Objective: To determine if immunization with non-myristoylated nef would elicit enhanced cellular immune responses resulting from improved presentation of Nef peptides by MHC-I on the cell surface, and enhanced T-cell help.
Design: The myristoylation site of HIV and SIV Nef is required for several Nef functions that modulate the immune response in an infected host, including downregulation of MHC-I, MHC-II, and CD4, and increased expression of the invariant chain on the cell surface. We constructed replication-competent Ad5- and Ad7-HIV recombinants encoding wild-type nef (nefWT) or a nef mutant (nefNM) lacking 19 amino-terminal amino acids, including the myristoylation site, and sequentially immunized chimpanzees mucosally, first with Ad5-HIVnef recombinants and subsequently with Ad7-HIVnef recombinants.
Methods: Peripheral blood lymphocytes were evaluated over the immunization course for Nef-specific cellular immune responses by interferon (IFN)-γ ELISPOT and T-cell proliferation assays. Nef-specific CD4 and CD8 memory T cells that produced intracellular IFN-γ, interleukin-2, and tumor necrosis factor (TNF)-α were assessed by flow cytometry.
Results: In comparison to immunization with Ad-HIVnefWT, Ad-HIVnefNM elicited statistically significant increases in numbers of IFN-γ-secreting cells after the Ad7-HIVnefNM immunization and increased T-cell proliferative responses following both Ad5- and Ad7-HIVnefNM immunizations. Nef-specific CD4 and CD8 memory T-cell populations secreting TNF-α were also significantly increased in the Ad-HIVnefNM immunization group.
Conclusions: The results support the hypothesis that immunization with Ad-recombinants encoding HIVnefNM rather than HIVnefWT elicits enhanced cellular immunity resulting from improved antigen presentation and greater T-cell help.
From the aVaccine Branch, Center for Cancer Research, National Cancer Institute, Bethesda, Maryland, USA
bAdvanced BioScience Laboratories, Inc., Kensington, Maryland, USA
cData Management Services, National Cancer Institute-Frederick, Frederick, Maryland, USA
dSouthwest Foundation for Biomedical Research, San Antonio, Texas, USA.
Received 26 May, 2006
Revised 3 August, 2006
Accepted 5 September, 2006
Correspondence to M. Robert-Guroff, NIH, National Cancer Institute, 41 Medlars Drive, Building 41, Room D804, Bethesda, MD 20892-5065, USA. Tel: +1 301 496 2114; fax: +1 301 402 0055; e-mail: firstname.lastname@example.org