Adeno-associated virus 2 co-receptors?-first reply

Qing et al. reply—The conclusion by Qiu et al. that HEp-2 and A431 cells do not express FGFR is wrong. The Muggeridge et al. report they quote clearly shows that the FGFR number per cell is approximately 300. There are few details of how Qiu et al. generated the data presented in their table. The remarkably high multiplicity of infection used in these experiments is not standard, and it is difficult to reconcile their 60% transduction rate for HeLa cells when others have reported that AAV vectors do not transduce these cells well because of the rate-limiting viral second-strand DNA synthesis. Transduction efficiencies of 40% for HEp-2 and 10% for A431, respectively, are cited as proof that these cells can be transduced in the absence of FGFR expression. Yet, as stated above, these cells do indeed express FGFR (ref. 7). Thus, it seems that the analysis of FGFR by Qiu et al. using flow cytometry with a monoclonal antibody is inadequate to draw such a conclusion. We have compared the transduction efficiency of a recombinant AAV-lacZ vector (4 × 10 particles/cell) and found transduction efficiencies in HeLa and 293 cells of approximately 4% and 20%, respectively, and <1% in A431 cells which are known to efficiently bind AAV (ref. 13). The lack of trangene expression in A431 cells has previously been reported to be due to very high levels of expression of the epidermal growth factor receptor (EGFR) protein tyrosine kinase known to limit the viral second-strand DNA synthesis. The observed lack of transduction of M07e cells, which we showed do express FGFR (ref. 1), has previously been shown to be due to lack of expression of heparan sulfate proteoglycan (HSPG), a coreceptor of AAV. The absolute requirement for the deliberate expression of both HSPG and FGFR1 in Raji cells, which are known to lack expression of both of these genes, to render these cells permissive for AAV infection, strongly supports our contention that both HSPG and FGFR1 serve as coreceptors for AAV. Of course, other co-receptors may be used in other cells.