Telomerase Reverse Transcriptase Increases Proliferation and Lifespan of Human NK Cells without Immortalization

NK cells are the first line of defense against viruses and malignant cells, and their natural functionality makes these cells a promising candidate for cancer cell therapy. The genetic modifications of NK cells, allowing them to overcome some of their inherent limitations, such as low proliferative potential, can enable their use as a therapeutic product. We demonstrate that hTERT-engineered NK cell cultures maintain a high percentage of cells in the S/G2 phase for an extended time after transduction, while the life span of NK cells is measurably extended. Bulk and clonal NK cell cultures pre-activated in vitro with IL-2 and K562-mbIL21 feeder cells can be transduced with hTERT more efficiently compared with the cells activated with IL-2 alone. Overexpressed hTERT was functionally active in transduced NK cells, which displayed upregulated expression of the activation marker HLA-DR, and decreased expression of the maturation marker CD57 and activating receptor NKp46. Larger numbers of KIR2DL2/3+ cells in hTERT-engineered populations may indicate that NK cells with this phenotype are more susceptible to transduction. The hTERT-modified NK cells demonstrated a high natural cytotoxic response towards K562 cells and stably expressed Ki67, a proliferation marker. Overall, our data show that ectopic hTERT expression in NK cells enhances their activation and proliferation, extends in vitro life span, and can be a useful tool in developing NK-based cancer cell therapies.

Preferential Small Intestine Homing and Persistence of CD8 T Cells in Rhesus Macaques Achieved by Molecularly Engineered Expression of CCR9 and Reduced Ex Vivo Manipulation

Adoptive cell transfer (ACT) is a powerful experimental approach to directly study T-cell-mediated immunity in vivo In the rhesus macaque AIDS virus model, infusing simian immunodeficiency virus (SIV)-infected animals with CD8 T cells engineered to express anti-SIV T-cell receptor specificities enables direct experimentation to better understand antiviral T-cell immunity in vivo Limiting factors in ACT experiments include suboptimal trafficking to, and poor persistence in, the secondary lymphoid tissues targeted by AIDS viruses. Previously, we redirected CD8 T cells to B-cell follicles by ectopic expression of the CXCR5 homing protein. Here, we modify peripheral blood mononuclear cell (PBMC)-derived CD8 T cells to express the CCR9 chemokine receptor, which induces preferential homing of the engineered cells to the small intestine, a site of intense early AIDS virus replication and pathology in rhesus macaques. Additionally, we increase in vivo persistence and overall systemic distribution of infused CD8 T cells, especially in secondary lymphoid tissues, by minimizing ex vivo culture/manipulation, thereby avoiding the loss of CD28+/CD95+ central memory T cells by differentiation in culture. These proof-of-principle results establish the feasibility of preferentially localizing PBMC-derived CD8 T cells to the small intestine and enables the direct experimental ACT-based assessment of the potential role of the quality and timing of effective antiviral CD8 T-cell responses to inhibit viral infection and subsequent replication in small intestine CD4 T cells. More broadly, these results support the engineered expression of homing proteins to direct CD8 T cells to target tissues as a means for both experimental and potential therapeutic advances in T-cell immunotherapies, including cancer.IMPORTANCEAdoptive cell transfer (ACT) of T cells engineered with antigen-specific effector properties can deliver targeted immune responses against malignancies and infectious diseases. Current T-cell-based therapeutic ACT relies on circulatory distribution to deliver engineered T cells to their targets, an approach which has proven effective for some leukemias but provided only limited efficacy against solid tumors. Here, engineered expression of the CCR9 homing receptor redirected CD8 T cells to the small intestine in rhesus macaque ACT experiments. Targeted homing of engineered T-cell immunotherapies holds promise to increase the effectiveness of adoptively transferred cells in both experimental and clinical settings.

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.

Adoptive Transfer of Engineered Rhesus Simian Immunodeficiency Virus-Specific CD8+ T Cells Reduces the Number of Transmitted/Founder Viruses Established in Rhesus Macaques

AIDS virus infections are rarely controlled by cell-mediated immunity, in part due to viral immune evasion and immunodeficiency resulting from CD4+ T-cell infection. One likely aspect of this failure is that antiviral cellular immune responses are either absent or present at low levels during the initial establishment of infection. To test whether an extensive, timely, and effective response could reduce the establishment of infection from a high-dose inoculum, we adoptively transferred large numbers of T cells that were molecularly engineered with anti-simian immunodeficiency virus (anti-SIV) activity into rhesus macaques 3 days following an intrarectal SIV inoculation. To measure in vivo antiviral activity, we assessed the number of viruses transmitted using SIVmac239X, a molecularly tagged viral stock containing 10 genotypic variants, at a dose calculated to transmit 12 founder viruses. Single-genome sequencing of plasma virus revealed that the two animals receiving T cells expressing SIV-specific T-cell receptors (TCRs) had significantly fewer viral genotypes than the two control animals receiving non-SIV-specific T cells (means of 4.0 versus 7.5 transmitted viral genotypes; P = 0.044). Accounting for the likelihood of transmission of multiple viruses of a particular genotype, the calculated means of the total number of founder viruses transmitted were 4.5 and 14.5 in the experimental and control groups, respectively (P = 0.021). Thus, a large antiviral T-cell response timed with virus exposure can limit viral transmission. The presence of strong, preexisting T-cell responses, including those induced by vaccines, might help prevent the establishment of infection at the lower-exposure doses in humans that typically transmit only a single virus.

IMPORTANCE

The establishment of AIDS virus infection in an individual is essentially a race between the spreading virus and host immune defenses. Cell-mediated immune responses induced by infection or vaccination are important contributors in limiting viral replication. However, in human immunodeficiency virus (HIV)/SIV infection, the virus usually wins the race, irreversibly crippling the immune system before an effective cellular immune response is developed and active. We found that providing an accelerated response by adoptively transferring large numbers of antiviral T cells shortly after a high-dose mucosal inoculation, while not preventing infection altogether, limited the number of individual viruses transmitted. Thus, the presence of strong, preexisting T-cell responses, including those induced by vaccines, might prevent infection in humans, where the virus exposure is considerably lower.

Telomerase and primary T cells: biology and immortalization for adoptive immunotherapy

Telomeres are specialized repeats, present at the end of chromosomes, whose loss during cell division is followed by growth arrest, a central mechanism of replicative senescence in human cells. Telomere length in stem cells is maintained by telomerase, a specialized reverse transcriptase, whose function is to restore shortening telomeres. Unlike most somatic cell types, human T lymphocytes are capable of briefly reactivating telomerase expression at the time of stimulation. Telomerase expression in T lymphocytes is modulated by a variety of external stimuli and by viral infections. However, telomerase reactivation in stimulated, proliferating human T lymphocytes is limited and cannot prevent the ultimate onset of senescence. Ectopic telomerase expression can rescue human and macaque antigen-specific T cells from senescence. Primary T cells have been engineered with telomerase to have substantially extended replicative lifespans without the loss of primary cell functions or malignant transformation. 'Immortal' antigen-specific T-cell lines and clones overexpressing telomerase are an invaluable source of well-characterized quasi-primary T cells for research of T-cell biology and are potentially useful for immunotherapy of cancer and AIDS.

Immortalization of human and rhesus macaque primary antigen-specific T cells by retrovirally transduced telomerase reverse transcriptase

Human and rhesus macaque primary antigen-specific T cells derived from infected or immunized individuals or animals are a valuable material with which to study cellular immune responses against pathogens and tumors. Antigen-specific T cells can be expanded in vitro but have a finite proliferative life span. After a limited period in culture, primary T cells undergo replicative senescence and stop dividing. This restricts their applicability to short-term experiments and complicates their use in adoptive immunotherapy. The proliferative life span of primary human and rhesus macaque T cells can be considerably extended by ectopically expressed human telomerase reverse transcriptase (TERT). Antigen-specific T cells transduced with TERT-expressing retroviral vectors can proliferate and expand in culture for long periods of time while maintaining their primary T cell characteristics, including antigen-specific responses. Thus, TERT-immortalized T cells are an important and valuable resource for studying T cell-mediated immune responses and, potentially, for adoptive immunotherapy.

Transduction of SIV-specific TCR genes into rhesus macaque CD8+ T cells conveys the ability to suppress SIV replication

BACKGROUND

The SIV/rhesus macaque model for HIV/AIDS is a powerful system for examining the contribution of T cells in the control of AIDS viruses. To better our understanding of CD8(+) T-cell control of SIV replication in CD4(+) T cells, we asked whether TCRs isolated from rhesus macaque CD8(+) T-cell clones that exhibited varying abilities to suppress SIV replication could convey their suppressive properties to CD8(+) T cells obtained from an uninfected/unvaccinated animal.

PRINCIPAL FINDINGS

We transferred SIV-specific TCR genes isolated from rhesus macaque CD8(+) T-cell clones with varying abilities to suppress SIV replication in vitro into CD8(+) T cells obtained from an uninfected animal by retroviral transduction. After sorting and expansion, transduced CD8(+) T-cell lines were obtained that specifically bound their cognate SIV tetramer. These cell lines displayed appropriate effector function and specificity, expressing intracellular IFNγ upon peptide stimulation. Importantly, the SIV suppression properties of the transduced cell lines mirrored those of the original TCR donor clones: cell lines expressing TCRs transferred from highly suppressive clones effectively reduced wild-type SIV replication, while expression of a non-suppressing TCR failed to reduce the spread of virus. However, all TCRs were able to suppress the replication of an SIV mutant that did not downregulate MHC-I, recapitulating the properties of their donor clones.

CONCLUSIONS

Our results show that antigen-specific SIV suppression can be transferred between allogenic T cells simply by TCR gene transfer. This advance provides a platform for examining the contributions of TCRs versus the intrinsic effector characteristics of T-cell clones in virus suppression. Additionally, this approach can be applied to develop non-human primate models to evaluate adoptive T-cell transfer therapy for AIDS and other diseases.

Macrophage scavenger receptor A mediates the uptake of gold colloids by macrophages in vitro

AIMS

While numerous studies have reported on nanoparticle uptake by phagocytic cells, the mechanisms of this uptake are poorly understood. A metastudy of research focusing on biological particulate matter has postulated that nanoparticles cannot be phagocytosed and therefore must enter cells via pinocytosis. The purpose of this study was to identify the route(s) of uptake of gold nanoparticles in vitro and to determine if these route(s) depend on particle size.

MATERIALS & METHODS

The parent RAW264.7 cell line and its derivatives, transduced with a virus carrying siRNA to macrophage scavenger receptor A, were used as model phagocytes. Citrate-stabilized gold colloids were used as model nanoparticles. We used chemical inhibitors known to interfere with specific routes of particulate uptake. We developed multifocal light microscopy methods including multifocal stack analysis with NIH ImageJ software to analyze cell uptake.

RESULTS

Irrespective of size, gold nanoparticles are internalized by macrophages via multiple routes, including both phagocytosis and pinocytosis. If either route was blocked, the particles entered cells via the other route.

CONCLUSION

Gold nanoparticles with hydrodynamic sizes below 100 nm can be phagocytosed. Phagocytosis of anionic gold colloids by RAW264.7 cells is mediated by macrophage scavenger receptor A.

TCR triggering transcriptionally downregulates CCR5 expression on rhesus macaque CD4(+) T-cells with no measurable effect on susceptibility to SIV infection

Studies using transformed human cell lines suggest that most SIV strains use CCR5 as co-receptor. Our analysis of primary rhesus macaque CD4(+) T-cell clones revealed marked differences in susceptibility to SIV(mac)239 infection. We investigated whether different levels of CCR5 expression account for clonal differences in SIV(mac)239 susceptibility. Macaque CD4(+) T-cells showed significant CCR5 downregulation 1-2days following CD3 mAb stimulation, which gradually recovered at resting state, 7-10days after activation. Exposure of clones to SIV(mac)239 during their CCR5(low) or CCR5(high) expression states revealed differences in SIV susceptibility independent of surface CCR5 levels. Furthermore, a CCR5 antagonist similarly reduced SIV(mac)239 infection of clones during their CCR5(low) or CCR5(high) expression states. Our data suggest a model where i) very low levels of CCR5 are sufficient for efficient SIV infection, ii) CCR5 levels above this threshold do not enhance infection, and iii) low level infection can occur in the absence of CCR5.

Efficient inhibition of SIV replication in rhesus CD4+ T-cell clones by autologous immortalized SIV-specific CD8+ T-cell clones

CD8(+) cytotoxic T lymphocyte (CTL) responses play an important role in controlling the replication of primate lentiviruses. Induction of these responses is a key objective for most current AIDS vaccine approaches. Despite a variety of approaches for measuring properties and activities of CTL, the functions responsible for controlling viral replication in vivo have not been clearly identified. Assays measuring CTL-mediated suppression of viral replication in vitro are beginning to be used as possible correlates of in vivo virus suppressive activity, but the utility and interpretive value of these assays are typically limited by properties of the cells that have been used. We investigated the capacity of SIV-specific CTL clones (effectors), immortalized by transduction with human telomerase reverse transcriptase (hTERT), to suppress SIV replication in autologous hTERT immortalized CD4(+) T-cell clones (targets). Immortalized and non-immortalized SIV-specific effector cells showed IFN-gamma production and degranulation in response to viral antigen specific stimulation and significantly inhibited SIV(mac)239 replication (2 to 4 log decrease in viral RNA or cell-associated proviral DNA) (p<0.0005). Our in vitro assays of inhibition of viral replication, using T-cell clones as effectors and targets, provide a well-defined approach for evaluating possible mechanisms of CTL-mediated control of viral production which may involve direct killing of infected target cells and/or release of proinflammatory cytokines such as IFN-gamma and TNF-alpha. The use of hTERT immortalized effector and target cells for such assays preserves relevant functional properties while providing a convenient, reproducible means of conducting studies over time.

Transduction with human telomerase reverse transcriptase immortalizes a rhesus macaque CD8+ T cell clone with maintenance of surface marker phenotype and function

T cell lines and clones play a key role in basic studies of cellular immunology, and are also finding applications in adoptive immunotherapy. However, with proliferative expansion, T cells ultimately undergo cellular senescence and death, so that long-term culture of T cell clones is difficult to achieve. Expression of telomerase reverse transcriptase (TERT) in differentiated cells can maintain telomere length over many cell divisions, preventing senescence. We used a retroviral vector that expresses the human TERT (hTERT) gene to transduce a rhesus macaque-derived CD8(+) T cell clone specific for the MamuA*01-restricted immunodominant SIV gag epitope CM9. Extensive in vitro characterization revealed that the untransduced parental cells and the hTERT-transduced cells displayed comparable proliferation capacity, effector memory surface marker profiles, cytolytic activities, and cytokine profiles following antigen stimulation. The hTERT-transduced cells showed improved survival compared to parallel nontransduced cultures during in vitro propagation in long-term culture. Such immortalized T cells may be useful as a source of consistent controls for in vitro assays of cellular immune function, and as a potentially important reagent for autologous adoptive cellular immunotherapy studies in macaques.

Capture of antigen-specific T lymphocytes from human blood by selective immortalization to establish long-term T-cell lines maintaining primary cell characteristics☆

To establish long-term, antigen-specific T-cell lines and clones, we selectively immortalized antigen-responsive T cells from human peripheral blood mononuclear cells (PBMCs). PBMCs were stimulated with either alloantigen or soluble antigen, then infected with a murine leukemia virus-based retroviral vector carrying an immortalizing gene, either the Tax gene from human T-cell leukemia virus type 1, or the human telomerase-reverse transcriptase gene. Since such vectors can only integrate in dividing cells, only antigen-activated T cells are efficiently transduced. This approach generated immortalized antigen-specific CD4+ and CD8+ T-cell lines that maintained strictly IL-2-dependent growth and HLA-restricted, antigen-specific responsiveness, some of which have been in continuous culture for longer than 1 year, far in excess of the survival of parallel control non-immortalized cultures. Clones derived from these lines showed antigen-specific proliferation with induced cytokine and chemokine production, and, in the case of a CD8+ T-cell clone, antigen-specific cytolytic activity. This approach provides a convenient, reproducible means for generating a stable, continuously renewable source of antigen-specific T lymphocytes for a variety of studies of T cell biology.

Mutations of a residue within the polyproline-rich region of Env alter the replication rate and level of cytopathic effects in chimeric avian retroviral vectors

Previous attempts to extend the host range of the avian sarcoma/leukosis virus (ASLV)-based RCASBP vectors produced two viral vectors, RCASBP M2C (4070A) and RCASBP M2C (797-8), which replicate using the amphotropic murine leukemia virus 4070A Env protein (2). Both viruses were adapted to replicate efficiently in the avian cell line DF-1, but RCASBP M2C (4070A) caused extensive cytopathic effects (CPE) in DF-1 cells whereas RCASBP M2C (797-8) induced low levels of CPE. The two viruses differed only at amino acid 242 of the polyproline-rich region in the surface (SU) subunit of the Env protein. In RCASBP M2C (4070A), an isoleucine replaced the wild-type proline residue, whereas a threonine residue was found in RCASBP M2C (797-8). In the present study, we show that other amino acid substitutions at position 242 strongly influence the CPE and replication rate of the chimeric viruses. There was a correlation between the amount of unintegrated linear retroviral DNA present in infected DF-1 cells and the level of CPE. This suggests that there may be a role for superinfection in the CPE. The treatment of RCASBP M2C (4070A)-infected cells with dantrolene, which inhibits the release of calcium from the endoplasmic reticulum (ER), reduced the amount of CPE seen during infection with the highly cytotoxic virus. Dantrolene treatment did not appear to affect virus production, suggesting that Ca2+ release from the ER had a role in the CPE caused by these viruses.

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]

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]

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]

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.