Among all types of viruses currently used in clinical trials, those based on the murine leukemia virus retroviral vectors are the most frequently used, because of its capability of stable gene integration to the chromosomes of target cells. However, retroviruses can transducer only actively dividing cells. With the relatively short half-life of retroviral particles, the probability of infectious retroviruses encountering target cells is very low because they move in a random Brownian motion. Even if they can get close to the target cells, there is the repulsion force generated from the interaction between negatively charged retrovirus envelope and cell membrane. To overcome these limitations, physicochemical approaches used to increase cell-virus contact such as addition of polycation, flow-through of virus-containing medium, spinoculation, and magnetic field have been studied and showed improved results. However, the aforementioned transduction studies were focused on anchorage-dependent cells and not easy for large-scale settings. In this study, GFP-encoding VSV-G pseudotyped retrovirus vector, which is less fragile than the un-modified retroviral vector, will be used to infect cytokine-dependent hematopoietic cell lines and primary CD34+ hematopoietic cells within ultrasonic standing wave fields generated by piezoelectric transducer and reflector. Various cytokine cocktails will be employed to stimulate the hematopoietic cells entering cell cycle and thus enhance the retroviral transduction. According to the primary acoustic radiation force and drag force, the suspended cells can be estimated to arrive at the pressure nodal planes on the 1 -2 second time scale. We speculate that the first arrived and agglomerated cells may play a role on nucleating collection of the 100 nm-sized retroviruses at the nodal planes. Several design and operating approaches are proposed to decrease the undesired acoustic and thermal streaming which might prevent the aggregation of particulates with diameter around 100 nanometer such as retroviruses. The significance of the proposed research is the engineering approach (i.e., ultrasonic standing waves fields) could be harnessed to enhance the retroviral gene delivery efficiency to hematopoietic stem/progenitor cells, which are not easy to be retrovirally transduced with current medical approaches. The success of this proposed study will provide an innovative method to the field of gene therapy.
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