Recombinant expression vectors represent a powerful way to deliver whole
antigens (Ags) for immunization. Sustained Ag expression in vector-infected dendritic cells (DC) combines Ag-specific stimulation with powerful costimulation and, simultaneously, through 'self-selection' of ad hoc
epitopes broadens the scope of immunization beyond restrictions posed by individual patients'
human leukocyte antigen (HLA) phenotype. In this study, therefore, we evaluated the efficiency of a recombinant vaccinia virus encoding the gp100/PMel17
melanoma Ag (rVV-gp100) to infect immature (iDC) or mature dendritic cells (mDC) derived from circulating mononuclear cells and the effect of
infection on their status of maturation. In addition, we tested the ability of rVV-gp100-infected iDC and mDC to present the
HLA-A*0201-associated gp100:209-217
epitope (g209). Irrespective of status of maturation, rVV-gp100
infection induced gp100 expression while only partially reversing the expression of some maturation markers. However, endogenous presentation of the wild-type g209
epitope was inefficient. The low efficiency was
epitope-specific since
infection of DC with rVV encoding a gp100 construct containing the modified gp100:209-217 (210M) (g209-2M)
epitope characterized by high binding affinity for
HLA-A*0201 restored efficient Ag presentation. Presentation of an HLA-class II-associated
epitope and
cytokine release by DC was not altered by rVV
infection. Thus, Ag expression driven by rVV may be an efficient strategy for whole Ag delivery. However, since the effectiveness of Ag processing and presentation is subject to stringent HLA/
epitope pairing, and for other yet undefined rules, the assumption that whole Ag delivery may circumvent HLA restriction is incorrect and recombinant expression vectors encoding well-characterized polyepitopic constructs may prove more effective.