Vaccine-Induced Simian Immunodeficiency Virus-Specific CD8
+
T-Cell Responses Focused on a Single Nef Epitope Select for Escape Variants Shortly after Infection
Authors: Martins Mauricio A. , Tully Damien C. , Cruz Michael A. , Power Karen A. , Veloso de Santana Marlon G. , Bean David J. , Ogilvie Colin B. , Gadgil Rujuta , Lima Noemia S. , Magnani Diogo M. , Ejima Keisuke , Allison David B. , Piatak Michael , Altman John D. , Parks Christopher L. , Rakasz Eva G. , Capuano Saverio , Galler Ricardo , Bonaldo Myrna C. , Lifson Jeffrey D. , Allen Todd M. , Watkins David I. 
Published: August 2015

Certain major histocompatibility complex class I (MHC-I) alleles (e.g.,
HLA-B*27
) are enriched among human immunodeficiency virus type 1 (HIV-1)-infected individuals who suppress viremia without treatment (termed “elite controllers” [ECs]). Likewise,
Mamu-B*08
expression also predisposes rhesus macaques to control simian immunodeficiency virus (SIV) replication. Given the similarities between Mamu-B*08 and HLA-B*27, SIV-infected
Mamu-B*08
+
animals provide a model to investigate HLA-B*27-mediated elite control. We have recently shown that vaccination with three immunodominant Mamu-B*08-restricted epitopes (Vif RL8, Vif RL9, and Nef RL10) increased the incidence of elite control in
Mamu-B*08
+
macaques after challenge with the pathogenic SIVmac239 clone. Furthermore, a correlate analysis revealed that CD8
+
T cells targeting Nef RL10 was correlated with improved outcome. Interestingly, this epitope is conserved between SIV and HIV-1 and exhibits a delayed and atypical escape pattern. These features led us to postulate that a monotypic vaccine-induced Nef RL10-specific CD8
+
T-cell response would facilitate the development of elite control in
Mamu-B*08
+
animals following repeated intrarectal challenges with SIVmac239. To test this, we vaccinated
Mamu-B*08
+
animals with
nef
inserts in which Nef RL10 was either left intact (group 1) or disrupted by mutations (group 2). Although monkeys in both groups mounted Nef-specific cellular responses, only those in group 1 developed Nef RL10-specific CD8
+
T cells. These vaccine-induced effector memory CD8
+
T cells did not prevent infection. Escape variants emerged rapidly in the group 1 vaccinees, and ultimately, the numbers of ECs were similar in groups 1 and 2. High-frequency vaccine-induced CD8
+
T cells focused on a single conserved epitope and therefore did not prevent infection or increase the incidence of elite control in
Mamu-B*08
+
macaques.

IMPORTANCE
Since elite control of chronic-phase viremia is a classic example of an effective immune response against HIV/SIV, elucidating the basis of this phenomenon may provide useful insights into how to elicit such responses by vaccination. We have previously established that vaccine-induced CD8
+
T-cell responses against three immunodominant epitopes can increase the incidence of elite control in SIV-infected
Mamu-B*08

+

rhesus macaques—a model of HLA-B*27-mediated elite control. Here, we investigated whether a monotypic vaccine-induced CD8
+
T-cell response targeting the conserved “late-escaping” Nef RL10 epitope can increase the incidence of elite control in
Mamu-B*08

+

monkeys. Surprisingly, vaccine-induced Nef RL10-specific CD8
+
T cells selected for variants within days after infection and, ultimately, did not facilitate the development of elite control. Elite control is, therefore, likely to involve CD8
+
T-cell responses against more than one epitope. Together, these results underscore the complexity and multidimensional nature of virologic control of lentivirus infection.