Interference between effector RNAs expressed from conventional dual-function anti-HIV retroviral vectors can be circumvented using dual-effector-cassette retroviral vectors

Additive and antagonist effects of therapeutic gene combinations for suppression of HIV-1 infection

A previously described Moloney-based vector expressing a double copy anti-tat antisense tRNA (DC-tRNA-AT) (Biasolo et al., 1996. J. Virol. 70, 2154-2161) was modified to increase the copy number of the antisense molecule and to target the intra-cytoplasmic localization of the HIV genome. To this end, an anti-U5 hammerhead ribozyme, engineered as a hybrid small adenoviral VAI RNA (VAIalpha), was inserted into the vector as a single molecule or in combination with the double copy anti-tat sequence. The retroviral vector expressing only VAIalpha (DC-VAIalpha) inhibited HIV-1 replication to an extent comparable to that of DC-tRNA-AT. A more effective inhibition was produced by the vector expressing multiple copies of the anti-tat antisense (DC-6tRNA-AT). This higher effectiveness correlated with anti-tat stochiometry, i.e. with the absolute number of therapeutic molecules being produced on a per cell basis at the steady state. Surprisingly, when the tRNA-AT and VAIalpha genes were combined in the same vector (DC-AT-VAIalpha), an enhancement of viral replication was noticed. This study indicates that it is possible to potentiate the antiviral activity of a retroviral vector by increasing the steady-state level of the therapeutic molecule. Results also show that the combined expression of two singularly active therapeutic RNAs can have antagonistic rather than synergistic effects.

Assessment of transduction rates of porcine bone marrow

Although drug resistance is commonly used as an indicator of gene transfer in various cellular contexts, the assessment of drug resistance is often imprecise and over-estimated. To measure accurately transduction efficiencies of the retroviral-mediated transfer of genes encoding the neomycine phosphotransferase (Neo(r)) and porcine major histocompatibility (MHC) class II in pig bone marrow cells (BMC), the fraction of targeted progenitors was evaluated by both colony-forming unit granulocytes/macrophages assays (G418r CFU-GM) and by PCR analysis of the transgenes (Tg). Transduced and untransduced BMC were selected at different concentrations of G418 and revealed high individual variability of drug sensitivity. Comparison of the results obtained by estimating the CFU frequency and the PCR assays on drug-resistant colonies demonstrated a marked overestimation of BM transduction rates when determined by G418 resistance alone, because only approximately one-third of individual colonies were positive for both the Neo(r) and the class II Tg. Because this discrepancy is likely to affect the overall assessment of transduction rates using drug resistance markers, our data attest for the need of a combination of molecular assays to determine transduction efficiencies accurately.