Intratumoral delivery of tavokinogene telseplasmid yields systemic immune responses in metastatic melanoma patients.

BACKGROUND: Interleukin 12 (IL-12) is a pivotal regulator of innate and adaptive immunity. We conducted a prospective open-label, phase II clinical trial of electroporated plasmid IL-12 in advanced melanoma patients (NCT01502293). PATIENTS AND METHODS: Patients with stage III/IV melanoma were treated intratumorally with plasmid encoding IL-12 (tavokinogene telseplasmid; tavo), 0.5 mg/ml followed by electroporation (six pulses, 1500 V/cm) on days 1, 5, and 8 every 90 days in the main study and additional patients were treated in two alternative schedule exploration cohorts. Correlative analyses for programmed death-ligand 1 (PD-L1), flow cytometry to assess changes in immune cell subsets, and analysis of immune-related gene expression were carried out on pre- and post-treatment samples from study patients, as well as from additional patients treated during exploration of additional dosing schedules beyond the pre-specified protocol dosing schedule. Response was measured by study-specific criteria to maximize detection of latent and potentially transient immune responses in patients with multiple skin lesions and toxicities were graded by the Common Terminology Criteria for Adverse Events version 4.0 (CTCAE v4.0). RESULTS: The objective overall response rate was 35.7% in the main study (29.8% in all cohorts), with a complete response rate of 17.9% (10.6% in all cohorts). The median progression-free survival in the main study was 3.7 months while the median overall survival was not reached at a median follow up of 29.7 months. A total of 46% of patients in all cohorts with uninjected lesions experienced regression of at least one of these lesions and 25% had a net regression of all untreated lesions. Transcriptomic and immunohistochemistry analysis showed that immune activation and co-stimulatory transcripts were up-regulated but there was also increased adaptive immune resistance. CONCLUSIONS: Intratumoral Tavo was well tolerated and led to systemic immune responses in advanced melanoma patients. While tumor regression and increased immune infiltration were observed in treated as well as untreated/distal lesions, adaptive immune resistance limited the response.

Immunoscore and Immunoprofiling in cancer: an update from the melanoma and immunotherapy bridge 2015.

The fifth "Melanoma Bridge Meeting" took place in Naples, December 1-5th, 2015. The main topics discussed at this meeting were: Molecular and Immuno advances, Immunotherapies and Combination Therapies, Tumor Microenvironment and Biomarkers and Immunoscore. The natural history of cancer involves interactions between the tumor and the immune system of the host. The immune infiltration at the tumor site may be indicative of host response. Significant correlations were shown between the levels of immune cell infiltration in tumors and patient's clinical outcome. Moreover, incredible progress comes from the discovery of mutation-encoded tumor neoantigens. In fact, as tumors grow, they acquire mutations that are able to influence the response of patients to immune checkpoint inhibitors. It has been demonstrated that sensitivity to PD-1 and CTLA-4 blockade in patients with advanced NSCLC and melanoma was enhanced in tumors enriched for clonal neoantigens. The road ahead is still very long, but the knowledge of the mechanisms of immune escape, the study of tumor neo-antigens as well as of tumor microenvironment and the development of new immunotherapy strategies, will make cancer a more and more treatable disease.

Effector memory and central memory NY-ESO-1-specific re-directed T cells for treatment of multiple myeloma.

The cancer-testis antigen NY-ESO-1 is a potential target antigen for immune therapy expressed in a subset of patients with multiple myeloma. We generated chimeric antigen receptors (CARs) recognizing the immunodominant NY-ESO-1 peptide 157-165 in the context of HLA-A*02:01 to re-direct autologous CD8(+) T cells towards NY-ESO-1(+) myeloma cells. These re-directed T cells specifically lysed NY-ESO-1(157-165)/HLA-A*02:01-positive cells and secreted IFNγ. A total of 40% of CCR7(-) re-directed T cells had an effector memory phenotype and 5% a central memory phenotype. Based on CCR7 cell sorting, effector and memory CAR-positive T cells were separated and CCR7(+) memory cells demonstrated after antigen-specific re-stimulation downregulation of CCR7 as sign of differentiation towards effector cells accompanied by an increased secretion of memory signature cytokines such as IL-2. To evaluate NY-ESO-1 as potential target antigen, we screened 78 bone marrow biopsies of multiple myeloma patients where NY-ESO-1 protein was found to be expressed by immunohistochemistry in 9.7% of samples. Adoptively transferred NY-ESO-1-specific re-directed T cells protected mice against challenge with endogenously NY-ESO-1-positive myeloma cells in a xenograft model. In conclusion, re-directed effector- and central memory T cells specifically recognized NY-ESO-1(157-165)/ HLA-A*02:01-positive cells resulting in antigen-specific functionality in vitro and in vivo.

Assessing oncologic benefit in clinical trials of immunotherapy agents.

BACKGROUND: USA Food and Drug Administration approval for cancer therapy requires demonstration of patient benefit as a marker of clinical efficacy. Prolonged survival is the gold standard for demonstration of efficacy, but other end points such as antitumor response, progression-free survival, quality of life, or surrogate end points may be used. DESIGN: This study was developed based on discussion during a roundtable meeting of experts in the field of immunotherapy. RESULTS: In most clinical trials involving cytotoxic agents, response end points use RECIST based on the premise that 'effective' therapy causes tumor destruction, target lesion shrinkage, and prevention of new lesions. However, RECIST may not be appropriate in trials of immunotherapy. Like other targeted agents, immunotherapies may mediate cytostatic rather than direct cytotoxic effects, and these may be difficult to quantify with RECIST. Furthermore, significant time may elapse before clinical effects are quantifiable because of complex response pathways. Effective immunotherapy may even mediate transient lesion growth secondary to immune cell infiltration. CONCLUSIONS: RECIST may not be an optimal indicator of clinical benefit in immunotherapy trials. This article discusses alternative clinical trial designs and end points that may be more relevant for immunotherapy trials and may offer more effective prediction of survival in pivotal phase III studies.

Crystal structure of rhodopsin: A G protein-coupled receptor.

Heterotrimeric guanine nucleotide-binding protein (G protein)-coupled receptors (GPCRs) respond to a variety of different external stimuli and activate G proteins. GPCRs share many structural features, including a bundle of seven transmembrane alpha helices connected by six loops of varying lengths. We determined the structure of rhodopsin from diffraction data extending to 2.8 angstroms resolution. The highly organized structure in the extracellular region, including a conserved disulfide bridge, forms a basis for the arrangement of the seven-helix transmembrane motif. The ground-state chromophore, 11-cis-retinal, holds the transmembrane region of the protein in the inactive conformation. Interactions of the chromophore with a cluster of key residues determine the wavelength of the maximum absorption. Changes in these interactions among rhodopsins facilitate color discrimination. Identification of a set of residues that mediate interactions between the transmembrane helices and the cytoplasmic surface, where G-protein activation occurs, also suggests a possible structural change upon photoactivation.

A Four-Biomarker Blood Signature Discriminates Systemic Inflammation Due to Viral Infection Versus Other Etiologies.

The innate immune system of humans and other mammals responds to pathogen-associated molecular patterns (PAMPs) that are conserved across broad classes of infectious agents such as bacteria and viruses. We hypothesized that a blood-based transcriptional signature could be discovered indicating a host systemic response to viral infection. Previous work identified host transcriptional signatures to individual viruses including influenza, respiratory syncytial virus and dengue, but the generality of these signatures across all viral infection types has not been established. Based on 44 publicly available datasets and two clinical studies of our own design, we discovered and validated a four-gene expression signature in whole blood, indicative of a general host systemic response to many types of viral infection. The signature's genes are: Interferon Stimulated Gene 15 (ISG15), Interleukin 16 (IL16), 2',5'-Oligoadenylate Synthetase Like (OASL), and Adhesion G Protein Coupled Receptor E5 (ADGRE5). In each of 13 validation datasets encompassing human, macaque, chimpanzee, pig, mouse, rat and all seven Baltimore virus classification groups, the signature provides statistically significant (p < 0.05) discrimination between viral and non-viral conditions. The signature may have clinical utility for differentiating host systemic inflammation (SI) due to viral versus bacterial or non-infectious causes.

Adoptive immunotherapy with vaccine-primed lymph node cells secondarily activated with anti-CD3 and interleukin-2.

PURPOSE: In preclinical studies, we have reported the ability to induce immune T cells in lymph nodes (LN) primed by in vivo vaccination with tumor cells admixed with a bacterial adjuvant. These LN cells can be activated and expanded ex vivo for the successful immunotherapy of established tumors. We have applied these methods to generate vaccine-primed LN in patients with advanced melanoma and renal cell cancer (RCC) for therapy. MATERIALS AND METHODS: Irradiated autologous tumor cells admixed with bacille Calmette-Guérin (BCG) were used to vaccinate patients. Seven days later, draining LN were removed for activation with anti-CD3 monoclonal antibody (mAb) followed by expansion in interleukin-2 (IL-2). Activated LN cells were administered intravenously (IV) with the concomitant administration of IL-2. RESULTS: A total of 23 patients were evaluated (11 melanoma and 12 RCC). Vaccine-primed LN were expanded ex vivo with a mean of 8.4 x 10(10) cells administered per patient. Among 20 patients assessed, 15 demonstrated minimal cytotoxicity of autologous tumor cells by the activated LN cells, with the remaining mediating nonspecific cytotoxicity. By contrast, a majority of the activated LN cells showed highly specific release of granulocyte-macrophage colony-stimulating factor (GM-CSF) and interferon gamma (IFN-gamma) to autologous but not allogeneic tumor stimulation. This tumor-specific cytokine release was found to be major histocompatibility complex (MHC) class I-restricted, which indicates the involvement of CD8+ cells. Among 11 melanoma patients, one had a partial tumor response. Among 12 RCC patients, two had complete and two partial responses. A trend (P = .066) between the enhancement of delayed-type hypersensitivity (DTH) reactivity to autologous tumor after therapy and tumor regression was observed. CONCLUSION: Tumor vaccines can be used to induce immunologically specific T-cell responses against melanoma and RCC in draining LN. Anti-CD3/IL-2 activation of primed LN cells can be reliably performed for clinical therapy and appears to have activity in patients with metastatic RCC.

Characterization of a monoclonal antibody defining a macrophage activation-specific cell surface antigen.

Macrophages have been obtained from the peritoneal cavities of C57BL/6 mice following treatment with C. parvum, MVE-2, mineral oil, or thioglycollate. Cell populations were primarily composed of mononuclear phagocytes as determined by a latex bead uptake assay. Macrophages obtained from C. parvum or MVE-2 were activated as judged by enhanced cytostatic activity against two tumor cell target lines. Thioglycollate-elicited macrophages demonstrated much lower cytostatic ability. Rats were immunized with activated MVE-2 macrophages. Hybridomas were prepared by fusion with a non-secreting myeloma cell line followed by cloning. Cell supernates were selected on the basis of binding to activated but not elicited macrophages. The monoclonal antibody produced has been characterized by flow cytometry. The antibody does not react with syngeneic erythrocytes, thymocytes, or spleen cells. Reaction with thioglycollate macrophages is very low. Alternatively, intense binding is found on activated macrophages. This antigen which accompanies macrophage activation for tumor cell cytostasis is designated as macrophage activation antigen-1 (MAA-1). Several important physiological changes accompany the process of macrophage activation. For example, activated macrophages demonstrate enhanced microbicidal, phagocytic, secretory, and tumoricidal activity (for reviews see refs. 1,2). Concommitant alterations in cell surface properties have been observed. These include: (a) changes in surface morphology and spreading (3-5), (b) altered lipid and protein content (6,7), (c) decreases in 5'-nucleotidase activity and alkaline phosphodiesterase (8), increases in leucine aminopeptidase (8), decreases in mannose receptors (11,12), and antigen F4/80 (11), (d) increases in Ia antigens (11,12), and (e) increased tumor cell binding (13). These structural and functional modifications indicate that activated macrophages represent a unique class of functionally differentiated cells (9). Antigenic modifications accompanying macrophage differentiation are of special interest. Markers for specific macrophage classes might be useful in defining differentiation pathways, dissecting type-specific functional activities such as tumor cytotoxicity, and providing a means to identify macrophage subsets in heterogeneous cell populations. In the present work we have taken the first step in this direction by defining a cell surface macrophage activation antigen.

Genetic modification of human peripheral blood lymphocytes with a transdominant negative form of Rev: safety and toxicity.

A transdominant mutant form of the rev gene, M10, confers resistance to infection by the human immunodeficiency virus (HIV) in vitro and is currently under investigation as a potential intervention in acquired immunodeficiency syndrome (AIDS). In this report, we examine three issues relevant to the safety of autologous transfer of human T cells genetically modified with Rev M10. First, the potential for malignant transformation was assessed in vitro using interleukin-2 (IL-2) dependence and fibroblast transformation assays, and tumorigenicity was evaluated in severe combined immunodeficient (SCID) mice. Possible toxicity was evaluated by pathologic analysis following adoptive transfer of genetically modified human T cells into SCID mice. Second, methods were developed that permit T cell activation required for gene transfer but do not allow replication of endogenous HIV. Third, T cell function was evaluated in peripheral blood lymphocytes (PBL) of HIV-seropositive donors transduced with Rev M10 and compared to a negative control mutant, delta Rev M10. By all criteria, no oncogenicity or toxicity was observed. Human T cells transduced with these vectors did not grow in the absence of IL-2 in vitro, and no tumors were observed following transplantation of genetically modified human cells into recipient SCID mice. Histopathological analysis of heart, lung, liver, spleen, and kidney of animals 1-21 weeks following adoptive transfer of gene-modified human T cells revealed no significant abnormalities. Additionally, no differences were observed in the pattern of cytokine secretion in enriched human PBL expressing Rev M10 compared to delta Rev M10. (ABSTRACT TRUNCATED AT 250 WORDS)

Expression in bacteria of gB-glycoprotein-coding sequences of Herpes simplex virus type 2.

A plasmid with an insert that encodes the glycoprotein B(gB) gene of Herpes simplex virus type 2 (HSV-2) has been isolated. DNA sequences coding for a portion of the HSV-2 gB peptide were cloned into a bacterial lacZ alpha expression vector and used to transform Escherichia coli. Upon induction of lacZpo-promoted transcription, some of the bacteria became filamentous and produced inclusion bodies containing a large amount of a 65-kDal peptide that was shown to be precipitated by broad-spectrum antibodies to HSV-2 and HSV-1. The HSV-2 insert of one of these clones specifies amino acid residues corresponding to 135 through 629 of the gB of HSV-1 [Bzik et al., Virology 133 (1984) 301-314].

Lipofection indirectly increases expression of endogenous major histocompatibility complex class I molecules on tumor cells.

Direct intratumoral injection of a lipid/DNA complex encoding an allogeneic major histocompatibility complex (MHC) class I molecule leads to regression of both an immunogenic murine tumor and also melanoma lesions in some patients. We have sought to understand the mechanism(s) for this augmentation of antitumor activity. While optimizing parameters for in vitro gene transfer into the D5 subclone of B16BL6, it was noted that lipofected tumors not only expressed the new alloantigen but also exhibited increased expression of endogenous MHC class I, both H-2 Kb and H-2 Db. This increase in expression was not restricted to the small percentage of cells that expressed the transfected gene, but appeared to affect the majority of cells in culture. Class I expression was not increased by lipopolysaccharide, DNA alone, lipid, or lipid/lipopolysaccharide mixtures. Enhanced class I expression required a DNA/lipid complex and was greatest when parameters optimized for gene transfer of the alloantigen were used. All DNA plasmids tested had this effect, including one plasmid whose DNA was not transcribed because it lacked an expression cassette. Because of the critical role that MHC class I antigens play in immune recognition, we propose that lipid complex-mediated gene transfer may provide immunological advantages beyond those that are attributable to expression of the specific gene transferred.

Analysis of stage-specific transcripts of the Plasmodium falciparum serine repeat antigen (SERA) gene and transcription from the SERA locus.

We evaluated the stage-specific transcription and processing of serine repeat antigen (SERA) messenger RNA to further examine mechanisms regulating gene expression in Plasmodium falciparum. SERA mRNA was expressed exclusively in trophozoite and schizont stages. Transcription from the SERA gene was first detected between 24 and 29 h following erythrocyte invasion. The transcript mapping data revealed heterogeneity of the SERA mRNA 5' and 3' ends. RNA sequencing revealed that SERA transcripts were not generated by a trans-splicing mechanism. A new SERA gene, SERA3, was identified 1.8 kb upstream of SERA. The direction of transcription of the SERA locus genes, SERA3, SERA, and SERA2, was mapped relative to the location of other chromosome 2 genetic markers. The SERA locus and the closely linked MSA2 locus were found to be transcriptionally regulated in a coordinate fashion. Collectively, the results of these experiments show that parallel and coordinately controlled transcription units reside on chromosome 2. These results implicate a novel mechanism of transcriptional control in Plasmodium.

The primary structure of Plasmodium falciparum DNA polymerase delta is similar to drug sensitive delta-like viral DNA polymerases.

We report the isolation and sequencing of genomic DNA clones that encode the 1094-amino acid catalytic subunit of DNA polymerase delta from the human malaria parasite Plasmodium falciparum. Protein sequence comparison to other DNA polymerases revealed the presence of six highly conserved regions found in alpha-like DNA polymerases from different prokaryotic, viral, and eukaryotic sources. Five additional regions of amino acid sequence similarity that are only conserved in delta and delta-like DNA polymerases, so far, were present in P. falciparum DNA polymerase delta. P. falciparum DNA polymerase delta was highly similar to both Saccharomyces cerevisiae DNA polymerase delta (DNA polymerase III; CDC2) and Epstein-Barr virus DNA polymerase at the amino acid sequence, and the predicted protein secondary structure levels. The gene that encodes DNA polymerase delta resides as a single copy on chromosome 10, and is expressed as a 4.5-kb mRNA during the trophozoite and schizont stages when parasite chromosomal DNA synthesis is active.

Expression of Plasmodium falciparum lactate dehydrogenase in Escherichia coli.

A Plasmodium falciparum gene is described which encodes lactate dehydrogenase activity (P. falciparum LDH). The P. falciparum LDH gene contains no introns and is present in a single copy on chromosome 13. P. falciparum LDH was expressed in all asexual blood stages as a 1.6-kb mRNA. The predicted 316 amino acid protein coding region of P. falciparum LDH was inserted into the prokaryotic expression vector pKK223-3 and a 33-kDa protein having LDH activity was synthesized in Escherichia coli. P. falciparum LDH primary structure displays high amino acid similarity (50-57%) to vertebrate and bacterial LDH, but lacks the amino terminal extension observed in all vertebrate LDH. The majority of amino acid residues implicated in substrate and coenzyme binding and catalysis of other LDH are well conserved in P. falciparum LDH. However, several notable differences in amino acid composition were observed. P. falciparum LDH contained several distinctive single amino acid insertions and deletions compared to other LDH enzymes, and most remarkably, it contained a novel insertion of 5 amino acids within the conserved mobile loop region near arginine residue 109, a residue which is known to make contact with pyruvate in the ternary complex of other LDH. These results suggest that novel features of P. falciparum LDH primary structure may be correlated with previously characterized and distinctive kinetic, biochemical, immunochemical, and electrophoretic properties of P. falciparum LDH.

Stable transformation of Toxoplasma gondii based on a pyrimethamine resistant trifunctional dihydrofolate reductase-cytosine deaminase-thymidylate synthase gene that confers sensitivity to 5-fluorocytosine.

To improve genetic models available for the analysis of apicomplexan protozoan parasites, bacterial sequences encoding the 427 amino acid cytosine deaminase (CD) gene were fused, in-frame, to an engineered linker domain of the high level pyrimethamine resistant form of the parasite bifunctional dihydrofolate reductase-thymidylate synthase (DHFR-TS) gene. Toxoplasma gondii was transformed with the plasmid containing the fused pyrimethamine resistant dihydrofolate reductase-cytosine deaminase-thymidylate synthase (DHFRm2m3-CD-TS) gene and parasites were selected in a high level of pyrimethamine. Transfected parasites that acquired resistance to pyrimethamine were cloned and evaluated for expression of the CD genetic marker. CD transgenic parasites acquired a high sensitivity to 5-fluorocytosine due to the intraparasitic conversion of this non-toxic prodrug to the cytotoxic compound 5-fluorouracil. Exogenously supplied cytosine or uracil rescued the growth of CD transgenic T. gondii parasites that were cultured in the presence of cytotoxic concentrations of 5-fluorouracil or 5-fluorocytosine. Bacterial CD fused to the pyrimethamine resistant DHFR-TS marker provides a novel genetic tool for new positive and negative genetic selection strategies in several protozoan parasites. An advantage of the CD genetic marker is that it is derived from a bacterial gene and can therefore be used in nearly any parasite genetic background for negative selection. This novel system should facilitate new approaches for the development of improved model genetic systems for the biological investigation of apicomplexan parasites.

Molecular characterization of the largest subunit of Plasmodium falciparum RNA polymerase I.

Plasmodium species possess developmentally regulated ribosomal RNA (rRNA) genes. This report describes the expression and gene structure of the largest subunit of P. falciparum RNA polymerase I (RNAPI), which is responsible for the synthesis of rRNA. The RNAPI largest subunit gene was present as a single copy gene on chromosome 9. Three exons encode the 2910-amino acid RNAPI polypeptide (340 140 Da). A comparison of Plasmodium, Trypanosoma, and Saccharomyces cerevisiae nuclear RNAP largest subunits identified conserved amino acid positions and class-specific amino acid positions. Novel amino acid insertions were found between RNAPI conserved regions A and B (region A'), D and DE1 (region D'), DE2 and E (region DE2'), and F and G (region F'). Leucine zipper domains were found within regions D', DE2, and DE2'. A novel serine-rich repeat domain, a domain with homology to the C-terminal domain of eukaryotic upstream binding factor (UBF), and 4 highly conserved casein kinase II (CKII) Ser/Thr phosphorylation motifs were found within a 127-amino acid sub-region of enlarged region F'. The novel RNAPI serine-rich repeat contained a conserved motif, Ser-X3-Ser, which was also identified in the serine-rich repeat domains of the P. falciparum RNAPII and RNAPIII largest subunits, as well as within a highly homologous serine-rich repeat from trophozoite antigen R45. The results of this molecular analysis indicate that phosphorylation and dephosphorylation mechanisms regulate the activity of P. falciparum RNAPI.

Characterization of the gene encoding the largest subunit of Plasmodium falciparum RNA polymerase III.

We report here the isolation, sequence analysis, structure, and expression of the gene encoding the largest subunit of RNA polymerase III (RPIII) from Plasmodium falciparum. The P. falciparum RPIII gene consists of 5 exons and 4 introns, is expressed in all of the asexual erythrocytic stages of the parasite as a 8.5-kb mRNA, and is present in a single copy on chromosome 13. The predicted 2339 amino acid residue RPIII subunit contained 5 regions that were conserved between different eukaryotic RPIII subunits, and 4 variable regions that separated the conserved regions. Three of the variable regions were greatly enlarged in comparison to the corresponding variable regions in other RPIII subunits. Variable region C' represented nearly one-third of the P. falciparum RPIII subunit (750 amino acid residues), included a unique repeated decapeptide sequence, and had some homology with yeast DNA topoisomerase II. Noteworthy amino acid sequences and structures were identified in both the conserved regions and in the enlarged variable regions, and their possible role(s) as domains that regulate RPIII enzyme activity is discussed.

Kinetics of the MLR response following single donor-specific allogeneic blood transfusions.

Prior blood transfusion (BT) confers a significant improvement in transplant survival in recipients (1). However, increased survival across major histocompatibility barriers generally requires the administration of immunosuppressive agents (2-5). The mechanisms by which BT prolongs graft survival have not been fully elucidated. Experimental evidence suggests that suppressor cells (6,7), soluble suppressor factors (8), and blocking antibodies (9) may play a role.

A monoclonal antibody (BMA-1) reactive with murine B cells as well as resident and elicited but not activated macrophages.

Hybridoma technology has been employed to prepare a monoclonal antibody that recognizes a subpopulation of mononuclear leukocytes. Enzyme-linked immune assay revealed a cell clone producing a monoclonal antibody reactive with elicited but not activated C57Bi/6 peritoneal macrophages. Detailed analyses using fluorescence flow cytometry demonstrated that this monoclonal antibody binds to B cells, B cell blasts, as well as to the resident and elicited macrophages, but not to activated macrophages, T cells, red blood cells, or syngeneic fibroblasts. This antigen has been designated BMA-1. Antigenic expression is greatest upon resident macrophages. A bimodal level of expression is found on elicited macrophages while activated macrophages possess low levels of expression. The unique cellular distribution of this antigen indicates that it is lost during macrophage differentiation to the activated state. Immunoprecipitation studies indicate that this antigen is composed of multiple subunits; the primary subunit possesses a molecular weight of 38,000. This new tool should be valuable in the analysis of heterogeneous macrophage populations and in defining molecular differentiation pathways.

Manipulating the host response to autologous tumour vaccines.

From our way of thinking the problem facing vaccine strategies for cancer is not that we do not have "enough" tumour antigens. The problem is we cannot induce an immune response that is sufficient to mediate tumour regression. The normal "checks and balances" found in the body prevent the sustained expansion and subsequent persistence of immune killer cells. If vaccine strategies are going to become effective treatments for cancer patients, they will need to overcome this substantial roadblock. Recent developments in immunology have provided insights into the mechanisms that regulate the expansion and persistence of T cells. This has allowed investigators to reinterpret decades-old observations suggesting that chemotherapy administered before vaccination often led to a stronger immune response. This manuscript will review experiments that offer an explanation for these observations and present pre-clinical data from our laboratory that describes an innovative new approach to combining chemotherapy and vaccination. This approach is readily translatable to the clinic and is broadly applicable to any vaccine strategy for advanced cancer.