Methodology and software to detect viral integration site hot-spots
Modern gene therapy methods have limited control over where a therapeutic viral vector inserts into the host genome. Vector integration can activate local gene expression, which can cause cancer if the vector inserts near an oncogene.
Viral integration hot-spots or `common insertion sites'(CIS) are scrutinized to evaluate and predict patient safety. CIS are typically defined by a minimum density of insertions (such as 2-4 within a 30-100kb region), which unfortunately depends on the total number of observed VIS.
This is problematic for comparing hot-spot distributions across data sets and patients, where the VIS numbers may vary.
Results:
We develop two new methods for defining hot-spots that are relatively independent of data set size. Both methods operate on distributions of VIS across consecutive 1Mb `bins'of the genome.
The first method `z-threshold'tallies the number of VIS per bin, converts these counts to z-scores, and applies a threshold to define high density bins. The second method `BCP'applies a Bayesian change-point model to the z-scores to define hot-spots.
The novel hot-spot methods are compared with a conventional CIS method using simulated data sets and data sets from five published human studies, including the X-linked ALD (adrenoleukodystrophy), CGD (chronic granulomatous disease) and SCID-X1 (X-linked severe combined immunodeficiency) trials. The BCP analysis of the human X-linked ALD data for two patients separately (774 and 1627 VIS) and combined (2401 VIS) resulted in 5-6 hot-spots covering 0.17-0.251% of the genome and containing 5.56-7.74% of the total VIS.
In comparison, the CIS analysis resulted in 12-110 hot-spots covering 0.018-0.246% of the genome and containing 5.81-22.7% of the VIS, corresponding to a greater number of hot-spots as the data set size increased. Our hot-spot methods enable one to evaluate the extent of VIS clustering, and formally compare data sets in terms of hot-spot overlap.
Finally, we show that the BCP hot-spots from the repopulating samples coincide with greater gene and CpG island density than the median genome density.
Conclusions:
The z-threshold and BCP methods are useful for comparing hot-spot patterns across data sets of disparate sizes. The methodology and software provided here should enable one to study hot-spot conservation across a variety of VIS data sets and evaluate vector safety for gene therapy trials.
Author: Angela PressonNamshin KimYan XiaofeiIrvin ChenSanggu Kim
Credits/Source: BMC Bioinformatics 2011, 12:367
Published on: 2011-09-14
Copyright by the authors listed above - made available via BioMedCentral (Open Access). Please
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