CD8-mediated Immune Responses Research Articles

Intraperitoneal administration of a modified vaccinia virus Ankara confers single-chain interleukin-12 expression to the omentum and achieves immune-mediated efficacy against peritoneal carcinomatosis

BackgroundPeritoneal carcinomatosis is an advanced stage of cancer in which the disease has spread to the peritoneal cavity. In order to restore antitumor immunity subverted by tumor cells in this...

Invariant NKT Cells Promote the Development of Highly Cytotoxic Multipotent CXCR3+CCR4+CD8+ T Cells That Mediate Rapid Hepatocyte Allograft Rejection.

Hepatocyte transplant represents a treatment for metabolic disorders but is limited by immunogenicity. Our prior work identified the critical role of CD8+ T cells, with or without CD4+ T cell help, in mediating hepatocyte rejection. In this study, we evaluated the influence of invariant NKT (iNKT) cells, uniquely abundant in the liver, upon CD8-mediated immune responses in the presence and absence of CD4+ T cells. To investigate this, C57BL/6 (wild-type) and iNKT-deficient Jα18 knockout mice (cohorts CD4 depleted) were transplanted with allogeneic hepatocytes. Recipients were evaluated for alloprimed CD8+ T cell subset composition, allocytotoxicity, and hepatocyte rejection. We found that CD8-mediated allocytotoxicity was significantly decreased in iNKT-deficient recipients and was restored by adoptive transfer of iNKT cells. In the absence of both iNKT cells and CD4+ T cells, CD8-mediated allocytotoxicity and hepatocyte rejection was abrogated. iNKT cells enhance the proportion of a novel subset of multipotent, alloprimed CXCR3+CCR4+CD8+ cytolytic T cells that develop after hepatocyte transplant and are abundant in the liver. Alloprimed CXCR3+CCR4+CD8+ T cells express cytotoxic effector molecules (perforin/granzyme and Fas ligand) and are distinguished from alloprimed CXCR3+CCR4-CD8+ T cells by a higher proportion of cells expressing TNF-α and IFN-γ. Furthermore, alloprimed CXCR3+CCR4+CD8+ T cells mediate higher allocytotoxicity and more rapid allograft rejection. Our data demonstrate the important role of iNKT cells in promoting the development of highly cytotoxic, multipotent CXCR3+CCR4+CD8+ T cells that mediate rapid rejection of allogeneic hepatocytes engrafted in the liver. Targeting iNKT cells may be an efficacious therapy to prevent rejection of intrahepatic cellular transplants.

Boost of Immune Responses Against NY-ESO-1 Following Local Radiation Therapy in Patients with Multiple Myeloma: A Potential Contribution to Tumor Immunosurveillance

IntroductionLocal radiation therapy (RT) is commonly employed to treat bone lesions and/or extramedullary manifestations of multiple myeloma (MM) or solitary bone plasmacytoma (SBP). Besides providing sufficient control of local tumor growth, radiation therapy may also contribute to broader anti-tumor immunity by generating off-site cellular immune responses. Here, we put a focus on tumor-associated antigens (TAAs) well known for their expression in MM such as Wilms' Tumor Protein 1 (WT1), New York esophageal squamous cell carcinoma 1 (NY-ESO-1), human telomerase reverse transcriptase (hTERT), mucin 1 (MUC1), and preferentially expressed antigen of melanoma (PRAME) and assessed CD8-mediated immune responses before and during radiation.MethodsWe prospectively recruited HLA-A*02:01-positive patients with multiple myeloma or solitary plasmacytoma requiring local radiation therapy for bone and extramedullary lesions in this scientific, non-interventional study, supported by a grant of the Wilhelm Sander Foundation, Germany, and approved by our local ethical committee. All patients provided written informed consent. Immune responses against HLA-A*02:01-restricted peptides of WT1, NY-ESO-1, hTERT, MUC1, and PRAME were assessed at three different time points: prior to RT, end of RT and six to eight weeks after RT. CD8+ T lymphocytes were isolated from peripheral blood and stimulated with irradiated, peptide-pulsed T2 cells (174 x CEM.T2; ATCC® CRL-1992™). After extraction of total RNA, Interferon gamma (IFNγ) mRNA expression was analyzed by RT-qPCR. IFNγ mRNA levels were normalized to CD8 mRNA levels. IFNγ mRNA expression of cells stimulated with the irrelevant melanoma antigen Glycoprotein 100 (gp100) served as calibrator. An expression level of 2.0 or more as compared to gp100 was considered as a positive result. Furthermore, an intracellular cytokine staining assay to detect IFNγ release in peptide-stimulated cells was employed to confirm PCR results on a protein level. Peptide-pulsed T2 cells also served as targets in CD107a degranulation assays.ResultsTo date, 19 patients including 16 MM and three SBP patients received fractionated local RT with or without concomitant systemic therapy. 13 patients were previously untreated; three patients received prior allogeneic and five prior autologous hematopoietic stem cell transplantation. At baseline, positive immune responses were frequently detected against NY-ESO-1 (10 out of 17 assessed patients; 58.8%) but interestingly not against hTERT, WT1, MUC1 or PRAME (see Figure). Consequently, baseline immune responses against NY-ESO-1 were significantly higher (p<0.001) as compared to all other TAAs investigated (Kruskal Wallis test). These median response levels against NY-ESO-1 further increased in the course of radiation therapy and were confirmed by flow cytometry on a protein level. The functionality and specificity of these responses could be demonstrated in degranulation assays suggesting the ability to deliver efficient anti-tumor immunity.ConclusionsImmunity against NY-ESO-1 was preexisting in the majority of patients and was undergoing marked expansion under local radiotherapy. This phenomenon was not found for any other TAA investigated suggesting that NY-ESO-1 carries a unique immunogenicity justifying most recent attempts to employ NY-ESO-1 as a target for genetically engineered T lymphocytes. Finally, this tumor-specific immunity is likely to contribute to immunosurveillance of multiple myeloma additionally supported by immune modulatory drugs applied for treatment such as IMiDs and proteasome inhibitors. [Display omitted] DisclosuresKnop:Takeda: Consultancy. Einsele:Celgene: Consultancy, Honoraria, Speakers Bureau; Janssen: Consultancy, Honoraria, Speakers Bureau; Novartis: Consultancy, Honoraria; Amgen: Consultancy, Honoraria, Speakers Bureau. Mielke:MSD: Consultancy, Other: Travel grants; Gilead: Other: Travel grants; Novartis: Consultancy; Celgene: Other: Travel grants, Speakers Bureau; JAZZ Pharma: Speakers Bureau.

Anti-CD19 Chimeric Antigen Receptor-Modified T Cell Therapy for B Cell Non-Hodgkin Lymphoma and Chronic Lymphocytic Leukemia: Fludarabine and Cyclophosphamide Lymphodepletion Improves In Vivo Expansion and Persistence of CAR-T Cells and Clinical Outcomes

BACKGROUND:Autologous T cells genetically modified to express a CD19-specific chimeric antigen receptor (CAR) have demonstrated activity in patients with relapsed or refractory B cell NHL and CLL. The functional heterogeneity that is inherent in CAR-T cell products that are manufactured from undefined T cell subsets has hindered definition of dose-response relationships and identification of factors that may impact efficacy and toxicity, such as the lymphodepletion regimen and infused cell dose.We manufactured anti-CD19 CAR-T cells from a defined composition of CD4+ and CD8+ T cell subsets to treat adults with relapsed or refractory B cell NHL or CLL. T cell subsets were enriched from each patient, transduced with a CD19 CAR lentivirus and separately expanded in vitro before formulation for infusion in a 1:1 ratio of CD8+:CD4+ CAR+ T cells at one of three dose levels (2x105, 2x106 or 2x107 CAR-T cells/kg). CAR-T cells were administered 48-96 hours after lymphodepletion with either cyclophosphamide (Cy, 60 mg/kg)+/- etoposide or Cy (60 mg/kg) and fludarabine (25 mg/m2 daily for 3-5 days (Cy/Flu).RESULTS:Adult patients with relapsed/refractory CD19 expressing B cell NHL (n=28, median age 59 years, range 36-70) or CLL (n=6, median age 60 years, range 54-64) were treated with at least one CAR-T cell infusion. NHL histologies include diffuse large B cell or transformed NHL (DLBCL, n=18), follicular NHL (FL, n= 6) or mantle cell lymphoma (MCL, n=4). 15 patients had failed prior autologous (n=13) or allogeneic (n=3) transplants.Twelve of the 28 NHL patients received lymphodepletion with Cy-based regimens without fludarabine. Expansion of CAR-T cells and clinical responses were observed in 50% (CR=1 (DLBCL), PR=5 (2 FL, 2 DLBCL, 1 MCL), no response=6). Patients were treated at all three dose levels without dose limiting toxicity or severe cytokine release syndrome (sCRS). With this regimen, we observed short CAR-T cell persistence in most patients and demonstrated a CD8-mediated immune response to the murine scFv component of the CAR transgene that correlated with loss of CAR-T cells. Retreatment with CAR-T cells with or without chemotherapy in 5 patients led to no significant T cell expansion or clinical responses.To minimize transgene rejection fludarabine was added to the lymphodepletion regimen administered to the subsequent 16 NHL patients. Clinical responses were evaluated in 12 of 16 patients (2 not yet evaluable, 2 early deaths). Addition of Flu to the lymphodepletion regimen increased the CR rate to 42%, compared to 8% with Cy alone. Clinical responses were identified in 6 of 8 patients with DLBCL (3 CR, 3 PR) and 2 of 3 patients with FL (2 CR). The overall response rate was 67%. We noted higher peak CAR-T cell levels in blood in the Cy/Flu group (n=13) compared with the Cy only group (n=11) (CD8+ CAR-T cells, median 31.9 cells/ml vs 0.55 cells/ml, p = 0.009; CD4+ CAR-T cells, median 16.5 cells/ml vs 0.31 cells/ml, p= 0.007), and CAR-T cell persistence was longer in Flu-treated patients (see Figure 1 for patients treated at 2 x 107/kg). Surprisingly, 2 of 7 patients who received 2 x 107 CAR-T cells/kg experienced dose-limiting toxicity necessitating dose de-escalation. Markedly elevated IL-6 levels were observed within the first day after CAR-T cell infusion in patients who subsequently developed severe toxicity, which may provide an opportunity to test early interventional approaches to minimize toxicity.Six patients with relapsed and refractory CLL received CAR-T cells. Five of 6 restaged patients had complete clearance of blood and/or marrow disease by high-resolution flow cytometry 4 weeks following treatment. Overall clinical responses included 3 CR, 1 PR and 2 no response. One patient with a PR died from refractory pulmonary aspergillus infection. Patients with CR remain in remission at 1-10 months after therapy.CONCLUSION:Immunotherapy with CD19 CAR-T cells of defined subset composition is feasible in patients with NHL and CLL and has potent anti-tumor activity. Toxicity is related to cell dose. The addition of Flu to a Cy-based lymphodepletion regimen results in greater CAR-T cell expansion and persistence, and improves the CR rate after CD19 CAR-T cell therapy. [Display omitted] DisclosuresTurtle:Juno Therapeutics: Patents & Royalties, Research Funding. Berger:Juno Therapeutics: Patents & Royalties. Jensen:Juno Therapeutics: Equity Ownership, Patents & Royalties, Research Funding. Riddell:Juno Therapeutics: Equity Ownership, Patents & Royalties, Research Funding; Cell Medica: Membership on an entity's Board of Directors or advisory committees; Adaptive Biotechnologies: Consultancy. Maloney:Juno Therapeutics: Research Funding; Janssen Scientific Affairs: Honoraria; Seattle Genetics: Honoraria; Roche/Genentech: Honoraria.

Abstract 2490: CD40 ligand expressing recombinant vaccinia virus (rVV40L) modulation of central memory CD8-mediated immune response

Abstract In cancer immunotherapy, induction of tumor-reactive CD8+ T cells displaying phenotypic and functional profile of central memory T cells (TCM) is associated with favorable prognosis. A key element in the generation of TCM CD8+ cells is represented by the help provided by CD4+ T cells during the priming of naïve CD8+ T cells. In particular CD40 ligand (CD40L) expressed and/or secreted by activated CD4+ T cells triggers CD40 receptor expressed on antigen presenting cells (APCs) thereby enhancing their antigen presentation capacity. In order to bypass the requirement of CD4+ T cells we generated a non-replicating recombinant vaccinia virus encoding human CD40L (rVV40L) and compared its ability to shape CD8-mediated immune response to soluble CD40L recombinant protein (sCD40L). In this regard, our data clearly underline the different biological properties of membrane-bound CD40L, as provided by rVV40L infection, as compared to its soluble form, in CD14+ APCs activation. Notably, considering expression of IL-12p40, IFN-a and -b genes, cytokines of proven relevance for memory T cell induction, rVV40L-infection was much more potent than s40L-treatment alone or combine with WT infection. In parallel, s40L-stimulation induced a much more significant expression of IL-10 and indoleamine-2, 3-dioxygenase (IDO) genes encoding immunosuppressive factors. Considering a panel of molecules involved in the generation of the immunological synapse with T cells on CD14+ cells, rVV40L appeared to promote a less intense up regulation of CD80 co-stimulatory molecules but, most importantly, only a minor increase of programmed death ligand-1 (PD-L1). Therefore, gene expression and phenotypic profiles suggested that rVV40L-infected CD14+ cells might be highly effective APC in the induction of TCM CD8+ cells. Indeed, a single in vitro stimulation of naïve CD8+ T cells by rVV40L-infected CD14+ cells, in the absence of CD4+ T cells, was able to promote the rapid generation of central memory TAA (MAGE and MART-1) specific CD8+ T cells. These TCM were characterized by the typical central memory phenotype, as indicated by co-expression of CD45RO, CD62L and IL-7Ra, and by the high proliferative potential upon antigen recognition. Collectively our data indicate that rVV40L efficiently modulates the quality of different APC signals delivered during the formation of the immunological synapse with CD8+ T cells. These in-vitro observations validate the strong clinical potential of our recombinant vaccinia virus constructs co-expressing CD40L for cancer immunotherapies. Citation Format: Emanuele Trella, Evangelos Panopoulos, Nermin Raafat, Chantal Mengus, Emmanuel Traunecker, Swantje Heidtmann, Michael Heberer, Daniel Oertli, Giulio Cesare Spagnoli, Paul Zajac. CD40 ligand expressing recombinant vaccinia virus (rVV40L) modulation of central memory CD8-mediated immune response. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2490. doi:10.1158/1538-7445.AM2015-2490

DNA is an efficient booster of dendritic cell-based vaccine

DC-based therapeutic vaccines as a promising strategy against chronic infections and cancer have been validated in several clinical trials. However, DC-based vaccines are complex and require many in vitro manipulations, which makes this a personalized and expensive therapeutic approach. In contrast, DNA-based vaccines have many practical advantages including simplicity, low cost of manufacturing and potent immunogenicity already proven in non-human primates and humans. In this study, we explored whether DC-based vaccines can be simplified by the addition of plasmid DNA as prime or boost to achieve robust CD8-mediated immune responses. We compared the cellular immunity induced in BALB/c and C57BL/6 mice by DC vaccines, loaded either with peptides or optimized SIV Env DNA, and plasmid DNA-based vaccines delivered by electroporation (EP). We found that mature DC loaded with peptides (P-mDC) induced the highest CD8+ T cell responses in both strains of mice, but those responses were significantly higher in the C57BL/6 model. A heterologous prime-boost strategy (P-DC prime-DNA boost) induced CD8+ T cell responses similar to those obtained by the P-DC vaccine. Importantly, this strategy elicited robust polyfunctional T cells as well as highest antigen-specific central memory CD8+ T cells in C57BL/6 mice, suggesting long-term memory responses. These results indicate that a DC-based vaccine in combination with DNA in a heterologous DC prime-DNA boost strategy has potential as a repeatedly administered vaccine.

Langerin+ Dermal DC, but Not Langerhans Cells, Are Required for Effective CD8-Mediated Immune Responses after Skin Scarification with Vaccinia Virus

Skin scarification (s.s.) with Vaccinia virus (VACV) is essential for generation of an optimal protective T cell memory immune response. Dendritic Cells (DC), which are professional antigen presenting cells, are required for naïve T cell priming and activation. At least three subsets of skin resident DC have been identified: Langerhans Cells (LC), Dermal Langerin+ DC (Lang+dDC) and Dermal Langerin− DC (Lang−dDC). Using Langerin-diphtheria toxin receptor mice and established mouse model of VACV delivered by s.s., we demonstrated that Lang+dDC, but not LC, are absolutely required for the induction of a rapid and robust antigen-specific CD8+ T cell response after s.s. with VACV. The depletion of Lang+dDC led to a significant delay in the priming and proliferation of antigen-specific CD8+ T cells. Moreover CD8+ T cells generated after VACV s.s. in the absence of Lang+dDC lacked effector cytotoxic functions both in vitro and in vivo. While s.s.-immunized WT and LC depleted mice controlled the progression of OVA257–264 expressing T cell lymphoma EG7 (injected intradermally), the depletion of Lang+dDC led to rapid lymphoma progression and mortality. These data indicate that of all skin DC subsets, Lang+dDC the most critical for the generation of robust CD8+ T cell immunity after s.s. with VACV.

Stimulation of the immune system by small chemicals can be independent of hapten-protein conjugate formation and is regulated by the TCR avidity for the HLA-drug complex (106.51)

Abstract Rationale: The antiretroviral drug abacavir (abc) elicits a strong CD8-mediated immune response in HLA-B*5701+ subjects. We used this model to study the interaction of small chemicals with the immune system. Methods: We generated abc-specific T-cell clones (abc-TCC) from HLA-B*5701+ donors and analyzed their specific activation in Ca2+ influx assays and by annexin V staining. Results: Abc-metabolizing enzymes were absent in immune cells and inhibition of the proteasome in antigen presenting cells did not affect TCC reactivity. Five out of 50 abc-TCC reacted instantly (~120 sec) to soluble abc presented on HLA-B*5701, whereas many other TCC reacted after 20 min or later. Increasing the number of HLA-B*5701/abc immunogenic complexes by increasing the abc concentrations and/or using transfected cells with a high HLA-B*5701 expression accelerated the abc-TCC activation kinetic. Analysis of several abc-TCC revealed different TCR Vβ-segments, demonstrating their polyclonality. Conclusions: Since the observed abc-reactivity was metabolism- and processing- independent, an immune activation by small chemicals can occur without covalent drug binding to a carrier protein. Moreover, titration experiments revealed different TCC reactivity patterns. This finding suggests a crucial role of the TCR avidity for the drug in regulating T cell activation. These data have implications in drug regulation of the immune system as well as for understanding drug hypersensitivity.

Intrathymic injection of lentiviral vector curtails the immune response in the periphery of normal mice

Gene transfer in the thymus, based on HIV-derived lentiviral vectors, is a promising avenue for modulation of T cell selection and autoimmunity. However, the impact of intrathymic (IT) injections on an antigen-specific immune response elicited in the periphery of normal mice has not been investigated yet. Highly concentrated stocks of lentiviral vectors expressing the soluble form of hemaglutinin of the influenza virus (LvHA) were injected in the thymus of normal BALB/c mice. The CD4 and CD8-mediated immune responses to HA after peripheral immunization were measured by various parameters. We first show that a lentiviral vector expressing the luciferase was detected for at least 2 months after IT-injections. We then show that the LvHA vector could elicit a functional CD4- and CD8-T cell-mediated immune responses in the peripheral lymphoid organs of BALB/c mice. IT-injection of the LvHA vector significantly curbed this response: lower numbers of transferred HA-specific CD4(+) T cells were found in LvHA-injected compared to control animals. Furthermore, lower frequencies of HA-specific CD8(+) T cells, interferon γ-producing cells and cytotoxic cells were detected from 3 weeks to 3 months in LvHA-injected mice compared to controls. However, these reduced CD8-mediated responses were not increased after depletion of CD25(+) cells in vitro or in vivo. The results obtained in the present study show that injection of the LvHA lentiviral vector significantly curtailed the immune response to the same antigen in the periphery. Increased selection of HA-specific regulatory T cells and negative selection of HA-specific CD8(+) T cell precursors may explain the results. Our work establish the feasibility of IT-injections of lentiviral vectors to manipulate T cell tolerance in the thymus of normal mice, for basic and pre-clinical research.

Anti-Viral Immunity to CMV Reactivation in Allogeneic HSCT Recipients.

Abstract 1165Poster Board I-187 BackgroundOpportunistic CMV infections remain a major cause of morbidity and mortality in allogeneic hematopoetic stem cell transplant (HSCT) recipients, with prolonged periods of viremia associated with cytopenia and life-threatening end-organ infections. Although CMV infection in allogeneic HSCT recipients may be controlled using anti-viral drugs, re-occurrence of viremia when drug therapy is stopped is common, and the emergence of drug resistant viral strains may render the anti-viral agents ineffective. The lack of functional anti-viral immunity that leads to CMV reactivation in immunocompromized HSCT recipients is a complex phenomena and may be due to 1) failure or insufficient donor/host innate immunity to prevent reactivation of CMV from their latent state, 2) failure to effectively process and present CMV antigens by the appropriate APCs to anti-viral T cells due to conditioning regimens used to prevent graft rejection and graft-vs-host disease (GvHD); 3) lack of response of CMV specific memory T cells to control CMV infection. Lack of any or all of these three elements of immune responses are hypothesized to be responsible for clinical CMV reactivation or infections in allogeneic transplant recipients. Determining which of these three elements of effective anti-viral immunity are most critical to preventing CMV infection would help guide novel therapies designed to prevent or treat opportunistic viral infections of high-risk patients. MethodEmory is the core immune-monitoring laboratory for multi-center clinical study CTN 0201. As part of this study, we have samples from 69 HLA-A*2+ patients who received myeloablative conditioning and allogeneic HSCT from unrelated donors. HLA-A*2 restricted HCMV peptide pp65 (495-503, NLVPMVATV) specific tetramer+ CD8+ T-cells were determined from the blood samples obtained on 3, 6, and 12 months post transplant. Blood samples from three patients (2 HLA-A*2+ and 1 HLA-B*7+) treated at Emory had simultaneous data on both CMV viral load (measured by RT PCR) and the anti-CMV specific T-cells using the HLA-A*2 and HLA-B*7 [CMV pp65(NLVPMVATV)] tetramer reagents. ResultsOut of 69 patients, 5% had more than 1% CD8+ T-cells expressing the HLA-A*2 restricted CMV pp65 specific T-cell receptor at 3 months post-transplant, with an increasing proportion of patients showing the presence of at least 1% CMV-specific T-cells at 6 and 12 months post-transplant. Serial simultaneous measurements of CMV viral load and anti-CMV-specific T-cells are shown in Table 1 for 3 pts treated at Emory. In each case, evidence of active CMV replication was accompanied by a rapid expansion of CMV pp65-specific T-cells in the blood. Contraction of the CMV-specific T-cell compartment subsequently occurred, in conjunction with antiviral therapy and successful clearance of the virus. CMV reactivation events were not associated with major changes in the numbers of CD4+ T-cells, monocytes, or granulocytes. ConclusionsSuccessful control of CMV reactivation is associated with a rapid and specific CD8-mediated immune response, which works in conjunction with antiviral therapy to limit viral replication. We would predict that the inability to control CMV reactivation, which is observed in a subset of pts following allogeneic transplantation, may not be associated with the same degree of target-specific immune expansion. This may be due to low absolute T-cell numbers, lack of innate immune responses or suppression of the ability of memory T cells to become effector T cells. Ongoing analyses will correlate measurements of tetramer+ T-cells in the 0201 dataset with laboratory evidence for CMV viremia and clinical infection.Table 1Patient #, age and days after HSCTViral load, Copies/ml bloodAnti-viral therapy%Anti-viral CD8+ T cells*% CD8+ T cells*% CD4+ T cells*%Lym%Mo%Gra1. HLA-A*2+ 51 Yrs, D75400IV (ganciclovir)NDNDNDNDNDNDD831300IV11.492.76.738.58.353.2D903205.492.35.240.27.152.72. HLA-B*7, 37 Yrs, D602300IVNDNDNDNDNDNDD642900IV2.363.631.222.310.367.4D67710IV4.881.713.633.55.960.6D70<200IV4.565.430.433.96.060.1D77<200IV2.857.537.736.28.455.43. HLA-A*2, 58 Yrs, D19360Oral (valganciclovir)NDNDNDNDNDNDD27820oral18.782.211.911.78.579.8D29<200oral16.569.619.68.46.185.5D34<200oral10.667.528.820.57.172.4D43<200oral16.569.619.68.46.185.5*CD3 gated T cells and “ND” is for experiment “Not Done”. DisclosuresNo relevant conflicts of interest to declare.

IL-15 enhances survival and function of HIV-specific CD8+ T cells

AbstractHIV-specific CD8+ T cells are prone to undergo apoptosis, and this may affect their ability to control HIV infection. Because CD8-mediated immune responses play a key role in controlling HIV infection, enhancing the survival and effector function of HIV-specific CD8+ T cells may augment their ability to control HIV virus. We show here that interleukin 15 (IL-15) potently inhibits spontaneous and CD95/Fas-induced apoptosis of HIV-specific CD8+ T cells. IL-15 inhibits apoptosis in both CD45RA−CD62L− and CD45RA+CD62L− effector memory subpopulations of these cells. Furthermore, IL-15 greatly enhances the survival of HIV-specific CD8+ T cells in long-term cultures. Finally, IL-15 directly enhances activation, interferon γ (IFNγ) production, and direct ex vivo cytotoxicity of HIV-specific CD8+ T cells. Thus, IL-15 potently enhances the survival and effector function of HIV-specific CD8+ T cells and, therefore, may prove useful in augmenting the antiviral function of these cells.

Listeria monocytogenes as a short-lived delivery system for the induction of type 1 cell-mediated immunity against the p36/LACK antigen of Leishmania major.

Listeria monocytogenes has been used as an experimental live vector for the induction of CD8-mediated immune responses in various viral and tumoral experimental models. Susceptibility of BALB/c mice to Leishmania major infection has been correlated to the preferential development of Th2 CD4 T cells through an early production of interleukin 4 (IL-4) by a restricted population of CD4 T cells which react to a single parasite antigen, LACK (stands for Leishmania homologue of receptors for activated C kinase). Experimental vaccination with LACK can redirect the differentiation of CD4(+) T cells towards the Th1 pathway if LACK is coadministrated with IL-12. As IL-12 is known to be induced by L. monocytogenes, we have tested the ability of a recombinant attenuated actA mutant L. monocytogenes strain expressing LACK to induce the development of LACK-specific Th1 cells in both B10.D2 and BALB/c mice, which are resistant and susceptible to L. major, respectively. After a single injection of LACK-expressing L. monocytogenes, IL-12/p40 transcripts showed a rapid burst, and peaks of gamma interferon (IFN-gamma)-secreting LACK-specific Th1 cells were detected around day 5 in the spleens and livers of mice of both strains. These primed IFN-gamma-secreting LACK-reactive T cells were not detected ex vivo after day 7 of immunization but could be recruited and detected 15 days later in the draining lymph node after an L. major footpad challenge. Although immunization of BALB/c mice with LACK-expressing L. monocytogenes did not change the course of the infection with L. major, immunized B10.D2 mice exhibited significantly smaller lesions than nonimmunized controls. Thus, our results demonstrate that, in addition of its recognized use for the induction of effector CD8 T cells, L. monocytogenes can also be used as a live recombinant vector to favor the development of potentially protective IFN-gamma-secreting Th1 CD4 T lymphocytes.