-5 per diploid cell). Integrations were not elevated in tumour samples, no insertions appeared to drive tumorigenesis, and no clonal expansion of integration-containing cells occurred. During all follow-ups, >90% decreases from baseline in annualised treated bleeds and FVIII infusion rates were maintained. At the end of years 6 and 5, mean FVIII activity (chromogenic assay) was 9.8 IU/dL (median, 5.6 IU/dL) and 7.6 IU/dL (median, 7.1 IU/dL) for the 6 × 1013 and 4 × 1013 vg/kg cohorts, respectively, representing proportionally smaller year-over-year declines than earlier timepoints. CONCLUSIONS: Valoctocogene roxaparvovec safety and efficacy profiles remain largely unchanged; genomic investigations showed no association with a parotid tumour.

Two-Year Outcomes of Valoctocogene Roxaparvovec Therapy for Hemophilia A.

BACKGROUND: Valoctocogene roxaparvovec delivers a B-domain-deleted factor VIII coding sequence with an adeno-associated virus vector to prevent bleeding in persons with severe hemophilia A. The findings of a phase 3 study of the efficacy and safety of valoctocogene roxaparvovec therapy evaluated after 52 weeks in men with severe hemophilia A have been published previously. METHODS: We conducted an open-label, single-group, multicenter, phase 3 trial in which 134 men with severe hemophilia A who were receiving factor VIII prophylaxis received a single infusion of 6×1013 vector genomes of valoctocogene roxaparvovec per kilogram of body weight. The primary end point was the change from baseline in the annualized rate of treated bleeding events at week 104 after receipt of the infusion. The pharmacokinetics of valoctocogene roxaparvovec were modeled to estimate the bleeding risk relative to the activity of transgene-derived factor VIII. RESULTS: At week 104, a total of 132 participants, including 112 with data that were prospectively collected at baseline, remained in the study. The mean annualized treated bleeding rate decreased by 84.5% from baseline (P<0.001) among the participants. From week 76 onward, the trajectory of the transgene-derived factor VIII activity showed first-order elimination kinetics; the model-estimated typical half-life of the transgene-derived factor VIII production system was 123 weeks (95% confidence interval, 84 to 232). The risk of joint bleeding was estimated among the trial participants; at a transgene-derived factor VIII level of 5 IU per deciliter measured with chromogenic assay, we expected that participants would have 1.0 episode of joint bleeding per year. At 2 years postinfusion, no new safety signals had emerged and no new serious adverse events related to treatment had occurred. CONCLUSIONS: The study data show the durability of factor VIII activity and bleeding reduction and the safety profile of valoctocogene roxaparvovec at least 2 years after the gene transfer. Models of the risk of joint bleeding suggest that the relationship between transgene-derived factor VIII activity and bleeding episodes is similar to that reported with the use of epidemiologic data for persons with mild-to-moderate hemophilia A. (Funded by BioMarin Pharmaceutical; GENEr8-1 ClinicalTrials.gov number, NCT03370913.).

A randomized, phase II trial of adjuvant immunotherapy with durable TKI-free survival in patients with chronic phase CML.

PURPOSE: Chronic myeloid leukemia (CP-CML) patients can achieve undetectable minimal residual disease (UMRD) and discontinue tyrosine kinase inhibitors (TKIs). Cellular immunity plays an important role in CML disease control. We conducted a randomized, non-blinded phase II trial of adjuvant immunotherapy with TKIs to facilitate TKI discontinuation. METHODS: TKI-treated patients with CP-CML were randomized to receive the K562/GM-CSF vaccine (vaccine) OR Interferon-α + Sargramostim (IFN). If UMRD was achieved, then all treatment was stopped. Patients who did not achieve UMRD within one year, had a molecular relapse, or discontinued therapy for toxicity could crossover. RESULTS: Thirty-four patients were randomized to IFN (n = 18) or vaccine (n = 16), and 21 patients crossed over (IFN⟶vaccine: n = 9, vaccine⟶IFN, n = 12). TKIs at enrollment included imatinib (n = 31), nilotinib (n = 2), and dasatinib (n = 1). No patients discontinued vaccine due to side effects, while 33 % of IFN-treated patients discontinued treatment. More patients randomized to IFN (47.4 %, 95 % CI: 16.7-66.7 %) versus vaccine (25.0 %, 95 % CI: 0.5-43.5 %) achieved UMRD within one year. Seven patients randomized to IFN discontinued treatment with 28.6 % (95 % CI: 8.9-92.2 %) sustaining treatment-free remission (TFR) at 1 year, while three patients randomized to vaccine discontinued treatment with none sustaining TFR. Including crossover, there was a cumulative discontinuation success rate of 36.4 % (95 % CI: 16.6 %-79.5 %) after adjuvant IFN. Patients who sustained TFR received a median of 29 months of imatinib prior to discontinuation. CONCLUSION: Adjuvant IFN led to durable TFRs with limited prior TKI exposure with comparable success to prior discontinuation trials, but many patients stopped IFN early.

A CD40 Agonist and PD-1 Antagonist Antibody Reprogram the Microenvironment of Nonimmunogenic Tumors to Allow T-cell-Mediated Anticancer Activity.

In cancers with tumor-infiltrating lymphocytes (TILs), monoclonal antibodies (mAbs) that block immune checkpoints such as CTLA-4 and PD-1/PD-L1 promote antitumor T-cell immunity. Unfortunately, most cancers fail to respond to single-agent immunotherapies. T regulatory cells, myeloid derived suppressor cells (MDSCs), and extensive stromal networks within the tumor microenvironment (TME) dampen antitumor immune responses by preventing T-cell infiltration and/or activation. Few studies have explored combinations of immune-checkpoint antibodies that target multiple suppressive cell populations within the TME, and fewer have studied the combinations of both agonist and antagonist mAbs on changes within the TME. Here, we test the hypothesis that combining a T-cell-inducing vaccine with both a PD-1 antagonist and CD40 agonist mAbs (triple therapy) will induce T-cell priming and TIL activation in mouse models of nonimmunogenic solid malignancies. In an orthotopic breast cancer model and both subcutaneous and metastatic pancreatic cancer mouse models, only triple therapy was able to eradicate most tumors. The survival benefit was accompanied by significant tumor infiltration of IFNγ-, Granzyme B-, and TNFα-secreting effector T cells. Further characterization of immune populations was carried out by high-dimensional flow-cytometric clustering analysis and visualized by t-distributed stochastic neighbor embedding (t-SNE). Triple therapy also resulted in increased infiltration of dendritic cells, maturation of antigen-presenting cells, and a significant decrease in granulocytic MDSCs. These studies reveal that combination CD40 agonist and PD-1 antagonist mAbs reprogram immune resistant tumors in favor of antitumor immunity.

A Multi-center Phase I Trial of Ipilimumab in Patients with Myelodysplastic Syndromes following Hypomethylating Agent Failure.

Purpose: After failure of hypomethylating agents (HMA), patients with myelodysplastic syndromes (MDS) have dismal survival and no approved treatment options.Patients and Methods: We conducted a phase 1b investigator-initiated trial of ipilimumab in patients with higher risk MDS who have failed HMAs. Patients received monotherapy at two dose levels (DL; 3 and 10 mg/kg) with an induction followed by a maintenance phase. Toxicities and responses were evaluated with CTCAE.4 and IWG-2006 criteria, respectively. We also performed immunologic assays and T-cell receptor sequencing on serial samples.Results: Twenty-nine patients from 7 centers were enrolled. In the initial DL1 (3 mg), 3 of 6 patients experienced grade 2-4 immune-related adverse events (IRAE) that were reversible with drug discontinuation and/or systemic steroids. In DL2, 4 of 5 patients experienced grade 2 or higher IRAE; thus, DL1 (3 mg/kg) was expanded with no grade 2-4 IRAEs reported in 18 additional patients. Best responses included marrow complete response (mCR) in one patient (3.4%). Prolonged stable disease (PSD) for ≥46 weeks occurred in 7 patients (24% of entire cohort and 29% of those treated with 3 mg/kg dose), including 3 patients with more than a year of SD. Five patients underwent allografting without excessive toxicity. Median survival for the group was 294 days (95% CI, 240-671+). Patients who achieved PSD or mCR had significantly higher frequency of T cells expressing ICOS (inducible T-cell co-stimulator).Conclusions: Our findings suggest that ipilimumab dosed at 3 mg/kg in patients with MDS after HMA failure is safe but has limited efficacy as a monotherapy. Increased frequency of ICOS-expressing T cells might predict clinical benefit. Clin Cancer Res; 24(15); 3519-27. ©2018 AACR.

Related donor transplants: has posttransplantation cyclophosphamide nullified the detrimental effect of HLA mismatch?

We sought to identify whether posttransplantation cyclophosphamide (PT-Cy) reduces or eliminates the detrimental impact of HLA mismatching on outcomes of HLA-haploidentical related donor transplantation for acute leukemia. Data from 2143 donor-recipient pairs (n = 218 haploidentical sibling; n = 218 offspring; n = 1707 HLA-matched sibling) with acute myeloid or lymphoblastic leukemia were studied. All received a calcineurin inhibitor for graft-versus-host disease (GVHD) prophylaxis while high-dose PT-Cy was also given to recipients of haploidentical transplant. Patient age correlated with donor-recipient relationship: haploidentical siblings donated to patients aged 18 to 54 years whereas offspring donated to patients aged 55 to 76 years. Therefore, transplant outcomes were examined separately in the 2 patient age groups. In patients aged 18 to 54 years, there were no significant differences in outcomes except chronic GVHD, which was lower after haploidentical sibling compared to HLA-matched sibling transplant (hazard ratio [HR], 0.63; P < .001). In patients aged 55 to 76 years, despite lower chronic GVHD (HR, 0.42; P < .001), graft failure (14% vs 6%; P = .003), nonrelapse mortality (HR, 1.48; P = .02), and overall mortality (HR, 1.32; P = .003) were higher after transplant from offspring compared with an HLA-matched sibling. These data demonstrate a superior outcome in older recipients when using an HLA-matched sibling instead of offspring, although there were differences in transplant platforms (GVHD prophylaxis and graft type) between the 2 groups. Validation of these findings requires a prospective randomized trial wherein the transplant platforms can be closely matched.

Pilot trial of K562/GM-CSF whole-cell vaccination in MDS patients.

Myelodysplastic syndromes (MDS) are a heterogeneous group of clonal hematopoietic stem cell malignancies. Currently, approved drugs are given with non-curative intent as the only known cure is allogeneic bone marrow transplantation, which relies on the donor's immune system driving an allogeneic effect. Previous efforts to harness the endogenous immune system have been less successful. We present the results of a pilot study of K562/GM-CSF (GVAX) whole-cell vaccination in MDS patients. The primary objective of safety was met as there were no serious adverse events. One patient had a decrease in transfusion requirements and another demonstrated hematologic improvement suggesting a signal for clinical activity. In vitro correlative studies indicated biological effects on immune cells following vaccination. Although only a pilot study, results are encouraging that an immunotherapeutic approach with a whole-cell vaccine may be feasible in MDS patients.

Pirfenidone ameliorates murine chronic GVHD through inhibition of macrophage infiltration and TGF-ß production.

Allogeneic hematopoietic stem cell transplantation is hampered by chronic graft-versus-host disease (cGVHD), resulting in multiorgan fibrosis and diminished function. Fibrosis in lung and skin leads to progressive bronchiolitis obliterans (BO) and scleroderma, respectively, for which new treatments are needed. We evaluated pirfenidone, a Food and Drug Administration (FDA)-approved drug for idiopathic pulmonary fibrosis, for its therapeutic effect in cGVHD mouse models with distinct pathophysiology. In a full major histocompatibility complex (MHC)-mismatched, multiorgan system model with BO, donor T-cell responses that support pathogenic antibody production are required for cGVHD development. Pirfenidone treatment beginning one month post-transplant restored pulmonary function and reversed lung fibrosis, which was associated with reduced macrophage infiltration and transforming growth factor-ß production. Pirfenidone dampened splenic germinal center B-cell and T-follicular helper cell frequencies that collaborate to produce antibody. In both a minor histocompatibility antigen-mismatched as well as a MHC-haploidentical model of sclerodermatous cGVHD, pirfenidone significantly reduced macrophages in the skin, although clinical improvement of scleroderma was only seen in one model. In vitro chemotaxis assays demonstrated that pirfenidone impaired macrophage migration to monocyte chemoattractant protein-1 (MCP-1) as well as IL-17A, which has been linked to cGVHD generation. Taken together, our data suggest that pirfenidone is a potential therapeutic agent to ameliorate fibrosis in cGVHD.

Allogeneic stem cell transplantation for sickle cell disease.

PURPOSE OF REVIEW: As the safety and availability of allogeneic hematopoietic stem cell transplantation (HSCT) have improved, this procedure is becoming a viable option for nonmalignant conditions such as sickle cell disease (SCD). There are very few treatment options available for SCD, and even with optimal care SCD patients still suffer from a myriad of comorbidities to multiple organ systems and have a decreased life span. In this review, we will summarize results from trials of HSCT for children or adults with SCD using a variety of graft sources as well as conditioning and graft-versus-host disease prophylaxis regimens, and discuss the unique challenges that arise in these patients. RECENT FINDINGS: AlloHSCT for SCD has been performed on small numbers of patients at multiple centers around the world using several different transplant platforms, and early outcomes are encouraging. Overall survival is excellent, although graft failure remains a challenge. SUMMARY: As alloHSCT becomes safer and more widely available, the procedure should be considered for patients with severe disease phenotypes in whom the potential benefits of transplantation outweigh the complications from the disease. AlloHSCT has been shown to reverse or at least halt the progression of end-organ damage secondary to SCD. More research is needed to understand the mechanisms underlying graft failure in SCD recipients, as well as to understand the biopsychosocial underpinnings of persistent pain in the posttransplant period to maximize the benefit from the transplant procedure.

Haploidentical bone marrow and stem cell transplantation: experience with post-transplantation cyclophosphamide.

Allogeneic blood or bone marrow transplantation (BMT) is a potentially curative therapy for high-risk hematologic malignancies not curable by standard chemotherapy, but the procedure is limited by the availability of human leukocyte antigen-matched donors for many patients, as well as toxicities including graft-versus-host disease (GVHD). Our group has developed the use of high-dose post-transplantation cyclophosphamide (PTCy) to selectively remove alloreactive T cells without compromising engraftment. This protocol has allowed for successful transplantation of human leukocyte antigen (HLA)-haploidentical (haplo) grafts, thus expanding the donor pool for the many patients who would not otherwise be a candidate for this life-saving procedure. In this review we will summarize the data that led to the development of PTCy, then focus on the outcomes of haploBMT trials with PTCy across different transplant platforms for patients with malignant hematologic diseases, and finally we will discuss emerging evidence that suggests equivalency of haploBMT with PTCy compared with more traditional transplants.

Potential role for all-trans retinoic acid in nonpromyelocytic acute myeloid leukemia.

All-trans retinoic acid (ATRA) has been very successful in the subtype of acute myelogenous leukemia known as acute promyelocytic leukemia due to targeted reactivation of retinoic acid signaling. There has been great interest in applying this form of differentiation therapy to other cancers, and numerous clinical trials have been initiated. However, ATRA as monotherapy has thus far shown little benefit in nonacute promyelocytic leukemia acute myelogenous leukemia. Here, we review the literature on the use of ATRA in combination with chemotherapy, epigenetic modifying agents and targeted therapy, highlighting specific patient populations where the addition of ATRA to existing therapies may provide benefit. Furthermore, we discuss the impact of recent whole genome sequencing efforts in leading the design of rational combinatorial approaches.

DR5 activation of caspase-8 induces DC maturation and immune enhancement in vivo.

Non-homeostatic tissue apoptosis in vivo has been shown to induce inflammatory responses and facilitate the cross-presentation of proteins within apoptotic bodies. We hypothesize that in the presence of foreign antigens, the apoptotic-inflammatory process improves immune priming; further, molecules that trigger apoptosis may be adapted for use as immune adjuvants. One very attractive molecule in this context is the tumor necrosis factor receptor (TNFR) family molecule DR5/TRAIL-receptor 2. We show a significant improvement in CD8(+) T-cell mediated vaccine immunity with the use of death receptor-5 (DR5) as an immune adjuvant, a property that is correlated with the activation of caspases-8 (casp8) and dependent on its ability to induce apoptosis in vivo.

Protection against simian/human immunodeficiency virus (SHIV) 89.6P in macaques after coimmunization with SHIV antigen and IL-15 plasmid.

The cell-mediated immune profile induced by a recombinant DNA vaccine was assessed in the simian/HIV (SHIV) and macaque model. The vaccine strategy included coimmunization of a DNA-based vaccine alone or in combination with an optimized plasmid encoding macaque IL-15 (pmacIL-15). We observed strong induction of vaccine-specific IFN-gamma-producing CD8(+) and CD4(+) effector T cells in the vaccination groups. Animals were subsequently challenged with 89.6p. The vaccine groups were protected from ongoing infection, and the IL-15 covaccinated group showed a more rapidly controlled infection than the group treated with DNA vaccine alone. Lymphocytes isolated from the group covaccinated with pmacIL-15 had higher cellular proliferative responses than lymphocytes isolated from the macaques that received SHIV DNA alone. Vaccine antigen activation of lymphocytes was also studied for a series of immunological molecules. Although mRNA for IFN-gamma was up-regulated after antigen stimulation, the inflammatory molecules IL-8 and MMP-9 were down-regulated. These observed immune profiles are potentially reflective of the ability of the different groups to control SHIV replication. This study demonstrates that an optimized IL-15 immune adjuvant delivered with a DNA vaccine can impact the cellular immune profile in nonhuman primates and lead to enhanced suppression of viral replication.

SIV DNA vaccine co-administered with IL-12 expression plasmid enhances CD8 SIV cellular immune responses in cynomolgus macaques.

Current evidence suggests that a strong induced CD8 human immunodeficiency virus type 1 (HIV-1)-specific cell mediated immune response may be an important aspect of an HIV vaccine. The response rates and the magnitude of the CTL responses induced by current DNA vaccines in humans need to be improved and cellular immune responses to DNA vaccines can be enhanced in mice by co-delivering DNA plasmids expressing immune modulators. Two reported to work well in the mouse systems are interleukin (IL)-12 and CD40L. We sought to compare these molecular adjuvants in a primate model system. The cDNA for macaque IL-12 and CD40L were cloned into DNA vectors. Groups of cynomolgus macaques were immunized with 2 mg of plasmid expressing SIVgag alone or in combination with either IL-12 or CD40L. CD40L did not appear to enhance the cellular immune response to SIVgag antigen. However, more robust results were observed in animals co-injected with the IL-12 molecular adjuvant. The IL-12 expanded antigen-specific IFN-gamma positive effector cells as well as granzyme B production. The vaccine immune responses contained both a CD8 component as well a CD4 component. The adjuvanted DNA vaccines illustrate that IL-12 enhances a CD8 vaccine immune response, however, different cellular profiles.

DNA prime Listeria boost induces a cellular immune response to SIV antigens in the rhesus macaque model that is capable of limited suppression of SIV239 viral replication.

DNA vaccines and recombinant Listeria monocytogenes that express and secrete SIV Gag and Env antigens were combined in a nonhuman primate prime-boost immunogenicity study followed by a challenge with SIV239. We report that recombinant DNA vaccine delivered intramuscularly, and recombinant L. monocytogenes delivered orally each individually have the ability to induce CD8+ and CD4+ T cell immune responses in a nonhuman primate. Four rhesus monkeys were immunized at weeks 0, 4, 8, and 12 with the pCSIVgag and pCSIVenv DNA plasmids and boosted with SIV expressing L. monocytogenes vaccines at weeks 16, 20, and 28. Four rhesus monkeys received only the L. monocytogenes vaccines at weeks 16, 20, and 28. A final group of monkeys served as a control group. Blood samples were taken before vaccination and 2 weeks post each injection and analyzed by ELISPOT for CD4+ and CD8+ T cell responses. Moderate vaccine induced SIV-specific cellular immune responses were observed following immunization with either DNA or L. monocytogenes vectors. However, the SIV antigen-specific immune responses were significantly increased when Rhesus macaques were primed with SIV DNA vaccines and boosted with the SIV expressing L. monocytogenes vectors. In addition, the combined vaccine was able to impact SIV239 viral replication following an intrarectal challenge. This study demonstrates for the first time that oral L. monocytogenes can induce a cellular immune response in a nonhuman primate and is able to enhance the efficacy of a DNA vaccine as well as provide modest protection against SIV239 challenge.