Current Approaches to Engineering of NK Cells for Cancer Immunotherapy.

Natural Killer (NK) cells belong to a unique subtype of lymphocytes with a great potential for cancer immunotherapy due to their ability to rapidly recognize and efficiently kill tumor cells. Their anti-cancer potential can be further increased by genetic and non-genetic modifications. However, the attempts of genetic improvements of NK cells over the past 20 years have been hampered by the difficulties of gene delivery into this cell type, thus preventing researchers from producing clinically relevant numbers of viable and biologically active NK cells. Currently, several successful approaches to genetic modification of NK cells have been described, and clinically applicable cell therapy products have been characterized. Now that we understand much better the ways of NK cell optimization to enhance their tumor regression-inducing capabilities, novel approaches to engineering NK surface receptors are being developed. In this review, we focus on the advantages and perspectives of various approaches to modification of NK cells. Positive results of several preclinical studies are described, demonstrating that genetically modified NK cells can be comparable to therapeutic T cells in their efficiency of recognizing and destroying tumor targets. Moreover, using allogenic NK cells to treat a number of cancer types might have even wider and eager clinical adoption than cytotoxic T cells due to a much decreased risk of graft versus host reaction inherent in NK cell-based immunotherapeutic products.

Adaptation of chimeric retroviruses in vitro and in vivo: isolation of avian retroviral vectors with extended host range.

We have designed and characterized two new replication-competent avian sarcoma/leukosis virus-based retroviral vectors with amphotropic and ecotropic host ranges. The amphotropic vector RCASBP-M2C(797-8), was obtained by passaging the chimeric retroviral vector RCASBP-M2C(4070A) (6) in chicken embryos. The ecotropic vector, RCASBP(Eco), was created by replacing the env-coding region in the retroviral vector RCASBP(A) with the env region from an ecotropic murine leukemia virus. It replicates efficiently in avian DFJ8 cells that express murine ecotropic receptor. For both vectors, permanent cell lines that produce viral stocks with titers of about 5 x 10(6) CFU/ml on mammalian cells can be easily established by passaging transfected avian cells. Some chimeric viruses, for example, RCASBP(Eco), replicate efficiently without modifications. For those chimeric viruses that do require modification, adaptation by passage in vitro or in vivo is a general strategy. This strategy has been used to prepare vectors with altered host range and could potentially be used to develop vectors that would be useful for targeted gene delivery.

The EV-O-derived cell line DF-1 supports the efficient replication of avian leukosis-sarcoma viruses and vectors.

The lack of a well-behaved permanent, adherent, nontransformed chicken cell line has made some experiments with avian leukosis-sarcoma viruses (ASLV) and vectors considerably more difficult. The EV-O-derived line, DF-1, supports the efficient replication of subgroups (A), (B), and (C) ASLV, as well as amphotrophic murine leukemia virus and an ASLV-derived vector that has its env gene derived from the env gene from an amphotrophic murine leukemia virus. The cell line responds appropriately to the expression of a transforming oncogene (v-myc) to a growth suppressor gene [p21(waf1)] and can be sorted (using FACS) if infected by an ASLV vector that expresses GFP.

Inhibition of human immunodeficiency virus type 1 integrase by the Fab fragment of a specific monoclonal antibody suggests that different multimerization states are required for different enzymatic functions.

We have characterized a murine monoclonal antibody (MAb 35), which was raised against human immunodeficiency virus type 1 (HIV-1) integration protein (IN), and the corresponding Fab 35. Although MAb 35 does not inhibit HIV-1 IN, Fab 35 does. MAb 35 (and Fab 35) binds to an epitope in the C-terminal region of HIV-1 IN. Fab 35 inhibits 3'-end processing, strand transfer, and disintegration; however, DNA binding is not affected. The available data suggest that Fab 35 inhibits enzymatic activities of IN by interfering with the ability of IN to form multimers that are enzymatically active. This implies that the C-terminal region of HIV-1 IN participates in interactions that are essential for the multimerization of IN. Titration of the various IN-mediated enzymatic activities suggests that different degrees of multimerization are required for different activities of HIV-1 IN.

Gene transfer into mammalian cells by a Rous sarcoma virus-based retroviral vector with the host range of the amphotropic murine leukemia virus.

We have constructed and characterized a Rous sarcoma virus-based retroviral vector with the host range of the amphotropic murine leukemia virus (MLV). The chimeric retroviral genome was created by replacing the env coding region in the replication-competent retroviral vector RCASBP(A) with the env region from an amphotropic MLV. The recombinant vector RCASBP-M(4070A) forms particles containing MLV Env glycoproteins. The vector replicates efficiently in chicken embryo fibroblasts and is able to transfer genes into mammalian cells. Vector stocks with titers exceeding 10(6) CFU/ml on mammalian cells can be easily prepared by passaging transfected chicken embryo fibroblasts. Since the vector is inherently defective in mammalian cells, it appears to have the safety features required for gene therapy.

False-positive sera do not react with human immunodeficiency virus (HIV) gag-encoded recombinant antigen.

Ten sera from healthy blood donors positive by enzyme-linked immunoadsorbent assay (ELISA) were studied by immunoblot assay using natural and recombinant proteins. They interacted only with p17 or p24 proteins but were nonreactive with a recombinant protein (RP 50), which carries antigenic determinants to p17 and p24. Reactions were not blocked by preincubation of sera with genetically engineered p17 and p24 or purified viral p24, indicating that some new epitopes were formed during the Western blot procedure. Recombinant gag-encoded protein is required for confirmation of human immunodeficiency virus (HIV) seropositivity.

Multicopy expression vector based on temperature-regulated lac repressor: expression of human immunodeficiency virus env gene in Escherichia coli.

A new expression vector (pBB1) has been constructed for the regulated expression of genes in Escherichia coli. Based on the pUC plasmids, the pBB1 carries lacIts allele of the lac repressor gene. This makes it possible to control expression of cloned genes by shifting the temperature from 30 degrees C to 42 degrees C. Thus the vector combines advantages of the pUC plasmids with convenient regulation by temperature. Expression of a fragment of HIV-1 env gene was achieved with the help of this vector and shown by enzyme-linked immunosorbent assay and Western-blot analysis.

[Expression of gag gene of human immunodeficiency virus in recombinant vaccinia virus]. / Ekspressiia gena gag virusa immunodefitsita cheloveka v sostave rekombinantnogo virusa ospovaktsiny.

A fragment of HTLV-IIIB gag-gene, coding for the first 441 amino acids of the p53 gag-precursor was expressed in the recombinant vaccinia virus, vC5. Two HIV specific proteins were detected by western blot in CV-1 cells infected with vC5. Their relative molecular masses were 50 and 35 Kd, pointing out that the first of the proteins is a full length expression product of the cloned sequence, while the second one is a result of processing or abortive translation. Possibilities of using such a strain as a vaccine or in Western blot conformation test are discussed.

[Use of recombinant proteins carrying antigenic determinants of the envelope proteins of AIDS virus in the diagnosis of acquired immunodeficiency syndrome]. / Ispol'zovanie rekombinantnogo belka, nesushchego antigennye determinanty obolochechnogo belka virusa SPID, dlia diagnostiki sindroma priobretennogo immunodefitsita.

The testing of sera from patients with AIDS and AIDS-related complex, using ELISA with recombinant env protein produced by E. coli, gave a 94% coincidence with the results obtained on "Organon" test-system. Sera samples that gave different results in two tests lacked antibodies to env-encoded proteins, as revealed by immunoblotting assay. The application of the above test for the estimation of the disease prognosis is discussed.

[Generation of HTLV-III-specific polypeptides in E. coli cells]. / Poluchenie HTLV-III-spetsificheskikh polipeptidov v kletkakh E. coli.

Cloning and expression in E. coli cells of a fragment of the env gene of HTLV-III virus is described. This fragment coding for from 294 to 757 aminoacid residue of virus protein was cloned in plasmid pUC 18. Conditions are described contributing to the regulated functioning of Lac-promoter allowing the expression of proteins toxic for E. coli. Solid-phase enzyme-immunoassay demonstrated a specific reaction of polypeptides synthesized in E. coli with an AIDS patient's serum. The sizes of these polypeptides were determined by the Western-blot method. They were found to be 18, 24, and 32 kilodaltons. The polypeptides synthesized in E. coli may apparently be used for preparation of test-systems for AIDS diagnosis.