Session 7Oral Abstract Presentations Immune Responses to HIV Session Day and Time: Tuesday 10 am - 12:15 pm Presentation Time: 11:00 Room: Ballroom B
31 Comprehensive Analysis of HIV-specific CD4 Responses by IFN-gamma ELISpot in Early Chronic HIV-1 Infection Shows Marked Immunodominance of gag and nef and the Presence of Broadly Recognized Peptides D. Kaufmann*1, P. Bailey1, L. Cosimi2, P. Norris1, M. Addo1, M. Altfeld1, H. Truong1, M. Johnston1, C. Brander1, B. Walker1, E. Rosenberg1 1Partners AIDS Res Ctr, Massachusetts Gen Hosp, Boston, MA and 2Brigham and Women's Hosp, Boston, MA
Background: Increasing evidence suggests that HIV-specific CD4+ T-cell responses in addition to CD8 CTL are critical for effective immune control of HIV infection. However, comprehensive analyses of CD4 T-cell responses directed against the whole expressed genome are lacking.
Methods: Fresh CD8-depleted PBMCs from 23 HIV-1 infected subjects with CD4 > 350/mm3 (11 treated during primary infection, 7 chronic, and 5 LTNP) were screened for HIV-specific CD4 responses by IFN-gamma ELISpot using a matrix of pools of overlapping peptides spanning all expressed HIV proteins (HIV-1 clade B consensus sequence). Positive responses were confirmed at the single peptide level. The matrix approach was compared to direct screening using individual peptides instead of peptide pools. Purity of CD8 depletion was verified by FACS, and effector cells were determined to be CD4 by IFN-gamma intracellular cytokine staining.
Results: Total magnitude of responses ranged from 50 to > 50,000 SFC/106 CD8-depleted PBMCs and the total number of recognized HIV-1 peptides ranged from 0 to 78 (median 7). HIV-negative controls did not show any response to the 410 tested HIV peptides. Screening with single peptides was very comparable to using matrix peptide pools. Our data demonstrate that the peptide matrix approach is a valuable tool for comprehensive analysis of CD4 responses. Responses were dominated by gag and nef (mean 86% of responses per individual). In contrast, CD8 responses in the same patients showed a much broader distribution. Some peptides were frequently targeted by CD4 in individuals with different HLA Class II types.
Conclusion: Our analyses show that HIV-specific CD4 responses could be identified in the majority of the studied individuals with a wide spectrum in breadth and magnitude and an immunodominance of gag and nef. The paucity of CD4 responses to other proteins contrasts with the pattern of CD8 responses in the same subjects with broad responses to other proteins. The high frequency of responses to a limited subset of peptides suggests a focused recognition of peptides, which may be promiscuously presented by different HLA Class II alleles. These findings may have significant impact for the design of immunotherapeutic strategies.
