Comprehensive Analysis of CD4 T Cell Responses to CMV pp65 Antigen Restricted by Single HLA-DR, -DQ, and -DP Allotype Within an Individual.

Within an individual, six different HLA class II heterodimers are expressed co-dominantly by two alleles of HLA-DR, -DQ, and -DP loci. However, it remained unclear which HLA allotypes were used in T cell responses to a given antigen. For the measurement of the CD4 T cell responses restricted by a single HLA allotype, we established a panel of artificial antigen-presenting cells (aAPCs) expressing each single HLA allele of 20 HLA-DRB1, 16 HLA-DQ, and 13 HLA-DP alleles. CD4 T cell responses to cytomegalovirus (CMV) pp65 restricted by single HLA class II allotype defined in 45 healthy donors. The average magnitude of CD4 T cell responses by HLA-DR allotypes was higher than HLA-DQ and HLA-DP allotypes. CD4 T cell responses by DRA01:01/DRB104:06, DQA101:02/DQB106:02, DPA102:02/DPB105:01 were higher among the other alleles in each HLA-DR, -DQ, and -DP locus. Interestingly, the frequencies of HLA-DR alleles and the positivity of specific allotypes showed an inverse correlation. One allotype within individuals is dominantly used in CD4 T cell response in 49% of donors, and two allotypes showed that in 7% of donors, and any positive response was detected in 44% of donors. Even if one individual had several dominant alleles, CD4 T cell responses tended to be restricted by only one of them. Furthermore, CD8 and CD4 T cell responses by HLA class I and class II were correlated. Our results demonstrate that the CD4 T cell preferentially use a few dominant HLA class II allotypes within individuals, similar to CD8 T cell response to CMV pp65.