Integrin alpha v (Α_ν) expression on dendritic cells identifies a subset with unique antigen presentating activity following adenoviral transduction

Abstract

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Dendritic cells (DC) play a central role in presenting antigens and activating immune responses. Adenoviral (AdV) vectors have been used as a method for targeting DC to stimulate transgene-sepcific vaccine responses. However, DC lack high affinity CAR receptors and integrin receptors [α_νβ₃ and α_νβ₅, binds to Arg-Gly-Asp (RGD) sequence] primarily mediate their transduction. In the present study we evaluated the expression of alpha v (α_ν) integrin (CD51) on mouse bone marrow derived DC (BM-DC) to determine whether expression of this integrin identifies a distinct DC subset with unique antigen presenting activity. 20-25% of CD11c⁺ BM-DC expressed α_ν integrin receptor (α_ν⁺ DC) when stained by specific antibody. These α_ν⁺ DC also expressed high level of β₃ integrins, whereas α_ν^- DC expressed low level of β₃ integrins. The MHC class I, MHC class II and co-stimulatory molecules (B7.1, B7.2) were expressed equally on both the DC subsets. Transduction of BM-DC by a first generation AdV (AdV-GFP) revealed that α_ν⁺DC are preferentially transduced by AdV (Mean Fluorescent Intensity (MFI): 74) whereas α_ν^- DC are not (MFI 19). An AdV vector that was designed to express an RGD sequence in the fiber knob (RGD-AdV-GFP) produced even better transduction of α_ν⁺ DC (MFI: 794) and partial transduction of α_ν^- DC (MFI: 133). Transduction of BM-DC by AdV was shown to be RGD-dependent by using exogenous RGD peptide as a specific inhibitor. In order to assess these two different DC subsets for their antigen presenting activity, BM-DC were transduced with AdV expressing ova-albumin (AdV-OVA) and sorted into either α_ν⁺ DC or α_ν^-DC by flow cytometry. DC were then cultured with OVA specific OT-I T cells in vitro and proliferation measured as an indicator of antigen-presenting efficiency. The α_ν⁺ DC subset was 2-3 fold more efficient in OVA-specific antigen presentation than α_ν^- DC. Transduction of these DC subsets by AdV produced minor changes in MHC class I, Class II and costimulatory molecules. These DC subsets were also evaluated for their ability to stimulate allogenic T cell responses. Control α_ν⁺ DC, prior to transduction, induced lower allostimulatory activity than α_v^- DC. When BM-DC were transduced with AdV, the α_ν⁺DC remained weak stimulators whereas the allostimulatory activity of α_ν^- DC increased by 3 fold. This study indicates that BM-derived DC can be classified into two subsets on the basis of their α_ν integrin expression (α_ν⁺ DC and α_ν^- DC); which differ markedly in their transduction by AdV, presentation of transgene antigen, and allostimulatory capacity.