Cancer Transfer factors

Retroviruses require proliferative target cells to mediate effective gene transfer. Lentiviruses, the class of retrovirus that includes human immunodeficiency virus, are an exception. They can also integrate in nondividing cells. An additional obstacle for retroviruses is the high susceptibility of the virus particle to humoral factors that ablate their gene transfer capacity. Perhaps most important, retroviruses, even when used ex vivo, pose a low but real risk of cancer. 

C. R. Miller, D. J. Buchsbaum, P. N. Reynolds, J. T. Douglas, G. Y. Gillespie, M. S. Mayo, D. Raben, and D. T. Curiel, Differential susceptibility of primary and established human glioma cells to adenovirus infection targeting via the epidermal growth factor receptor achieves fiber receptor-independent gene transfer, Cancer Res. 58 5138 (1998). 

Particles can also be absorbed from the lungs but their size is a crucial factor. Those that are too big will be removed in the uppermost parts of the respiratory system, while those that are too small will not settle. However, the particles that are deposited in the air sacs may be absorbed into the blood, for example lead from car exhausts. Asbestos fibres that are absorbed into the cells of the lungs are not transferred into the blood, simply staying in situ. Hence they can eventually cause asbestosis and lung cancer. 

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