A Quantitative Comparison of Anti-HIV Gene Therapy Delivered to Hematopoietic Stem Cells versus CD4+ T Cells

<div><p>Gene therapy represents an alternative and promising anti-HIV modality to highly active antiretroviral therapy. It involves the introduction of a protective gene into a cell, thereby conferring protection against HIV. While clinical trials to date have delivered gene therapy to CD4+T cells or to CD34+ hematopoietic stem cells (HSC), the relative benefits of each of these two cellular targets have not been conclusively determined. In the present analysis, we investigated the relative merits of delivering a dual construct (CCR5 entry inhibitor + C46 fusion inhibitor) to either CD4+T cells or to CD34+ HSC. Using mathematical modelling, we determined the impact of each scenario in terms of total CD4+T cell counts over a 10 year period, and also in terms of inhibition of CCR5 and CXCR4 tropic virus. Our modelling determined that therapy delivery to CD34+ HSC generally resulted in better outcomes than delivery to CD4+T cells. An early one-off therapy delivery to CD34+ HSC, assuming that 20% of CD34+ HSC in the bone marrow were gene-modified (G+), resulted in total CD4+T cell counts ≥180 cells/ µL in peripheral blood after 10 years. If the uninfected G+ CD4+T cells (in addition to exhibiting lower likelihood of becoming productively infected) also exhibited reduced levels of bystander apoptosis (92.5% reduction) over non gene-modified (G-) CD4+T cells, then total CD4+T cell counts of ≥350 cells/ µL were observed after 10 years, even if initially only 10% of CD34+ HSC in the bone marrow received the protective gene. Taken together our results indicate that: 1.) therapy delivery to CD34+ HSC will result in better outcomes than delivery to CD4+T cells, and 2.) a greater impact of gene therapy will be observed if G+ CD4+T cells exhibit reduced levels of bystander apoptosis over G- CD4+T cells.</p></div

Repeated annual delivery of gene therapy to CD34+ HSC assuming that 20% of CD34+ HSC in the bone marrow receive the gene construct every year from year 1 (i.e. every year, starting from year 1, 20% of G- CD34+ HSC become G+ CD34+ HSC).

<p>The legend for this figure is the same as for <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1003681#pcbi-1003681-g005" target="_blank">Figure 5</a>.</p

Progression of untreated HIV infection over a 10-year period.

<p>Here year 0 denotes the end of primary HIV infection (PHI). Solid lines denote median values, dashed lines denote the 5^th and 95^th percentile ranges. Also shown is the AIDS threshold of 200 cells/ µL (solid horizontal black line); A) Total CD4+T cell count and B) R5 Viral Load for a single simulation of untreated infection with R5 virus only (i.e. assuming throughout the course of infection); C) Total CD4+T cell count, D) R5 Viral Load and E) ×4 Viral Load for Monte Carlo simulations (100 trials) of untreated infection assuming initial infection with R5 virus, but now including ×4 virus.</p

Repeated annual delivery of gene therapy to CD4+T cells assuming that 20% of CD4+T cells receive the gene construct every year from year 1 (i.e. every year, starting from year 1, 20% of G- CD4+T cells become G+ CD4+T cells).

<p>Therapy is first administered at year 1 and then annually thereafter. Shown are the simulation outcomes under the standard scenario (STD) and also under Assumption +A1 of reduced bystander apoptosis in G+ CD4+T cells (+A1); Solid lines denote median values, dashed lines denote 5^th and 95^th percentiles for outcomes when ×4 virus can develop. Also shown is the AIDS threshold of 200 cells/ µL (solid horizontal black line); A) Total CD4+T cell count, B) G+ CD4+T cell count and C) R5 Viral Load for a single simulation with R5 virus only (i.e. assuming throughout the course of infection); D) Total CD4+T cell count, E) G+ CD4+T cell count F) R5 Viral Load and G) ×4 Viral Load for Monte Carlo simulations assuming initial infection with R5 virus, but now including ×4 virus.</p

Differences between entries of Tables 4 and 2, when ×4 virus can develop.

<p>Differences in final total CD4+T cell counts (for each simulated case from <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1003681#pcbi-1003681-t001" target="_blank">Tables 1</a> and <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1003681#pcbi-1003681-t002" target="_blank">2</a>) between therapy delivery to CD4+T cells and therapy delivery to CD34+ HSC, with ×4 virus included in the simulations. Positive entries denote cases where therapy delivery to CD34+ HSC results in higher final total CD4+T cell counts than therapy delivery to CD4+T cells.</p

Differences between entries of Tables 3 and 1 (delivery to CD34 minus delivery to CD4), in the absence of ×4 virus.

<p>Differences in final total CD4+T cell counts (for each simulated case from <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1003681#pcbi-1003681-t001" target="_blank">Tables 1</a> and <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1003681#pcbi-1003681-t002" target="_blank">2</a>) between therapy delivery to CD4+T cells and therapy delivery to CD34+ HSC, assuming no ×4 virus in the simulations. Positive entries denote cases where therapy delivery to CD34+ HSC results in higher final total CD4+T cell counts than therapy delivery to CD4+T cells.</p

Total CD4+T cell counts in PB (cells/ µL) 10 years after commencement of therapy assuming no ×4 virus in these simulations when therapy is delivered to CD34+ HSC cells – medians (5%, 95%) from sensitivity analyses.

<p>Final total CD4+T cell counts in PB (cells/ µL) 10 years after commencement of therapy when therapy is delivered to CD34+ HSC cells, assuming no ×4 virus in these simulations (i.e. for all times ). Descriptions as for <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1003681#pcbi-1003681-t001" target="_blank">Table 1</a>.</p

Total CD4+T cell counts in PB (cells/ µL) 10 years after commencement of therapy when therapy is delivered to CD34+ HSC, and ×4 virus can develop.

<p>Mean total CD4+T cell counts in PB (cells/ µL) 10 years after commencement of therapy when therapy is delivered to CD34+ HSC cells, with ×4 virus included in the simulations. Descriptions as for <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1003681#pcbi-1003681-t002" target="_blank">Table 2</a>.</p

Compartment model of cellular and of viral dynamics.

<p>Here , and denote compartments of resting naive, activated and resting memory CD4+T cells respectively, with respectively denoting non gene-modified () or gene-modified () CD4+T cells. G+ CD4+T cells are assumed to contain a dual anti-HIV gene construct (CCR5 entry inhibitor + C46 fusion inhibitor, see <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1003681#s2" target="_blank">Methods</a>). The variables and denote compartments of productively infected CD4+T cells with R5 and ×4 virus respectively. and respectively denote compartments of R5 and ×4 virions.</p

Severe Painful Vaso-Occlusive Crises and Mortality in a Contemporary Adult Sickle Cell Anemia Cohort Study

<div><p>Background</p><p>Frequent painful vaso-occlusive crises (VOCs) were associated with mortality in the Cooperative Study of Sickle Cell Disease (CSSCD) over twenty years ago. Modern therapies for sickle cell anemia (SCA) like hydroxyurea are believed to have improved overall patient survival. The current study sought to determine the relevance of the association between more frequent VOCs and death and its relative impact upon overall mortality compared to other known risk factors in a contemporary adult SCA cohort.</p> <p>Methods</p><p>Two hundred sixty four SCA adults were assigned into two groups based on patient reported outcomes for emergency department (ED) visits or hospitalizations for painful VOC treatment during the 12 months prior to evaluation.</p> <p>Results</p><p>Higher baseline hematocrit (p = 0.0008), ferritin (p = 0.005), and HDL cholesterol (p = 0.01) were independently associated with 1 or more painful VOCs requiring an ED visit or hospitalization for acute pain. During a median follow-up of 5 years, mortality was higher in the ED visit/hospitalization group (relative risk [RR] 2.68, 95% CI 1.1-6.5, p = 0.03). Higher tricuspid regurgitatant jet velocity (TRV) (RR 2.41, 95% CI 1.5-3.9, p < 0.0001), elevated ferritin (RR 4.00, 95% CI 1.8-9.0, p = 0.001) and lower glomerular filtration rate (RR=2.73, 95% CI 1.6-4.6, p < 0.0001) were also independent risk factors for mortality. </p> <p>Conclusions</p><p>Severe painful VOCs remain a marker for SCA disease severity and premature mortality in a modern cohort along with other known risk factors for death including high TRV, high ferritin and lower renal function. The number of patient reported pain crises requiring healthcare utilization is an easily obtained outcome that could help to identify high risk patients for disease modifying therapies.</p> <p>Trial Registration</p><p>ClinicalTrials.gov NCT00011648 <a href="http://clinicaltrials.gov/" target="_blank"><u>http://clinicaltrials.gov/</u></a></p> </div