Host immune responses to salivary gland administration of recombinant adeno-associated virus serotype 2 vectors

Background

Salivary glands (SGs) provide a novel target site at which gene transfer can be accomplished in a minimally invasive manner [1]. SGs are also capable of producing large amounts of proteins, and human SGs are well encapsulated, a circumstance likely to minimize the undesirable access of administered vectors and transgenes to other tissues [2]. Previous studies have indicated that intravenous, intramuscular and intranasal administration of rAAV2 vectors induce relatively mild host immune responses.

Objective

The aim of the study was to examine the effects on immune responsiveness of rAAV2 vector delivery into SGs.

Methods

The main excretory ducts of the submandibular glands of Balb/c mice were cannulated and vectors administered by retrograde infusion [1]. On day 0 we delivered a rAAV2 encoding β-galactosidase or saline (control) to adult mice. On day 28, we administered a second rAAV2 vector encoding either human erythropoeitin (Epo) or human growth hormone to one-third of each group. Immune activities were evaluated in saliva, serum, SGs and spleens collected at different times.

Results

Vector delivery had little effect on salivary flow rates at all time points studied. Histological examination of SGs on day 1 did not indicate any significant inflammatory cell infiltration due to rAAV2 vectors. Ex vivo stimulation, with rAAV2, of splenocytes on days 28 and 56 resulted in elevated interferon-γ levels in culture media from rAAV2-administered mice, but not from control mice. Significant titers of neutralizing antibodies to rAAV2 were detected in serum, with generally lower levels found in saliva. We were unable to observe transduction of SG cells by rAAV2Epo in mice previously infected with rAAV2LacZ (i.e. no elevations in hematocrit [Hct] and serum Epo levels were seen in the virus re-administration group). Conversely, we found significant elevations in Hct and serum Epo levels in mice previously administered saline.

Conclusion

We conclude that after a single administration of rAAV2 to murine SGs there is no significant innate immune response. However, we observe a modest adaptive immune response that abrogates the efficacy of additional rAAV2 administration.