Decay characteristics of HIV-1- infected compartments during combination therapy

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1 Decay characteristics of HIV-1- infected compartments during combination therapy Perelson et al Kelsey Collins BIOL0380 September 28, 2009

2 SUMMARY Analyzed decay patterns of viral load of HIV- 1-infected patients after treatment with antiretroviral agents Created mathematical model to determine relative contributions of short-lived, longlived, and latently infected cells to the viral load over time

3 BIOLOGY OF HIV Primarily affects vital cells in the human immune system Helper T cells (CD4+, specifically) Macrophages Dendritic cells SEM of HIV-1 budding from cultured lymphocyte

4 BIOLOGY OF HIV Infection leads to low levels of CD4 + T cells through 3 main mechanisms: Direct viral killing of infected cells Increased rates of apoptosis in infected cells Killing of infected CD4 + T cells by CD8 cytotoxic lymphocytes When CD4 + T cell numbers drop below a critical level, cell-mediated immunity is lost & body becomes progressively more susceptible to opportunistic infections

5 HIV-1 More virulent strain Easily transmitted Cause of majority of HIV infections globally Ancestry traced to SIV (simian immunodeficiency virus)

6 PROCEDURE Subjects: 8 HIV-1 infected patients, naïve to antiretroviral agents Subjects given antiretroviral treatment (protease inhibitor, 2 reverse transcriptase inhibitors) Measured HIV-1 RNA concentration in plasma weekly for 1 st month, then every 2 weeks using branched DNA assay

7 OBSERVATIONS Each patient had similar pattern of viral decay: Phase 1: initial rapid exponential decline Phase 2: slower exponential decline By 8 weeks, plasma viraemia in all patients dropped below standard detection threshold of 500 copies/ml

8 HYPOTHESES Rapid decline of phase 1: decay of productively infected CD4 + T cells with short t 1/2 Slower decline of phase 2: secondary source(s) are main producers of virions 2 distinct phases in data from each patient suggest there is only 1 major secondary source of virions

9 QUESTION What types of cells constitute 'secondary sources' and what are their relative contributions to the production of virions during the second decay phase?

10 KINETIC MODEL (1) dt*/dt = kvt + al δt* (2) dl/dt = fkvt μ L L (3) dm*/dt = k M VM μ M M* (4) dv/dt = NδT* + pm* - cv

11 RATE OF CHANGE OF T* dt*/dt = kvt + al δt* T*: # of infected CD4 + T cells k: rate constant at which T* cells are generated from uninfected CD4 + T cells V: # of virions T: # of uninfected CD4 + T cells a: rate constant at which latently infected lymphocytes are converted to productively infected cells L: # of latently infected lymphocytes δ: rate constant at which T* cells are lost

12 RATE OF CHANGE OF L dl/dt = fkvt μ L L L: # of latently infected lymphocytes fk: rate constant at which latently infected T cells containing infectious provirus are generated V: # of virions T: # of uninfected CD4+ T cells μ L : total rate constant of loss for latently infected lymphocytes

13 RATE OF CHANGE OF M* dm*/dt = k M VM μ M M* M*: # of long-lived infected cells k M : rate constant at which uninfected M cells become M* cells V: # of virions μ M : rate at which M* cells are lost

14 RATE OF CHANGE OF V dv/dt = NδT* + pm* - cv V: # of virions N: burst size of a T* cell T*: # of infected CD4+ T cells p: average rate of virus production per M* cell M*: # of long-lived infected cells c: rate constant of virion clearance

15 VIRAL DECAY MODEL The level of plasma virus after drug therapy should decay as follows: V(t) = V o [Ae -δt + Be -μ Lt + Ce -μmt +(1 A B C)e -ct ] Assumptions: HIV-1 reverse transcriptase & protease are completely inhibited by antiretroviral regimen System at steady-state before treatment, with baseline viral load V o & CD4+ cell count T o

16 APPLICATION OF MODEL Used nonlinear least-squares regression to fit data with 2 models derived from V(t): Long-lived infected cell model Latently-infected cell model 2 models indistinguishable: need more data

17 PBMC INFECTIVITY ASSAYS Used limiting dilution to measure infectivity titre of HIV-1 in PBMC at each time point Infected CD4+ T cells Long-lived productively infected cells Latently infected cells activated in vitro

18 PARAMETER ESTIMATES Simultaneously fit plasma viraemia & PBMC data to equations for V(t) & I(t) to yield estimates of decay rate constants

19 FINDINGS Long-lived infected cells are the major contributor of virions to phase 2 of plasma viraemia decay long-dashed/short-dashed line: contribution of preexisting productively infected T cells and latently infected T cells as they are gradually activated dashed line: contribution of long-lived infected cells

20 IMPLICATIONS 1 st direct evidence for rapid decay of productively infected cells Known compartments of virus could be completely eradicated after years of treatment with 100%-inhibitory antiretroviral regimen Complete elimination of HIV-1 from infected person may require longer treatment period Need further study of latently infected cells that could not be experimentally activated

Homework 6 Solutions

Homework 6 Solutions Math 314, Fall 216 Problem 1 The HIV virus targets CD4+ T cells, sometimes called helper T cells During an infection, the total number T t) of helper T cells in the blood, the number