CD8⁺ T-cell expansion and maintenance after recombinant adenovirus immunization rely upon cooperation between hematopoietic and nonhematopoietic antigen-presenting cells

We have recently reported that CD8⁺ T-cell memory maintenance after immunization with recombinant human adenovirus type 5 (rHuAd5) is dependent upon persistent transgene expression beyond the peak of the response. In this report, we have further investigated the location and nature of the cell populations responsible for this sustained response. The draining lymph nodes were found to be important for primary expansion but not for memory maintenance, suggesting that antigen presentation through a nonlymphoid source was required. Using bone marrow chimeric mice, we determined that antigen presentation by nonhematopoietic antigenpresenting cells (APCs) was sufficient for maintenance of CD8⁺ T-cell numbers. However, antigen presentation by this mechanism alone yielded a memory population that displayed alterations in phenotype, cytokine production and protective capacity, indicating that antigen presentation through both hematopoietic and non-hematopoietic APCs ultimately defines the memory CD8⁺ T-cell response produced by rHuAd5. These results shed new light on the immunobiology of rHuAd5 vectors and provide evidence for a mechanism of CD8⁺ T-cell expansion and memory maintenance that relies upon both hematopoietic and nonhematopoietic APCs.