The Journal of Immunology
Responses against a Subdominant CD8+T Cell Epitope
Protect against Immunopathology Caused by a Dominant
Tracy J. Ruckwardt,* Cindy Luongo,†Allison M. W. Malloy,* Jie Liu,* Man Chen,*
Peter L. Collins,†and Barney S. Graham*
CD8+T cell responses are critical for the control of virus infections. Following infection, epitope-specific responses establish an
unpredictable but reproducible pattern of dominance that is dictated by a large number of both positive and negative factors.
Immunodomination, or diminution of subdominant epitope-specific responses by dominant epitopes, can play a substantial role in
the establishment of epitope hierarchy. To determine the role of a dominant (KdM282–90) and a subdominant (DbM187–195) epitope
of respiratory syncytial virus in viral control and immunodomination, MHC-binding anchor residues in the two epitopes were
mutated individually in recombinant infectious viruses, greatly reducing or deleting the epitope-specific CD8+T cell responses.
Neither mutation negatively affected viral clearance in mice, and compensation by the unmutated epitope was seen in both cases,
whereas compensation by five other subdominant epitopes was minimal. Mutation of the dominant KdM282–90response resulted in
effective viral clearance by the subdominant epitope with less illness, whereas mutation of the subdominant DbM187–195response
resulted in overcompensation of the already dominant KdM282–90epitope, and increased severity of illness. Increased illness was
associated with poor functionality of the abundant population of CD8+T cells specific to the dominant KdM282–90epitope, as
measured by the percentage and magnitude of IFN-g production. These data demonstrate efficient viral clearance, and a pro-
tective effect of subdominant CD8+T cell responses.The Journal of Immunology, 2010, 185: 4673–4680.
the context of MHC class I molecules for recognition by CD8+
T cells (1). The requirements for presentation by MHC class I
limit the number of viral epitopes that can be recognized by CD8+
T cells, and responses are often limited to a surprisingly small
number of epitopes. Within responding CD8+T cells, reproducible
epitope dominance patterns are often established, creating an im-
munodominance hierarchy. Many factors can contribute to epitope
hierarchy, including those related to epitope processing and pre-
sentation, those inherent to CD8+T cell frequency and function,
and regulation imposed by other elements of the immune response
or local environment (2–5). The primary factors responsible for
the establishment of epitope dominancemay varydepending on the
system and infection studied, and additional factors may come
into play and alter immunodominance during chronic infection or
following reinfection (2–9).
Respiratory syncytial virus (RSV) is a virus that can cause
severe disease in infants, the institutionalized elderly, and hosts
ytotoxic T lymphocytes are the primary immune mecha-
nism to control infection by viruses and other intracellular
pathogens. Viral peptides are processed and presented in
with compromised cellular immunity. It is the major cause of bron-
chiolitis, pneumonia, mechanical ventilation, respiratory failure,
and hospitalization in infants in the United States (10). The role of
CD8+T cells in RSV infection is still somewhat controversial.
Although some studies show an extensive presence of Ag and
a near absence of CD8+T cells in infants that experience severe
infection or died of severe RSV (11, 12), we demonstrated that,
although not the predominant cell type, CD8+T cells are found
in the peribronchiolar and interstitial infiltrates and significantly
outnumbered CD4+T cells in the lungs of an RSV-infected infant
(13). Robust, systemic virus-specific CD8+T cell responses have
been found in infants with severe disease and do not correlate with
disease severity (14, 15). In fact, the RSV-specific T cell responses
peak during convalescence, and are unlikely to contribute to dis-
ease (14). In addition to their role in viral clearance, CD8+T cells
have been found to protect against vaccine-enhanced illness after
vaccination with formalin-inactived RSVin the mouse model (16).
Immune responses to RSVare often studied in the mouse model,
where CD8+T cell responses are strong and sufficient to eliminate
the virus, but are also the source of immunopathology and illness
(17). We use the CB6F1 mouse model, where both d- and b-allele
responses can be measured simultaneously, and the majority of
the response is to two viral epitopes, KdM282–90and DbM187–195,
which respond in a predictable hierarchy (18). To determine the
contribution of individual epitope-specific responses, we mutated
peptide anchor residues to eliminate or alter the response to the
KdM282–90and DbM187–195epitopes. Either dramatically reducing
an epitope-specific response, or eliminating the response all to-
gether resulted in compensation by the other epitope, with little
compensation observed by five other subdominant epitopes. This
indicates a reciprocity between the KdM282–90and the DbM187–195
epitope, and showed that both epitopes immunodominate the other
five epitopes during primary RSV infection. Surprisingly, having
*Vaccine Research Center and†Laboratory of Infectious Diseases, National Institute
of Allergy and Infectious Disease, National Institutes of Health, Bethesda, MD 20892
Received for publication May 14, 2010. Accepted for publication August 9, 2010.
This work was supported by the National Institute of Allergy and Infectious Disease
Intramural Research Program.
Address correspondence and reprint request to Dr. Barney S. Graham, Vaccine Re-
search Center, National Institute of Allergy and Infectious Disease, National Insti-
tutes of Health, 40 Convent Drive, Building 40, Room 2502, Bethesda, MD 20892-
3017. E-mail address: email@example.com
The online version of this article contains supplemental material.
Abbreviations used in this paper: CMTMR, chloromethylbenzoylaminotetramethyl-
rhodamine; EMEM, Eagle’s MEM; ICS, intracellular cytokine staining; MFI, median
fluorescence intensity; RSV, respiratory syncytial virus; wt, wild-type.
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4680 SUBDOMINANT T CELL RESPONSES ARE PROTECTIVE IN RSV INFECTION