Real-world use of avatrombopag in patients with chronic liver disease and thrombocytopenia undergoing a procedure

The phase 4 observational cohort study assessed the effectiveness and safety of the thrombopoietin receptor agonist avatrombopag in patients with chronic liver disease (CLD) and thrombocytopenia undergoing a procedure. Patients with CLD may have thrombocytopenia, increasing the risk of periprocedural bleeding. Prophylactic platelet transfusions used to reduce this risk have limitations including lack of efficacy and transfusion-associated reactions. Prophylactic thrombopoietin receptor agonists have been shown to increase platelet counts and decrease platelet transfusions. Effectiveness was assessed by change from baseline in platelet count and proportion of patients needing a platelet transfusion. Safety was assessed by monitoring adverse events (AEs). Of 50 patients enrolled, 48 were unique patients and 2 patients were enrolled twice for separate procedures. The mean (standard deviation) change in platelet count from baseline to procedure day was 41.1 × 109/L (33.29 × 109/L, n = 38), returning to near baseline at the post-procedure visit (change from baseline -1.9 × 109/L [15.03 × 109/L], n = 11). The proportion of patients not requiring a platelet transfusion after baseline and up to 7 days following the procedure was 98% (n = 49). Serious AEs were infrequent (n = 2 [4%]). No treatment-emergent AEs were considered related to avatrombopag. There were 2 mild bleeding events, no thromboembolic events or deaths, and no patients received rescue procedures (excluding transfusions). This study found that in a real-world setting, treatment with avatrombopag was well tolerated, increased the mean platelet count by procedure day, and reduced the need for intraoperative platelet transfusions in patients with CLD and thrombocytopenia.

Avatrombopag ethnic sensitivity analysis in chronic liver disease and thrombocytopenia patients: individual-level pooled analysis

INTRODUCTION

Few data have been published on the ethnic sensitivity of effectiveness, pharmacokinetics (PK), and pharmacodynamics (PD) of avatrombopag for the management of thrombocytopenia in patients with chronic liver disease (CLD).

METHODS

An ethnic sensitivity analysis was performed based on the results from two phase III studies (ADAPT-1 and ADAPT-2), with a primary endpoint of the proportion of patients without the requirement of platelet transfusion or rescue treatment for bleeding after randomization to 7 days following a scheduled procedure, and three phase I studies in healthy subjects. Cochran-Mantel-Haenszel and Fisher's exact tests were used to compare the differences in effectiveness in different ethnicities and overall population.

RESULTS

In total, 435 patients (placebo, n = 158; avatrombopag, n = 277) were stratified into various ethnic groups: 121 East Asians, including the subgroup of 27 Chinese, and 259 Caucasians. The proportion of patients who did not receive a platelet transfusion and those with a platelet count ⩾50 × 10⁹/L in the avatrombopag 40 and 60 mg groups were higher than that of placebo for all ethnicities and in the overall population. Statistical significance was obtained in the overall population and for all ethnicities other than Chinese patients, a group with a very small sample size. No significant difference was observed in the proportion of responders in each ethnic group compared to overall population (p > 0.05). The incidence of adverse events in East Asians was similar to that in both Caucasians and the overall population.

CONCLUSION

Avatrombopag was effective and safe in the management of thrombocytopenia in Chinese patients with CLD. Ethnicity does not appear to influence the efficacy, safety, PK, or PD of avatrombopag.

Phase 3 randomised study of avatrombopag, a novel thrombopoietin receptor agonist for the treatment of chronic immune thrombocytopenia

Avatrombopag, an oral thrombopoietin receptor agonist, was compared with placebo in a 6-month, multicentre, randomised, double-blind, parallel-group Phase 3 study, with an open-label extension phase, to assess the efficacy and safety of avatrombopag (20 mg/day) in adults with chronic immune thrombocytopenia (ITP) and a platelet count <30 × 10⁹ /l (ClinicalTrials.gov identifier NCT01438840). The primary endpoint was the cumulative number of weeks of platelet response (platelet count ≥50 × 10⁹ /l) without rescue therapy for bleeding; secondary endpoints included platelet response rate at day 8 and reductions in the use of concomitant medications. Amongst the 49 patients randomised, avatrombopag (N = 32) was superior to placebo (N = 17) in the median cumulative number of weeks of platelet response (12·4 vs. 0·0 weeks, respectively; P < 0·0001). At day 8, a greater platelet response rate was also observed for patients treated with avatrombopag compared with placebo (65·63% vs. 0·0%; P < 0·0001), and use of concomitant ITP medications was also reduced amongst patients receiving avatrombopag. The safety profile of avatrombopag was consistent with Phase 2 studies; the most common adverse events were headache and contusion. Overall, avatrombopag was well tolerated and efficacious for the treatment of chronic ITP.

Development of an Adult Physiologically Based Pharmacokinetic Model of Solithromycin in Plasma and Epithelial Lining Fluid

Solithromycin is a fluoroketolide antibiotic under investigation for community-acquired bacterial pneumonia (CABP). We developed a whole-body physiologically based pharmacokinetic (PBPK) model for solithromycin in adults using PK-Sim and MoBi version 6.2, which incorporated time-dependent CYP3A4 auto-inhibition. The model was developed and evaluated using plasma and epithelial lining fluid (ELF) concentration data from 100 healthy subjects and 22 patients with CABP (1,966 plasma, 30 ELF samples). We performed population simulations and calculated the number of observations falling outside the 90% prediction interval. For the oral regimen (800 mg on day 1 and 400 mg daily on days 2-5) that was evaluated in phase III studies, 11% and 23% of observations from healthy adults fell outside the 90% prediction interval for plasma and ELF, respectively. This regimen should be effective because ≥97% of simulated adults achieved area under the concentration vs. time curve (AUC) to minimum inhibitory concentration ratios associated with a log₁₀ colony forming unit reduction in ELF.

SOLITAIRE-IV: A Randomized, Double-Blind, Multicenter Study Comparing the Efficacy and Safety of Intravenous-to-Oral Solithromycin to Intravenous-to-Oral Moxifloxacin for Treatment of Community-Acquired Bacterial Pneumonia

BACKGROUND

Solithromycin, a novel macrolide antibiotic with both intravenous and oral formulations dosed once daily, has completed 2 global phase 3 trials for treatment of community-acquired bacterial pneumonia.

METHODS

A total of 863 adults with community-acquired bacterial pneumonia (Pneumonia Outcomes Research Team [PORT] class II-IV) were randomized 1:1 to receive either intravenous-to-oral solithromycin or moxifloxacin for 7 once-daily doses. All patients received 400 mg intravenously on day 1 and were permitted to switch to oral dosing when clinically indicated. The primary objective was to demonstrate noninferiority (10% margin) of solithromycin to moxifloxacin in achievement of early clinical response (ECR) assessed 3 days after first dose in the intent-to-treat (ITT) population. Secondary endpoints included demonstrating noninferiority in ECR in the microbiological ITT population (micro-ITT) and determination of investigator-assessed success rates at the short-term follow-up (SFU) visit 5-10 days posttherapy.

RESULTS

In the ITT population, 79.3% of solithromycin patients and 79.7% of moxifloxacin patients achieved ECR (treatment difference, -0.46; 95% confidence interval [CI], -6.1 to 5.2). In the micro-ITT population, 80.3% of solithromycin patients and 79.1% of moxifloxacin patients achieved ECR (treatment difference, 1.26; 95% CI, -8.1 to 10.6). In the ITT population, 84.6% of solithromycin patients and 88.6% of moxifloxacin patients achieved clinical success at SFU based on investigator assessment. Mostly mild/moderate infusion events led to higher incidence of adverse events overall in the solithromycin group. Other adverse events were comparable between treatment groups.

CONCLUSIONS

Intravenous-to-oral solithromycin was noninferior to intravenous-to-oral moxifloxacin. Solithromycin has potential to provide an intravenous and oral option for monotherapy for community-acquired bacterial pneumonia.

CLINICAL TRIALS REGISTRATION

NCT01968733.

Safety and Pharmacokinetics of Solithromycin in Subjects with Hepatic Impairment

Solithromycin, a new macrolide and the first fluoroketolide, is in late-stage clinical development and, like older macrolides, is primarily metabolized and excreted through liver-dependent mechanisms. This study evaluated the safety and pharmacokinetics of solithromycin in patients with chronic liver disease. This open-label, multiple-dose study in subjects with hepatic impairment and in healthy control subjects (matched for age, weight, and sex) enrolled 8 Child-Pugh class A (mild), 8 class B (moderate), and 8 class C (severe) patients and 9 healthy controls. Subjects (n = 33) received one 800-mg dose on day 1 followed by once-daily doses of 400 mg on days 2 through 5. The most commonly reported adverse events were mild diarrhea and mild headache, and no significant differences were noted between hepatically impaired subjects and healthy controls. The pharmacokinetics of plasma solithromycin in subjects with mild and moderate impairment was similar to that in control subjects. In subjects with severe impairment, total exposure to solithromycin at steady state (area under the plasma concentration-time curve [AUC0-tau]) was decreased compared to that in control subjects, which may have been related to the higher body mass index of individuals in this group. No greater accumulation was noted in any hepatically impaired cohort on day 5 compared to that in control subjects. No decrease in dosage is therefore needed when administering solithromycin to patients with mild, moderate, or severe hepatic impairment. Solithromycin was well tolerated in this patient population, and no significant differences in safety, compared to healthy controls, were noted.

A Phase 2 Trial of Oral Solithromycin 1200 mg or 1000 mg as Single-Dose Oral Therapy for Uncomplicated Gonorrhea

BACKGROUND

Progressive resistance to antimicrobial agents has reduced options for gonorrhea therapy worldwide. Solithromycin (CEM-101) is a novel oral fluoroketolide antimicrobial with substantial in vitro activity against Neisseria gonorrhoeae.

METHODS

We conducted a phase 2 trial of 2 oral doses of solithromycin (1200 and 1000 mg) for treatment of uncomplicated gonorrhea.

RESULTS

A total of 59 participants were enrolled and treated in this trial; 28 participants received 1200 mg of solithromycin and 31 received 1000 mg. Forty-six (78%) participants had positive cultures for N. gonorrhoeae at the time of enrollment: 24 of the 28 persons (86%) who received 1200 mg of oral solithromycin, and 22 of 31 (71%) who received 1000 mg. In addition, 8 participants had positive pharyngeal gonococcal cultures, and 4 had positive rectal cultures. All patients with positive cultures for N. gonorrhoeae were cured at all sites of infection. Chlamydia trachomatis and Mycoplasma genitalium coinfections were evaluated using nucleic acid amplification tests and were negative at 1 week of follow-up in 9 of 11 (82%) participants positive for C. trachomatis and 7 of 10 (70%) participants positive for M. genitalium. Mild dose-related gastrointestinal side effects (nausea, loose stools, vomiting) were common but did not limit therapy.

CONCLUSIONS

Oral single-dose solithromycin, in doses of 1000 mg and 1200 mg, was 100% effective for treatment of culture-proven gonorrhea at genital, oral, and rectal sites of infection and is a promising new agent for gonorrhea treatment.

CLINICAL TRIALS REGISTRATION

NCT01591447.

Preferential depletion of gut CD4-expressing iNKT cells contributes to systemic immune activation in HIV-1 infection

Chronic inappropriate immune activation is the central defect-driving loss of CD4(+) T helper cells and progression to AIDS in persons with HIV-1 infection, but the mechanisms remain controversial. We examined key regulatory invariant receptor natural killer T (iNKT) cells in the gut, the largest reservoir of lymphocytes and a key arena of HIV-1 pathogenesis. In healthy control persons, the anti-inflammatory CD4(+) iNKT-cell subset predominated over the pro-inflammatory CD4(-) iNKT-cell subset in the gut, but not in the blood, compartment. HIV-1 infection resulted in a preferential loss of this anti-inflammatory CD4(+) iNKT-cell subset within the gut. The degree of loss of the CD4(+) iNKT-cell subset in the gut, but not in the blood, correlated to the systemic immune activation and exhaustion that have been linked to disease progression. These results suggest a potentially important contribution of gut iNKT-cell imbalance in determining the systemic immune activation that is the hallmark of HIV-1 pathogenesis.

Thoracic and lumbar paravertebral blocks for outpatient lithotripsy

Paravertebral nerve block has been used for a variety of surgical procedures to provide unilateral anesthesia and postoperative analgesia. We report the successful application of this regional anesthesia modality for outpatient lithotripsy. Preoperatively, thoracic and lumbar paravertebral nerve blocks with 0.5% ropivacaine were placed with ultrasound and nerve stimulator guidance for two patients with ureteral calculi. One patient scheduled for cystoscopy and ureteroscopy with laser lithotripsy received general anesthesia intraoperatively. The second patient underwent extracorporeal shock wave lithotripsy with propofol intravenous sedation. Postoperatively, both patients reported pain scores of zero (Visual Analog Scale) for 24 hours and required no opioid rescue analgesia.

[Delleman syndrome: anesthetic considerations]

We herein report a case of a 5-year-old patient with Delleman Syndrome, a rare congenital disorder affecting the eyes, skin, and central nervous system, who underwent general anesthesia for conjuctivoplasty. This is only the second report of the anesthetic management of a patient with this condition. We attempt to summarize some of the anesthetic implications of this syndrome.

Comparison of cell cycle arrest, transactivation, and apoptosis induced by the simian immunodeficiency virus SIVagm and human immunodeficiency virus type 1 vpr genes

All primate lentiviruses known to date contain one or two open reading frames with homology to the human immunodeficiency virus type 1 (HIV-1) vpr gene. HIV-1 vpr encodes a 96-amino-acid protein with multiple functions in the viral life cycle. These functions include modulation of the viral replication kinetics, transactivation of the long terminal repeat, participation in the nuclear import of preintegration complexes, induction of G2 arrest, and induction of apoptosis. The simian immunodeficiency virus (SIV) that infects African green monkeys (SIVagm) contains a vpr homologue, which encodes a 118-amino-acid protein. SIVagm vpr is structurally and functionally related to HIV-1 vpr. The present study focuses on how three specific functions (transactivation, induction of G2 arrest, and induction of apoptosis) are related to one another at a functional level, for HIV-1 and SIVagm vpr. While our study supports previous reports demonstrating a causal relationship between induction of G2 arrest and transactivation for HIV-1 vpr, we demonstrate that the same is not true for SIVagm vpr. Transactivation by SIVagm vpr is independent of cell cycle perturbation. In addition, we show that induction of G2 arrest is necessary for the induction of apoptosis by HIV-1 vpr but that the induction of apoptosis by SIVagm vpr is cell cycle independent. Finally, while SIVagm vpr retains its transactivation function in human cells, it is unable to induce G2 arrest or apoptosis in such cells, suggesting that the cytopathic effects of SIVagm vpr are species specific. Taken together, our results suggest that while the multiple functions of vpr are conserved between HIV-1 and SIVagm, the mechanisms leading to the execution of such functions are divergent.

Genotyping TAP2 variants in North American Caucasians, Brazilians, and Africans

The protein forms of transporter associated with antigen processing, subunit 2 (TAP2), differ either by amino acid substitutions (Thr374Ala, Ile379Val, Ile467Val, Thr565Ala, Val577Met, Cys651Arg, and Ala665Thr) or by a truncation (Gln687Stop) of 17 amino acid residues at the C-terminus. Nonsynonymous single nucleotide polymorphisms (N-SNPs) causing these amino acid variations except 577Val were detected in genomic DNA samples from North American Caucasians (n = 76), Brazilians (n = 148), Rwandans (n = 285), and Zambians (n = 117). Exclusive (100%) and nearly exclusive (>95%) linkage disequilibrium was seen with a number of N-SNPs. The average heterozygosity at any given dimorphic site ranged from 7.3% to 44.6%, and at least four N-SNPs showed clear population specificity. N-SNP combinations alone led to the identification of 16 relatively common alleles, which appeared to form at least three lineages. Further analyses of 101 cDNA samples from Brazilians detected nine expressed TAP2 alleles, four of which matched the official assignments. Genetic complexity at the TAP2 locus was further enhanced by two out of five synonymous SNPs (S-SNPs), especially the GGT386GGG (Gly) that had similar heterozygosity rates in Caucasians (28.9%), Rwandans (33.3%), and Zambians (33.3%). Overall, distribution of both synonymous and nonsynonymous SNPs in the various ethnic groups examined here conformed well to the Hardy-Weinberg equilibrium, and between 57.9% and 77.0% of subjects in each ethnic group were heterozygous with two TAP2 alleles predicted to differ by at least one amino acid residue. Such complexity of TAP2 polymorphisms, in the form of SNPs as well as alleles, is likely to complicate the analyses of disease associations and haplotype structures in the HLA class II region.

Simultaneous flow cytometric measurement of viability and lymphocyte subset proliferation

Combined analysis of DNA content and immunofluorescence on single cells by flow cytometry provides information on the proliferative response of cellular sub-populations in mixed cell preparations. However, the presence of considerable numbers of dead (nonviable) cells impairs accurate flow cytometric data analysis, mainly, because dead cells can bind antibodies non-specifically and show alterations in their DNA staining profiles. We developed a rapid method for identification of dead cells by fluorescence in cell preparations that are stained simultaneously for two-color immunofluorescence and DNA content. Cells are stained with 7-aminoactinomycin D (7-AAD) for dead cell discrimination and with fluorescein-isothiocyanate (FITC) and phycoerythrin (PE)-labeled monoclonal antibodies (mAb) for cell surface immunofluorescence. Diffusion of 7-AAD from stained, dead cells into unstained, live cells after cell permeabilization is blocked by the addition of its non-fluorescent analogue actinomycin D (AD). DNA is stained with red-excitable TO-PRO-3 iodide (TP3) which has an emission spectrum that can be effectively separated from the emissions of FITC, PE, and 7-AAD. TP3 staining is performed in the presence of ribonuclease A (RNAse) in phosphate-citrate buffer containing saponin (PCBS) at low pH. FITC fluorescence is sensitive to acid pH; therefore, PCBS is replaced after DNA staining with 1x PBS at pH 7.2 containing saponin to permit accurate detection of FITC immunofluorescence on the flow cytometer. We apply this method to the analysis of differential proliferation of lymphocyte subsets in cultures of human peripheral blood mononuclear cells (PBMC) with low viability.

Human immunodeficiency virus type 1-induced hematopoietic inhibition is independent of productive infection of progenitor cells in vivo

Human immunodeficiency virus (HIV)-infected individuals exhibit a variety of hematopoietic dysfunctions. The SCID-hu mouse (severe combined immunodeficient mouse transplanted with human fetal thymus and liver tissues) can be used to model the loss of human hematopoietic precursor cell function following HIV infection and has a distinct advantage in that data can be obtained in the absence of confounding factors often seen in infected humans. In this study, we establish that HIV type 1 (HIV-1) bearing a reporter gene inserted into the viral vpr gene is highly aggressive in depleting human myeloid and erythroid colony-forming precursor activity in vivo. Human CD34(+) progenitor cells can be efficiently recovered from infected implants yet do not express the viral reporter gene, despite severe functional defects. Our results indicate that HIV-1 infection alone leads to hematopoietic inhibition in vivo; however, this effect is due to indirect mechanisms rather than to direct infection of CD34(+) cells in vivo.

Reconstitution of human thymic implants is limited by human immunodeficiency virus breakthrough during antiretroviral therapy

Human immunodeficiency virus type 1 (HIV-1)-infected SCID-hu thymic implants depleted of CD4(+) cells can support renewed thymopoiesis derived from both endogenous and exogenous T-cell progenitors after combination antiretroviral therapy. However, successful production of new thymocytes occurs transiently. Possible explanations for the temporary nature of this thymic reconstitution include cessation of the thymic stromal support function, exhaustion of T-cell progenitors, and viral resurgence. Distinguishing between these processes is important for the development of therapeutic strategies aimed at reconstituting the CD4(+) T-cell compartment in HIV-1 infection. Using an HIV-1 strain engineered to express the murine HSA heat-stable antigen surface marker, we explored the relationship between HIV-1 expression and CD4(+) cell resurgence kinetics in HIV-1-depleted SCID-hu implants following drug therapy. Antiviral therapy significantly suppressed HIV-1 expression in double-positive (DP) CD4/CD8 thymocytes, and the eventual secondary decline of DP thymocytes following therapy was associated with renewed viral expression in this cell subset. Thymocytes derived from exogenous T-cell progenitors induced to differentiate in HIV-1-depleted, drug-treated thymic implants also became infected. These results indicate that in this model, suppression of viral replication occurs transiently and that, in spite of drug therapy, virus resurgence contributes to the transient nature of the renewed thymic function.

Generation of functional thymocytes in the human adult

Reconstituting the immune response will be critical for the survival of HIV-infected individuals once viral load is brought under control. While the adult thymus was previously thought to be relatively inactive, new data suggest it may play a role in T cell reconstitution. We examined thymopoiesis in adults up to 56 years of age and found active T cell receptor (TCR) rearrangement, generating a diverse TCR Vbeta repertoire. The resulting thymocytes are functional and are capable of responding to costimulatory signals. These data demonstrate that the adult thymus remains active late in life and contributes functional T cells to the peripheral lymphoid pool.

cAMP up-regulates cell surface expression of lymphocyte CXCR4: implications for chemotaxis and HIV-1 infection

The chemokine receptor CXCR4 mediates lymphocyte chemotaxis in response to stromal cell-derived factor-1 (SDF-1) and functions as a coreceptor for T cell-tropic strains of HIV-1. We examined the role of the cAMP-protein kinase A (PKA) signaling pathway in regulating expression of CXCR4. In response to exogenous dibutyryl cAMP or cAMP-inducing ligands, cell surface expression of CXCR4 was increased by up to 10-fold on CD3/CD28-stimulated PBMC and by up to sixfold on unstimulated PBMC. cAMP did not alter receptor mRNA levels or affect the size of the total CXCR4 pool. However, cAMP did significantly reduce CXCR4 internalization rates and thereby increased the fraction of the total CXCR4 pool expressed on the cell surface. cAMP-induced increases in CXCR4 expression counteracted SDF-1-induced receptor internalization and enhanced both chemotactic response to SDF-1 and cellular vulnerability to HIV-1 infection. Thus, altered chemokine receptor expression may provide one mechanism by which cAMP-inducing ligands influence lymphocyte localization and HIV pathogenesis.

Changes in thymic function with age and during the treatment of HIV infection

The thymus represents the major site of the production and generation of T cells expressing alphabeta-type T-cell antigen receptors. Age-related involution may affect the ability of the thymus to reconstitute T cells expressing CD4 cell-surface antigens that are lost during HIV infection; this effect has been seen after chemotherapy and bone-marrow transplantation. Adult HIV-infected patients treated with highly active antiretroviral therapy (HAART) show a progressive increase in their number of naive CD4-positive T cells. These cells could arise through expansion of existing naive T cells in the periphery or through thymic production of new naive T cells. Here we quantify thymic output by measuring the excisional DNA products of TCR-gene rearrangement. We find that, although thymic function declines with age, substantial output is maintained into late adulthood. HIV infection leads to a decrease in thymic function that can be measured in the peripheral blood and lymphoid tissues. In adults treated with HAART, there is a rapid and sustained increase in thymic output in most subjects. These results indicate that the adult thymus can contribute to immune reconstitution following HAART.

In vivo pathogenesis of a human immunodeficiency virus type 1 reporter virus

Our understanding of human immunodeficiency virus type 1 (HIV-1)-induced pathogenesis is hampered by the inability to detect HIV-1 gene expression in infected viable cells. In this report, we describe two HIV-1 reporter constructs that are replication competent and cytopathic in vivo. These constructs contain DNA regions of two different lengths that bear the cDNA for the murine heat-stable antigen in the vpr region of a CXCR4-tropic virus. We used the SCID-hu mouse model and these reporter viruses to perform detailed kinetic studies of HIV-1 infection of human thymocytes in vivo. We document that the CD4(+)/CD8(+) thymocytes are the first to express virus and that this subset demonstrates the most rapid and extensive HIV-1-induced cell depletion. Following depletion of this subset, subsequent virus expression occurs predominantly in phenotypically CD4(-) cells, suggesting that CD4 down-regulation occurs in HIV-1-infected thymocytes in vivo. These results demonstrate the utility of these HIV-1 reporter constructs to monitor HIV pathogenesis in vitro and in vivo.

Effects of megakaryocyte growth and development factor on survival and retroviral transduction of T lymphoid progenitor cells

Murine retroviral vectors have the potential to mediate stable gene transfer into hematopoietic progenitor cells. A known drawback to the use of these vectors is that transduction can only take place in cells actively progressing through the cell cycle. Thrombopoietin, the c-mpl ligand, is known to support division of hematopoietic precursors of primitive origin. Polyethylene glycol (PEG)-conjugated recombinant human megakaryocyte growth and development factor (MGDF) is a polypeptide related to thrombopoietin that stimulates megakaryocyte production. To investigate whether MGDF would also induce stem cell division and support retroviral transduction of CD34+ cells, we compared the effects of MGDF, stem cell factor (SCF), interleukin-3 (IL-3), and IL-6, alone or in combination, using amphotropic and vesicular stomatitis virus (VSV-G) pseudotyped murine retroviral vectors. Similar transduction efficiency was observed when CD34+ cells were transduced in the presence of SCF and MGDF as compared to SCF, IL-3, and IL-6. Using the SCID-hu mouse model of thymopoiesis, we investigated whether CD34+ cells transduced in the presence of these cytokines could reconstitute irradiated thymic implants, and whether vector sequences were present in mature thymocytes. At early timepoints, no significant differences were observed on engraftment of donor progenitors incubated with each cytokine combination. However, a significant difference in the percentage of donor derived CD4+/CD8+ immature thymocytes was observed 9 weeks after implantation of CD34+ cells exposed to the combination of SCF and MGDF as compared to SCF, IL-3, and IL-6 (p = 0.04), indicating that MGDF/SCF better supported the survival of thymocyte precursor cells. Approximately 4% of thymocytes in both cytokine groups harbored vector sequences. These studies provide evidence that MGDF and SCF in combination can mediate transduction of hematopoietic progenitors capable of contributing to long-term thymopoiesis. These results may have important applications for the implementation of gene therapy strategies in disorders affecting the T lymphoid system.

High viral burden and rapid CD4+ cell depletion in human immunodeficiency virus type 1-infected SCID-hu mice suggest direct viral killing of thymocytes in vivo

The mechanism of CD4+ cell loss in lymphoid organs is unknown. In this study, human immunodeficiency virus (HIV) infection of human fetal thymus/liver implants in severe combined immunodeficient mice was used to investigate the mechanism of HIV-induced depletion of CD4-bearing cells in vivo. The implants were assessed for depletion of CD4+ thymocytes, apoptosis, and viral burden. We detected two phases of CD4 cell depletion, an initial rapid phase and a more gradual later phase. Compared to mock-infected implants, HIV-infected implants did not demonstrate detectable increases in the levels of apoptosis while severe depletion of CD4-bearing cells was ongoing. During peak loss of CD4+ cells, high viral burden was observed, suggesting that loss of CD4+ cells in this in vivo system is due to direct killing of infected thymocytes. Increased levels of apoptosis were observed during the later phase of thymocyte depletion; however, these apoptotic cells lacked CD4. This finding suggests that a second indirect mechanism may be responsible for the destruction of CD4- CD8+ thymocytes in vivo. Taken together, these results suggest that CD4+ and CD4- cells may die by different mechanism(s).

Transient renewal of thymopoiesis in HIV-infected human thymic implants following antiviral therapy

Stem cell gene therapy strategies for AIDS require that differentiation-inducing stromal elements of HIV-infected individuals remain functionally intact to support the maturation of exogenous progenitor cells into mature CD4+ cells. To investigate the feasibility of stem cell reconstitution strategies in AIDS, we used the SCID-hu mouse to examine the ability of HIV-infected CD4+ cell-depleted human thymic implants to support renewed thymopoiesis. Here we report that following treatment of these implants with antiretroviral drugs, new thymopoiesis is initiated. This suggests that antiviral therapies might allow de novo production of T lymphocytes and provides support for the concept of therapeutic strategies aimed at reconstitution of the peripheral CD4+ T-cell compartment.

Loss of T cell receptor Vbeta repertoires in HIV type 1-infected SCID-hu mice

Late-stage HIV-1 disease in humans has been associated with perturbations of the T cell receptor (TCR) Vbeta repertoire. It is not known if the observed loss of certain Vbeta families is attributable directly to HIV-1 infection or whether this is a consequence of multiple opportunistic infections. Putative HIV-1-associated superantigens have been postulated to be the cause of the perturbed TCR Vbeta repertoire and the subsequent CD4+ T cell depletion in HIV-1-infected humans. In this study, we examined the human TCR Vbeta repertoire in SCID-hu mice, housed in a pathogen-free environment and infected with a molecularly cloned virus strain, to ascertain directly the effect of HIV-1 on the human TCR Vbeta repertoire in the absence of other infectious agents. We demonstrate that mock-infected human thymus/liver (Thy/Liv) implants in SCID-hu mice have complete TCR Vbeta repertoires, reflective of a normal human thymus. However, HIV-1-infected implants in SCID-hu mice had depleted TCR Vbeta repertoires, corresponding with thymocyte depletion. These results indicate that HIV-1-specific mechanisms are the cause of the TCR Vbeta repertoire depletion in infected implants. However, these thymocyte depletions were not restricted to specific TCR Vbeta subsets. These results are not consistent with the hypothesis that HIV-1 acts as a superantigen in vivo. The disruption of the TCR Vbeta repertoire in the human Thy/Liv implants of the SCID-hu mice suggests that HIV-1 infection may be influencing T cell development in the thymus, contributing to both the overall CD4+ T cell depletion in AIDS and limited TCR repertoire diversity.

The SCID-hu mouse: an in-vivo model for HIV-1 pathogenesis and stem cell gene therapy for AIDS

Animal models are critical to the investigation of human immunodeficiency virus type 1 (HIV-1) pathogenesis. However, normal animal models are either uninfectable with HIV-1, or if infected, do not display HIV-1 induced pathology. Here, we describe how the severe combined immunodeficient mouse (SCID), implanted with human fetal thymus and liver, has been used to model HIV-1 pathogenesis and anti-retroviral gene therapy. Unable to reject the human tissue, these chimeric mice provide the investigator with a human hematolymphoid organ which, following infection by HIV-1, may more closely mimic the situation seen in humans than standard in-vitro culture systems.

Differential tropism of HIV-1 isolates for distinct thymocyte subsets in vitro

OBJECTIVE

Understanding the interaction between HIV and developing thymocytes is crucial in determining how HIV infection perturbs the immune system. We determined which thymocyte subsets can harbor and express HIV.

DESIGN

HIV expression in mature and immature thymocytes obtained from surgical specimens from non-infected children was determined after in vitro infection with the syncytium-inducing, cytopathic NL4-3 and the non-syncytium-inducing, relatively noncytopathic JR-CSF isolates.

METHODS

Intracellular staining for the HIV p24gag antigen was combined with cell surface phenotyping to determine thymocyte subsets expressing HIV. Infection was quantitated by polymerase chain reaction on sorted subsets.

RESULTS

NL4-3 replicated faster and to higher titers and caused a more severe decrease of all CD4-bearing thymocytes than did JR-CSF. In addition, both immature CD1+ and mature CD1-thymocytes expressed NL4-3, whereas only mature CD1-cells expressed JR-CSF. The tropism of NL4-3 for these immature cells suggests a mechanism for a more profound impact on T-cell maturation than that seen with JR-CSF. We also found that thymocytes lacking cell surface CD4 (CD4-CD8- and CD4-CD8+ subsets) expressed virus with either isolate late in infection, when viral levels were high. The CD4-CD8- cells expressing HIV were mature CD3bright T-cell receptor (TCR) alpha/beta bright cells.

CONCLUSIONS

These results show that NL4-3 can be expressed by thymocytes at immature and mature stages of differentiation and cause severe loss of CD4+ cells. Thus, tropism of a virus for immature cells can affect the capability of the thymus to produce new T lymphocytes leading to a greater impact on development and functions of the immune system. It is proposed that this in vitro model can be used to study pathogenic mechanisms in the thymus.

Intestinal intraepithelial lymphocytes respond to systemic lymphocytic choriomeningitis virus infection

Intestinal intraepithelial lymphocytes (IEL) are a population of cells consisting mostly of CD8+ T lymphocytes. Although their function is unknown, because of their location within the epithelium it has been postulated that IEL may be involved in defense against infection of the gut mucosa by pathogens including viruses. To address this issue, we have examined IEL populations from BALB/c mice systemically infected with lymphocytic choriomeningitis virus (LCMV). Viral infection induced a virus-specific cytotoxic response by IEL at 8 days postinfection. This virus-specific cytotoxic T lymphocyte (CTL) response was MHC class I restricted, and as is true for splenic T cells, recognition of viral antigen occurred predominantly in the context of the Ld molecule. The effector cells could be depleted by treatment with anti-CD8 antibody plus complement. In vivo treatment of mice with anti-alpha beta T cell receptor (TCR) antibody during the course of viral infection abrogated the response, suggesting that the virus-specific CTL were cells that express the alpha beta rather than gamma delta TCR. Consistent with this, no virus-specific IEL response could be detected in athymic mice, which have TCR gamma delta+ but not TCR alpha beta+ IEL. LCMV antigen could not be detected in the epithelium of the intestine, suggesting that viral antigen may have been encountered elsewhere. These data demonstrate for the first time a specific response by IEL to virus given by a non-oral route, and they suggest that thymus-derived alpha beta T cells can migrate to the intestinal epithelium following activation, where they may play a role in the response to virus and perhaps other infections.

In vivo pathogenic properties of two clonal human immunodeficiency virus type 1 isolates

We have investigated the in vivo pathogenic properties of two molecularly cloned strains of human immunodeficiency virus type 1 (HIV-1), HIV-1NL4-3 and HIV-1JR-CSF, in human fetal thymus/liver implants in severe combined immunodeficient mice. Studies comparing their in vivo replication kinetics and abilities to induce CD4+ thymocyte depletion were performed. HIV-1NL4-3 replicated in vivo with faster kinetics and induced greater levels of CD4+ thymocyte depletion than did HIV-1JR-CSF. These results demonstrate that different viral isolates have different pathogenic properties in this system. In the SCID-hu model, this pathogenesis most likely occurs in the absence of an immune response. Therefore, we investigated whether the absence of immune selection resulted in extensive genetic variation and the generation of viral quasispecies. To this end, DNA corresponding to the fourth variable domain region of the viral envelope gp120 protein recovered from biopsy samples at 6 weeks postinfection was sequenced. Little genetic variation was noted in either HIV-1JR-CSF- or HIV-1NL4-3-infected implants. The mutation levels demonstrated in both viral strains were more reflective of the acute rather than the chronic phase of HIV-1 infection in humans. These results suggest that the SCID-hu mouse model can be used to study the in vivo pathogenicity of different HIV-1 isolates in the absence of host immune selective pressures.

Cytotoxic T-cell memory without antigen

Memory is a hallmark of the immune system and ever since its recognition there has been considerable interest in understanding how immunity is maintained. The current model is that long-term memory is dependent on persistent antigenic stimulation. We report here results that challenge this view and provide evidence that antigen is not essential for the maintenance of CD8+ T-cell memory. We show that memory CD8+ cytotoxic T lymphocytes persist indefinitely in the absence of priming antigen, retain the memory phenotype (CD44hi), and provide protection against virus challenge. These findings suggest a re-evaluation of our current thinking on mechanisms involved in maintaining immunity and have implications towards designing effective vaccination strategies.

Requirement of human immunodeficiency virus type 1 nef for in vivo replication and pathogenicity

The role of human immunodeficiency virus type 1 (HIV-1) accessory genes in pathogenesis has remained unclear because of the lack of a suitable in vivo model. The most controversial of these genes is nef. We investigated the requirement for Nef for in vivo replication and pathogenicity of two isolates of HIV-1 (HIV-1JR-CSF and HIV-1NL4-3) in human fetal thymus and liver implants in severe combined immunodeficient mice. HIV-1JR-CSF and HIV-1NL4-3 differ in their in vitro phenotypes in that HIV-1JR-CSF does not induce syncytia and is relatively noncytopathic, while HIV-1NL4-3 is highly cytopathic and readily induces syncytia. The nef mutants of both isolates grew with kinetics similar to those of parental virus strains in stimulated peripheral blood lymphocytes but demonstrated attenuated growth properties in vivo. HIV-1NL4-3 induced severe depletion of human thymocytes within 6 weeks of infection, whereas its nef mutant did not. Thus, HIV-1 Nef is required for efficient in vivo viral replication and pathogenicity.

Viral infection of the thymus

We have examined infection of the thymus during congenitally acquired chronic lymphocytic choriomeningitis virus (LCMV) infection of mice, a classic model of antigen-specific T-cell tolerance. Our results show that (i) infection starts at the fetal stage and is maintained throughout adulthood, and (ii) this chronic infection of the thymus can be eliminated by transfer of virus-specific cytotoxic T lymphocytes (CTL) that infiltrate the thymus and clear all viral products from both medullary and cortical regions. Elimination of virus from the thymus results in abrogation of tolerance. During the fetal stage, the predominant cell type infected is the earliest precursor of T cells with a surface phenotype of Thy1+ CD4- CD8- J11d+. In the adult thymus, infection is confined primarily to the cortisone-resistant thymocytes present in the medullary region. The infected cells are CD4+ and J11d+. The presence of J11d, a marker usually associated with immature thymocytes, on infected single positive CD4+ "mature" thymocytes is intriguing and suggests that infection by this noncytolytic virus may affect development of T cells. There is minimal infection of the CD8+ medullary thymocytes or of the double positive (CD4+ CD8+) cells present in the cortex. Infection within the cortex is confined to the stromal cells. Interestingly, there is infection of the double negative (CD4- CD8-) thymocytes in the adult thymus, showing that even during adulthood the newly developing T cells are susceptible to infection by LCMV. Virus can be eliminated from the thymuses of these carrier mice by adoptive transfer of medullary region first and then from the thymic cortex. This result clearly shows the need to reevaluate the widely held notion that mature T cells are unable to reenter the thymus. In fact, in our experiments the donor T cells made up to 20 to 30% of the total cells in the thymus at 5 to 7 days after the transfer. The number of donor T cells declined as virus was eliminated from the thymus, and at 1 month posttransfer, the donor T cells were hardly detectable. The results of this study examining the dynamics of viral infection and clearance from the thymus, the primary site of T-cell development, have implications for understanding tolerance induction in chronic viral infections.

Abrogation of tolerance to a chronic viral infection

This study documents failure of peripheral tolerance mechanisms in a chronic viral infection and shows that T cell tolerance to a viral Ag seen as self from fetal life can be broken despite the presence of this Ag in extrathymic tissues. Congenital infection of mice with lymphocytic choriomeningitis virus (LCMV) results in T cell tolerance to the virus. Such mice become carriers for life harboring virus in many tissues including the thymus and exhibit no LCMV-specific CTL responses. Our previous studies have documented the curing of this congenitally acquired chronic infection after adoptive transfer of CD8+ T cells from LCMV-immune mice and the presence of host-derived, LCMV-specific CTL in these "cured" carriers. In this study we have examined the mechanism by which these carriers acquired T cell competence and show that these CTL differentiated from the bone marrow after elimination of viral Ag from the thymus. These results demonstrate that even when a chronic infection has been established in utero, the adult thymus retains the ability to restore immunocompetence to the host and to provide protection against reinfection. Surprisingly, these LCMV specific CTL were acquired at a time when infectious virus and intracellular viral Ag, although cleared from the thymus, were readily detectable in organs such as the kidney, testes, and brain. In fact, active viral replication in peripheral tissues was ongoing when these mice acquired new virus-specific T cells. These results show that clearance of virus form the thymus was sufficient to abrogate tolerance to a congenitally acquired chronic infection and that Ag in peripheral tissues did not tolerize newly developing T cells. These findings suggest that mechanisms that operate on immature cells within the thymus to silence self-reactive T cells are effective in induction of tolerance to viruses, but mechanisms of tolerizing mature T cells are likely to breakdown. This has implications for virus-induced autoimmunity and for treatment of chronic infections.

Abrogation of tolerance to a chronic viral infection

This study documents failure of peripheral tolerance mechanisms in a chronic viral infection and shows that T cell tolerance to a viral Ag seen as self from fetal life can be broken despite the presence of this Ag in extrathymic tissues. Congenital infection of mice with lymphocytic choriomeningitis virus (LCMV) results in T cell tolerance to the virus. Such mice become carriers for life harboring virus in many tissues including the thymus and exhibit no LCMV-specific CTL responses. Our previous studies have documented the curing of this congenitally acquired chronic infection after adoptive transfer of CD8+ T cells from LCMV-immune mice and the presence of host-derived, LCMV-specific CTL in these "cured" carriers. In this study we have examined the mechanism by which these carriers acquired T cell competence and show that these CTL differentiated from the bone marrow after elimination of viral Ag from the thymus. These results demonstrate that even when a chronic infection has been established in utero, the adult thymus retains the ability to restore immunocompetence to the host and to provide protection against reinfection. Surprisingly, these LCMV specific CTL were acquired at a time when infectious virus and intracellular viral Ag, although cleared from the thymus, were readily detectable in organs such as the kidney, testes, and brain. In fact, active viral replication in peripheral tissues was ongoing when these mice acquired new virus-specific T cells. These results show that clearance of virus form the thymus was sufficient to abrogate tolerance to a congenitally acquired chronic infection and that Ag in peripheral tissues did not tolerize newly developing T cells. These findings suggest that mechanisms that operate on immature cells within the thymus to silence self-reactive T cells are effective in induction of tolerance to viruses, but mechanisms of tolerizing mature T cells are likely to breakdown. This has implications for virus-induced autoimmunity and for treatment of chronic infections.

T cell memory. Long-term persistence of virus-specific cytotoxic T cells

This study documents that virus-specific CTL can persist indefinitely in vivo. This was accomplished by transferring Thy-1.1 T cells into Thy-1.2 recipient mice to specifically identify the donor T cell population and to characterize its antigenic specificity and function by using a virus-specific CTL assay. Thy-1.1+ T cells from mice previously immunized with lymphocytic choriomeningitis virus (LCMV) were transferred into Thy-1.2 mice persistently infected with LCMV. The transferred LCMV-specific CTL (Thy-1.1+ CD8+) eliminate virus from the chronically infected carriers and persist in the recipient mice in small numbers, comprising only a minor fraction of the total T cells. Upon re-exposure to virus, these long-lived "resting" CD8+ T cells proliferate in vivo to become the predominant cell population. These donor CD8+ T cells can be recovered up to a year post-transfer and still retain antigenic specificity and biological function. They kill LCMV infected H-2-matched cells in vitro and can eliminate virus upon transfer into a second infected host. In addition, these long-lived CD8+ T cells appear not to be dependent on help from CD4+ T cells, since depletion of CD4+ T cells has minimal or no effect on their biological properties (proliferation, CTL response, viral clearance). These donor CTL also exhibit an immunodominance over the host-derived LCMV-specific CTL response. When both host and donor T cells are present, the donor CTL response is dominant over the potential CTL response of the cured carrier host. Taken together, these results suggest that virus-specific CTL can persist for the life span of the host as memory cells.

T-cell tolerance: exposure to virus in utero does not cause a permanent deletion of specific T cells

This study documents the curing of a congenitally acquired chronic viral infection and the acquisition of T-cell competence by a previously tolerant host. Infection of mice with lymphocytic choriomeningitis virus (LCMV) is a classic model of viral persistence and antigen-specific T-cell unresponsiveness. Mice infected at birth or in utero become lifelong carriers with no detectable virus-specific cytotoxic T lymphocyte (CTL) responses. This chronic infection can be eliminated by adoptive transfer of Lyt-2+ T cells from LCMV-immune mice. To determine whether these cured carriers were capable of generating their own LCMV-specific CTL response, mice congenic at the Thy-1 locus (Thy-1.1 and Thy-1.2) were used in the adoptive transfer experiments. Host-derived T-cell responses were checked after treating the cured carriers with a monoclonal antibody to deplete the immune donor T cells. Such cured carrier mice were able to generate a host-derived virus-specific CTL response and resisted a second LCMV challenge in the absence of any donor T cells. In addition, bone marrow cells from these cured carriers could functionally reconstitute irradiated mice. Thus this report demonstrates the acquisition of LCMV-specific T-cell competence by previously unresponsive carrier mice infected in utero. These results show that exposure to a virus even during embryonic life does not cause a permanent deletion of specific T cells. These findings are of significance to the understanding of tolerance mechanisms and have implications for the treatment of chronic viral infections.

Immune therapy of a persistent and disseminated viral infection

The mechanism of viral clearance was studied by using the mouse model of chronic infection with lymphocytic choriomeningitis virus. Distinct patterns of viral clearance and histopathology were observed in different organs after adoptive immune therapy of persistently infected (carrier) mice. Clearance from the liver occurred within 30 days and was accompanied by extensive mononuclear cell infiltrates and necrosis of hepatocytes. Infectious virus and viral antigen were eliminated concurrently. This pattern of viral clearance was also seen in most other tissues (i.e., lung, spleen, lymph nodes, pancreas, etc.). In contrast, a different pattern of clearance was observed in the brain. Infectious virus was eliminated within 30 days, but viral antigen persisted in the central nervous systems of treated carrier mice for up to 90 days. The urinary system was the most resistant to immune therapy. Elimination of infectious virus and viral antigen from the kidney took greater than 200 days and even then was not complete; trace levels of infectious virus were still present in the kidneys of some treated carrier mice. After immune therapy, viral antigen in the kidney was located within renal tubules that costained for intracellular mouse immunoglobulin G. This unusual staining pattern, coupled with the observation of large numbers of plasma cells within the kidney, suggests that virus-immunoglobulin G complexes found in the tubules may represent in situ immune complex formation as opposed to deposition of circulating immune complexes. In conclusion, these results suggest that the site (organ) of viral persistence is an important consideration in developing treatment strategies for controlling chronic viral infections.

Effective clearance of a persistent viral infection requires cooperation between virus-specific Lyt2+ T cells and nonspecific bone marrow-derived cells

The lifelong chronic lymphocytic choriomeningitis virus (LCMV) infection established in neonatally or congenitally infected mice can be eliminated by adoptive transfer of lymphoid cells from LCMV-immune mice. In this study, we have identified the effector cells mediating the clearance of persistent and disseminated LCMV infection. Using mice that are recombinant in the H-2 region and by selective depletion of lymphocyte subpopulations, we show that viral clearance was mediated by LCMV-specific Lyt2+ L3T4- T cells that are restricted to the class I genes of the major histocompatibility complex. In addition, our results show a requirement for host-derived bone marrow cells for the effective elimination of virus from the liver. These studies emphasize the importance of virus-specific T cells and an intact bone marrow function in viral clearance.

Driving offenders and the defensive driving course--an archival study

Two hundred and seventy-five drivers who had been required by court order to attend a Defensive Driving Course (DDC) were compared on six posttreatment driving measures obtained from archival data with 275 drivers who also had had a court appearance and standard treatment. The DDC group showed greater reductions in serious and accident-promoting convictions but no greater reduction in accidents when compared with the standard treatment comparison group.

The "risky-shift" phenomenon with a heterogeneous sample

12 choice dilemma items were administered to a sample of New Zealand Ss of wide age and occupational ranges. Groups in the discussion condition manifested the familiar “risky-shift” phenomenon.