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[eth-1.sup.r], a thermosensitive allele of the Neurospora crassa S-adenosylmethionine (AdoMet) synthetase gene that confers ethionine resistance, has been cloned and sequenced. Replacement of an aspartic amino acid residue ([D.sup.48] [right arrow] [N.sup.48]), perfectly conserved in prokaryotic, fungal and higher eukaryotic AdoMet synthetases, was found responsible for both thermosensitivity and ethionine resistance conferred by [eth-1.sup.r]. Gene fusion constructs, designed to overexpress [eth-1.sup.r] in vivo, render transformant cells resistant to ethionine. Dominance of ethionine resistance was further demonstrated in [eth-1.sup.+]/[eth-1.sup.r] partial diploids carrying identical gene doses of both alleles. Heterozygous [eth-1.sup.+]/[eth-1.sup.r] cells have, at the same time, both the thermotolerance conferred by [eth-1.sup.+] and the ethionine-resistant phenotype conferred by [eth-1.sup.r]. AdoMet levels and AdoMet synthetase activities were dramatically decreased in heterozygous [eth-1.sup.+]/[eth-1.sup.r] cells. We propose that this negative effect exerted by [eth-1.sup.r] results from the in vivo formation of heteromeric [eth-1.sup.+]/[eth-1.sup.r] AdoMet synthetase molecules.

Intense biochemical and genetic research on the eth-[1.sup.r] mutant of Neurospora crassa suggested that this locus might encode S-adenosylmethionine synthetase (S-Adomet synthetase). We have used protoplast transformation and phenotypic rescue of a thermosensitive phenotype associated with the eth-[1.sup.r] mutation to clone the locus. Nucleotide sequence analysis demonstrated that it encodes S-Adomet synthetase. Homology analyses of prokaryotic, fungal and higher eukaryotic S-Adomet synthetase polypeptide sequences show a remarkable evolutionary conservation of the enzyme. N. crassa strains carrying S-Adomet synthetase coding sequences fused to a strong heterologous promoter were constructed to assess the phenotypic consequences of in vivo S-Adomet synthetase overexpression. Studies of growth rates and microscopic examination of vegetative development revealed that normal growth and morphogenesis take place in N. crassa even at abnormally high levels of cellular S-Adomet. The degree of cytosine methylation of a naturally methylated genomic region was dependent on the cellular levels of S-Adomet. We conclude that variation in S-Adomet levels in N. crassa cells, which in addition to the status of genomic DNA methylation could modify the flux of other S-Adomet-dependent metabolic pathways, does not affect growth rate or morphogenesis.

The distribution of meiotic crossover events over specific genetic spacing was studied using a general restriction fragment length polymorphism-based technique. Sixty four recombinant chromosomes, with independent meiotic crossover events in the genetic space eth-l-un-2 on linkage group I of Neurospora crassa, were isolated during the experiment. The study suggests a method for the definition of the centromeric-telomeric orientation of single cloned DNA fragments.

The tumor microenvironment is profoundly immunosuppressive. We show that multiple tumor types create intratumoral immune suppression driven by a specialized form of regulatory T cell (Treg) activation dependent on the PTEN (phosphatase and tensin homolog) lipid phosphatase. PTEN acted to stabilize Tregs in tumors, preventing them from reprogramming into inflammatory effector cells. In mice with a Treg-specific deletion of PTEN, tumors grew slowly, were inflamed, and could not create an immunosuppressive tumor microenvironment. In normal mice, exposure to apoptotic tumor cells rapidly elicited PTEN-expressing Tregs, and PTEN-deficient mice were unable to maintain tolerance to apoptotic cells. In wild-type mice with large established tumors, pharmacologic inhibition of PTEN after chemotherapy or immunotherapy profoundly reconfigured the tumor microenvironment, changing it from a suppressive to an inflammatory milieu, and tumors underwent rapid regression. Thus, the immunosuppressive milieu in tumors must be actively maintained, and tumors become susceptible to immune attack if the PTEN pathway in Tregs is disrupted.

A novel class of 5-substituted 5 H -imidazo[5,1- a ]isoindoles are described as potent inhibitors of indoleamine 2,3-dioxygenase 1 (IDO1). A structure-based drug design approach was used to elaborate the 5 H -imidazo[5,1- a ]isoindole core and to improve potency and pharmacological properties. Suitably placed hydrophobic and polar functional groups in the lead molecule allowed improvement of IDO1 inhibitory activity while minimizing off-target liabilities. Structure-activity relationship studies focused on optimizing IDO1 inhibition potency and a pharmacokinetic profile amenable to oral dosing while controlling CYP450 and hERG inhibitory properties.

Owing to the absence of alphaGal epitopes in human cells and constant stimulation of the immune system by the symbiotic bacterial flora, humans develop high titers of natural antibodies against these epitopes. It has been demonstrated that syngeneic whole cell vaccines modified to express alphaGal epitopes could be used to generate a potent anticancer vaccine. In this study, we tested whether allogeneic whole cell cancer vaccines modified to express alphaGal epitopes would be effective for the treatment of murine melanoma. The alpha(1,3)galactosyltransferase (alphaGT) knockout mice (H-2) with preexisting subcutaneous and pulmonary tumors [alphaGal B16, H-2] received therapeutic vaccinations with S91M3alphaGal (H-2) whole cell allogeneic vaccines. These mice had better survival and reduced pulmonary metastasis burden compared with control mice treated with S91M3 vaccine cells. Vaccination with S91M3alphaGal-induced cytotoxic CD8 T cells recognizing the syngeneic alphaGal B16 tumors measured by adoptive transfer to recipients bearing pulmonary metastases. The presence of allo-antigens did not dominate the induction of immunity to "cryptic" tumor antigens and had helped in the generation of a more efficient vaccine to treat preexisting tumors when compared with classic autologous vaccines. Vaccination with allogeneic alphaGal vaccines did not induce signs of toxicity including changes in weight, hematology, chemistry, and histopathology of major perfused organs or autoimmunity in long-term murine models for breast, lung, and melanoma. This study established the safety and efficacy data of allogeneic alphaGal whole cell vaccines and constituted the basis for the initiation of human clinical trials to treat human malignancies.

The hyperacute immune response in humans is a potent mechanism of xenograft rejection mediated by complement-fixing natural antibodies recognizing alpha(1,3)-galactosyl epitopes (alphaGal) not present on human cells. We exploited this immune mechanism to create a whole cell cancer vaccine to treat melanoma tumors. B16 melanoma vaccines genetically engineered to express alphaGal epitopes (B16alphaGal) effectively treated preexisting s.c. and pulmonary alphaGal-negative melanoma (B16Null) tumors in the alpha(1,3)-galactosyltransferase knockout mouse model. T cells from mice vaccinated with B16alphaGal recognized B16Null melanoma cells measured by detection of intracellular tumor necrosis factor-alpha. We showed successful adoptive transfer of immunity to recipient mice bearing lung melanoma metastasis. Mice receiving lymphocytes from donors previously immunized with B16alphaGal had reduced pulmonary metastases. The transfer of lymphocytes from mice vaccinated with control vaccine had no effect in the pulmonary metastasis burden. This study unequivocally establishes for the first time efficacy in the treatment of preexisting melanoma tumors using whole cell vaccines expressing alphaGal epitopes. Vaccination with B16alphagal induced strong long-lasting cell-mediated antitumor immunity extended to B16Null. These data formed the basis for the testing of this therapeutic strategy in human clinical trials currently under way.

Lentiviral vectors based on HIV-1, HIV-2, or SIV have the ability to transduce dividing and non-dividing T cells, dendritic cells, hematopoietic stem cells and macrophages, which are the main target cells for gene therapy of HIV-1 infection. Besides their function as gene delivery vehicles, lentiviral vector backbones containing the cis-acting sequences necessary to perform a complete replication cycle in the presence of viral proteins provided in trans, have the ability to inhibit HIV-1 replication by several mechanisms that include sequestration of the regulatory proteins Tat and Rev, competition for packaging into virions and possibly by inhibition of reverse transcription in heterodimeric virions. Expression of anti-HIV-1 genes in these vectors would strengthen the potency of this inhibition. To avoid self-inhibition of the vector packaging system, lentiviral vectors have to be modified to become resistant to the anti-HIV-1 genes encoded by them. This review discusses the different genetic intervention strategies for gene therapy of HIV-1 infection focusing in the use of lentiviral vectors as the main agents to mediate inhibition of HIV-1 replication. It also discusses possible strategies to adapt HIV-1 or HIV-2 vectors to express the different classes of anti-HIV-1 genes and approaches to improve in vivo vector mobilization.