Greengenes2 unifies microbial data in a single reference tree

Studies using 16S rRNA and shotgun metagenomics typically yield different results, usually attributed to PCR amplification biases. We introduce Greengenes2, a reference tree that unifies genomic and 16S rRNA databases in a consistent, integrated resource. By inserting sequences into a whole-genome phylogeny, we show that 16S rRNA and shotgun metagenomic data generated from the same samples agree in principal coordinates space, taxonomy and phenotype effect size when analyzed with the same tree.

Abstract 6349: Targeting the CXCR3 pathway with a novel peptide drug candidate mobilizes the immune system to enhance anti-tumor immunity

Immune-checkpoint inhibitor (ICI) therapy releases the molecular “brakes” on the immune system thereby promoting robust anti-tumor immune responses. However, many patients do not respond to ICI therapy due to development of primary and secondary resistance, and this population represents a large unmet medical need. The critical role of C-X-C motif chemokine receptor 3 (CXCR3) signaling in eliciting an effective response to anti-PD-1 therapy has been recently demonstrated. The CXCR3 chemokine system is instrumental in effector cell recruitment to the tumor and augments intratumoral CD8+ T cell proliferation and function, which are key mechanisms driving anti-tumor immunity and responses to ICI therapy.

We used our proprietary peptide discovery platform to identify a unique microbiome-derived peptide, SG-3-00802, from bacterial strains associated with response to anti-PD1 inhibitors in patients with melanoma. We subsequently determined that CXCR3 is the target receptor for SG-3-00802 and demonstrated that SG-3-00802 enhanced the activity of CXCR3 in the presence of its endogenous ligands CXCL9/CXCL10/CXCL11. Optimization of SG-3-00802 pharmacological properties led to the selection of a novel drug development candidate SG-3-00802DC with improved potency and PK properties. Mechanistically, it increases CXCR3 activation by CXCL11 by greater than 10-fold from a nM to a pM range. As a positive allosteric modulator, SG-3-00802DC can potentially alter the conformation of the primary orthosteric binding site of CXCR3 and enhance the binding affinity of CXCL11, causing increased CXCR3 signaling activity, which is known to drive TIL infiltration that improves overall survival in mouse tumor models and cancer patients. Supporting this concept, we demonstrated that SG-3-00802DC showed anti-tumor activity in pre-clinical mouse tumor models, alone and in combination with anti-PD-1, improved overall survival and increased recruitment of CXCR3+ effector cells into the tumor microenvironment.

Numerous strategies are currently undergoing clinical evaluation to improve long-lasting disease control in broader patient populations by combining ICIs with approved and novel therapeutic agents and procedures. SG-3-00802DC, with its well validated and unique mechanism of action to safely target the CXCR3-driven anti-tumor immune response offers a novel orthogonal approach complementary not only to immunotherapies, but also as a combination strategy with chemotherapy or radiotherapy.

Citation Format: Dhwani Haria, Jina Lee, Justy Guagua, Archana Nagaraja, Kyle Roskamp, Bum-Yeol Hwang, Divya Ravichandar, Michi Willcoxon, Todd DeSantis, Karim Dabbagh, Helena Kiefel. Targeting the CXCR3 pathway with a novel peptide drug candidate mobilizes the immune system to enhance anti-tumor immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6349.

Abstract B28: A novel intestinal microbiome-derived peptide modulates immune cell activity and the tumor microenvironment

The composition of the gut microbiota affects cancer development, progression, and response to therapy. A number of commensal bacteria, including Bifidobacterium, have been associated with increased response to immune checkpoint inhibitors in mouse tumor models, as well as in melanoma patients. We hypothesized that secreted peptides or proteins contribute to the effects mediated by Bifidobacterium strains in vivo. We used our unique bioinformatics-driven discovery platform to nominate putatively secreted Bifidobacterium-derived peptides for evaluation in immune cell effector assays. We have previously described bacterial peptides that induce secretion of proinflammatory cytokines (e.g., IL-6, TNF) by in vitro-generated mouse and human dendritic cells, as well as effector cytokine secretion (e.g., IFNγ, IL-2) by mouse splenic T lymphocytes in vitro. To investigate the function of Bifidobacterium-derived peptides in the context of the tumor microenvironment, we injected a candidate peptide, termed SG-A, directly into the tumors of tumor-bearing mice. We then performed immune phenotyping via the Nanostring PanCancer Immune Profiling panel, as well as by flow cytometry. Both Nanostring and flow cytometry analysis demonstrated an increase in CD45+ lymphocytes within the tumors of mice treated with SG-A. Peptide SG-A also induced upregulation of dendritic cell function genes (CD40, CD83, and CD86) and multiple effector cytokines and chemokines. Restimulation of tumor-draining lymph node cells with a tumor-derived peptide antigen also increased induction of IFNγ in SG-A treated animals (vs. vehicle-treated controls). Collectively, our results demonstrate the utility of the Second Genome discovery platform for leveraging microbiome science to identify novel immunomodulatory factors. This platform offers the potential to identify agents that may complement or enhance efficacy of existing approaches to immunotherapy for melanoma and other cancers.

Citation Format: Helena Kiefel, Dhwani Haria, Yuliya Katlinskaya, Divya Ravichandar, Sunit Jain, Thomas Weinmaier, Shoko Iwai, Todd DeSantis, Toshi Takeuchi, Karim Dabbagh, Kareem Graham. A novel intestinal microbiome-derived peptide modulates immune cell activity and the tumor microenvironment [abstract]. In: Proceedings of the AACR Special Conference on Melanoma: From Biology to Target; 2019 Jan 15-18; Houston, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(19 Suppl):Abstract nr B28.

Abstract PR08: Novel microbiome-derived peptides modulate immune cell activity and the tumor microenvironment

The gut microbiota has emerged as an important player in cancer pathology, and increasing evidence supports its role in clinical response to immune checkpoint inhibitor (ICI) therapy. However, the specific microbiome-derived factors responsible for the improved response to ICI therapy remain unknown. Second Genome has developed a unique discovery platform to identify, screen, and validate microbiome-derived peptides that promote response to cancer immunotherapy. Using our multitechnology meta-analysis of published datasets and characterizing the baseline microbiome of melanoma patients treated with anti-PD-1, we have identified gut microbiome strains differentially abundant in responders versus nonresponders that are concordant across multiple cohorts. Next, peptides from strains associated with responder signatures were predicted from their genome sequences. In addition, we predicted peptides from assembled metagenomes that were associated with responders. The predicted peptides were screened using phage display technology to identify binders to immune cells known to play a role in the tumor microenvironment (TME). Peptides that bound to specific immune cells were then evaluated for activity in cell-based assays using isolated primary human T cells, dendritic cells (DCs), and macrophages. We have demonstrated that several microbiome-derived peptides induce secretion of proinflammatory cytokines and chemokines such as CXCL10 and TNF-α by primary human monocyte-derived dendritic cells (moDCs), as well as secretion of effector cytokines such as IFNγ and IL-2 by primary human T cells. We have also identified microbiome-derived peptides with the capacity to inhibit an M2-like phenotype in macrophages (decreased LPS-induced IL-10 secretion). These effects were dose dependent and evident across immune cells derived from multiple human blood donors. In a coculture assay using allogeneic moDCs and T cells from human donors, combination of our DC-activating peptides with CD40 agonistic antibody and/or anti-PD-L1 induced secretion of proinflammatory cytokines such as IFNγ and TNF-α. In vivo, peritumoral administration of a candidate DC-activating peptide into RENCA tumor-bearing mice led to a significant reduction in tumor volume as compared to the control-treated mice. Collectively, these data demonstrate the potential of the microbiome-derived peptides identified by Second Genome’s discovery platform to modulate immune-cell effector functions in vitro and promote antitumor immunity in vivo. These results validate the unique approach of Second Genome’s discovery platform to identify novel microbiome-derived agents with potential for use as therapeutics in cancer immunotherapy.

This abstract is also being presented as Poster B19.

Citation Format: Dhwani D. Haria, Jayamary Divya Ravichandar, Lynn Yamamoto, Bernat Baeza-Raja, Ashil Bans, Cheryl-Emiliane Chow, Jill Desnoyer, Joanna Dreux, Shoko Iwai, Sabina Lau, Jina Lee, Michelle Lin, Paul Loriaux, Nicole Narayan, Eskedar Nigatu, Erica Rutherford, Michi Wilcoxon, Yonggan Wu, Todd DeSantis, Toshihiko Takeuchi, Karim Dabbagh, Helena Kiefel. Novel microbiome-derived peptides modulate immune cell activity and the tumor microenvironment [abstract]. In: Proceedings of the AACR Special Conference on the Microbiome, Viruses, and Cancer; 2020 Feb 21-24; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2020;80(8 Suppl):Abstract nr PR08.

Abstract 1490: Novel microbiome-derived peptides activate the host innate immune system by regulation of TLR signaling

The gut microbiome is a key contributor to the maintenance of host physiology. At the same time, increasing evidence implicates microbiome dysbiosis as a key determinant of numerous metabolic and inflammatory disorders. It is, therefore, of paramount importance to understand the interactions between the host and gut microbiota. Second Genome has developed a proprietary, bioinformatics-driven discovery platform to identify novel microbiome-derived peptides with the potential to modulate host immune responses. We have leveraged this platform to evaluate immunomodulatory functions of novel, secreted peptides derived from gut-resident bacterial species Bifidobacterium longum and Bifidobacterium breve. Previously, the microbial genus Bifidobacterium (‘Bifido’) has been shown to be associated with enhanced dendritic cell functions and antitumor effects. Here, we identify Bifido-derived peptides that are putative agonists of certain murine and human Toll-like receptors (TLRs). These peptides induce secretion of pro-inflammatory cytokines such as TNF-α and IL-6 by in vitro-generated mouse dendritic cells and peritoneal macrophages in a TLR4 and CD14-dependent manner. One of the peptides, SG-A, also induces secretion of Th1-type cytokines and chemokines such as IL-21, GRO-α, and IP-10 by human monocytes and monocyte-derived dendritic cells. Moreover, in vivo administration of SG-A in mice elicited a systemic pro-inflammatory immune response in the absence of any secondary stimulus. Collectively, our results demonstrate the ability of a novel bacterial-derived peptide to engage the host innate immune system. Moreover, our findings validate the potential of the Second Genome discovery platform for identification of novel microbiome-derived agents that: i) have the ability to modulate host cell functions; and ii) may be developed into therapeutic agents for immune and inflammatory disorders.

Citation Format: Dhwani Haria, Helena Kiefel, Yuliya Katlinskaya, Sunit Jain, Thomas Weinmaier, Shoko Iwai, Todd DeSantis, Toshi Takeuchi, Karim Dabbagh, Kareem Graham. Novel microbiome-derived peptides activate the host innate immune system by regulation of TLR signaling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1490.

Abstract 576: A novel intestinal microbiome-derived peptide modulates host T cell activation

The microbiome shapes the metabolic and immunological landscape of individuals in health and disease and represents a new robust source of bioactive molecules with therapeutic potential. Second Genome’s large and curated microbiome database coupled with its proprietary bioinformatics and machine learning pipeline enables the discovery of novel microbiome-derived drug candidates across multiple disease areas, including immuno-oncology (IO). Microbial genus Bifidobacterium previously showed a positive association with antitumor T cell responses in mouse models and was overrepresented in melanoma patients responding to immunotherapy with anti-PD-1 antibody. Our hypothesis is that bioactive molecules derived from these Bifidobacteria help drive these antitumor responses and could function as cancer therapeutics or adjuvants for cancer immunotherapy. Thus, we nominated protein and peptide candidates with high scores of secretability, uniqueness, stability, and expressability from Bifidobacterium breve and Bifidobacterium longum genomes for screening in cell-based assays. Initial evaluation of more than 50 Bifidobacterium peptides revealed candidates capable of inducing immune activation. Here, we describe a B. breve-derived peptide (termed SG-B) that induced up-regulation of co-stimulatory (OX40 and ICOS) and inhibitory (PD-1) molecules on CD4+ and CD8+ T cells in both: i) a purified human pan-T cell system; and ii) PBMC cultures stimulated with low-dose anti-CD3 antibody. Furthermore, SG-B stimulated secretion of effector cytokines by in vitro-cultured purified T cells (TNF-a, IL-2, IFN-g, and IL-10) and PBMCs (IL-1b, IL-6, and IL-8). These effects were dose-dependent and evident across multiple human blood donors. In the CT26 syngeneic tumor model, peri-tumoral administration of SG-B induced an increase in the proportion of NK cells and CD4+ T cells within the tumor. The peptide also induced up-regulation of activation marker on CD8+ T cells (CD25, Ki67, and OX40). Collectively, these data suggest that SG-B can modulate adaptive immunity via T cell potentiation and may enhance tumor inflammation in vivo. The peptide’s ability to up-regulate key co-stimulatory and checkpoint molecules on T cells provides a strong rationale for its potential future use in combination with approved or IO agents in current development. These results validate the capability of the Second Genome drug discovery platform to identify novel microbial agents of potential therapeutic relevance in IO and demonstrate a unique approach that can identify microbial factors involved in modulating immune cell effector functions and/or immune cell differentiation.

Citation Format: Yuliya V. Katlinskaya, Dhwani Haria, Lily McLaughlin, Sunit Jain, Shoko Iwai, Todd DeSantis, Thomas Weinmaier, Toshi Takeuchi, Anu Hoey, Karim Dabbagh, Kareem Graham, Helena Kiefel. A novel intestinal microbiome-derived peptide modulates host T cell activation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 576.

Abstract 4963: A novel intestinal microbiome-derived peptide modulates immune cell activity and the tumor microenvironment

The composition of the gut microbiota affects cancer development, progression, and response to therapy. A number of commensal bacteria, including Bifidobacterium, have been associated with increased response to immune checkpoint inhibitors in mouse tumor models and in cancer patients.

We hypothesized that secreted peptides or proteins are driving the Bifidobacterium-mediated effects. Using our unique bioinformatic-driven discovery platform we nominated putatively secreted Bifidobacterium-derived peptides for evaluation in immune cell effector assays. We demonstrate that several of the peptides induce secretion of pro-inflammatory cytokines (e.g., IL-6, TNF) by in vitro-generated mouse and human dendritic cells, as well as effector cytokine secretion (e.g., IFNγ, IL-2) by mouse splenic T lymphocytes in vitro.

To investigate the function of Bifidobacterium-derived peptides in the context of the tumor microenvironment we injected the candidate peptide SG-A directly into the tumor of CT26 tumor-bearing mice and analyzed the immune phenotype using the Nanostring PanCancer Immune Profiling panel and flow cytometry. Both Nanostring as well as flow cytometry analysis showed an increase in CD45+ tumor-infiltrating lymphocytes in SG-A treated tumors. SG-A peptide also induced the upregulation of dendritic cell function genes (CD40, CD83, and CD86) and multiple effector cytokines and chemokines. Re-stimulation of tumor-draining lymph node cells with AH1 peptide (a CT26 tumor-derived antigen) also increased induction of IFNγ in SG-A treated animals (vs. vehicle-treated controls).

Collectively, our results demonstrate the utility of the Second Genome discovery platform for leveraging microbiome science to identify novel immunoregulatory factors. This platform offers a promising approach to identify agents with potential for use as therapeutics in cancer immunotherapy.

Citation Format: Helena Kiefel, Dhwani Haria, Yuliya Katlinskaya, Divya Ravichandar, Lily McLaughlin, Sunit Jain, Thomas Weinmaier, Shoko Iwai, Todd DeSantis, Toshi Takeuchi, Karim Dabbagh, Kareem Graham. A novel intestinal microbiome-derived peptide modulates immune cell activity and the tumor microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4963.

The microbial community of the cystic fibrosis airway is disrupted in early life

BACKGROUND

Molecular techniques have uncovered vast numbers of organisms in the cystic fibrosis (CF) airways, the clinical significance of which is yet to be determined. The aim of this study was to describe and compare the microbial communities of the lower airway of clinically stable children with CF and children without CF.

METHODS

Bronchoalveolar lavage (BAL) fluid and paired oropharyngeal swabs from clinically stable children with CF (n = 13) and BAL from children without CF (n = 9) were collected. DNA was isolated, the 16S rRNA regions amplified, fragmented, biotinylated and hybridised to a 16S rRNA microarray. Patient medical and demographic information was recorded and standard microbiological culture was performed.

RESULTS

A diverse bacterial community was detected in the lower airways of children with CF and children without CF. The airway microbiome of clinically stable children with CF and children without CF were significantly different as measured by Shannon's Diversity Indices (p = 0.001; t test) and Principle coordinate analysis (p = 0.01; Adonis test). Overall the CF airway microbial community was more variable and had a less even distribution than the microbial community in the airways of children without CF. We highlighted several bacteria of interest, particularly Prevotella veroralis, CW040 and a Corynebacterium, which were of significantly differential abundance between the CF and non-CF lower airways. Both Pseudomonas aeruginosa and Streptococcus pneumoniae culture abundance were found to be associated with CF airway microbial community structure. The CF upper and lower airways were found to have a broadly similar microbial milieu.

CONCLUSION

The microbial communities in the lower airways of stable children with CF and children without CF show significant differences in overall diversity. These discrepancies indicate a disruption of the airway microflora occurring early in life in children with CF.

A microbiota signature associated with experimental food allergy promotes allergic sensitization and anaphylaxis

BACKGROUND

Commensal microbiota play a critical role in maintaining oral tolerance. The effect of food allergy on the gut microbial ecology remains unknown.

OBJECTIVE

We sought to establish the composition of the gut microbiota in experimental food allergy and its role in disease pathogenesis.

METHODS

Food allergy-prone mice with a gain-of-function mutation in the IL-4 receptor α chain (Il4raF709) and wild-type (WT) control animals were subjected to oral sensitization with chicken egg ovalbumin (OVA). Enforced tolerance was achieved by using allergen-specific regulatory T (Treg) cells. Community structure analysis of gut microbiota was performed by using a high-density 16S rDNA oligonucleotide microarrays (PhyloChip) and massively parallel pyrosequencing of 16S rDNA amplicons.

RESULTS

OVA-sensitized Il4raF709 mice exhibited a specific microbiota signature characterized by coordinate changes in the abundance of taxa of several bacterial families, including the Lachnospiraceae, Lactobacillaceae, Rikenellaceae, and Porphyromonadaceae. This signature was not shared by similarly sensitized WT mice, which did not exhibit an OVA-induced allergic response. Treatment of OVA-sensitized Il4raF709 mice with OVA-specific Treg cells led to a distinct tolerance-associated signature coincident with the suppression of the allergic response. The microbiota of allergen-sensitized Il4raF709 mice differentially promoted OVA-specific IgE responses and anaphylaxis when reconstituted in WT germ-free mice.

CONCLUSION

Mice with food allergy exhibit a specific gut microbiota signature capable of transmitting disease susceptibility and subject to reprogramming by enforced tolerance. Disease-associated microbiota may thus play a pathogenic role in food allergy.

Bacterial diversity of terrestrial crystalline volcanic rocks, Iceland

Bacteria inhabiting crystalline rocks from two terrestrial Icelandic volcanic lava flows of similar age and from the same geographical region, but differing in porosity and mineralogy, were characterised. Microarray (PhyloChip) and clone library analysis of 16S rRNA genes revealed the presence of a diverse assemblage of bacteria in each lava flow. Both methods suggested a more diverse community at the Dómadalshraun site (rhyolitic/andesitic lava flow) than that present at the Hnausahraun site (basaltic lava flow). Proteobacteria dominated the clone library at the Dómadalshraun site, while Acidobacteria was the most abundant phylum in the Hnausahraun site. Although analysis of similarities of denaturing gradient gel electrophoresis profiles suggested a strong correlation of community structure with mineralogy, rock porosity may also play an important role in shaping the bacterial community in crystalline volcanic rocks. Clone sequences were most similar to uncultured microorganisms, mainly from soil environments. Of these, Antarctic soils and temperate rhizosphere soils were prominent, as were clones retrieved from Hawaiian and Andean volcanic soils. The novel diversity of these Icelandic microbial communities was supported by the finding that up to 46% of clones displayed <85% sequence identities to sequences currently deposited in the RDP database.

Molecular bacterial community analysis of clean rooms where spacecraft are assembled

Molecular bacterial community composition was characterized from three geographically distinct spacecraft-associated clean rooms to determine whether such populations are influenced by the surrounding environment or the maintenance of the clean rooms. Samples were collected from facilities at the Jet Propulsion Laboratory (JPL), Kennedy Space Flight Center (KSC), and Johnson Space Center (JSC). Nine clone libraries representing different surfaces within the spacecraft facilities and three libraries from the surrounding air were created. Despite the highly desiccated, nutrient-bare conditions within these clean rooms, a broad diversity of bacteria was detected, covering all the main bacterial phyla. Furthermore, the bacterial communities were significantly different from each other, revealing only a small subset of microorganisms common to all locations (e.g. Sphingomonas, Staphylococcus). Samples from JSC assembly room surfaces showed the greatest diversity of bacteria, particularly within the Alpha- and Gammaproteobacteria and Actinobacteria. The bacterial community structure of KSC assembly surfaces revealed a high presence of proteobacterial groups, whereas the surface samples collected from the JPL assembly facility showed a predominance of Firmicutes. Our study presents the first extended molecular survey and comparison of NASA spacecraft assembly facilities, and provides new insights into the bacterial diversity of clean room environments .

Molecular bacterial community analysis of clean rooms where spacecraft are assembled

Molecular bacterial community composition was characterized from three geographically distinct spacecraft-associated clean rooms to determine whether such populations are influenced by the surrounding environment or the maintenance of the clean rooms. Samples were collected from facilities at the Jet Propulsion Laboratory (JPL), Kennedy Space Flight Center (KSC), and Johnson Space Center (JSC). Nine clone libraries representing different surfaces within the spacecraft facilities and three libraries from the surrounding air were created. Despite the highly desiccated, nutrient-bare conditions within these clean rooms, a broad diversity of bacteria was detected, covering all the main bacterial phyla. Furthermore, the bacterial communities were significantly different from each other, revealing only a small subset of microorganisms common to all locations (e.g. Sphingomonas, Staphylococcus). Samples from JSC assembly room surfaces showed the greatest diversity of bacteria, particularly within the Alpha- and Gammaproteobacteria and Actinobacteria. The bacterial community structure of KSC assembly surfaces revealed a high presence of proteobacterial groups, whereas the surface samples collected from the JPL assembly facility showed a predominance of Firmicutes. Our study presents the first extended molecular survey and comparison of NASA spacecraft assembly facilities, and provides new insights into the bacterial diversity of clean room environments .

Insulin-like growth factor 1 and insulin inhibit HIV type 1 replication in cultured cells

Insulin-like growth factor 1 and insulin, considered primarily as metabolic and growth modulatory hormones, were found to inhibit the replication of HIV-1 in cultured cord blood mononuclear cells and chronically HIV-infected U937 cells. The effect of IGF-1 was seen at physiological concentrations or lower (1.7 x 10(-10) M) while that of insulin was observed at supraphysiological concentrations (8 x 10(-7) M). The EC50 for IGF-1 was found to be in the physiological range (2.5-4.5 x 10(-9) M) while that for insulin was considerably higher (1.1-3.3 x 10(-6) M). Insulin-like growth factor 1 and insulin at the concentrations employed exhibited no toxicity on the cells used in these studies. Furthermore, neither IGF-1 nor insulin exhibited any inhibitory activity on purified reverse transcriptase in vitro. Epidermal growth factor from 1.6 x 10(-10) to 1.6 x 10(-8) M demonstrated no inhibition of HIV-1 replication, while IGF-1 inhibited p24 antigen production 49 and 42% at 1.3 x 10(-9) and 1.3 x 10(-8) M IGF-1, respectively. These results suggest that IGF-1 under certain conditions has significant inhibitory effects on HIV-1 replication at physiological concentrations. This may prove to be of therapeutic value in patients infected with HIV-1.